import Link from 'next/link';

import { ArrowLeft, ChevronLeft, ChevronRight } from 'lucide-react';

import { getSupabaseServerClient } from '@kit/supabase/server-client';
import { Badge } from '@kit/ui/badge';
import { Button } from '@kit/ui/button';
import { Card, CardContent, CardHeader, CardTitle } from '@kit/ui/card';

import { createCourseManagementApi } from '@kit/course-management/api';

import { CmsPageShell } from '~/components/cms-page-shell';
import { AccountNotFound } from '~/components/account-not-found';

interface PageProps {
  params: Promise<{ account: string }>;
}

const WEEKDAYS = ['Mo', 'Di', 'Mi', 'Do', 'Fr', 'Sa', 'So'];

const MONTH_NAMES = [
  'Januar',
  'Februar',
  'März',
  'April',
  'Mai',
  'Juni',
  'Juli',
  'August',
  'September',
  'Oktober',
  'November',
  'Dezember',
];

function getDaysInMonth(year: number, month: number): number {
  return new Date(year, month + 1, 0).getDate();
}

function getFirstWeekday(year: number, month: number): number {
  const day = new Date(year, month, 1).getDay();
  return day === 0 ? 6 : day - 1;
}

export default async function CourseCalendarPage({ params }: PageProps) {
  const { account } = await params;
  const client = getSupabaseServerClient();

  const { data: acct } = await client
    .from('accounts')
    .select('id')
    .eq('slug', account)
    .single();

  if (!acct) return <AccountNotFound />;

  const api = createCourseManagementApi(client);
  const courses = await api.listCourses(acct.id, { page: 1, pageSize: 100 });

  const now = new Date();
  const year = now.getFullYear();
  const month = now.getMonth();
  const daysInMonth = getDaysInMonth(year, month);
  const firstWeekday = getFirstWeekday(year, month);

  // Build set of days that have running courses
  const courseDates = new Set<number>();

  for (const course of courses.data) {
    const c = course as Record<string, unknown>;
    if (c.status === 'cancelled') continue;
    const startDate = c.start_date ? new Date(String(c.start_date)) : null;
    const endDate = c.end_date ? new Date(String(c.end_date)) : null;

    if (!startDate) continue;

    const courseStart = startDate;
    const courseEnd = endDate ?? startDate;

    for (let d = 1; d <= daysInMonth; d++) {
      const dayDate = new Date(year, month, d);
      if (dayDate >= courseStart && dayDate <= courseEnd) {
        courseDates.add(d);
      }
    }
  }

  // Build calendar grid
  const cells: Array<{ day: number | null; hasCourse: boolean; isToday: boolean }> = [];

  for (let i = 0; i < firstWeekday; i++) {
    cells.push({ day: null, hasCourse: false, isToday: false });
  }

  for (let d = 1; d <= daysInMonth; d++) {
    cells.push({
      day: d,
      hasCourse: courseDates.has(d),
      isToday: d === now.getDate() && month === now.getMonth() && year === now.getFullYear(),
    });
  }

  while (cells.length % 7 !== 0) {
    cells.push({ day: null, hasCourse: false, isToday: false });
  }

  const activeCourses = courses.data.filter(
    (c: Record<string, unknown>) =>
      c.status === 'open' || c.status === 'running',
  );

  return (
    <CmsPageShell account={account} title="Kurskalender">
      <div className="flex w-full flex-col gap-6">
        {/* Header */}
        <div className="flex items-center justify-between">
          <div className="flex items-center gap-4">
            <Link href={`/home/${account}/courses`}>
              <Button variant="ghost" size="icon">
                <ArrowLeft className="h-4 w-4" />
              </Button>
            </Link>
            <p className="text-muted-foreground">
              Kurstermine im Überblick
            </p>
          </div>
        </div>

        {/* Month Calendar */}
        <Card>
          <CardHeader>
            <div className="flex items-center justify-between">
              <Button variant="ghost" size="icon" disabled>
                <ChevronLeft className="h-4 w-4" />
              </Button>
              <CardTitle>
                {MONTH_NAMES[month]} {year}
              </CardTitle>
              <Button variant="ghost" size="icon" disabled>
                <ChevronRight className="h-4 w-4" />
              </Button>
            </div>
          </CardHeader>
          <CardContent>
            {/* Weekday Header */}
            <div className="grid grid-cols-7 gap-1 mb-1">
              {WEEKDAYS.map((day) => (
                <div
                  key={day}
                  className="text-center text-xs font-medium text-muted-foreground py-2"
                >
                  {day}
                </div>
              ))}
            </div>

            {/* Calendar Grid */}
            <div className="grid grid-cols-7 gap-1">
              {cells.map((cell, idx) => (
                <div
                  key={idx}
                  className={`relative flex h-12 items-center justify-center rounded-md text-sm transition-colors ${
                    cell.day === null
                      ? 'bg-transparent'
                      : cell.hasCourse
                        ? 'bg-emerald-500/15 text-emerald-700 dark:text-emerald-400 font-semibold'
                        : 'bg-muted/30 hover:bg-muted/50'
                  } ${cell.isToday ? 'ring-2 ring-primary ring-offset-1' : ''}`}
                >
                  {cell.day !== null && (
                    <>
                      <span>{cell.day}</span>
                      {cell.hasCourse && (
                        <span className="absolute bottom-1 left-1/2 -translate-x-1/2 h-1.5 w-1.5 rounded-full bg-emerald-500" />
                      )}
                    </>
                  )}
                </div>
              ))}
            </div>

            {/* Legend */}
            <div className="mt-4 flex items-center gap-4 text-xs text-muted-foreground">
              <div className="flex items-center gap-1.5">
                <span className="inline-block h-3 w-3 rounded-sm bg-emerald-500/15" />
                Kurstag
              </div>
              <div className="flex items-center gap-1.5">
                <span className="inline-block h-3 w-3 rounded-sm bg-muted/30" />
                Frei
              </div>
              <div className="flex items-center gap-1.5">
                <span className="inline-block h-3 w-3 rounded-sm ring-2 ring-primary" />
                Heute
              </div>
            </div>
          </CardContent>
        </Card>

        {/* Active Courses this Month */}
        <Card>
          <CardHeader>
            <CardTitle>Aktive Kurse ({activeCourses.length})</CardTitle>
          </CardHeader>
          <CardContent>
            {activeCourses.length === 0 ? (
              <p className="text-sm text-muted-foreground">
                Keine aktiven Kurse in diesem Monat.
              </p>
            ) : (
              <div className="space-y-3">
                {activeCourses.map((course: Record<string, unknown>) => (
                  <div
                    key={String(course.id)}
                    className="flex items-center justify-between rounded-md border p-3"
                  >
                    <div>
                      <Link
                        href={`/home/${account}/courses/${String(course.id)}`}
                        className="font-medium hover:underline"
                      >
                        {String(course.name)}
                      </Link>
                      <p className="text-xs text-muted-foreground">
                        {course.start_date
                          ? new Date(String(course.start_date)).toLocaleDateString('de-DE')
                          : '—'}{' '}
                        –{' '}
                        {course.end_date
                          ? new Date(String(course.end_date)).toLocaleDateString('de-DE')
                          : '—'}
                      </p>
                    </div>
                    <Badge variant={String(course.status) === 'running' ? 'info' : 'default'}>
                      {String(course.status) === 'running' ? 'Laufend' : 'Offen'}
                    </Badge>
                  </div>
                ))}
              </div>
            )}
          </CardContent>
        </Card>
      </div>
    </CmsPageShell>
  );
}