// Server-only. Kept out of the package index so browser bundles never load `node:fs`.
import { readFile } from "node:fs/promises";
import path from "node:path";

/** Upper bound on a project summary, so it stays a short brief for the project's main agent. */
export const PROJECT_SUMMARY_MAX_LENGTH = 600;
const FILE_READ_LIMIT = 64 * 1024;
const README_NAMES = ["README.md", "README.markdown", "README.rst", "README.txt", "README"];

export interface ProjectFiles {
  readme?: string | null;
  packageJson?: string | null;
  pyproject?: string | null;
  cargoToml?: string | null;
}

function clamp(text: string): string {
  const flat = text.replace(/\s+/g, " ").trim();
  if (flat.length <= PROJECT_SUMMARY_MAX_LENGTH) return flat;
  return `${flat.slice(0, PROJECT_SUMMARY_MAX_LENGTH - 1).trimEnd()}…`;
}

/** The first prose paragraph of a README: no headings, badges, images, HTML, or code. */
function readmeParagraph(readme: string): string | null {
  let inFence = false;
  const paragraph: string[] = [];
  for (const raw of readme.split(/\r?\n/)) {
    const line = raw.trim();
    if (line.startsWith("```") || line.startsWith("~~~")) {
      inFence = !inFence;
      if (paragraph.length) break;
      continue;
    }
    if (inFence) continue;
    const prose =
      line &&
      !/^(#|=+$|-+$|<|!\[|\[!\[|\||>)/.test(line) &&
      // A line of only links is navigation, not a description.
      line.replace(/\[[^\]]*\]\([^)]*\)/g, "").replace(/[\s|·•-]/g, "") !== "";
    if (prose) {
      paragraph.push(line);
    } else if (paragraph.length) {
      break;
    }
  }
  if (!paragraph.length) return null;
  const text = paragraph
    .join(" ")
    .replace(/!\[[^\]]*\]\([^)]*\)/g, "")
    .replace(/\[([^\]]*)\]\([^)]*\)/g, "$1")
    .replace(/[*_`]/g, "");
  return text.trim() || null;
}

function manifestDescription(files: ProjectFiles): string | null {
  if (files.packageJson) {
    try {
      const parsed = JSON.parse(files.packageJson) as { description?: unknown };
      if (typeof parsed.description === "string" && parsed.description.trim()) {
        return parsed.description.trim();
      }
    } catch {
      // An unreadable manifest has no description.
    }
  }
  for (const toml of [files.pyproject, files.cargoToml]) {
    const match = toml?.match(/^\s*description\s*=\s*"([^"\n]+)"/m);
    if (match?.[1]?.trim()) return match[1].trim();
  }
  return null;
}

/**
 * What a project is about, from the files a folder already has: the README's first paragraph,
 * else a manifest description. Returns null when neither says anything.
 */
export function summarizeProjectFiles(files: ProjectFiles): string | null {
  const summary =
    (files.readme ? readmeParagraph(files.readme) : null) ?? manifestDescription(files);
  return summary ? clamp(summary) : null;
}

async function readSmallFile(file: string): Promise<string | null> {
  try {
    const content = await readFile(file, "utf8");
    return content.slice(0, FILE_READ_LIMIT);
  } catch {
    return null;
  }
}

/** Reads a linked project folder's README and manifests; nothing else in it is opened. */
export async function readProjectSummary(directory: string): Promise<string | null> {
  let readme: string | null = null;
  for (const name of README_NAMES) {
    readme = await readSmallFile(path.join(directory, name));
    if (readme) break;
  }
  const [packageJson, pyproject, cargoToml] = await Promise.all([
    readSmallFile(path.join(directory, "package.json")),
    readSmallFile(path.join(directory, "pyproject.toml")),
    readSmallFile(path.join(directory, "Cargo.toml")),
  ]);
  return summarizeProjectFiles({ readme, packageJson, pyproject, cargoToml });
}