<?php
/**
 * Tournament data loading and simulation.
 *
 * A "team" is ['seed' => int, 'name' => string] and flows through the whole
 * simulation unchanged, so every round knows the seed of whoever advanced.
 */

const DATA_DIR = __DIR__ . '/../data';

/** Order of seeds down one region, top to bottom. Fixed by the NCAA; never changes. */
const SEED_ORDER = [1, 16, 8, 9, 5, 12, 4, 13, 6, 11, 3, 14, 7, 10, 2, 15];

/**
 * [top, bottom] win weights, indexed by round then game-within-region.
 *
 * Counted from 1999-2018 results. These were previously duplicated per region
 * and had drifted apart; South, West and Midwest agreed with each other in
 * every game, so their values are the ones kept here.
 */
const WEIGHTS = [
    // First round: 1v16, 8v9, 5v12, 4v13, 6v11, 3v14, 7v10, 2v15
    1 => [[20, 1], [13, 7], [13, 7], [16, 4], [11, 9], [19, 1], [14, 6], [18, 2]],
    2 => [[15, 5], [9, 11], [9, 11], [8, 12]],   // round of 32
    3 => [[15, 5], [7, 13]],                     // sweet 16
    // TODO: 12:8 is an estimate (~60:40 toward the half holding the 1 seed),
    // not a recount of the source data. The old per-region values were East
    // 17:3 (too steep for an Elite Eight game) and 1:1 elsewhere (a coin flip
    // that ignores seeding entirely), so neither could be carried over.
    4 => [[12, 8]],                              // elite 8
    5 => [[1, 1]],                               // final 4
    6 => [[1, 1]],                               // national championship
];

/** Years with a data file, newest first. */
function bracket_years(): array
{
    $years = [];
    foreach (glob(DATA_DIR . '/*.json') as $path) {
        $years[] = (int) basename($path, '.json');
    }
    rsort($years);
    return $years;
}

/**
 * Load a year's data, falling back to the newest year. $requested comes
 * straight off the query string, so it may be any type and is matched against
 * the known years rather than interpolated into a path.
 */
function bracket_load(mixed $requested = null): array
{
    $years = bracket_years();
    if (!$years) {
        throw new RuntimeException('No tournament data found in ' . DATA_DIR);
    }

    $wanted = is_scalar($requested) ? (int) $requested : 0;
    $year   = in_array($wanted, $years, true) ? $wanted : $years[0];
    $data = json_decode(file_get_contents(DATA_DIR . "/$year.json"), true);
    if (!is_array($data)) {
        throw new RuntimeException("data/$year.json is not valid JSON");
    }
    return $data;
}

/** Pick a winner, weighted. Replaces the old array_fill/array_merge shuffle. */
function pick(array $top, array $bottom, int $wTop, int $wBottom): array
{
    return mt_rand(1, $wTop + $wBottom) <= $wTop ? $top : $bottom;
}

/** One played game. */
function game(array $top, array $bottom, int $wTop, int $wBottom): array
{
    return ['top' => $top, 'bottom' => $bottom, 'winner' => pick($top, $bottom, $wTop, $wBottom)];
}

/** The team that lost a game. */
function loser(array $game): array
{
    return $game['winner'] === $game['top'] ? $game['bottom'] : $game['top'];
}

/**
 * Play one region. Returns 0 => the 16 seeded teams in bracket order,
 * then 1..4 => the winners of each round.
 */
function simulate_region(array $teams): array
{
    $current = array_map(
        fn(int $seed) => ['seed' => $seed, 'name' => $teams[$seed]],
        SEED_ORDER
    );
    $rounds = [0 => $current];

    for ($r = 1; $r <= 4; $r++) {
        $next = [];
        foreach (array_chunk($current, 2) as $g => [$top, $bottom]) {
            $next[] = pick($top, $bottom, ...WEIGHTS[$r][$g]);
        }
        $rounds[$r] = $current = $next;
    }
    return $rounds;
}

/**
 * Play the whole tournament. Region keys are bracket positions:
 * TL/BL are the left half, TR/BR the right half.
 */
function simulate_tournament(array $data): array
{
    $regions = [];
    foreach ($data['regions'] as $key => $region) {
        $regions[$key] = [
            'label'  => $region['label'],
            'rounds' => simulate_region($region['teams']),
        ];
    }

    $semiLeft  = game($regions['TL']['rounds'][4][0], $regions['BL']['rounds'][4][0], ...WEIGHTS[5][0]);
    $semiRight = game($regions['TR']['rounds'][4][0], $regions['BR']['rounds'][4][0], ...WEIGHTS[5][0]);
    $final     = game($semiLeft['winner'], $semiRight['winner'], ...WEIGHTS[6][0]);

    return [
        'regions'  => $regions,
        'national' => [5 => [$semiLeft, $semiRight], 6 => [$final]],
        'left'     => $semiLeft['winner'],
        'right'    => $semiRight['winner'],
        'champion' => $final['winner'],
        'runnerUp' => loser($final),
    ];
}