// Copyright (c) The OpenTofu Authors
// SPDX-License-Identifier: MPL-2.0
// Copyright (c) 2023 HashiCorp, Inc.
// SPDX-License-Identifier: MPL-2.0

package command

// This file contains all the Backend-related function calls on Meta,
// exported and private.

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"log"
	"path/filepath"
	"strconv"
	"strings"

	"github.com/hashicorp/hcl/v2"
	"github.com/zclconf/go-cty/cty"
	ctyjson "github.com/zclconf/go-cty/cty/json"

	"github.com/opentofu/opentofu/internal/backend"
	"github.com/opentofu/opentofu/internal/cloud"
	"github.com/opentofu/opentofu/internal/command/arguments"
	"github.com/opentofu/opentofu/internal/command/clistate"
	"github.com/opentofu/opentofu/internal/command/views"
	"github.com/opentofu/opentofu/internal/configs"
	"github.com/opentofu/opentofu/internal/encryption"
	"github.com/opentofu/opentofu/internal/plans"
	"github.com/opentofu/opentofu/internal/states/statemgr"
	"github.com/opentofu/opentofu/internal/tfdiags"
	"github.com/opentofu/opentofu/internal/tofu"
	"github.com/opentofu/opentofu/internal/tracing"

	backendInit "github.com/opentofu/opentofu/internal/backend/init"
	backendLocal "github.com/opentofu/opentofu/internal/backend/local"
)

// BackendOpts are the options used to initialize a backend.Backend.
type BackendOpts struct {
	// Config is a representation of the backend configuration block given in
	// the root module, or nil if no such block is present.
	Config *configs.Backend

	// ConfigOverride is an hcl.Body that, if non-nil, will be used with
	// configs.MergeBodies to override the type-specific backend configuration
	// arguments in Config.
	ConfigOverride hcl.Body

	// Init should be set to true if initialization is allowed. If this is
	// false, then any configuration that requires configuration will show
	// an error asking the user to reinitialize.
	Init bool

	// ForceLocal will force a purely local backend, including state.
	// You probably don't want to set this.
	ForceLocal bool

	// ViewOptions will set console output format for the
	// initialization operation (JSON or human-readable).
	View views.Backend
}

func (b *BackendOpts) backendView(base *views.View) views.Backend {
	if b != nil && b.View != nil {
		return b.View
	}
	return views.NewBackendHuman(base)
}

// BackendWithRemoteTerraformVersion is a shared interface between the 'remote' and 'cloud' backends
// for simplified type checking when calling functions common to those particular backends.
type BackendWithRemoteTerraformVersion interface {
	IgnoreVersionConflict()
	VerifyWorkspaceTerraformVersion(workspace string) tfdiags.Diagnostics
	IsLocalOperations() bool
}

// Backend initializes and returns the backend for this CLI session.
//
// The backend is used to perform the actual OpenTofu operations. This
// abstraction enables easily sliding in new OpenTofu behavior such as
// remote state storage, remote operations, etc. while allowing the CLI
// to remain mostly identical.
//
// This will initialize a new backend for each call, which can carry some
// overhead with it. Please reuse the returned value for optimal behavior.
//
// Only one backend should be used per Meta. This function is stateful
// and is unsafe to create multiple backends used at once. This function
// can be called multiple times with each backend being "live" (usable)
// one at a time.
//
// A side-effect of this method is the population of m.backendState, recording
// the final resolved backend configuration after dealing with overrides from
// the "tofu init" command line, etc.
func (m *Meta) Backend(ctx context.Context, opts *BackendOpts, enc encryption.StateEncryption) (backend.Enhanced, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics

	ctx, span := tracing.Tracer().Start(ctx, "Initialize Backend")
	defer span.End()

	// If no opts are set, then initialize
	if opts == nil {
		opts = &BackendOpts{}
	}

	if m.AllowExperimentalFeatures {
		// TEMP: While we're in early development of the new language runtime
		// we have an experimental shim to enable it using an environment
		// variable, but that's allowed only in builds where experimental
		// features are enabled. Refer to the file containing the following
		// function for more information. This should be completely removed
		// once the experiment is concluded.
		tofu.SetExperimentalRuntimeAllowed(true)
	}

	// Initialize a backend from the config unless we're forcing a purely
	// local operation.
	var b backend.Backend
	if !opts.ForceLocal {
		var backendDiags tfdiags.Diagnostics
		b, backendDiags = m.backendFromConfig(ctx, opts, enc)
		diags = diags.Append(backendDiags)

		if diags.HasErrors() {
			return nil, diags
		}

		log.Printf("[TRACE] Meta.Backend: instantiated backend of type %T", b)
	}

	// Set up the CLI opts we pass into backends that support it.
	cliOpts, err := m.backendCLIOpts(ctx)
	if err != nil {
		if errs := providerPluginErrors(nil); errors.As(err, &errs) {
			// This is a special type returned by m.providerFactories, which
			// indicates one or more inconsistencies between the dependency
			// lock file and the provider plugins actually available in the
			// local cache directory.
			//
			// If initialization is allowed, we ignore this error, as it may
			// be resolved by the later step where providers are fetched.
			if !opts.Init {
				var buf bytes.Buffer
				for addr, err := range errs {
					fmt.Fprintf(&buf, "\n  - %s: %s", addr, err)
				}
				suggestion := "To download the plugins required for this configuration, run:\n  tofu init"
				if m.RunningInAutomation {
					// Don't mention "tofu init" specifically if we're running in an automation wrapper
					suggestion = "You must install the required plugins before running OpenTofu operations."
				}
				diags = diags.Append(tfdiags.Sourceless(
					tfdiags.Error,
					"Required plugins are not installed",
					fmt.Sprintf(
						"The installed provider plugins are not consistent with the packages selected in the dependency lock file:%s\n\nOpenTofu uses external plugins to integrate with a variety of different infrastructure services. %s",
						buf.String(), suggestion,
					),
				))
				return nil, diags
			}
		} else {
			// All other errors just get generic handling.
			diags = diags.Append(err)
			return nil, diags
		}
	}
	cliOpts.Validation = true

	// If the backend supports CLI initialization, do it.
	if cli, ok := b.(backend.CLI); ok {
		if err := cli.CLIInit(cliOpts); err != nil {
			diags = diags.Append(fmt.Errorf(
				"Error initializing backend %T: %w\n\n"+
					"This is a bug; please report it to the backend developer",
				b, err,
			))
			return nil, diags
		}
	}

	// If the result of loading the backend is an enhanced backend,
	// then return that as-is. This works even if b == nil (it will be !ok).
	if enhanced, ok := b.(backend.Enhanced); ok {
		log.Printf("[TRACE] Meta.Backend: backend %T supports operations", b)
		return enhanced, nil
	}

	// We either have a non-enhanced backend or no backend configured at
	// all. In either case, we use local as our enhanced backend and the
	// non-enhanced (if any) as the state backend.

	if !opts.ForceLocal {
		log.Printf("[TRACE] Meta.Backend: backend %T does not support operations, so wrapping it in a local backend", b)
	}

	// Build the local backend
	local := backendLocal.NewWithBackend(b, enc)
	if err := local.CLIInit(cliOpts); err != nil {
		// Local backend isn't allowed to fail. It would be a bug.
		panic(err)
	}

	// If we got here from backendFromConfig returning nil then m.backendState
	// won't be set, since that codepath considers that to be no backend at all,
	// but our caller considers that to be the local backend with no config
	// and so we'll synthesize a backend state so other code doesn't need to
	// care about this special case.
	//
	// FIXME: We should refactor this so that we more directly and explicitly
	// treat the local backend as the default, including in the UI shown to
	// the user, since the local backend should only be used when learning or
	// in exceptional cases and so it's better to help the user learn that
	// by introducing it as a concept.
	if m.backendState == nil {
		// NOTE: This synthetic object is intentionally _not_ retained in the
		// on-disk record of the backend configuration, which was already dealt
		// with inside backendFromConfig, because we still need that codepath
		// to be able to recognize the lack of a config as distinct from
		// explicitly setting local until we do some more refactoring here.
		m.backendState = &clistate.BackendState{
			Type:      "local",
			ConfigRaw: json.RawMessage("{}"),
		}
	}

	return local, nil
}

// selectWorkspace gets a list of existing workspaces and then checks
// if the currently selected workspace is valid. If not, it will ask
// the user to select a workspace from the list.
func (m *Meta) selectWorkspace(ctx context.Context, b backend.Backend) error {
	workspaces, err := b.Workspaces(ctx)
	if err == backend.ErrWorkspacesNotSupported {
		return nil
	}
	if err != nil {
		return fmt.Errorf("Failed to get existing workspaces: %w", err)
	}
	if len(workspaces) == 0 {
		if c, ok := b.(*cloud.Cloud); ok && m.input {
			// len is always 1 if using Name; 0 means we're using Tags and there
			// aren't any matching workspaces. Which might be normal and fine, so
			// let's just ask:
			name, err := m.UIInput().Input(context.Background(), &tofu.InputOpts{
				Id:          "create-workspace",
				Query:       "\n[reset][bold][yellow]No workspaces found.[reset]",
				Description: fmt.Sprintf(inputCloudInitCreateWorkspace, strings.Join(c.WorkspaceMapping.Tags, ", ")),
			})
			if err != nil {
				return fmt.Errorf("Couldn't create initial workspace: %w", err)
			}
			name = strings.TrimSpace(name)
			if name == "" {
				return fmt.Errorf("Couldn't create initial workspace: no name provided")
			}
			log.Printf("[TRACE] Meta.selectWorkspace: selecting the new TFC workspace requested by the user (%s)", name)
			return m.SetWorkspace(name)
		} else {
			return fmt.Errorf("%s", strings.TrimSpace(errBackendNoExistingWorkspaces))
		}
	}

	// Get the currently selected workspace.
	workspace, err := m.Workspace(ctx)
	if err != nil {
		return err
	}

	// Check if any of the existing workspaces matches the selected
	// workspace and create a numbered list of existing workspaces.
	var list strings.Builder
	for i, w := range workspaces {
		if w == workspace {
			log.Printf("[TRACE] Meta.selectWorkspace: the currently selected workspace is present in the configured backend (%s)", workspace)
			return nil
		}
		fmt.Fprintf(&list, "%d. %s\n", i+1, w)
	}

	// If the backend only has a single workspace, select that as the current workspace
	if len(workspaces) == 1 {
		log.Printf("[TRACE] Meta.selectWorkspace: automatically selecting the single workspace provided by the backend (%s)", workspaces[0])
		return m.SetWorkspace(workspaces[0])
	}

	if !m.input {
		return fmt.Errorf("Currently selected workspace %q does not exist", workspace)
	}

	// Otherwise, ask the user to select a workspace from the list of existing workspaces.
	v, err := m.UIInput().Input(context.Background(), &tofu.InputOpts{
		Id: "select-workspace",
		Query: fmt.Sprintf(
			"\n[reset][bold][yellow]The currently selected workspace (%s) does not exist.[reset]",
			workspace),
		Description: fmt.Sprintf(
			strings.TrimSpace(inputBackendSelectWorkspace), list.String()),
	})
	if err != nil {
		return fmt.Errorf("Failed to select workspace: %w", err)
	}

	idx, err := strconv.Atoi(v)
	if err != nil || (idx < 1 || idx > len(workspaces)) {
		return fmt.Errorf("Failed to select workspace: input not a valid number")
	}

	workspace = workspaces[idx-1]
	log.Printf("[TRACE] Meta.selectWorkspace: setting the current workspace according to user selection (%s)", workspace)
	return m.SetWorkspace(workspace)
}

// BackendForLocalPlan is similar to Backend, but uses backend settings that were
// stored in a plan.
//
// The current workspace name is also stored as part of the plan, and so this
// method will check that it matches the currently-selected workspace name
// and produce error diagnostics if not.
func (m *Meta) BackendForLocalPlan(ctx context.Context, settings plans.Backend, enc encryption.StateEncryption) (backend.Enhanced, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics

	if m.AllowExperimentalFeatures {
		// TEMP: While we're in early development of the new language runtime
		// we have an experimental shim to enable it using an environment
		// variable, but that's allowed only in builds where experimental
		// features are enabled. Refer to the file containing the following
		// function for more information. This should be completely removed
		// once the experiment is concluded.
		tofu.SetExperimentalRuntimeAllowed(true)
	}

	f, canonType := backendInit.Backend(settings.Type)
	if f == nil {
		diags = diags.Append(fmt.Errorf(strings.TrimSpace(errBackendSavedUnknown), settings.Type))
		return nil, diags
	}
	if canonType != settings.Type {
		// We should always save the canonical name in a plan -- never an alias
		// name -- so getting here suggests a bug in the code that generated
		// this plan.
		diags = diags.Append(fmt.Errorf("saved plan should use canonical backend type %q, not alias %q; this is a bug in OpenTofu", canonType, settings.Type))
		return nil, diags
	}
	b := f(enc)
	log.Printf("[TRACE] Meta.BackendForLocalPlan: instantiated backend of type %T", b)

	schema := b.ConfigSchema()
	configVal, err := settings.Config.Decode(schema.ImpliedType())
	if err != nil {
		diags = diags.Append(fmt.Errorf("saved backend configuration is invalid: %w", err))
		return nil, diags
	}

	newVal, validateDiags := b.PrepareConfig(configVal)
	diags = diags.Append(validateDiags)
	if validateDiags.HasErrors() {
		return nil, diags
	}

	configureDiags := b.Configure(ctx, newVal)
	diags = diags.Append(configureDiags)
	if configureDiags.HasErrors() {
		return nil, diags
	}

	// If the backend supports CLI initialization, do it.
	if cli, ok := b.(backend.CLI); ok {
		cliOpts, err := m.backendCLIOpts(ctx)
		if err != nil {
			diags = diags.Append(err)
			return nil, diags
		}
		if err := cli.CLIInit(cliOpts); err != nil {
			diags = diags.Append(fmt.Errorf(
				"Error initializing backend %T: %w\n\n"+
					"This is a bug; please report it to the backend developer",
				b, err,
			))
			return nil, diags
		}
	}

	// If the result of loading the backend is an enhanced backend,
	// then return that as-is. This works even if b == nil (it will be !ok).
	if enhanced, ok := b.(backend.Enhanced); ok {
		log.Printf("[TRACE] Meta.BackendForPlan: backend %T supports operations", b)
		if err := m.setupEnhancedBackendAliases(enhanced); err != nil {
			diags = diags.Append(err)
			return nil, diags
		}
		return enhanced, nil
	}

	// Otherwise, we'll wrap our state-only remote backend in the local backend
	// to cause any operations to be run locally.
	log.Printf("[TRACE] Meta.BackendForLocalPlan: backend %T does not support operations, so wrapping it in a local backend", b)
	cliOpts, err := m.backendCLIOpts(ctx)
	if err != nil {
		diags = diags.Append(err)
		return nil, diags
	}
	cliOpts.Validation = false // don't validate here in case config contains file(...) calls where the file doesn't exist
	local := backendLocal.NewWithBackend(b, enc)
	if err := local.CLIInit(cliOpts); err != nil {
		// Local backend should never fail, so this is always a bug.
		panic(err)
	}

	return local, diags
}

// backendCLIOpts returns a backend.CLIOpts object that should be passed to
// a backend that supports local CLI operations.
func (m *Meta) backendCLIOpts(ctx context.Context) (*backend.CLIOpts, error) {
	contextOpts, err := m.contextOpts(ctx)
	if contextOpts == nil && err != nil {
		return nil, err
	}
	return &backend.CLIOpts{
		View:                views.NewBackendRemote(m.View),
		StatePath:           m.statePath,
		StateOutPath:        m.stateOutPath,
		StateBackupPath:     m.backupPath,
		ContextOpts:         contextOpts,
		Input:               m.Input(),
		RunningInAutomation: m.RunningInAutomation,
	}, err
}

// Operation initializes a new backend.Operation struct.
//
// This prepares the operation. After calling this, the caller is expected
// to modify fields of the operation such as Sequence to specify what will
// be called.
func (m *Meta) Operation(ctx context.Context, b backend.Backend, view views.Backend, enc encryption.Encryption) *backend.Operation {
	schema := b.ConfigSchema()
	workspace, err := m.Workspace(ctx)
	if err != nil {
		// An invalid workspace error would have been raised when creating the
		// backend, and the caller should have already exited. Seeing the error
		// here first is a bug, so panic.
		panic(fmt.Sprintf("invalid workspace: %s", err))
	}
	planOutBackend, err := m.backendState.ForPlan(schema, workspace)
	if err != nil {
		// Always indicates an implementation error in practice, because
		// errors here indicate invalid encoding of the backend configuration
		// in memory, and we should always have validated that by the time
		// we get here.
		panic(fmt.Sprintf("failed to encode backend configuration for plan: %s", err))
	}

	stateLocker := clistate.NewNoopLocker()
	if m.stateLock {
		stateLocker = clistate.NewLocker(m.stateLockTimeout, view.StateLocker())
	}

	depLocks, diags := m.lockedDependencies()
	if diags.HasErrors() {
		// We can't actually report errors from here, but m.lockedDependencies
		// should always have been called earlier to prepare the "ContextOpts"
		// for the backend anyway, so we should never actually get here in
		// a real situation. If we do get here then the backend will inevitably
		// fail downstream somewhere if it tries to use the empty depLocks.
		log.Printf("[WARN] Failed to load dependency locks while preparing backend operation (ignored): %s", diags.Err().Error())
	}

	return &backend.Operation{
		Encryption:      enc,
		PlanOutBackend:  planOutBackend,
		UIIn:            m.UIInput(),
		Workspace:       workspace,
		StateLocker:     stateLocker,
		DependencyLocks: depLocks,
	}
}

// backendConfig returns the local configuration for the backend
func (m *Meta) backendConfig(ctx context.Context, opts *BackendOpts) (*configs.Backend, int, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics

	if opts.Config == nil {
		// check if the config was missing, or just not required
		conf, moreDiags := m.loadBackendConfig(ctx, ".")
		diags = diags.Append(moreDiags)
		if moreDiags.HasErrors() {
			return nil, 0, diags
		}

		if conf == nil {
			log.Println("[TRACE] Meta.Backend: no config given or present on disk, so returning nil config")
			return nil, 0, nil
		}

		log.Printf("[TRACE] Meta.Backend: BackendOpts.Config not set, so using settings loaded from %s", conf.DeclRange)
		opts.Config = conf
	}

	c := opts.Config

	if c == nil {
		log.Println("[TRACE] Meta.Backend: no explicit backend config, so returning nil config")
		return nil, 0, nil
	}

	bf, canonType := backendInit.Backend(c.Type)
	if bf == nil {
		detail := fmt.Sprintf("There is no backend type named %q.", c.Type)
		if msg, removed := backendInit.RemovedBackends[c.Type]; removed {
			detail = msg
		}

		diags = diags.Append(&hcl.Diagnostic{
			Severity: hcl.DiagError,
			Summary:  "Invalid backend type",
			Detail:   detail,
			Subject:  &c.TypeRange,
		})
		return nil, 0, diags
	}
	b := bf(nil) // Just using this for config/schema, don't need encryption here

	configSchema := b.ConfigSchema()
	configBody := c.Config
	configHash, cfgDiags := c.Hash(ctx, configSchema)
	diags = diags.Append(cfgDiags)
	if diags.HasErrors() {
		return nil, 0, diags
	}

	// If we have an override configuration body then we must apply it now.
	if opts.ConfigOverride != nil {
		log.Println("[TRACE] Meta.Backend: merging -backend-config=... CLI overrides into backend configuration")
		configBody = configs.MergeBodies(configBody, opts.ConfigOverride)
	}

	log.Printf("[TRACE] Meta.Backend: built configuration for %q backend with hash value %d", c.Type, configHash)

	// We'll shallow-copy configs.Backend here so that we can replace the
	// body without affecting others that hold this reference.
	configCopy := *c
	configCopy.Config = configBody
	if c.Type != canonType {
		log.Printf("[DEBUG] Meta.Backend: using canonical backend type %q instead of alias %q", canonType, c.Type)
		configCopy.Type = canonType
	}
	return &configCopy, configHash, diags
}

// backendFromConfig returns the initialized (not configured) backend
// directly from the config/state..
//
// This function handles various edge cases around backend config loading. For
// example: new config changes, backend type changes, etc.
//
// Legacy remote state is no longer supported.
// This function may query the user for input unless input is disabled, in
// which case this function will error.
func (m *Meta) backendFromConfig(ctx context.Context, opts *BackendOpts, enc encryption.StateEncryption) (backend.Backend, tfdiags.Diagnostics) {
	// Get the local backend configuration.
	// Note that [Meta.backendConfig] returns a possibly-modified copy of
	// the original configuration, and in particular has the backend type
	// already translated from an alias to the canonical name so everything
	// using "c" after this can assume that c.Type is definitely the canonical
	// name for a backend that actually exists and is not an alias.
	c, cHash, diags := m.backendConfig(ctx, opts)
	if diags.HasErrors() {
		return nil, diags
	}

	// ------------------------------------------------------------------------
	// For historical reasons, current backend configuration for a working
	// directory is kept in a *state-like* file using clistate.CLIState.
	// It is not actually an OpenTofu resource state, and so only the
	// "backend" portion of it is actually used.
	//
	// The remainder of this code often confusingly refers to this as a "state",
	// so it's unfortunately important to remember that this is not actually
	// what we _usually_ think of as "state", and is instead a local working
	// directory "backend configuration state" that is never persisted anywhere
	// except the .terraform directory.
	// ------------------------------------------------------------------------

	// Get the path to where we store a local cache of backend configuration
	// if we're using a remote backend. This may not yet exist which means
	// we haven't used a non-local backend before. That is okay.
	statePath := filepath.Join(m.WorkingDir.DataDir(), arguments.DefaultStateFilename)
	sMgr := &clistate.LocalState{Path: statePath}
	if err := sMgr.RefreshState(context.TODO()); err != nil {
		diags = diags.Append(fmt.Errorf("Failed to load state: %w", err))
		return nil, diags
	}

	// Load the state, it must be non-nil for the tests below but can be empty
	s := sMgr.State()
	if s == nil {
		log.Printf("[TRACE] Meta.Backend: backend has not previously been initialized in this working directory")
		s = clistate.NewState()
	} else if s.Backend != nil {
		log.Printf("[TRACE] Meta.Backend: working directory was previously initialized for %q backend", s.Backend.Type)
	} else {
		log.Printf("[TRACE] Meta.Backend: working directory was previously initialized but has no backend configuration")
	}

	// if we want to force reconfiguration of the backend, we set the backend
	// state to nil on this copy. This will direct us through the correct
	// configuration path in the switch statement below.
	if m.reconfigure {
		s.Backend = nil
	}

	// Upon return, we want to set the state we're using in-memory so that
	// we can access it for commands.
	m.backendState = nil
	defer func() {
		if s := sMgr.State(); s != nil && !s.Backend.Empty() {
			m.backendState = s.Backend
		}
	}()

	// This switch statement covers all the different combinations of
	// configuring new backends, updating previously-configured backends, etc.
	switch {
	// No configuration set at all. Pure local state.
	case c == nil && s.Backend.Empty():
		log.Printf("[TRACE] Meta.Backend: using default local state only (no backend configuration, and no existing initialized backend)")
		return nil, nil

	// We're unsetting a backend (moving from backend => local)
	case c == nil && !s.Backend.Empty():
		log.Printf("[TRACE] Meta.Backend: previously-initialized %q backend is no longer present in config", s.Backend.Type)

		initReason := fmt.Sprintf("Unsetting the previously set backend %q", s.Backend.Type)
		if !opts.Init {
			diags = diags.Append(tfdiags.Sourceless(
				tfdiags.Error,
				"Backend initialization required, please run \"tofu init\"",
				fmt.Sprintf(strings.TrimSpace(errBackendInit), initReason),
			))
			return nil, diags
		}

		if s.Backend.Type != "cloud" && !m.migrateState {
			diags = diags.Append(migrateOrReconfigDiag)
			return nil, diags
		}

		return m.backend_c_r_S(ctx, c, cHash, sMgr, true, opts, enc)

	// Configuring a backend for the first time or -reconfigure flag was used
	case c != nil && s.Backend.Empty():
		log.Printf("[TRACE] Meta.Backend: moving from default local state only to %q backend", c.Type)
		if !opts.Init {
			if c.Type == "cloud" {
				initReason := "Initial configuration of cloud backend"
				diags = diags.Append(tfdiags.Sourceless(
					tfdiags.Error,
					"Cloud backend initialization required: please run \"tofu init\"",
					fmt.Sprintf(strings.TrimSpace(errBackendInitCloud), initReason),
				))
			} else {
				initReason := fmt.Sprintf("Initial configuration of the requested backend %q", c.Type)
				diags = diags.Append(tfdiags.Sourceless(
					tfdiags.Error,
					"Backend initialization required, please run \"tofu init\"",
					fmt.Sprintf(strings.TrimSpace(errBackendInit), initReason),
				))
			}
			return nil, diags
		}
		return m.backend_C_r_s(ctx, c, cHash, sMgr, opts, enc)
	// Potentially changing a backend configuration
	case c != nil && !s.Backend.Empty():
		// We are not going to migrate if...
		//
		// We're not initializing
		// AND the backend cache hash values match, indicating that the stored config is valid and completely unchanged.
		// AND we're not providing any overrides. An override can mean a change overriding an unchanged backend block (indicated by the hash value).
		if (uint64(cHash) == s.Backend.Hash) && (!opts.Init || opts.ConfigOverride == nil) {
			log.Printf("[TRACE] Meta.Backend: using already-initialized, unchanged %q backend configuration", c.Type)
			savedBackend, diags := m.savedBackend(ctx, sMgr, enc)
			// Verify that selected workspace exist. Otherwise prompt user to create one
			if opts.Init && savedBackend != nil {
				if err := m.selectWorkspace(ctx, savedBackend); err != nil {
					diags = diags.Append(err)
					return nil, diags
				}
			}
			return savedBackend, diags
		}

		// If our configuration (the result of both the literal configuration and given
		// -backend-config options) is the same, then we're just initializing a previously
		// configured backend. The literal configuration may differ, however, so while we
		// don't need to migrate, we update the backend cache hash value.
		if !m.backendConfigNeedsMigration(ctx, c, s.Backend) {
			log.Printf("[TRACE] Meta.Backend: using already-initialized %q backend configuration", c.Type)
			savedBackend, moreDiags := m.savedBackend(ctx, sMgr, enc)
			diags = diags.Append(moreDiags)
			if moreDiags.HasErrors() {
				return nil, diags
			}

			// It's possible for a backend to be unchanged, and the config itself to
			// have changed by moving a parameter from the config to `-backend-config`
			// In this case, we update the Hash.
			moreDiags = m.updateSavedBackendHash(cHash, sMgr)
			if moreDiags.HasErrors() {
				return nil, diags
			}
			// Verify that selected workspace exist. Otherwise prompt user to create one
			if opts.Init && savedBackend != nil {
				if err := m.selectWorkspace(ctx, savedBackend); err != nil {
					diags = diags.Append(err)
					return nil, diags
				}
			}

			return savedBackend, diags
		}
		log.Printf("[TRACE] Meta.Backend: backend configuration has changed (from type %q to type %q)", s.Backend.Type, c.Type)

		cloudMode := cloud.DetectConfigChangeType(s.Backend, c, false)

		if !opts.Init {
			// user ran another cmd that is not init but they are required to initialize because of a potential relevant change to their backend configuration
			initDiag := m.determineInitReason(s.Backend.Type, c.Type, cloudMode)
			diags = diags.Append(initDiag)
			return nil, diags
		}

		if !cloudMode.InvolvesCloud() && !m.migrateState {
			diags = diags.Append(migrateOrReconfigDiag)
			return nil, diags
		}

		log.Printf("[WARN] backend config has changed since last init")
		return m.backend_C_r_S_changed(ctx, c, cHash, sMgr, true, opts, enc)

	default:
		diags = diags.Append(fmt.Errorf(
			"Unhandled backend configuration state. This is a bug. Please\n"+
				"report this error with the following information.\n\n"+
				"Config Nil: %v\n"+
				"Saved Backend Empty: %v\n",
			c == nil, s.Backend.Empty(),
		))
		return nil, diags
	}
}

func (m *Meta) determineInitReason(previousBackendType string, currentBackendType string, cloudMode cloud.ConfigChangeMode) tfdiags.Diagnostics {
	initReason := ""
	switch cloudMode {
	case cloud.ConfigMigrationIn:
		initReason = fmt.Sprintf("Changed from backend %q to cloud backend", previousBackendType)
	case cloud.ConfigMigrationOut:
		initReason = fmt.Sprintf("Changed from cloud backend to backend %q", previousBackendType)
	case cloud.ConfigChangeInPlace:
		initReason = "Cloud backend configuration block has changed"
	default:
		switch {
		case previousBackendType != currentBackendType:
			initReason = fmt.Sprintf("Backend type changed from %q to %q", previousBackendType, currentBackendType)
		default:
			initReason = "Backend configuration block has changed"
		}
	}

	var diags tfdiags.Diagnostics
	switch cloudMode {
	case cloud.ConfigChangeInPlace:
		diags = diags.Append(tfdiags.Sourceless(
			tfdiags.Error,
			"Cloud backend initialization required: please run \"tofu init\"",
			fmt.Sprintf(strings.TrimSpace(errBackendInitCloud), initReason),
		))
	case cloud.ConfigMigrationIn:
		diags = diags.Append(tfdiags.Sourceless(
			tfdiags.Error,
			"Cloud backend initialization required: please run \"tofu init\"",
			fmt.Sprintf(strings.TrimSpace(errBackendInitCloud), initReason),
		))
	default:
		diags = diags.Append(tfdiags.Sourceless(
			tfdiags.Error,
			"Backend initialization required: please run \"tofu init\"",
			fmt.Sprintf(strings.TrimSpace(errBackendInit), initReason),
		))
	}

	return diags
}

// backendFromState returns the initialized (not configured) backend directly
// from the backend state. This should be used only when a user runs
// `tofu init -backend=false`. This function returns a local backend if
// there is no backend state or no backend configured.
func (m *Meta) backendFromState(ctx context.Context, enc encryption.StateEncryption) (backend.Backend, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics
	// Get the path to where we store a local cache of backend configuration
	// if we're using a remote backend. This may not yet exist which means
	// we haven't used a non-local backend before. That is okay.
	statePath := filepath.Join(m.WorkingDir.DataDir(), arguments.DefaultStateFilename)
	sMgr := &clistate.LocalState{Path: statePath}
	if err := sMgr.RefreshState(context.TODO()); err != nil {
		diags = diags.Append(fmt.Errorf("Failed to load state: %w", err))
		return nil, diags
	}
	s := sMgr.State()
	if s == nil {
		// no state, so return a local backend
		log.Printf("[TRACE] Meta.Backend: backend has not previously been initialized in this working directory")
		return backendLocal.New(enc), diags
	}
	if s.Backend == nil {
		// s.Backend is nil, so return a local backend
		log.Printf("[TRACE] Meta.Backend: working directory was previously initialized but has no backend configuration")
		return backendLocal.New(enc), diags
	}
	log.Printf("[TRACE] Meta.Backend: working directory was previously initialized for %q backend", s.Backend.Type)

	// backend init function
	if s.Backend.Type == "" {
		return backendLocal.New(enc), diags
	}
	f, canonType := backendInit.Backend(s.Backend.Type)
	if f == nil {
		diags = diags.Append(fmt.Errorf(strings.TrimSpace(errBackendSavedUnknown), s.Backend.Type))
		return nil, diags
	}
	if canonType != s.Backend.Type {
		// The "state" (really: the working directory state managed by
		// the clistate package) should always record the canonical backend
		// type, not an alias for it. If we get here then there's a bug in
		// the code that generated the s.Backend values.
		diags = diags.Append(fmt.Errorf("working directory is configured for backend alias %q instead of the canonical name %q; this is a bug in OpenTofu", s.Backend.Type, canonType))
		return nil, diags
	}
	b := f(enc)

	// The configuration saved in the working directory state file is used
	// in this case, since it will contain any additional values that
	// were provided via -backend-config arguments on tofu init.
	schema := b.ConfigSchema()
	configVal, err := s.Backend.Config(schema)
	if err != nil {
		diags = diags.Append(tfdiags.Sourceless(
			tfdiags.Error,
			"Failed to decode current backend config",
			fmt.Sprintf("The backend configuration created by the most recent run of \"tofu init\" could not be decoded: %s. The configuration may have been initialized by an earlier version that used an incompatible configuration structure. Run \"tofu init -reconfigure\" to force re-initialization of the backend.", err),
		))
		return nil, diags
	}

	// Validate the config and then configure the backend
	newVal, validDiags := b.PrepareConfig(configVal)
	diags = diags.Append(validDiags)
	if validDiags.HasErrors() {
		return nil, diags
	}

	configDiags := b.Configure(ctx, newVal)
	diags = diags.Append(configDiags)
	if configDiags.HasErrors() {
		return nil, diags
	}

	// If the result of loading the backend is an enhanced backend,
	// then set up enhanced backend service aliases.
	if enhanced, ok := b.(backend.Enhanced); ok {
		log.Printf("[TRACE] Meta.BackendForPlan: backend %T supports operations", b)

		if err := m.setupEnhancedBackendAliases(enhanced); err != nil {
			diags = diags.Append(err)
			return nil, diags
		}
	}

	return b, diags
}

// -------------------------------------------------------------------
// Backend Config Scenarios
//
// The functions below cover handling all the various scenarios that
// can exist when loading a backend. They are named in the format of
// "backend_C_R_S" where C, R, S may be upper or lowercase. Lowercase
// means it is false, uppercase means it is true. The full set of eight
// possible cases is handled.
//
// The fields are:
//
//   * C - Backend configuration is set and changed in TF files
//   * R - Legacy remote state is set
//   * S - Backend configuration is set in the state
//
// -------------------------------------------------------------------

// Unconfiguring a backend (moving from backend => local).
func (m *Meta) backend_c_r_S(
	ctx context.Context,
	c *configs.Backend, cHash int, sMgr *clistate.LocalState, output bool, opts *BackendOpts, enc encryption.StateEncryption) (backend.Backend, tfdiags.Diagnostics) {

	var diags tfdiags.Diagnostics
	view := opts.backendView(m.View)

	s := sMgr.State()

	cloudMode := cloud.DetectConfigChangeType(s.Backend, c, false)
	diags = diags.Append(m.assertSupportedCloudInitOptions(cloudMode))
	if diags.HasErrors() {
		return nil, diags
	}

	// Get the backend type for output
	backendType := s.Backend.Type

	if cloudMode == cloud.ConfigMigrationOut {
		view.MigratingFromCloudToLocal()
	} else {
		view.UnconfiguringBackendType(s.Backend.Type)
	}

	// Grab a purely local backend to get the local state if it exists
	localB, moreDiags := m.Backend(ctx, &BackendOpts{ForceLocal: true, Init: true, View: view}, enc)
	diags = diags.Append(moreDiags)
	if moreDiags.HasErrors() {
		return nil, diags
	}

	// Initialize the configured backend
	b, moreDiags := m.savedBackend(ctx, sMgr, enc)
	diags = diags.Append(moreDiags)
	if moreDiags.HasErrors() {
		return nil, diags
	}

	// Perform the migration
	err := m.backendMigrateState(ctx, &backendMigrateOpts{
		SourceType:      s.Backend.Type,
		DestinationType: "local",
		Source:          b,
		Destination:     localB,
		View:            view,
	})
	if err != nil {
		diags = diags.Append(err)
		return nil, diags
	}

	// Remove the stored metadata
	s.Backend = nil
	if err := sMgr.WriteState(s); err != nil {
		diags = diags.Append(fmt.Errorf(strings.TrimSpace(errBackendClearSaved), err))
		return nil, diags
	}
	if err := sMgr.PersistState(context.TODO()); err != nil {
		diags = diags.Append(fmt.Errorf(strings.TrimSpace(errBackendClearSaved), err))
		return nil, diags
	}

	if output {
		view.BackendTypeUnset(backendType)
	}

	// Return no backend
	return nil, diags
}

// Configuring a backend for the first time.
func (m *Meta) backend_C_r_s(ctx context.Context, c *configs.Backend, cHash int, sMgr *clistate.LocalState, opts *BackendOpts, enc encryption.StateEncryption) (backend.Backend, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics

	view := opts.backendView(m.View)
	// Grab a purely local backend to get the local state if it exists
	localB, localBDiags := m.Backend(ctx, &BackendOpts{ForceLocal: true, Init: true, View: view}, enc)
	if localBDiags.HasErrors() {
		diags = diags.Append(localBDiags)
		return nil, diags
	}

	workspaces, err := localB.Workspaces(ctx)
	if err != nil {
		diags = diags.Append(fmt.Errorf(errBackendLocalRead, err))
		return nil, diags
	}

	var localStates []statemgr.Full
	for _, workspace := range workspaces {
		localState, err := localB.StateMgr(ctx, workspace)
		if err != nil {
			diags = diags.Append(fmt.Errorf(errBackendLocalRead, err))
			return nil, diags
		}
		if err := localState.RefreshState(context.TODO()); err != nil {
			diags = diags.Append(fmt.Errorf(errBackendLocalRead, err))
			return nil, diags
		}

		// We only care about non-empty states.
		if localS := localState.State(); !localS.Empty() {
			log.Printf("[TRACE] Meta.Backend: will need to migrate workspace states because of existing %q workspace", workspace)
			localStates = append(localStates, localState)
		} else {
			log.Printf("[TRACE] Meta.Backend: ignoring local %q workspace because its state is empty", workspace)
		}
	}

	cloudMode := cloud.DetectConfigChangeType(nil, c, len(localStates) > 0)
	diags = diags.Append(m.assertSupportedCloudInitOptions(cloudMode))
	if diags.HasErrors() {
		return nil, diags
	}

	// Get the backend
	b, configVal, moreDiags := m.backendInitFromConfig(ctx, c, enc, view)
	diags = diags.Append(moreDiags)
	if diags.HasErrors() {
		return nil, diags
	}

	if len(localStates) > 0 {
		// Perform the migration
		err = m.backendMigrateState(ctx, &backendMigrateOpts{
			SourceType:      "local",
			DestinationType: c.Type,
			Source:          localB,
			Destination:     b,
			View:            view,
		})
		if err != nil {
			diags = diags.Append(err)
			return nil, diags
		}

		// we usually remove the local state after migration to prevent
		// confusion, but adding a default local backend block to the config
		// can get us here too. Don't delete our state if the old and new paths
		// are the same.
		erase := true
		if newLocalB, ok := b.(*backendLocal.Local); ok {
			if localB, ok := localB.(*backendLocal.Local); ok {
				if newLocalB.PathsConflictWith(localB) {
					erase = false
					log.Printf("[TRACE] Meta.Backend: both old and new backends share the same local state paths, so not erasing old state")
				}
			}
		}

		if erase {
			log.Printf("[TRACE] Meta.Backend: removing old state snapshots from old backend")
			for _, localState := range localStates {
				// We always delete the local state, unless that was our new state too.
				if err := localState.WriteState(nil); err != nil {
					diags = diags.Append(fmt.Errorf(errBackendMigrateLocalDelete, err))
					return nil, diags
				}
				if err := localState.PersistState(context.TODO(), nil); err != nil {
					diags = diags.Append(fmt.Errorf(errBackendMigrateLocalDelete, err))
					return nil, diags
				}
			}
		}
	}

	if m.stateLock {
		stateLocker := clistate.NewLocker(m.stateLockTimeout, view.StateLocker())
		if d := stateLocker.Lock(sMgr, "backend from plan"); d != nil {
			diags = diags.Append(fmt.Errorf("Error locking state: %s", d))
			return nil, diags
		}
		defer stateLocker.Unlock()
	}

	configJSON, err := ctyjson.Marshal(configVal, b.ConfigSchema().ImpliedType())
	if err != nil {
		diags = diags.Append(fmt.Errorf("Can't serialize backend configuration as JSON: %w", err))
		return nil, diags
	}

	// Store the metadata in our saved state location
	s := sMgr.State()
	if s == nil {
		s = clistate.NewState()
	}
	s.Backend = &clistate.BackendState{
		Type:      c.Type,
		ConfigRaw: json.RawMessage(configJSON),
		Hash:      uint64(cHash),
	}

	// Verify that selected workspace exists in the backend.
	if opts.Init && b != nil {
		err := m.selectWorkspace(ctx, b)
		if err != nil {
			diags = diags.Append(err)

			// FIXME: A compatibility oddity with the 'remote' backend.
			// As an awkward legacy UX, when the remote backend is configured and there
			// are no workspaces, the output to the user saying that there are none and
			// the user should create one with 'workspace new' takes the form of an
			// error message - even though it's happy path, expected behavior.
			//
			// Therefore, only return nil with errored diags for everything else, and
			// allow the remote backend to continue and write its configuration to state
			// even though no workspace is selected.
			if c.Type != "remote" {
				return nil, diags
			}
		}
	}

	if err := sMgr.WriteState(s); err != nil {
		diags = diags.Append(fmt.Errorf(errBackendWriteSaved, err))
		return nil, diags
	}
	if err := sMgr.PersistState(context.TODO()); err != nil {
		diags = diags.Append(fmt.Errorf(errBackendWriteSaved, err))
		return nil, diags
	}

	// By now the backend is successfully configured.  If using Terraform Cloud, the success
	// message is handled as part of the final init message
	if _, ok := b.(*cloud.Cloud); !ok {
		view.BackendTypeSet(s.Backend.Type)
	}

	return b, diags
}

// Changing a previously saved backend.
func (m *Meta) backend_C_r_S_changed(ctx context.Context, c *configs.Backend, cHash int, sMgr *clistate.LocalState, output bool, opts *BackendOpts, enc encryption.StateEncryption) (backend.Backend, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics

	view := opts.backendView(m.View)

	// Get the old state
	s := sMgr.State()

	cloudMode := cloud.DetectConfigChangeType(s.Backend, c, false)
	diags = diags.Append(m.assertSupportedCloudInitOptions(cloudMode))
	if diags.HasErrors() {
		return nil, diags
	}

	if output {
		// Notify the user
		switch cloudMode {
		case cloud.ConfigChangeInPlace:
			view.CloudBackendUpdated()
		case cloud.ConfigMigrationIn:
			view.MigratingLocalTypeToCloud(s.Backend.Type)
		case cloud.ConfigMigrationOut:
			view.MigratingCloudToLocalType(c.Type)
		default:
			if s.Backend.Type != c.Type {
				view.BackendTypeChanged(s.Backend.Type, c.Type)
			} else {
				view.BackendReconfigured()
			}
		}
	}

	// Get the backend
	b, configVal, moreDiags := m.backendInitFromConfig(ctx, c, enc, view)
	diags = diags.Append(moreDiags)
	if moreDiags.HasErrors() {
		return nil, diags
	}

	// If this is a migration into, out of, or irrelevant to Terraform Cloud
	// mode then we will do state migration here. Otherwise, we just update
	// the working directory initialization directly, because Terraform Cloud
	// doesn't have configurable state storage anyway -- we're only changing
	// which workspaces are relevant to this configuration, not where their
	// state lives.
	if cloudMode != cloud.ConfigChangeInPlace {
		// Grab the existing backend
		oldB, oldBDiags := m.savedBackend(ctx, sMgr, enc)
		diags = diags.Append(oldBDiags)
		if oldBDiags.HasErrors() {
			return nil, diags
		}

		// Perform the migration
		err := m.backendMigrateState(ctx, &backendMigrateOpts{
			SourceType:      s.Backend.Type,
			DestinationType: c.Type,
			Source:          oldB,
			Destination:     b,
			View:            view,
		})
		if err != nil {
			diags = diags.Append(err)
			return nil, diags
		}

		if m.stateLock {
			stateLocker := clistate.NewLocker(m.stateLockTimeout, view.StateLocker())
			if d := stateLocker.Lock(sMgr, "backend from plan"); d != nil {
				diags = diags.Append(fmt.Errorf("Error locking state: %s", d))
				return nil, diags
			}
			defer stateLocker.Unlock()
		}
	}

	configJSON, err := ctyjson.Marshal(configVal, b.ConfigSchema().ImpliedType())
	if err != nil {
		diags = diags.Append(fmt.Errorf("Can't serialize backend configuration as JSON: %w", err))
		return nil, diags
	}

	// Update the backend state
	s = sMgr.State()
	if s == nil {
		s = clistate.NewState()
	}
	s.Backend = &clistate.BackendState{
		Type:      c.Type,
		ConfigRaw: json.RawMessage(configJSON),
		Hash:      uint64(cHash),
	}

	// Verify that selected workspace exist. Otherwise prompt user to create one
	if opts.Init && b != nil {
		if err := m.selectWorkspace(ctx, b); err != nil {
			diags = diags.Append(err)
			return b, diags
		}
	}

	if err := sMgr.WriteState(s); err != nil {
		diags = diags.Append(fmt.Errorf(errBackendWriteSaved, err))
		return nil, diags
	}
	if err := sMgr.PersistState(context.TODO()); err != nil {
		diags = diags.Append(fmt.Errorf(errBackendWriteSaved, err))
		return nil, diags
	}

	if output {
		// By now the backend is successfully configured.  If using Terraform Cloud, the success
		// message is handled as part of the final init message
		if _, ok := b.(*cloud.Cloud); !ok {
			view.BackendTypeSet(s.Backend.Type)
		}
	}

	return b, diags
}

// Initializing a saved backend from the cache file (legacy state file)
//
// TODO: This is extremely similar to Meta.backendFromState() but for legacy reasons this is the
// function used by the migration APIs within this file. The other handles 'init -backend=false',
// specifically.
func (m *Meta) savedBackend(ctx context.Context, sMgr *clistate.LocalState, enc encryption.StateEncryption) (backend.Backend, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics

	s := sMgr.State()

	// Get the backend
	f, canonName := backendInit.Backend(s.Backend.Type)
	if f == nil {
		diags = diags.Append(fmt.Errorf(strings.TrimSpace(errBackendSavedUnknown), s.Backend.Type))
		return nil, diags
	}
	if s.Backend.Type != canonName {
		// We should always save the canonical name in the clistate, so if we
		// get here then it's a bug in whatever generated the clistate.
		diags = diags.Append(fmt.Errorf("working directory state uses alias %q instead of canonical backend type %q; this is a bug in OpenTofu", s.Backend.Type, canonName))
		return nil, diags
	}
	b := f(enc)

	// The configuration saved in the working directory state file is used
	// in this case, since it will contain any additional values that
	// were provided via -backend-config arguments on tofu init.
	schema := b.ConfigSchema()
	configVal, err := s.Backend.Config(schema)
	if err != nil {
		diags = diags.Append(tfdiags.Sourceless(
			tfdiags.Error,
			"Failed to decode current backend config",
			fmt.Sprintf("The backend configuration created by the most recent run of \"tofu init\" could not be decoded: %s. The configuration may have been initialized by an earlier version that used an incompatible configuration structure. Run \"tofu init -reconfigure\" to force re-initialization of the backend.", err),
		))
		return nil, diags
	}

	// Validate the config and then configure the backend
	newVal, validDiags := b.PrepareConfig(configVal)
	diags = diags.Append(validDiags)
	if validDiags.HasErrors() {
		return nil, diags
	}

	configDiags := b.Configure(ctx, newVal)
	diags = diags.Append(configDiags)
	if configDiags.HasErrors() {
		return nil, diags
	}

	// If the result of loading the backend is an enhanced backend,
	// then set up enhanced backend service aliases.
	if enhanced, ok := b.(backend.Enhanced); ok {
		log.Printf("[TRACE] Meta.BackendForPlan: backend %T supports operations", b)

		if err := m.setupEnhancedBackendAliases(enhanced); err != nil {
			diags = diags.Append(err)
			return nil, diags
		}
	}

	return b, diags
}

func (m *Meta) updateSavedBackendHash(cHash int, sMgr *clistate.LocalState) tfdiags.Diagnostics {
	var diags tfdiags.Diagnostics

	s := sMgr.State()

	if s.Backend.Hash != uint64(cHash) {
		s.Backend.Hash = uint64(cHash)
		if err := sMgr.WriteState(s); err != nil {
			diags = diags.Append(err)
		}
	}

	return diags
}

// -------------------------------------------------------------------
// Reusable helper functions for backend management
// -------------------------------------------------------------------

// backendConfigNeedsMigration returns true if migration might be required to
// move from the configured backend to the given cached backend config.
//
// This must be called with the synthetic *configs.Backend that results from
// merging in any command-line options for correct behavior.
//
// If either the given configuration or cached configuration are invalid then
// this function will conservatively assume that migration is required,
// expecting that the migration code will subsequently deal with the same
// errors.
func (m *Meta) backendConfigNeedsMigration(ctx context.Context, c *configs.Backend, s *clistate.BackendState) bool {
	if s == nil || s.Empty() {
		log.Print("[TRACE] backendConfigNeedsMigration: no cached config, so migration is required")
		return true
	}

	// We need the backend's schema to do our comparison here.
	f, canonType := backendInit.Backend(c.Type)
	if f == nil {
		log.Printf("[TRACE] backendConfigNeedsMigration: no backend of type %q, which migration codepath must handle", c.Type)
		return true // let the migration codepath deal with the missing backend
	}
	if canonType != c.Type {
		log.Printf("[TRACE] backendConfigNeedsMigration: using canonical backend type %q instead of configured alias %q", canonType, c.Type)
	}
	if canonType != s.Type {
		log.Printf("[TRACE] backendConfigNeedsMigration: type changed from %q to %q, so migration is required", s.Type, canonType)
		return true
	}
	b := f(nil) // We don't need encryption here as it's only used for config/schema

	// We use "NoneRequired" here because we're only evaluating the body written directly
	// in the root module configuration, and we're intentionally not including any
	// additional arguments passed on the command line (using -backend-config), so
	// some of the required arguments might be satisfied from outside of the body we're
	// evaluating here.
	schema := b.ConfigSchema().NoneRequired()
	givenVal, diags := c.Decode(ctx, schema)
	if diags.HasErrors() {
		log.Printf("[TRACE] backendConfigNeedsMigration: failed to decode given config; migration codepath must handle problem: %s", diags.Error())
		return true // let the migration codepath deal with these errors
	}

	cachedVal, err := s.Config(schema)
	if err != nil {
		log.Printf("[TRACE] backendConfigNeedsMigration: failed to decode cached config; migration codepath must handle problem: %s", err)
		return true // let the migration codepath deal with the error
	}

	// If we get all the way down here then it's the exact equality of the
	// two decoded values that decides our outcome. It's safe to use RawEquals
	// here (rather than Equals) because we know that unknown values can
	// never appear in backend configurations.
	if cachedVal.RawEquals(givenVal) {
		log.Print("[TRACE] backendConfigNeedsMigration: given configuration matches cached configuration, so no migration is required")
		return false
	}
	log.Print("[TRACE] backendConfigNeedsMigration: configuration values have changed, so migration is required")
	return true
}

func (m *Meta) backendInitFromConfig(ctx context.Context, c *configs.Backend, enc encryption.StateEncryption, view views.Backend) (backend.Backend, cty.Value, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics

	// Get the backend
	// Note that Meta.backendConfig should already have rewritten c.Type to be
	// canonical before we were called, so we are expecting canonType to
	// match c.Type now.
	f, canonType := backendInit.Backend(c.Type)
	if f == nil {
		diags = diags.Append(fmt.Errorf(strings.TrimSpace(errBackendNewUnknown), c.Type))
		return nil, cty.NilVal, diags
	}
	if c.Type != canonType {
		diags = diags.Append(fmt.Errorf("backend configuration still contains alias type %q instead of canonical %q; this is a bug in OpenTofu", c.Type, canonType))
		return nil, cty.NilVal, diags
	}
	b := f(enc)

	schema := b.ConfigSchema()
	configVal, hclDiags := c.Decode(ctx, schema.NoneRequired())
	diags = diags.Append(hclDiags)
	if hclDiags.HasErrors() {
		return nil, cty.NilVal, diags
	}

	if !configVal.IsWhollyKnown() {
		diags = diags.Append(tfdiags.Sourceless(
			tfdiags.Error,
			"Unknown values within backend definition",
			"The `tofu` configuration block should contain only concrete and static values. Another diagnostic should contain more information about which part of the configuration is problematic."))
		return nil, cty.NilVal, diags
	}

	// TODO: test
	if m.Input() {
		var err error
		configVal, err = m.inputForSchema(configVal, schema, view)
		if err != nil {
			diags = diags.Append(fmt.Errorf("Error asking for input to configure backend %q: %w", canonType, err))
		}

		// We get an unknown here if the if the user aborted input, but we can't
		// turn that into a config value, so set it to null and let the provider
		// handle it in PrepareConfig.
		if !configVal.IsKnown() {
			configVal = cty.NullVal(configVal.Type())
		}
	}

	newVal, validateDiags := b.PrepareConfig(configVal)
	diags = diags.Append(validateDiags.InConfigBody(c.Config, ""))
	if validateDiags.HasErrors() {
		return nil, cty.NilVal, diags
	}

	configureDiags := b.Configure(ctx, newVal)
	diags = diags.Append(configureDiags.InConfigBody(c.Config, ""))

	// If the result of loading the backend is an enhanced backend,
	// then set up enhanced backend service aliases.
	if enhanced, ok := b.(backend.Enhanced); ok {
		log.Printf("[TRACE] Meta.BackendForPlan: backend %T supports operations", b)
		if err := m.setupEnhancedBackendAliases(enhanced); err != nil {
			diags = diags.Append(err)
			return nil, cty.NilVal, diags
		}
	}

	return b, configVal, diags
}

// Helper method to get aliases from the enhanced backend and alias them
// in the Meta service discovery. It's unfortunate that the Meta backend
// is modifying the service discovery at this level, but the owner
// of the service discovery pointer does not have easy access to the backend.
func (m *Meta) setupEnhancedBackendAliases(b backend.Enhanced) error {
	// Set up the service discovery aliases specified by the enhanced backend.
	serviceAliases, err := b.ServiceDiscoveryAliases()
	if err != nil {
		return err
	}

	for _, alias := range serviceAliases {
		m.Services.Alias(alias.From, alias.To)
	}
	return nil
}

// Helper method to ignore remote/cloud backend version conflicts. Only call this
// for commands which cannot accidentally upgrade remote state files.
func (m *Meta) ignoreRemoteVersionConflict(b backend.Backend) {
	if back, ok := b.(BackendWithRemoteTerraformVersion); ok {
		back.IgnoreVersionConflict()
	}
}

// Helper method to check the local OpenTofu version against the configured
// version in the remote workspace, returning diagnostics if they conflict.
func (m *Meta) remoteVersionCheck(b backend.Backend, workspace string) tfdiags.Diagnostics {
	var diags tfdiags.Diagnostics

	if back, ok := b.(BackendWithRemoteTerraformVersion); ok {
		// Allow user override based on command-line flag
		if m.ignoreRemoteVersion {
			back.IgnoreVersionConflict()
		}
		// If the override is set, this check will return a warning instead of
		// an error
		versionDiags := back.VerifyWorkspaceTerraformVersion(workspace)
		diags = diags.Append(versionDiags)
		// If there are no errors resulting from this check, we do not need to
		// check again
		if !diags.HasErrors() {
			back.IgnoreVersionConflict()
		}
	}

	return diags
}

// assertSupportedCloudInitOptions returns diagnostics with errors if the
// init-related command line options (implied inside the Meta receiver)
// are incompatible with the given cloud configuration change mode.
func (m *Meta) assertSupportedCloudInitOptions(mode cloud.ConfigChangeMode) tfdiags.Diagnostics {
	var diags tfdiags.Diagnostics
	if mode.InvolvesCloud() {
		log.Printf("[TRACE] Meta.Backend: Cloud backend mode initialization type: %s", mode)
		if m.reconfigure {
			if mode.IsCloudMigration() {
				diags = diags.Append(tfdiags.Sourceless(
					tfdiags.Error,
					"Invalid command-line option",
					"The -reconfigure option is unsupported when migrating to cloud backend, because activating cloud backend involves some additional steps.",
				))
			} else {
				diags = diags.Append(tfdiags.Sourceless(
					tfdiags.Error,
					"Invalid command-line option",
					"The -reconfigure option is for in-place reconfiguration of state backends only, and is not needed when changing cloud backend settings.\n\nWhen using cloud backend, initialization automatically activates any new Cloud configuration settings.",
				))
			}
		}
		if m.migrateState {
			name := "-migrate-state"
			if m.forceInitCopy {
				// -force copy implies -migrate-state in "tofu init",
				// so m.migrateState is forced to true in this case even if
				// the user didn't actually specify it. We'll use the other
				// name here to avoid being confusing, then.
				name = "-force-copy"
			}
			if mode.IsCloudMigration() {
				diags = diags.Append(tfdiags.Sourceless(
					tfdiags.Error,
					"Invalid command-line option",
					fmt.Sprintf("The %s option is for migration between state backends only, and is not applicable when using cloud backend.\n\nCloud backend migration has additional steps, configured by interactive prompts.", name),
				))
			} else {
				diags = diags.Append(tfdiags.Sourceless(
					tfdiags.Error,
					"Invalid command-line option",
					fmt.Sprintf("The %s option is for migration between state backends only, and is not applicable when using cloud backend.\n\nState storage is handled automatically by cloud backend and so the state storage location is not configurable.", name),
				))
			}
		}
	}
	return diags
}

// -------------------------------------------------------------------
// Output constants and initialization code
// -------------------------------------------------------------------

const errBackendLocalRead = `
Error reading local state: %w

OpenTofu is trying to read your local state to determine if there is
state to migrate to your newly configured backend. OpenTofu can't continue
without this check because that would risk losing state. Please resolve the
error above and try again.
`

const errBackendMigrateLocalDelete = `
Error deleting local state after migration: %w

Your local state is deleted after successfully migrating it to the newly
configured backend. As part of the deletion process, a backup is made at
the standard backup path unless explicitly asked not to. To cleanly operate
with a backend, we must delete the local state file. Please resolve the
issue above and retry the command.
`

const errBackendNewUnknown = `
The backend %q could not be found.

This is the backend specified in your OpenTofu configuration file.
This error could be a simple typo in your configuration, but it can also
be caused by using a OpenTofu version that doesn't support the specified
backend type. Please check your configuration and your OpenTofu version.

If you'd like to run OpenTofu and store state locally, you can fix this
error by removing the backend configuration from your configuration.
`

const errBackendNoExistingWorkspaces = `
No existing workspaces.

Use the "tofu workspace" command to create and select a new workspace.
If the backend already contains existing workspaces, you may need to update
the backend configuration.
`

const errBackendSavedUnknown = `
The backend %q could not be found.

This is the backend that this OpenTofu environment is configured to use
both in your configuration and saved locally as your last-used backend.
If it isn't found, it could mean an alternate version of OpenTofu was
used with this configuration. Please use the proper version of OpenTofu that
contains support for this backend.

If you'd like to force remove this backend, you must update your configuration
to not use the backend and run "tofu init" (or any other command) again.
`

const errBackendClearSaved = `
Error clearing the backend configuration: %w

OpenTofu removes the saved backend configuration when you're removing a
configured backend. This must be done so future OpenTofu runs know to not
use the backend configuration. Please look at the error above, resolve it,
and try again.
`

const errBackendInit = `
Reason: %s

The "backend" is the interface that OpenTofu uses to store state,
perform operations, etc. If this message is showing up, it means that the
OpenTofu configuration you're using is using a custom configuration for
the OpenTofu backend.

Changes to backend configurations require reinitialization. This allows
OpenTofu to set up the new configuration, copy existing state, etc. Please run
"tofu init" with either the "-reconfigure" or "-migrate-state" flags to
use the current configuration.

If the change reason above is incorrect, please verify your configuration
hasn't changed and try again. At this point, no changes to your existing
configuration or state have been made.
`

const errBackendInitCloud = `
Reason: %s.

Changes to the cloud backend configuration block require reinitialization, to discover any changes to the available workspaces.

To re-initialize, run:
  tofu init

OpenTofu has not yet made changes to your existing configuration or state.
`

const errBackendWriteSaved = `
Error saving the backend configuration: %w

OpenTofu saves the complete backend configuration in a local file for
configuring the backend on future operations. This cannot be disabled. Errors
are usually due to simple file permission errors. Please look at the error
above, resolve it, and try again.
`

const inputCloudInitCreateWorkspace = `
There are no workspaces with the configured tags (%s)
in your cloud backend organization. To finish initializing, OpenTofu needs at
least one workspace available.

OpenTofu can create a properly tagged workspace for you now. Please enter a
name to create a new cloud backend workspace.
`

var migrateOrReconfigDiag = tfdiags.Sourceless(
	tfdiags.Error,
	"Backend configuration changed",
	"A change in the backend configuration has been detected, which may require migrating existing state.\n\n"+
		"If you wish to attempt automatic migration of the state, use \"tofu init -migrate-state\".\n"+
		`If you wish to store the current configuration with no changes to the state, use "tofu init -reconfigure".`)
