const fs = require("fs");
const path = require("path");
const etag = require("etag");
const babel = require("babel-core");

const IndexPage = require("../components/IndexPage");
const unpkgRewrite = require("../plugins/unpkgRewrite");
const renderPage = require("../utils/renderPage");
const getMetadata = require("../utils/getMetadata");
const getFileContentType = require("../utils/getFileContentType");
const getEntries = require("../utils/getEntries");

/**
 * Automatically generate HTML pages that show package contents.
 */
const AutoIndex = !process.env.DISABLE_INDEX;

/**
 * Maximum recursion depth for meta listings.
 */
const MaximumDepth = 128;

function serveMetadata(req, res) {
  getMetadata(
    req.packageDir,
    req.filename,
    req.stats,
    MaximumDepth,
    (error, metadata) => {
      if (error) {
        console.error(error);

        res
          .status(500)
          .type("text")
          .send(
            `Cannot generate metadata for ${req.packageSpec}${req.filename}`
          );
      } else {
        // Cache metadata for 1 year.
        res
          .set({
            "Cache-Control": "public, max-age=31536000",
            "Cache-Tag": "meta"
          })
          .send(metadata);
      }
    }
  );
}

function rewriteBareModuleIdentifiers(file, packageConfig, callback) {
  const dependencies = Object.assign(
    {},
    packageConfig.peerDependencies,
    packageConfig.dependencies
  );

  const options = {
    // Ignore .babelrc and package.json babel config
    // because we haven't installed dependencies so
    // we can't load plugins; see #84
    babelrc: false,
    plugins: [unpkgRewrite(dependencies)]
  };

  babel.transformFile(file, options, (error, result) => {
    callback(error, result && result.code);
  });
}

function serveJavaScriptModule(req, res) {
  if (getFileContentType(req.filename) !== "application/javascript") {
    return res
      .status(403)
      .type("text")
      .send("?module mode is available only for JavaScript files");
  }

  const file = path.join(req.packageDir, req.filename);

  rewriteBareModuleIdentifiers(file, req.packageConfig, (error, code) => {
    if (error) {
      console.error(error);

      const errorName = error.constructor.name;
      const errorMessage = error.message.replace(
        /^.*?\/unpkg-.+?\//,
        `/${req.packageSpec}/`
      );
      const codeFrame = error.codeFrame;
      const debugInfo = `${errorName}: ${errorMessage}\n\n${codeFrame}`;

      res
        .status(500)
        .type("text")
        .send(
          `Cannot generate module for ${req.packageSpec}${
            req.filename
          }\n\n${debugInfo}`
        );
    } else {
      // Cache modules for 1 year.
      res
        .set({
          "Content-Type": "application/javascript; charset=utf-8",
          "Content-Length": Buffer.byteLength(code),
          "Cache-Control": "public, max-age=31536000",
          "Cache-Tag": "file,js-file,js-module"
        })
        .send(code);
    }
  });
}

function serveStaticFile(req, res) {
  const tags = ["file"];

  const ext = path.extname(req.filename).substr(1);
  if (ext) {
    tags.push(`${ext}-file`);
  }

  let contentType = getFileContentType(req.filename);
  if (contentType === "application/javascript") {
    contentType += "; charset=utf-8";
  }

  // Cache files for 1 year.
  res.set({
    "Content-Type": contentType,
    "Content-Length": req.stats.size,
    "Cache-Control": "public, max-age=31536000",
    "Last-Modified": req.stats.mtime.toUTCString(),
    ETag: etag(req.stats),
    "Cache-Tag": tags.join(",")
  });

  const file = path.join(req.packageDir, req.filename);
  const stream = fs.createReadStream(file);

  stream.on("error", error => {
    console.error(`Cannot send file ${req.packageSpec}${req.filename}`);
    console.error(error);
    res.sendStatus(500);
  });

  stream.pipe(res);
}

function serveIndex(req, res) {
  const dir = path.join(req.packageDir, req.filename);

  getEntries(dir).then(
    entries => {
      const html = renderPage(IndexPage, {
        packageInfo: req.packageInfo,
        version: req.packageVersion,
        dir: req.filename,
        entries
      });

      // Cache HTML directory listings for 1 minute.
      res
        .set({
          "Cache-Control": "public, max-age=60",
          "Cache-Tag": "index"
        })
        .send(html);
    },
    error => {
      console.error(error);

      res
        .status(500)
        .type("text")
        .send(`Cannot read entries for ${req.packageSpec}${req.filename}`);
    }
  );
}

/**
 * Send the file, JSON metadata, or HTML directory listing.
 */
function serveFile(req, res) {
  if (req.query.meta != null) {
    serveMetadata(req, res);
  } else if (req.stats.isFile()) {
    if (req.query.module != null) {
      serveJavaScriptModule(req, res);
    } else {
      serveStaticFile(req, res);
    }
  } else if (req.stats.isDirectory() && AutoIndex) {
    serveIndex(req, res);
  } else {
    res
      .status(403)
      .type("text")
      .send(`Cannot serve ${req.packageSpec}${req.filename}; it's not a file`);
  }
}

module.exports = serveFile;