import fs from "node:fs/promises";
import path from "node:path";
import { createHash } from "node:crypto";

async function packages(directory) {
  const result = new Map();
  for (const entry of await fs.readdir(directory)) {
    if (entry.startsWith(".")) continue;
    if (entry.startsWith("@")) {
      for (const name of await fs.readdir(path.join(directory, entry)))
        result.set(`${entry}/${name}`, path.join(directory, entry, name));
    } else result.set(entry, path.join(directory, entry));
  }
  return result;
}
async function packageDigest(directory) {
  const digest = createHash("sha256");
  async function visit(relative) {
    for (const entry of (await fs.readdir(path.join(directory, relative), { withFileTypes: true })).sort((a, b) =>
      a.name.localeCompare(b.name),
    )) {
      if (entry.name === "node_modules") continue;
      const name = path.join(relative, entry.name),
        file = path.join(directory, name);
      if (entry.isDirectory()) await visit(name);
      else {
        const bytes = await fs.readFile(file);
        digest.update(JSON.stringify([name, bytes.length]));
        digest.update(bytes);
      }
    }
  }
  await visit("");
  return digest.digest("hex");
}
/** Merge at package granularity: a scope such as @types is not a reserved package. */
export async function installDependencies({ destination, application, defaults = [], selected = {}, reserved = [] }) {
  const entries = new Map();
  for (const root of defaults) for (const [name, file] of await packages(root)) entries.set(name, file);
  for (const [name, file] of Object.entries(selected)) entries.set(name, file);
  if (application)
    for (const [name, file] of await packages(application)) {
      if (reserved.includes(name)) {
        const canonical = entries.get(name);
        if (!canonical || (await packageDigest(file)) !== (await packageDigest(canonical)))
          throw Error("Application dependencies cannot substitute selected React/client types or checked SDK: " + name);
      } else entries.set(name, file);
    }
  for (const [name, file] of entries) {
    await fs.mkdir(path.dirname(path.join(destination, name)), { recursive: true });
    await fs.symlink(file, path.join(destination, name));
  }
}