package fileops

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

// WriteFileAtomic writes data to dst atomically via temp file + rename.
func WriteFileAtomic(dst string, data []byte, perm os.FileMode) error {
	if strings.TrimSpace(dst) == "" {
		return fmt.Errorf("destination path is required")
	}
	if err := EnsureWorkspaceDirectory(filepath.Dir(dst)); err != nil {
		return fmt.Errorf("create destination directory: %w", err)
	}

	base := filepath.Base(dst)
	tmp, err := os.CreateTemp(filepath.Dir(dst), "."+base+".tmp-*")
	if err != nil {
		return fmt.Errorf("create temp file: %w", err)
	}
	tmpPath := tmp.Name()
	removeTmp := true
	defer func() {
		if removeTmp {
			_ = os.Remove(tmpPath)
		}
	}()

	if _, err := tmp.Write(data); err != nil {
		_ = tmp.Close()
		return fmt.Errorf("write temp file: %w", err)
	}
	if err := tmp.Sync(); err != nil {
		_ = tmp.Close()
		return fmt.Errorf("sync temp file: %w", err)
	}
	if err := tmp.Close(); err != nil {
		return fmt.Errorf("close temp file: %w", err)
	}
	if err := os.Chmod(tmpPath, perm); err != nil {
		return fmt.Errorf("set temp file permissions: %w", err)
	}
	if err := os.Rename(tmpPath, dst); err != nil {
		return fmt.Errorf("install temp file: %w", err)
	}
	removeTmp = false
	return nil
}

// CopyFileAtomic copies src to dst atomically via temp file + rename.
func CopyFileAtomic(src, dst string, perm os.FileMode) error {
	_, err := CopyFileAtomicWithChecksum(src, dst, perm)
	return err
}

// CopyFileAtomicWithChecksum copies src to dst atomically and returns the SHA-256 checksum.
func CopyFileAtomicWithChecksum(src, dst string, perm os.FileMode) (string, error) {
	if strings.TrimSpace(src) == "" || strings.TrimSpace(dst) == "" {
		return "", fmt.Errorf("source and destination paths are required")
	}

	in, err := os.Open(src)
	if err != nil {
		return "", fmt.Errorf("open source file: %w", err)
	}
	defer func() { _ = in.Close() }()

	if err := EnsureWorkspaceDirectory(filepath.Dir(dst)); err != nil {
		return "", fmt.Errorf("create destination directory: %w", err)
	}

	base := filepath.Base(dst)
	tmp, err := os.CreateTemp(filepath.Dir(dst), "."+base+".tmp-*")
	if err != nil {
		return "", fmt.Errorf("create temp file: %w", err)
	}
	tmpPath := tmp.Name()
	removeTmp := true
	defer func() {
		if removeTmp {
			_ = os.Remove(tmpPath)
		}
	}()

	digest := sha256.New()
	if _, err := io.Copy(io.MultiWriter(tmp, digest), in); err != nil {
		_ = tmp.Close()
		return "", fmt.Errorf("copy file: %w", err)
	}
	if err := tmp.Sync(); err != nil {
		_ = tmp.Close()
		return "", fmt.Errorf("sync temp file: %w", err)
	}
	if err := tmp.Close(); err != nil {
		return "", fmt.Errorf("close temp file: %w", err)
	}
	if err := os.Chmod(tmpPath, perm); err != nil {
		return "", fmt.Errorf("set temp file permissions: %w", err)
	}
	if err := os.Rename(tmpPath, dst); err != nil {
		return "", fmt.Errorf("install temp file: %w", err)
	}
	removeTmp = false
	return hex.EncodeToString(digest.Sum(nil)), nil
}

// InstallDownloadedTempFile installs a previously downloaded temp file at dst.
func InstallDownloadedTempFile(tmpPath, dst string, perm os.FileMode) error {
	if strings.TrimSpace(tmpPath) == "" || strings.TrimSpace(dst) == "" {
		return fmt.Errorf("temp and destination paths are required")
	}
	if err := EnsureWorkspaceDirectory(filepath.Dir(dst)); err != nil {
		return fmt.Errorf("create destination directory: %w", err)
	}
	if err := os.Chmod(tmpPath, perm); err != nil {
		return fmt.Errorf("set temp file permissions: %w", err)
	}
	if err := os.Rename(tmpPath, dst); err != nil {
		return fmt.Errorf("install downloaded file: %w", err)
	}
	return nil
}