import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
import { homedir } from "node:os";
import { join, dirname } from "node:path";
import { fileURLToPath } from "node:url";
import { logError, logWarn } from "../logger.js";
import { getModelFamily } from "../request/model-map.js";

const __dirname = dirname(fileURLToPath(import.meta.url));
const CACHE_DIR = join(homedir(), ".chatgpt-codex-router", "cache");

const GITHUB_API_RELEASES =
  "https://api.github.com/repos/openai/codex/releases/latest";
const GITHUB_HTML_RELEASES =
  "https://github.com/openai/codex/releases/latest";

type ModelFamily = "gpt-5.2-codex" | "codex-max" | "codex" | "gpt-5.2" | "gpt-5.1";

const PROMPT_FILES: Record<ModelFamily, string> = {
  "gpt-5.2-codex": "gpt-5.2-codex_prompt.md",
  "codex-max": "gpt-5.1-codex-max_prompt.md",
  codex: "gpt_5_codex_prompt.md",
  "gpt-5.2": "gpt_5_2_prompt.md",
  "gpt-5.1": "gpt_5_1_prompt.md",
};

const CACHE_FILES: Record<ModelFamily, string> = {
  "gpt-5.2-codex": "gpt-5.2-codex-instructions.md",
  "codex-max": "codex-max-instructions.md",
  codex: "codex-instructions.md",
  "gpt-5.2": "gpt-5.2-instructions.md",
  "gpt-5.1": "gpt-5.1-instructions.md",
};

interface CacheMetadata {
  etag: string | null;
  tag: string | null;
  lastChecked: number | null;
  url: string;
}

async function getLatestReleaseTag(): Promise<string> {
  try {
    const response = await fetch(GITHUB_API_RELEASES);
    if (response.ok) {
      const data = (await response.json()) as { tag_name: string };
      if (data.tag_name) {
        return data.tag_name;
      }
    }
  } catch {
  }

  const htmlResponse = await fetch(GITHUB_HTML_RELEASES);
  if (!htmlResponse.ok) {
    throw new Error(
      `Failed to fetch latest release: ${htmlResponse.status}`,
    );
  }

  const finalUrl = htmlResponse.url;
  if (finalUrl) {
    const parts = finalUrl.split("/tag/");
    const last = parts[parts.length - 1];
    if (last && !last.includes("/")) {
      return last;
    }
  }

  const html = await htmlResponse.text();
  const match = html.match(/\/openai\/codex\/releases\/tag\/([^"]+)/);
  if (match && match[1]) {
    return match[1];
  }

  throw new Error("Failed to determine latest release tag from GitHub");
}

async function getCodexInstructions(
  normalizedModel = "gpt-5.1-codex",
): Promise<string> {
  const modelFamily = getModelFamily(normalizedModel) as ModelFamily;
  const promptFile = PROMPT_FILES[modelFamily];
  const cacheFile = join(CACHE_DIR, CACHE_FILES[modelFamily]);
  const cacheMetaFile = join(
    CACHE_DIR,
    `${CACHE_FILES[modelFamily].replace(".md", "-meta.json")}`,
  );

  try {
    let cachedETag: string | null = null;
    let cachedTag: string | null = null;
    let cachedTimestamp: number | null = null;

    if (existsSync(cacheMetaFile)) {
      const metadata = JSON.parse(
        readFileSync(cacheMetaFile, "utf8"),
      ) as CacheMetadata;
      cachedETag = metadata.etag;
      cachedTag = metadata.tag;
      cachedTimestamp = metadata.lastChecked;
    }

    const CACHE_TTL_MS = 15 * 60 * 1000; 
    if (
      cachedTimestamp &&
      Date.now() - cachedTimestamp < CACHE_TTL_MS &&
      existsSync(cacheFile)
    ) {
      return readFileSync(cacheFile, "utf8");
    }

    const latestTag = await getLatestReleaseTag();
    const CODEX_INSTRUCTIONS_URL = `https://raw.githubusercontent.com/openai/codex/${latestTag}/codex-rs/core/${promptFile}`;

    if (cachedTag !== latestTag) {
      cachedETag = null;
    }

    const headers: Record<string, string> = {};
    if (cachedETag) {
      headers["If-None-Match"] = cachedETag;
    }

    const response = await fetch(CODEX_INSTRUCTIONS_URL, { headers });

    if (response.status === 304) {
      if (existsSync(cacheFile)) {
        return readFileSync(cacheFile, "utf8");
      }
    }

    if (response.ok) {
      const instructions = await response.text();
      const newETag = response.headers.get("etag");

      if (!existsSync(CACHE_DIR)) {
        mkdirSync(CACHE_DIR, { recursive: true });
      }

      writeFileSync(cacheFile, instructions, "utf8");
      writeFileSync(
        cacheMetaFile,
        JSON.stringify({
          etag: newETag,
          tag: latestTag,
          lastChecked: Date.now(),
          url: CODEX_INSTRUCTIONS_URL,
        } satisfies CacheMetadata),
        "utf8",
      );

      return instructions;
    }

    throw new Error(`HTTP ${response.status}`);
  } catch (error) {
    const err = error as Error;
    logError(null, `Failed to fetch ${modelFamily} instructions from GitHub: ${err.message}`);

    if (existsSync(cacheFile)) {
      logWarn(null, `Using cached ${modelFamily} instructions`);
      return readFileSync(cacheFile, "utf8");
    }

    logWarn(null, `Using fallback instructions for ${modelFamily}`);
    return getFallbackPrompt();
  }
}

function getFallbackPrompt(): string {
  return `You are a helpful AI assistant with strong coding capabilities. 
You can help users with a wide range of programming tasks, including:
- Writing and debugging code
- Explaining programming concepts
- Refactoring and optimizing code
- Generating code examples
- Answering technical questions

Be concise, accurate, and provide practical solutions.`;
}

export { getCodexInstructions };