import React, { useRef, useState } from 'react';
import './Slider.css';

/* 滑动选择器（移动端）— 规格 §35
   轨道可视高度只有 4px，但**整条热区高度是 44px**：直接点轨道任意位置也要能跳到该处。
   浏览器端手势用 Pointer Events（pointerdown / pointermove / pointerup + setPointerCapture）；
   uni-app 端同一手势改用 @touch*（小程序与 App 端没有 PointerEvent）。
   值按 step 吸附并夹在 [min, max]；mode=range 时左值不越过右值。
   受控：本端不存储值，只回传目标值 onChange，是否采纳由宿主决定。 */

export default function Slider({
  value = 0,
  valueMax = 100,
  min = 0,
  max = 100,
  step = 1,
  mode = 'single',
  marks = false,
  showValue = true,
  disabled = false,
  label = '滑动选择',
  onChange,
  children = null,
}) {
  const railRef = useRef(null);
  const [dragging, setDragging] = useState(false);
  const [active, setActive] = useState(-1);
  /* 双滑块的两个值；单滑块只用到第一个 */
  const [inner, setInner] = useState(null);
  const values = inner || (mode === 'range' ? [value, valueMax] : [value]);
  const range = mode === 'range';

  const cls =
    'kole-m-slider' +
    (range ? ' kole-m-slider--range' : '') +
    (marks ? ' kole-m-slider--marks' : '') +
    (dragging ? ' is-dragging' : '') +
    (disabled ? ' is-disabled' : '');

  const ratio = (v) => (max === min ? 0 : (v - min) / (max - min));
  const clamp = (v) => {
    const snapped = Math.round((v - min) / step) * step + min;
    return Math.max(min, Math.min(max, snapped));
  };

  function valueAt(clientX) {
    const el = railRef.current;
    if (!el) return min;
    const rect = el.getBoundingClientRect();
    if (!rect.width) return min;
    return clamp(min + ((clientX - rect.left) / rect.width) * (max - min));
  }

  function nearest(v) {
    if (!range) return 0;
    return Math.abs(values[0] - v) <= Math.abs(values[1] - v) ? 0 : 1;
  }

  function commit(index, v) {
    /* 双滑块：左值不越过右值、右值不越过左值（各留一个 step 的间距） */
    let next = clamp(v);
    if (range) {
      const other = values[1 - index];
      next = index === 0 ? Math.min(next, other - step) : Math.max(next, other + step);
    }
    const out = range ? [values[0], values[1]] : [next];
    out[index] = next;
    setInner(out);
    if (onChange) onChange(range ? out : out[0]);
  }

  /* 手势起止都放在根元素上：整个控件（含两侧留白）都是有效起点 */
  function onPointerDown(e) {
    if (disabled) return;
    if (e.target && e.target.closest && e.target.closest('.kole-m-slider__value')) return;
    const v = valueAt(e.clientX);
    setActive(nearest(v));
    setDragging(true);
    commit(nearest(v), v);
    const el = railRef.current;
    if (el && el.setPointerCapture) {
      try {
        el.setPointerCapture(e.pointerId);
      } catch (err) {
        /* 指针捕获不可用时靠冒泡事件继续跟随 */
      }
    }
  }

  function onPointerMove(e) {
    if (active < 0) return;
    commit(active, valueAt(e.clientX));
  }

  function onPointerUp() {
    if (active < 0) return;
    setActive(-1);
    setDragging(false);
  }

  function onKeyDown(e) {
    if (disabled || range) return;
    const delta =
      e.key === 'ArrowLeft' || e.key === 'ArrowDown' ? -step : e.key === 'ArrowRight' || e.key === 'ArrowUp' ? step : 0;
    if (!delta) return;
    e.preventDefault();
    commit(0, values[0] + delta);
  }

  return (
    <div
      className={cls}
      onPointerDown={onPointerDown}
      onPointerMove={onPointerMove}
      onPointerUp={onPointerUp}
      onPointerCancel={onPointerUp}
      onKeyDown={onKeyDown}
    >
      <span className="kole-m-slider__rail" role={range ? 'group' : 'slider'} tabIndex={disabled ? undefined : 0} ref={railRef} aria-label={label} aria-valuemin={min} aria-valuemax={max} aria-valuenow={range ? undefined : values[0]}>
        <span className="kole-m-slider__track">
          <span
            className="kole-m-slider__filled"
            style={range ? { left: ratio(values[0]) * 100 + '%', right: 100 - ratio(values[1]) * 100 + '%' } : undefined}
          />
          {/* 刻度点：marks=true 时按 step 的可整除位置画（只标位置，不写文案） */}
          {marks
            ? [0, 1, 2, 3, 4].map((i) => (
                <span className="kole-m-slider__mark" key={'m' + i} style={{ left: i * 25 + '%' }} />
              ))
            : null}
          {range
            ? values.map((v, i) => (
                <span className="kole-m-slider__thumb" key={i} style={{ left: ratio(v) * 100 + '%' }} />
              ))
            : <span className="kole-m-slider__thumb" style={{ left: ratio(values[0]) * 100 + '%' }} />}
        </span>
      </span>
      {showValue ? (
        <span className="kole-m-slider__value">{range ? values[0] + '~' + values[1] : values[0]}</span>
      ) : null}
      {children}
    </div>
  );
}