package config

import (
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"
)

const backupDirName = ".backups"

// BackupInfo holds metadata about a single backup.
type BackupInfo struct {
	Version   string `json:"version"`
	Timestamp string `json:"timestamp"`
	Path      string `json:"path"`
}

// CreateBackup copies the current file into a timestamped backup before modification.
// Returns the backup version string. If the source file doesn't exist, returns "" with no error.
func CreateBackup(baseDir, relPath string, maxBackups int) (string, error) {
	srcPath, err := FullPath(baseDir, relPath)
	if err != nil {
		return "", err
	}

	if _, err := os.Stat(srcPath); os.IsNotExist(err) {
		return "", nil
	}

	data, err := os.ReadFile(srcPath)
	if err != nil {
		return "", fmt.Errorf("read source for backup: %w", err)
	}

	backupDir := filepath.Join(baseDir, backupDirName, filepath.Dir(filepath.Clean(relPath)))
	if err := os.MkdirAll(backupDir, 0o755); err != nil {
		return "", fmt.Errorf("create backup dir: %w", err)
	}

	version := time.Now().UTC().Format("20060102T150405Z")
	base := filepath.Base(relPath)
	ext := filepath.Ext(base)
	name := strings.TrimSuffix(base, ext)
	backupName := fmt.Sprintf("%s.%s%s", name, version, ext)
	backupPath := filepath.Join(backupDir, backupName)

	if err := AtomicWrite(backupPath, data, 0o644); err != nil {
		return "", fmt.Errorf("write backup: %w", err)
	}

	if err := pruneBackups(backupDir, name, ext, maxBackups); err != nil {
		return "", fmt.Errorf("prune backups: %w", err)
	}

	return version, nil
}

// ListBackups returns all backup versions for a given config file, newest first.
func ListBackups(baseDir, relPath string) ([]BackupInfo, error) {
	if err := ValidatePath(relPath); err != nil {
		return nil, err
	}

	backupDir := filepath.Join(baseDir, backupDirName, filepath.Dir(filepath.Clean(relPath)))
	base := filepath.Base(relPath)
	ext := filepath.Ext(base)
	name := strings.TrimSuffix(base, ext)
	prefix := name + "."

	entries, err := os.ReadDir(backupDir)
	if os.IsNotExist(err) {
		return nil, nil
	}
	if err != nil {
		return nil, fmt.Errorf("read backup dir: %w", err)
	}

	var backups []BackupInfo
	for _, e := range entries {
		fname := e.Name()
		if !strings.HasPrefix(fname, prefix) || !strings.HasSuffix(fname, ext) {
			continue
		}
		version := strings.TrimSuffix(strings.TrimPrefix(fname, prefix), ext)
		backups = append(backups, BackupInfo{
			Version:   version,
			Timestamp: version,
			Path:      filepath.Join(backupDir, fname),
		})
	}

	sort.Slice(backups, func(i, j int) bool {
		return backups[i].Version > backups[j].Version
	})

	return backups, nil
}

// Rollback restores a config file to the given backup version.
func Rollback(baseDir, relPath, version string) error {
	if err := ValidatePath(relPath); err != nil {
		return err
	}

	backupDir := filepath.Join(baseDir, backupDirName, filepath.Dir(filepath.Clean(relPath)))
	base := filepath.Base(relPath)
	ext := filepath.Ext(base)
	name := strings.TrimSuffix(base, ext)
	backupName := fmt.Sprintf("%s.%s%s", name, version, ext)
	backupPath := filepath.Join(backupDir, backupName)

	data, err := os.ReadFile(backupPath)
	if err != nil {
		return fmt.Errorf("read backup %q: %w", version, err)
	}

	targetPath, err := FullPath(baseDir, relPath)
	if err != nil {
		return err
	}

	return AtomicWrite(targetPath, data, 0o644)
}

// pruneBackups removes oldest backups exceeding maxBackups.
func pruneBackups(backupDir, name, ext string, maxBackups int) error {
	if maxBackups <= 0 {
		return nil
	}

	prefix := name + "."
	entries, err := os.ReadDir(backupDir)
	if err != nil {
		return err
	}

	var matching []string
	for _, e := range entries {
		if strings.HasPrefix(e.Name(), prefix) && strings.HasSuffix(e.Name(), ext) {
			matching = append(matching, e.Name())
		}
	}

	sort.Strings(matching)

	if len(matching) > maxBackups {
		for _, old := range matching[:len(matching)-maxBackups] {
			os.Remove(filepath.Join(backupDir, old))
		}
	}

	return nil
}