import React, { useState } from "react";
import { View, Pressable, StyleSheet } from "react-native";
import { Text } from "@/components/ui/text";
import { ArrowLeft, ArrowRight, ChevronDown } from "@/lib/icons";
import { useColorScheme } from "nativewind";

const MONTHS = [
  "January",
  "February",
  "March",
  "April",
  "May",
  "June",
  "July",
  "August",
  "September",
  "October",
  "November",
  "December",
];

const WEEKDAYS = ["Mo", "Tu", "We", "Th", "Fr", "Sa", "Su"];

interface CalendarGridProps {
  onSelect: (v: string) => void;
  selectedDate: string;
}

export function CalendarGrid({ onSelect, selectedDate }: CalendarGridProps) {
  const { colorScheme } = useColorScheme();
  const isDark = colorScheme === "dark";

  const initialDate = selectedDate ? new Date(selectedDate) : new Date();
  const [viewDate, setViewDate] = useState(
    new Date(initialDate.getFullYear(), initialDate.getMonth(), 1),
  );

  const year = viewDate.getFullYear();
  const month = viewDate.getMonth();

  // Days in current month
  const daysInMonth = new Date(year, month + 1, 0).getDate();

  // Starting day of the week (0-6), where 0 is Sunday
  let firstDayOfMonth = new Date(year, month, 1).getDay();
  // Adjust for Monday start: Mon=0 ... Sun=6
  firstDayOfMonth = firstDayOfMonth === 0 ? 6 : firstDayOfMonth - 1;

  // Days in previous month to fill the start
  const prevMonthLastDay = new Date(year, month, 0).getDate();

  const changeMonth = (delta: number) => {
    setViewDate(new Date(year, month + delta, 1));
  };

  const days = [];

  // Fill previous month days (muted)
  for (let i = firstDayOfMonth - 1; i >= 0; i--) {
    days.push({
      date: new Date(year, month - 1, prevMonthLastDay - i),
      currentMonth: false,
    });
  }

  // Fill current month days
  for (let i = 1; i <= daysInMonth; i++) {
    days.push({
      date: new Date(year, month, i),
      currentMonth: true,
    });
  }

  // Fill next month days (muted) to complete the grid (usually 42 cells for 6 weeks)
  const remaining = 42 - days.length;
  for (let i = 1; i <= remaining; i++) {
    days.push({
      date: new Date(year, month + 1, i),
      currentMonth: false,
    });
  }

  return (
    <View className="bg-card px-2 pb-6">
      <View className="flex-row justify-between items-center mb-10 mt-2">
        <Pressable
          onPress={() => changeMonth(-1)}
          className="h-12 w-12 bg-white rounded-[12px] items-center justify-center border border-border"
          style={isDark ? { backgroundColor: "#1e1e1e" } : undefined}
        >
          <ArrowLeft size={18} color="#64748b" strokeWidth={2} />
        </Pressable>

        <View className="flex-row items-center gap-2">
          <Text className="text-foreground text-base font-medium tracking-tight">
            {MONTHS[month]} {year}
          </Text>
        </View>

        <Pressable
          onPress={() => changeMonth(1)}
          className="h-12 w-12 bg-white rounded-[12px] items-center justify-center border border-border"
          style={isDark ? { backgroundColor: "#1e1e1e" } : undefined}
        >
          <ArrowRight size={18} color="#64748b" strokeWidth={2} />
        </Pressable>
      </View>

      {/* WeekDays Header: Mo Tu We Th Fr Sa Su */}
      <View className="flex-row mb-6">
        {WEEKDAYS.map((day, idx) => (
          <View key={idx} className="w-[14.28%] items-center">
            <Text className="text-[13px] font-semibold text-slate-400 opacity-80">
              {day}
            </Text>
          </View>
        ))}
      </View>

      {/* Grid */}
      <View className="flex-row flex-wrap">
        {days.map((item, i) => {
          const d = item.date;
          const iso = d.toISOString().split("T")[0];
          const isSelected = iso === selectedDate && item.currentMonth;
          const isToday = iso === new Date().toISOString().split("T")[0];

          return (
            <View
              key={i}
              className="w-[14.28%] aspect-square items-center justify-center mb-1"
            >
              <Pressable
                onPress={() => onSelect(iso)}
                className={`w-11 h-11 items-center justify-center rounded-full ${
                  isSelected ? "bg-primary" : ""
                }`}
              >
                <Text
                  className={`text-[15px] ${
                    isSelected
                      ? "text-white font-bold"
                      : item.currentMonth
                        ? "text-foreground font-medium"
                        : "text-slate-300 font-medium"
                  } ${isToday && !isSelected ? "text-primary" : ""}`}
                >
                  {d.getDate()}
                </Text>
                {isToday && !isSelected && (
                  <View className="absolute bottom-1 w-2 h-2 bg-primary rounded-full" />
                )}
              </Pressable>
            </View>
          );
        })}
      </View>
    </View>
  );
}