package database

import (
	"crypto/sha256"
	"embed"
	"encoding/hex"
	"fmt"
	"io/fs"
	"path/filepath"
	"sort"
	"strings"
	"time"

	"gorm.io/gorm"
)

//go:embed migrations/*.sql
var migrationFiles embed.FS

type schemaMigration struct {
	Version   string    `gorm:"primaryKey;size:64"`
	Name      string    `gorm:"size:255;not null"`
	Checksum  string    `gorm:"size:64;not null"`
	AppliedAt time.Time `gorm:"not null"`
}

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

// Migrate 使用显式 SQL 迁移管理表结构，避免大型项目依赖隐式结构同步。
// 自营商户、默认钱包与商品目录种子数据均在 001_init.sql 中完成，无需在 Go 层补充。
func Migrate(db *gorm.DB) error {
	return db.Transaction(func(tx *gorm.DB) error {
		if err := tx.Exec("SELECT pg_advisory_xact_lock(hashtext(?))", "affiliate_dash_schema_migrations").Error; err != nil {
			return fmt.Errorf("lock schema migrations: %w", err)
		}
		if err := ensureMigrationTable(tx); err != nil {
			return err
		}
		return applySQLMigrations(tx)
	})
}

func ensureMigrationTable(tx *gorm.DB) error {
	statements := []string{
		`
CREATE TABLE IF NOT EXISTS schema_migrations (
	version varchar(64) PRIMARY KEY,
	name varchar(255) NOT NULL,
	checksum varchar(64) NOT NULL,
	applied_at timestamptz NOT NULL
)`,
		`ALTER TABLE schema_migrations ADD COLUMN IF NOT EXISTS name varchar(255) NOT NULL DEFAULT ''`,
		`ALTER TABLE schema_migrations ADD COLUMN IF NOT EXISTS checksum varchar(64) NOT NULL DEFAULT ''`,
		`ALTER TABLE schema_migrations ADD COLUMN IF NOT EXISTS applied_at timestamptz NOT NULL DEFAULT now()`,
	}
	for _, statement := range statements {
		if err := tx.Exec(statement).Error; err != nil {
			return fmt.Errorf("ensure schema_migrations: %w", err)
		}
	}
	return nil
}

func applySQLMigrations(tx *gorm.DB) error {
	paths, err := fs.Glob(migrationFiles, "migrations/*.sql")
	if err != nil {
		return fmt.Errorf("list migrations: %w", err)
	}
	sort.Strings(paths)
	for _, path := range paths {
		content, err := migrationFiles.ReadFile(path)
		if err != nil {
			return fmt.Errorf("read migration %s: %w", path, err)
		}
		version, name := parseMigrationName(path)
		checksum := migrationChecksum(content)

		var existing schemaMigration
		err = tx.Where("version = ?", version).First(&existing).Error
		if err == nil {
			if existing.Checksum == "" {
				if err := tx.Model(&schemaMigration{}).Where("version = ?", version).Updates(map[string]interface{}{
					"name":     name,
					"checksum": checksum,
				}).Error; err != nil {
					return fmt.Errorf("adopt migration %s: %w", version, err)
				}
				continue
			}
			if existing.Checksum != checksum {
				return fmt.Errorf("migration %s checksum mismatch: 已执行版本不能被修改", version)
			}
			continue
		}
		if err != gorm.ErrRecordNotFound {
			return fmt.Errorf("query migration %s: %w", version, err)
		}
		sql := strings.TrimSpace(string(content))
		if sql == "" {
			return fmt.Errorf("migration %s is empty", path)
		}
		if err := tx.Exec(sql).Error; err != nil {
			return fmt.Errorf("apply migration %s: %w", path, err)
		}
		if err := tx.Create(&schemaMigration{
			Version:   version,
			Name:      name,
			Checksum:  checksum,
			AppliedAt: time.Now(),
		}).Error; err != nil {
			return fmt.Errorf("record migration %s: %w", version, err)
		}
	}
	return nil
}

func parseMigrationName(path string) (string, string) {
	base := filepath.Base(path)
	name := strings.TrimSuffix(base, filepath.Ext(base))
	parts := strings.SplitN(name, "_", 2)
	if len(parts) == 1 {
		return parts[0], name
	}
	return parts[0], parts[1]
}

func migrationChecksum(content []byte) string {
	sum := sha256.Sum256(content)
	return hex.EncodeToString(sum[:])
}