import { resolve } from "node:path";

export interface Config {
  host: string;
  port: number;
  storageDir: string;
  maxFileSize: number;
  fileTtlMs: number;
  rateLimitEnabled: boolean;
  rateLimitMax: number;
  rateLimitWindowMs: number;
  trustProxy: boolean;
}

const DEFAULT_TTL_MS = 7 * 24 * 60 * 60 * 1000; // 1 week

const SIZE_UNITS: Record<string, number> = {
  B: 1,
  K: 1 << 10,
  KB: 1 << 10,
  KIB: 1 << 10,
  M: 1 << 20,
  MB: 1 << 20,
  MIB: 1 << 20,
  G: 1 << 30,
  GB: 1 << 30,
  GIB: 1 << 30,
  T: 1 << 40,
  TB: 1 << 40,
  TIB: 1 << 40,
};

export function parseSize(value: string): number {
  const match = /^\s*(\d+(?:\.\d+)?)\s*([A-Za-z]*)\s*$/.exec(value);
  if (!match) throw new Error(`Invalid size value: "${value}"`);
  const num = parseFloat(match[1]!);
  const unit = (match[2] || "B").toUpperCase();
  const factor = SIZE_UNITS[unit];
  if (factor === undefined) throw new Error(`Invalid size unit in: "${value}"`);
  return Math.floor(num * factor);
}

function boolFromEnv(value: string | undefined, fallback: boolean): boolean {
  if (value === undefined) return fallback;
  return !["0", "false", "no", "off"].includes(value.trim().toLowerCase());
}

export function loadConfig(env: Record<string, string | undefined> = process.env): Config {
  const port = Number(env.PORT ?? "3000");
  if (!Number.isInteger(port) || port < 1 || port > 65535) {
    throw new Error(`Invalid PORT: ${env.PORT}`);
  }
  const host = env.HOST ?? "0.0.0.0";
  const storageDir = resolve(env.STORAGE_DIR ?? "./storage");
  const maxFileSize = parseSize(env.MAX_FILE_SIZE ?? "10GB");
  if (maxFileSize < 1024) throw new Error("MAX_FILE_SIZE must be at least 1KB");

  const fileTtlMs = Number(env.FILE_TTL_MS ?? String(DEFAULT_TTL_MS));
  if (!Number.isInteger(fileTtlMs) || fileTtlMs < 1) {
    throw new Error(`Invalid FILE_TTL_MS: ${env.FILE_TTL_MS}`);
  }

  const rateLimitMax = Number(env.RATE_LIMIT_MAX ?? "300");
  if (!Number.isInteger(rateLimitMax) || rateLimitMax < 1) {
    throw new Error(`Invalid RATE_LIMIT_MAX: ${env.RATE_LIMIT_MAX}`);
  }
  const rateLimitWindowMs = Number(env.RATE_LIMIT_WINDOW_MS ?? "60000");
  if (!Number.isInteger(rateLimitWindowMs) || rateLimitWindowMs < 1000) {
    throw new Error(`Invalid RATE_LIMIT_WINDOW_MS: ${env.RATE_LIMIT_WINDOW_MS}`);
  }

  return {
    host,
    port,
    storageDir,
    maxFileSize,
    fileTtlMs,
    rateLimitEnabled: boolFromEnv(env.RATE_LIMIT_ENABLED, true),
    rateLimitMax,
    rateLimitWindowMs,
    trustProxy: boolFromEnv(env.TRUST_PROXY, false),
  };
}