package config

import (
	"fmt"
	"os"

	"go.yaml.in/yaml/v3"
)

// Config 对应 DEVELOPMENT 第 11.1 节的配置文件。
type Config struct {
	Listen               string        `yaml:"listen"`
	AdminListen          string        `yaml:"admin_listen"`
	TLS                  TLSConfig     `yaml:"tls"`
	TrustedProxies       []string      `yaml:"trusted_proxies"`
	DataDir              string        `yaml:"data_dir"`
	Limits               LimitsConfig  `yaml:"limits"`
	SessionIdleDays      int           `yaml:"session_idle_days"`
	RecordRetentionDays  int           `yaml:"record_retention_days"`
	IdempotencyHours     int           `yaml:"idempotency_hours"`
	ReceiptRetentionDays int           `yaml:"receipt_retention_days"`
	SQLiteSynchronous    string        `yaml:"sqlite_synchronous"`
	Metrics              MetricsConfig `yaml:"metrics"`
	Log                  LogConfig     `yaml:"log"`
}

type TLSConfig struct {
	CertFile       string `yaml:"cert_file"`
	KeyFile        string `yaml:"key_file"`
	AllowPlaintext bool   `yaml:"allow_plaintext"`
}

type LimitsConfig struct {
	MaxBodyBytes          int `yaml:"max_body_bytes"`
	MaxMetaBytes          int `yaml:"max_meta_bytes"`
	MaxFrameBytes         int `yaml:"max_frame_bytes"`
	MaxTTLSeconds         int `yaml:"max_ttl_seconds"`
	MaxScheduleSeconds    int `yaml:"max_schedule_seconds"`
	MaxGroupMembers       int `yaml:"max_group_members"`
	GraceSeconds          int `yaml:"grace_seconds"`
	AckTimeoutSeconds     int `yaml:"ack_timeout_seconds"`
	DeliveryWindow        int `yaml:"delivery_window"`
	ReceiptWindow         int `yaml:"receipt_window"`
	RequestsPerSecond     int `yaml:"requests_per_second"`
	MaxPendingPerSender   int `yaml:"max_pending_per_sender"`
	MaxPendingPerReceiver int `yaml:"max_pending_per_receiver"`
}

type MetricsConfig struct {
	Token string `yaml:"token"`
}

type LogConfig struct {
	Level string `yaml:"level"`
}

// Default 返回与 DEVELOPMENT 11.1 示例一致的默认值。
func Default() Config {
	return Config{
		Listen:      ":7443",
		AdminListen: "",
		TLS: TLSConfig{
			AllowPlaintext: false,
		},
		TrustedProxies: nil,
		DataDir:        "./data",
		Limits: LimitsConfig{
			MaxBodyBytes:          262144,
			MaxMetaBytes:          4096,
			MaxFrameBytes:         786432,
			MaxTTLSeconds:         2592000,
			MaxScheduleSeconds:    31536000,
			MaxGroupMembers:       1000,
			GraceSeconds:          60,
			AckTimeoutSeconds:     300,
			DeliveryWindow:        32,
			ReceiptWindow:         64,
			RequestsPerSecond:     50,
			MaxPendingPerSender:   10000,
			MaxPendingPerReceiver: 10000,
		},
		SessionIdleDays:      30,
		RecordRetentionDays:  7,
		IdempotencyHours:     24,
		ReceiptRetentionDays: 7,
		SQLiteSynchronous:    "FULL",
		Metrics:              MetricsConfig{},
		Log: LogConfig{
			Level: "info",
		},
	}
}

// Load 从路径加载 YAML 配置；空字段保留默认值。
func Load(path string) (Config, error) {
	cfg := Default()
	data, err := os.ReadFile(path)
	if err != nil {
		return Config{}, fmt.Errorf("read config: %w", err)
	}
	if err := yaml.Unmarshal(data, &cfg); err != nil {
		return Config{}, fmt.Errorf("parse config: %w", err)
	}
	if cfg.Listen == "" {
		cfg.Listen = Default().Listen
	}
	if cfg.DataDir == "" {
		cfg.DataDir = Default().DataDir
	}
	if cfg.SQLiteSynchronous == "" {
		cfg.SQLiteSynchronous = Default().SQLiteSynchronous
	}
	return cfg, nil
}

// PathFromEnv 返回 NIXMSG_CONFIG 或默认 ./config.yaml。
func PathFromEnv() string {
	if p := os.Getenv("NIXMSG_CONFIG"); p != "" {
		return p
	}
	return "./config.yaml"
}