import { existsSync, readFileSync } from "node:fs";
import { homedir } from "node:os";
import { dirname, join, resolve } from "node:path";

export interface PiWebConfig {
  host?: string;
  port?: number;
  allowedHosts?: string[] | true;
}

export interface LoadedPiWebConfig {
  path: string;
  exists: boolean;
  config: PiWebConfig;
}

interface LoadOptions {
  env?: NodeJS.ProcessEnv;
  cwd?: string;
}

export function defaultPiWebConfigPath(env: NodeJS.ProcessEnv = process.env): string {
  const xdgConfigHome = env["XDG_CONFIG_HOME"];
  return join(xdgConfigHome !== undefined && xdgConfigHome !== "" ? xdgConfigHome : join(homedir(), ".config"), "pi-web", "config.json");
}

export function piWebConfigPath(env: NodeJS.ProcessEnv = process.env, cwd = process.cwd()): string {
  const configured = env["PI_WEB_CONFIG"];
  if (configured === undefined || configured === "") return defaultPiWebConfigPath(env);
  return resolve(cwd, configured);
}

export function loadPiWebConfig(options: LoadOptions = {}): LoadedPiWebConfig {
  const env = options.env ?? process.env;
  const path = piWebConfigPath(env, options.cwd ?? process.cwd());
  if (!existsSync(path)) return { path, exists: false, config: {} };

  const parsed: unknown = JSON.parse(readFileSync(path, "utf8"));
  if (!isRecord(parsed)) throw new Error(`Pi Web config must be a JSON object: ${path}`);

  return { path, exists: true, config: parsePiWebConfig(parsed, path) };
}

export function effectivePiWebConfig(options: LoadOptions = {}): LoadedPiWebConfig {
  const loaded = loadPiWebConfig(options);
  const env = options.env ?? process.env;
  const host = env["PI_WEB_HOST"];
  const port = env["PI_WEB_PORT"] ?? env["PORT"];
  const allowedHosts = env["PI_WEB_ALLOWED_HOSTS"];

  return {
    ...loaded,
    config: {
      ...loaded.config,
      ...(host !== undefined && host !== "" ? { host } : {}),
      ...(port !== undefined && port !== "" ? { port: parsePort(port, "PI_WEB_PORT") } : {}),
      ...(allowedHosts !== undefined && allowedHosts !== "" ? { allowedHosts: parseAllowedHostsEnv(allowedHosts) } : {}),
    },
  };
}

function parsePiWebConfig(value: Record<string, unknown>, path: string): PiWebConfig {
  return {
    ...(value["host"] !== undefined ? { host: parseString(value["host"], "host", path) } : {}),
    ...(value["port"] !== undefined ? { port: parsePort(value["port"], "port", path) } : {}),
    ...(value["allowedHosts"] !== undefined ? { allowedHosts: parseAllowedHosts(value["allowedHosts"], path) } : {}),
  };
}

function parseString(value: unknown, key: string, path: string): string {
  if (typeof value !== "string" || value === "") throw new Error(`Pi Web config ${key} must be a non-empty string: ${path}`);
  return value;
}

function parsePort(value: unknown, key: string, path = "environment"): number {
  const port = typeof value === "number" ? value : typeof value === "string" && value !== "" ? Number(value) : NaN;
  if (!Number.isInteger(port) || port < 1 || port > 65535) throw new Error(`Pi Web config ${key} must be an integer from 1 to 65535: ${path}`);
  return port;
}

function parseAllowedHosts(value: unknown, path: string): string[] | true {
  if (value === true) return true;
  if (!isNonEmptyStringArray(value)) {
    throw new Error(`Pi Web config allowedHosts must be true or an array of non-empty strings: ${path}`);
  }
  return value;
}

function parseAllowedHostsEnv(value: string): string[] | true {
  if (value === "true") return true;
  return value.split(",").map((host) => host.trim()).filter((host) => host !== "");
}

function isRecord(value: unknown): value is Record<string, unknown> {
  return typeof value === "object" && value !== null && !Array.isArray(value);
}

function isNonEmptyStringArray(value: unknown): value is string[] {
  return Array.isArray(value) && value.every((item) => typeof item === "string" && item !== "");
}

export function examplePiWebConfig(config: PiWebConfig = {}): string {
  return `${JSON.stringify({ host: config.host ?? "127.0.0.1", port: config.port ?? 8504, allowedHosts: config.allowedHosts ?? [] }, null, 2)}\n`;
}

export function piWebConfigDir(env: NodeJS.ProcessEnv = process.env): string {
  return dirname(defaultPiWebConfigPath(env));
}