package config

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"
)

const envPrefix = "MQTT_SCRUBBER_"

type Config struct {
	MQTT   MQTTConfig   `json:"mqtt"`
	Influx InfluxConfig `json:"influx"`
	App    AppConfig    `json:"app"`
}

type MQTTConfig struct {
	Broker   string   `json:"broker"`
	Username string   `json:"username"`
	Password string   `json:"password"`
	ClientID string   `json:"client_id"`
	Topics   []string `json:"topics"`
	QoS      byte     `json:"qos"`
}

type InfluxConfig struct {
	URL       string `json:"url"`
	Database  string `json:"database"`
	Token     string `json:"token"`
	Precision string `json:"precision"`
}

type AppConfig struct {
	BatchSize     int           `json:"batch_size"`
	BufferSize    int           `json:"buffer_size"`
	FlushInterval DurationValue `json:"flush_interval"`
	FlushTimeout  DurationValue `json:"flush_timeout"`
	LogLevel      string        `json:"log_level"`
	HealthAddress string        `json:"health_address"`
}

type DurationValue struct {
	time.Duration
}

func (value *DurationValue) UnmarshalJSON(data []byte) error {
	var raw string
	if err := json.Unmarshal(data, &raw); err != nil {
		return fmt.Errorf("duration must be a string: %w", err)
	}

	parsed, err := time.ParseDuration(raw)
	if err != nil {
		return fmt.Errorf("invalid duration %q: %w", raw, err)
	}

	value.Duration = parsed
	return nil
}

func Load(path string) (Config, error) {
	cfg := defaultConfig()

	if path != "" {
		contents, err := os.ReadFile(path)
		if err != nil {
			return Config{}, fmt.Errorf("read config file: %w", err)
		}

		if err := json.Unmarshal(contents, &cfg); err != nil {
			return Config{}, fmt.Errorf("parse config file: %w", err)
		}
	}

	if err := applyEnvOverrides(&cfg); err != nil {
		return Config{}, err
	}

	if err := cfg.Validate(); err != nil {
		return Config{}, err
	}

	return cfg, nil
}

func (cfg Config) Validate() error {
	if cfg.MQTT.Broker == "" {
		return errors.New("mqtt broker is required")
	}
	if cfg.MQTT.ClientID == "" {
		return errors.New("mqtt client_id is required")
	}
	if len(cfg.MQTT.Topics) == 0 {
		return errors.New("at least one mqtt topic is required")
	}
	if cfg.Influx.URL == "" {
		return errors.New("influx url is required")
	}
	if cfg.Influx.Database == "" {
		return errors.New("influx database is required")
	}
	if cfg.Influx.Precision == "" {
		return errors.New("influx precision is required")
	}
	if cfg.App.BatchSize <= 0 {
		return errors.New("app batch_size must be greater than zero")
	}
	if cfg.App.BufferSize <= 0 {
		return errors.New("app buffer_size must be greater than zero")
	}
	if cfg.App.FlushInterval.Duration <= 0 {
		return errors.New("app flush_interval must be greater than zero")
	}
	if cfg.App.FlushTimeout.Duration <= 0 {
		return errors.New("app flush_timeout must be greater than zero")
	}

	return nil
}

func defaultConfig() Config {
	return Config{
		MQTT: MQTTConfig{
			Broker:   "tcp://127.0.0.1:1883",
			ClientID: "mqqt-scrubber",
			Topics: []string{
				"tele/+/SENSOR",
				"tele/+/STATE",
			},
			QoS: 0,
		},
		Influx: InfluxConfig{
			URL:       "http://127.0.0.1:8181",
			Database:  "home",
			Precision: "ns",
		},
		App: AppConfig{
			BatchSize:     200,
			BufferSize:    1000,
			FlushInterval: DurationValue{Duration: 10 * time.Second},
			FlushTimeout:  DurationValue{Duration: 10 * time.Second},
			LogLevel:      "info",
			HealthAddress: ":8080",
		},
	}
}

func applyEnvOverrides(cfg *Config) error {
	setString(&cfg.MQTT.Broker, envPrefix+"MQTT_BROKER")
	setString(&cfg.MQTT.Username, envPrefix+"MQTT_USERNAME")
	setString(&cfg.MQTT.Password, envPrefix+"MQTT_PASSWORD")
	setString(&cfg.MQTT.ClientID, envPrefix+"MQTT_CLIENT_ID")
	setString(&cfg.Influx.URL, envPrefix+"INFLUX_URL")
	setString(&cfg.Influx.Database, envPrefix+"INFLUX_DATABASE")
	setString(&cfg.Influx.Token, envPrefix+"INFLUX_TOKEN")
	setString(&cfg.Influx.Precision, envPrefix+"INFLUX_PRECISION")
	setString(&cfg.App.LogLevel, envPrefix+"APP_LOG_LEVEL")
	setString(&cfg.App.HealthAddress, envPrefix+"APP_HEALTH_ADDRESS")

	if raw, ok := os.LookupEnv(envPrefix + "MQTT_TOPICS"); ok {
		cfg.MQTT.Topics = splitAndTrim(raw)
	}

	if raw, ok := os.LookupEnv(envPrefix + "MQTT_QOS"); ok {
		parsed, err := strconv.Atoi(raw)
		if err != nil {
			return fmt.Errorf("parse %sMQTT_QOS: %w", envPrefix, err)
		}
		cfg.MQTT.QoS = byte(parsed)
	}

	if raw, ok := os.LookupEnv(envPrefix + "APP_BATCH_SIZE"); ok {
		parsed, err := strconv.Atoi(raw)
		if err != nil {
			return fmt.Errorf("parse %sAPP_BATCH_SIZE: %w", envPrefix, err)
		}
		cfg.App.BatchSize = parsed
	}

	if raw, ok := os.LookupEnv(envPrefix + "APP_BUFFER_SIZE"); ok {
		parsed, err := strconv.Atoi(raw)
		if err != nil {
			return fmt.Errorf("parse %sAPP_BUFFER_SIZE: %w", envPrefix, err)
		}
		cfg.App.BufferSize = parsed
	}

	if raw, ok := os.LookupEnv(envPrefix + "APP_FLUSH_INTERVAL"); ok {
		parsed, err := time.ParseDuration(raw)
		if err != nil {
			return fmt.Errorf("parse %sAPP_FLUSH_INTERVAL: %w", envPrefix, err)
		}
		cfg.App.FlushInterval = DurationValue{Duration: parsed}
	}

	if raw, ok := os.LookupEnv(envPrefix + "APP_FLUSH_TIMEOUT"); ok {
		parsed, err := time.ParseDuration(raw)
		if err != nil {
			return fmt.Errorf("parse %sAPP_FLUSH_TIMEOUT: %w", envPrefix, err)
		}
		cfg.App.FlushTimeout = DurationValue{Duration: parsed}
	}

	return nil
}

func setString(target *string, key string) {
	if value, ok := os.LookupEnv(key); ok {
		*target = value
	}
}

func splitAndTrim(value string) []string {
	parts := strings.Split(value, ",")
	result := make([]string, 0, len(parts))

	for _, part := range parts {
		trimmed := strings.TrimSpace(part)
		if trimmed != "" {
			result = append(result, trimmed)
		}
	}

	return result
}