<?php

declare(strict_types=1);

const DB_DIR = __DIR__ . '/data';
const DB_FILE = DB_DIR . '/go.sqlite';

if (PHP_SAPI === 'cli') {
    try {
        run_cli($argv ?? []);
    } catch (Throwable $e) {
        fwrite(STDERR, $e->getMessage() . PHP_EOL);
        exit(1);
    }
}

header('Content-Type: application/json; charset=utf-8');

try {
    $db = db();
    migrate($db);

    $method = $_SERVER['REQUEST_METHOD'] ?? 'GET';
    $action = $_GET['action'] ?? null;

    if ($method === 'GET') {
        if ($action === null || $action === 'state') {
            respond([
                'settings' => get_settings($db),
                'entries' => get_entries($db),
                'corrections' => get_corrections($db),
                'feriefridage_overrides' => get_feriefridage_overrides($db),
                'flex_overrides' => get_flex_overrides($db),
            ]);
        }
        fail('Unknown GET action', 404);
    }

    if ($method === 'POST') {
        $payload = json_decode(file_get_contents('php://input') ?: '{}', true);
        if (!is_array($payload)) {
            fail('Invalid JSON payload', 400);
        }
        $action = $payload['action'] ?? $action;

        switch ($action) {
            case 'saveSettings':
                save_settings($db, $payload['settings'] ?? []);
                respond(['ok' => true, 'settings' => get_settings($db)]);
                break;

            case 'publishHa':
                publish_ha_state($payload['state'] ?? []);
                respond(['ok' => true]);
                break;

            case 'saveCorrection':
                save_correction($db, (int)($payload['year'] ?? 0), (int)($payload['month'] ?? 0), $payload['value'] ?? null);
                respond(['ok' => true, 'corrections' => get_corrections($db)]);
                break;

            case 'saveFeriefridageOverride':
                save_feriefridage_override($db, (int)($payload['year'] ?? 0), (int)($payload['month'] ?? 0), $payload['value'] ?? null);
                respond(['ok' => true, 'feriefridage_overrides' => get_feriefridage_overrides($db)]);
                break;

            case 'saveFlexOverride':
                save_flex_override($db, (int)($payload['year'] ?? 0), (int)($payload['month'] ?? 0), $payload['value'] ?? null);
                respond(['ok' => true, 'flex_overrides' => get_flex_overrides($db)]);
                break;

            case 'createEntry':
                $id = save_entry($db, $payload['entry'] ?? []);
                respond(['ok' => true, 'id' => $id, 'entries' => get_entries($db)]);
                break;

            case 'updateEntry':
                $id = (int)($payload['id'] ?? 0);
                if ($id <= 0) {
                    fail('Missing entry id', 400);
                }
                save_entry($db, $payload['entry'] ?? [], $id);
                respond(['ok' => true, 'entries' => get_entries($db)]);
                break;

            case 'deleteEntry':
                $id = (int)($payload['id'] ?? 0);
                if ($id <= 0) {
                    fail('Missing entry id', 400);
                }
                $stmt = $db->prepare('DELETE FROM entries WHERE id = :id');
                $stmt->execute([':id' => $id]);
                respond(['ok' => true, 'entries' => get_entries($db)]);
                break;

            default:
                fail('Unknown POST action', 404);
        }
    }

    fail('Unsupported method', 405);
} catch (Throwable $e) {
    fail($e->getMessage(), 500);
}

function app_config(): array
{
    $defaults = [
        'name' => 'GO Vacation Planner',
        'topic_prefix' => 'go',
        'mqtt_host' => '192.168.0.203',
        'mqtt_port' => 1883,
    ];
    $file = __DIR__ . '/config.php';
    if (is_file($file)) {
        $config = require $file;
        if (is_array($config)) return array_replace($defaults, $config);
    }
    return $defaults;
}

function mqtt_pub(array $config, string $topic, string $payload, bool $retain = true): void
{
    $host = $config['mqtt_host'];
    $port = (int)($config['mqtt_port'] ?? 1883);
    $cmd = 'mosquitto_pub -h ' . escapeshellarg($host)
        . ' -p ' . escapeshellarg((string)$port)
        . ' -t ' . escapeshellarg($topic)
        . ' -m ' . escapeshellarg($payload)
        . ($retain ? ' -r' : '');
    @shell_exec($cmd . ' 2>/dev/null');
}

function publish_ha_discovery(array $config): void
{
    $p = trim($config['topic_prefix'], '/');
    $dev = ['identifiers' => ['go_vacation_planner'], 'name' => $config['name']];
    $sensors = [
        'feriefridage' => ['name' => 'Feriefridage', 'unit' => 'd', 'topic' => "$p/feriefridage"],
        'vacation_days' => ['name' => 'Vacation days', 'unit' => 'd', 'topic' => "$p/vacation_days"],
        'flex_hours' => ['name' => 'FLEX hours', 'unit' => 'h', 'topic' => "$p/flex_hours"],
        'total_days' => ['name' => 'Total available days', 'unit' => 'd', 'topic' => "$p/total_days"],
        'upcoming_vacations' => ['name' => 'Upcoming vacations', 'unit' => '', 'topic' => "$p/upcoming_vacations", 'attributes_topic' => "$p/upcoming_vacations/attributes"],
    ];

    foreach ($sensors as $id => $sensor) {
        $payload = [
            'name' => $sensor['name'],
            'state_topic' => $sensor['topic'],
            'unique_id' => "go_$id",
            'device' => $dev,
        ];
        if ($sensor['unit'] !== '') $payload['unit_of_measurement'] = $sensor['unit'];
        if (isset($sensor['attributes_topic'])) $payload['json_attributes_topic'] = $sensor['attributes_topic'];
        mqtt_pub($config, "homeassistant/sensor/go_$id/config", json_encode($payload, JSON_UNESCAPED_SLASHES));
    }
}

function publish_ha_state(array $state): void
{
    $config = app_config();
    $p = trim($config['topic_prefix'], '/');
    publish_ha_discovery($config);

    $numeric = ['feriefridage', 'vacation_days', 'flex_hours', 'total_days'];
    foreach ($numeric as $key) {
        $value = isset($state[$key]) && is_numeric($state[$key]) ? round((float)$state[$key], 2) : 0;
        mqtt_pub($config, "$p/$key", (string)$value);
    }

    $upcoming = is_array($state['upcoming_vacations'] ?? null) ? $state['upcoming_vacations'] : [];
    $first = $upcoming[0] ?? null;
    $summary = is_array($first)
        ? (($first['title'] ?? 'Vacation') . ' ' . ($first['start'] ?? '') . ' → ' . ($first['end'] ?? ''))
        : 'none';
    mqtt_pub($config, "$p/upcoming_vacations", $summary);
    mqtt_pub($config, "$p/upcoming_vacations/attributes", json_encode(['vacations' => $upcoming], JSON_UNESCAPED_SLASHES));
    mqtt_pub($config, "$p/state", json_encode($state, JSON_UNESCAPED_SLASHES));
}

function db(): PDO
{
    if (!is_dir(DB_DIR) && !mkdir(DB_DIR, 0775, true) && !is_dir(DB_DIR)) {
        throw new RuntimeException('Could not create data directory');
    }

    $db = new PDO('sqlite:' . DB_FILE);
    $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $db->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
    $db->exec('PRAGMA foreign_keys = ON');
    return $db;
}

function migrate(PDO $db): void
{
    $db->exec("CREATE TABLE IF NOT EXISTS settings (
        key TEXT PRIMARY KEY,
        value TEXT NOT NULL
    )");

    $db->exec("CREATE TABLE IF NOT EXISTS entries (
        id INTEGER PRIMARY KEY AUTOINCREMENT,
        title TEXT NOT NULL,
        start_date TEXT NOT NULL,
        end_date TEXT NOT NULL,
        source TEXT NOT NULL DEFAULT 'auto',
        status TEXT NOT NULL DEFAULT 'planned',
        allow_unpaid INTEGER NOT NULL DEFAULT 0,
        non_working_days REAL NOT NULL DEFAULT 0,
        note TEXT NOT NULL DEFAULT '',
        created_at TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP,
        updated_at TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP
    )");

    $columns = array_column($db->query('PRAGMA table_info(entries)')->fetchAll(), 'name');
    if (!in_array('non_working_days', $columns, true)) {
        $db->exec('ALTER TABLE entries ADD COLUMN non_working_days REAL NOT NULL DEFAULT 0');
    }

    $db->exec("CREATE TABLE IF NOT EXISTS monthly_corrections (
        year INTEGER NOT NULL,
        month INTEGER NOT NULL,
        vacation_days REAL NOT NULL DEFAULT 0,
        PRIMARY KEY (year, month)
    )");

    $db->exec("CREATE TABLE IF NOT EXISTS monthly_feriefridage_overrides (
        year INTEGER NOT NULL,
        month INTEGER NOT NULL,
        feriefridage_days REAL NOT NULL DEFAULT 0,
        PRIMARY KEY (year, month)
    )");

    $db->exec("CREATE TABLE IF NOT EXISTS monthly_flex_overrides (
        year INTEGER NOT NULL,
        month INTEGER NOT NULL,
        flex_hours REAL NOT NULL DEFAULT 0,
        PRIMARY KEY (year, month)
    )");

    $defaults = [
        'planning_start_year' => '2026',
        'planning_start_month' => '1',
        'planning_years' => '3',
        'planning_months' => '36',
        'previous_months' => '5',
        'future_months' => '30',
        'vacation_days_per_month' => '2.08',
        'feriefridage_per_year' => '5',
        'feriefridage_expiry_month' => '8',
        'normal_day_hours' => '7.5',
        'friday_hours' => '7',
        'opening_vacation_days' => '-1.97',
        'opening_feriefridage_days' => '0',
        'opening_flex_hours' => '0',
        'current_flex_hours' => '46.5',
    ];

    $stmt = $db->prepare('INSERT OR IGNORE INTO settings (key, value) VALUES (:key, :value)');
    foreach ($defaults as $key => $value) {
        $stmt->execute([':key' => $key, ':value' => $value]);
    }
}

function get_settings(PDO $db): array
{
    $rows = $db->query('SELECT key, value FROM settings')->fetchAll();
    $settings = [];
    foreach ($rows as $row) {
        $settings[$row['key']] = numeric_value($row['value']);
    }
    return $settings;
}

function save_settings(PDO $db, array $settings): void
{
    $allowed = [
        'planning_start_year',
        'planning_start_month',
        'planning_years',
        'planning_months',
        'previous_months',
        'future_months',
        'vacation_days_per_month',
        'feriefridage_per_year',
        'feriefridage_expiry_month',
        'normal_day_hours',
        'friday_hours',
        'opening_vacation_days',
        'opening_feriefridage_days',
        'opening_flex_hours',
        'current_flex_hours',
    ];

    $stmt = $db->prepare('INSERT INTO settings (key, value) VALUES (:key, :value)
        ON CONFLICT(key) DO UPDATE SET value = excluded.value');

    foreach ($allowed as $key) {
        if (array_key_exists($key, $settings)) {
            $stmt->execute([':key' => $key, ':value' => (string)$settings[$key]]);
        }
    }
}

function get_corrections(PDO $db): array
{
    $rows = $db->query('SELECT year, month, vacation_days FROM monthly_corrections ORDER BY year, month')->fetchAll();
    $corrections = [];
    foreach ($rows as $row) {
        $corrections[$row['year'] . '-' . str_pad((string)$row['month'], 2, '0', STR_PAD_LEFT)] = (float)$row['vacation_days'];
    }
    return $corrections;
}

function save_correction(PDO $db, int $year, int $month, mixed $value): void
{
    if ($year < 1900 || $year > 2200 || $month < 1 || $month > 12) {
        fail('Invalid correction year/month', 400);
    }

    if ($value === null || $value === '') {
        $stmt = $db->prepare('DELETE FROM monthly_corrections WHERE year = :year AND month = :month');
        $stmt->execute([':year' => $year, ':month' => $month]);
        return;
    }

    $stmt = $db->prepare('INSERT INTO monthly_corrections (year, month, vacation_days)
        VALUES (:year, :month, :value)
        ON CONFLICT(year, month) DO UPDATE SET vacation_days = excluded.vacation_days');
    $stmt->execute([':year' => $year, ':month' => $month, ':value' => (float)$value]);
}

function get_feriefridage_overrides(PDO $db): array
{
    $rows = $db->query('SELECT year, month, feriefridage_days FROM monthly_feriefridage_overrides ORDER BY year, month')->fetchAll();
    $overrides = [];
    foreach ($rows as $row) {
        $overrides[$row['year'] . '-' . str_pad((string)$row['month'], 2, '0', STR_PAD_LEFT)] = (float)$row['feriefridage_days'];
    }
    return $overrides;
}

function save_feriefridage_override(PDO $db, int $year, int $month, mixed $value): void
{
    if ($year < 1900 || $year > 2200 || $month < 1 || $month > 12) {
        fail('Invalid feriefridage override year/month', 400);
    }

    if ($value === null || $value === '') {
        $stmt = $db->prepare('DELETE FROM monthly_feriefridage_overrides WHERE year = :year AND month = :month');
        $stmt->execute([':year' => $year, ':month' => $month]);
        return;
    }

    $stmt = $db->prepare('INSERT INTO monthly_feriefridage_overrides (year, month, feriefridage_days)
        VALUES (:year, :month, :value)
        ON CONFLICT(year, month) DO UPDATE SET feriefridage_days = excluded.feriefridage_days');
    $stmt->execute([':year' => $year, ':month' => $month, ':value' => (float)$value]);
}

function get_flex_overrides(PDO $db): array
{
    $rows = $db->query('SELECT year, month, flex_hours FROM monthly_flex_overrides ORDER BY year, month')->fetchAll();
    $overrides = [];
    foreach ($rows as $row) {
        $overrides[$row['year'] . '-' . str_pad((string)$row['month'], 2, '0', STR_PAD_LEFT)] = (float)$row['flex_hours'];
    }
    return $overrides;
}

function save_flex_override(PDO $db, int $year, int $month, mixed $value): void
{
    if ($year < 1900 || $year > 2200 || $month < 1 || $month > 12) {
        fail('Invalid FLEX override year/month', 400);
    }

    if ($value === null || $value === '') {
        $stmt = $db->prepare('DELETE FROM monthly_flex_overrides WHERE year = :year AND month = :month');
        $stmt->execute([':year' => $year, ':month' => $month]);
        return;
    }

    $stmt = $db->prepare('INSERT INTO monthly_flex_overrides (year, month, flex_hours)
        VALUES (:year, :month, :value)
        ON CONFLICT(year, month) DO UPDATE SET flex_hours = excluded.flex_hours');
    $stmt->execute([':year' => $year, ':month' => $month, ':value' => (float)$value]);
}

function get_entries(PDO $db): array
{
    return $db->query('SELECT id, title, start_date, end_date, source, status, allow_unpaid, non_working_days, note
        FROM entries ORDER BY start_date, end_date, id')->fetchAll();
}

function save_entry(PDO $db, array $entry, ?int $id = null): int
{
    $title = trim((string)($entry['title'] ?? ''));
    $start = trim((string)($entry['start_date'] ?? ''));
    $end = trim((string)($entry['end_date'] ?? ''));
    $source = (string)($entry['source'] ?? 'auto');
    $status = (string)($entry['status'] ?? 'planned');
    $allowUnpaid = !empty($entry['allow_unpaid']) ? 1 : 0;
    $nonWorkingDays = (float)($entry['non_working_days'] ?? 0);
    $note = trim((string)($entry['note'] ?? '')); 

    if ($title === '') {
        fail('Title is required', 400);
    }
    if (!valid_date($start) || !valid_date($end)) {
        fail('Start/end date must be YYYY-MM-DD', 400);
    }
    if ($start > $end) {
        fail('Start date must be before end date', 400);
    }
    if (!in_array($source, ['auto', 'vacation', 'feriefridag', 'flex', 'unpaid'], true)) {
        fail('Invalid source', 400);
    }
    if ($nonWorkingDays < 0 || fmod($nonWorkingDays * 2, 1.0) !== 0.0) {
        fail('Additional non-working days must be in steps of 0.5', 400);
    }
    if ($status === 'confirmed') {
        $status = 'approved';
    }
    if (!in_array($status, ['planned', 'approved'], true)) {
        fail('Invalid status', 400);
    }

    $params = [
        ':title' => $title,
        ':start_date' => $start,
        ':end_date' => $end,
        ':source' => $source,
        ':status' => $status,
        ':allow_unpaid' => $allowUnpaid,
        ':non_working_days' => $nonWorkingDays,
        ':note' => $note,
    ];

    if ($id === null) {
        $stmt = $db->prepare('INSERT INTO entries
            (title, start_date, end_date, source, status, allow_unpaid, non_working_days, note)
            VALUES (:title, :start_date, :end_date, :source, :status, :allow_unpaid, :non_working_days, :note)');
        $stmt->execute($params);
        return (int)$db->lastInsertId();
    }

    $params[':id'] = $id;
    $stmt = $db->prepare('UPDATE entries SET
        title = :title,
        start_date = :start_date,
        end_date = :end_date,
        source = :source,
        status = :status,
        allow_unpaid = :allow_unpaid,
        non_working_days = :non_working_days,
        note = :note,
        updated_at = CURRENT_TIMESTAMP
        WHERE id = :id');
    $stmt->execute($params);
    return $id;
}

function build_ha_state(PDO $db): array
{
    $settings = get_settings($db);
    $entries = array_map('normalize_entry_for_plan', get_entries($db));
    $corrections = get_corrections($db);
    $feriefridageOverrides = get_feriefridage_overrides($db);
    $flexOverrides = get_flex_overrides($db);

    $current = calculate_current_snapshot($settings, $entries, $corrections, $feriefridageOverrides, $flexOverrides);
    $entrySummaries = calculate_entry_summaries($settings, $entries, $corrections, $feriefridageOverrides, $flexOverrides);

    return [
        'feriefridage' => (float)$current['feriefridage'],
        'vacation_days' => (float)$current['vacation'],
        'flex_hours' => (float)$current['flex'],
        'total_days' => (float)$current['totalDays'],
        'upcoming_vacations' => upcoming_vacations_for_ha($entries, $entrySummaries),
        'updated_at' => gmdate('Y-m-d\\TH:i:s\\Z'),
    ];
}

function run_cli(array $argv): never
{
    $command = $argv[1] ?? '';
    if (!in_array($command, ['ha-state', 'publish-ha', 'publishHaNow', 'publishHa'], true)) {
        fwrite(STDERR, "Usage: php api.php ha-state|publish-ha\n");
        exit(1);
    }

    $db = db();
    migrate($db);
    $state = build_ha_state($db);

    if ($command !== 'ha-state') {
        publish_ha_state($state);
    }

    echo json_encode(['ok' => true, 'published' => $command !== 'ha-state', 'state' => $state], JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE) . PHP_EOL;
    exit(0);
}

function normalize_entry_for_plan(array $entry): array
{
    $entry['id'] = (int)$entry['id'];
    $entry['allow_unpaid'] = (int)$entry['allow_unpaid'];
    $entry['non_working_days'] = (float)($entry['non_working_days'] ?? 0);
    if (($entry['status'] ?? '') === 'confirmed') {
        $entry['status'] = 'approved';
    }
    return $entry;
}

function calculate_entry_summaries(array $settings, array $entries, array $corrections = [], array $feriefridageOverrides = [], array $flexOverrides = []): array
{
    $today = date_from_parts((int)date('Y'), (int)date('n'), (int)date('j'));
    $previousMonths = (int)($settings['previous_months'] ?? 5);
    $futureMonths = (int)($settings['future_months'] ?? 30);
    $startCursor = date_from_parts((int)$today->format('Y'), (int)$today->format('n') + 1 - $previousMonths, 1);
    $startYear = (int)$startCursor->format('Y');
    $startMonth = (int)$startCursor->format('n');
    $monthCount = $previousMonths + $futureMonths + 1;
    $startDate = date_from_parts($startYear, $startMonth, 1);
    $endDate = date_from_parts($startYear, $startMonth + $monthCount, 0);

    $entrySummaries = [];
    $entriesById = [];
    $allWorkdays = [];
    foreach ($entries as $entry) {
        $entriesById[(int)$entry['id']] = $entry;
        $grossDates = workdays_between($entry['start_date'], $entry['end_date']);
        $units = workday_units_for_entry($entry);
        $entrySummaries[(int)$entry['id']] = [
            'workdays' => sum_fractions($units),
            'grossWorkdays' => count($grossDates),
            'nonWorkingDays' => (float)($entry['non_working_days'] ?? 0),
            'usedVacation' => 0.0,
            'usedFeriefridage' => 0.0,
            'usedFlex' => 0.0,
            'usedFlexDays' => 0.0,
            'usedUnpaid' => 0.0,
        ];
        foreach ($units as $unit) {
            if ($unit['date'] < $startDate || $unit['date'] > $endDate) continue;
            $allWorkdays[] = ['date' => $unit['date'], 'fraction' => $unit['fraction'], 'entryId' => (int)$entry['id']];
        }
    }

    usort($allWorkdays, fn($a, $b) => ($a['date'] <=> $b['date']) ?: ($a['entryId'] <=> $b['entryId']));

    $workdaysByMonth = [];
    foreach ($allWorkdays as $item) {
        $key = month_key((int)$item['date']->format('Y'), (int)$item['date']->format('n'));
        $workdaysByMonth[$key][] = $item;
    }

    $vacationBalance = (float)($settings['opening_vacation_days'] ?? 0);
    $feriefridageBalance = (float)($settings['opening_feriefridage_days'] ?? 0);
    $flexBalance = (float)($settings['opening_flex_hours'] ?? 0);
    $currentFlexHours = (float)($settings['current_flex_hours'] ?? $flexBalance);

    for ($i = 0; $i < $monthCount; $i++) {
        $cursor = date_from_parts($startYear, $startMonth + $i, 1);
        $year = (int)$cursor->format('Y');
        $month = (int)$cursor->format('n');
        $current = ['usedVacation' => 0.0, 'usedFeriefridage' => 0.0, 'usedFlex' => 0.0, 'usedUnpaid' => 0.0, 'entries' => []];

        if ($month === 1) {
            $feriefridageBalance += (float)($settings['feriefridage_per_year'] ?? 0);
        }

        if ($month === (int)($settings['feriefridage_expiry_month'] ?? 8) + 1 && $feriefridageBalance > 0.001) {
            $feriefridageBalance = 0.0;
        }

        $key = month_key($year, $month);
        $monthItems = $workdaysByMonth[$key] ?? [];
        $isThisMonth = $year === (int)$today->format('Y') && $month === (int)$today->format('n');

        $applyWorkday = function (array $item) use (&$vacationBalance, &$feriefridageBalance, &$flexBalance, &$current, &$entrySummaries, $entriesById, $settings): void {
            $entry = $entriesById[$item['entryId']];
            $allocation = allocate_day($entry, $item['date'], [
                'vacationBalance' => $vacationBalance,
                'feriefridageBalance' => $feriefridageBalance,
                'flexBalance' => $flexBalance,
            ], $settings, (float)$item['fraction']);

            $vacationBalance = $allocation['balances']['vacationBalance'];
            $feriefridageBalance = $allocation['balances']['feriefridageBalance'];
            $flexBalance = $allocation['balances']['flexBalance'];

            $current['usedVacation'] += $allocation['usedVacation'];
            $current['usedFeriefridage'] += $allocation['usedFeriefridage'];
            $current['usedFlex'] += $allocation['usedFlex'];
            $current['usedUnpaid'] += $allocation['usedUnpaid'];

            $id = (int)$entry['id'];
            $entrySummaries[$id]['usedVacation'] += $allocation['usedVacation'];
            $entrySummaries[$id]['usedFeriefridage'] += $allocation['usedFeriefridage'];
            $entrySummaries[$id]['usedFlex'] += $allocation['usedFlex'];
            $entrySummaries[$id]['usedFlexDays'] += $allocation['usedFlexDays'];
            $entrySummaries[$id]['usedUnpaid'] += $allocation['usedUnpaid'];

            $monthEntryIndex = null;
            foreach ($current['entries'] as $index => $row) {
                if ($row['id'] === $id) {
                    $monthEntryIndex = $index;
                    break;
                }
            }
            if ($monthEntryIndex === null) {
                $current['entries'][] = ['id' => $id, 'usedVacation' => 0.0, 'usedUnpaid' => 0.0, 'allowUnpaid' => (bool)$entry['allow_unpaid']];
                $monthEntryIndex = count($current['entries']) - 1;
            }
            $current['entries'][$monthEntryIndex]['usedVacation'] += $allocation['usedVacation'];
            $current['entries'][$monthEntryIndex]['usedUnpaid'] += $allocation['usedUnpaid'];
        };

        if ($isThisMonth) {
            foreach ($monthItems as $item) {
                if ($item['date'] <= $today) $applyWorkday($item);
            }
            $flexBalance = $currentFlexHours;
            foreach ($monthItems as $item) {
                if ($item['date'] > $today) $applyWorkday($item);
            }
        } else {
            foreach ($monthItems as $item) $applyWorkday($item);
        }

        $vacationBalance += (float)($settings['vacation_days_per_month'] ?? 0);

        if ($vacationBalance < -0.001) {
            $vacationBalance = convert_negative_vacation_to_unpaid($current, $entrySummaries, $vacationBalance);
        }

        if (has_correction($corrections, $year, $month)) $vacationBalance = correction_for($corrections, $year, $month);
        if (has_correction($feriefridageOverrides, $year, $month)) $feriefridageBalance = correction_for($feriefridageOverrides, $year, $month);
        if (has_correction($flexOverrides, $year, $month)) $flexBalance = correction_for($flexOverrides, $year, $month);
    }

    return $entrySummaries;
}

function convert_negative_vacation_to_unpaid(array &$month, array &$entrySummaries, float $vacationBalance): float
{
    $remaining = -$vacationBalance;
    for ($i = count($month['entries']) - 1; $i >= 0 && $remaining > 0.001; $i--) {
        if (!$month['entries'][$i]['allowUnpaid'] || $month['entries'][$i]['usedVacation'] <= 0) continue;
        $convert = min($month['entries'][$i]['usedVacation'], $remaining);
        $month['entries'][$i]['usedVacation'] -= $convert;
        $month['entries'][$i]['usedUnpaid'] += $convert;
        $month['usedVacation'] -= $convert;
        $month['usedUnpaid'] += $convert;
        $id = (int)$month['entries'][$i]['id'];
        if (isset($entrySummaries[$id])) {
            $entrySummaries[$id]['usedVacation'] -= $convert;
            $entrySummaries[$id]['usedUnpaid'] += $convert;
        }
        $vacationBalance += $convert;
        $remaining -= $convert;
    }
    return $vacationBalance;
}

function calculate_current_snapshot(array $settings, array $entries, array $corrections = [], array $feriefridageOverrides = [], array $flexOverrides = []): array
{
    $today = date_from_parts((int)date('Y'), (int)date('n'), (int)date('j'));
    $previousMonths = (int)($settings['previous_months'] ?? 5);
    $startCursor = date_from_parts((int)$today->format('Y'), (int)$today->format('n') + 1 - $previousMonths, 1);
    $startYear = (int)$startCursor->format('Y');
    $startMonth = (int)$startCursor->format('n');
    $startDate = date_from_parts($startYear, $startMonth, 1);
    $avgDayHours = average_day_hours($settings);

    $vacationBalance = (float)($settings['opening_vacation_days'] ?? 0);
    $feriefridageBalance = (float)($settings['opening_feriefridage_days'] ?? 0);
    $flexBalance = (float)($settings['opening_flex_hours'] ?? 0);
    $currentFlexHours = (float)($settings['current_flex_hours'] ?? $flexBalance);

    if ($today < $startDate) {
        $flexBalance = $currentFlexHours;
        return current_snapshot_result($vacationBalance, $feriefridageBalance, $flexBalance, $avgDayHours);
    }

    $workdays = [];
    foreach ($entries as $entry) {
        foreach (workday_units_for_entry($entry) as $unit) {
            if ($unit['date'] >= $startDate && $unit['date'] <= $today) {
                $workdays[] = ['date' => $unit['date'], 'fraction' => $unit['fraction'], 'entry' => $entry];
            }
        }
    }
    usort($workdays, fn($a, $b) => ($a['date'] <=> $b['date']) ?: ((int)$a['entry']['id'] <=> (int)$b['entry']['id']));

    $workdayIndex = 0;
    $monthCount = (((int)$today->format('Y') - $startYear) * 12) + ((int)$today->format('n') - $startMonth) + 1;
    for ($i = 0; $i < $monthCount; $i++) {
        $cursor = date_from_parts($startYear, $startMonth + $i, 1);
        $year = (int)$cursor->format('Y');
        $month = (int)$cursor->format('n');

        if ($month === 1) $feriefridageBalance += (float)($settings['feriefridage_per_year'] ?? 0);

        if ($month === (int)($settings['feriefridage_expiry_month'] ?? 8) + 1 && $feriefridageBalance > 0.001) {
            $feriefridageBalance = 0.0;
        }

        $monthStart = date_from_parts($year, $month, 1);
        $monthEnd = date_from_parts($year, $month + 1, 0);
        $limit = $today < $monthEnd ? $today : $monthEnd;
        while ($workdayIndex < count($workdays) && $workdays[$workdayIndex]['date'] >= $monthStart && $workdays[$workdayIndex]['date'] <= $limit) {
            $item = $workdays[$workdayIndex++];
            $allocation = allocate_day($item['entry'], $item['date'], [
                'vacationBalance' => $vacationBalance,
                'feriefridageBalance' => $feriefridageBalance,
                'flexBalance' => $flexBalance,
            ], $settings, (float)$item['fraction']);
            $vacationBalance = $allocation['balances']['vacationBalance'];
            $feriefridageBalance = $allocation['balances']['feriefridageBalance'];
            $flexBalance = $allocation['balances']['flexBalance'];
        }

        if ($today >= $monthEnd) {
            $vacationBalance += (float)($settings['vacation_days_per_month'] ?? 0);
        }

        if ($year === (int)$today->format('Y') && $month === (int)$today->format('n')) {
            $flexBalance = $currentFlexHours;
        }

        if (has_correction($corrections, $year, $month)) $vacationBalance = correction_for($corrections, $year, $month);
        if (has_correction($feriefridageOverrides, $year, $month)) $feriefridageBalance = correction_for($feriefridageOverrides, $year, $month);
        if (has_correction($flexOverrides, $year, $month)) $flexBalance = correction_for($flexOverrides, $year, $month);
    }

    if (!has_correction($flexOverrides, (int)$today->format('Y'), (int)$today->format('n'))) {
        $flexBalance = $currentFlexHours;
    }

    return current_snapshot_result($vacationBalance, $feriefridageBalance, $flexBalance, $avgDayHours);
}

function current_snapshot_result(float $vacationBalance, float $feriefridageBalance, float $flexBalance, float $avgDayHours): array
{
    return [
        'vacation' => $vacationBalance,
        'feriefridage' => $feriefridageBalance,
        'flex' => $flexBalance,
        'totalDays' => $vacationBalance + $feriefridageBalance + ($flexBalance / $avgDayHours),
    ];
}

function allocate_day(array $entry, DateTimeImmutable $date, array $balances, array $settings, float $fraction = 1.0): array
{
    $source = (string)($entry['source'] ?? 'auto');
    $allowUnpaid = (bool)($entry['allow_unpaid'] ?? false);
    $baseDayHours = hours_for_date($date, $settings);
    $dayHours = $baseDayHours * $fraction;
    $vacationBalance = (float)$balances['vacationBalance'];
    $feriefridageBalance = (float)$balances['feriefridageBalance'];
    $flexBalance = (float)$balances['flexBalance'];
    $result = ['usedVacation' => 0.0, 'usedFeriefridage' => 0.0, 'usedFlex' => 0.0, 'usedFlexDays' => 0.0, 'usedUnpaid' => 0.0];

    $useVacation = function () use (&$result, &$vacationBalance, $allowUnpaid, $fraction): void {
        if ($allowUnpaid && $vacationBalance < $fraction) {
            $use = max(0.0, $vacationBalance);
            $result['usedVacation'] += $use;
            $result['usedUnpaid'] += $fraction - $use;
            $vacationBalance = 0.0;
        } else {
            $result['usedVacation'] += $fraction;
            $vacationBalance -= $fraction;
        }
    };
    $useFeriefridag = function () use (&$result, &$feriefridageBalance, $allowUnpaid, $fraction): void {
        if ($allowUnpaid && $feriefridageBalance < $fraction) {
            $use = max(0.0, $feriefridageBalance);
            $result['usedFeriefridage'] += $use;
            $result['usedUnpaid'] += $fraction - $use;
            $feriefridageBalance = 0.0;
        } else {
            $result['usedFeriefridage'] += $fraction;
            $feriefridageBalance -= $fraction;
        }
    };
    $useFlex = function () use (&$result, &$flexBalance, $allowUnpaid, $dayHours, $baseDayHours, $fraction): void {
        if ($allowUnpaid && $flexBalance < $dayHours) {
            $useHours = max(0.0, $flexBalance);
            $result['usedFlex'] += $useHours;
            $result['usedFlexDays'] += $useHours / $baseDayHours;
            $result['usedUnpaid'] += $fraction - ($useHours / $baseDayHours);
            $flexBalance = 0.0;
        } else {
            $result['usedFlex'] += $dayHours;
            $result['usedFlexDays'] += $fraction;
            $flexBalance -= $dayHours;
        }
    };

    if ($source === 'unpaid') {
        $result['usedUnpaid'] = $fraction;
    } elseif ($source === 'vacation') {
        $useVacation();
    } elseif ($source === 'feriefridag') {
        $useFeriefridag();
    } elseif ($source === 'flex') {
        $useFlex();
    } else {
        $remaining = $fraction;
        if ($remaining > 0 && $feriefridageBalance > 0 && is_before_feriefridage_expiry($date, $settings)) {
            $use = min($feriefridageBalance, $remaining);
            $result['usedFeriefridage'] += $use;
            $feriefridageBalance -= $use;
            $remaining -= $use;
        }
        if ($remaining > 0 && $vacationBalance > 0) {
            $use = min($vacationBalance, $remaining);
            $result['usedVacation'] += $use;
            $vacationBalance -= $use;
            $remaining -= $use;
        }
        if ($remaining > 0 && $flexBalance > 0) {
            $use = min($flexBalance / $baseDayHours, $remaining);
            $result['usedFlex'] += $use * $baseDayHours;
            $result['usedFlexDays'] += $use;
            $flexBalance -= $use * $baseDayHours;
            $remaining -= $use;
        }
        if ($remaining > 0) {
            $result['usedVacation'] += $remaining;
            $vacationBalance -= $remaining;
        }
    }

    $result['balances'] = ['vacationBalance' => $vacationBalance, 'feriefridageBalance' => $feriefridageBalance, 'flexBalance' => $flexBalance];
    return $result;
}

function upcoming_vacations_for_ha(array $entries, array $entrySummaries): array
{
    $today = date('Y-m-d');
    $upcoming = array_values(array_filter($entries, fn($entry) => (string)$entry['end_date'] >= $today));
    usort($upcoming, fn($a, $b) => strcmp((string)$a['start_date'], (string)$b['start_date']) ?: ((int)$a['id'] <=> (int)$b['id']));

    return array_map(function (array $entry) use ($entrySummaries): array {
        $summary = $entrySummaries[(int)$entry['id']] ?? ['workdays' => 0, 'usedVacation' => 0, 'usedFeriefridage' => 0, 'usedFlex' => 0, 'usedFlexDays' => 0];
        return [
            'title' => $entry['title'],
            'start' => $entry['start_date'],
            'end' => $entry['end_date'],
            'start_display' => format_date_for_ha((string)$entry['start_date']),
            'end_display' => format_date_for_ha((string)$entry['end_date']),
            'status' => $entry['status'],
            'source' => $entry['source'],
            'workdays' => (float)($summary['workdays'] ?? 0),
            'vacation_days' => (float)($summary['usedVacation'] ?? 0),
            'feriefridage' => (float)($summary['usedFeriefridage'] ?? 0),
            'flex_hours' => (float)($summary['usedFlex'] ?? 0),
            'flex_days' => (float)($summary['usedFlexDays'] ?? 0),
        ];
    }, $upcoming);
}

function workday_units_for_entry(array $entry): array
{
    $units = array_map(fn($date) => ['date' => $date, 'fraction' => 1.0], workdays_between((string)$entry['start_date'], (string)$entry['end_date']));
    $remaining = max(0.0, (float)($entry['non_working_days'] ?? 0));
    for ($i = count($units) - 1; $i >= 0 && $remaining > 0; $i--) {
        $reduction = min($units[$i]['fraction'], $remaining);
        $units[$i]['fraction'] -= $reduction;
        $remaining -= $reduction;
    }
    return array_values(array_filter($units, fn($unit) => $unit['fraction'] > 0.0001));
}

function workdays_between(string $start, string $end): array
{
    $days = [];
    $current = parse_date($start);
    $stop = parse_date($end);
    while ($current <= $stop) {
        $dow = (int)$current->format('N');
        if ($dow >= 1 && $dow <= 5) $days[] = $current;
        $current = $current->modify('+1 day');
    }
    return $days;
}

function sum_fractions(array $units): float
{
    return array_reduce($units, fn($sum, $unit) => $sum + (float)$unit['fraction'], 0.0);
}

function hours_for_date(DateTimeImmutable $date, array $settings): float
{
    return (int)$date->format('N') === 5 ? (float)($settings['friday_hours'] ?? 7) : (float)($settings['normal_day_hours'] ?? 7.5);
}

function average_day_hours(array $settings): float
{
    return ((((float)($settings['normal_day_hours'] ?? 7.5)) * 4) + (float)($settings['friday_hours'] ?? 7)) / 5;
}

function is_before_feriefridage_expiry(DateTimeImmutable $date, array $settings): bool
{
    return (int)$date->format('n') <= (int)($settings['feriefridage_expiry_month'] ?? 8);
}

function date_from_parts(int $year, int $month, int $day): DateTimeImmutable
{
    return (new DateTimeImmutable('now'))->setDate($year, $month, $day)->setTime(12, 0, 0);
}

function parse_date(string $value): DateTimeImmutable
{
    [$year, $month, $day] = array_map('intval', explode('-', $value));
    return date_from_parts($year, $month, $day);
}

function month_key(int $year, int $month): string
{
    return $year . '-' . str_pad((string)$month, 2, '0', STR_PAD_LEFT);
}

function correction_for(array $corrections, int $year, int $month): float
{
    return (float)($corrections[month_key($year, $month)] ?? 0);
}

function has_correction(array $corrections, int $year, int $month): bool
{
    return array_key_exists(month_key($year, $month), $corrections);
}

function format_date_for_ha(string $value): string
{
    $parts = explode('-', $value);
    if (count($parts) !== 3) return $value;
    return $parts[2] . '/' . $parts[1] . '/' . $parts[0];
}

function valid_date(string $date): bool
{
    $d = DateTime::createFromFormat('Y-m-d', $date);
    return $d && $d->format('Y-m-d') === $date;
}

function numeric_value(string $value): int|float|string
{
    if (is_numeric($value)) {
        return str_contains($value, '.') ? (float)$value : (int)$value;
    }
    return $value;
}

function respond(array $data): never
{
    echo json_encode($data, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE);
    exit;
}

function fail(string $message, int $status): never
{
    http_response_code($status);
    echo json_encode(['error' => $message], JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE);
    exit;
}