<?php
declare(strict_types=1);

/*
 * SERUBI cashback engine, server side. Line-by-line port of assets/js/engine.js
 * (sheet "COB" and "CALCULATOR CASHBACK SERUBI" of the reference workbook), so
 * the public calculator gets results without receiving the bank's internal
 * parameters. Both engines are validated against tests/excel-fixtures.json.
 */

const ENGINE_PRODUCTS = ['giro' => 'Giro Umum', 'simanja' => 'Tabungan SIMANJA', 'simpeda' => 'Tabungan SIMPEDA'];

/** Excel ROUNDDOWN(x, 0) on 15 significant digits (same as Number(x.toPrecision(15)) in JS). */
function engine_rounddown(float $x): float
{
    $v = (float)sprintf('%.14e', $x);
    return $v < 0 ? ceil($v) : floor($v);
}

/** Tiers [{max: float|null, rate}], ascending; first tier with n <= max wins, null max = "di atas". */
function engine_tier_rate(?array $tiers, float $n): float
{
    foreach ($tiers ?? [] as $t) {
        if (!isset($t['max']) || $n <= $t['max']) {
            return (float)($t['rate'] ?? 0);
        }
    }
    return 0.0;
}

/** Cashback sharing [{min, nasabah}]: highest min that n reaches wins (COB!I34:I35). */
function engine_share(array $params, float $n, int $tenor): array
{
    if (!in_array($tenor, $params['cashbackTenors'] ?? [], true)) {
        return ['share' => null, 'reason' => 'tenor'];
    }
    $tiers = $params['cashbackTiers'] ?? [];
    usort($tiers, fn($a, $b) => $b['min'] <=> $a['min']);
    foreach ($tiers as $t) {
        if ($n >= $t['min']) {
            return ['share' => (float)$t['nasabah'], 'reason' => null];
        }
    }
    return ['share' => null, 'reason' => 'nominal'];
}

function engine_min_cashback_nominal(array $params): float
{
    $mins = array_column($params['cashbackTiers'] ?? [], 'min');
    return $mins ? (float)min($mins) : 0.0;
}

function engine_deposito_rate(array $params, float $n, int $tenor): float
{
    if ($n < $params['settings']['deposito_min']) {   // COB!K14: F4<1000000 -> 0
        return 0.0;
    }
    return engine_tier_rate($params['depositoRates'][$tenor] ?? null, $n);
}

function engine_calculate(array $params, float $nominal, int $tenor, string $customerType): array
{
    $p = $params['settings'];
    $n = max(0.0, $nominal);
    $t = $tenor;
    $customerType = $customerType === 'badan' ? 'badan' : 'perorangan';
    $year = $p['hari_setahun'];
    $month = $p['hari_sebulan'];

    // Pengelolaan dana (COB!F23:F38)
    $gwm = $n * $p['gwm'];
    $kas = $n * $p['kas'];
    $managed = $n - ($gwm + $kas);
    $puabBase = $managed * $p['porsi_puab'];
    $puabIncome = $puabBase * $p['puab'] * ($month / $year) * $t;
    $creditBase = $managed * $p['porsi_kredit'];
    $creditIncome = $creditBase * $p['kredit'] * ($t / 12);
    $income = $puabIncome + $creditIncome;

    $sh = engine_share($params, $n, $t);
    $eligible = $sh['share'] !== null;
    $share = $eligible ? $sh['share'] : 0.0;

    // Biaya & spread per produk (COB!H22:R37)
    $lps = min($n, $p['lps_batas']) * $p['premi_lps'];
    $ohc = $puabIncome * $p['ohc'];
    $products = [];
    foreach (ENGINE_PRODUCTS as $key => $name) {
        $rate = engine_tier_rate($params['productRates'][$key] ?? null, $n);
        $bunga = engine_rounddown((($n * $rate * $month) / $year) * $t);
        $program = $key === 'simanja' ? $p['biaya_program'] : 0.0;
        $cost = $bunga + $program + $ohc + $lps;
        $spread = $income - $cost;
        $bungaTax = $bunga * $p['pajak_tabungan'];
        $products[$key] = [
            'key' => $key, 'name' => $name, 'rate' => $rate,
            'bungaGross' => $bunga, 'bungaTax' => $bungaTax, 'bungaNet' => $bunga - $bungaTax,
            'program' => $program, 'ohc' => $ohc, 'lps' => $lps, 'cost' => $cost, 'spread' => $spread,
            'cashbackGross' => $spread * $share,
            'costOfFund' => $managed > 0 ? ($cost + $spread * $share) / $managed : 0.0,
        ];
    }

    // Cashback = rata-rata 3 produk (COB!H7:H10)
    $gross = $eligible ? ($products['giro']['cashbackGross'] + $products['simanja']['cashbackGross'] + $products['simpeda']['cashbackGross']) / 3 : 0.0;
    $negative = $gross < 0;
    if ($negative) {
        $gross = 0.0;
    }
    $taxRate = $customerType === 'badan' ? $p['pajak_cashback_badan'] : $p['pajak_cashback_perorangan'];
    $tax = $gross * $taxRate;
    $net = $gross - $tax;
    $equiv = $n > 0 && $t > 0 ? ($net / $n) * ($year / ($month * $t)) : 0.0;

    // Deposito pembanding (COB!K14:L17)
    $dRate = engine_deposito_rate($params, $n, $t);
    $dGross = engine_rounddown((($n * $dRate * $month) / $year) * $t);
    $dTax = $dGross * $p['pajak_deposito'];
    $dNet = $dGross - $dTax;
    $deposito = ['rate' => $dRate, 'gross' => $dGross, 'tax' => $dTax, 'net' => $dNet, 'monthly' => $t ? $dNet / $t : 0.0];

    // Perbandingan (CALC!A10:F13)
    $comparison = [];
    foreach (ENGINE_PRODUCTS as $key => $name) {
        $pr = $products[$key];
        $total = $pr['bungaNet'] + $net;
        $comparison[] = [
            'key' => $key, 'name' => $name, 'rate' => $pr['rate'], 'bungaNet' => $pr['bungaNet'],
            'cashbackNet' => $net, 'total' => $total, 'totalRate' => $pr['rate'] + $equiv, 'diff' => $total - $dNet,
        ];
    }
    $best = array_reduce($comparison, fn($a, $b) => $a === null || $b['total'] > $a['total'] ? $b : $a);

    // Pinalti pencairan sebelum jatuh tempo (CALC!A17:B22)
    $penalty = ['refund' => $net, 'tax' => $gross * $taxRate, 'fee' => $net * $p['pinalti']];
    $penalty['total'] = $penalty['refund'] + $penalty['tax'] + $penalty['fee'];

    return [
        'input' => ['nominal' => $n, 'tenor' => $t, 'customerType' => $customerType],
        'eligible' => $eligible && !$negative,
        'reason' => $negative ? 'spread' : $sh['reason'],
        'minNominal' => engine_min_cashback_nominal($params),
        'share' => $share, 'shareBank' => $eligible ? 1 - $share : 0.0,
        'fund' => [
            'gwm' => $gwm, 'kas' => $kas, 'managed' => $managed, 'puabBase' => $puabBase, 'puabIncome' => $puabIncome,
            'creditBase' => $creditBase, 'creditIncome' => $creditIncome, 'income' => $income,
        ],
        'products' => $products,
        'cashback' => ['gross' => $gross, 'taxRate' => $taxRate, 'tax' => $tax, 'net' => $net, 'monthly' => $t ? $net / $t : 0.0, 'equiv' => $equiv],
        'deposito' => $deposito,
        'comparison' => $comparison,
        'best' => $best,
        'penalty' => $penalty,
    ];
}

/**
 * What a visitor without an admin session may see: the customer-facing result
 * only. Cost structure, spread, sharing tiers and the deposito comparison stay
 * on the server.
 */
function engine_public_result(array $r, array $params): array
{
    return [
        'input' => $r['input'],
        'eligible' => $r['eligible'],
        'reason' => $r['reason'],
        'minNominal' => $r['minNominal'],
        'share' => $r['share'],
        'cashback' => $r['cashback'],
        'comparison' => array_map(fn($c) => array_diff_key($c, ['diff' => 1]), $r['comparison']),
        'penalty' => $r['penalty'] + ['rate' => $params['settings']['pinalti']],
    ];
}

/**
 * Model for the public in-browser engine (assets/js/engine-public.js), so the
 * calculator answers instantly and offline. The bank's cost structure is folded
 * into one margin per tenor:
 *
 *   pendapatan PUAB − OHC + pendapatan kredit = nominal × margin[tenor]
 *   margin = (1 − GWM − kas) × (porsi PUAB × rate PUAB × hari sebulan/hari setahun × tenor × (1 − OHC)
 *                               + porsi kredit × bunga kredit × tenor/12)
 *
 * GWM, kas, porsi PUAB/kredit, rate PUAB, bunga kredit, OHC and the deposito
 * rates are not sent. Everything else is customer-facing (product rates, taxes,
 * penalty, LPS rules) or, like the sharing tiers, can be read off the results.
 */
function engine_client_model(array $params): array
{
    $p = $params['settings'];
    $year = $p['hari_setahun'];
    $month = $p['hari_sebulan'];
    $margin = [];
    foreach ($params['tenors'] as $t) {
        $margin[(string)$t] = (1 - ($p['gwm'] + $p['kas']))
            * ($p['porsi_puab'] * $p['puab'] * ($month / $year) * $t * (1 - $p['ohc'])
               + $p['porsi_kredit'] * $p['kredit'] * ($t / 12));
    }
    return [
        'tenors' => $params['tenors'],
        'cashbackTenors' => $params['cashbackTenors'],
        'minNominal' => engine_min_cashback_nominal($params),
        'days' => ['month' => $month, 'year' => $year],
        'margin' => $margin,
        'programAvg' => $p['biaya_program'] / 3,   // SIMANJA programme fee, averaged over the 3 products
        'lps' => ['rate' => $p['premi_lps'], 'cap' => $p['lps_batas']],
        'productRates' => $params['productRates'],
        'cashbackTiers' => $params['cashbackTiers'],
        'tax' => ['bunga' => $p['pajak_tabungan'], 'perorangan' => $p['pajak_cashback_perorangan'], 'badan' => $p['pajak_cashback_badan']],
        'pinalti' => $p['pinalti'],
        'paramsAt' => $params['updatedAt'],
        'generatedAt' => date('c'),
    ];
}