// package utils provides shared utility functions (hashing, HTTP helpers, ZIP).

package utils

import (
	"archive/zip"
	"bytes"
	"crypto/sha1"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"strings"
)

// ── Hashing ────────────────────────────────────────────────────

// SHA1Bytes returns the SHA-1 hex string of the given data.
func SHA1Bytes(data []byte) string {
	h := sha1.Sum(data)
	return hex.EncodeToString(h[:])
}

// SHA256Bytes returns the SHA-256 hex string of the given data.
func SHA256Bytes(data []byte) string {
	h := sha256.Sum256(data)
	return hex.EncodeToString(h[:])
}

// SHA1File computes the SHA-1 hash of a file at the given path.
func SHA1File(path string) (string, error) {
	f, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer f.Close()

	h := sha1.New()
	if _, err := io.Copy(h, f); err != nil {
		return "", err
	}
	return hex.EncodeToString(h.Sum(nil)), nil
}

// ── HTTP helpers ───────────────────────────────────────────────

// WriteJSON writes a JSON response with the given status code.
func WriteJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

// WriteError writes a JSON error response.
func WriteError(w http.ResponseWriter, status int, msg string) {
	WriteJSON(w, status, map[string]string{"error": msg})
}

// ── ZIP ────────────────────────────────────────────────────────

// Unzip extracts a ZIP archive to the destination directory.
// Returns the list of extracted file paths.
// Protects against zip-slip by validating that each entry's target path
// stays within the destination directory.
func Unzip(data []byte, dest string) ([]string, error) {
	reader, err := zip.NewReader(bytes.NewReader(data), int64(len(data)))
	if err != nil {
		return nil, err
	}

	var extracted []string
	for _, f := range reader.File {
		if f.FileInfo().IsDir() {
			continue
		}

		target := filepath.Join(dest, f.Name)

		// Zip-slip protection.
		if !strings.HasPrefix(target, filepath.Clean(dest)+string(os.PathSeparator)) {
			continue
		}

		if err := os.MkdirAll(filepath.Dir(target), 0o755); err != nil {
			continue
		}

		rc, err := f.Open()
		if err != nil {
			continue
		}

		out, err := os.OpenFile(target, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, f.Mode())
		if err != nil {
			rc.Close()
			continue
		}

		io.Copy(out, rc)
		out.Close()
		rc.Close()

		extracted = append(extracted, f.Name)
	}
	return extracted, nil
}