/**
 * "Who is this for?" picker, shared by the lesson-booking and group-class
 * registration forms.
 *
 * The list arrives from the server already ordered children-first, with the
 * account holder last, and this module preserves that order: a guardian's
 * default selection is their first child, never themselves. Booking for the
 * wrong child is a correctable mistake; quietly enrolling the parent in a class
 * meant for their kid is not.
 */
(function () {
    'use strict';

    function escHtml(str) {
        return String(str)
            .replace(/&/g, '&')
            .replace(/</g, '&lt;')
            .replace(/>/g, '&gt;')
            .replace(/"/g, '&quot;');
    }

    /**
     * Read the server-rendered student list off a `data-students` attribute.
     * Anything unparseable degrades to an empty list, which renders no picker
     * and books for the signed-in user — the pre-guardian behaviour.
     */
    function parseStudents(raw) {
        if (!raw) return [];
        try {
            const list = JSON.parse(raw);
            return Array.isArray(list) ? list : [];
        } catch (e) {
            return [];
        }
    }

    /**
     * The picker's markup, or an empty string when there is nothing to choose:
     * an account with only itself on the list never sees the question.
     */
    function selectorHtml(students, id) {
        if (!students || students.length < 2) return '';

        const options = students.map((s) => {
            // The account holder reads as "Myself" — their own name next to their
            // children's is ambiguous about which row is the parent.
            const label = s.is_self ? `Myself (${s.name})` : s.name;
            return `<option value="${Number(s.id)}">${escHtml(label)}</option>`;
        }).join('');

        return `
            <p class="us-student-picker">
                <label for="${id}">Who is this for?<br>
                <select id="${id}" required>${options}</select></label>
            </p>`;
    }

    /**
     * The chosen student id, or 0 when no picker was rendered — the server
     * reads 0 as "the caller books for themselves".
     */
    function selectedId(id) {
        const el = document.getElementById(id);
        return el ? Number(el.value) || 0 : 0;
    }

    window.usGuardian = { parseStudents, selectorHtml, selectedId };
}());