<?php
// Pure index builder. Must produce the same index and cards as assets/engine.js buildIndex (tests/parity.php checks it).
defined( 'ABSPATH' ) || exit;

const SPOTFIND_CHUNK = 64;

function spotfind_fold( string $s ): string {
	$s = html_entity_decode( $s, ENT_QUOTES | ENT_HTML5, 'UTF-8' );
	$s = mb_strtolower( $s ); // lowercase first: NFKD then turns "™" into upper-case "TM", which the a-z split drops
	if ( class_exists( 'Normalizer' ) ) { // NFKD turns ligatures like "ﬁ" into "fi", same as the JS side
		return preg_replace( '/\p{Mn}/u', '', Normalizer::normalize( $s, Normalizer::FORM_KD ) ?: $s );
	}
	return function_exists( 'remove_accents' ) ? remove_accents( $s ) : $s;
}

// Joined neighbours ("a7 iv" -> "a7iv") only when both pieces are model-number sized.
function spotfind_tokens( string $text ): array {
	$t   = preg_split( '/[^a-z0-9]+/', spotfind_fold( $text ), -1, PREG_SPLIT_NO_EMPTY );
	$out = $t;
	for ( $i = 0, $n = count( $t ) - 1; $i < $n; $i++ ) {
		if ( strlen( $t[ $i ] ) <= 3 && strlen( $t[ $i + 1 ] ) <= 3 ) {
			$out[] = $t[ $i ] . $t[ $i + 1 ];
		}
	}
	return $out;
}

// Groups of single words -> term => other words of its groups. Multi-word or non a-z0-9 entries are ignored.
function spotfind_synonym_map( array $groups ): array {
	$map = array();
	foreach ( $groups as $g ) {
		$w = array_values( array_unique( array_filter( array_map( static fn( $s ) => strtolower( trim( (string) $s ) ), $g ), static fn( $s ) => preg_match( '/^[a-z0-9]+$/', $s ) ) ) );
		foreach ( $w as $t ) {
			$map[ 'k' . $t ] = array_merge( $map[ 'k' . $t ] ?? array(), array_values( array_diff( $w, array( $t ) ) ) );
		}
	}
	return $map;
}

/**
 * @param array[] $products each: id, n (name), p (price), img, u (url), s (in stock), b[] brands, c[] categories, sku, sales
 * @param array[] $synonyms groups of words, e.g. [["tv","television"]]
 * @param array[] $terms    category and brand rows: ["c"|"b", name, url, count]
 * @return array{index: array, cards: array[]}
 * Products are stored most popular first (sales desc, then input order). Posting value = doc * 8 + field, ascending per term,
 * delta coded. Fields: 0 name, 1 brand, 2 category, 3 sku, 4 name after "for/fits/compatible".
 */
function spotfind_build( array $products, array $synonyms = array(), array $terms = array() ): array {
	$syn = spotfind_synonym_map( $synonyms );
	foreach ( array_values( $products ) as $i => $p ) {
		$products[ $i ]['_i'] = $i;
	}
	$products = array_values( $products );
	usort( $products, static fn( $a, $b ) => ( ( $b['sales'] ?? 0 ) <=> ( $a['sales'] ?? 0 ) ) ?: ( $a['_i'] <=> $b['_i'] ) ); // explicit tie-break: usort is not stable before PHP 8
	$post  = array();
	$cards = array();
	$ids   = array();
	$stock = '';
	foreach ( $products as $i => $p ) {
		$name = html_entity_decode( $p['n'], ENT_QUOTES | ENT_HTML5, 'UTF-8' );
		$m    = array();
		$has  = (bool) preg_match( '/^(.*?)\s+(?:for|fits|compatible)\s+(.*)$/isu', $name, $m ); // /u: \s must match a non-breaking space like JS does
		$list = array(
			array( 0, $has ? $m[1] : $name ),
			array( 1, implode( ' ', $p['b'] ?? array() ) ),
			array( 2, implode( ' ', $p['c'] ?? array() ) ),
			array( 3, $p['sku'] ?? '' ),
		);
		if ( $has ) {
			$list[] = array( 4, $m[2] );
		}
		foreach ( $list as list( $f, $txt ) ) {
			$t = spotfind_tokens( $txt );
			foreach ( $t as $w ) {
				array_push( $t, ...( $syn[ 'k' . $w ] ?? array() ) );
			}
			foreach ( array_unique( $t ) as $x ) {
				$post[ 'k' . $x ][] = $i * 8 + $f; // prefix: PHP turns numeric string keys into ints
			}
		}
		$ids[]                                    = $p['id'];
		$stock                                   .= empty( $p['s'] ) ? '0' : '1';
		$reg                                      = (float) ( $p['r'] ?? 0 );
		$cards[ intdiv( $i, SPOTFIND_CHUNK ) ][] = array( $name, $p['p'], $p['img'] ?? '', $p['u'], $reg > (float) $p['p'] ? $reg : 0 ); // 5th: regular price, only when on sale
	}
	ksort( $post, SORT_STRING );
	$delta = static function ( array $a ): array {
		$out = array();
		foreach ( $a as $i => $x ) {
			$out[] = $i ? $x - $a[ $i - 1 ] : $x;
		}
		return $out;
	};
	return array(
		'index' => array(
			'v'     => 3,
			'n'     => count( $products ),
			'pop'   => array_filter( array_column( $products, 'sales' ), static fn( $s ) => $s > 0 ) ? 1 : 0,
			'ids'   => $ids,
			's'     => $stock,
			't'     => $terms,
			'vocab' => array_map( static fn( $k ) => substr( $k, 1 ), array_keys( $post ) ),
			'post'  => array_map( $delta, array_values( $post ) ),
		),
		'cards' => array_values( $cards ),
	);
}