// Package backup creates rotating copies of the SQLite logbook so a single
// disk failure or accidental delete doesn't wipe the user's QSO history.
// The strategy is intentionally simple: a daily snapshot of the .db file
// (optionally zipped), keeping the last N. SQLite's atomic-commit format
// lets us copy the raw file safely as long as we copy after a checkpoint.
package backup

import (
	"archive/zip"
	"context"
	"database/sql"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"
)

// Settings holds the user-tweakable backup configuration. Stored as flat
// key/value pairs in the settings table (so we don't need a schema change
// every time we add a field).
type Settings struct {
	Enabled      bool   `json:"enabled"`
	Folder       string `json:"folder"`        // empty → DefaultFolder
	Rotation     int    `json:"rotation"`      // how many backups to keep; 0/neg = 5
	Zip          bool   `json:"zip"`           // compress with deflate
	LastBackupAt string `json:"last_backup_at"`// RFC3339; empty if never
}

// DefaultFolder returns the folder used when Settings.Folder is empty.
// It sits next to the database file (in <appdata>/hamlog/backups) which
// keeps it portable when the user moves the data directory.
func DefaultFolder(dataDir string) string {
	return filepath.Join(dataDir, "backups")
}

// Run executes one backup pass: checkpoint WAL → copy the database file
// → optionally zip → rotate. Returns the path of the file that was
// written so the caller can surface it to the UI.
//
// dbConn is used to issue the WAL checkpoint so the on-disk file is
// self-consistent before we copy it. It's the same *sql.DB the app uses;
// SQLite tolerates concurrent reads during the copy.
func Run(ctx context.Context, dbConn *sql.DB, dbPath, folder string, rotation int, doZip bool) (string, error) {
	if dbConn == nil {
		return "", fmt.Errorf("nil db connection")
	}
	if rotation <= 0 {
		rotation = 5
	}
	if folder == "" {
		return "", fmt.Errorf("backup folder not set")
	}
	if err := os.MkdirAll(folder, 0o755); err != nil {
		return "", fmt.Errorf("create backup folder: %w", err)
	}
	// Flush WAL into the main file so a raw copy is a complete database.
	// TRUNCATE removes the -wal file's contents after checkpointing.
	if _, err := dbConn.ExecContext(ctx, `PRAGMA wal_checkpoint(TRUNCATE);`); err != nil {
		return "", fmt.Errorf("wal_checkpoint: %w", err)
	}

	stamp := time.Now().Format("2006-01-02")
	base := fmt.Sprintf("opslog-%s", stamp)
	var dstPath string
	if doZip {
		dstPath = filepath.Join(folder, base+".db.zip")
		if err := copyZipped(dbPath, dstPath); err != nil {
			return "", err
		}
	} else {
		dstPath = filepath.Join(folder, base+".db")
		if err := copyFile(dbPath, dstPath); err != nil {
			return "", err
		}
	}

	if err := rotate(folder, rotation); err != nil {
		// Rotation errors are non-fatal — the backup itself succeeded.
		return dstPath, fmt.Errorf("rotate: %w (backup OK at %s)", err, dstPath)
	}
	return dstPath, nil
}

// copyFile performs a plain file copy. We don't use os.Rename because
// the source is the live database; we want a fresh standalone file.
func copyFile(src, dst string) error {
	in, err := os.Open(src)
	if err != nil {
		return fmt.Errorf("open source: %w", err)
	}
	defer in.Close()
	out, err := os.Create(dst)
	if err != nil {
		return fmt.Errorf("create dest: %w", err)
	}
	if _, err := io.Copy(out, in); err != nil {
		out.Close()
		os.Remove(dst)
		return fmt.Errorf("copy: %w", err)
	}
	return out.Close()
}

// copyZipped writes a single-entry deflate zip containing the database.
// The inner filename is just the base of the source so unzip restores
// "hamlog.db" wherever the user extracts.
func copyZipped(src, dst string) error {
	in, err := os.Open(src)
	if err != nil {
		return fmt.Errorf("open source: %w", err)
	}
	defer in.Close()

	out, err := os.Create(dst)
	if err != nil {
		return fmt.Errorf("create dest: %w", err)
	}
	zw := zip.NewWriter(out)
	w, err := zw.Create(filepath.Base(src))
	if err != nil {
		zw.Close()
		out.Close()
		os.Remove(dst)
		return fmt.Errorf("zip entry: %w", err)
	}
	if _, err := io.Copy(w, in); err != nil {
		zw.Close()
		out.Close()
		os.Remove(dst)
		return fmt.Errorf("zip write: %w", err)
	}
	if err := zw.Close(); err != nil {
		out.Close()
		os.Remove(dst)
		return fmt.Errorf("zip close: %w", err)
	}
	return out.Close()
}

// rotate keeps the most recent `keep` backups in folder and deletes the
// rest. Only files matching the opslog-*.db / opslog-*.db.zip pattern
// are touched — never user files that happen to live in the same folder.
func rotate(folder string, keep int) error {
	entries, err := os.ReadDir(folder)
	if err != nil {
		return err
	}
	type item struct {
		path string
		mod  time.Time
	}
	matches := make([]item, 0, len(entries))
	for _, e := range entries {
		if e.IsDir() {
			continue
		}
		name := e.Name()
		if !strings.HasPrefix(name, "opslog-") {
			continue
		}
		if !(strings.HasSuffix(name, ".db") || strings.HasSuffix(name, ".db.zip")) {
			continue
		}
		info, err := e.Info()
		if err != nil {
			continue
		}
		matches = append(matches, item{path: filepath.Join(folder, name), mod: info.ModTime()})
	}
	if len(matches) <= keep {
		return nil
	}
	sort.Slice(matches, func(i, j int) bool { return matches[i].mod.After(matches[j].mod) })
	var firstErr error
	for _, m := range matches[keep:] {
		if err := os.Remove(m.path); err != nil && firstErr == nil {
			firstErr = err
		}
	}
	return firstErr
}

// HasBackupToday returns true if a backup for today's date already exists
// in folder. Used by the startup auto-backup to skip when the user has
// already restarted the app once today.
func HasBackupToday(folder string) bool {
	if folder == "" {
		return false
	}
	stamp := time.Now().Format("2006-01-02")
	for _, ext := range []string{".db", ".db.zip"} {
		if _, err := os.Stat(filepath.Join(folder, "opslog-"+stamp+ext)); err == nil {
			return true
		}
	}
	return false
}