package schema

import (
	"context"
	"database/sql"
	"fmt"
	"net/url"
	"regexp"
	"strings"
)

var dbNameRe = regexp.MustCompile(`^[a-z][a-z0-9_]{1,47}$`)

type Runner interface {
	ExecDDL(ctx context.Context, stmts []string) error
	EnsureDatabase(ctx context.Context, dbName string) error
}

type NoopRunner struct{}

func (NoopRunner) ExecDDL(context.Context, []string) error   { return nil }
func (NoopRunner) EnsureDatabase(context.Context, string) error { return nil }

type PostgresRunner struct {
	DB          *sql.DB
	AdminDSN    string // 用于 CREATE DATABASE（连到 postgres 库）
}

func (r *PostgresRunner) ExecDDL(ctx context.Context, stmts []string) error {
	tx, err := r.DB.BeginTx(ctx, nil)
	if err != nil {
		return err
	}
	defer func() { _ = tx.Rollback() }()
	for _, s := range stmts {
		if _, err := tx.ExecContext(ctx, s); err != nil {
			return fmt.Errorf("ddl failed: %w\nsql: %s", err, s)
		}
	}
	return tx.Commit()
}

func (r *PostgresRunner) EnsureDatabase(ctx context.Context, dbName string) error {
	if !dbNameRe.MatchString(dbName) {
		return fmt.Errorf("invalid database name: %s", dbName)
	}
	admin := r.DB
	var err error
	if r.AdminDSN != "" {
		admin, err = sql.Open("postgres", r.AdminDSN)
		if err != nil {
			return err
		}
		defer admin.Close()
	}
	var exists bool
	if err := admin.QueryRowContext(ctx,
		`SELECT EXISTS(SELECT 1 FROM pg_database WHERE datname=$1)`, dbName,
	).Scan(&exists); err != nil {
		return err
	}
	if exists {
		return nil
	}
	// CREATE DATABASE 不能在事务中
	_, err = admin.ExecContext(ctx, fmt.Sprintf(`CREATE DATABASE %s`, quoteIdent(dbName)))
	return err
}

// DSNForDatabase 把原 DSN 的库名替换为目标库。
func DSNForDatabase(baseDSN, dbName string) (string, error) {
	if !dbNameRe.MatchString(dbName) {
		return "", fmt.Errorf("invalid database name")
	}
	u, err := url.Parse(baseDSN)
	if err != nil {
		return "", err
	}
	u.Path = "/" + dbName
	return u.String(), nil
}

func QuoteIdentExport(name string) string { return quoteIdent(name) }

func SanitizeDBName(tenantID int64, slug string) string {
	name := fmt.Sprintf("appdb_t%d_%s", tenantID, slug)
	name = strings.ToLower(name)
	if len(name) > 48 {
		name = name[:48]
	}
	return name
}