my_add_product_structured_data.php

<?php
// OPTIONAL: disable WooCommerce's built-in product schema to avoid duplicates
// add_filter('woocommerce_structured_data_product', '__return_false', 9999);

add_action('wp_head', 'my_add_product_structured_data', 99);
function my_add_product_structured_data() {
    if ( ! is_product() ) {
        return;
    }

    // Always resolve the product explicitly (wp_head runs early)
    $product_id = get_queried_object_id();
    if ( ! $product_id ) {
        return;
    }
    $product = wc_get_product( $product_id );
    if ( ! $product ) {
        return;
    }

    // Basic fields
    $name        = $product->get_name();
    $desc        = wp_strip_all_tags( $product->get_description() ?: $product->get_short_description() );
    $permalink   = get_permalink( $product->get_id() );
    $currency    = get_woocommerce_currency();
    $in_stock    = $product->is_in_stock();
    $sku         = $product->get_sku();

    // Images: primary + a few gallery images
    $images = [];
    $main_img = wp_get_attachment_image_url( $product->get_image_id(), 'full' );
    if ( $main_img ) {
        $images[] = $main_img;
    }
    foreach ( array_slice( (array) $product->get_gallery_image_ids(), 0, 4 ) as $att_id ) {
        $url = wp_get_attachment_image_url( $att_id, 'full' );
        if ( $url ) {
            $images[] = $url;
        }
    }
    // Fallback placeholder if truly no images
    if ( empty( $images ) ) {
        $placeholder = wc_placeholder_img_src( 'full' );
        if ( $placeholder ) {
            $images[] = $placeholder;
        }
    }

    // Brand (custom meta) — adjust meta keys to your store
    $brand = get_post_meta( $product->get_id(), '_product_brand', true );
    $brand_schema = $brand ? [ '@type' => 'Brand', 'name' => $brand ] : null;

    // GTIN (custom meta) — support common keys
    $gtin = get_post_meta( $product->get_id(), '_product_gtin', true );
    if ( ! $gtin ) {
        $gtin = get_post_meta( $product->get_id(), '_wc_gpf_gtin', true ); // example alt key
    }

    // Optional: set a price validity (e.g., 30 days from today) for better completeness
    $price_valid_until = gmdate( 'Y-m-d', strtotime( '+30 days' ) );

    // Build offers
    $offers = null;
    if ( $product->is_type( 'variable' ) ) {
        $children     = $product->get_children();
        $variations   = [];
        $prices       = [];

        foreach ( $children as $variation_id ) {
            $v = wc_get_product( $variation_id );
            if ( ! $v ) {
                continue;
            }
            $price = $v->get_price();
            if ( $price === '' ) {
                continue;
            }

            $prices[] = (float) $price;

            $variations[] = [
                '@type'           => 'Offer',
                'url'             => get_permalink( $variation_id ),
                'sku'             => $v->get_sku() ?: null,
                'priceCurrency'   => $currency,
                'price'           => wc_format_decimal( $price, wc_get_price_decimals() ),
                'availability'    => $v->is_in_stock() ? 'https://schema.org/InStock' : 'https://schema.org/OutOfStock',
                'itemCondition'   => 'https://schema.org/NewCondition',
                'priceValidUntil' => $price_valid_until,
            ];
        }

        $prices = array_filter( $prices, 'is_numeric' );
        if ( ! empty( $prices ) ) {
            $offers = [
                '@type'         => 'AggregateOffer',
                'priceCurrency' => $currency,
                'lowPrice'      => wc_format_decimal( min( $prices ), wc_get_price_decimals() ),
                'highPrice'     => wc_format_decimal( max( $prices ), wc_get_price_decimals() ),
                'offerCount'    => count( $variations ),
                'offers'        => $variations,
            ];
        }
    } else {
        // Simple/grouped/external – single offer
        $price = $product->get_price();
        if ( $price !== '' ) {
            $offers = [
                '@type'           => 'Offer',
                'url'             => $permalink,
                'priceCurrency'   => $currency,
                'price'           => wc_format_decimal( $price, wc_get_price_decimals() ),
                'availability'    => $in_stock ? 'https://schema.org/InStock' : 'https://schema.org/OutOfStock',
                'itemCondition'   => 'https://schema.org/NewCondition',
                'priceValidUntil' => $price_valid_until,
            ];
        }
    }

    // Aggregate rating
    $rating_count = (int) $product->get_rating_count();
    $aggregate_rating = null;
    if ( $rating_count > 0 ) {
        $aggregate_rating = [
            '@type'       => 'AggregateRating',
            'ratingValue' => (string) $product->get_average_rating(),
            'reviewCount' => $rating_count,
        ];
    }

    // Compose schema
    $schema = [
        '@context'    => 'https://schema.org',
        '@type'       => 'Product',
        '@id'         => trailingslashit( $permalink ) . '#product',
        'name'        => $name,
        'description' => $desc,
        'image'       => array_values( array_unique( $images ) ),
        'sku'         => $sku ?: null,
        'brand'       => $brand_schema,
        'offers'      => $offers,
        'aggregateRating' => $aggregate_rating,
        'itemCondition'   => 'https://schema.org/NewCondition', // also valid at Product level
    ];

    // GTIN: choose the most appropriate property (gtin13 here)
    if ( $gtin ) {
        $schema['gtin13'] = (string) $gtin;
    }

    // Clean nulls
    $schema = array_filter( $schema, function( $v ) { return ! is_null( $v ); } );

    echo '<script type="application/ld+json">' . esc_html( wp_json_encode( $schema, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE ) ) . '</script>' . "\n";
}