// Package main is the migration runner. It applies embedded SQL migrations to the
// configured database. Intended to run as a one-shot container/job before the API.
//
// Usage: migrate [up|down|version|force <n>]
package main

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"os"
	"time"

	"github.com/golang-migrate/migrate/v4"
	_ "github.com/golang-migrate/migrate/v4/database/postgres"
	"github.com/golang-migrate/migrate/v4/source/iofs"

	"github.com/mitbringsl/backend/internal/config"
	"github.com/mitbringsl/backend/internal/logging"
	"github.com/mitbringsl/backend/migrations"
)

func main() {
	cfg, err := config.Load()
	if err != nil {
		fmt.Fprintf(os.Stderr, "config: %v\n", err)
		os.Exit(1)
	}
	logging.Init(cfg.LogLevel)

	cmd := "up"
	if len(os.Args) > 1 {
		cmd = os.Args[1]
	}

	if err := run(cfg, cmd); err != nil {
		slog.Error("migration failed", "cmd", cmd, "error", err)
		os.Exit(1)
	}
}

func run(cfg *config.Config, cmd string) error {
	src, err := iofs.New(migrations.FS, ".")
	if err != nil {
		return fmt.Errorf("create source: %w", err)
	}

	// Use the configured DATABASE_URL; golang-migrate accepts the same DSN
	// form pgx uses (postgres://...). Allow a short startup grace period.
	dbURL := cfg.DatabaseURL

	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()

	var m *migrate.Migrate
	var lastErr error
	for attempt := 0; attempt < 30; attempt++ {
		m, lastErr = migrate.NewWithSourceInstance("iofs", src, dbURL)
		if lastErr == nil {
			break
		}
		select {
		case <-ctx.Done():
			return fmt.Errorf("db not ready: %w", lastErr)
		case <-time.After(time.Second):
		}
	}
	if lastErr != nil {
		return fmt.Errorf("create migrate instance: %w", lastErr)
	}
	defer m.Close()

	switch cmd {
	case "up":
		if err := m.Up(); err != nil && !errors.Is(err, migrate.ErrNoChange) {
			return err
		}
		slog.Info("migrations applied (up)")
	case "down":
		if err := m.Down(); err != nil && !errors.Is(err, migrate.ErrNoChange) {
			return err
		}
		slog.Info("migrations applied (down)")
	case "version":
		v, dirty, err := m.Version()
		if err != nil {
			return err
		}
		fmt.Printf("version=%d dirty=%v\n", v, dirty)
	case "force":
		if len(os.Args) < 3 {
			return errors.New("force requires a version argument")
		}
		var v int
		fmt.Sscanf(os.Args[2], "%d", &v)
		if err := m.Force(v); err != nil {
			return err
		}
		slog.Info("forced migration version", "version", v)
	default:
		return fmt.Errorf("unknown command %q (use up|down|version|force)", cmd)
	}
	return nil
}