bower/lib/util/prune.js

// ==========================================
// BOWER: PRUNE
// ==========================================
// Copyright 2012 Twitter, Inc
// Licensed under The MIT License
// http://opensource.org/licenses/MIT
// ==========================================

var semver = require('semver');
var sort   = require('stable');

var versionRequirements = function (dependencyMap) {
  var result = {};

  for (var name in dependencyMap) {
    dependencyMap[name].forEach(function (pkg) {
      result[name] = result[name] || [];
      if (pkg.originalTag && result[name].indexOf(pkg.originalTag) === -1) {
        result[name].push(pkg.originalTag);
      }
    });
  }

  return result;
};

var validVersions = function (versions, dependency) {
  if (!versions || !versions.length) return true;

  // If a non resolved dependency is passed, we simply ignore it
  if (!dependency.version) return false;

  if (!semver.valid(dependency.version)) {
    throw new Error('Invalid semver version ' + dependency.version + ' specified in ' + dependency.name);
  }

  return versions.every(function (version) {
    return semver.satisfies(dependency.version, version);
  });
};

module.exports = function (dependencyMap) {
  // generate version requirements
  // compare dependency map with version requirements
  // raise exceptions when requirements are not satisified
  // remove duplicates
  // select best version
  // return a pruned dependencyMap

  var result     = {};
  var versionMap = versionRequirements(dependencyMap);

  for (var name in dependencyMap) {
    var matches = dependencyMap[name].filter(validVersions.bind(this, versionMap[name]));
    // Sort the packages using a stable sort algorithm
    // This is because if two packages are equal, the initial order should be respected
    dependencyMap[name] = sort(matches, function (a, b) {
      if (semver.gt(a.version, b.version)) return -1;
      if (semver.lt(a.version, b.version)) return 1;

      // If the comparison determines that both packages are equal, do not give priority to local ones
      if (a.path === a.localPath && b.path !== b.localPath) return 1;
      return 0;
    });

    if (!dependencyMap[name].length) {
      throw new Error('No resolvable dependency for: ' + name);
    }

    result[name] = [ dependencyMap[name][0] ];
  }

  return result;
};