package app

import (
	"bytes"
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"

	"gitea.maximumdirect.net/eric/narratio/internal/adapters/storage"
	"gitea.maximumdirect.net/eric/narratio/internal/artifacts"
	"gitea.maximumdirect.net/eric/narratio/internal/audio"
	"gitea.maximumdirect.net/eric/narratio/internal/config"
	"gitea.maximumdirect.net/eric/narratio/internal/fileops"
	"gitea.maximumdirect.net/eric/narratio/internal/manifest"
)

// RestoreExecutionResult captures concrete file-install results for one restore execution.
type RestoreExecutionResult struct {
	DownloadedCount int
}

func executeRestorePlan(
	ctx context.Context,
	cfg *config.Config,
	current *RemoteCurrentState,
	plan *RestorePlan,
	report *RestoreReport,
	store storage.ObjectStore,
) (*RestoreExecutionResult, error) {
	if cfg == nil || cfg.Pipeline == nil || cfg.Session == nil {
		return nil, fmt.Errorf("resolved config with pipeline/session is required")
	}
	if current == nil {
		return nil, fmt.Errorf("remote current state is required")
	}
	if plan == nil {
		return nil, fmt.Errorf("restore plan is required")
	}
	if store == nil {
		return nil, fmt.Errorf("remote object store is required")
	}

	sessionRoot := artifacts.SessionWorkDirForCampaign(cfg.Pipeline.Workspace.Root, cfg.Session.Campaign, cfg.Session.SessionID)
	if err := fileops.EnsureWorkspaceDirectory(sessionRoot); err != nil {
		return nil, fmt.Errorf("create session root for restore: %w", err)
	}
	root, err := os.OpenRoot(sessionRoot)
	if err != nil {
		return nil, fmt.Errorf("open session root for restore: %w", err)
	}
	defer func() { _ = root.Close() }()
	manifestActions := make([]RestoreAction, 0, 1)
	actions := make([]RestoreAction, 0, len(plan.Actions))
	for _, action := range plan.Actions {
		if action.Kind != RestoreActionDownload {
			continue
		}
		if action.LocalRelativePath == config.PathManifestFile {
			manifestActions = append(manifestActions, action)
			continue
		}
		actions = append(actions, action)
	}
	if len(manifestActions) > 1 {
		return nil, fmt.Errorf("restore plan includes multiple manifest download actions")
	}
	if len(manifestActions) == 1 {
		actions = append(actions, manifestActions[0])
	}

	result := &RestoreExecutionResult{}
	for _, action := range actions {
		if err := executeRestoreDownloadAction(ctx, cfg, sessionRoot, root, current, action, store); err != nil {
			if report != nil {
				report.markFailed(action, err)
			}
			return nil, fmt.Errorf("install %q from %q: %w", action.LocalRelativePath, action.RemoteKey, err)
		}
		if report != nil {
			report.markDownloaded(action)
		}
		result.DownloadedCount++
	}

	return result, nil
}

func executeRestoreDownloadAction(
	ctx context.Context,
	cfg *config.Config,
	sessionRoot string,
	root *os.Root,
	current *RemoteCurrentState,
	action RestoreAction,
	store storage.ObjectStore,
) error {
	safeLocalPath, err := joinWithinSessionRoot(sessionRoot, action.LocalRelativePath)
	if err != nil {
		return fmt.Errorf("resolve safe local path: %w", err)
	}
	if strings.TrimSpace(action.LocalPath) != "" && filepath.Clean(action.LocalPath) != safeLocalPath {
		return fmt.Errorf("restore plan local path mismatch for %q", action.LocalRelativePath)
	}
	parent, leaf, err := openRestoreDestinationParent(root, action.LocalRelativePath)
	if err != nil {
		return err
	}
	defer func() { _ = parent.Close() }()
	if err := validateRestoreDestinationLeaf(parent, leaf); err != nil {
		return err
	}

	if restoreActionIsAudio(action) {
		return executeRestoreAudioAction(ctx, cfg, safeLocalPath, parent, leaf, action, store)
	}

	temporaryPath, err := downloadRestoreTemp(safeLocalPath, func(destination io.Writer) error {
		if len(action.VerifiedContent) > 0 {
			_, err := io.Copy(destination, bytes.NewReader(action.VerifiedContent))
			return err
		}
		return storage.DownloadTo(ctx, store, action.RemoteKey, destination)
	})
	if err != nil {
		return fmt.Errorf("download to temp file: %w", err)
	}
	defer func() { _ = os.Remove(temporaryPath) }()
	if err := verifyRestoredObject(ctx, store, action, temporaryPath); err != nil {
		return err
	}

	if isRestoreManifest(action.LocalRelativePath) {
		file, err := os.Open(temporaryPath)
		if err != nil {
			return fmt.Errorf("open restored manifest: %w", err)
		}
		destinationRoot := sessionRoot
		requireCurrentIdentity := action.LocalRelativePath == config.PathManifestFile
		if !requireCurrentIdentity {
			destinationRoot = filepath.Dir(safeLocalPath)
		}
		restored, prepareErr := prepareRestoredManifest(ctx, cfg, current, file, destinationRoot, requireCurrentIdentity)
		closeErr := file.Close()
		if prepareErr != nil {
			return prepareErr
		}
		if closeErr != nil {
			return fmt.Errorf("close restored manifest: %w", closeErr)
		}
		if err := validateRestoreDestinationLeaf(parent, leaf); err != nil {
			return err
		}
		if err := (&manifest.LocalStore{}).Save(ctx, safeLocalPath, restored); err != nil {
			return fmt.Errorf("install rebased manifest atomically: %w", err)
		}
		return nil
	}

	if err := validateRestoreDestinationLeaf(parent, leaf); err != nil {
		return err
	}
	if err := fileops.InstallSiblingTempFile(temporaryPath, safeLocalPath, fileops.WorkspaceFileMode); err != nil {
		return fmt.Errorf("install file atomically: %w", err)
	}

	return nil
}

func openRestoreDestinationParent(root *os.Root, relative string) (*os.Root, string, error) {
	if root == nil {
		return nil, "", fmt.Errorf("restore session root is required")
	}
	name := filepath.Clean(filepath.FromSlash(strings.TrimSpace(relative)))
	if name == "." || name == ".." || filepath.IsAbs(name) || strings.HasPrefix(name, ".."+string(filepath.Separator)) {
		return nil, "", fmt.Errorf("restore path %q is not a normalized relative path", relative)
	}
	parts := strings.Split(name, string(filepath.Separator))
	current := root
	for _, part := range parts[:len(parts)-1] {
		info, err := current.Lstat(part)
		if errors.Is(err, os.ErrNotExist) {
			if err := current.Mkdir(part, fileops.WorkspaceDirectoryMode.Perm()); err != nil && !errors.Is(err, os.ErrExist) {
				if current != root {
					_ = current.Close()
				}
				return nil, "", fmt.Errorf("create restore destination directory %q: %w", part, err)
			}
			info, err = current.Lstat(part)
		}
		if err != nil {
			if current != root {
				_ = current.Close()
			}
			return nil, "", fmt.Errorf("inspect restore destination ancestor %q: %w", part, err)
		}
		if !info.IsDir() || info.Mode()&os.ModeSymlink != 0 {
			if current != root {
				_ = current.Close()
			}
			return nil, "", fmt.Errorf("restore destination ancestor %q is not a directory", part)
		}
		if err := current.Chmod(part, fileops.WorkspaceDirectoryMode); err != nil {
			if current != root {
				_ = current.Close()
			}
			return nil, "", fmt.Errorf("set restore destination directory permissions %q: %w", part, err)
		}
		next, err := current.OpenRoot(part)
		if current != root {
			_ = current.Close()
		}
		if err != nil {
			return nil, "", fmt.Errorf("open restore destination ancestor %q: %w", part, err)
		}
		current = next
	}
	return current, parts[len(parts)-1], nil
}

func validateRestoreDestinationLeaf(parent *os.Root, leaf string) error {
	info, err := parent.Lstat(leaf)
	if errors.Is(err, os.ErrNotExist) {
		return nil
	}
	if err != nil {
		return fmt.Errorf("inspect restore destination %q: %w", leaf, err)
	}
	if !info.Mode().IsRegular() || info.Mode()&os.ModeSymlink != 0 {
		return fmt.Errorf("restore destination %q is not an eligible regular file", leaf)
	}
	return nil
}

func isRestoreManifest(relativePath string) bool {
	clean := filepath.ToSlash(filepath.Clean(strings.TrimSpace(relativePath)))
	return clean == config.PathManifestFile || clean == config.PathPreviousDirSegment+"/"+config.PathManifestFile
}

func downloadRestoreTemp(destination string, download func(io.Writer) error) (string, error) {
	if strings.TrimSpace(destination) == "" {
		return "", fmt.Errorf("restore destination path is required")
	}
	if download == nil {
		return "", fmt.Errorf("restore temporary writer is required")
	}
	directory := filepath.Dir(destination)
	if err := fileops.EnsureWorkspaceDirectory(directory); err != nil {
		return "", fmt.Errorf("create destination directory: %w", err)
	}
	temporary, err := os.CreateTemp(directory, "."+filepath.Base(destination)+".tmp-*")
	if err != nil {
		return "", fmt.Errorf("create sibling temporary file: %w", err)
	}
	temporaryPath := temporary.Name()
	if err := download(temporary); err != nil {
		_ = temporary.Close()
		_ = os.Remove(temporaryPath)
		return "", err
	}
	if err := temporary.Close(); err != nil {
		_ = os.Remove(temporaryPath)
		return "", fmt.Errorf("close sibling temporary file: %w", err)
	}
	return temporaryPath, nil
}

func verifyRestoredObject(ctx context.Context, store storage.ObjectStore, action RestoreAction, temporaryPath string) error {
	if strings.TrimSpace(action.SHA256) == "" && strings.TrimSpace(action.Generation) == "" {
		return nil
	}
	if strings.TrimSpace(action.SHA256) == "" || strings.TrimSpace(action.Generation) == "" {
		return fmt.Errorf("committed object identity for %q is incomplete", action.RemoteKey)
	}
	file, err := os.Open(temporaryPath)
	if err != nil {
		return fmt.Errorf("open downloaded object for verification: %w", err)
	}
	digest := sha256.New()
	count, copyErr := io.Copy(digest, file)
	closeErr := file.Close()
	if copyErr != nil {
		return fmt.Errorf("checksum downloaded object: %w", copyErr)
	}
	if closeErr != nil {
		return fmt.Errorf("close downloaded object: %w", closeErr)
	}
	if count != action.Size {
		return fmt.Errorf("committed object size mismatch for %q: got %d, want %d", action.RemoteKey, count, action.Size)
	}
	if got := hex.EncodeToString(digest.Sum(nil)); got != action.SHA256 {
		return fmt.Errorf("committed object checksum mismatch for %q: got %s, want %s", action.RemoteKey, got, action.SHA256)
	}
	objects, err := store.List(ctx, action.RemoteKey)
	if err != nil {
		return fmt.Errorf("read committed object identity for %q: %w", action.RemoteKey, err)
	}
	var found *storage.ObjectInfo
	for _, object := range objects {
		if normalizeRemoteKey(object.Key) != normalizeRemoteKey(action.RemoteKey) {
			continue
		}
		if found != nil {
			return fmt.Errorf("committed object %q is ambiguous", action.RemoteKey)
		}
		copy := object
		found = &copy
	}
	if found == nil {
		return fmt.Errorf("committed object %q is missing", action.RemoteKey)
	}
	if found.Size != action.Size || strings.TrimSpace(found.ETag) != action.Generation {
		return fmt.Errorf("committed object generation mismatch for %q", action.RemoteKey)
	}
	return nil
}

func executeRestoreAudioAction(
	ctx context.Context,
	cfg *config.Config,
	safeLocalPath string,
	parent *os.Root,
	leaf string,
	action RestoreAction,
	store storage.ObjectStore,
) error {
	if cfg == nil || cfg.Pipeline == nil || cfg.Pipeline.Storage.S3 == nil || cfg.Session == nil {
		return fmt.Errorf("resolved s3 config and session are required")
	}
	spoolDir := artifacts.SessionSpoolRestoreAudioDir(cfg.Pipeline.Spool.Root, cfg.Session.Campaign, cfg.Session.SessionID)
	spoolPath := filepath.Join(spoolDir, filepath.Base(safeLocalPath))
	temporary, err := os.CreateTemp(filepath.Dir(safeLocalPath), "."+filepath.Base(safeLocalPath)+".restore-*")
	if err != nil {
		return fmt.Errorf("create sibling audio staging file: %w", err)
	}
	temporaryPath := temporary.Name()
	if err := temporary.Close(); err != nil {
		_ = os.Remove(temporaryPath)
		return fmt.Errorf("close sibling audio staging file: %w", err)
	}
	defer func() { _ = os.Remove(temporaryPath) }()

	cacheEnabled := cfg.Pipeline.Cache.S3Audio == nil || *cfg.Pipeline.Cache.S3Audio
	_, err = audio.MaterializeS3Audio(ctx, audio.S3MaterializeRequest{
		Store: store,
		Object: storage.ObjectInfo{
			Key:  action.RemoteKey,
			Size: action.Size,
			ETag: action.ETag,
		},
		Bucket:       strings.TrimSpace(cfg.Pipeline.Storage.S3.Bucket),
		CacheRoot:    strings.TrimSpace(cfg.Pipeline.Cache.Root),
		CacheEnabled: cacheEnabled,
		SpoolPath:    spoolPath,
		DestPath:     temporaryPath,
	})
	if err != nil {
		return fmt.Errorf("materialize audio: %w", err)
	}
	if err := verifyRestoredObject(ctx, store, action, temporaryPath); err != nil {
		return err
	}
	if err := validateRestoreDestinationLeaf(parent, leaf); err != nil {
		return err
	}
	if err := fileops.InstallSiblingTempFile(temporaryPath, safeLocalPath, fileops.WorkspaceFileMode); err != nil {
		return fmt.Errorf("install verified audio atomically: %w", err)
	}
	return nil
}