package api

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

// SimpleFSStore is a minimal FS-backed implementation of BlobStore.
// Layout under root:
//
//	<root>/<hash>        - content
//	<root>/<hash>.priv   - presence means "private"
type SimpleFSStore struct {
	root string
}

func NewSimpleFSStore(root string) *SimpleFSStore {
	return &SimpleFSStore{root: root}
}

func (fs *SimpleFSStore) ensureRoot() error {
	return os.MkdirAll(fs.root, 0o755)
}

func (fs *SimpleFSStore) pathFor(hash string) string {
	return filepath.Join(fs.root, hash)
}
func (fs *SimpleFSStore) privPathFor(hash string) string {
	return filepath.Join(fs.root, hash+".priv")
}

// Get implements BlobStore.Get
func (fs *SimpleFSStore) Get(hash string) (io.ReadCloser, int64, error) {
	if err := fs.ensureRoot(); err != nil {
		return nil, 0, err
	}
	f, err := os.Open(fs.pathFor(hash))
	if err != nil {
		return nil, 0, err
	}
	st, err := f.Stat()
	if err != nil {
		_ = f.Close()
		return nil, 0, err
	}
	return f, st.Size(), nil
}

// Put implements BlobStore.Put
func (fs *SimpleFSStore) Put(r io.Reader, private bool) (string, int64, time.Time, error) {
	if err := fs.ensureRoot(); err != nil {
		return "", 0, time.Time{}, err
	}
	tmp, err := os.CreateTemp(fs.root, "put-*")
	if err != nil {
		return "", 0, time.Time{}, err
	}
	defer func() {
		_ = tmp.Close()
		_ = os.Remove(tmp.Name())
	}()

	h := sha256.New()
	w := io.MultiWriter(tmp, h)

	n, err := io.Copy(w, r)
	if err != nil {
		return "", 0, time.Time{}, err
	}
	hash := hex.EncodeToString(h.Sum(nil))

	final := fs.pathFor(hash)
	if err := os.Rename(tmp.Name(), final); err != nil {
		return "", 0, time.Time{}, err
	}

	if private {
		if err := os.WriteFile(fs.privPathFor(hash), nil, 0o600); err != nil {
			_ = os.Remove(final)
			return "", 0, time.Time{}, err
		}
	}

	st, err := os.Stat(final)
	if err != nil {
		return "", 0, time.Time{}, err
	}
	return hash, n, st.ModTime().UTC(), nil
}

// Delete implements BlobStore.Delete
func (fs *SimpleFSStore) Delete(hash string) error {
	if err := fs.ensureRoot(); err != nil {
		return err
	}
	_ = os.Remove(fs.privPathFor(hash))
	return os.Remove(fs.pathFor(hash))
}

// Walk implements BlobStore.Walk
func (fs *SimpleFSStore) Walk(fn func(hash string, bytes int64, private bool, storedAt time.Time) error) (int, error) {
	if err := fs.ensureRoot(); err != nil {
		return 0, err
	}
	ents, err := os.ReadDir(fs.root)
	if err != nil {
		return 0, err
	}
	count := 0
	for _, e := range ents {
		if e.IsDir() {
			continue
		}
		name := e.Name()
		// skip sidecars and non-64-hex filenames
		if strings.HasSuffix(name, ".priv") || len(name) != 64 || !isHex(name) {
			continue
		}
		full := fs.pathFor(name)
		st, err := os.Stat(full)
		if err != nil {
			continue
		}
		private := false
		if _, err := os.Stat(fs.privPathFor(name)); err == nil {
			private = true
		}
		if err := fn(name, st.Size(), private, st.ModTime().UTC()); err != nil {
			return count, err
		}
		count++
	}
	return count, nil
}

func isHex(s string) bool {
	for i := 0; i < len(s); i++ {
		c := s[i]
		if !((c >= '0' && c <= '9') ||
			(c >= 'a' && c <= 'f') ||
			(c >= 'A' && c <= 'F')) {
			return false
		}
	}
	return true
}