package mover

import (
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"syscall"
)

// safeRename moves src to dst. Refuses to overwrite an existing dst.
// Falls back to copy+remove on EXDEV (cross-device) errors.
func safeRename(src, dst string) error {
	if _, err := os.Stat(dst); err == nil {
		return fmt.Errorf("destination %s already exists", dst)
	} else if !errors.Is(err, os.ErrNotExist) {
		return fmt.Errorf("stat destination %s: %w", dst, err)
	}

	err := os.Rename(src, dst)
	if err == nil {
		return nil
	}

	var linkErr *os.LinkError
	if !errors.As(err, &linkErr) || !errors.Is(err, syscall.EXDEV) {
		return fmt.Errorf("renaming %s to %s: %w", src, dst, err)
	}

	return copyAndRemove(src, dst)
}

// copyAndRemove implements the cross-device fallback: copy src to dst, fsync,
// then remove src. Uses O_EXCL to belt-and-suspenders against a race.
func copyAndRemove(src, dst string) error {
	in, err := os.Open(src)
	if err != nil {
		return fmt.Errorf("opening source %s: %w", src, err)
	}
	defer in.Close()

	out, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0644)
	if err != nil {
		return fmt.Errorf("creating destination %s: %w", dst, err)
	}

	if _, err := io.Copy(out, in); err != nil {
		out.Close()
		os.Remove(dst)
		return fmt.Errorf("copying %s to %s: %w", src, dst, err)
	}

	if err := out.Sync(); err != nil {
		out.Close()
		os.Remove(dst)
		return fmt.Errorf("syncing destination %s: %w", dst, err)
	}

	if err := out.Close(); err != nil {
		os.Remove(dst)
		return fmt.Errorf("closing destination %s: %w", dst, err)
	}

	if err := in.Close(); err != nil {
		return fmt.Errorf("closing source %s: %w", src, err)
	}

	if err := os.Remove(src); err != nil {
		return fmt.Errorf("removing source %s: %w", src, err)
	}

	return nil
}

func MoveToFailed(input, failedDir string) error {
	if err := os.MkdirAll(failedDir, 0755); err != nil {
		return fmt.Errorf("creating failed dir: %w", err)
	}
	dest := filepath.Join(failedDir, filepath.Base(input))
	return safeRename(input, dest)
}

func MoveToOriginals(input, originalsDir string) error {
	if err := os.MkdirAll(originalsDir, 0755); err != nil {
		return fmt.Errorf("creating originals dir: %w", err)
	}
	dest := filepath.Join(originalsDir, filepath.Base(input))
	return safeRename(input, dest)
}

func Delete(path string) error {
	return os.Remove(path)
}

func Rename(source, dest string) error {
	return safeRename(source, dest)
}