/**
 * 一路画面：canvas 绘制 + 缩放/平移 + 网格 + 瞄准器 + 命中反馈。
 *
 * # 为什么画在 canvas 上而不是用 CSS 变换 `<img>`
 *
 * 瞄准器必须跟着**画面**走：它标的是相机光轴上的一个点。用 DOM 摆一个 `<img>` 再叠一层
 * `transform` 的话，"图像落在哪、瞄准点落在哪"要算两遍，而两份实现迟早会不一致——表现
 * 是放大之后瞄准器偏了，恰恰发生在这件事最要紧的时候。
 *
 * 所以变换只算一次（`layout()`），图像、网格、瞄准器、伤害数字全都用同一组数画出来。
 *
 * # 尺寸与缩放的关系
 *
 * - 图像按 `contain` 放进窗格，再乘 `zoom`。
 * - **网格**画在图像矩形里，跟着缩放走：它标的是画面里的比例，用来估距离。
 * - **瞄准器**的**位置**跟着图像走，**大小**不跟着：像真瞄具一样，放大之后准星不会
 *   跟着变粗，而是覆盖画面里更小的一块——那正是放大有用武之地的原因。
 * - 镜像靠 `scale(-1, 1)`，同时把拖动方向也翻过来，否则向右拖画面会往左走。
 */

import { useEffect, useRef, type ReactNode } from "react";

import { streamClient } from "../lib/store";
import { withAlpha } from "../lib/format";
import type { CrosshairConfig, GridConfig, HitFeedbackConfig } from "../lib/types";

export interface ViewTransform {
  zoom: number;
  x: number;
  y: number;
}

export const IDENTITY_VIEW: ViewTransform = { zoom: 1, x: 0, y: 0 };

/** 缩放上下限。再多只是把像素拉大。 */
export const MIN_ZOOM = 1;
export const MAX_ZOOM = 8;
export const ZOOM_STEP = 1.25;

export interface HitPulse {
  /** 每次命中都不同，用来重启动画。 */
  seq: number;
  damage: number;
  /** `performance.now()` 时刻。 */
  at: number;
}

interface Props {
  camera: number | null;
  emptyText: string;
  mirrored: boolean;
  crosshair: CrosshairConfig | null;
  grid: GridConfig | null;
  view: ViewTransform;
  onView: (view: ViewTransform) => void;
  /** 校准模式：拖动画面来挪瞄准点。 */
  calibrating?: boolean;
  onCalibrate?: (dxFraction: number, dyFraction: number) => void;
  /** 命中脉冲。只有属于这一路的命中才该传进来。 */
  hit?: HitPulse | null;
  hitFeedback: HitFeedbackConfig;
  showZoom: boolean;
  children?: ReactNode;
}

export function VideoSurface({
  camera,
  emptyText,
  mirrored,
  crosshair,
  grid,
  view,
  onView,
  calibrating = false,
  onCalibrate,
  hit = null,
  hitFeedback,
  showZoom,
  children,
}: Props) {
  const canvasRef = useRef<HTMLCanvasElement | null>(null);

  // 绘制循环不随 props 重建，所以最新一份 props 放在 ref 里给它读。
  const props = useRef({ camera, mirrored, crosshair, grid, view, hit, hitFeedback });
  props.current = { camera, mirrored, crosshair, grid, view, hit, hitFeedback };

  const drag = useRef<{ x: number; y: number; originX: number; originY: number } | null>(null);
  const dirty = useRef(true);
  const lastFrameId = useRef<number | null>(null);

  useEffect(() => {
    dirty.current = true;
  }, [camera, mirrored, crosshair, grid, view, hit, hitFeedback]);

  // canvas 的像素尺寸跟着 CSS 尺寸与 DPR 走。不这么做的话在 Retina 上会糊。
  useEffect(() => {
    const canvas = canvasRef.current;
    if (!canvas) return;

    const resize = () => {
      const dpr = window.devicePixelRatio || 1;
      const width = Math.max(1, Math.round(canvas.clientWidth * dpr));
      const height = Math.max(1, Math.round(canvas.clientHeight * dpr));

      if (canvas.width !== width || canvas.height !== height) {
        canvas.width = width;
        canvas.height = height;
        dirty.current = true;
      }
    };

    resize();

    const observer = new ResizeObserver(resize);
    observer.observe(canvas);
    return () => observer.disconnect();
  }, []);

  useEffect(() => {
    const canvas = canvasRef.current;
    if (!canvas) return;

    let raf = 0;

    const loop = (timestamp: number) => {
      raf = requestAnimationFrame(loop);

      const current = props.current;
      const frame = streamClient().latest(current.camera);

      if (frame && frame.frameId !== lastFrameId.current) {
        lastFrameId.current = frame.frameId;
        dirty.current = true;
      }

      // 命中动画期间必须持续重绘，否则闪红/伤害数字只画了一帧就停住。
      //
      // **抖动没有了**（见 `HitFeedbackConfig::shake` 的文档）：不再有"整幅图跟着晃"的
      // 那一路，所以这里也不再需要因为抖动而复绘。
      const pulseAge = current.hit ? timestamp - current.hit.at : Number.POSITIVE_INFINITY;
      const animating =
        pulseAge < 700 && (current.hitFeedback.marker || current.hitFeedback.flash);

      if (!dirty.current && !animating) return;
      dirty.current = false;

      draw(canvas, current, frame, timestamp);
    };

    raf = requestAnimationFrame(loop);
    return () => cancelAnimationFrame(raf);
  }, []);

  // ---- 输入 ----

  const onWheel = (event: React.WheelEvent<HTMLDivElement>) => {
    const factor = event.deltaY > 0 ? 1 / ZOOM_STEP : ZOOM_STEP;
    const zoom = clamp(view.zoom * factor, MIN_ZOOM, MAX_ZOOM);

    // 缩回 1 时顺便归位：此时画面完整可见，平移没有意义，留着会让下一次放大从偏移位置
    // 开始，看起来像"跳了一下"。
    onView(zoom <= MIN_ZOOM ? IDENTITY_VIEW : { ...view, zoom });
  };

  const onPointerDown = (event: React.PointerEvent<HTMLDivElement>) => {
    event.currentTarget.setPointerCapture(event.pointerId);
    drag.current = { x: event.clientX, y: event.clientY, originX: view.x, originY: view.y };
  };

  const onPointerMove = (event: React.PointerEvent<HTMLDivElement>) => {
    const start = drag.current;
    if (!start) return;

    const dx = event.clientX - start.x;
    const dy = event.clientY - start.y;

    if (calibrating) {
      // 校准：把屏幕上的位移换算成画面里的比例位移。用当前显示出来的图像尺寸做分母，
      // 所以放大之后校准更精细——这正是需要的。
      const box = canvasRef.current;
      if (!box || !onCalibrate) return;

      const frame = streamClient().latest(camera);
      if (!frame) return;

      const { drawWidth, drawHeight } = layout(box, frame.width, frame.height, view);
      if (drawWidth <= 0 || drawHeight <= 0) return;

      // 一次移动一小步，然后把起点挪过来。
      drag.current = { ...start, x: event.clientX, y: event.clientY };
      const sign = mirrored ? -1 : 1;
      onCalibrate((sign * dx) / drawWidth, dy / drawHeight);
      return;
    }

    if (view.zoom <= MIN_ZOOM) return;

    // 镜像时把横向拖动也翻过来：否则向右拖，画面往左走，看起来像拖动坏了。
    const sign = mirrored ? -1 : 1;
    onView({ ...view, x: start.originX + sign * dx, y: start.originY + dy });
  };

  const endDrag = () => {
    drag.current = null;
  };

  const cursor = calibrating ? "crosshair" : view.zoom > MIN_ZOOM ? "grab" : "default";

  return (
    <div
      className="video-surface"
      style={{ cursor }}
      onWheel={onWheel}
      onPointerDown={onPointerDown}
      onPointerMove={onPointerMove}
      onPointerUp={endDrag}
      onPointerCancel={endDrag}
      onDoubleClick={() => onView(IDENTITY_VIEW)}
    >
      <canvas ref={canvasRef} className="video-canvas" />

      {emptyText !== "" && <div className="video-empty">{emptyText}</div>}

      {showZoom && view.zoom > MIN_ZOOM + 0.05 && (
        <div className="video-badge video-badge--zoom">×{view.zoom.toFixed(2)}</div>
      )}

      {(view.zoom > MIN_ZOOM + 0.05 || view.x !== 0 || view.y !== 0) && (
        <button className="video-badge video-badge--reset" onClick={() => onView(IDENTITY_VIEW)}>
          复位
        </button>
      )}

      {calibrating && <div className="video-calibrating">校准中：拖动画面挪动瞄准点</div>}

      {children}
    </div>
  );
}

// ---------------------------------------------------------------------------
// 绘制
// ---------------------------------------------------------------------------

interface CanvasProps {
  camera: number | null;
  mirrored: boolean;
  crosshair: CrosshairConfig | null;
  grid: GridConfig | null;
  view: ViewTransform;
  hit: HitPulse | null;
  hitFeedback: HitFeedbackConfig;
}

interface Box {
  clientWidth: number;
  clientHeight: number;
}

/** 图像在窗格里的落点与大小（CSS 像素）。 */
function layout(box: Box, frameWidth: number, frameHeight: number, view: ViewTransform) {
  const width = box.clientWidth;
  const height = box.clientHeight;

  if (frameWidth <= 0 || frameHeight <= 0) {
    return { left: 0, top: 0, drawWidth: 0, drawHeight: 0 };
  }

  const fit = Math.min(width / frameWidth, height / frameHeight);
  const drawWidth = frameWidth * fit * view.zoom;
  const drawHeight = frameHeight * fit * view.zoom;

  return {
    left: (width - drawWidth) / 2 + view.x,
    top: (height - drawHeight) / 2 + view.y,
    drawWidth,
    drawHeight,
  };
}

function draw(
  canvas: HTMLCanvasElement,
  current: CanvasProps,
  frame: { bitmap: ImageBitmap; width: number; height: number } | undefined,
  timestamp: number,
) {
  const dpr = window.devicePixelRatio || 1;
  const width = canvas.clientWidth;
  const height = canvas.clientHeight;

  const ctx = canvas.getContext("2d");
  if (!ctx) return;

  ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
  ctx.clearRect(0, 0, width, height);

  const box = { clientWidth: width, clientHeight: height };

  // 没有画面时把瞄准器留在窗格中心：录像断了，准星不该跟着消失。
  const fallback = { left: 0, top: 0, drawWidth: 0, drawHeight: 0 };
  const geometry = frame
    ? layout(box, frame.width, frame.height, current.view)
    : fallback;

  if (frame) {
    ctx.save();

    if (current.mirrored) {
      ctx.translate(width, 0);
      ctx.scale(-1, 1);
    }

    // 放大超过 3 倍时关掉插值：这时候要看的是像素本身，双线性插值只会把它糊掉。
    ctx.imageSmoothingEnabled = current.view.zoom < 3;
    ctx.drawImage(frame.bitmap, geometry.left, geometry.top, geometry.drawWidth, geometry.drawHeight);
    ctx.restore();

    if (current.grid?.visible) {
      drawGrid(ctx, geometry, current.grid);
    }
  }

  // 瞄准点的屏幕位置：图像坐标系里的 (0.5 + offsetX, 0.5 + offsetY)。
  const crosshair = current.crosshair;
  let aimX = width / 2;
  let aimY = height / 2;

  if (crosshair && frame && geometry.drawWidth > 0) {
    const rawX = geometry.left + (0.5 + crosshair.offsetX) * geometry.drawWidth;
    aimX = current.mirrored ? width - rawX : rawX;
    aimY = geometry.top + (0.5 + crosshair.offsetY) * geometry.drawHeight;
  }

  if (crosshair?.visible) {
    drawCrosshair(ctx, aimX, aimY, Math.min(width, height), crosshair);
  }

  // 伤害数字：画在屏幕坐标里，不跟着缩放走。
  if (current.hit && current.hitFeedback.marker) {
    const age = timestamp - current.hit.at;
    if (age >= 0 && age < 700) {
      const progress = age / 700;

      ctx.save();
      ctx.globalAlpha = 1 - progress;
      ctx.fillStyle = "#ff8a8a";
      ctx.font = `600 ${Math.round(Math.max(14, Math.min(width, height) * 0.05))}px ui-sans-serif, system-ui, sans-serif`;
      ctx.textAlign = "left";
      ctx.textBaseline = "middle";
      ctx.fillText(`-${current.hit.damage}`, aimX + 24, aimY - 26 - progress * 26);
      ctx.restore();
    }
  }
}

function drawGrid(
  ctx: CanvasRenderingContext2D,
  geometry: { left: number; top: number; drawWidth: number; drawHeight: number },
  grid: GridConfig,
) {
  if (geometry.drawWidth <= 0 || geometry.drawHeight <= 0) return;

  ctx.save();
  ctx.strokeStyle = `rgba(255, 255, 255, ${grid.opacity})`;
  ctx.lineWidth = 1;

  const x0 = geometry.left;
  const y0 = geometry.top;
  const x1 = x0 + geometry.drawWidth;
  const y1 = y0 + geometry.drawHeight;

  if (grid.style === "thirds") {
    for (const fraction of [1 / 3, 2 / 3]) {
      line(ctx, x0 + geometry.drawWidth * fraction, y0, x0 + geometry.drawWidth * fraction, y1);
      line(ctx, x0, y0 + geometry.drawHeight * fraction, x1, y0 + geometry.drawHeight * fraction);
    }
  } else if (grid.style === "squares") {
    const divisions = Math.max(2, grid.divisions);
    for (let i = 1; i < divisions; i += 1) {
      const fraction = i / divisions;
      line(ctx, x0 + geometry.drawWidth * fraction, y0, x0 + geometry.drawWidth * fraction, y1);
      line(ctx, x0, y0 + geometry.drawHeight * fraction, x1, y0 + geometry.drawHeight * fraction);
    }
  } else {
    // 中心十字。
    line(ctx, x0 + geometry.drawWidth / 2, y0, x0 + geometry.drawWidth / 2, y1);
    line(ctx, x0, y0 + geometry.drawHeight / 2, x1, y0 + geometry.drawHeight / 2);
  }

  ctx.restore();
}

function line(ctx: CanvasRenderingContext2D, x0: number, y0: number, x1: number, y1: number) {
  // 半像素偏移，让 1px 的线落在像素中心而不是跨两个像素发虚。
  ctx.beginPath();
  ctx.moveTo(Math.round(x0) + 0.5, Math.round(y0) + 0.5);
  ctx.lineTo(Math.round(x1) + 0.5, Math.round(y1) + 0.5);
  ctx.stroke();
}

function drawCrosshair(
  ctx: CanvasRenderingContext2D,
  cx: number,
  cy: number,
  shortSide: number,
  config: CrosshairConfig,
) {
  const arm = Math.max(3, config.size * shortSide);
  const gap = config.gap * shortSide;
  const thickness = Math.max(1, config.thickness * shortSide);

  // 外描一圈深色：浅色背景下亮绿准星会消失，这一圈让它始终看得见。
  const halo = withAlpha("#000000", 0.55);

  const stroke = (color: string, width: number, radius: number) => {
    ctx.strokeStyle = color;
    ctx.lineWidth = width;
    ctx.beginPath();

    if (config.style === "circle-dot") {
      ctx.arc(cx, cy, radius, 0, Math.PI * 2);
    } else {
      // 四臂，中心留 gap 的空隙。
      ctx.moveTo(cx - radius, cy);
      ctx.lineTo(cx - gap, cy);
      ctx.moveTo(cx + gap, cy);
      ctx.lineTo(cx + radius, cy);
      ctx.moveTo(cx, cy - radius);
      ctx.lineTo(cx, cy - gap);
      ctx.moveTo(cx, cy + gap);
      ctx.lineTo(cx, cy + radius);
    }

    ctx.stroke();
  };

  stroke(halo, thickness + 2, arm + 1);
  stroke(config.color, thickness, arm);

  // 中心点：`cross` 之外都画。
  if (config.style !== "cross") {
    const dot = Math.max(1.2, thickness * 0.9);
    ctx.fillStyle = halo;
    ctx.beginPath();
    ctx.arc(cx, cy, dot + 1, 0, Math.PI * 2);
    ctx.fill();

    ctx.fillStyle = config.color;
    ctx.beginPath();
    ctx.arc(cx, cy, dot, 0, Math.PI * 2);
    ctx.fill();
  }
}

function clamp(value: number, min: number, max: number): number {
  return Math.min(max, Math.max(min, value));
}