<?php
/** api#326: внешняя граница UTM; semantic-контекст шаблонов остаётся прежним. */
declare(strict_types=1);

function prelandUtmEnums(): array
{
    return ['theme'=>['1'=>'dark','2'=>'light'], 'reg'=>['1'=>'before','2'=>'after'], 'banch'=>['1'=>'b','2'=>'a'], 'focus'=>['1'=>'face','2'=>'center']];
}

/** Совместимость host-config при доставке кода до точечной миграции. */
function prelandNumericUtmConfig(array $config): array
{
    $settings = is_array($config['utm'] ?? null) ? $config['utm'] : [];
    foreach (['registration'=>'reg','chob'=>'banch','bchoice'=>'banch'] as $old=>$new) {
        if (!isset($settings[$new]) && isset($settings[$old])) $settings[$new] = $settings[$old];
        unset($settings[$old]);
    }
    unset($settings['chb']);
    foreach (prelandUtmEnums() as $key=>$map) {
        if (!is_array($settings[$key] ?? null)) continue;
        $weights=[];
        foreach ((array)($settings[$key]['weights'] ?? []) as $variant=>$weight) {
            $digit=array_search((string)$variant,$map,true);
            $weights[$digit === false ? $variant : $digit]=$weight;
        }
        $settings[$key]['weights']=$weights;
        $default=$settings[$key]['default'] ?? null;
        $digit=array_search($default,$map,true);
        if ($digit !== false) $settings[$key]['default']=(string)$digit;
    }
    $config['utm']=$settings;
    return $config;
}

/** Выбирает random один раз, до рендера/сохранения загрузки. */
function prelandResolveUtm(array $query, array $config): array
{
    $config=prelandNumericUtmConfig($config);
    $defaults=['indpic'=>'1','theme'=>'2','degr'=>'1','reg'=>'2','banch'=>'2','tp'=>'1','cons'=>'2','focus'=>'1'];
    $enums=prelandUtmEnums(); $digits=[]; $context=$query;
    foreach (['registration','bchoice','chob','chb'] as $old) unset($context[$old]);
    foreach ($defaults as $key=>$fallback) {
        unset($context[$key]);
        $settings=$config['utm'][$key] ?? [];
        $valid=static fn($digit): bool => preg_match('/^[1-9]$/D',(string)$digit)===1
            && (!isset($enums[$key]) || isset($enums[$key][$digit]))
            && (in_array($key,['cons','theme','reg','banch','focus'],true) || isset($settings['weights'][$digit]));
        $default=(string)($settings['default'] ?? $fallback);
        if (!$valid($default)) $default=$fallback;
        $value=$query[$key] ?? null;
        $digit=is_string($value) && preg_match('/\A.{4}([0-9])/us',$value,$match) ? $match[1] : null;
        if ($digit==='0') {
            // Generic resolver исторически выбирает первый ключ при sum<=0;
            // cons имеет отдельный контракт: только положительные веса и default.
            if ($key !== 'cons') {
                $weights=(array)($settings['weights'] ?? []);
                $total=array_sum($weights);
                $digit=$weights ? (string)array_key_first($weights) : $default;
                if ($total>0 && is_finite((float)$total)) {
                    $point=mt_rand()/mt_getrandmax()*$total; $current=0.0;
                    foreach ($weights as $variant=>$weight) {
                        $current+=(float)$weight;
                        $digit=(string)$variant;
                        if ($point<=$current) break;
                    }
                }
            } else {
                $weights=[];
                foreach ((array)($settings['weights'] ?? []) as $variant=>$weight) {
                    if ($valid($variant) && is_numeric($weight) && is_finite((float)$weight) && (float)$weight>0) $weights[$variant]=(float)$weight;
                }
                $total=array_sum($weights); $digit=$default;
                if ($total>0 && is_finite($total)) {
                    $point=mt_rand()/(mt_getrandmax()+1.0)*$total;
                    foreach ($weights as $variant=>$weight) {
                        if ($point<$weight) { $digit=(string)$variant; break; }
                        $point-=$weight;
                    }
                }
            }
        }
        if (!$valid($digit ?? '')) $digit=$default;
        $digits[$key]=$digit;
        $internal=['reg'=>'registration','banch'=>'bchoice'][$key] ?? $key;
        $context[$internal]=$enums[$key][$digit] ?? $digit;
    }
    return ['digits'=>$digits,'context'=>$context];
}