package storage

import (
	"context"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"mime"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strings"
)

// errInvalidKey is returned for object keys that are empty, absolute or attempt
// to escape the storage root.
var errInvalidKey = errors.New("fs: invalid object key")

// FS is a Backend backed by a local directory tree. Blobs live under Root at the
// path formed by the opaque key. Because a local directory has no external URL,
// FS serves blobs through the app using the shared Signer.
type FS struct {
	root   string
	signer *Signer
}

// NewFS builds a local file-system storage backend rooted at root. signer issues
// and validates the app URLs used to serve blobs.
func NewFS(root string, signer *Signer) (*FS, error) {
	if strings.TrimSpace(root) == "" {
		return nil, errors.New("fs: root is required")
	}
	if signer == nil {
		return nil, errors.New("fs: signer is required")
	}
	abs, err := filepath.Abs(root)
	if err != nil {
		return nil, fmt.Errorf("fs: resolve root: %w", err)
	}
	if err := os.MkdirAll(abs, 0o755); err != nil {
		return nil, fmt.Errorf("fs: create root: %w", err)
	}
	return &FS{root: abs, signer: signer}, nil
}

func (f *FS) Bucket() string { return f.root }

func (f *FS) EnsureBucket(context.Context) error {
	return os.MkdirAll(f.root, 0o755)
}

func (f *FS) Ping(context.Context) error {
	info, err := os.Stat(f.root)
	if err != nil {
		return err
	}
	if !info.IsDir() {
		return errors.New("fs: root is not a directory")
	}
	return nil
}

// objectPath maps an opaque key to an absolute path inside the root, rejecting
// absolute keys and any key that resolves outside the root.
func (f *FS) objectPath(key string) (string, error) {
	if key == "" || filepath.IsAbs(key) {
		return "", errInvalidKey
	}
	clean := filepath.Clean(key)
	if clean == ".." || strings.HasPrefix(clean, ".."+string(os.PathSeparator)) {
		return "", errInvalidKey
	}
	p := filepath.Join(f.root, clean)
	rel, err := filepath.Rel(f.root, p)
	if err != nil || rel == ".." || strings.HasPrefix(rel, ".."+string(os.PathSeparator)) {
		return "", errInvalidKey
	}
	return p, nil
}

func (f *FS) Put(_ context.Context, key string, body io.Reader, _ int64, _ string) error {
	p, err := f.objectPath(key)
	if err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
		return fmt.Errorf("fs: mkdir: %w", err)
	}
	tmp, err := os.CreateTemp(filepath.Dir(p), ".upload-*")
	if err != nil {
		return fmt.Errorf("fs: temp file: %w", err)
	}
	tmpName := tmp.Name()
	defer func() { _ = os.Remove(tmpName) }()
	if _, err := io.Copy(tmp, body); err != nil {
		_ = tmp.Close()
		return fmt.Errorf("fs: write: %w", err)
	}
	if err := tmp.Close(); err != nil {
		return fmt.Errorf("fs: close: %w", err)
	}
	if err := os.Rename(tmpName, p); err != nil {
		return fmt.Errorf("fs: rename: %w", err)
	}
	return nil
}

func (f *FS) Get(_ context.Context, key string) ([]byte, error) {
	p, err := f.objectPath(key)
	if err != nil {
		return nil, err
	}
	data, err := os.ReadFile(p)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return nil, ErrObjectNotFound
		}
		return nil, err
	}
	return data, nil
}

// Open streams a blob from disk for processing without buffering it fully.
func (f *FS) Open(_ context.Context, key string) (io.ReadCloser, error) {
	p, err := f.objectPath(key)
	if err != nil {
		return nil, err
	}
	file, err := os.Open(p)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return nil, ErrObjectNotFound
		}
		return nil, err
	}
	return file, nil
}

func (f *FS) Delete(_ context.Context, keys ...string) error {
	var errs []error
	for _, key := range keys {
		p, err := f.objectPath(key)
		if err != nil {
			errs = append(errs, err)
			continue
		}
		if err := os.Remove(p); err != nil && !errors.Is(err, os.ErrNotExist) {
			errs = append(errs, err)
		}
	}
	return errors.Join(errs...)
}

// URL returns a signed app URL served by this process.
func (f *FS) URL(_ context.Context, key string) (string, error) {
	if _, err := f.objectPath(key); err != nil {
		return "", err
	}
	return f.signer.URL(key), nil
}

// List returns every blob under prefix as a key relative to the storage root.
func (f *FS) List(_ context.Context, prefix string) ([]ObjectInfo, error) {
	var out []ObjectInfo
	err := filepath.WalkDir(f.root, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			return nil
		}
		rel, err := filepath.Rel(f.root, path)
		if err != nil {
			return err
		}
		rel = filepath.ToSlash(rel)
		if prefix != "" && !strings.HasPrefix(rel, prefix) {
			return nil
		}
		info, err := d.Info()
		if err != nil {
			return err
		}
		out = append(out, ObjectInfo{Key: rel, Size: info.Size(), ModTime: info.ModTime()})
		return nil
	})
	if err != nil {
		return nil, err
	}
	return out, nil
}

// ServeObject validates the signed URL and serves the blob. It supports range
// requests and sets the content type from the key extension. It writes the
// response itself and returns nil on success.
func (f *FS) ServeObject(w http.ResponseWriter, r *http.Request, key string) error {
	if unescaped, err := url.PathUnescape(key); err == nil {
		key = unescaped
	}
	if err := f.signer.VerifyRequest(key, r); err != nil {
		return err
	}
	p, err := f.objectPath(key)
	if err != nil {
		return ErrSignedURLInvalid
	}
	file, err := os.Open(p)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return ErrObjectNotFound
		}
		return err
	}
	defer file.Close()
	info, err := file.Stat()
	if err != nil {
		return err
	}
	w.Header().Set("Content-Type", contentTypeForKey(key))
	http.ServeContent(w, r, info.Name(), info.ModTime(), file)
	return nil
}

var imageContentTypes = map[string]string{
	".jpg":  "image/jpeg",
	".jpeg": "image/jpeg",
	".png":  "image/png",
	".gif":  "image/gif",
	".webp": "image/webp",
	".heic": "image/heic",
	".heif": "image/heif",
	".tiff": "image/tiff",
	".tif":  "image/tiff",
	".bmp":  "image/bmp",
	".avif": "image/avif",
}

func contentTypeForKey(key string) string {
	ext := strings.ToLower(filepath.Ext(key))
	if ct, ok := imageContentTypes[ext]; ok {
		return ct
	}
	if ct := mime.TypeByExtension(ext); ct != "" {
		return ct
	}
	return "application/octet-stream"
}