/**
 * DayView - single-day view with hourly time slots.
 *
 * Click an empty slot -> fires `onCreateAt(date)`.
 * Click an entry -> fires `onEditEntry(entry)`.
 * Drag an entry to another time slot -> calls `onMoveEntry(entry, newStart)`.
 */

import React, { useMemo } from 'react';
import { useTranslation } from 'react-i18next';
import clsx from 'clsx';
import type { CalendarEntry } from '@/api/calendar';

export interface DayViewProps {
  visibleDay: Date;
  entries: CalendarEntry[];
  loading?: boolean;
  onCreateAt: (date: Date) => void;
  onEditEntry: (entry: CalendarEntry) => void;
  onMoveEntry: (entry: CalendarEntry, newStart: Date) => void | Promise<void>;
}

const HOUR_START = 0;
const HOUR_END = 24;
const SLOT_HEIGHT = 56; // px per hour - slightly taller for single-day view

function startOfDay(d: Date): Date {
  return new Date(d.getFullYear(), d.getMonth(), d.getDate());
}

function sameDay(a: Date, b: Date): boolean {
  return a.getFullYear() === b.getFullYear() && a.getMonth() === b.getMonth() && a.getDate() === b.getDate();
}

function fmtTime(d: Date): string {
  const pad = (n: number) => String(n).padStart(2, '0');
  return `${pad(d.getHours())}:${pad(d.getMinutes())}`;
}

export function DayView({
  visibleDay,
  entries,
  loading,
  onCreateAt,
  onEditEntry,
  onMoveEntry,
}: DayViewProps) {
  const { t } = useTranslation();

  const today = startOfDay(new Date());
  const day = startOfDay(visibleDay);
  const isToday = sameDay(day, today);
  const weekdays = t('calendar.weekdays', { returnObjects: true }) as string[];
  const months = t('calendar.months', { returnObjects: true }) as string[];
  const weekdayIdx = (day.getDay() + 6) % 7; // 0 = Monday

  const hours = useMemo(() => {
    return Array.from({ length: HOUR_END - HOUR_START }, (_, i) => HOUR_START + i);
  }, []);

  const dayEntries = useMemo(() => {
    return entries.filter((e) => {
      if (!e.start_at) return false;
      return sameDay(new Date(e.start_at), day);
    });
  }, [entries, day]);

  const handleDragStart = (e: React.DragEvent<HTMLDivElement>, entry: CalendarEntry) => {
    e.dataTransfer.setData('application/x-calendar-entry', entry.id);
    e.dataTransfer.effectAllowed = 'move';
  };

  const handleDragOver = (e: React.DragEvent<HTMLDivElement>) => {
    if (e.dataTransfer.types.includes('application/x-calendar-entry')) {
      e.preventDefault();
      e.dataTransfer.dropEffect = 'move';
    }
  };

  const handleDrop = (e: React.DragEvent<HTMLDivElement>, hour: number) => {
    e.preventDefault();
    const id = e.dataTransfer.getData('application/x-calendar-entry');
    if (!id) return;
    const entry = entries.find((x) => x.id === id);
    if (!entry || !entry.start_at) return;
    const oldStart = new Date(entry.start_at);
    const newStart = new Date(
      day.getFullYear(),
      day.getMonth(),
      day.getDate(),
      hour,
      oldStart.getMinutes(),
      oldStart.getSeconds(),
    );
    void onMoveEntry(entry, newStart);
  };

  return (
    <div className="flex flex-col h-full bg-white" data-testid="day-view">
      {/* Header */}
      <div
        className={clsx(
          'flex items-center gap-3 px-4 py-3 border-b border-secondary-200',
          isToday && 'bg-primary-50',
        )}
      >
        <div className="text-xs font-medium text-secondary-600 uppercase tracking-wide">
          {weekdays[weekdayIdx]}
        </div>
        <div
          className={clsx(
            'text-sm font-semibold inline-flex items-center justify-center h-7 w-7 rounded-full',
            isToday && 'bg-primary-600 text-white',
          )}
        >
          {day.getDate()}
        </div>
        <div className="text-sm text-secondary-700">
          {months[day.getMonth()]} {day.getFullYear()}
        </div>
      </div>

      {/* Scrollable time grid */}
      <div className="flex-1 overflow-y-auto" data-testid="day-view-grid">
        <div className="flex">
          {/* Time labels */}
          <div className="w-20 flex-shrink-0">
            {hours.map((hour) => (
              <div
                key={hour}
                className="text-xs text-secondary-400 text-right pr-3 border-b border-secondary-100"
                style={{ height: `${SLOT_HEIGHT}px` }}
              >
                {String(hour).padStart(2, '0')}:00
              </div>
            ))}
          </div>

          {/* Day column */}
          <div
            className={clsx(
              'flex-1 relative border-l border-secondary-200',
              isToday && 'bg-primary-50/30',
            )}
          >
            {/* Hour slots */}
            {hours.map((hour) => (
              <div
                key={hour}
                className="border-b border-secondary-100 hover:bg-primary-50 cursor-pointer"
                style={{ height: `${SLOT_HEIGHT}px` }}
                onClick={() =>
                  !loading &&
                  onCreateAt(new Date(day.getFullYear(), day.getMonth(), day.getDate(), hour, 0))
                }
                onDragOver={handleDragOver}
                onDrop={(e) => handleDrop(e, hour)}
                data-testid={`day-slot-${hour}`}
              />
            ))}

            {/* Entries positioned absolutely */}
            {dayEntries.map((entry) => {
              if (!entry.start_at) return null;
              const start = new Date(entry.start_at);
              const end = entry.end_at ? new Date(entry.end_at) : new Date(start.getTime() + 60 * 60 * 1000);
              const startHour = start.getHours() + start.getMinutes() / 60;
              const endHour = end.getHours() + end.getMinutes() / 60;
              const durationHours = Math.max(endHour - startHour, 0.5);
              const top = (startHour - HOUR_START) * SLOT_HEIGHT;
              const height = durationHours * SLOT_HEIGHT;
              return (
                <div
                  key={entry.id}
                  draggable
                  onDragStart={(e) => handleDragStart(e, entry)}
                  onClick={(e) => {
                    e.stopPropagation();
                    onEditEntry(entry);
                  }}
                  className={clsx(
                    'absolute left-2 right-2 rounded px-2 py-1 text-sm cursor-grab active:cursor-grabbing',
                    'bg-primary-100 text-primary-900 hover:bg-primary-200 overflow-hidden',
                    entry.entry_type === 'task' && 'bg-warning-100 text-warning-900 hover:bg-warning-200',
                  )}
                  style={{ top: `${top}px`, height: `${height}px`, minHeight: '24px' }}
                  title={entry.title}
                  data-testid={`day-entry-${entry.id}`}
                >
                  <div className="font-medium truncate">{entry.title}</div>
                  <div className="text-xs opacity-75">
                    {fmtTime(start)}{entry.end_at ? ` - ${fmtTime(end)}` : ''}
                  </div>
                  {entry.location && (
                    <div className="text-xs opacity-60 truncate">@ {entry.location}</div>
                  )}
                </div>
              );
            })}
          </div>
        </div>
      </div>
    </div>
  );
}

export default DayView;