package store

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

// #38: blob storage abstraction. Files live outside SQLite on the data
// volume behind this interface so a MinIO/S3 backend can replace the fs
// implementation later without touching handlers or the UI.

// ErrBlobNotFound is returned by Get/Stat when the key does not exist.
var ErrBlobNotFound = errors.New("blob not found")

// BlobStore persists attachment bytes by key.
type BlobStore interface {
	Put(key string, r io.Reader) (sha string, size int64, err error)
	Get(key string) (io.ReadSeekCloser, error)
	Delete(key string) error
	Stat(key string) (int64, error)
}

// FsBlobStore is the filesystem implementation: blobs are stored under
// root/<key>, where key is "<paste-id>/<sha256-hex>" (see SanitizeBlobKey).
type FsBlobStore struct {
	root string
}

// NewFsBlobStore creates the blob root directory.
func NewFsBlobStore(root string) (*FsBlobStore, error) {
	if err := os.MkdirAll(root, 0o700); err != nil {
		return nil, err
	}
	return &FsBlobStore{root: root}, nil
}

// SanitizeBlobKey validates a blob key and returns the safe on-disk path
// under root. Keys must be exactly "<paste-id>/<sha256-hex>"; anything with
// separators outside that shape, "..", or absolute paths is rejected, so a
// crafted key can never escape the blob root (traversal).
func (f *FsBlobStore) path(key string) (string, error) {
	clean := filepath.ToSlash(key)
	parts := strings.Split(clean, "/")
	if len(parts) != 2 || parts[0] == "" || parts[1] == "" ||
		parts[0] == "." || parts[0] == ".." || parts[1] == "." || parts[1] == ".." {
		return "", fmt.Errorf("invalid blob key %q", key)
	}
	return filepath.Join(f.root, filepath.FromSlash(clean)), nil
}

func (f *FsBlobStore) Put(key string, r io.Reader) (string, int64, error) {
	dst, err := f.path(key)
	if err != nil {
		return "", 0, err
	}
	if err := os.MkdirAll(filepath.Dir(dst), 0o700); err != nil {
		return "", 0, err
	}
	h := sha256.New()
	tmp := dst + ".tmp"
	out, err := os.OpenFile(tmp, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o600)
	if err != nil {
		return "", 0, err
	}
	size, err := io.Copy(io.MultiWriter(out, h), r)
	if cerr := out.Close(); err == nil {
		err = cerr
	}
	if err != nil {
		os.Remove(tmp)
		return "", 0, err
	}
	sha := hex.EncodeToString(h.Sum(nil))
	// The caller-supplied key must match the content hash; rename to the
	// canonical "<paste-id>/<sha256>" path so keys are always content-derived.
	canonical, err := f.path(key[:strings.IndexByte(key, '/')] + "/" + sha)
	if err != nil {
		os.Remove(tmp)
		return "", 0, err
	}
	if err := os.MkdirAll(filepath.Dir(canonical), 0o700); err != nil {
		os.Remove(tmp)
		return "", 0, err
	}
	if err := os.Rename(tmp, canonical); err != nil {
		os.Remove(tmp)
		return "", 0, err
	}
	return sha, size, nil
}

func (f *FsBlobStore) Get(key string) (io.ReadSeekCloser, error) {
	dst, err := f.path(key)
	if err != nil {
		return nil, err
	}
	file, err := os.Open(dst)
	if os.IsNotExist(err) {
		return nil, ErrBlobNotFound
	}
	return file, err
}

func (f *FsBlobStore) Delete(key string) error {
	dst, err := f.path(key)
	if err != nil {
		return err
	}
	err = os.Remove(dst)
	if os.IsNotExist(err) {
		return ErrBlobNotFound
	}
	if err == nil {
		// best-effort cleanup of the now-empty paste directory
		os.Remove(filepath.Dir(dst))
	}
	return err
}

func (f *FsBlobStore) Stat(key string) (int64, error) {
	dst, err := f.path(key)
	if err != nil {
		return 0, err
	}
	fi, err := os.Stat(dst)
	if os.IsNotExist(err) {
		return 0, ErrBlobNotFound
	}
	if err != nil {
		return 0, err
	}
	return fi.Size(), nil
}