Move DATA to autoloading class

`DATA` was previously only used within `data.php` to create the `$DATA`
object. This is now done in `init.php`, and the new `Data` class is
autoloaded.

classes/Data.php

@@ -0,0 +1,219 @@
+<?php
+
+namespace MySociety\TheyWorkForYou;
+
+/**
+ * Data Class
+ *
+ * Includes a metadata file that contains the actual data. It will have an array like:
+ *
+ * ```php
+ * $this->page = array (
+ *     "default" => array (
+ *         "sitetitle"    => "Haddock Directory",
+ *         "session_vars" => array()
+ *     ),
+ *     "previous" => array (
+ *         "title"   => "Previous links",
+ *         "url"     => "previouslinks/",
+ *         "section" => "blah"
+ *     )
+ *     etc...
+ * );
+ * ```
+ *
+ * And a $this->section array, although this is as yet unspecified. Something like:
+ *
+ * ```php
+ * $this->section = array (
+ *     "blah" => array (
+ *         "title" => "Blah",
+ *         "menu"  => array (
+ *             "text"  => "Blah",
+ *             "title" => "Here's a link to Blah"
+ *         )
+ *     )
+ * );
+ * ```
+ *
+ * At some points we have a function where $type is passed in as, say, "page"
+ * and then we do:
+ *
+ * ```php
+ * $dataarray =& $this->$type;
+ * return $dataarray[$item][$key];
+ * ```
+ *
+ * Why? Because doing `$this->$type[$item][$key]` doesn't seem to work and
+ * we need to use the reference to get it working.
+ *
+ * @author Phil Gyford <phil@gyford.com>
+ */
+
+class Data {
+
+    public function __construct() {
+
+        include_once METADATAPATH; // defined in config.php
+
+    }
+
+    /**
+     * Set $this_section depending on this page's section.
+     *
+     * Special function for setting $this_section depending on the value of $this_page.
+     */
+
+    public function set_section() {
+        // This should be called at the start of a page.
+        global $this_section, $this_page;
+
+        $this_section = $this->page_metadata($this_page, "section");
+    }
+
+    /**
+     * Get page metadata
+     *
+     * @param string $page Page name
+     * @param string $key  The element of metadata you want to retrieve
+     */
+
+    public function page_metadata($page, $key) {
+        return $this->getMetadata(
+            array(
+                'page' => $page,
+                'key'  => $key
+            ),
+            'page'
+        );
+    }
+
+    /**
+     * Get section metadata
+     *
+     * @param string $section Section name
+     * @param string $key     The element of metadata you want to retrieve
+     */
+
+    public function section_metadata($section, $key) {
+        return $this->getMetadata(
+            array(
+                'section' => $section,
+                'key'     => $key
+            ),
+            'section'
+        );
+    }
+
+    /**
+     * Set page metadata
+     *
+     * @param $page  Page name
+     * @param $key   The element of metadata you want to set
+     * @param $value The value to set
+     */
+
+    public function set_page_metadata($page, $key, $value) {
+        $this->setMetadata(array("page"=>$page, "key"=>$key, "value"=>$value));
+    }
+
+    /**
+     * Set section metadata
+     *
+     * @param $section Section name
+     * @param $key     The element of metadata you want to set
+     * @param $value   The value to set
+     */
+
+    public function set_section_metadata($section, $key, $value) {
+        $this->setMetadata(array("section"=>$section, "key"=>$key, "value"=>$value));
+    }
+
+    /**
+     * Directly access an item.
+     *
+     * @deprecated
+     */
+
+    public function metadata($type, $item, $key) {
+        if ($this->test_for_metadata($type, $item, $key)) {
+            return $this->$type[$item][$key];
+        } else {
+            return "INVALID METADATA: $type[$item][$key]";
+        }
+    }
+
+    /**
+     * Test for the presence of something
+     *
+     * eg $exists = $DATA->test_for_metadata("page", "about", "title")
+     */
+
+    public function test_for_metadata($type, $item, $key) {
+        $dataarray = & $this->$type;
+
+        if (isset($dataarray[$item][$key])) {
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    /**
+     * @param string $type
+     */
+
+    private function getMetadata($args = "", $type) {
+        // $type is either 'page' or 'section'
+        global $this_page, $this_section;
+
+        if (is_array($args)) {
+            $item = $args[$type];
+            $key = $args['key'];
+        } else {
+            $var = "this_" . $type;
+            $item = $$var; // $this_page or $this_section.
+            $key = $args;
+        }
+
+        twfy_debug("DATA", "$type: $item, $key");
+        $dataarray = & $this->$type;
+
+        if ($this->test_for_metadata($type, $item, $key)) {
+            $return = $dataarray[$item][$key];
+            $debugtext = "Key: " . $type . "[" . $item . "][" . $key . "]";
+
+        } elseif ($this->test_for_metadata($type, "default", $key)) {
+            $return = $dataarray["default"][$key];
+            $debugtext = "Key: " . $type . "['default'][" . $key . "]";
+
+        } else {
+            $return = false;
+            $debugtext = "No metadata found for key '$key'";
+        }
+
+        twfy_debug("DATA", "$debugtext, returning '" . (is_scalar($return) ? $return : gettype($return)) . "'.");
+
+        return $return;
+    }
+
+    private function setMetadata($args) {
+
+        if (isset($args["section"])) {
+            $type = "section";
+            $item = $args["section"];
+        } else {
+            $type = "page";
+            $item = $args["page"];
+        }
+
+        $key = $args["key"];
+        $value = $args["value"];
+
+        twfy_debug("DATA", "Setting: " . $type . "[" . $item . "][" . $key . "] = '" . print_r($value, 1) . "'");
+
+        $dataarray = & $this->$type;
+        $dataarray[$item][$key] = $value;
+    }
+
+}