added Json parsing abstraction

src/Composer/Json/JsonFile.php

@@ -0,0 +1,93 @@
+<?php
+
+/*
+ * This file is part of Composer.
+ *
+ * (c) Nils Adermann <naderman@naderman.de>
+ *     Jordi Boggiano <j.boggiano@seld.be>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Composer\Json;
+
+use Composer\Repository\RepositoryManager;
+
+/**
+ * Reads/writes json files.
+ *
+ * @author Konstantin Kudryashiv <ever.zet@gmail.com>
+ */
+class JsonFile
+{
+    private $path;
+
+    /**
+     * Initializes json file reader/parser.
+     *
+     * @param   string  $lockFile   path to a lockfile
+     */
+    public function __construct($path)
+    {
+        $this->path = $path;
+    }
+
+    /**
+     * Checks whether json file exists.
+     *
+     * @return  Boolean
+     */
+    public function exists()
+    {
+        return is_file($this->path);
+    }
+
+    /**
+     * Reads json file.
+     *
+     * @param   string  $json   path or json string
+     *
+     * @return  array
+     */
+    public function read()
+    {
+        $json   = file_get_contents($this->path);
+        $config = json_decode($json, true);
+        if (!$config) {
+            switch (json_last_error()) {
+            case JSON_ERROR_NONE:
+                $msg = 'No error has occurred, is your composer.json file empty?';
+                break;
+            case JSON_ERROR_DEPTH:
+                $msg = 'The maximum stack depth has been exceeded';
+                break;
+            case JSON_ERROR_STATE_MISMATCH:
+                $msg = 'Invalid or malformed JSON';
+                break;
+            case JSON_ERROR_CTRL_CHAR:
+                $msg = 'Control character error, possibly incorrectly encoded';
+                break;
+            case JSON_ERROR_SYNTAX:
+                $msg = 'Syntax error';
+                break;
+            case JSON_ERROR_UTF8:
+                $msg = 'Malformed UTF-8 characters, possibly incorrectly encoded';
+                break;
+            }
+            throw new \UnexpectedValueException('Incorrect composer.json file: '.$msg);
+        }
+
+        return $config;
+    }
+
+    /**
+     * Writes json file.
+     *
+     * @param   array   $hash   writes hash into json file
+     */
+    public function write(array $hash)
+    {
+        file_put_contents($this->path, json_encode($hash));
+    }
+}