// Package config loads runtime configuration from environment variables.
//
// On startup Load() reads a .env file (if present) from the current
// working directory and merges its values into the process environment.
// Existing process env vars take precedence over .env so deployments
// can override .env without modifying the file.
package config

import (
	"fmt"
	"os"
	"strconv"
	"time"

	"github.com/joho/godotenv"
)

// Config holds all runtime parameters.
type Config struct {
	HTTPAddr     string        // Address to listen on, e.g. ":8080"
	TickRate     int           // Race tick rate (Hz)
	TickInterval time.Duration // Derived from TickRate
	LogLevel     string        // "debug" | "info" | "warn" | "error"
	MaxClients   int           // Maximum concurrent WS clients
	SnapshotRate int           // Snapshot fan-out rate (Hz)
	DevMode      bool          // If true, allow multiple clients without auth

	DatabaseURL string // Postgres connection string; required at runtime

	UDPVideoAddr string // UDP address to listen on for video, e.g. ":9999"
	ESPCmdPort   int    // Port on ESP32 that listens for commands, e.g. 8888
}

// Load reads configuration from environment variables, applying defaults.
//
// A .env file in the current working directory (or any path listed in
// X0GP_DOTENV) is loaded before reading the environment. Missing .env
// is not an error — production deployments set vars directly.
func Load() (*Config, error) {
	loadDotEnv()

	c := &Config{
		HTTPAddr:     getEnv("X0GP_HTTP_ADDR", ":8080"),
		TickRate:     getEnvInt("X0GP_TICK_RATE", 60),
		LogLevel:     getEnv("X0GP_LOG_LEVEL", "info"),
		MaxClients:   getEnvInt("X0GP_MAX_CLIENTS", 100),
		SnapshotRate: getEnvInt("X0GP_SNAPSHOT_RATE", 30),
		DevMode:      getEnvBool("X0GP_DEV_MODE", true),
		DatabaseURL:  getEnv("DATABASE_URL", ""),
		UDPVideoAddr: getEnv("X0GP_UDP_VIDEO_ADDR", ":9999"),
		ESPCmdPort:   getEnvInt("X0GP_ESP_CMD_PORT", 8888),
	}

	if c.TickRate <= 0 || c.TickRate > 240 {
		return nil, fmt.Errorf("X0GP_TICK_RATE must be in (0, 240], got %d", c.TickRate)
	}
	c.TickInterval = time.Second / time.Duration(c.TickRate)

	if c.SnapshotRate <= 0 || c.SnapshotRate > c.TickRate {
		return nil, fmt.Errorf("X0GP_SNAPSHOT_RATE must be in (0, %d], got %d",
			c.TickRate, c.SnapshotRate)
	}

	return c, nil
}

func getEnv(key, fallback string) string {
	if v, ok := os.LookupEnv(key); ok {
		return v
	}
	return fallback
}

// loadDotEnv merges a .env file into the process environment. Files
// that do not exist are silently ignored. Paths can be overridden with
// X0GP_DOTENV (colon-separated). Existing process env vars take
// precedence over .env values so deploys can override without
// editing the file (godotenv.Load, not Overload).
func loadDotEnv() {
	if paths := os.Getenv("X0GP_DOTENV"); paths != "" {
		for _, p := range splitPaths(paths) {
			_ = godotenv.Load(p)
		}
		return
	}
	_ = godotenv.Load(".env")
}

func splitPaths(s string) []string {
	out := make([]string, 0, 4)
	start := 0
	for i := 0; i < len(s); i++ {
		if s[i] == ':' || s[i] == ';' {
			if i > start {
				out = append(out, s[start:i])
			}
			start = i + 1
		}
	}
	if start < len(s) {
		out = append(out, s[start:])
	}
	return out
}

func getEnvInt(key string, fallback int) int {
	if v, ok := os.LookupEnv(key); ok {
		if n, err := strconv.Atoi(v); err == nil {
			return n
		}
	}
	return fallback
}

func getEnvBool(key string, fallback bool) bool {
	if v, ok := os.LookupEnv(key); ok {
		if b, err := strconv.ParseBool(v); err == nil {
			return b
		}
	}
	return fallback
}