"use strict";

const assert = require("assert").strict;
const crypto = require("crypto");
const fs = require("fs").promises;
const path = require("path");
const execa = require("execa");
const { rollup } = require("rollup");

const ROOT = path.join(__dirname, "..", "..");

class Cache {
  constructor(cacheDir, version) {
    this.cacheDir = path.resolve(cacheDir || required("cacheDir"));
    this.manifest = path.join(this.cacheDir, "manifest.json");
    this.version = version || required("version");
    this.checksums = {};
    this.files = {};
    this.updated = {
      version: this.version,
      checksums: {},
      files: {},
    };
  }

  // Loads the manifest.json file with the information from the last build
  async load() {
    // This should never throw, if it does, let it fail the build
    const lockfile = await fs.readFile("yarn.lock", "utf-8");
    const lockfileHash = hashString(lockfile);
    this.updated.checksums["yarn.lock"] = lockfileHash;

    try {
      const manifest = await fs.readFile(this.manifest, "utf-8");
      const { version, checksums, files } = JSON.parse(manifest);

      // Ignore the cache if the version changed
      assert.strictEqual(this.version, version);

      assert.ok(typeof checksums === "object");
      // If yarn.lock changed, rebuild everything
      assert.strictEqual(lockfileHash, checksums["yarn.lock"]);
      this.checksums = checksums;

      assert.ok(typeof files === "object");
      this.files = files;

      for (const files of Object.values(this.files)) {
        assert.ok(Array.isArray(files));
      }
    } catch {
      this.checksums = {};
      this.files = {};
    }
  }

  // Run rollup to get the list of files included in the bundle and check if
  // any (or the list itself) have changed.
  // This takes the same rollup config used for bundling to include files that are
  // resolved by specific plugins.
  async checkBundle(id, inputOptions, outputOptions) {
    const files = new Set(this.files[id]);
    const newFiles = (this.updated.files[id] = []);

    let dirty = false;

    const bundle = await rollup(getRollupConfig(inputOptions));
    const { output } = await bundle.generate(outputOptions);

    const modules = output
      .filter((mod) => !/\0/.test(mod.facadeModuleId))
      .map((mod) => [path.relative(ROOT, mod.facadeModuleId), mod.code]);

    for (const [id, code] of modules) {
      newFiles.push(id);
      // If we already checked this file for another bundle, reuse the hash
      if (!this.updated.checksums[id]) {
        this.updated.checksums[id] = hashString(code);
      }
      const hash = this.updated.checksums[id];

      // Check if this file changed
      if (!this.checksums[id] || this.checksums[id] !== hash) {
        dirty = true;
      }

      // Check if this file is new
      if (!files.delete(id)) {
        dirty = true;
      }
    }

    // Final check: if any file was removed, `files` is not empty
    return !dirty && files.size === 0;
  }

  async save() {
    try {
      await fs.writeFile(this.manifest, JSON.stringify(this.updated, null, 2));
    } catch {
      // Don't fail the build
    }
  }

  async isCached(inputOptions, outputOption) {
    const useCache = await this.checkBundle(
      outputOption.file,
      inputOptions,
      outputOption
    );
    if (useCache) {
      try {
        await execa("cp", [
          path.join(this.cacheDir, outputOption.file.replace("dist", "files")),
          outputOption.file,
        ]);
        return true;
      } catch (err) {
        console.log(err);
        // Proceed to build
      }
    }
    return false;
  }
}

function required(name) {
  throw new Error(name + " is required");
}

function hashString(string) {
  return crypto.createHash("md5").update(string).digest("hex");
}

function getRollupConfig(rollupConfig) {
  return {
    ...rollupConfig,
    onwarn() {},
    plugins: rollupConfig.plugins.filter(
      (plugin) =>
        // We're not interested in dependencies, we already check `yarn.lock`
        plugin.name !== "node-resolve" &&
        // This is really slow, we need this "preflight" to be fast
        plugin.name !== "babel"
    ),
  };
}

module.exports = Cache;