Add export functionality to generate Excel file

This commit adds a new file, `export/excel.php`, which contains code to export data from the Moodle database to a CSV file. The exported file can be downloaded as an Excel file. The code uses Respect\Validation library for input validation and PDO for database queries. The exported data includes information about users and their grades in courses.

export/excel.php

@@ -0,0 +1,36 @@
+<?php
+require_once "{$_SERVER['DOCUMENT_ROOT']}/dependencies.php";
+
+// Exportar a archivo separado por comas
+// Must receive from POST associative array with keys and values
+use Respect\Validation\Validator as v;
+
+$query = json_decode(file_get_contents('php://input'), true);
+$queries = array(
+    'usuarios' => "SELECT * FROM mdl_user",
+    'calificaciones' => "SELECT  c.id AS courseid, c.shortname, COALESCE(cc2.name, cc.name) AS AREA, CASE WHEN cc2.name IS NULL THEN NULL ELSE cc.name END AS GRUPO, prof.username AS profesor_clave, CONCAT(prof.firstname, ' ', prof.lastname) AS profesor_nombre, c.fullname AS course_fullname, CASE WHEN COALESCE(MIN(mgi.calculation) <> '', false) THEN 'Sí' ELSE 'No' END AS formula, CASE WHEN MAX(mgi.AGGREGATIONCOEF) > 0  THEN 'Sí' ELSE 'No' END AS ponderacion FROM mdl_course c JOIN mdl_grade_items mgi ON c.id = mgi.courseid JOIN mdl_course_categories cc ON cc.id = c.category LEFT JOIN mdl_course_categories cc2 ON cc.parent = cc2.id JOIN mdl_context ctx ON ctx.instanceid = c.id JOIN mdl_role_assignments ra ON ra.contextid = ctx.id AND ra.roleid = 3 JOIN mdl_user prof ON ra.userid = prof.id WHERE mgi.itemtype IN ('course', 'category') GROUP BY c.id, c.shortname, cc.name, cc2.name, c.fullname, prof.firstname, prof.lastname, prof.username ORDER BY AREA, GRUPO, profesor_nombre;",
+);
+
+methods(['POST' => v::keySet(
+    v::key('query', v::in(array_keys($queries))),
+)]);
+
+// method must be POST
+if (!isset($_SESSION['user'], $moodle_db)) {
+    serverError(title: 'Error de conexión', message: 'No se ha iniciado sesión o no se ha establecido una conexión con la base de datos de Moodle');
+    exit();
+}
+$data = $moodle_db->query($queries[$query['query']]);
+$filename = 'test.csv';
+
+header('Content-Type: text/csv; charset=ANSI');
+header("Content-Disposition: attachment; filename=$filename");
+$fp = fopen('php://output', 'wb');
+// insert header
+fputcsv($fp, array_keys($data[0]));
+// insert data
+foreach ($data as $line) {
+    fputcsv($fp, $line);
+}
+fclose($fp);
+exit();