package database

import (
	"context"
	"errors"
	"fmt"
	"net/url"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/stdlib"
	"gorm.io/driver/postgres"
	"gorm.io/gorm"
)

const (
	expectedDatabaseName    = "ops_licence"
	databaseApplicationName = "ops-licence"
	databaseConnectTimeout  = 10 * time.Second
)

var pgEnvironmentVariables = [...]string{
	"PGHOST",
	"PGPORT",
	"PGDATABASE",
	"PGUSER",
	"PGPASSWORD",
	"PGPASSFILE",
	"PGAPPNAME",
	"PGCONNECT_TIMEOUT",
	"PGSSLMODE",
	"PGSSLKEY",
	"PGSSLCERT",
	"PGSSLSNI",
	"PGSSLROOTCERT",
	"PGSSLPASSWORD",
	"PGTARGETSESSIONATTRS",
	"PGSERVICE",
	"PGSERVICEFILE",
}

type databaseTarget struct {
	normalizedURL string
	username      string
	password      string
	host          string
	port          uint16
	sslMode       string
}

func Open(ctx context.Context, dsn string) (*gorm.DB, error) {
	target, err := parseDatabaseTarget(dsn)
	if err != nil {
		return nil, err
	}
	if err := rejectPGEnvironmentVariables(); err != nil {
		return nil, err
	}
	config, err := pgx.ParseConfig(target.normalizedURL)
	if err != nil {
		return nil, errors.New("解析数据库连接配置失败")
	}
	if err := validatePGXConfig(config, target); err != nil {
		return nil, err
	}

	sqlDB := stdlib.OpenDB(*config)
	closeOnFailure := true
	defer func() {
		if closeOnFailure {
			_ = sqlDB.Close()
		}
	}()

	sqlDB.SetMaxOpenConns(10)
	sqlDB.SetMaxIdleConns(5)
	sqlDB.SetConnMaxLifetime(30 * time.Minute)
	sqlDB.SetConnMaxIdleTime(5 * time.Minute)

	db, err := gorm.Open(postgres.New(postgres.Config{Conn: sqlDB}), &gorm.Config{
		DisableAutomaticPing: true,
	})
	if err != nil {
		return nil, errors.New("初始化数据库连接失败")
	}
	if err := sqlDB.PingContext(ctx); err != nil {
		return nil, errors.New("连接数据库失败")
	}

	var databaseName string
	if err := sqlDB.QueryRowContext(ctx, "SELECT current_database()").Scan(&databaseName); err != nil {
		return nil, errors.New("读取当前数据库名称失败")
	}
	if databaseName != expectedDatabaseName {
		return nil, fmt.Errorf("数据库名称必须为 %q，实际为 %q", expectedDatabaseName, databaseName)
	}

	closeOnFailure = false
	return db, nil
}

func parseDatabaseTarget(dsn string) (databaseTarget, error) {
	parsed, err := url.ParseRequestURI(dsn)
	if err != nil || !parsed.IsAbs() || parsed.Opaque != "" {
		return databaseTarget{}, errors.New("数据库 DSN 必须是完整的 PostgreSQL URL")
	}
	if parsed.Scheme != "postgres" && parsed.Scheme != "postgresql" {
		return databaseTarget{}, errors.New("数据库 DSN 协议必须是 postgres 或 postgresql")
	}
	if parsed.Fragment != "" || parsed.RawFragment != "" || strings.Contains(dsn, "#") {
		return databaseTarget{}, errors.New("数据库 DSN 不能包含 fragment")
	}
	if parsed.User == nil || parsed.User.Username() == "" {
		return databaseTarget{}, errors.New("数据库 DSN 必须显式包含非空用户名")
	}
	password, hasPassword := parsed.User.Password()
	if !hasPassword || password == "" {
		return databaseTarget{}, errors.New("数据库 DSN 必须显式包含非空密码")
	}
	if parsed.Host == "" || strings.Contains(parsed.Host, ",") {
		return databaseTarget{}, errors.New("数据库 DSN 必须包含单一主机")
	}
	host := parsed.Hostname()
	if host == "" {
		return databaseTarget{}, errors.New("数据库 DSN 必须显式包含非空主机")
	}
	portText := parsed.Port()
	port, err := strconv.ParseUint(portText, 10, 16)
	if err != nil || port == 0 {
		return databaseTarget{}, errors.New("数据库 DSN 必须显式包含有效端口")
	}
	if parsed.Path != "/"+expectedDatabaseName || parsed.EscapedPath() != "/"+expectedDatabaseName {
		return databaseTarget{}, fmt.Errorf("数据库 DSN 的数据库路径必须精确为 /%s", expectedDatabaseName)
	}

	query, err := url.ParseQuery(parsed.RawQuery)
	if err != nil {
		return databaseTarget{}, errors.New("数据库 DSN 查询参数无效")
	}
	for name, values := range query {
		if !isAllowedDatabaseOption(name) {
			return databaseTarget{}, errors.New("数据库 DSN 包含不允许的连接选项")
		}
		if len(values) != 1 || values[0] == "" {
			return databaseTarget{}, errors.New("数据库 DSN 的连接选项必须是单个非空值")
		}
	}
	sslModeValues, exists := query["sslmode"]
	if !exists || !isAllowedSSLMode(sslModeValues[0]) {
		return databaseTarget{}, errors.New("数据库 DSN 的 sslmode 必须是 disable、require、verify-ca 或 verify-full")
	}
	sslMode := sslModeValues[0]

	rootCertificate := query["sslrootcert"]
	clientCertificate := query["sslcert"]
	clientKey := query["sslkey"]
	sslPassword := query["sslpassword"]
	for _, option := range []string{"sslrootcert", "sslcert", "sslkey"} {
		if values, exists := query[option]; exists && !filepath.IsAbs(values[0]) {
			return databaseTarget{}, errors.New("数据库 DSN 的 TLS 文件路径必须是绝对路径")
		}
	}
	if (len(clientCertificate) == 1) != (len(clientKey) == 1) {
		return databaseTarget{}, errors.New("数据库 DSN 的 sslcert 与 sslkey 必须成对配置")
	}
	if len(sslPassword) == 1 && len(clientKey) == 0 {
		return databaseTarget{}, errors.New("数据库 DSN 的 sslpassword 必须与 sslkey 一同配置")
	}
	if (sslMode == "verify-ca" || sslMode == "verify-full") && len(rootCertificate) == 0 {
		return databaseTarget{}, errors.New("verify-ca 和 verify-full 必须配置 sslrootcert")
	}
	if sslMode == "disable" && (len(rootCertificate) != 0 || len(clientCertificate) != 0 || len(sslPassword) != 0) {
		return databaseTarget{}, errors.New("sslmode=disable 不能配置 TLS 证书或密码")
	}

	query.Set("passfile", os.DevNull)
	query.Set("application_name", databaseApplicationName)
	query.Set("connect_timeout", strconv.Itoa(int(databaseConnectTimeout/time.Second)))
	query.Set("target_session_attrs", "any")
	query.Set("sslsni", "1")
	parsed.RawQuery = query.Encode()
	parsed.ForceQuery = false

	return databaseTarget{
		normalizedURL: parsed.String(),
		username:      parsed.User.Username(),
		password:      password,
		host:          host,
		port:          uint16(port),
		sslMode:       sslMode,
	}, nil
}

func isAllowedDatabaseOption(name string) bool {
	switch name {
	case "sslmode", "sslrootcert", "sslcert", "sslkey", "sslpassword":
		return true
	default:
		return false
	}
}

func isAllowedSSLMode(mode string) bool {
	switch mode {
	case "disable", "require", "verify-ca", "verify-full":
		return true
	default:
		return false
	}
}

func rejectPGEnvironmentVariables() error {
	for _, name := range pgEnvironmentVariables {
		if _, exists := os.LookupEnv(name); exists {
			return fmt.Errorf("不允许设置数据库环境变量 %s", name)
		}
	}
	return nil
}

func validatePGXConfig(config *pgx.ConnConfig, target databaseTarget) error {
	if config.Host != target.host ||
		config.Port != target.port ||
		config.Database != expectedDatabaseName ||
		config.User != target.username ||
		config.Password != target.password ||
		config.ConnectTimeout != databaseConnectTimeout ||
		config.ValidateConnect != nil ||
		len(config.Fallbacks) != 0 {
		return errors.New("数据库连接配置解析结果不符合预期")
	}
	if len(config.RuntimeParams) != 1 || config.RuntimeParams["application_name"] != databaseApplicationName {
		return errors.New("数据库连接运行参数不符合预期")
	}

	tlsRequired := target.sslMode != "disable"
	if tlsRequired != (config.TLSConfig != nil) {
		return errors.New("数据库连接 TLS 配置不符合预期")
	}
	if target.sslMode == "verify-full" &&
		(config.TLSConfig.ServerName != target.host || config.TLSConfig.InsecureSkipVerify) {
		return errors.New("数据库连接 verify-full 配置不符合预期")
	}
	return nil
}