// SPDX-License-Identifier: GPL-2.0-or-later
// Copyright (C) 2026 Bryan Joshua Pedini

package main

import (
	"fmt"
	"os"
	"strconv"
)

type Config struct {
	PDNSAPIKey   string
	ListenAddr   string
	MySQLDSN     string
	TablePrefix  string
	PDNSServerID string
	DefaultTTL   int
	LogLevel     string
	PUID         int
	PGID         int
}

// LoadConfig reads configuration exclusively from environment variables.
// Missing/invalid required variables are a fatal startup error.
func LoadConfig() *Config {
	c := &Config{
		ListenAddr:   envOrDefault("LISTEN_ADDR", ":3000"),
		TablePrefix:  envOrDefault("TABLE_PREFIX", "coredns_"),
		PDNSServerID: envOrDefault("PDNS_SERVER_ID", "localhost"),
		LogLevel:     envOrDefault("LOG_LEVEL", "info"),
	}

	c.PDNSAPIKey = requireEnv("PDNS_API_KEY")
	c.MySQLDSN = requireEnv("MYSQL_DSN")

	c.DefaultTTL = requirePositiveInt("DEFAULT_TTL", 120)

	switch c.LogLevel {
	case "debug", "info", "warn", "error":
	default:
		fatalf("invalid LOG_LEVEL %q: must be one of debug, info, warn, error", c.LogLevel)
	}

	c.PUID = requireInt("PUID")
	c.PGID = requireInt("PGID")
	if c.PUID == 0 || c.PGID == 0 {
		fatalf("refusing to serve as root: PUID and PGID must both be non-zero")
	}

	return c
}

func envOrDefault(key, def string) string {
	if v, ok := os.LookupEnv(key); ok && v != "" {
		return v
	}
	return def
}

func requireEnv(key string) string {
	v, ok := os.LookupEnv(key)
	if !ok || v == "" {
		fatalf("missing required environment variable: %s", key)
	}
	return v
}

func requireInt(key string) int {
	v := requireEnv(key)
	n, err := strconv.Atoi(v)
	if err != nil {
		fatalf("invalid %s: %q is not an integer", key, v)
	}
	return n
}

func requirePositiveInt(key string, def int) int {
	v, ok := os.LookupEnv(key)
	if !ok || v == "" {
		return def
	}
	n, err := strconv.Atoi(v)
	if err != nil || n <= 0 {
		fatalf("invalid %s: %q is not a positive integer", key, v)
	}
	return n
}

func fatalf(format string, args ...any) {
	fmt.Fprintf(os.Stderr, "config error: "+format+"\n", args...)
	os.Exit(1)
}