package cas

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

type Store struct{ dir string }

func New(dir string) *Store { os.MkdirAll(dir, 0o755); return &Store{dir: dir} }

func (s *Store) pathOf(hash string) string {
	if len(hash) < 2 {
		return filepath.Join(s.dir, hash)
	}
	return filepath.Join(s.dir, hash[:2], hash)
}

func (s *Store) Has(hash string) bool { _, err := os.Stat(s.pathOf(hash)); return err == nil }

func (s *Store) PutStream(r io.Reader) (string, error) {
	h := sha256.New()
	tmp, err := os.CreateTemp(s.dir, "put-*.tmp")
	if err != nil {
		return "", err
	}
	defer os.Remove(tmp.Name())
	mw := io.MultiWriter(h, tmp)
	if _, err := io.Copy(mw, r); err != nil {
		tmp.Close()
		return "", err
	}
	tmp.Close()
	sum := hex.EncodeToString(h.Sum(nil))
	dst := s.pathOf(sum)
	if err := os.MkdirAll(filepath.Dir(dst), 0o755); err != nil {
		return "", err
	}
	if err := os.Rename(tmp.Name(), dst); err != nil {
		return "", err
	}
	return sum, nil
}

func (s *Store) Get(hash string, w io.Writer) error {
	f, err := os.Open(s.pathOf(hash))
	if err != nil {
		return errors.New("not found")
	}
	defer f.Close()
	_, err = io.Copy(w, f)
	return err
}