// Package migrate configures Goose providers for embedded application migrations.
// Applications own their database, migration files, and startup ordering.
package migrate

import (
	"database/sql"
	"embed"
	"fmt"
	"io/fs"
	"log/slog"

	"github.com/pressly/goose/v3"
	"github.com/pressly/goose/v3/lock"
)

// New returns a provider for SQL files in dir and optional provider-local Go
// migrations. Pass "." for files at the embedded root and a nonnil logger.
// The selected directory must exist, including when using only Go migrations.
// Construction does not connect to db; the caller owns and closes db.
//
// PostgreSQL uses Goose's session advisory locker with its default lock ID and
// retry limits. Other dialects require the caller to serialize migration runs
// across providers/processes. PostgreSQL connections must preserve session
// affinity (transaction-pooling proxies cannot safely hold session locks).
//
// Use the returned Provider's Up, UpTo, DownTo, Status, GetDBVersion, GetVersions,
// and HasPending methods directly. Create migration files with Goose's create
// command; lexical filename order must match numeric version order. Go migrations
// are registered per provider; global Go registration is ignored.
func New(db *sql.DB, dialect goose.Dialect, files embed.FS, dir string, logger *slog.Logger, migrations ...*goose.Migration) (*goose.Provider, error) {
	for i, migration := range migrations {
		if migration == nil {
			return nil, fmt.Errorf("migrate: Go migration %d must not be nil", i)
		}
	}
	root, err := fs.Sub(files, dir)
	if err != nil {
		return nil, fmt.Errorf("migrate: directory %q: %w", dir, err)
	}
	info, err := fs.Stat(root, ".")
	if err != nil {
		return nil, fmt.Errorf("migrate: directory %q: %w", dir, err)
	}
	if !info.IsDir() {
		return nil, fmt.Errorf("migrate: directory %q: not a directory", dir)
	}
	opts := []goose.ProviderOption{
		goose.WithDisableGlobalRegistry(true),
		goose.WithGoMigrations(migrations...),
		goose.WithSlog(logger),
		goose.WithVerbose(true),
	}
	if dialect == goose.DialectPostgres {
		locker, err := lock.NewPostgresSessionLocker()
		if err != nil {
			return nil, fmt.Errorf("migrate: postgres locker: %w", err)
		}
		opts = append(opts, goose.WithSessionLocker(locker))
	}
	provider, err := goose.NewProvider(dialect, db, root, opts...)
	if err != nil {
		return nil, fmt.Errorf("migrate: new provider: %w", err)
	}
	return provider, nil
}