Voxel API exposer (Joachim Brindeau)

<?php
add_action('init', 'expose_voxel_cpts_to_rest_api', 99);
add_action('rest_api_init', 'register_custom_fields_in_rest_api', 15);

function expose_voxel_cpts_to_rest_api() {
    $voxel_post_types = json_decode(get_option('voxel:post_types'), true) ?: [];
    foreach ($voxel_post_types as $post_type => $post_type_data) {
        if (!in_array($post_type, ['post', 'page'])) {
            $obj = get_post_type_object($post_type);
            if ($obj) {
                $obj->show_in_rest = true;
                $obj->rest_base = $post_type;
                $obj->rest_controller_class = 'WP_REST_Posts_Controller';
            }
        }
    }
}

function register_custom_fields_in_rest_api() {
    $voxel_post_types = json_decode(get_option('voxel:post_types'), true) ?: [];
    foreach ($voxel_post_types as $post_type => $post_type_data) {
        if (isset($post_type_data['fields'])) {
            foreach ($post_type_data['fields'] as $field) {
                if (in_array($field['type'], ['ui-step', 'title'])) continue;

                register_rest_field($post_type, $field['key'], [
                    'get_callback' => function($post_arr) use ($field) {
                        return get_custom_field_value($post_arr['id'], $field);
                    },
                    'update_callback' => function($value, $post, $field_name) use ($field) {
                        return update_custom_field_value($post->ID, $field, $value);
                    },
                    'schema' => [
                        'description' => $field['label'],
                        'type'        => get_schema_type_for_field($field['type']),
                        'context'     => ['view', 'edit'],
                    ],
                ]);

                if ($field['type'] === 'post-relation') {
                    $relation_field_name = get_relation_field_name($field);
                    register_rest_field($post_type, $relation_field_name, [
                        'get_callback' => function($post_arr) use ($field) {
                            return get_post_relation_value($post_arr['id'], $field['key']);
                        },
                        'update_callback' => function($value, $post, $field_name) use ($field) {
                            return update_post_relation_value($post->ID, $field['key'], $value);
                        },
                        'schema' => [
                            'description' => $field['label'] . ' (FK)',
                            'type'        => 'array',
                            'items'       => ['type' => 'integer'],
                            'context'     => ['view', 'edit'],
                        ],
                    ]);
                }
            }
        }
    }
}

function get_relation_field_name($field) {
    $related_post_type = $field['post_types'][0] ?? 'post';
    $related_post_type = ($related_post_type === 'page') ? 'pages' : $related_post_type;
    $related_post_type = ($related_post_type === 'post') ? 'posts' : $related_post_type;
    return $field['key'] . '_fk_' . $related_post_type;
}

function get_custom_field_value($post_id, $field) {
    $value = get_post_meta($post_id, $field['key'], true);

    switch ($field['type']) {
        case 'repeater':
            $repeater_values = [];
            if (is_array($value)) {
                foreach ($value as $index => $repeater_item) {
                    $repeater_values[$index] = [];
                    foreach ($field['fields'] as $sub_field) {
                        $sub_key = $field['key'] . '_' . $index . '_' . $sub_field['key'];
                        $repeater_values[$index][$sub_field['key']] = get_post_meta($post_id, $sub_key, true);
                    }
                }
            }
            return $repeater_values;
        case 'post-relation':
            return null; // We'll handle this separately
        case 'image':
        case 'file':
            return (int) $value;
        case 'location':
            return maybe_unserialize($value);
        default:
            return $value;
    }
}

function update_custom_field_value($post_id, $field, $value) {
    switch ($field['type']) {
        case 'repeater':
            if (is_array($value)) {
                delete_post_meta($post_id, $field['key']);
                foreach ($value as $index => $repeater_item) {
                    foreach ($field['fields'] as $sub_field) {
                        if (isset($repeater_item[$sub_field['key']])) {
                            $sub_key = $field['key'] . '_' . $index . '_' . $sub_field['key'];
                            update_post_meta($post_id, $sub_key, $repeater_item[$sub_field['key']]);
                        }
                    }
                }
                update_post_meta($post_id, $field['key'], array_keys($value));
            }
            break;
        case 'post-relation':
            // We'll handle this separately
            break;
        case 'location':
            update_post_meta($post_id, $field['key'], maybe_serialize($value));
            break;
        default:
            update_post_meta($post_id, $field['key'], $value);
    }
    return true;
}

function get_schema_type_for_field($field_type) {
    switch ($field_type) {
        case 'number':
        case 'switcher':
            return 'number';
        case 'image':
        case 'file':
            return 'integer';
        case 'post-relation':
        case 'repeater':
            return 'array';
        case 'select':
            return ['string', 'array'];
        case 'location':
            return 'object';
        default:
            return 'string';
    }
}

function get_post_relation_value($post_id, $relation_key) {
    global $wpdb;
    $child_ids = $wpdb->get_col($wpdb->prepare(
        "SELECT child_id FROM {$wpdb->prefix}voxel_relations WHERE parent_id = %d AND relation_key = %s",
        $post_id,
        $relation_key
    ));
    return array_map('intval', $child_ids);
}

function update_post_relation_value($post_id, $relation_key, $child_ids) {
    global $wpdb;
    $wpdb->delete("{$wpdb->prefix}voxel_relations", [
        'parent_id' => $post_id,
        'relation_key' => $relation_key,
    ]);
    if (is_array($child_ids)) {
        foreach ($child_ids as $child_id) {
            $wpdb->insert("{$wpdb->prefix}voxel_relations", [
                'parent_id' => $post_id,
                'child_id' => (int) $child_id,
                'relation_key' => $relation_key,
            ]);
        }
    }
    return true;
}