BundleCache.java

/* vim: set ts=2 et sw=2 cindent fo=qroca: */

package com.globant.katari.jsmodule.domain;

import java.nio.charset.Charset;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.commons.codec.binary.Hex;
import org.apache.commons.lang.Validate;

/** Manages the cache of the bundled files.
 *
 * @author ivan.bedecarats@globant.com.
 */
public class BundleCache {

  /** Map that contains the cache of the bundled files.
   *
   * The key is a {@link String} generated by concatenating an MD5 hash with
   * ".js". This MD5 hash was created by concatenating the paths of those files
   * which had been used for looking for the dependency files of the bundled
   * file. Each concatenated file path is ordered alphabetically and separated
   * by a |.
   * The value is a {@link String} which represents the content of the bundled
   * file cached in the Map.
   *
   */
  private Map<String, String> bundledFiles =
    new HashMap<String, String>();

  /** Generates a Key for a bundled file which will be cached in the Map.
   *
   * Implementation note: the key is generated by concatenating the list of
   * files separated by '|', calculating its MD5 hash, and concatenating a .js
   * suffix. The key is order dependent (no sorting is done to calculate the
   * key.)
   *
   * @param files The files used for generating the Key. These files are the
   * ones used for looking for the dependency files of bundled file.
   * Cannot be null nor empty.
   *
   * @return A unique key generated from the source files. Never return null.
   */
  private String generateKey(final List<String> files) {
    Validate.notEmpty(files, "There must be at least one file.");
    StringBuilder concatenatedFile = new StringBuilder();
    String generatedKey = null;
    for (int i = 0; i < files.size(); i++) {
      if (concatenatedFile.length() != 0) {
        concatenatedFile.append("|");
      }
      concatenatedFile.append(files.get(i));
    }
    MessageDigest messageDigest;
    try {
      messageDigest = MessageDigest.getInstance("MD5");
    } catch (NoSuchAlgorithmException e) {
      throw new RuntimeException("Unable to generate the MD5 hash.", e);
    }
    messageDigest.reset();
    String inputForHash = concatenatedFile.toString();
    messageDigest.update(inputForHash.getBytes(Charset.forName("UTF8")));
    byte[] resultBytes = messageDigest.digest();
    generatedKey = new String(Hex.encodeHex(resultBytes)) + ".js";
    return generatedKey;
  }

  /** Finds a {@link String} which represents the content of the Bundled File
   * for the given Key in the Map of Cached Files.
   *
   * @param key The key in the Map of Cached Files for the given files. Cannot
   * be null nor empty.
   * @return Gets a {@link String} which represents the content of the Cached
   * Bundled File for the given files. If there is no cached file in the map for
   * the given files then it returns null.
   */
  public String findContent(final String key) {
    Validate.notEmpty(key, "The Key cannot be null nor empty.");
    return bundledFiles.get(key);
  }

  /** Finds the key in Map that contains the cache of the bundled files.
   *
   * @param files The files used for generating the Key. These files are the
   * ones used for looking for the dependency files which were later on bundled.
   * Cannot be null nor empty.
   * @return The key in the Map of Cached Files for the given files. If there is
   * no cached file for them, then it returns null.
   */
  public String findKey(final List<String> files) {
    Validate.notEmpty(files, "There must be at least one file.");
    String generatedKey = generateKey(files);
    if (bundledFiles.containsKey(generatedKey)) {
      return generatedKey;
    }
    return null;
  }

  /** Stores a bundled file for the given files in the Map of Cached Files.
   *
   * @param files The files used for generating the Key. These files are the
   * ones used for looking for the dependency files which were later on bundled.
   * Cannot be null nor empty.
   * @param bundledContent A {@link String} which represents the of the Cached
   * Bundled. Cannot be empty.
   * File for the given files.
   * @return The {@link String} which represents the key of the newly stored
   * bundled file in the Map of Cached Files. It's never null.
   */
  public String store(final List<String> files, final String bundledContent) {
    Validate.notEmpty(files, "There must be at least one file.");
    Validate.notEmpty(bundledContent,
        "The bundled content cannot be null");
    String bundleKey = generateKey(files);
    bundledFiles.put(bundleKey, bundledContent);
    return bundleKey;
  }
}