package db

import (
	"crypto/rand"
	"database/sql"
	"encoding/hex"
	"fmt"
	"io"
	"log"
	"os"
	"sort"
	"strings"
	"time"

	_ "modernc.org/sqlite"
)

var DB *sql.DB

const SchemaVersion = "v2"

// ================================================================
// 初始化
// ================================================================

func InitDB() error {
	if err := os.MkdirAll("./data", 0755); err != nil {
		return fmt.Errorf("创建数据目录失败: %w", err)
	}

	dbPath := "./data/frpc-console.db"
	var err error
	DB, err = sql.Open("sqlite", dbPath)
	if err != nil {
		return err
	}

	if err := createTables(); err != nil {
		return err
	}

	if err := runMigrations(); err != nil {
		return err
	}

	if err := ensureJwtSecret(); err != nil {
		return err
	}

	log.Println("✅ 数据库初始化完成 (Schema " + SchemaVersion + ")")
	return nil
}

func createTables() error {
	_, err := DB.Exec(`
        CREATE TABLE IF NOT EXISTS users (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            username TEXT UNIQUE NOT NULL,
            password_hash TEXT NOT NULL,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
        )
    `)
	if err != nil {
		return err
	}

	_, err = DB.Exec(`
        CREATE TABLE IF NOT EXISTS global_config (
            id INTEGER PRIMARY KEY CHECK (id = 1),
            server_addr TEXT NOT NULL DEFAULT 'frp.example.com',
            server_port INTEGER NOT NULL DEFAULT 7000,
            token TEXT NOT NULL DEFAULT 'CHANGE_ME',
            log_level TEXT NOT NULL DEFAULT 'info',
            log_max_days INTEGER NOT NULL DEFAULT 3,
            tcp_mux INTEGER NOT NULL DEFAULT 1,
            tcp_mux_keepalive INTEGER NOT NULL DEFAULT 30,
            heartbeat_interval INTEGER NOT NULL DEFAULT 15,
            heartbeat_timeout INTEGER NOT NULL DEFAULT 70,
            pool_count INTEGER NOT NULL DEFAULT 8,
            wire_protocol_v2 INTEGER NOT NULL DEFAULT 0,
            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
        )
    `)
	if err != nil {
		return err
	}

	_, err = DB.Exec(`
        CREATE TABLE IF NOT EXISTS proxies (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            name TEXT UNIQUE NOT NULL,
            type TEXT NOT NULL DEFAULT 'tcp',
            local_ip TEXT NOT NULL,
            local_port INTEGER NOT NULL,
            remote_port INTEGER NOT NULL,
            enabled INTEGER NOT NULL DEFAULT 1,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
        )
    `)
	if err != nil {
		return err
	}

	_, err = DB.Exec(`
        CREATE TABLE IF NOT EXISTS app_config (
            key TEXT PRIMARY KEY,
            value TEXT NOT NULL,
            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
        )
    `)
	if err != nil {
		return err
	}

	var count int
	DB.QueryRow("SELECT COUNT(*) FROM global_config").Scan(&count)
	if count == 0 {
		_, err = DB.Exec(`
            INSERT INTO global_config (
                id, server_addr, server_port, token, log_level, log_max_days,
                tcp_mux, tcp_mux_keepalive, heartbeat_interval, heartbeat_timeout, pool_count,
                wire_protocol_v2
            ) VALUES (1, 'frp.example.com', 7000, 'CHANGE_ME', 'info', 3, 1, 30, 15, 70, 8, 0)
        `)
		if err != nil {
			return err
		}
		log.Println("✅ 全局配置初始化完成")
	}

	return nil
}

// ================================================================
// JWT 密钥管理
// ================================================================

func ensureJwtSecret() error {
	var value string
	err := DB.QueryRow("SELECT value FROM app_config WHERE key = 'jwt_secret'").Scan(&value)
	if err == nil && value != "" {
		return nil
	}

	bytes := make([]byte, 32)
	if _, err := rand.Read(bytes); err != nil {
		return err
	}
	secret := hex.EncodeToString(bytes)

	_, err = DB.Exec(`
        INSERT INTO app_config (key, value) VALUES ('jwt_secret', ?)
    `, secret)
	if err != nil {
		return err
	}
	log.Printf("✅ JWT 密钥已生成")
	return nil
}

func GetJwtSecret() (string, error) {
	var secret string
	err := DB.QueryRow("SELECT value FROM app_config WHERE key = 'jwt_secret'").Scan(&secret)
	if err != nil {
		return "", err
	}
	return secret, nil
}

// ================================================================
// 迁移引擎
// ================================================================

func getCurrentSchemaVersion() string {
	var version string
	err := DB.QueryRow("SELECT value FROM app_config WHERE key = 'schema_version'").Scan(&version)
	if err != nil {
		if err == sql.ErrNoRows {
			var count int
			DB.QueryRow("SELECT COUNT(*) FROM users").Scan(&count)
			if count > 0 {
				return "v1"
			}
			return SchemaVersion
		}
		log.Printf("⚠️ 读取 Schema 版本失败: %v", err)
		return "v1"
	}
	return version
}

func setSchemaVersion(version string) error {
	_, err := DB.Exec(`
        INSERT INTO app_config (key, value) VALUES ('schema_version', ?)
        ON CONFLICT(key) DO UPDATE SET value = excluded.value, updated_at = CURRENT_TIMESTAMP
    `, version)
	return err
}

func backupDatabase() (string, error) {
	src := "./data/frpc-console.db"
	if _, err := os.Stat(src); os.IsNotExist(err) {
		return "", nil
	}

	timestamp := time.Now().Format("20060102_150405")
	dst := fmt.Sprintf("./data/frpc-console.db.pre-%s.%s", SchemaVersion, timestamp)

	srcFile, err := os.Open(src)
	if err != nil {
		return "", fmt.Errorf("打开源数据库失败: %w", err)
	}
	defer srcFile.Close()

	dstFile, err := os.Create(dst)
	if err != nil {
		return "", fmt.Errorf("创建备份文件失败: %w", err)
	}
	defer dstFile.Close()

	if _, err := io.Copy(dstFile, srcFile); err != nil {
		return "", fmt.Errorf("复制数据库失败: %w", err)
	}

	log.Printf("✅ 数据库备份完成: %s", dst)
	return dst, nil
}

func restoreDatabase(backupPath string) error {
	srcFile, err := os.Open(backupPath)
	if err != nil {
		return err
	}
	defer srcFile.Close()

	dstFile, err := os.Create("./data/frpc-console.db")
	if err != nil {
		return err
	}
	defer dstFile.Close()

	if _, err := io.Copy(dstFile, srcFile); err != nil {
		return err
	}

	log.Printf("✅ 数据库已从备份恢复: %s", backupPath)
	return nil
}

func runMigrations() error {
	currentVer := getCurrentSchemaVersion()
	targetVer := SchemaVersion

	log.Printf("📌 当前数据库 Schema: %s, 目标版本: %s", currentVer, targetVer)

	if currentVer == targetVer {
		var userCount int
		err := DB.QueryRow("SELECT COUNT(*) FROM users").Scan(&userCount)
		if err != nil || userCount == 0 {
			log.Println("  数据库为空或无效，无需迁移，直接初始化")
			return nil
		}
		log.Println("✅ Schema 已是最新，数据库有效")
		return nil
	}

	log.Printf("🔄 检测到版本变更 (%s → %s)，开始迁移...", currentVer, targetVer)

	backupPath, err := backupDatabase()
	if err != nil {
		return fmt.Errorf("备份数据库失败: %w", err)
	}
	if backupPath != "" {
		log.Printf("📦 备份文件: %s", backupPath)
	}

	currentSchema := getSchemaDef(currentVer)
	targetSchema := getSchemaDef(targetVer)

	if targetSchema == nil {
		return fmt.Errorf("目标 Schema 版本 %s 未定义", targetVer)
	}

	if currentSchema == nil || schemaVersionsEqual(currentSchema, targetSchema) {
		log.Println("  迁移类型: 轻量复制（Schema 无变更）")
		var userCount int
		err := DB.QueryRow("SELECT COUNT(*) FROM users").Scan(&userCount)
		if err != nil || userCount == 0 {
			log.Println("  数据库为空或无效，跳过迁移，直接初始化")
			return nil
		}
		log.Println("  数据库有效，继续使用")
	} else {
		log.Println("  迁移类型: 重型迁移（Schema 有变更，新建表 + 搬数据）")
		if err := heavyMigration(currentSchema, targetSchema); err != nil {
			if backupPath != "" {
				log.Printf("❌ 迁移失败，尝试恢复备份: %s", backupPath)
				if restoreErr := restoreDatabase(backupPath); restoreErr != nil {
					log.Printf("⚠️ 恢复备份失败: %v", restoreErr)
				}
			}
			return fmt.Errorf("重型迁移失败: %w", err)
		}
	}

	if err := setSchemaVersion(targetVer); err != nil {
		return fmt.Errorf("更新 Schema 版本失败: %w", err)
	}

	log.Printf("✅ 迁移完成，当前 Schema: %s", targetVer)
	return nil
}

func heavyMigration(oldDef, newDef *SchemaVersionDef) error {
	if oldDef == nil {
		return fmt.Errorf("旧 Schema 定义为空，无法执行重型迁移")
	}

	oldTable := oldDef.TableName
	newTable := oldTable + "_new"

	createSQL := buildCreateTableSQL(newTable, newDef)
	log.Printf("  创建新表: %s", newTable)
	if _, err := DB.Exec(createSQL); err != nil {
		return fmt.Errorf("创建新表失败: %w", err)
	}

	insertSQL, err := buildInsertSQL(oldTable, newTable, oldDef, newDef)
	if err != nil {
		return fmt.Errorf("构建数据迁移 SQL 失败: %w", err)
	}
	log.Printf("  迁移数据: %s → %s", oldTable, newTable)
	if _, err := DB.Exec(insertSQL); err != nil {
		return fmt.Errorf("数据迁移失败: %w", err)
	}

	var oldCount, newCount int
	DB.QueryRow(fmt.Sprintf("SELECT COUNT(*) FROM %s", oldTable)).Scan(&oldCount)
	DB.QueryRow(fmt.Sprintf("SELECT COUNT(*) FROM %s", newTable)).Scan(&newCount)
	if oldCount != newCount {
		return fmt.Errorf("数据迁移不完整: 旧表 %d 行，新表 %d 行", oldCount, newCount)
	}
	log.Printf("  数据迁移验证通过: %d 行", newCount)

	tempTable := oldTable + "_old_temp"
	if _, err := DB.Exec(fmt.Sprintf("ALTER TABLE %s RENAME TO %s", oldTable, tempTable)); err != nil {
		return fmt.Errorf("重命名旧表失败: %w", err)
	}
	if _, err := DB.Exec(fmt.Sprintf("ALTER TABLE %s RENAME TO %s", newTable, oldTable)); err != nil {
		DB.Exec(fmt.Sprintf("ALTER TABLE %s RENAME TO %s", tempTable, oldTable))
		return fmt.Errorf("重命名新表失败: %w", err)
	}
	if _, err := DB.Exec(fmt.Sprintf("DROP TABLE %s", tempTable)); err != nil {
		log.Printf("⚠️ 删除临时表失败（不影响使用）: %v", err)
	}

	log.Printf("  表交换完成: %s (新表已生效)", oldTable)
	return nil
}

func buildCreateTableSQL(tableName string, def *SchemaVersionDef) string {
	var cols []string
	var primaryKey string

	for name, col := range def.Columns {
		parts := []string{name, col.Type}
		if col.NotNull {
			parts = append(parts, "NOT NULL")
		}
		if col.Default != "" {
			parts = append(parts, "DEFAULT "+col.Default)
		}
		if col.Primary {
			primaryKey = "PRIMARY KEY (" + name + ")"
		} else {
			cols = append(cols, strings.Join(parts, " "))
		}
	}

	if primaryKey != "" {
		cols = append(cols, primaryKey)
	}

	return fmt.Sprintf("CREATE TABLE %s (\n    %s\n)", tableName, strings.Join(cols, ",\n    "))
}

func buildInsertSQL(oldTable, newTable string, oldDef, newDef *SchemaVersionDef) (string, error) {
	var newCols []string
	for name := range newDef.Columns {
		newCols = append(newCols, name)
	}
	sort.Strings(newCols)

	var selectParts []string
	var colNames []string

	for _, name := range newCols {
		colNames = append(colNames, name)
		if _, ok := oldDef.Columns[name]; ok {
			selectParts = append(selectParts, name)
		} else {
			colDef := newDef.Columns[name]
			if colDef.Default != "" {
				selectParts = append(selectParts, colDef.Default+" AS "+name)
			} else if colDef.Type == "INTEGER" {
				selectParts = append(selectParts, "0 AS "+name)
			} else if colDef.Type == "TEXT" {
				selectParts = append(selectParts, "'' AS "+name)
			} else {
				selectParts = append(selectParts, "NULL AS "+name)
			}
		}
	}

	return fmt.Sprintf(
		"INSERT INTO %s (%s) SELECT %s FROM %s",
		newTable,
		strings.Join(colNames, ", "),
		strings.Join(selectParts, ", "),
		oldTable,
	), nil
}