import { effect, h, signal } from '@ui-arch/frame';
import type { Signal } from '@ui-arch/frame';
import { bindOutside, pushOverlay } from './overlay.js';
import { flip } from './position.js';
import type { DatePickerProps, DatePreset } from './types.js';
import { fmt, pad, parse, shiftDay, today } from './dateKit.js';

/*** 日期选择：单月网格 + 上下月翻页 + 今天快捷键，value 信号双向绑定，方向键/PageUp/PageDown 可导航 ***/ 
export function datePicker(props: DatePickerProps): HTMLElement {
  // —— 状态集中声明 ——
  const value: Signal<string> = props.value ?? signal(''); // 已选日期（区间模式下是起点）
  const end: Signal<string> = props.end ?? signal('');     // 区间终点，非区间模式恒为空
  const open = signal(false);                             // 弹层开合
  const place = signal<'top' | 'bottom'>('bottom');       // 实际方位
  const initial = parse(value()) ?? today();              // 初始视图：跟随已选，否则今天
  const view = signal<[number, number]>([initial[0], initial[1]]); // 当前展示的年月
  const focus = signal<string>(value() || fmt(...today()));        // 键盘焦点日
  let releaseEsc: (() => void) | null = null;             // Esc 栈注销函数

  const grid = h('div', { class: 'ua-datepicker-grid', role: 'grid' }) as HTMLElement;
  const label = h('span', { class: 'ua-datepicker-label' }) as HTMLElement;
  const head = h(
    'div',
    { class: 'ua-datepicker-head' },
    h('button', { type: 'button', class: 'ua-datepicker-nav', 'aria-label': '上一月', onClick: () => turn(-1) }, '‹'),
    label,
    h('button', { type: 'button', class: 'ua-datepicker-nav', 'aria-label': '下一月', onClick: () => turn(1) }, '›'),
  );
  const presetRow = props.range && props.presets?.length // 快捷区间只在区间模式有意义
    ? h('div', { class: 'ua-datepicker-presets' }, ...props.presets.map((p) => h('button', {
        type: 'button', class: 'ua-datepicker-preset', onClick: () => applyPreset(p),
      }, p.label)))
    : null;
  const pop = h(
    'div',
    { class: () => `ua-datepicker-pop${open() ? ' ua-open' : ''}${place() === 'top' ? ' is-flip' : ''}` },
    head,
    ...(presetRow ? [presetRow] : []),
    h('div', { class: 'ua-datepicker-week' }, ...['日', '一', '二', '三', '四', '五', '六'].map((w) => h('span', {}, w))),
    grid,
    h('div', { class: 'ua-datepicker-foot' }, h('button', { type: 'button', class: 'ua-datepicker-today', onClick: () => commit(fmt(...today())) }, '今天')),
  ) as HTMLElement;

  /*** 翻月：只改视图，不改已选值；跨年自动进位 ***/
  function turn(delta: number): void {
    const [y, m] = view();
    const d = new Date(y, m + delta, 1);
    view([d.getFullYear(), d.getMonth()]);
  }

  /*** 提交：单日模式写值即收起；区间模式首点定起点并留在弹层，次点补终点后收起 ***/
  function commit(date: string): void {
    if (!props.range) {
      value(date);
      props.onChange?.(date);
      open(false);
      trigger.focus();
      return;
    }
    if (!value() || end()) { // 未选起点或上一段区间已完整：从这个日期重开一段
      value(date);
      end('');
      render(); // 清掉上一段的区间底色
      return;
    }
    const [start, stop] = date < value() ? [date, value()] : [value(), date]; // 点早了就自动交换
    value(start);
    end(stop);
    props.onRangeChange?.(start, stop);
    open(false);
    trigger.focus();
  }

  /*** 应用快捷区间：days 优先（今天往前共 N 天），否则用绝对 from/to；按 min/max 钳制后写值并收起 ***/
  function applyPreset(p: DatePreset): void {
    const stop = p.days ? fmt(...today()) : (p.to || fmt(...today()));
    const start = p.days ? shiftDay(stop, -(p.days - 1)) : (p.from || stop);
    const [lo, hi] = start <= stop ? [start, stop] : [stop, start]; // 防御：from 晚于 to 时自动交换
    const fit = (v: string): string => (props.min && v < props.min ? props.min : props.max && v > props.max ? props.max : v); // 钳进合法区间
    value(fit(lo));
    end(fit(hi));
    props.onRangeChange?.(value(), end());
    open(false);
    trigger.focus();
  }

  /*** 是否越界：min / max 为闭区间，缺省视为不限制 ***/
  const outOfRange = (date: string): boolean => (props.min ? date < props.min : false) || (props.max ? date > props.max : false);

  /*** 重绘网格：前置空位对齐星期、今天/选中/焦点分别打标 ***/
  function render(): void {
    const [y, m] = view();
    const lead = new Date(y, m, 1).getDay();              // 当月 1 号是周几
    const total = new Date(y, m + 1, 0).getDate();        // 当月天数
    const cells: HTMLElement[] = [];
    for (let i = 0; i < lead; i++) cells.push(h('span', { class: 'ua-datepicker-blank' })); // 月初留白
    for (let d = 1; d <= total; d++) {
      const date = fmt(y, m, d);
      const dead = outOfRange(date);
      const edge = date === value() || Boolean(props.range && end() && date === end()); // 区间两端
      const between = Boolean(props.range && value() && end() && date > value() && date < end()); // 区间内部
      const cls = `ua-datepicker-day${edge ? ' is-selected' : ''}${between ? ' is-in-range' : ''}${date === fmt(...today()) ? ' is-today' : ''}${dead ? ' is-disabled' : ''}`;
      cells.push(
        h('button', {
          type: 'button',
          class: cls,
          role: 'gridcell',
          tabindex: date === focus() ? '0' : '-1', // 漫游 tabindex：只有焦点日可 Tab 进入
          'aria-selected': String(edge),
          disabled: dead,
          'aria-label': date,
          onClick: () => commit(date),
        }, String(d)),
      );
    }
    grid.replaceChildren(...cells);
    label.textContent = `${y} 年 ${m + 1} 月`;
    requestAnimationFrame(() => {
      if (!open()) return; // 卫语句：收起时不抢焦点
      (grid.querySelector('.ua-datepicker-day[tabindex="0"]') as HTMLElement | null)?.focus();
    });
  }

  /*** 触发器文案：单日回显日期；区间回显「起 ~ 止」，只定了起点时后面跟省略号 ***/
  const labelText = (): string => {
    if (!props.range) return value() || props.placeholder || '请选择日期';
    if (!value()) return props.placeholder || '请选择日期范围';
    return end() ? `${value()} ~ ${end()}` : `${value()} ~ …`;
  };
  const trigger = h(
    'button',
    {
      type: 'button',
      class: 'ua-datepicker-trigger',
      'aria-haspopup': 'dialog',
      'aria-expanded': () => String(open()),
      disabled: props.disabled,
      onClick: () => {
        if (!open()) {
          const p = parse(value()) ?? today(); // 打开时视图对准已选日期（无选则今天）
          view([p[0], p[1]]);
          focus(value() || fmt(...p));
        }
        open(!open());
      },
    },
    h('span', { class: () => `ua-datepicker-value${value() ? '' : ' is-empty'}` }, () => labelText()),
    h('span', { class: 'ua-datepicker-caret', 'aria-hidden': 'true' }, '▤'),
  );
  const root = h('div', { class: () => `ua-datepicker${open() ? ' ua-open' : ''}` }, trigger, pop) as HTMLElement;

  // 键盘：←→ 逐日、↑↓ 逐周、PageUp/PageDown 逐月、Enter 提交，Esc 交给弹层栈
  pop.addEventListener('keydown', (e: KeyboardEvent) => {
    const step: Record<string, number> = { ArrowLeft: -1, ArrowRight: 1, ArrowUp: -7, ArrowDown: 7 };
    if (step[e.key]) {
      e.preventDefault();
      const next = shiftDay(focus(), step[e.key]);
      const p = parse(next) ?? today();
      focus(next);
      if (p[0] !== view()[0] || p[1] !== view()[1]) view([p[0], p[1]]); // 跨月自动翻页
      render();
      return;
    }
    if (e.key === 'PageUp' || e.key === 'PageDown') { e.preventDefault(); turn(e.key === 'PageUp' ? -1 : 1); return; }
    if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); if (!outOfRange(focus())) commit(focus()); }
  });
  bindOutside(root, open, () => open(false)); // 点外部收起：仅展开期间挂监听，收起即摘
  effect(render); // 依赖 view / value / focus
  effect(() => {
    if (open()) releaseEsc ??= pushOverlay(() => { open(false); trigger.focus(); }); // 入栈逐层关闭
    else { releaseEsc?.(); releaseEsc = null; }
  });
  effect(() => { if (open()) place(flip(trigger, pop, 'bottom')); }); // 空间不足自动翻转
  return root;
}