<?php

declare(strict_types=1);

namespace App\Tests\Model;

use App\Model\MonthGrid;
use PHPUnit\Framework\TestCase;

class MonthGridTest extends TestCase
{
    public function testTheGridIsAlwaysSixWeeksOfSevenDays(): void
    {
        // February 2026 needs four rows; the grid still renders six, so paging never changes its
        // height.
        $grid = MonthGrid::around(new \DateTimeImmutable('2026-02-15'), new \DateTimeImmutable('2026-02-15'));

        self::assertCount(6, $grid->weeks);

        foreach ($grid->weeks as $week) {
            self::assertCount(7, $week);
        }
    }

    public function testItStartsOnTheMondayOnOrBeforeTheFirst(): void
    {
        // 1 September 2026 is a Tuesday, so the grid opens on 31 August.
        $grid = MonthGrid::around(new \DateTimeImmutable('2026-09-21'), new \DateTimeImmutable('2026-09-21'));

        self::assertSame('2026-08-31', $grid->gridStart->format('Y-m-d'));
        self::assertSame('2026-09-01', $grid->monthStart->format('Y-m-d'));
        self::assertSame('1', $grid->gridStart->format('N'));
    }

    public function testAMonthBeginningOnAMondayStartsOnThatMonday(): void
    {
        // 1 June 2026 is a Monday: no leading days at all.
        $grid = MonthGrid::around(new \DateTimeImmutable('2026-06-10'), new \DateTimeImmutable('2026-06-10'));

        self::assertSame('2026-06-01', $grid->gridStart->format('Y-m-d'));
    }

    public function testTheEndIsTheLastCellOfTheGrid(): void
    {
        $grid = MonthGrid::around(new \DateTimeImmutable('2026-09-21'), new \DateTimeImmutable('2026-09-21'));

        self::assertSame('2026-10-11', $grid->gridEnd->format('Y-m-d'));
        self::assertEquals($grid->weeks[5][6]->date, $grid->gridEnd);
    }

    public function testEveryCellIsTheDayAfterTheOneBefore(): void
    {
        // Guards the modify('+1 day') walk: March and October carry the DST switches, where naive
        // arithmetic on timestamps would repeat or skip a day.
        foreach (['2026-03-15', '2026-10-15'] as $inMonth) {
            $grid = MonthGrid::around(new \DateTimeImmutable($inMonth), new \DateTimeImmutable($inMonth));

            $expected = $grid->gridStart;
            foreach ($grid->weeks as $week) {
                foreach ($week as $day) {
                    self::assertSame($expected->format('Y-m-d'), $day->date->format('Y-m-d'));
                    self::assertSame('00:00:00', $day->date->format('H:i:s'));
                    $expected = $expected->modify('+1 day');
                }
            }
        }
    }

    public function testDaysOutsideTheMonthAreFlagged(): void
    {
        $grid = MonthGrid::around(new \DateTimeImmutable('2026-09-21'), new \DateTimeImmutable('2026-09-21'));

        self::assertFalse($grid->weeks[0][0]->inMonth, '31 August is a leading day.');
        self::assertTrue($grid->weeks[0][1]->inMonth, '1 September is in the month.');
        self::assertFalse($grid->weeks[5][6]->inMonth, '11 October is a trailing day.');
    }

    public function testTodayIsNeitherPastNorAnyOtherDay(): void
    {
        $today = new \DateTimeImmutable('2026-09-21');
        $grid = MonthGrid::around($today, $today);

        $flagged = [];
        foreach ($grid->weeks as $week) {
            foreach ($week as $day) {
                if ($day->isToday) {
                    $flagged[] = $day->date->format('Y-m-d');
                    self::assertFalse($day->isPast, 'Today is not past.');
                }
            }
        }

        self::assertSame(['2026-09-21'], $flagged);
    }

    public function testPastAndWeekendFlags(): void
    {
        $grid = MonthGrid::around(new \DateTimeImmutable('2026-09-21'), new \DateTimeImmutable('2026-09-21'));

        $days = [];
        foreach ($grid->weeks as $week) {
            foreach ($week as $day) {
                $days[$day->key()] = $day;
            }
        }

        self::assertTrue($days['2026-09-20']->isPast);
        self::assertFalse($days['2026-09-22']->isPast);
        // 19/20 September 2026 is a Saturday/Sunday.
        self::assertTrue($days['2026-09-19']->isWeekend);
        self::assertTrue($days['2026-09-20']->isWeekend);
        self::assertFalse($days['2026-09-21']->isWeekend);
    }

    public function testTheTimePartOfTheGivenDayIsIgnored(): void
    {
        $grid = MonthGrid::around(new \DateTimeImmutable('2026-09-21 17:43:12'), new \DateTimeImmutable('2026-09-21'));

        self::assertSame('2026-09-01 00:00:00', $grid->monthStart->format('Y-m-d H:i:s'));
        self::assertTrue($grid->weeks[3][0]->isToday, 'Today must still be recognised.');
    }

    public function testTheKeyIsTheDayItIndexesPayloadBy(): void
    {
        $grid = MonthGrid::around(new \DateTimeImmutable('2026-09-21'), new \DateTimeImmutable('2026-09-21'));

        self::assertSame('2026-08-31', $grid->weeks[0][0]->key());
    }
}