package local

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"os"
	"path/filepath"
	"strings"

	"gitea.maximumdirect.net/eric/distributor/internal/storage"
)

const backendName = "local"

type Backend struct {
	root string
}

func New(root string) (*Backend, error) {
	if root == "" {
		return nil, storage.NewError(storage.OpOpenBackend, backendName, "", storage.ErrInvalidPath, nil)
	}
	absRoot, err := filepath.Abs(root)
	if err != nil {
		return nil, storage.NewError(storage.OpOpenBackend, backendName, root, storage.ErrInvalidPath, err)
	}
	return &Backend{root: filepath.Clean(absRoot)}, nil
}

func (b *Backend) ReadFile(ctx context.Context, path string) ([]byte, error) {
	reader, err := b.OpenReader(ctx, path)
	if err != nil {
		return nil, err
	}
	defer reader.Close()
	data, err := io.ReadAll(reader)
	if err != nil {
		return nil, storage.NewError(storage.OpReadFile, backendName, path, storage.ErrUnknown, err)
	}
	return data, nil
}

func (b *Backend) OpenReader(ctx context.Context, path string) (io.ReadCloser, error) {
	if err := ctx.Err(); err != nil {
		return nil, err
	}
	nativePath, err := b.nativePath(path, false)
	if err != nil {
		return nil, err
	}
	if err := b.rejectSymlinkAncestors(nativePath, true); err != nil {
		return nil, err
	}
	info, err := os.Lstat(nativePath)
	if err != nil {
		return nil, b.translateError(storage.OpOpenReader, path, err)
	}
	if !info.Mode().IsRegular() {
		return nil, storage.NewError(storage.OpOpenReader, backendName, path, storage.ErrUnsupported, nil)
	}
	file, err := os.Open(nativePath)
	if err != nil {
		return nil, b.translateError(storage.OpOpenReader, path, err)
	}
	return file, nil
}

func (b *Backend) WriteFile(ctx context.Context, path string, data []byte, opts storage.WriteOptions) (storage.Entry, error) {
	opts.Size = int64(len(data))
	opts.SizeKnown = true
	return b.WriteFrom(ctx, path, bytes.NewReader(data), opts)
}

func (b *Backend) WriteFrom(ctx context.Context, path string, r io.Reader, opts storage.WriteOptions) (storage.Entry, error) {
	if err := ctx.Err(); err != nil {
		return storage.Entry{}, err
	}
	nativePath, err := b.nativePath(path, false)
	if err != nil {
		return storage.Entry{}, err
	}
	parent := filepath.Dir(nativePath)
	if err := b.rejectSymlinkAncestors(parent, true); err != nil {
		return storage.Entry{}, err
	}
	if info, err := os.Lstat(nativePath); err == nil {
		if !opts.Overwrite {
			return storage.Entry{}, storage.NewError(storage.OpWriteFrom, backendName, path, storage.ErrAlreadyExist, nil)
		}
		if !info.Mode().IsRegular() {
			return storage.Entry{}, storage.NewError(storage.OpWriteFrom, backendName, path, storage.ErrConflict, nil)
		}
	} else if !errors.Is(err, fs.ErrNotExist) {
		return storage.Entry{}, b.translateError(storage.OpWriteFrom, path, err)
	}

	if err := os.MkdirAll(parent, 0o755); err != nil {
		return storage.Entry{}, b.translateError(storage.OpWriteFrom, path, err)
	}
	temp, err := os.CreateTemp(parent, ".distributor-write-*")
	if err != nil {
		return storage.Entry{}, b.translateError(storage.OpWriteFrom, path, err)
	}
	tempPath := temp.Name()
	cleanup := true
	defer func() {
		if cleanup {
			_ = os.Remove(tempPath)
		}
	}()

	written, copyErr := io.Copy(temp, r)
	closeErr := temp.Close()
	if copyErr != nil {
		return storage.Entry{}, storage.NewError(storage.OpWriteFrom, backendName, path, storage.ErrUnknown, copyErr)
	}
	if closeErr != nil {
		return storage.Entry{}, storage.NewError(storage.OpWriteFrom, backendName, path, storage.ErrUnknown, closeErr)
	}
	if opts.SizeKnown && written != opts.Size {
		return storage.Entry{}, storage.NewError(storage.OpWriteFrom, backendName, path, storage.ErrConflict, fmt.Errorf("stream size %d does not match expected size %d", written, opts.Size))
	}
	if err := os.Rename(tempPath, nativePath); err != nil {
		return storage.Entry{}, b.translateError(storage.OpWriteFrom, path, err)
	}
	cleanup = false
	return b.Stat(ctx, path)
}

func (b *Backend) Stat(ctx context.Context, path string) (storage.Entry, error) {
	if err := ctx.Err(); err != nil {
		return storage.Entry{}, err
	}
	nativePath, err := b.nativePath(path, true)
	if err != nil {
		return storage.Entry{}, err
	}
	info, err := os.Lstat(nativePath)
	if err != nil {
		return storage.Entry{}, b.translateError(storage.OpStat, path, err)
	}
	return entryFromInfo(path, info), nil
}

func (b *Backend) Walk(ctx context.Context, prefix string, opts storage.WalkOptions, fn storage.WalkFunc) error {
	if err := ctx.Err(); err != nil {
		return err
	}
	nativePrefix, err := b.nativePath(prefix, true)
	if err != nil {
		return err
	}
	info, err := os.Lstat(nativePrefix)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			return nil
		}
		return b.translateError(storage.OpWalk, prefix, err)
	}
	emitter := storage.NewWalkEmitter(ctx, backendName, opts, fn)

	if !info.IsDir() {
		return storage.FinishWalk(emitter.Emit(entryFromInfo(prefix, info)))
	}

	walkErr := filepath.WalkDir(nativePrefix, func(nativePath string, dirEntry fs.DirEntry, err error) error {
		if err != nil {
			return b.translateError(storage.OpWalk, prefix, err)
		}
		if nativePath == nativePrefix {
			return nil
		}
		relPath, err := filepath.Rel(b.root, nativePath)
		if err != nil {
			return b.translateError(storage.OpWalk, prefix, err)
		}
		logicalPath := filepath.ToSlash(relPath)
		if !opts.Recursive && filepath.Dir(nativePath) != nativePrefix {
			if dirEntry.IsDir() {
				return filepath.SkipDir
			}
			return nil
		}
		info, err := dirEntry.Info()
		if err != nil {
			return b.translateError(storage.OpWalk, logicalPath, err)
		}
		return emitter.Emit(entryFromInfo(logicalPath, info))
	})
	return storage.FinishWalk(walkErr)
}

func (b *Backend) HasAny(ctx context.Context, prefix string) (bool, error) {
	return storage.HasAny(ctx, b, prefix)
}

func (b *Backend) DeleteManagedBundle(ctx context.Context, bundlePath string, managedOutputPaths []string, opts storage.DeleteOptions) error {
	if err := ctx.Err(); err != nil {
		return err
	}
	targets, err := storage.ManagedBundleTargets(bundlePath, managedOutputPaths)
	if err != nil {
		return err
	}

	for _, logicalPath := range targets {
		nativePath, err := b.nativePath(logicalPath, false)
		if err != nil {
			return err
		}
		if nativePath == b.root {
			return storage.NewError(storage.OpDeleteManagedBundle, backendName, logicalPath, storage.ErrInvalidPath, nil)
		}
		info, err := os.Lstat(nativePath)
		if err != nil {
			if opts.IgnoreMissing && errors.Is(err, fs.ErrNotExist) {
				continue
			}
			return b.translateError(storage.OpDeleteManagedBundle, logicalPath, err)
		}
		if info.IsDir() {
			return storage.NewError(storage.OpDeleteManagedBundle, backendName, logicalPath, storage.ErrUnsupported, nil)
		}
		if err := os.Remove(nativePath); err != nil {
			return b.translateError(storage.OpDeleteManagedBundle, logicalPath, err)
		}
		if opts.PruneEmptyDirs {
			b.pruneEmptyParents(filepath.Dir(nativePath))
		}
	}
	return nil
}

func (b *Backend) DeletePrefix(ctx context.Context, prefix string, opts storage.DeleteOptions) error {
	if err := ctx.Err(); err != nil {
		return err
	}
	nativePrefix, err := b.nativePath(prefix, true)
	if err != nil {
		return err
	}
	if err := b.rejectSymlinkAncestors(nativePrefix, false); err != nil {
		return err
	}
	if prefix == "" {
		entries, err := os.ReadDir(nativePrefix)
		if err != nil {
			if opts.IgnoreMissing && errors.Is(err, fs.ErrNotExist) {
				return nil
			}
			return b.translateError(storage.OpDeletePrefix, prefix, err)
		}
		for _, entry := range entries {
			if err := ctx.Err(); err != nil {
				return err
			}
			child := filepath.Join(nativePrefix, entry.Name())
			if err := os.RemoveAll(child); err != nil {
				return b.translateError(storage.OpDeletePrefix, entry.Name(), err)
			}
		}
		return nil
	}
	if _, err := os.Lstat(nativePrefix); err != nil {
		if opts.IgnoreMissing && errors.Is(err, fs.ErrNotExist) {
			return nil
		}
		return b.translateError(storage.OpDeletePrefix, prefix, err)
	}
	if err := os.RemoveAll(nativePrefix); err != nil {
		return b.translateError(storage.OpDeletePrefix, prefix, err)
	}
	if opts.PruneEmptyDirs {
		b.pruneEmptyParents(filepath.Dir(nativePrefix))
	}
	return nil
}

func (b *Backend) nativePath(logicalPath string, allowEmpty bool) (string, error) {
	if logicalPath == "" {
		if !allowEmpty {
			return "", storage.NewError(storage.OpValidatePath, backendName, logicalPath, storage.ErrInvalidPath, nil)
		}
		return b.root, nil
	}
	if err := storage.ValidatePath(logicalPath); err != nil {
		return "", err
	}
	nativePath := filepath.Clean(filepath.Join(b.root, filepath.FromSlash(logicalPath)))
	rel, err := filepath.Rel(b.root, nativePath)
	if err != nil {
		return "", storage.NewError(storage.OpValidatePath, backendName, logicalPath, storage.ErrInvalidPath, err)
	}
	if rel == ".." || strings.HasPrefix(rel, ".."+string(filepath.Separator)) || filepath.IsAbs(rel) {
		return "", storage.NewError(storage.OpValidatePath, backendName, logicalPath, storage.ErrInvalidPath, nil)
	}
	return nativePath, nil
}

func (b *Backend) rejectSymlinkAncestors(nativePath string, includeFinal bool) error {
	rel, err := filepath.Rel(b.root, nativePath)
	if err != nil {
		return storage.NewError(storage.OpValidatePath, backendName, nativePath, storage.ErrInvalidPath, err)
	}
	if rel == "." {
		return nil
	}
	segments := strings.Split(rel, string(filepath.Separator))
	limit := len(segments)
	if !includeFinal {
		limit--
	}
	current := b.root
	for i := 0; i < limit; i++ {
		current = filepath.Join(current, segments[i])
		info, err := os.Lstat(current)
		if err != nil {
			if errors.Is(err, fs.ErrNotExist) {
				return nil
			}
			return b.translateError(storage.OpStat, filepath.ToSlash(filepath.Join(segments[:i+1]...)), err)
		}
		if info.Mode()&os.ModeSymlink != 0 {
			return storage.NewError(storage.OpStat, backendName, filepath.ToSlash(filepath.Join(segments[:i+1]...)), storage.ErrUnsupported, nil)
		}
	}
	return nil
}

func (b *Backend) pruneEmptyParents(start string) {
	for current := start; current != b.root && strings.HasPrefix(current, b.root); current = filepath.Dir(current) {
		err := os.Remove(current)
		if err != nil {
			return
		}
	}
}

func (b *Backend) translateError(op, path string, err error) error {
	kind := storage.ErrUnknown
	switch {
	case errors.Is(err, fs.ErrNotExist):
		kind = storage.ErrNotFound
	case errors.Is(err, fs.ErrExist):
		kind = storage.ErrAlreadyExist
	case errors.Is(err, fs.ErrPermission):
		kind = storage.ErrPermission
	}
	return storage.NewError(op, backendName, path, kind, err)
}

func entryFromInfo(path string, info fs.FileInfo) storage.Entry {
	entryType := storage.EntryTypeOther
	switch {
	case info.Mode()&os.ModeSymlink != 0:
		entryType = storage.EntryTypeSymlink
	case info.Mode().IsRegular():
		entryType = storage.EntryTypeFile
	case info.IsDir():
		entryType = storage.EntryTypeDirectory
	}
	return storage.Entry{
		Path: path,
		Type: entryType,
		Size: info.Size(),
	}
}