Add option cover for ebook generation

lib/generate/ebook/index.js

@@ -4,7 +4,7 @@ var Q = require("q");
 var _ = require("lodash");
 var exec = require('child_process').exec;
 
-var fs = require("../fs");
+var fs = require("fs");
 var parse = require("../../parse");
 var BaseGenerator = require("../page");
 
@@ -19,6 +19,10 @@ var Generator = function() {
     this.options = _.defaults(this.options, {
         extension: "epub"
     });
+
+    if (!this.options.cover && fs.existsSync(path.join(this.options.input, "cover.png"))) {
+        this.options.cover = path.join(this.options.input, "cover.png")
+    }
 };
 util.inherits(Generator, BaseGenerator);
 
@@ -29,10 +33,22 @@ Generator.prototype.finish = function() {
     .then(function() {
         var d = Q.defer();
 
+        var _options = {
+            "--cover": that.options.cover
+        };
+
         var command = [
             "ebook-convert",
             path.join(that.options.output, "index.html"),
-            path.join(that.options.output, "index."+that.options.extension)
+            path.join(that.options.output, "index."+that.options.extension),
+            _.chain(_options)
+            .map(function(value, key) {
+                if (value == null) return null;
+                return key+"="+value;
+            })
+            .compact()
+            .value()
+            .join(" ")
         ].join(" ");
 
         exec(command, function (error, stdout, stderr) {