package database

import (
	"context"
	"database/sql"
	"fmt"
	"regexp"
	"strings"
	"time"

	"github.com/golang-migrate/migrate/v4"
	migratepg "github.com/golang-migrate/migrate/v4/database/postgres"
	_ "github.com/golang-migrate/migrate/v4/source/file"
	"github.com/jackc/pgx/v5/pgxpool"
	"github.com/jackc/pgx/v5/stdlib"
)

var validTenantID = regexp.MustCompile(`^[a-zA-Z0-9_-]{1,63}$`)

type DB struct {
	Pool *pgxpool.Pool
	dsn  string
}

func New(dsn string) (*DB, error) {
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	pool, err := pgxpool.New(ctx, dsn)
	if err != nil {
		return nil, fmt.Errorf("database: failed to create pool: %w", err)
	}

	if err := pool.Ping(ctx); err != nil {
		pool.Close()
		return nil, fmt.Errorf("database: failed to ping: %w", err)
	}

	return &DB{Pool: pool, dsn: dsn}, nil
}

func (db *DB) Ping() error {
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	return db.Pool.Ping(ctx)
}

func (db *DB) Close() {
	db.Pool.Close()
}

func tenantSchema(tenantID string) string {
	return fmt.Sprintf("tenant_%s", strings.ReplaceAll(tenantID, "-", "_"))
}

func (db *DB) SetTenantSchema(ctx context.Context, tenantID string) error {
	if !validTenantID.MatchString(tenantID) {
		return fmt.Errorf("database: invalid tenantID %q", tenantID)
	}
	schema := tenantSchema(tenantID)
	_, err := db.Pool.Exec(ctx, fmt.Sprintf(`SET search_path = "%s", public`, schema))
	return err
}

func (db *DB) ResetSchema(ctx context.Context) error {
	_, err := db.Pool.Exec(ctx, "SET search_path = public")
	return err
}

func (db *DB) stdDB(dsn string) (*sql.DB, error) {
	cfg, err := pgxpool.ParseConfig(dsn)
	if err != nil {
		return nil, err
	}
	return stdlib.OpenDB(*cfg.ConnConfig), nil
}

func (db *DB) MigratePublic(dsn, migrationsPath string) error {
	stdDB, err := db.stdDB(dsn)
	if err != nil {
		return fmt.Errorf("migrate: %w", err)
	}
	defer stdDB.Close()

	driver, err := migratepg.WithInstance(stdDB, &migratepg.Config{SchemaName: "public"})
	if err != nil {
		return fmt.Errorf("migrate: driver: %w", err)
	}

	m, err := migrate.NewWithDatabaseInstance(
		"file://"+migrationsPath,
		"postgres",
		driver,
	)
	if err != nil {
		return fmt.Errorf("migrate: %w", err)
	}

	if err := m.Up(); err != nil && err != migrate.ErrNoChange {
		return fmt.Errorf("migrate: %w", err)
	}
	return nil
}

// MigrateTenantSchema ensures the tenant schema exists and runs all pending migrations.
// Safe to call on existing tenants — golang-migrate tracks state in schema_migrations.
// The 000001 migration uses IF NOT EXISTS so re-running it is idempotent.
func (db *DB) MigrateTenantSchema(ctx context.Context, tenantID, migrationsPath string) error {
	if !validTenantID.MatchString(tenantID) {
		return fmt.Errorf("database: invalid tenantID %q", tenantID)
	}
	schema := tenantSchema(tenantID)

	// Ensure schema exists before handing off to golang-migrate.
	conn, err := db.Pool.Acquire(ctx)
	if err != nil {
		return fmt.Errorf("migrate tenant: acquire: %w", err)
	}
	_, execErr := conn.Exec(ctx, fmt.Sprintf(`CREATE SCHEMA IF NOT EXISTS "%s"`, schema))
	conn.Release()
	if execErr != nil {
		return fmt.Errorf("migrate tenant: create schema: %w", execErr)
	}

	// Append search_path to DSN so every connection golang-migrate opens
	// automatically resolves unqualified table names to the tenant schema.
	tenantDSN := db.dsn
	sep := "?"
	if strings.Contains(tenantDSN, "?") {
		sep = "&"
	}
	tenantDSN += sep + "search_path=" + schema

	stdDB, err := db.stdDB(tenantDSN)
	if err != nil {
		return fmt.Errorf("migrate tenant: open stdDB: %w", err)
	}
	defer stdDB.Close()

	driver, err := migratepg.WithInstance(stdDB, &migratepg.Config{SchemaName: schema})
	if err != nil {
		return fmt.Errorf("migrate tenant: driver: %w", err)
	}

	m, err := migrate.NewWithDatabaseInstance("file://"+migrationsPath, "postgres", driver)
	if err != nil {
		return fmt.Errorf("migrate tenant: init: %w", err)
	}

	if err := m.Up(); err != nil && err != migrate.ErrNoChange {
		return fmt.Errorf("migrate tenant %s: %w", tenantID, err)
	}
	return nil
}

// ProvisionTenantSchema is an alias kept for call-site compatibility.
func (db *DB) ProvisionTenantSchema(ctx context.Context, tenantID, migrationsPath string) error {
	return db.MigrateTenantSchema(ctx, tenantID, migrationsPath)
}

// MigrateAllTenantSchemas runs pending migrations against every registered tenant.
// Called at startup so existing tenants always get new migration files applied.
func (db *DB) MigrateAllTenantSchemas(ctx context.Context, migrationsPath string) error {
	rows, err := db.Pool.Query(ctx, `SELECT id FROM public.tenants`)
	if err != nil {
		return fmt.Errorf("migrate all tenants: query: %w", err)
	}
	defer rows.Close()

	var ids []string
	for rows.Next() {
		var id string
		if err := rows.Scan(&id); err != nil {
			return fmt.Errorf("migrate all tenants: scan: %w", err)
		}
		ids = append(ids, id)
	}

	for _, id := range ids {
		if err := db.MigrateTenantSchema(ctx, id, migrationsPath); err != nil {
			return err
		}
	}
	return nil
}