// Portions of this file are derived from https://github.com/go-gormigrate/gormigrate
// MIT License
// Copyright (c) 2016 Andrey Nering
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE

package migrator

import (
	"context"
	"errors"
	"fmt"
	"reflect"
	"time"

	"gorm.io/gorm"
)

const (
	initSchemaMigrationID = "SCHEMA_INIT"
)

// MigrateFunc is the func signature for migrating.
type MigrateFunc func(*gorm.DB) error

// RollbackFunc is the func signature for rollbacking.
type RollbackFunc func(*gorm.DB) error

// InitSchemaFunc is the func signature for initializing the schema.
type InitSchemaFunc func(*gorm.DB) error

// Options define options for all migrations.
type Options struct {
	// TableName is the migration table.
	TableName string
	// IDColumnName is the name of column where the migration id will be stored.
	IDColumnName string
	// IDColumnSize is the length of the migration id column
	IDColumnSize int
	// SequenceColumnName is the name of the auto-incrementing numeric column.
	SequenceColumnName string
	// AppliedAtColumnName is the name of the column storing when the migration was applied.
	AppliedAtColumnName string
	// StatusColumnName is the name of the column storing the migration status (success/failure).
	StatusColumnName string
	// UseTransaction makes Gormigrate execute migrations inside a single transaction.
	// Keep in mind that not all databases support DDL commands inside transactions.
	UseTransaction bool
	// ValidateUnknownMigrations will cause migrate to fail if there's unknown migration
	// IDs in the database
	ValidateUnknownMigrations bool
}

// Migration represents a database migration (a modification to be made on the database).
type Migration struct {
	// ID is the migration identifier. Usually a timestamp like "201601021504".
	ID string
	// Migrate is a function that will br executed while running this migration.
	Migrate MigrateFunc
	// Rollback will be executed on rollback. Can be nil.
	Rollback RollbackFunc
}

// Gormigrate represents a collection of all migrations of a database schema.
type Gormigrate struct {
	db         *gorm.DB
	tx         *gorm.DB
	options    *Options
	migrations []*Migration
	initSchema InitSchemaFunc
}

// ReservedIDError is returned when a migration is using a reserved ID
type ReservedIDError struct {
	ID string
}

func (e *ReservedIDError) Error() string {
	return fmt.Sprintf(`gormigrate: Reserved migration ID: "%s"`, e.ID)
}

// DuplicatedIDError is returned when more than one migration have the same ID
type DuplicatedIDError struct {
	ID string
}

func (e *DuplicatedIDError) Error() string {
	return fmt.Sprintf(`gormigrate: Duplicated migration ID: "%s"`, e.ID)
}

var (
	// DefaultOptions can be used if you don't want to think about options.
	DefaultOptions = &Options{
		TableName:                 "migrations",
		IDColumnName:              "id",
		IDColumnSize:              255,
		SequenceColumnName:        "sequence",
		AppliedAtColumnName:       "applied_at",
		StatusColumnName:          "status",
		UseTransaction:            true,
		ValidateUnknownMigrations: false,
	}

	// ErrRollbackImpossible is returned when trying to rollback a migration
	// that has no rollback function.
	ErrRollbackImpossible = errors.New("gormigrate: It's impossible to rollback this migration")

	// ErrNoMigrationDefined is returned when no migration is defined.
	ErrNoMigrationDefined = errors.New("gormigrate: No migration defined")

	// ErrMissingID is returned when the ID od migration is equal to ""
	ErrMissingID = errors.New("gormigrate: Missing ID in migration")

	// ErrNoRunMigration is returned when any run migration was found while
	// running RollbackLast
	ErrNoRunMigration = errors.New("gormigrate: Could not find last run migration")

	// ErrMigrationIDDoesNotExist is returned when migrating or rolling back to a migration ID that
	// does not exist in the list of migrations
	ErrMigrationIDDoesNotExist = errors.New("gormigrate: Tried to migrate to an ID that doesn't exist")

	// ErrUnknownPastMigration is returned if a migration exists in the DB that doesn't exist in the code
	ErrUnknownPastMigration = errors.New("gormigrate: Found migration in DB that does not exist in code")
)

// New returns a new Gormigrate.
func New(db *gorm.DB, options *Options, migrations []*Migration) *Gormigrate {
	if options == nil {
		options = DefaultOptions
	}
	if options.TableName == "" {
		options.TableName = DefaultOptions.TableName
	}
	if options.IDColumnName == "" {
		options.IDColumnName = DefaultOptions.IDColumnName
	}
	if options.IDColumnSize == 0 {
		options.IDColumnSize = DefaultOptions.IDColumnSize
	}
	if options.SequenceColumnName == "" {
		options.SequenceColumnName = DefaultOptions.SequenceColumnName
	}
	if options.AppliedAtColumnName == "" {
		options.AppliedAtColumnName = DefaultOptions.AppliedAtColumnName
	}
	if options.StatusColumnName == "" {
		options.StatusColumnName = DefaultOptions.StatusColumnName
	}
	return &Gormigrate{
		db:         db,
		options:    options,
		migrations: migrations,
	}
}

// InitSchema sets a function that is run if no migration is found.
// The idea is preventing to run all migrations when a new clean database
// is being migrating. In this function you should create all tables and
// foreign key necessary to your application.
func (g *Gormigrate) InitSchema(initSchema InitSchemaFunc) {
	g.initSchema = initSchema
}

// Migrate executes all migrations that did not run yet.
func (g *Gormigrate) Migrate() error {
	if !g.hasMigrations() {
		return ErrNoMigrationDefined
	}
	var targetMigrationID string
	if len(g.migrations) > 0 {
		targetMigrationID = g.migrations[len(g.migrations)-1].ID
	}
	return g.migrate(targetMigrationID)
}

// MigrateTo executes all migrations that did not run yet up to the migration that matches `migrationID`.
func (g *Gormigrate) MigrateTo(migrationID string) error {
	if err := g.checkIDExist(migrationID); err != nil {
		return err
	}
	return g.migrate(migrationID)
}

func (g *Gormigrate) migrate(migrationID string) error {
	if !g.hasMigrations() {
		return ErrNoMigrationDefined
	}

	if err := g.checkReservedID(); err != nil {
		return err
	}

	if err := g.checkDuplicatedID(); err != nil {
		return err
	}

	g.begin()
	defer g.rollback()

	if err := g.createMigrationTableIfNotExists(); err != nil {
		return err
	}

	if g.options.ValidateUnknownMigrations {
		unknownMigrations, err := g.unknownMigrationsHaveHappened()
		if err != nil {
			return err
		}
		if unknownMigrations {
			return ErrUnknownPastMigration
		}
	}

	if g.initSchema != nil {
		canInitializeSchema, err := g.canInitializeSchema()
		if err != nil {
			return err
		}
		if canInitializeSchema {
			if err := g.runInitSchema(); err != nil {
				return err
			}
			return g.commit()
		}
	}

	for _, migration := range g.migrations {
		if err := g.runMigration(migration); err != nil {
			return err
		}
		if migrationID != "" && migration.ID == migrationID {
			break
		}
	}
	return g.commit()
}

// There are migrations to apply if either there's a defined
// initSchema function or if the list of migrations is not empty.
func (g *Gormigrate) hasMigrations() bool {
	return g.initSchema != nil || len(g.migrations) > 0
}

// Check whether any migration is using a reserved ID.
// For now there's only have one reserved ID, but there may be more in the future.
func (g *Gormigrate) checkReservedID() error {
	for _, m := range g.migrations {
		if m.ID == initSchemaMigrationID {
			return &ReservedIDError{ID: m.ID}
		}
	}
	return nil
}

func (g *Gormigrate) checkDuplicatedID() error {
	lookup := make(map[string]struct{}, len(g.migrations))
	for _, m := range g.migrations {
		if _, ok := lookup[m.ID]; ok {
			return &DuplicatedIDError{ID: m.ID}
		}
		lookup[m.ID] = struct{}{}
	}
	return nil
}

func (g *Gormigrate) checkIDExist(migrationID string) error {
	for _, migrate := range g.migrations {
		if migrate.ID == migrationID {
			return nil
		}
	}
	return ErrMigrationIDDoesNotExist
}

// RollbackLast undo the last migration
func (g *Gormigrate) RollbackLast() error {
	if len(g.migrations) == 0 {
		return ErrNoMigrationDefined
	}

	g.begin()
	defer g.rollback()

	lastRunMigration, err := g.getLastRunMigration()
	if err != nil {
		return err
	}

	if err := g.rollbackMigration(lastRunMigration); err != nil {
		return err
	}
	return g.commit()
}

// RollbackTo undoes migrations up to the given migration that matches the `migrationID`.
// Migration with the matching `migrationID` is not rolled back.
func (g *Gormigrate) RollbackTo(migrationID string) error {
	if len(g.migrations) == 0 {
		return ErrNoMigrationDefined
	}

	if err := g.checkIDExist(migrationID); err != nil {
		return err
	}

	g.begin()
	defer g.rollback()

	for i := len(g.migrations) - 1; i >= 0; i-- {
		migration := g.migrations[i]
		if migration.ID == migrationID {
			break
		}
		migrationRan, err := g.migrationRan(migration)
		if err != nil {
			return err
		}
		if migrationRan {
			if err := g.rollbackMigration(migration); err != nil {
				return err
			}
		}
	}
	return g.commit()
}

func (g *Gormigrate) getLastRunMigration() (*Migration, error) {
	for i := len(g.migrations) - 1; i >= 0; i-- {
		migration := g.migrations[i]

		migrationRan, err := g.migrationRan(migration)
		if err != nil {
			return nil, err
		}

		if migrationRan {
			return migration, nil
		}
	}
	return nil, ErrNoRunMigration
}

// RollbackMigration undo a migration.
func (g *Gormigrate) RollbackMigration(m *Migration) error {
	g.begin()
	defer g.rollback()

	if err := g.rollbackMigration(m); err != nil {
		return err
	}
	return g.commit()
}

func (g *Gormigrate) rollbackMigration(m *Migration) error {
	if m.Rollback == nil {
		return ErrRollbackImpossible
	}

	if err := m.Rollback(g.tx); err != nil {
		return err
	}

	cond := fmt.Sprintf("%s = ?", g.options.IDColumnName)
	return g.tx.Table(g.options.TableName).Where(cond, m.ID).Delete(g.model()).Error
}

func (g *Gormigrate) runInitSchema() error {
	if err := g.initSchema(g.tx); err != nil {
		return err
	}
	if err := g.insertMigration(initSchemaMigrationID); err != nil {
		return err
	}

	for _, migration := range g.migrations {
		if err := g.insertMigration(migration.ID); err != nil {
			return err
		}
	}

	return nil
}

func (g *Gormigrate) runMigration(migration *Migration) error {
	if len(migration.ID) == 0 {
		return ErrMissingID
	}

	migrationRan, err := g.migrationRan(migration)
	if err != nil {
		return err
	}
	if !migrationRan {
		if err := migration.Migrate(g.tx); err != nil {
			return err
		}

		if err := g.insertMigration(migration.ID); err != nil {
			return err
		}
	}
	return nil
}

// model returns pointer to dynamically created gorm migration model struct value
func (g *Gormigrate) model() any {
	fields := []reflect.StructField{
		{
			Name: "ID",
			Type: reflect.TypeOf(""),
			Tag: reflect.StructTag(fmt.Sprintf(
				`gorm:"primaryKey;column:%s;size:%d"`,
				g.options.IDColumnName,
				g.options.IDColumnSize,
			)),
		},
		{
			Name: "Sequence",
			Type: reflect.TypeOf(int64(0)),
			Tag:  reflect.StructTag(fmt.Sprintf(`gorm:"column:%s"`, g.options.SequenceColumnName)),
		},
		{
			Name: "AppliedAt",
			Type: reflect.TypeOf(time.Time{}),
			Tag:  reflect.StructTag(fmt.Sprintf(`gorm:"column:%s"`, g.options.AppliedAtColumnName)),
		},
		{
			Name: "Status",
			Type: reflect.TypeOf(""),
			Tag:  reflect.StructTag(fmt.Sprintf(`gorm:"column:%s;size:20"`, g.options.StatusColumnName)),
		},
	}
	structType := reflect.StructOf(fields)
	structValue := reflect.New(structType).Elem()
	return structValue.Addr().Interface()
}

func (g *Gormigrate) createMigrationTableIfNotExists() error {
	if err := g.tx.Table(g.options.TableName).AutoMigrate(g.model()); err != nil {
		return err
	}
	return g.backfillMigrationMetadata()
}

// backfillMigrationMetadata populates sequence, applied_at, and status for
// rows that predate the addition of these columns (all marked as success
// with the same timestamp). Rows are sequenced by their natural insertion
// order (rowid for SQLite, ctid for PostgreSQL) so that the sequence column
// reflects the actual order migrations were originally applied.
func (g *Gormigrate) backfillMigrationMetadata() error {
	var orderCol string
	switch g.tx.Dialector.Name() {
	case "sqlite":
		orderCol = "rowid"
	case "postgres":
		orderCol = "ctid"
	default:
		orderCol = g.options.IDColumnName
	}

	var ids []string
	err := g.tx.Table(g.options.TableName).
		Where(fmt.Sprintf("%s IS NULL OR %s = ''", g.options.StatusColumnName, g.options.StatusColumnName)).
		Order(orderCol).
		Pluck(g.options.IDColumnName, &ids).Error
	if err != nil {
		return err
	}

	if len(ids) == 0 {
		return nil
	}

	now := time.Now()

	var maxSeq int64
	if err := g.tx.Table(g.options.TableName).
		Select(fmt.Sprintf("COALESCE(MAX(%s), 0)", g.options.SequenceColumnName)).
		Scan(&maxSeq).Error; err != nil {
		return err
	}

	for i, id := range ids {
		err := g.tx.Table(g.options.TableName).
			Where(fmt.Sprintf("%s = ?", g.options.IDColumnName), id).
			Updates(map[string]interface{}{
				g.options.SequenceColumnName:  maxSeq + int64(i) + 1,
				g.options.AppliedAtColumnName: now,
				g.options.StatusColumnName:    "success",
			}).Error
		if err != nil {
			return err
		}
	}

	return nil
}

func (g *Gormigrate) migrationRan(m *Migration) (bool, error) {
	var count int64
	err := g.tx.
		Table(g.options.TableName).
		Where(fmt.Sprintf("%s = ?", g.options.IDColumnName), m.ID).
		Count(&count).
		Error
	return count > 0, err
}

// The schema can be initialised only if it hasn't been initialised yet
// and no other migration has been applied already.
func (g *Gormigrate) canInitializeSchema() (bool, error) {
	migrationRan, err := g.migrationRan(&Migration{ID: initSchemaMigrationID})
	if err != nil {
		return false, err
	}
	if migrationRan {
		return false, nil
	}

	// If the ID doesn't exist, we also want the list of migrations to be empty
	var count int64
	err = g.tx.
		Table(g.options.TableName).
		Count(&count).
		Error
	return count == 0, err
}

func (g *Gormigrate) unknownMigrationsHaveHappened() (bool, error) {
	rows, err := g.tx.Table(g.options.TableName).Select(g.options.IDColumnName).Rows()
	if err != nil {
		return false, err
	}
	defer func() {
		if err := rows.Close(); err != nil {
			g.tx.Logger.Error(context.TODO(), err.Error())
		}
	}()

	validIDSet := make(map[string]struct{}, len(g.migrations)+1)
	validIDSet[initSchemaMigrationID] = struct{}{}
	for _, migration := range g.migrations {
		validIDSet[migration.ID] = struct{}{}
	}

	for rows.Next() {
		var pastMigrationID string
		if err := rows.Scan(&pastMigrationID); err != nil {
			return false, err
		}
		if _, ok := validIDSet[pastMigrationID]; !ok {
			return true, nil
		}
	}

	return false, nil
}

func (g *Gormigrate) nextSequence() (int64, error) {
	var maxSeq int64
	err := g.tx.Table(g.options.TableName).
		Select(fmt.Sprintf("COALESCE(MAX(%s), 0)", g.options.SequenceColumnName)).
		Scan(&maxSeq).Error
	if err != nil {
		return 0, err
	}
	return maxSeq + 1, nil
}

func (g *Gormigrate) insertMigration(id string) error {
	seq, err := g.nextSequence()
	if err != nil {
		return err
	}

	record := g.model()
	v := reflect.ValueOf(record).Elem()
	v.FieldByName("ID").SetString(id)
	v.FieldByName("Sequence").SetInt(seq)
	v.FieldByName("AppliedAt").Set(reflect.ValueOf(time.Now()))
	v.FieldByName("Status").SetString("success")
	return g.tx.Table(g.options.TableName).Create(record).Error
}

func (g *Gormigrate) begin() {
	if g.options.UseTransaction {
		g.tx = g.db.Begin()
	} else {
		g.tx = g.db
	}
}

func (g *Gormigrate) commit() error {
	if g.options.UseTransaction {
		return g.tx.Commit().Error
	}
	return nil
}

func (g *Gormigrate) rollback() {
	if g.options.UseTransaction {
		g.tx.Rollback()
	}
}