package tool

import (
	"context"
	"database/sql"
	"encoding/json"
	"fmt"
	"log/slog"
	"regexp"
	"strings"
	"sync"
	"time"

	_ "github.com/go-sql-driver/mysql"
	"github.com/mark3labs/mcp-go/mcp"
	"github.com/mark3labs/mcp-go/server"

	_ "github.com/jackc/pgx/v5/stdlib"
)

const (
	maxRows     = 1000
	maxSQLBytes = 4096
	queryTimeout = 30 * time.Second
)

// 禁止的 SQL 关键词（大写，用于只读防护的第二层）
var forbiddenKeywords = regexp.MustCompile(
	`\b(DROP|TRUNCATE|ALTER|CREATE|INSERT|UPDATE|DELETE|GRANT|REVOKE|REPLACE|LOAD|IMPORT|EXPORT)\b`,
)

// DatabaseConf 数据库连接配置
type DatabaseConf struct {
	Alias  string
	Driver string // postgres | mysql
	DSN    string
}

// DatabaseTool 提供只读数据库查询工具。
type DatabaseTool struct {
	configs map[string]DatabaseConf
	pools   map[string]*sql.DB
	mu      sync.RWMutex
}

func NewDatabaseTool(configs []DatabaseConf) *DatabaseTool {
	cfgMap := make(map[string]DatabaseConf, len(configs))
	for _, c := range configs {
		cfgMap[c.Alias] = c
	}
	return &DatabaseTool{configs: cfgMap, pools: make(map[string]*sql.DB)}
}

func (d *DatabaseTool) Name() string        { return "database" }
func (d *DatabaseTool) Description() string { return "数据库只读查询" }

func (d *DatabaseTool) Initialize(ctx context.Context) error {
	for alias, cfg := range d.configs {
		// 强制追加只读参数
		dsn := d.enforceReadOnly(cfg)
		pool, err := sql.Open(cfg.Driver, dsn)
		if err != nil {
			return fmt.Errorf("open %s: %w", alias, err)
		}
		pool.SetMaxOpenConns(5)
		pool.SetMaxIdleConns(2)
		pool.SetConnMaxLifetime(5 * time.Minute)

		if err := pool.PingContext(ctx); err != nil {
			return fmt.Errorf("ping %s: %w", alias, err)
		}
		d.pools[alias] = pool
		slog.Info("database connected", "alias", alias, "driver", cfg.Driver)
	}
	return nil
}

func (d *DatabaseTool) enforceReadOnly(cfg DatabaseConf) string {
	switch cfg.Driver {
	case "postgres", "pgx":
		if !strings.Contains(cfg.DSN, "default_transaction_read_only") {
			sep := "?"
			if strings.Contains(cfg.DSN, "?") {
				sep = "&"
			}
			return cfg.DSN + sep + "default_transaction_read_only=on"
		}
	case "mysql":
		// mysql 驱动在 DSN 中不支持这个参数，通过连接时设置
	}
	return cfg.DSN
}

func (d *DatabaseTool) Shutdown(_ context.Context) error {
	for alias, pool := range d.pools {
		if err := pool.Close(); err != nil {
			slog.Error("close db pool", "alias", alias, "err", err)
		}
	}
	return nil
}

func (d *DatabaseTool) HealthCheck(ctx context.Context) error {
	for alias, pool := range d.pools {
		if err := pool.PingContext(ctx); err != nil {
			return fmt.Errorf("%s: %w", alias, err)
		}
	}
	return nil
}

func (d *DatabaseTool) Register(mcpServer *server.MCPServer) error {
	mcpServer.AddTool(mcp.NewTool("db_query",
		mcp.WithDescription("执行只读 SQL 查询（参数化）"),
		mcp.WithString("database", mcp.Required(), mcp.Description("数据库别名")),
		mcp.WithString("sql", mcp.Required(), mcp.Description("SQL 查询语句")),
		mcp.WithString("params", mcp.Description("JSON 数组格式的参数，如 [1, 'hello']")),
	), d.handleQuery)

	mcpServer.AddTool(mcp.NewTool("db_tables",
		mcp.WithDescription("列出数据库中的所有表"),
		mcp.WithString("database", mcp.Required(), mcp.Description("数据库别名")),
		mcp.WithString("schema", mcp.Description("schema 名称（PostgreSQL），默认 public")),
	), d.handleTables)

	mcpServer.AddTool(mcp.NewTool("db_table_info",
		mcp.WithDescription("查看表结构和索引"),
		mcp.WithString("database", mcp.Required(), mcp.Description("数据库别名")),
		mcp.WithString("table", mcp.Required(), mcp.Description("表名")),
	), d.handleTableInfo)

	mcpServer.AddTool(mcp.NewTool("db_explain",
		mcp.WithDescription("EXPLAIN 分析查询计划"),
		mcp.WithString("database", mcp.Required(), mcp.Description("数据库别名")),
		mcp.WithString("sql", mcp.Required(), mcp.Description("要分析的 SQL")),
	), d.handleExplain)

	return nil
}

// --- 安全校验 ---

func (d *DatabaseTool) validateSQL(sqlStr string) error {
	if len(sqlStr) > maxSQLBytes {
		return fmt.Errorf("SQL too long: %d bytes (max %d)", len(sqlStr), maxSQLBytes)
	}
	// 禁止多语句
	if strings.Contains(sqlStr, ";") {
		return fmt.Errorf("multiple statements not allowed")
	}
	// 禁止危险关键词
	upper := strings.ToUpper(sqlStr)
	if loc := forbiddenKeywords.FindStringIndex(upper); loc != nil {
		return fmt.Errorf("forbidden keyword detected near position %d", loc[0])
	}
	return nil
}

func (d *DatabaseTool) getPool(alias string) (*sql.DB, string, error) {
	d.mu.RLock()
	defer d.mu.RUnlock()

	pool, ok := d.pools[alias]
	if !ok {
		return nil, "", fmt.Errorf("unknown database: %s (available: %v)", alias, d.listAliases())
	}

	cfg := d.configs[alias]
	return pool, cfg.Driver, nil
}

func (d *DatabaseTool) listAliases() []string {
	aliases := make([]string, 0, len(d.pools))
	for a := range d.pools {
		aliases = append(aliases, a)
	}
	return aliases
}

func parseParams(raw string) ([]any, error) {
	if raw == "" {
		return nil, nil
	}
	var params []any
	if err := json.Unmarshal([]byte(raw), &params); err != nil {
		return nil, fmt.Errorf("params must be a JSON array: %w", err)
	}
	return params, nil
}

// --- Handlers ---

func (d *DatabaseTool) handleQuery(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
	args := getArgs(req)
	alias, _ := args["database"].(string)
	sqlStr, _ := args["sql"].(string)
	rawParams, _ := args["params"].(string)

	if err := d.validateSQL(sqlStr); err != nil {
		return mcp.NewToolResultError(err.Error()), nil
	}

	pool, driver, err := d.getPool(alias)
	if err != nil {
		return mcp.NewToolResultError(err.Error()), nil
	}

	params, err := parseParams(rawParams)
	if err != nil {
		return mcp.NewToolResultError(err.Error()), nil
	}

	ctx, cancel := context.WithTimeout(ctx, queryTimeout)
	defer cancel()

	// 对 MySQL 连接设置只读
	if driver == "mysql" {
		if _, err := pool.ExecContext(ctx, "SET SESSION TRANSACTION READ ONLY"); err == nil {
			defer pool.ExecContext(context.Background(), "SET SESSION TRANSACTION READ WRITE")
		}
	}

	sqlStr = limitQuery(sqlStr, driver)

	rows, err := pool.QueryContext(ctx, sqlStr, params...)
	if err != nil {
		return mcp.NewToolResultError(fmt.Sprintf("query error: %v", err)), nil
	}
	defer rows.Close()

	return formatRows(rows, maxRows)
}

func (d *DatabaseTool) handleTables(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
	args := getArgs(req)
	alias, _ := args["database"].(string)
	schema, _ := args["schema"].(string)

	pool, driver, err := d.getPool(alias)
	if err != nil {
		return mcp.NewToolResultError(err.Error()), nil
	}

	var query string
	switch driver {
	case "postgres", "pgx":
		if schema == "" {
			schema = "public"
		}
		query = `SELECT table_name FROM information_schema.tables WHERE table_schema = $1 ORDER BY table_name`
	case "mysql":
		if schema == "" {
			schema = ""
		}
		query = `SELECT table_name FROM information_schema.tables WHERE table_schema = ? ORDER BY table_name`
	default:
		query = `SELECT table_name FROM information_schema.tables WHERE table_schema = ? ORDER BY table_name`
	}

	ctx, cancel := context.WithTimeout(ctx, queryTimeout)
	defer cancel()

	var rows *sql.Rows
	var err2 error
	if schema != "" {
		rows, err2 = pool.QueryContext(ctx, query, schema)
	} else {
		rows, err2 = pool.QueryContext(ctx, query)
	}
	if err2 != nil {
		return mcp.NewToolResultError(err2.Error()), nil
	}
	defer rows.Close()

	return formatRows(rows, maxRows)
}

func (d *DatabaseTool) handleTableInfo(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
	args := getArgs(req)
	alias, _ := args["database"].(string)
	table, _ := args["table"].(string)

	pool, driver, err := d.getPool(alias)
	if err != nil {
		return mcp.NewToolResultError(err.Error()), nil
	}

	// 校验表名只包含安全字符
	if !regexp.MustCompile(`^[a-zA-Z_][a-zA-Z0-9_]*$`).MatchString(table) {
		return mcp.NewToolResultError("invalid table name"), nil
	}

	var query string
	switch driver {
	case "postgres", "pgx":
		query = `SELECT column_name, data_type, is_nullable, column_default FROM information_schema.columns WHERE table_name = $1 ORDER BY ordinal_position`
	case "mysql":
		query = `SELECT column_name, data_type, is_nullable, column_default FROM information_schema.columns WHERE table_name = ? ORDER BY ordinal_position`
	default:
		query = `SELECT column_name, data_type, is_nullable, column_default FROM information_schema.columns WHERE table_name = ? ORDER BY ordinal_position`
	}

	ctx, cancel := context.WithTimeout(ctx, queryTimeout)
	defer cancel()

	rows, err := pool.QueryContext(ctx, query, table)
	if err != nil {
		return mcp.NewToolResultError(err.Error()), nil
	}
	defer rows.Close()

	return formatRows(rows, maxRows)
}

func (d *DatabaseTool) handleExplain(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
	args := getArgs(req)
	alias, _ := args["database"].(string)
	sqlStr, _ := args["sql"].(string)

	if err := d.validateSQL(sqlStr); err != nil {
		return mcp.NewToolResultError(err.Error()), nil
	}

	pool, driver, err := d.getPool(alias)
	if err != nil {
		return mcp.NewToolResultError(err.Error()), nil
	}

	explainPrefix := "EXPLAIN"
	if driver == "mysql" {
		explainPrefix = "EXPLAIN"
	}

	ctx, cancel := context.WithTimeout(ctx, queryTimeout)
	defer cancel()

	rows, err := pool.QueryContext(ctx, explainPrefix+" "+sqlStr)
	if err != nil {
		return mcp.NewToolResultError(err.Error()), nil
	}
	defer rows.Close()

	return formatRows(rows, maxRows)
}

// --- Helpers ---

// limitQuery 追加 LIMIT 防止返回过多行（如果查询中没有 LIMIT）。
func limitQuery(sqlStr, driver string) string {
	upper := strings.ToUpper(sqlStr)
	if strings.Contains(upper, "LIMIT") {
		return sqlStr
	}
	return sqlStr + fmt.Sprintf(" LIMIT %d", maxRows)
}

func formatRows(rows *sql.Rows, limit int) (*mcp.CallToolResult, error) {
	columns, err := rows.Columns()
	if err != nil {
		return mcp.NewToolResultError(err.Error()), nil
	}

	var result []map[string]any
	count := 0
	for rows.Next() {
		if count >= limit {
			break
		}
		values := make([]any, len(columns))
		valuePtrs := make([]any, len(columns))
		for i := range values {
			valuePtrs[i] = &values[i]
		}
		if err := rows.Scan(valuePtrs...); err != nil {
			return mcp.NewToolResultError(err.Error()), nil
		}
		row := make(map[string]any, len(columns))
		for i, col := range columns {
			row[col] = formatValue(values[i])
		}
		result = append(result, row)
		count++
	}

	data, _ := json.MarshalIndent(result, "", "  ")
	output := fmt.Sprintf("Rows: %d\nColumns: %s\n\n%s", count, strings.Join(columns, ", "), string(data))
	return mcp.NewToolResultText(output), nil
}

func formatValue(v any) any {
	switch val := v.(type) {
	case []byte:
		return string(val)
	case time.Time:
		return val.Format(time.RFC3339)
	default:
		return v
	}
}