#!/usr/bin/env node

import { mkdir, readFile, writeFile } from "node:fs/promises";
import path from "node:path";
import { fileURLToPath } from "node:url";

const rootDir = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");

const config = JSON.parse(await readText("scripts/llms-config.json"));

for (const key of ["title", "summary", "repoUrl", "llmsFullUrl"]) {
  if (!config[key]) throw new Error(`Missing llms config key: ${key}`);
}

const docs = await loadDocs(config.docs);
const optionalDocs = await loadDocs(config.optionalDocs || []);

if (docs.length === 0) {
  throw new Error("No source docs found for llms generation");
}

await writeOutputs(config.shortOutputs, buildShortFile(config, docs, optionalDocs));
await writeOutputs(config.fullOutputs, buildFullFile(config, docs, optionalDocs));

function buildShortFile(config, docs, optionalDocs) {
  const lines = [
    `# ${config.title}`,
    "",
    `> ${config.summary}`,
    "",
    "This file is generated by `scripts/generate-llms-files.mjs`. Do not hand-edit it; update the source docs or generator config, then run `yarn llms:generate`.",
    "",
    "## Canonical Links",
    "",
    ...config.links.map(([label, url]) => `- [${label}](${url})`),
    `- [llms-full.txt](${config.llmsFullUrl}): Expanded inline corpus generated from the curated source docs.`,
    "",
    "## Critical Context",
    "",
    ...config.notes.map((note) => `- ${note}`),
    "",
    "## Source Of Truth",
    "",
    "- Code, tests, package manifests, source docs, and live/runtime evidence when relevant are source of truth.",
    "- This generated file is compiled context for orientation. Verify behavioral claims against source files before editing or concluding.",
    "- Repo-managed AI instructions live in `AGENTS.md` and any directory-specific `AGENTS.md` files.",
    "",
    "## Core Documents",
    "",
    ...docs.map(formatDocLink)
  ];

  if (optionalDocs.length > 0) {
    lines.push("", "## Optional", "", ...optionalDocs.map(formatDocLink));
  }

  return `${lines.join("\n")}\n`;
}

function buildFullFile(config, docs, optionalDocs) {
  const allDocs = [...docs, ...optionalDocs];
  const lines = [
    `# ${config.title} Full LLM Context`,
    "",
    `> ${config.summary}`,
    "",
    "This file is generated by `scripts/generate-llms-files.mjs`. Do not hand-edit it; update the source docs or generator config, then run `yarn llms:generate`.",
    "",
    "Use this as compiled context only. Source files, tests, manifests, and live/runtime evidence remain authoritative.",
    "",
    "## Index",
    "",
    ...allDocs.map((doc) => `- [${doc.relativePath}](#${anchorFor(doc.relativePath)})`),
    "",
    "---"
  ];

  for (const doc of allDocs) {
    lines.push(
      "",
      `## ${doc.relativePath}`,
      "",
      `Source: ${doc.url}`,
      "",
      "```markdown",
      doc.content.trim(),
      "```",
      "",
      "---"
    );
  }

  return `${lines.join("\n")}\n`;
}

function formatDocLink(doc) {
  return `- [${doc.title}](${doc.url}): ${doc.summary}`;
}

async function loadDocs(relativePaths) {
  const docs = [];

  for (const relativePath of relativePaths) {
    const content = await readOptional(relativePath);
    if (!content) continue;

    docs.push({
      relativePath,
      content,
      title: titleFromMarkdown(content, relativePath),
      summary: summaryFromMarkdown(content),
      url: `${config.repoUrl}/blob/master/${encodeURI(relativePath).replace(/%2F/g, "/")}`
    });
  }

  return docs;
}

function titleFromMarkdown(content, fallback) {
  if (fallback.endsWith("CHANGELOG.md")) return "Changelog";
  if (fallback.endsWith("TODO.md")) return "TODO";

  let inFence = false;
  let inFrontmatter = false;
  let fallbackHeading = "";
  const lines = content.split(/\r?\n/);

  for (let index = 0; index < lines.length; index += 1) {
    const trimmed = lines[index].trim();

    if (index === 0 && trimmed === "---") {
      inFrontmatter = true;
      continue;
    }

    if (inFrontmatter) {
      if (trimmed === "---") inFrontmatter = false;
      continue;
    }

    if (trimmed.startsWith("```")) {
      inFence = !inFence;
      continue;
    }

    if (inFence) continue;

    const h1 = trimmed.match(/^#\s+(.+)$/);
    if (h1) return h1[1].trim();

    const h2 = trimmed.match(/^##\s+(.+)$/);
    if (h2 && !fallbackHeading) fallbackHeading = h2[1].trim();
  }

  return fallbackHeading || fallback;
}

function summaryFromMarkdown(content) {
  const lines = content.split(/\r?\n/);
  const paragraphs = [];
  let current = [];
  let inFence = false;
  let inFrontmatter = false;

  for (let index = 0; index < lines.length; index += 1) {
    const line = lines[index];
    const trimmed = line.trim();

    if (index === 0 && trimmed === "---") {
      inFrontmatter = true;
      continue;
    }

    if (inFrontmatter) {
      if (trimmed === "---") inFrontmatter = false;
      continue;
    }

    if (trimmed.startsWith("```")) {
      inFence = !inFence;
      continue;
    }

    if (inFence || !trimmed || trimmed.startsWith("#") || trimmed.startsWith("|")) {
      if (current.length > 0) {
        paragraphs.push(current.join(" "));
        current = [];
      }
      continue;
    }

    if (
      trimmed.startsWith("[![") ||
      trimmed.startsWith("_Telegram") ||
      trimmed.startsWith("<img") ||
      trimmed.startsWith("<p") ||
      trimmed.startsWith("<br") ||
      trimmed.startsWith("</") ||
      trimmed.startsWith("<!--")
    ) {
      continue;
    }

    current.push(trimmed.replace(/\s+/g, " "));
  }

  if (current.length > 0) paragraphs.push(current.join(" "));

  const summary = paragraphs.find(Boolean) || "Repository documentation.";
  return summary.length > 220 ? `${summary.slice(0, 217).trimEnd()}...` : summary;
}

function anchorFor(value) {
  return value
    .toLowerCase()
    .replace(/[^a-z0-9\s-]/g, "")
    .trim()
    .replace(/\s+/g, "-");
}

async function writeOutputs(relativePaths, content) {
  for (const relativePath of relativePaths) {
    const absolutePath = path.join(rootDir, relativePath);
    await mkdir(path.dirname(absolutePath), { recursive: true });
    await writeFile(absolutePath, content);
    console.log(`[llms] wrote ${relativePath}`);
  }
}

async function readOptional(relativePath) {
  try {
    return await readText(relativePath);
  } catch (error) {
    if (error && error.code === "ENOENT") return "";
    throw error;
  }
}

async function readText(relativePath) {
  return readFile(path.join(rootDir, relativePath), "utf8");
}