import React, { useState, useMemo } from 'react';
import {
    format,
    startOfMonth,
    endOfMonth,
    startOfWeek,
    endOfWeek,
    eachDayOfInterval,
    isSameMonth,
    isSameDay,
    addMonths,
    subMonths,
    isToday,
    parseISO
} from 'date-fns';
import { ChevronLeft, ChevronRight, Calendar as CalendarIcon, Clock } from 'lucide-react';
import { Button } from '@/components/ui/button';
import { cn } from '@/lib/utils';
import { TimeLog } from '@/services/timeLogApi';
import { Badge } from '@/components/ui/badge';
import { Tooltip, TooltipContent, TooltipProvider, TooltipTrigger } from '@/components/ui/tooltip';

interface Task {
    id: number;
    title: string;
}

interface MonthlyCalendarProps {
    timeLogs: TimeLog[];
    tasks: Task[];
    onSelectDate?: (date: Date) => void;
    isLoading?: boolean;
}

export const MonthlyCalendar: React.FC<MonthlyCalendarProps> = ({
    timeLogs,
    tasks,
    onSelectDate,
    isLoading = false
}) => {
    const [currentMonth, setCurrentMonth] = useState(new Date());

    const nextMonth = () => setCurrentMonth(addMonths(currentMonth, 1));
    const prevMonth = () => setCurrentMonth(subMonths(currentMonth, 1));
    const goToToday = () => setCurrentMonth(new Date());

    const monthStart = startOfMonth(currentMonth);
    const monthEnd = endOfMonth(monthStart);
    const startDate = startOfWeek(monthStart);
    const endDate = endOfWeek(monthEnd);

    const calendarDays = eachDayOfInterval({ start: startDate, end: endDate });

    const weekDays = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];

    // Memoize grouped logs for performance
    const logsByDate = useMemo(() => {
        const grouped: Record<string, TimeLog[]> = {};
        timeLogs.forEach(log => {
            // Create a date string that represents the local date of the workDate
            // Assuming workDate is ISO string e.g., "2023-10-27T00:00:00.000Z"
            const dateStr = format(parseISO(log.workDate), 'yyyy-MM-dd');
            if (!grouped[dateStr]) {
                grouped[dateStr] = [];
            }
            grouped[dateStr].push(log);
        });
        return grouped;
    }, [timeLogs]);

    const getLogsForDate = (date: Date) => {
        const dateStr = format(date, 'yyyy-MM-dd');
        return logsByDate[dateStr] || [];
    };

    const getTaskTitle = (taskId: number) => {
        const task = tasks.find(t => t.id === taskId);
        return task ? task.title : `Task #${taskId}`;
    };

    const getTotalHoursForDate = (logs: TimeLog[]) => {
        return logs.reduce((total, log) => total + log.hrsSpent, 0);
    };

    const formatHours = (hours: number) => Number.isInteger(hours) ? hours : hours.toFixed(1);

    if (isLoading) {
        return (
            <div className="flex justify-center items-center h-96 bg-white rounded-xl shadow-sm border border-gray-100">
                <div className="flex flex-col items-center gap-3">
                    <div className="animate-spin rounded-full h-8 w-8 border-b-2 border-indigo-600"></div>
                    <p className="text-sm text-gray-500">Loading calendar...</p>
                </div>
            </div>
        );
    }

    return (
        <div className="bg-white rounded-xl shadow-sm border border-gray-200 overflow-hidden flex flex-col h-full min-h-[600px]">
            {/* Calendar Header */}
            <div className="flex flex-col sm:flex-row items-center justify-between p-4 border-b border-gray-200 gap-4 bg-white">
                <div className="flex items-center gap-3">
                    <div className="h-10 w-10 rounded-full bg-indigo-50 flex items-center justify-center text-indigo-600">
                        <CalendarIcon className="h-5 w-5" />
                    </div>
                    <div>
                        <h2 className="text-xl font-bold text-gray-800 leading-none">
                            {format(currentMonth, 'MMMM yyyy')}
                        </h2>
                        <p className="text-sm text-gray-500 mt-1">
                            {timeLogs.length} entries for selected range
                        </p>
                    </div>
                </div>
                <div className="flex items-center gap-2 bg-gray-50 p-1 rounded-lg border border-gray-100">
                    <Button variant="ghost" size="icon" onClick={prevMonth} className="h-8 w-8 hover:bg-white hover:shadow-sm">
                        <ChevronLeft className="h-4 w-4" />
                    </Button>
                    <Button variant="ghost" size="sm" onClick={goToToday} className="h-8 text-xs font-medium px-3 hover:bg-white hover:shadow-sm">
                        Today
                    </Button>
                    <Button variant="ghost" size="icon" onClick={nextMonth} className="h-8 w-8 hover:bg-white hover:shadow-sm">
                        <ChevronRight className="h-4 w-4" />
                    </Button>
                </div>
            </div>

            {/* Week Days Header */}
            <div className="grid grid-cols-7 border-b border-gray-200 bg-gray-50/50">
                {weekDays.map(day => (
                    <div key={day} className="py-3 text-center text-xs font-semibold text-gray-500 uppercase tracking-wider">
                        {day}
                    </div>
                ))}
            </div>

            {/* Calendar Grid */}
            <div className="grid grid-cols-7 flex-1 auto-rows-fr bg-gray-100 gap-px">
                {calendarDays.map((day, dayIdx) => {
                    const logs = getLogsForDate(day);
                    const totalHours = getTotalHoursForDate(logs);
                    const isCurrentMonth = isSameMonth(day, currentMonth);
                    const isDayToday = isToday(day);

                    return (
                        <div
                            key={day.toString()}
                            className={cn(
                                "bg-white p-2 min-h-[100px] flex flex-col gap-1 transition-all hover:bg-gray-50/80 relative group",
                                !isCurrentMonth && "bg-gray-50/30 text-gray-400",
                                isDayToday && "bg-indigo-50/10 ring-1 ring-inset ring-indigo-500/20"
                            )}
                            onClick={() => onSelectDate && onSelectDate(day)}
                        >
                            <div className="flex justify-between items-start mb-1">
                                <span className={cn(
                                    "text-sm font-medium h-7 w-7 flex items-center justify-center rounded-full transition-colors",
                                    isDayToday
                                        ? "bg-indigo-600 text-white shadow-sm"
                                        : "text-gray-700 group-hover:bg-gray-200"
                                )}>
                                    {format(day, 'd')}
                                </span>
                                {totalHours > 0 && (
                                    <div className={cn(
                                        "flex items-center gap-1 text-[10px] font-bold px-1.5 py-0.5 rounded-full",
                                        totalHours >= 8
                                            ? "bg-emerald-100 text-emerald-700"
                                            : totalHours > 4
                                                ? "bg-indigo-100 text-indigo-700"
                                                : "bg-amber-100 text-amber-700"
                                    )}>
                                        <Clock className="h-3 w-3" />
                                        {formatHours(totalHours)}h
                                    </div>
                                )}
                            </div>

                            <div className="flex-1 flex flex-col gap-1 overflow-y-auto max-h-[120px] custom-scrollbar">
                                {logs.map((log, idx) => (
                                    <TooltipProvider key={log.id}>
                                        <Tooltip delayDuration={0}>
                                            <TooltipTrigger asChild>
                                                <div className={cn(
                                                    "text-[10px] p-1.5 rounded-md border truncate cursor-pointer transition-all shadow-sm transform hover:scale-[1.02]",
                                                    "bg-white border-gray-200 hover:border-indigo-300 hover:shadow-md hover:z-10",
                                                    log.taskId % 4 === 0 ? "border-l-4 border-l-purple-500" :
                                                        log.taskId % 4 === 1 ? "border-l-4 border-l-blue-500" :
                                                            log.taskId % 4 === 2 ? "border-l-4 border-l-emerald-500" :
                                                                "border-l-4 border-l-amber-500"
                                                )}>
                                                    <span className="font-semibold block truncate text-gray-700 mb-0.5">
                                                        {getTaskTitle(log.taskId)}
                                                    </span>
                                                    <div className="flex justify-between items-center text-gray-500 text-[9px]">
                                                        <span className="truncate max-w-[60%]">{log.startTime}</span>
                                                        <span className="font-medium bg-gray-100 px-1 rounded">{formatHours(log.hrsSpent)}h</span>
                                                    </div>
                                                </div>
                                            </TooltipTrigger>
                                            <TooltipContent side="right" className="p-0 border-none shadow-xl">
                                                <div className="w-64 bg-white rounded-lg border border-gray-200 overflow-hidden">
                                                    <div className="bg-gray-50 px-3 py-2 border-b border-gray-200 flex justify-between items-center">
                                                        <span className="font-semibold text-xs text-gray-700">Task Details</span>
                                                        <Badge variant="outline" className="text-[10px] bg-white">
                                                            {log.hrsSpent}h
                                                        </Badge>
                                                    </div>
                                                    <div className="p-3">
                                                        <h4 className="font-bold text-sm text-gray-800 mb-1">{getTaskTitle(log.taskId)}</h4>
                                                        {log.comments && (
                                                            <div
                                                                className="text-xs text-gray-600 mt-2 bg-gray-50 p-2 rounded border border-gray-100"
                                                                dangerouslySetInnerHTML={{ __html: log.comments }}
                                                            />
                                                        )}
                                                        <div className="flex items-center gap-2 mt-3 pt-2 border-t border-gray-100 text-xs text-gray-500">
                                                            <Clock className="h-3 w-3" />
                                                            <span>{log.startTime} - {log.endTime}</span>
                                                        </div>
                                                    </div>
                                                </div>
                                            </TooltipContent>
                                        </Tooltip>
                                    </TooltipProvider>
                                ))}
                            </div>
                        </div>
                    );
                })}
            </div>
        </div>
    );
};