package data

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

	"gorm.io/gorm"
	"kra/internal/config"
	"kra/pkg/database/migration"
	"kra/pkg/module"
)

// MigrateDatabase opens only the configured primary database. It does not
// create a database, start a scheduler, open SDK clients, or initialize users.
func MigrateDatabase(ctx context.Context, c *config.Database, catalog module.Catalog, logger *slog.Logger, checkOnly bool) error {
	if !databaseConnectionConfigured(c) {
		return fmt.Errorf("migration requires an existing configured database")
	}
	migrationConfig := *c
	// One connection holds the advisory lock, a second executes migrations.
	if !checkOnly && migrationConfig.MaxOpenConns > 0 && migrationConfig.MaxOpenConns < 2 {
		migrationConfig.MaxOpenConns = 2
	}
	db, err := openDatabase(&migrationConfig, false, "", logger)
	if err != nil {
		return fmt.Errorf("open migration database: %w", err)
	}
	defer closeGormDB(db)
	db = db.WithContext(ctx)
	if checkOnly {
		return checkMigratedSchema(db, catalog)
	}
	// A dedicated connection owns the lock even when a migration uses a
	// transaction or temporarily changes connection-local SQL compatibility.
	run := func() error {
		if err := catalog.CheckPrerequisites(db); err != nil {
			return err
		}
		if err := migrateAll(db, catalog); err != nil {
			return err
		}
		return checkMigratedSchema(db, catalog)
	}
	if db.Dialector.Name() != "mysql" {
		return run()
	}
	return db.Connection(func(conn *gorm.DB) error {
		var name string
		if err := conn.Raw("SELECT CONCAT('sw_to_kra:', MD5(DATABASE()))").Scan(&name).Error; err != nil {
			return err
		}
		var locked int
		if err := conn.Session(&gorm.Session{NewDB: true}).Raw("SELECT GET_LOCK(?, 0)", name).Scan(&locked).Error; err != nil {
			return err
		}
		if locked != 1 {
			return fmt.Errorf("another migration owns the database lock")
		}
		defer func() {
			cleanup, cancel := context.WithTimeout(context.WithoutCancel(ctx), 5*time.Second)
			defer cancel()
			conn.Session(&gorm.Session{NewDB: true}).WithContext(cleanup).Exec("DO RELEASE_LOCK(?)", name)
		}()
		return run()
	})
}

func checkMigratedSchema(db *gorm.DB, catalog module.Catalog) error {
	db = db.Session(&gorm.Session{NewDB: true})
	if err := migration.CheckApplied(db, catalog.MigrationSteps()); err != nil {
		return fmt.Errorf("run -migrate before starting the service: %w", err)
	}
	if err := catalog.CheckSchema(db); err != nil {
		return fmt.Errorf("database schema is incomplete: %w", err)
	}
	return nil
}