// Package config loads, defaults, and validates the Cyrene v2 configuration
// from environment variables and an optional .env file (development only).
//
// Every setting is sourced from an environment variable (no hard-coded values
// in code). Nested groups map to struct fields tagged with `env:"NAME"`.
// Missing required values cause Load/MustLoad to return an error so startup
// can fail fast.
package config

import (
	"fmt"
	"reflect"
	"strings"
)

// Config is the root configuration tree.
type Config struct {
	Env             string   `env:"ENV" default:"development"`
	LogLevel        string   `env:"LOG_LEVEL" default:"debug"`
	Timezone        string   `env:"TZ" default:"Asia/Shanghai"`
	DataDir         string   `env:"DATA_DIR" default:"./data"`
	AllowedOrigins  []string `env:"ALLOWED_ORIGINS" default:"http://localhost:5173,http://localhost:3000"`

	Server    ServerConfig
	Auth      AuthConfig
	DB        DBConfig
	LLM       LLMConfig
	Embedding EmbeddingConfig
	IoT       IoTConfig
	Voice     VoiceConfig
	Background BackgroundConfig
	WSHub     WSHubConfig
}

// ServerConfig holds the single gateway listener settings.
type ServerConfig struct {
	Host string `env:"HOST" default:"0.0.0.0"`
	Port int    `env:"PORT" default:"8080"`
}

// AuthConfig holds authentication and admin credential settings.
type AuthConfig struct {
	JWTSecret           string `env:"JWT_SECRET" validate:"required,min=32"`
	AdminUser           string `env:"ADMIN_USERNAME" default:"admin"`
	AdminPass           string `env:"ADMIN_PASSWORD" default:"admin12345"`
	RegistrationEnabled bool   `env:"REGISTRATION_ENABLED" default:"true"`
}

// DBConfig holds database connection settings. SQLite is the default; PGURL is
// the optional PostgreSQL+pgvector enhancement.
type DBConfig struct {
	SQLitePath string `env:"DB_SQLITE_PATH" default:"./data/cyrene.db"`
	PGURL      string `env:"DB_PG_URL"`
}

// LLMConfig holds the multi-supplier LLM adapter settings.
type LLMConfig struct {
	BaseURL  string `env:"LLM_BASE_URL"`
	APIKey   string `env:"LLM_API_KEY"`
	Model    string `env:"LLM_MODEL"`
	Fallback string `env:"LLM_FALLBACK_MODEL"`
}

// EmbeddingConfig holds the optional semantic embedding API settings. When
// unset, the runtime falls back to built-in n-gram/FTS vectors.
type EmbeddingConfig struct {
	APIURL string `env:"EMBEDDING_API_URL"`
	APIKey string `env:"EMBEDDING_API_KEY"`
	Model  string `env:"EMBEDDING_MODEL"`
}

// IoTConfig selects the IoT device provider.
type IoTConfig struct {
	Provider string `env:"IOT_PROVIDER" default:"mock"`
}

// VoiceConfig holds TTS/STT provider settings.
type VoiceConfig struct {
	TTSProvider      string `env:"TTS_PROVIDER" default:"edge-tts"`
	STTProvider      string `env:"STT_PROVIDER" default:"dashscope"`
	DashscopeAPIKey  string `env:"DASHSCOPE_API_KEY"`
}

// BackgroundConfig holds the autonomous thinking settings.
type BackgroundConfig struct {
	Enabled         bool `env:"ENABLE_BACKGROUND_THINKING" default:"true"`
	IntervalSec     int  `env:"THINK_INTERVAL_SEC" default:"300"`
	SilenceTimeout  int  `env:"THINK_SILENCE_TIMEOUT_SEC" default:"120"`
}

// WSHubConfig holds the WebSocket hub limits.
type WSHubConfig struct {
	MaxConnections     int `env:"WS_MAX_CONNECTIONS" default:"1000"`
	SessionIdleTimeout int `env:"SESSION_IDLE_TIMEOUT_MIN" default:"30"`
}

// Load reads configuration, merging an optional .env file (development only)
// with process environment variables. Process environment variables always take
// precedence over .env values, which take precedence over code defaults.
//
// Passing an empty envPath skips .env entirely. A missing .env file is not an
// error; only missing required values are.
func Load(envPath string) (*Config, error) {
	fromEnv := map[string]string{}
	if envPath != "" {
		m, err := parseDotEnv(envPath)
		if err != nil {
			return nil, fmt.Errorf("config: read %s: %w", envPath, err)
		}
		fromEnv = m
	}

	cfg := &Config{}
	if err := decodeValue(reflect.ValueOf(cfg), fromEnv); err != nil {
		return nil, err
	}

	if errs := validateStruct(reflect.ValueOf(cfg).Elem()); len(errs) > 0 {
		parts := make([]string, 0, len(errs))
		for _, e := range errs {
			parts = append(parts, e.Error())
		}
		return nil, fmt.Errorf("config: validation failed: %s", strings.Join(parts, "; "))
	}

	return cfg, nil
}

// MustLoad is Load that panics on error. It is intended for startup, matching
// the "schema validation fails at boot" rule.
func MustLoad(envPath string) *Config {
	cfg, err := Load(envPath)
	if err != nil {
		panic(err)
	}
	return cfg
}