package migrate

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"io/fs"
	"path"

	"gitea.auvem.com/go-toolkit/app"
	"gitea.auvem.com/go-toolkit/dbx"
	"github.com/pressly/goose/v3"
)

// SQLOFunc returns the SQL database handle for migrations.
type SQLOFunc func() *sql.DB

var (
	ErrNotInitialized      = errors.New("migrations module not initialized")
	ErrPendingMigrations   = errors.New("pending migrations detected but auto-migration is disabled")
	ErrInvalidMigrationCfg = errors.New("invalid migration configuration")
)

// MigrationOpts defines options for the migrations module.
type MigrationOpts struct {
	// SQLO is the SQL database handle getter used for migrations. REQUIRED.
	SQLO SQLOFunc

	// Dialect is the database dialect used for migrations (e.g., "mysql", "postgres").
	// REQUIRED. Must match the dialect used in dbx.
	Dialect goose.Dialect

	// FS is the filesystem where migration files are stored.
	FS fs.FS

	// BasePath is the directory within FS where migration files are located.
	// Defaults to "." if not set.
	BasePath string
}

const (
	ModuleMigrationsName   = "migrations"
	ModuleMigrateUpName    = "migrate up"
	ModuleMigrateBlankName = "migrate down to blank"
	ModuleAutoMigrateName  = "auto migrate"
)

var (
	migrationProvider  *goose.Provider
	migrationsConfig   MigrationOpts
	migrationsModule   *app.Module
	moduleMigrateBlank *app.Module
	moduleMigrateUp    *app.Module
	autoMigrateEnabled bool
	autoMigrateModule  *app.Module
)

// MigrationsConfig returns a copy of the active migration configuration.
func MigrationsConfig() MigrationOpts {
	migrationsModule.RequireLoaded()
	return migrationsConfig
}

// ModuleMigrations returns the migrations module with the provided configuration.
func ModuleMigrations(cfg *MigrationOpts) (*app.Module, error) {
	if migrationsModule != nil {
		return nil, fmt.Errorf("ModuleMigrations initialized multiple times")
	}
	if err := validateMigrationOpts(cfg); err != nil {
		return nil, err
	}
	migrationsConfig = *cfg
	migrationsModule = app.NewModule(ModuleMigrationsName, app.ModuleOpts{
		Setup:   setupMigrations,
		Depends: []string{dbx.ModuleDBName},
	})
	return migrationsModule, nil
}

// MustModuleMigrations is like [ModuleMigrations] but panics on error.
func MustModuleMigrations(cfg *MigrationOpts) *app.Module {
	mod, err := ModuleMigrations(cfg)
	if err != nil {
		panic(err)
	}
	return mod
}

// ModuleMigrateUp returns a module that applies pending migrations on setup.
func ModuleMigrateUp() *app.Module {
	if moduleMigrateUp != nil {
		panic("ModuleMigrateUp initialized multiple times")
	}
	moduleMigrateUp = app.NewModule(ModuleMigrateUpName, app.ModuleOpts{
		Setup: func(_ *app.Module) error {
			_, err := ApplyPendingMigrations(context.Background(), -1)
			return err
		},
		Depends: []string{ModuleMigrationsName},
	})
	return moduleMigrateUp
}

// ModuleMigrateBlank returns a module that rolls back all migrations.
func ModuleMigrateBlank() *app.Module {
	if moduleMigrateBlank != nil {
		panic("ModuleMigrateBlank initialized multiple times")
	}
	moduleMigrateBlank = app.NewModule(ModuleMigrateBlankName, app.ModuleOpts{
		Setup: func(_ *app.Module) error {
			_, err := MigrateToBlank(context.Background())
			return err
		},
		Depends: []string{ModuleMigrationsName},
	})
	return moduleMigrateBlank
}

// ModuleAutoMigrate returns a module that auto-applies pending migrations when enabled.
func ModuleAutoMigrate(enabled bool) *app.Module {
	if autoMigrateModule != nil {
		panic("ModuleAutoMigrate initialized multiple times")
	}
	autoMigrateEnabled = enabled
	autoMigrateModule = app.NewModule(ModuleAutoMigrateName, app.ModuleOpts{
		Setup: func(_ *app.Module) error {
			return AutoMigrate(context.Background())
		},
		Depends: []string{ModuleMigrationsName},
	})
	return autoMigrateModule
}

func validateMigrationOpts(cfg *MigrationOpts) error {
	if cfg == nil {
		return fmt.Errorf("%w: config is nil", ErrInvalidMigrationCfg)
	}
	if cfg.SQLO == nil {
		return fmt.Errorf("%w: SQLO is required", ErrInvalidMigrationCfg)
	}
	if cfg.FS == nil {
		return fmt.Errorf("%w: FS is required", ErrInvalidMigrationCfg)
	}
	if cfg.Dialect == "" {
		return fmt.Errorf("%w: Dialect is required", ErrInvalidMigrationCfg)
	}
	if cfg.BasePath == "" {
		cfg.BasePath = "."
	}
	return nil
}

func migrationFS(cfg MigrationOpts) (fs.FS, error) {
	if cfg.BasePath == "." || cfg.BasePath == "" {
		return cfg.FS, nil
	}
	return fs.Sub(cfg.FS, cfg.BasePath)
}

func normalizeCreateDir(basePath string) string {
	if basePath == "." || basePath == "" {
		return "migrations"
	}
	return path.Clean(basePath)
}