package config

import (
	"encoding/json"
	"fmt"
	"os"
)

type Config struct {
	BackendURL        string `json:"backendUrl"`
	Identifier        string `json:"identifier"`
	APIKey            string `json:"apiKey"`
	ReportIntervalSec int    `json:"reportIntervalSec"`
	LogLevel          string `json:"logLevel"`
}

func Load(path string) (Config, error) {
	cfg := Config{
		BackendURL:        getenv("HF_MONITOR_BACKEND_URL", "https://monitor.hangman-lab.top"),
		Identifier:        getenv("HF_MONITOR_IDENTIFIER", hostnameOr("unknown-host")),
		APIKey:            os.Getenv("HF_MONITOR_API_KEY"),
		ReportIntervalSec: getenvInt("HF_MONITOR_REPORT_INTERVAL", 30),
		LogLevel:          getenv("HF_MONITOR_LOG_LEVEL", "info"),
	}

	if path != "" {
		if fileCfg, err := loadFile(path); err == nil {
			merge(&cfg, fileCfg)
		} else if !os.IsNotExist(err) {
			return cfg, fmt.Errorf("load config file: %w", err)
		}
	}

	// env always wins over file
	cfg.BackendURL = getenv("HF_MONITOR_BACKEND_URL", cfg.BackendURL)
	cfg.Identifier = getenv("HF_MONITOR_IDENTIFIER", cfg.Identifier)
	if v := os.Getenv("HF_MONITOR_API_KEY"); v != "" {
		cfg.APIKey = v
	}
	cfg.ReportIntervalSec = getenvInt("HF_MONITOR_REPORT_INTERVAL", cfg.ReportIntervalSec)
	cfg.LogLevel = getenv("HF_MONITOR_LOG_LEVEL", cfg.LogLevel)

	if cfg.BackendURL == "" {
		return cfg, fmt.Errorf("backendUrl is required")
	}
	if cfg.Identifier == "" {
		return cfg, fmt.Errorf("identifier is required")
	}
	if cfg.ReportIntervalSec <= 0 {
		cfg.ReportIntervalSec = 30
	}
	return cfg, nil
}

func loadFile(path string) (Config, error) {
	var cfg Config
	buf, err := os.ReadFile(path)
	if err != nil {
		return cfg, err
	}
	if err := json.Unmarshal(buf, &cfg); err != nil {
		return cfg, err
	}
	return cfg, nil
}

func merge(dst *Config, src Config) {
	if src.BackendURL != "" {
		dst.BackendURL = src.BackendURL
	}
	if src.Identifier != "" {
		dst.Identifier = src.Identifier
	}
	if src.APIKey != "" {
		dst.APIKey = src.APIKey
	}
	if src.ReportIntervalSec > 0 {
		dst.ReportIntervalSec = src.ReportIntervalSec
	}
	if src.LogLevel != "" {
		dst.LogLevel = src.LogLevel
	}
}

func getenv(key, fallback string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return fallback
}

func getenvInt(key string, fallback int) int {
	if v := os.Getenv(key); v != "" {
		var out int
		if _, err := fmt.Sscanf(v, "%d", &out); err == nil && out > 0 {
			return out
		}
	}
	return fallback
}

func hostnameOr(fallback string) string {
	name, err := os.Hostname()
	if err != nil || name == "" {
		return fallback
	}
	return name
}