Add method to install plugin from npm

Add tests for it

lib/plugins/registry.js

@@ -1,4 +1,10 @@
 var npm = require('npm');
+var npmi = require('npmi');
+var semver = require('semver');
+var _ = require('lodash');
+
+var Promise = require('../utils/promise');
+var gitbook = require('../gitbook');
 
 var PLUGIN_PREFIX = 'gitbook-plugin-';
 
@@ -18,14 +24,84 @@ function validateId(name) {
     return name.indexOf(PLUGIN_PREFIX) === 0;
 }
 
+// Initialize NPM for operations
+var initNPM = _.memoize(function() {
+    return Promise.nfcall(npm.load, {
+        silent: true,
+        loglevel: 'silent'
+    });
+});
+
 // Link a plugin for use in a specific book
 function linkPlugin(book, pluginPath) {
     book.log('linking', pluginPath);
 }
 
+// Resolve the latest version for a plugin
+function resolveVersion(plugin) {
+    var npnName = npmId(plugin);
+
+    return initNPM()
+    .then(function() {
+        return Promise.nfcall(npm.commands.view, [npnName+'@*', 'engines'], true);
+    })
+    .then(function(versions) {
+        return _.chain(versions)
+            .pairs()
+            .map(function(v) {
+                return {
+                    version: v[0],
+                    gitbook: (v[1].engines || {}).gitbook
+                };
+            })
+            .filter(function(v) {
+                return v.gitbook && gitbook.satisfies(v.gitbook);
+            })
+            .sort(function(v1, v2) {
+                return semver.lt(v1.version, v2.version)? 1 : -1;
+            })
+            .pluck('version')
+            .first()
+            .value();
+    });
+}
+
+
 // Install a plugin in a book
-function installPlugin(book, pluginId) {
-    book.log('installing plugin', pluginId);
+function installPlugin(book, plugin, version) {
+    book.log.info.ln('installing plugin', plugin);
+
+    var npnName = npmId(plugin);
+
+    return Promise()
+    .then(function() {
+        if (version) return version;
+
+        book.log.info.ln('No version specified, resolve plugin "' + plugin + '"');
+        return resolveVersion(plugin);
+    })
+
+    // Install the plugin with the resolved version
+    .then(function(version) {
+        if (!version) {
+            throw new Error('Found no satisfactory version for plugin "' + plugin + '"');
+        }
+
+        book.log.info.ln('install plugin' + plugin +'" from npm ('+npnName+') with version', version);
+        return Promise.nfcall(npmi, {
+            'name': npnName,
+            'version': version,
+            'path': book.root,
+            'npmLoad': {
+                'loglevel': 'silent',
+                'loaded': true,
+                'prefix': book.root
+            }
+        });
+    })
+    .then(function() {
+        book.log.info.ok('plugin "' + plugin.name + '" installed with success');
+    });
 }
 
 module.exports = {
@@ -33,6 +109,7 @@ module.exports = {
     pluginId: pluginId,
     validateId: validateId,
 
+    resolve: resolveVersion,
     link: linkPlugin,
     install: installPlugin
 };

test/all.js

@@ -10,6 +10,7 @@ require('./parse');
 require('./git');
 require('./template');
 require('./conrefs');
+require('./plugins');
 
 // Page and HTML generation
 require('./page');

test/plugins.js

@@ -0,0 +1,37 @@
+var mock = require('./mock');
+var registry = require('../lib/plugins/registry');
+
+describe('Plugins', function() {
+    var book;
+
+    before(function() {
+        return mock.setupBook({})
+        .then(function(_book) {
+            book = _book;
+        });
+    });
+
+    describe('Resolve Version', function() {
+
+        it('should resolve a plugin version', function() {
+            return registry.resolve('ga')
+            .should.be.fulfilled();
+        });
+
+    });
+
+    describe('Installation', function() {
+
+        it('should install a plugin from NPM without a specific version', function() {
+            return registry.install(book, 'ga')
+            .should.be.fulfilled();
+        });
+
+        it('should install a plugin from NPM with a specific version', function() {
+            return registry.install(book, 'ga', '1.0.0')
+            .should.be.fulfilled();
+        });
+
+    });
+});
+