package database

import (
	"errors"
	"fmt"
	"time"

	"gorm.io/gorm"
)

const CurrentSchemaVersion int64 = 1

const baselineSchemaChecksum = "sha256:open-ai-canvas-schema-v1-20260830"

const postgresSchemaMigrationLockID int64 = 73123910420260830

type SchemaStatus struct {
	Current  int64 `json:"current"`
	Expected int64 `json:"expected"`
	Ready    bool  `json:"ready"`
}

type schemaMigration struct {
	Version   int64     `gorm:"primaryKey"`
	Name      string    `gorm:"size:160;not null"`
	Checksum  string    `gorm:"size:96;not null"`
	AppliedAt time.Time `gorm:"not null"`
}

func (schemaMigration) TableName() string { return "schema_migrations" }

type migration struct {
	version  int64
	name     string
	checksum string
	apply    func(*gorm.DB) error
}

var schemaMigrations = []migration{
	{version: 1, name: "baseline_gorm_schema", checksum: baselineSchemaChecksum, apply: migrateSchemaV1},
}

func MigrateSchema(db *gorm.DB) error {
	return db.Transaction(func(tx *gorm.DB) error {
		if tx.Dialector.Name() == "postgres" {
			if err := tx.Exec("SELECT pg_advisory_xact_lock(?)", postgresSchemaMigrationLockID).Error; err != nil {
				return fmt.Errorf("获取数据库迁移锁：%w", err)
			}
		}
		if err := tx.AutoMigrate(&schemaMigration{}); err != nil {
			return fmt.Errorf("初始化数据库迁移记录：%w", err)
		}
		for _, item := range schemaMigrations {
			var applied schemaMigration
			err := tx.First(&applied, "version = ?", item.version).Error
			if err == nil {
				if err := validateMigrationRecord(applied, item); err != nil {
					return err
				}
				continue
			}
			if !errors.Is(err, gorm.ErrRecordNotFound) {
				return fmt.Errorf("读取数据库迁移 %d：%w", item.version, err)
			}
			if err := item.apply(tx); err != nil {
				return fmt.Errorf("执行数据库迁移 %d（%s）：%w", item.version, item.name, err)
			}
			record := schemaMigration{Version: item.version, Name: item.name, Checksum: item.checksum, AppliedAt: time.Now().UTC()}
			if err := tx.Create(&record).Error; err != nil {
				return fmt.Errorf("记录数据库迁移 %d：%w", item.version, err)
			}
		}
		return RequireSchemaVersion(tx)
	})
}

func ReadSchemaStatus(db *gorm.DB) (SchemaStatus, error) {
	status := SchemaStatus{Expected: CurrentSchemaVersion}
	if !db.Migrator().HasTable(&schemaMigration{}) {
		return status, nil
	}
	if err := db.Model(&schemaMigration{}).Select("COALESCE(MAX(version), 0)").Scan(&status.Current).Error; err != nil {
		return status, fmt.Errorf("读取数据库结构版本：%w", err)
	}
	if status.Current != status.Expected {
		return status, nil
	}
	if err := validateMigrationRecords(db); err != nil {
		return status, err
	}
	status.Ready = true
	return status, nil
}

func validateMigrationRecords(db *gorm.DB) error {
	for _, item := range schemaMigrations {
		var applied schemaMigration
		if err := db.First(&applied, "version = ?", item.version).Error; err != nil {
			if errors.Is(err, gorm.ErrRecordNotFound) {
				return fmt.Errorf("数据库缺少迁移记录 %d（%s）", item.version, item.name)
			}
			return fmt.Errorf("读取数据库迁移 %d：%w", item.version, err)
		}
		if err := validateMigrationRecord(applied, item); err != nil {
			return err
		}
	}
	return nil
}

func validateMigrationRecord(applied schemaMigration, expected migration) error {
	if applied.Name != expected.name {
		return fmt.Errorf("数据库迁移 %d 名称不一致：记录为 %s，程序期望 %s", expected.version, applied.Name, expected.name)
	}
	if applied.Checksum != expected.checksum {
		return fmt.Errorf("数据库迁移 %d 校验和不一致：记录为 %s，程序期望 %s", expected.version, applied.Checksum, expected.checksum)
	}
	return nil
}

func RequireSchemaVersion(db *gorm.DB) error {
	status, err := ReadSchemaStatus(db)
	if err != nil {
		return err
	}
	if status.Current < status.Expected {
		return fmt.Errorf("数据库结构版本过旧：当前 %d，程序要求 %d，请先执行 migrate-schema up", status.Current, status.Expected)
	}
	if status.Current > status.Expected {
		return fmt.Errorf("数据库结构版本 %d 高于程序支持的 %d，拒绝使用旧程序连接新数据库", status.Current, status.Expected)
	}
	return nil
}