import { execFile } from "node:child_process";
import { promisify } from "node:util";

import type { AppearanceMode, DetectionResult } from "./types.js";

const execFileAsync = promisify(execFile);

function parseMode(value: string | undefined): AppearanceMode | undefined {
  const normalized = value?.trim().toLowerCase();
  if (!normalized) return undefined;
  if (normalized === "dark" || normalized === "1" || normalized === "true") return "dark";
  if (normalized === "light" || normalized === "0" || normalized === "false") return "light";
  return undefined;
}

async function detectMacOs(): Promise<DetectionResult | undefined> {
  if (process.platform !== "darwin") return undefined;

  try {
    const { stdout } = await execFileAsync("osascript", [
      "-e",
      'tell application "System Events" to tell appearance preferences to return dark mode',
    ]);

    const darkMode = stdout.trim();
    if (darkMode === "true") return { mode: "dark", source: "macos" };
    if (darkMode === "false") return { mode: "light", source: "macos" };
  } catch {
    // Ignore detector failure and continue down the chain.
  }

  return undefined;
}

async function detectWindows(): Promise<DetectionResult | undefined> {
  if (process.platform !== "win32") return undefined;

  try {
    const { stdout } = await execFileAsync("powershell.exe", [
      "-NoProfile",
      "-NonInteractive",
      "-Command",
      "$v=(Get-ItemProperty -Path HKCU:\\Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize -Name AppsUseLightTheme -ErrorAction Stop).AppsUseLightTheme; if ($v -eq 0) { 'dark' } elseif ($v -eq 1) { 'light' }",
    ]);

    const mode = parseMode(stdout);
    if (mode) return { mode, source: "windows" };
  } catch {
    // Ignore detector failure and continue down the chain.
  }

  return undefined;
}

async function detectTmux(): Promise<DetectionResult | undefined> {
  if (!process.env.TMUX && process.env.TERM_PROGRAM !== "tmux") return undefined;

  try {
    const { stdout } = await execFileAsync("tmux", ["display-message", "-p", "#{client_theme}"]);
    const mode = parseMode(stdout);
    if (mode) return { mode, source: "tmux" };
  } catch {
    // Ignore detector failure and continue down the chain.
  }

  return undefined;
}

function detectDarkModeEnv(): DetectionResult | undefined {
  const mode = parseMode(process.env.DARK_MODE);
  return mode ? { mode, source: "env:DARK_MODE" } : undefined;
}

function detectColorFgBg(): DetectionResult | undefined {
  const colorfgbg = process.env.COLORFGBG || "";
  if (!colorfgbg) return undefined;

  const parts = colorfgbg.split(";");
  if (parts.length < 2) return undefined;

  const bg = Number.parseInt(parts[1] ?? "", 10);
  if (Number.isNaN(bg)) return undefined;

  return {
    mode: bg < 8 ? "dark" : "light",
    source: "heuristic:COLORFGBG",
  };
}

export async function detectAppearance(defaultMode: AppearanceMode = "dark"): Promise<DetectionResult> {
  return (
    (await detectMacOs()) ??
    (await detectWindows()) ??
    (await detectTmux()) ??
    detectDarkModeEnv() ??
    detectColorFgBg() ??
    { mode: defaultMode, source: `fallback:${defaultMode}` }
  );
}