package migrate

import (
	"database/sql"
	"errors"
	"fmt"
	"strings"
	"time"

	"github.com/go-sql-driver/mysql"
)

// EnsureSchema applies all "up" migrations when the database has no tables.
func EnsureSchema(db *sql.DB, dir string) error {
	columnName, err := ensureSchemaMigrations(db)
	if err != nil {
		return err
	}

	empty, err := isDatabaseEmpty(db)
	if err != nil {
		return err
	}

	runner := Runner{Dir: dir}
	migrations, err := runner.Load(Up)
	if err != nil {
		return err
	}
	if empty {
		for _, migration := range migrations {
			if err := execStatements(db, migration.SQL); err != nil {
				return fmt.Errorf("apply %s: %w", migration.Name, err)
			}
			if err := recordMigration(db, columnName, migration.Name); err != nil {
				return err
			}
		}
		return nil
	}

	applied, err := loadAppliedMigrations(db, columnName)
	if err != nil {
		return err
	}
	for _, migration := range migrations {
		if applied[migration.Name] {
			continue
		}
		if err := execStatements(db, migration.SQL); err != nil {
			return fmt.Errorf("apply %s: %w", migration.Name, err)
		}
		if err := recordMigration(db, columnName, migration.Name); err != nil {
			return err
		}
	}

	return nil
}

func isDatabaseEmpty(db *sql.DB) (bool, error) {
	var count int
	if err := db.QueryRow(`SELECT COUNT(*) FROM information_schema.tables WHERE table_schema = DATABASE()`).Scan(&count); err != nil {
		return false, err
	}
	return count == 0, nil
}

func execStatements(db *sql.DB, sqlText string) error {
	statements := strings.Split(sqlText, ";")
	for _, stmt := range statements {
		stmt = strings.TrimSpace(stmt)
		if stmt == "" {
			continue
		}
		if _, err := db.Exec(stmt); err != nil {
			var mysqlErr *mysql.MySQLError
			if errors.As(err, &mysqlErr) && (mysqlErr.Number == 1060 || mysqlErr.Number == 1061) {
				continue
			}
			return err
		}
	}
	return nil
}

func ensureSchemaMigrations(db *sql.DB) (string, error) {
	column, err := schemaMigrationsColumn(db)
	if err != nil {
		return "", err
	}
	if column != "" {
		return column, nil
	}

	if _, err := db.Exec(`CREATE TABLE IF NOT EXISTS schema_migrations (
		id BIGINT PRIMARY KEY AUTO_INCREMENT,
		name VARCHAR(255) NOT NULL UNIQUE,
		applied_at TIMESTAMP NOT NULL
	)`); err != nil {
		return "", err
	}

	return "name", nil
}

func schemaMigrationsColumn(db *sql.DB) (string, error) {
	var nameCount int
	if err := db.QueryRow(`
		SELECT COUNT(*)
		FROM information_schema.columns
		WHERE table_schema = DATABASE()
		  AND table_name = 'schema_migrations'
		  AND column_name = 'name'
	`).Scan(&nameCount); err != nil {
		return "", err
	}
	if nameCount > 0 {
		return "name", nil
	}

	var versionCount int
	if err := db.QueryRow(`
		SELECT COUNT(*)
		FROM information_schema.columns
		WHERE table_schema = DATABASE()
		  AND table_name = 'schema_migrations'
		  AND column_name = 'version'
	`).Scan(&versionCount); err != nil {
		return "", err
	}
	if versionCount > 0 {
		return "version", nil
	}

	return "", nil
}

func loadAppliedMigrations(db *sql.DB, column string) (map[string]bool, error) {
	query := fmt.Sprintf("SELECT %s FROM schema_migrations", column)
	rows, err := db.Query(query)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	applied := map[string]bool{}
	for rows.Next() {
		var name string
		if err := rows.Scan(&name); err != nil {
			return nil, err
		}
		applied[name] = true
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}
	return applied, nil
}

func recordMigration(db *sql.DB, column, name string) error {
	query := fmt.Sprintf("INSERT INTO schema_migrations (%s, applied_at) VALUES (?, ?)", column)
	_, err := db.Exec(query, name, time.Now().UTC())
	return err
}