[Plugin] download plugin from github.

* e.g. if provided 'lintcode', install plugin from github.
* otherwise, if provided 'lintcode.js', install from local filesystem.

Signed-off-by: Eric Wang <skygragon@gmail.com>

Author: skygragon

lib/commands/plugin.js

@@ -1,13 +1,15 @@
 var fs = require('fs');
 var path = require('path');
 
+var request = require('request');
+
 var h = require('../helper');
 var log = require('../log');
 var Plugin = require('../plugin');
 var session = require('../session');
 
 var cmd = {
-  command: 'plugin [name]>',
+  command: 'plugin [name]',
   desc:    'show plugins',
   builder: {
     install: {
@@ -37,16 +39,35 @@ var cmd = {
   }
 };
 
-function install(name) {
+var URL_PLUGIN = 'https://github.com/skygragon/leetcode-cli-plugins/raw/master/plugins/$name.js';
+
+function install(src) {
+  // assume to be a raw plugin name if not js file.
+  if (path.extname(src) !== '.js') {
+    src = URL_PLUGIN.replace('$name', src);
+  }
+
   // copy to plugins folder
-  var newname = path.join(Plugin.dir, path.basename(name));
-  var src = fs.createReadStream(name);
-  src.pipe(fs.createWriteStream(newname));
-  src.on('end', function() {
-    log.debug('copied to ' + newname);
+  var dst = path.join(Plugin.dir, path.basename(src));
+  var dststream = fs.createWriteStream(dst);
+
+  log.debug('copying from ' + src);
+  var srcstream = src.startsWith('https://') ? request(src) : fs.createReadStream(src);
+  srcstream.on('response', function(resp) {
+    if (resp.statusCode !== 200)
+      srcstream.emit('error', 'HTTP Error: ' + resp.statusCode);
+  });
+  srcstream.on('error', function(e) {
+    log.error(e);
+    fs.unlinkSync(dst);
+  });
+
+  srcstream.pipe(dststream);
+  dststream.on('end', function() {
+    log.debug('copied to ' + dst);
 
     // install dependencies
-    var plugin = require(path.relative(__dirname, newname));
+    var plugin = require(path.relative(__dirname, dst));
     if (plugin.deps.length === 0) return;
 
     var cmd = 'npm install --save ' + plugin.deps.join(' ');
@@ -61,10 +82,8 @@ cmd.handler = function(argv) {
   session.argv = argv;
   var name = argv.name;
 
-  if (argv.install) {
-    if (!name || !fs.existsSync(name)) return log.error('Plugin not found!');
+  if (argv.install)
     return install(name);
-  }
 
   var plugins = Plugin.plugins;
   if (name) {