"use client";

import React, { useMemo } from "react";
import { cn } from "@/lib/utils";
import { DateCell, ZoomLevel } from "../types";
import { dayLabels, monthLabels } from "../config";

interface TimelineHeaderProps {
  /** 시작 날짜 */
  startDate: Date;
  /** 종료 날짜 */
  endDate: Date;
  /** 줌 레벨 */
  zoomLevel: ZoomLevel;
  /** 셀 너비 */
  cellWidth: number;
  /** 헤더 높이 */
  headerHeight: number;
  /** 리소스 컬럼 너비 */
  resourceColumnWidth: number;
  /** 오늘 표시선 */
  showTodayLine?: boolean;
}

/**
 * 날짜 범위 내의 모든 날짜 셀 생성
 */
const generateDateCells = (
  startDate: Date,
  endDate: Date,
  zoomLevel: ZoomLevel
): DateCell[] => {
  const cells: DateCell[] = [];
  const today = new Date();
  today.setHours(0, 0, 0, 0);

  const current = new Date(startDate);
  current.setHours(0, 0, 0, 0);

  while (current <= endDate) {
    const date = new Date(current);
    const dayOfWeek = date.getDay();
    const isToday = date.getTime() === today.getTime();
    const isWeekend = dayOfWeek === 0 || dayOfWeek === 6;
    const isMonthStart = date.getDate() === 1;

    let label = "";
    if (zoomLevel === "day") {
      label = `${date.getDate()}(${dayLabels[dayOfWeek]})`;
    } else if (zoomLevel === "week") {
      // 주간: 월요일 기준 주 시작
      if (dayOfWeek === 1 || cells.length === 0) {
        label = `${date.getMonth() + 1}/${date.getDate()}`;
      }
    } else if (zoomLevel === "month") {
      // 월간: 월 시작일만 표시
      if (isMonthStart || cells.length === 0) {
        label = monthLabels[date.getMonth()];
      }
    }

    cells.push({
      date,
      label,
      isToday,
      isWeekend,
      isMonthStart,
    });

    current.setDate(current.getDate() + 1);
  }

  return cells;
};

/**
 * 월 헤더 그룹 생성 (상단 행)
 */
const generateMonthGroups = (
  cells: DateCell[]
): { month: string; year: number; count: number }[] => {
  const groups: { month: string; year: number; count: number }[] = [];

  cells.forEach((cell) => {
    const month = monthLabels[cell.date.getMonth()];
    const year = cell.date.getFullYear();

    if (
      groups.length === 0 ||
      groups[groups.length - 1].month !== month ||
      groups[groups.length - 1].year !== year
    ) {
      groups.push({ month, year, count: 1 });
    } else {
      groups[groups.length - 1].count++;
    }
  });

  return groups;
};

export function TimelineHeader({
  startDate,
  endDate,
  zoomLevel,
  cellWidth,
  headerHeight,
  resourceColumnWidth,
  showTodayLine = true,
}: TimelineHeaderProps) {
  // 날짜 셀 생성
  const dateCells = useMemo(
    () => generateDateCells(startDate, endDate, zoomLevel),
    [startDate, endDate, zoomLevel]
  );

  // 월 그룹 생성
  const monthGroups = useMemo(() => generateMonthGroups(dateCells), [dateCells]);

  // 오늘 위치 계산
  const todayPosition = useMemo(() => {
    const today = new Date();
    today.setHours(0, 0, 0, 0);

    const todayIndex = dateCells.findIndex(
      (cell) => cell.date.getTime() === today.getTime()
    );

    if (todayIndex === -1) return null;

    return resourceColumnWidth + todayIndex * cellWidth + cellWidth / 2;
  }, [dateCells, cellWidth, resourceColumnWidth]);

  return (
    <div
      className="sticky top-0 z-20 border-b bg-background"
      style={{ height: headerHeight }}
    >
      {/* 상단 행: 월/년도 */}
      <div className="flex" style={{ height: headerHeight / 2 }}>
        {/* 리소스 컬럼 헤더 */}
        <div
          className="flex shrink-0 items-center justify-center border-r bg-muted/50 text-[10px] font-medium sm:text-sm"
          style={{ width: resourceColumnWidth }}
        >
          리소스
        </div>

        {/* 월 그룹 */}
        {monthGroups.map((group, idx) => (
          <div
            key={`${group.year}-${group.month}-${idx}`}
            className="flex items-center justify-center border-r text-[10px] font-medium text-muted-foreground sm:text-xs"
            style={{ width: group.count * cellWidth }}
          >
            {group.year}년 {group.month}
          </div>
        ))}
      </div>

      {/* 하단 행: 일자 */}
      <div className="flex" style={{ height: headerHeight / 2 }}>
        {/* 리소스 컬럼 (빈칸) */}
        <div
          className="shrink-0 border-r bg-muted/50"
          style={{ width: resourceColumnWidth }}
        />

        {/* 날짜 셀 */}
        {dateCells.map((cell, idx) => (
          <div
            key={idx}
            className={cn(
              "flex items-center justify-center border-r text-[10px] sm:text-xs",
              cell.isToday && "bg-primary/10 font-bold text-primary",
              cell.isWeekend && !cell.isToday && "bg-muted/30 text-muted-foreground",
              cell.isMonthStart && "border-l-2 border-l-primary/30"
            )}
            style={{ width: cellWidth }}
          >
            {cell.label}
          </div>
        ))}
      </div>

      {/* 오늘 표시선 */}
      {showTodayLine && todayPosition !== null && (
        <div
          className="pointer-events-none absolute bottom-0 top-0 z-30 w-0.5 bg-primary"
          style={{ left: todayPosition }}
        />
      )}
    </div>
  );
}