package database

import (
	"context"
	"crypto/sha256"
	"database/sql"
	"encoding/hex"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"runtime"
	"strings"
	"sync"
	"time"

	mysqldriver "github.com/go-sql-driver/mysql"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"gorm.io/gorm/logger"
)

// DefaultTestDSN 指向本地 Docker 开发环境的 MySQL 测试库。
// 可通过 HFB_TEST_DSN 覆盖，库名必须包含 test 或 e2e。
const DefaultTestDSN = "hfb:secret@tcp(127.0.0.1:13306)/hfb_sys_test?charset=utf8mb4&parseTime=True&loc=Local"

const (
	schemaMetaTable = "_test_schema_meta"
	templateSuffix  = "__template"
)

var (
	testPrepareOnce sync.Once
	testConn        *gorm.DB
	testPrepareErr  error
)

// NewTestDB 返回指向 MySQL 测试库的干净连接。
//
// 表结构来自 backend/migrations 的真实迁移，与生产一致。
// 迁移只在模板库上执行一次；各测试包克隆模板库，指纹未变则跨 `go test`
// 调用复用，避免每个包、每次运行都 DROP + 重放 68 条迁移。
// 每次调用仍会清空业务表，使测试从空库开始。
func NewTestDB() *gorm.DB {
	db, err := sharedTestDB()
	if err != nil {
		panic(fmt.Sprintf("初始化 MySQL 测试库失败: %v", err))
	}
	if err := truncateAllTables(db); err != nil {
		panic(fmt.Sprintf("清空 MySQL 测试库失败: %v", err))
	}
	return db
}

func sharedTestDB() (*gorm.DB, error) {
	testPrepareOnce.Do(func() {
		testConn, testPrepareErr = openTestDatabase()
	})
	return testConn, testPrepareErr
}

// NewDryRunDB 返回 MySQL 方言的 DryRun 连接：只生成 SQL 不执行，也无需数据库运行。
// 用于断言查询语句形态的测试。
func NewDryRunDB() *gorm.DB {
	db, err := gorm.Open(mysql.New(mysql.Config{
		DSN:                       DefaultTestDSN,
		SkipInitializeWithVersion: true,
	}), &gorm.Config{
		DryRun:               true,
		DisableAutomaticPing: true,
		Logger:               logger.Default.LogMode(logger.Silent),
	})
	if err != nil {
		panic(fmt.Sprintf("初始化 MySQL DryRun 连接失败: %v", err))
	}
	return db
}

// AutoMigrateIfMissing 只对尚不存在的表执行 AutoMigrate。
//
// 测试库的表结构由 migrations 建立，直接 AutoMigrate 会去改迁移定义的
// 索引与约束（例如 DROP 掉被外键依赖的唯一索引），因此已存在的表一律跳过，
// 仅保留给测试专用的临时表使用。
func AutoMigrateIfMissing(db *gorm.DB, models ...any) error {
	for _, target := range models {
		if db.Migrator().HasTable(target) {
			continue
		}
		if err := db.AutoMigrate(target); err != nil {
			return err
		}
	}
	return nil
}

func openTestDatabase() (*gorm.DB, error) {
	dsn := strings.TrimSpace(os.Getenv("HFB_TEST_DSN"))
	if dsn == "" {
		dsn = DefaultTestDSN
	}
	cfg, err := mysqldriver.ParseDSN(dsn)
	if err != nil {
		return nil, fmt.Errorf("解析测试库 DSN 失败: %w", err)
	}
	baseName := cfg.DBName
	templateName := baseName + templateSuffix
	packageName := baseName + "_" + packageSuffix()
	if err := assertTestDatabaseName(templateName); err != nil {
		return nil, err
	}
	if err := assertTestDatabaseName(packageName); err != nil {
		return nil, err
	}

	dir, err := migrationDir()
	if err != nil {
		return nil, err
	}
	fingerprint, err := migrationFingerprint(dir)
	if err != nil {
		return nil, err
	}

	serverCfg := cfg.Clone()
	serverCfg.DBName = ""
	serverCfg.MultiStatements = false
	serverDB, err := sql.Open("mysql", serverCfg.FormatDSN())
	if err != nil {
		return nil, fmt.Errorf("连接 MySQL 服务失败: %w", err)
	}
	defer func() { _ = serverDB.Close() }()
	if err := serverDB.Ping(); err != nil {
		return nil, fmt.Errorf("连接 MySQL 服务失败: %w", err)
	}

	if err := ensureTemplate(serverDB, templateName, dir, fingerprint); err != nil {
		return nil, err
	}
	if err := ensurePackageClone(serverDB, templateName, packageName, fingerprint); err != nil {
		return nil, err
	}

	cfg.DBName = packageName
	cfg.ParseTime = true
	cfg.MultiStatements = true
	sqlDB, err := sql.Open("mysql", cfg.FormatDSN())
	if err != nil {
		return nil, fmt.Errorf("连接测试库失败: %w", err)
	}
	sqlDB.SetMaxOpenConns(8)
	sqlDB.SetMaxIdleConns(8)
	sqlDB.SetConnMaxLifetime(30 * time.Minute)
	gormDB, err := gorm.Open(mysql.New(mysql.Config{Conn: sqlDB}), &gorm.Config{
		Logger: logger.Default.LogMode(logger.Silent),
	})
	if err != nil {
		_ = sqlDB.Close()
		return nil, fmt.Errorf("打开 gorm 连接失败: %w", err)
	}
	return gormDB, nil
}

func ensureTemplate(serverDB *sql.DB, name, dir, fingerprint string) error {
	return withMySQLLock(serverDB, mysqlLockName("tpl", name), func() error {
		if readFingerprint(serverDB, name) == fingerprint {
			return nil
		}
		if _, err := serverDB.Exec("DROP DATABASE IF EXISTS `" + name + "`"); err != nil {
			return fmt.Errorf("删除模板库失败: %w", err)
		}
		if _, err := serverDB.Exec("CREATE DATABASE `" + name + "` CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci"); err != nil {
			return fmt.Errorf("创建模板库失败: %w", err)
		}
		if err := applyMigrationsTo(name, dir); err != nil {
			return err
		}
		return writeFingerprint(serverDB, name, fingerprint)
	})
}

func ensurePackageClone(serverDB *sql.DB, templateName, packageName, fingerprint string) error {
	return withMySQLLock(serverDB, mysqlLockName("pkg", packageName), func() error {
		if readFingerprint(serverDB, packageName) == fingerprint {
			return nil
		}
		return cloneDatabase(serverDB, templateName, packageName)
	})
}

func applyMigrationsTo(dbName, dir string) error {
	cfg, err := parseTestDSN()
	if err != nil {
		return err
	}
	cfg.DBName = dbName
	cfg.ParseTime = true
	cfg.MultiStatements = true
	db, err := sql.Open("mysql", cfg.FormatDSN())
	if err != nil {
		return fmt.Errorf("连接模板库失败: %w", err)
	}
	defer func() { _ = db.Close() }()
	return applyMigrations(db, dir)
}

func parseTestDSN() (*mysqldriver.Config, error) {
	rawDSN := strings.TrimSpace(os.Getenv("HFB_TEST_DSN"))
	if rawDSN == "" {
		rawDSN = DefaultTestDSN
	}
	cfg, err := mysqldriver.ParseDSN(rawDSN)
	if err != nil {
		return nil, fmt.Errorf("解析测试库 DSN 失败: %w", err)
	}
	return cfg, nil
}

func applyMigrations(db *sql.DB, dir string) error {
	entries, err := os.ReadDir(dir)
	if err != nil {
		return fmt.Errorf("读取迁移目录失败: %w", err)
	}
	for _, entry := range entries {
		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".sql") {
			continue
		}
		raw, err := os.ReadFile(filepath.Join(dir, entry.Name()))
		if err != nil {
			return fmt.Errorf("读取迁移 %s 失败: %w", entry.Name(), err)
		}
		if _, err := db.Exec(gooseUpSQL(string(raw))); err != nil {
			return fmt.Errorf("执行迁移 %s 失败: %w", entry.Name(), err)
		}
	}
	return nil
}

func cloneDatabase(serverDB *sql.DB, src, dest string) error {
	if _, err := serverDB.Exec("DROP DATABASE IF EXISTS `" + dest + "`"); err != nil {
		return fmt.Errorf("删除测试库 %s 失败: %w", dest, err)
	}
	if _, err := serverDB.Exec("CREATE DATABASE `" + dest + "` CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci"); err != nil {
		return fmt.Errorf("创建测试库 %s 失败: %w", dest, err)
	}

	tables, err := listBaseTables(serverDB, src)
	if err != nil {
		return err
	}

	cfg, err := parseTestDSN()
	if err != nil {
		return err
	}
	cfg.DBName = dest
	cfg.MultiStatements = false
	destDB, err := sql.Open("mysql", cfg.FormatDSN())
	if err != nil {
		return fmt.Errorf("连接测试库 %s 失败: %w", dest, err)
	}
	defer func() { _ = destDB.Close() }()

	ctx := context.Background()
	conn, err := destDB.Conn(ctx)
	if err != nil {
		return err
	}
	defer func() { _ = conn.Close() }()
	if _, err := conn.ExecContext(ctx, "SET FOREIGN_KEY_CHECKS = 0"); err != nil {
		return err
	}
	defer func() { _, _ = conn.ExecContext(ctx, "SET FOREIGN_KEY_CHECKS = 1") }()

	for _, table := range tables {
		var name, create string
		if err := serverDB.QueryRow("SHOW CREATE TABLE `"+src+"`.`"+table+"`").Scan(&name, &create); err != nil {
			return fmt.Errorf("读取表结构 %s.%s 失败: %w", src, table, err)
		}
		if _, err := conn.ExecContext(ctx, create); err != nil {
			return fmt.Errorf("克隆表 %s 失败: %w", table, err)
		}
		if _, err := conn.ExecContext(ctx, "INSERT INTO `"+table+"` SELECT * FROM `"+src+"`.`"+table+"`"); err != nil {
			return fmt.Errorf("克隆表数据 %s 失败: %w", table, err)
		}
	}
	return nil
}

func listBaseTables(db *sql.DB, schema string) ([]string, error) {
	rows, err := db.Query(
		"SELECT table_name FROM information_schema.tables "+
			"WHERE table_schema = ? AND table_type = 'BASE TABLE' ORDER BY table_name",
		schema,
	)
	if err != nil {
		return nil, err
	}
	defer func() { _ = rows.Close() }()
	var tables []string
	for rows.Next() {
		var name string
		if err := rows.Scan(&name); err != nil {
			return nil, err
		}
		tables = append(tables, name)
	}
	return tables, rows.Err()
}

func writeFingerprint(db *sql.DB, schema, fingerprint string) error {
	ddl := "CREATE TABLE IF NOT EXISTS `" + schema + "`.`" + schemaMetaTable + "` (" +
		"k VARCHAR(64) NOT NULL PRIMARY KEY," +
		"v VARCHAR(128) NOT NULL" +
		") ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci"
	if _, err := db.Exec(ddl); err != nil {
		return fmt.Errorf("创建模板指纹表失败: %w", err)
	}
	if _, err := db.Exec(
		"REPLACE INTO `"+schema+"`.`"+schemaMetaTable+"` (k, v) VALUES (?, ?)",
		"fingerprint", fingerprint,
	); err != nil {
		return fmt.Errorf("写入模板指纹失败: %w", err)
	}
	return nil
}

func readFingerprint(db *sql.DB, schema string) string {
	var value string
	err := db.QueryRow(
		"SELECT v FROM `" + schema + "`.`" + schemaMetaTable + "` WHERE k = 'fingerprint'",
	).Scan(&value)
	if err != nil {
		return ""
	}
	return value
}

func withMySQLLock(db *sql.DB, name string, fn func() error) error {
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
	defer cancel()
	conn, err := db.Conn(ctx)
	if err != nil {
		return err
	}
	defer func() { _ = conn.Close() }()

	var got int
	if err := conn.QueryRowContext(ctx, "SELECT GET_LOCK(?, 120)", name).Scan(&got); err != nil {
		return fmt.Errorf("GET_LOCK %s 失败: %w", name, err)
	}
	if got != 1 {
		return fmt.Errorf("GET_LOCK %s 未拿到锁", name)
	}
	defer func() {
		_, _ = conn.ExecContext(context.Background(), "SELECT RELEASE_LOCK(?)", name)
	}()
	return fn()
}

func mysqlLockName(kind, dbName string) string {
	raw := "hfb:" + kind + ":" + dbName
	if len(raw) <= 64 {
		return raw
	}
	sum := sha256.Sum256([]byte(raw))
	return ("hfb:" + kind + ":") + hex.EncodeToString(sum[:12])
}

func migrationFingerprint(dir string) (string, error) {
	entries, err := os.ReadDir(dir)
	if err != nil {
		return "", fmt.Errorf("读取迁移目录失败: %w", err)
	}
	h := sha256.New()
	for _, entry := range entries {
		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".sql") {
			continue
		}
		_, _ = fmt.Fprintf(h, "%s\n", entry.Name())
		raw, err := os.ReadFile(filepath.Join(dir, entry.Name()))
		if err != nil {
			return "", fmt.Errorf("读取迁移 %s 失败: %w", entry.Name(), err)
		}
		_, _ = h.Write(raw)
	}
	return hex.EncodeToString(h.Sum(nil)), nil
}

// assertTestDatabaseName 拒绝重置非测试库，避免误删生产数据。
func assertTestDatabaseName(name string) error {
	if name == "" {
		return errors.New("测试库 DSN 必须包含数据库名")
	}
	if !regexp.MustCompile(`^[A-Za-z0-9_]+$`).MatchString(name) {
		return fmt.Errorf("测试库名只允许字母、数字、下划线: %q", name)
	}
	if len(name) > 64 {
		return fmt.Errorf("测试库名超过 MySQL 上限 64 字符: %q", name)
	}
	lower := strings.ToLower(name)
	if !strings.Contains(lower, "test") && !strings.Contains(lower, "e2e") {
		return fmt.Errorf("拒绝重置非测试库 %q，库名需包含 test 或 e2e", name)
	}
	return nil
}

// packageSuffix 用当前测试进程的工作目录名（即被测包目录）作为库名后缀。
// go test 会把工作目录设为包的源目录，因此同包共享一个库、不同包互相隔离。
func packageSuffix() string {
	wd, err := os.Getwd()
	if err != nil {
		return "unknown"
	}
	suffix := regexp.MustCompile(`[^A-Za-z0-9_]`).ReplaceAllString(filepath.Base(wd), "_")
	if suffix == "" {
		return "unknown"
	}
	return suffix
}

func migrationDir() (string, error) {
	_, currentFile, _, ok := runtime.Caller(0)
	if !ok {
		return "", errors.New("无法定位 database 包路径")
	}
	return filepath.Join(filepath.Dir(currentFile), "..", "..", "migrations"), nil
}

// gooseUpSQL 截取 goose 迁移文件的 Up 段，Down 段与 goose 指令行原样保留，
// 后者在 MySQL 中属于注释，不影响执行。
func gooseUpSQL(raw string) string {
	if i := strings.Index(raw, "-- +goose Up"); i >= 0 {
		raw = raw[i+len("-- +goose Up"):]
	}
	if i := strings.Index(raw, "-- +goose Down"); i >= 0 {
		raw = raw[:i]
	}
	return raw
}

// truncateAllTables 清空测试库中的全部业务表，使每个测试从空库开始。
// 指纹表保留，以便跨进程复用已克隆的库。
//
// 先用一条多语句 DELETE 清数据（测试数据量很小，通常几十毫秒），再把用过的
// AUTO_INCREMENT 表打回 1。全量 TRUNCATE 61 张表是 DDL，单次约 0.6s–1.4s，
// 而不少测试硬编码了 id=1，所以自增必须重置。
func truncateAllTables(db *gorm.DB) error {
	sqlDB, err := db.DB()
	if err != nil {
		return err
	}
	tables, err := listCurrentDatabaseTables(sqlDB)
	if err != nil {
		return err
	}
	var b strings.Builder
	b.WriteString("SET FOREIGN_KEY_CHECKS=0;")
	count := 0
	for _, table := range tables {
		if table == schemaMetaTable {
			continue
		}
		b.WriteString("DELETE FROM `")
		b.WriteString(table)
		b.WriteString("`;")
		count++
	}
	if count == 0 {
		return nil
	}
	b.WriteString("SET FOREIGN_KEY_CHECKS=1;")
	if _, err := sqlDB.Exec(b.String()); err != nil {
		return fmt.Errorf("清空测试表失败: %w", err)
	}

	aiTables, err := listAutoIncrementTables(sqlDB)
	if err != nil {
		return err
	}
	if len(aiTables) == 0 {
		return nil
	}
	b.Reset()
	for _, table := range aiTables {
		b.WriteString("ALTER TABLE `")
		b.WriteString(table)
		b.WriteString("` AUTO_INCREMENT=1;")
	}
	if _, err := sqlDB.Exec(b.String()); err != nil {
		return fmt.Errorf("重置自增失败: %w", err)
	}
	return nil
}

func listAutoIncrementTables(db *sql.DB) ([]string, error) {
	ctx := context.Background()
	conn, err := db.Conn(ctx)
	if err != nil {
		return nil, err
	}
	defer func() { _ = conn.Close() }()
	// MySQL 8 默认缓存 information_schema 的统计信息（86400s），
	// 直接读取 auto_increment 可能拿到陈旧值并跳过重置，必须在本连接关闭缓存后再查。
	if _, err := conn.ExecContext(ctx, "SET SESSION information_schema_stats_expiry = 0"); err != nil {
		return nil, err
	}
	rows, err := conn.QueryContext(ctx,
		"SELECT table_name FROM information_schema.tables "+
			"WHERE table_schema = DATABASE() AND table_name <> ? AND auto_increment > 1",
		schemaMetaTable,
	)
	if err != nil {
		return nil, err
	}
	defer func() { _ = rows.Close() }()
	var tables []string
	for rows.Next() {
		var name string
		if err := rows.Scan(&name); err != nil {
			return nil, err
		}
		tables = append(tables, name)
	}
	return tables, rows.Err()
}

func listCurrentDatabaseTables(db *sql.DB) ([]string, error) {
	rows, err := db.Query(
		"SELECT table_name FROM information_schema.tables " +
			"WHERE table_schema = DATABASE() AND table_type = 'BASE TABLE'",
	)
	if err != nil {
		return nil, err
	}
	defer func() { _ = rows.Close() }()
	var tables []string
	for rows.Next() {
		var name string
		if err := rows.Scan(&name); err != nil {
			return nil, err
		}
		tables = append(tables, name)
	}
	return tables, rows.Err()
}