import { DOCUMENT } from '@angular/common';
import {
  afterNextRender,
  Component,
  DestroyRef,
  ElementRef,
  inject,
  NgZone,
  ViewChild,
} from '@angular/core';
import {
  isBrowserPlatform,
  prefersCoarsePointer,
  prefersReducedMotion,
} from '../../core/platform/browser';
import { Dot } from '../../models/dot';

@Component({
  selector: 'app-dot-background',
  imports: [],
  templateUrl: './dot-background.html',
  styleUrl: './dot-background.scss',
  host: {
    'aria-hidden': 'true',
  },
})
export class DotBackground {
  @ViewChild('canvas') canvasRef!: ElementRef<HTMLCanvasElement>;

  private readonly document = inject(DOCUMENT);
  private readonly ngZone = inject(NgZone);
  private readonly destroyRef = inject(DestroyRef);
  private readonly isBrowser = isBrowserPlatform();
  private readonly coarsePointer = prefersCoarsePointer();
  private readonly reducedMotion = prefersReducedMotion();

  private ctx: CanvasRenderingContext2D | undefined;
  private dots: Dot[] = [];
  private mouse = { x: -1000, y: -1000 };
  private animationId = 0;
  private resizeFrameId = 0;
  private loopActive = false;
  private tornDown = false;
  private readonly teardowns: Array<() => void> = [];

  private readonly INITIAL_DOT_COUNT_MIN = 6;
  private readonly INITIAL_DOT_COUNT_MAX = 24;
  private readonly INITIAL_DOT_COUNT_MAX_COARSE = 12;
  private readonly INITIAL_DOT_AREA_DIVISOR = 130_000;
  private readonly MAX_DOT_COUNT = 100;
  private readonly MAX_DOT_COUNT_MOBILE = 40;
  private readonly COLORS = ['#6366f1', '#8b5cf6', '#a855f7', '#3b82f6'];
  private readonly MOUSE_RADIUS = 150;

  private ballSpawnId = 0;
  private ballSpawnNextColor = 0;

  constructor() {
    this.destroyRef.onDestroy(() => this.teardown());

    afterNextRender(() => {
      this.init();
    });
  }

  private view(): Window | null {
    return this.document.defaultView;
  }

  private init(): void {
    if (this.tornDown || !this.isBrowser) {
      return;
    }

    const view = this.view();

    if (!view) {
      return;
    }

    const canvas = this.canvasRef?.nativeElement;

    if (!canvas) {
      return;
    }

    let ctx: CanvasRenderingContext2D | null = null;

    try {
      ctx = canvas.getContext('2d');
    } catch {
      return;
    }

    if (!ctx) {
      return;
    }

    this.ctx = ctx;
    this.resize();
    this.initDots();

    this.listen(view, 'resize', this.onResize);
    this.listen(this.document, 'visibilitychange', this.onVisibilityChange);

    if (!this.reducedMotion && !this.coarsePointer) {
      this.listen(view, 'mousemove', this.onMouseMove);
      this.listen(view, 'click', this.onMouseClick);
    }

    if (this.reducedMotion) {
      this.drawFrame();
      return;
    }

    this.ngZone.runOutsideAngular(() => this.startLoop());
  }

  private listen(target: EventTarget, type: string, handler: EventListener): void {
    target.addEventListener(type, handler);
    this.teardowns.push(() => target.removeEventListener(type, handler));
  }

  private requestFrame(callback: FrameRequestCallback): number {
    const view = this.view();
    return view ? view.requestAnimationFrame(callback) : 0;
  }

  private cancelFrame(id: number): void {
    const view = this.view();

    if (!view || id === 0) {
      return;
    }

    view.cancelAnimationFrame(id);
  }

  private startLoop(): void {
    if (this.loopActive || this.reducedMotion || this.tornDown) {
      return;
    }

    this.loopActive = true;
    this.scheduleAnimate();
  }

  private stopLoop(): void {
    this.loopActive = false;
    this.cancelFrame(this.animationId);
    this.animationId = 0;
  }

  private scheduleAnimate(): void {
    this.animationId = this.requestFrame(this.animate);
  }

  private teardown(): void {
    if (this.tornDown) {
      return;
    }

    this.tornDown = true;
    this.stopLoop();
    this.cancelFrame(this.resizeFrameId);
    this.resizeFrameId = 0;

    for (const dispose of this.teardowns) {
      dispose();
    }

    this.teardowns.length = 0;
  }

  private onResize = (): void => {
    if (this.resizeFrameId !== 0) {
      return;
    }

    this.resizeFrameId = this.requestFrame(() => {
      this.resizeFrameId = 0;
      this.resize();
    });
  };

  private onVisibilityChange = (): void => {
    if (this.document.hidden) {
      this.stopLoop();
      return;
    }

    if (!this.reducedMotion) {
      this.ngZone.runOutsideAngular(() => this.startLoop());
    }
  };

  private resize = (): void => {
    const view = this.view();
    const canvas = this.canvasRef?.nativeElement;

    if (!view || !canvas) {
      return;
    }

    const width = view.innerWidth;
    const height = view.innerHeight;

    const dx = width === 0 ? 0 : Math.abs(width - canvas.width) / width;
    const dy = height === 0 ? 0 : Math.abs(height - canvas.height) / height;

    if (!this.coarsePointer || dy > 0.2 || dx > 0.05) {
      canvas.width = width;
      canvas.height = height;

      for (const dot of this.dots) {
        dot.x = Math.max(dot.radius, Math.min(width - dot.radius, dot.x));
        dot.y = Math.max(dot.radius, Math.min(height - dot.radius, dot.y));
      }

      if (this.reducedMotion && this.ctx) {
        this.drawFrame();
      }
    }
  };

  private onMouseMove = (event: Event): void => {
    if (!(event instanceof MouseEvent)) {
      return;
    }

    const view = this.view();
    const canvas = this.canvasRef?.nativeElement;

    if (!view || !canvas) {
      return;
    }

    this.mouse.x = (event.clientX / view.innerWidth) * canvas.width;
    this.mouse.y = (event.clientY / view.innerHeight) * canvas.height;
  };

  private onMouseClick = (): void => {
    const dot = this.spawnDot();
    dot.x = this.mouse.x;
    dot.y = this.mouse.y;
  };

  private targetDotCount(width: number, height: number): number {
    const maxInitial = this.coarsePointer
      ? this.INITIAL_DOT_COUNT_MAX_COARSE
      : this.INITIAL_DOT_COUNT_MAX;
    const area = Math.max(0, width) * Math.max(0, height);
    const fromArea = Math.round(area / this.INITIAL_DOT_AREA_DIVISOR);
    return Math.min(maxInitial, Math.max(this.INITIAL_DOT_COUNT_MIN, fromArea));
  }

  private spawnDot(): Dot {
    const dotId = this.ballSpawnId++;
    const maxCount = this.coarsePointer ? this.MAX_DOT_COUNT_MOBILE : this.MAX_DOT_COUNT;
    let dot: Dot;

    if (dotId < maxCount) {
      dot = {
        x: 0,
        y: 0,
        vx: 0,
        vy: 0,
        radius: 1,
        color: '#000000',
      };

      this.dots.push(dot);
    } else {
      dot = this.dots[dotId % this.dots.length];
    }

    this.populateDot(dot);

    return dot;
  }

  private populateDot(dot: Dot): void {
    const { width, height } = this.canvasRef.nativeElement;

    dot.x = Math.random() * width;
    dot.y = Math.random() * height;
    dot.vx = (Math.random() - 0.5) * 0.5;
    dot.vy = (Math.random() - 0.5) * 0.5;
    dot.radius = Math.random() * 60 + 40;
    dot.color = this.COLORS[this.ballSpawnNextColor++ % this.COLORS.length];
  }

  private initDots(): void {
    const { width, height } = this.canvasRef.nativeElement;
    const count = this.targetDotCount(width, height);

    for (let i = 0; i < count; i++) {
      this.spawnDot();
    }
  }

  private animate = (): void => {
    this.animationId = 0;
    this.drawFrame();

    if (this.loopActive && !this.tornDown) {
      this.scheduleAnimate();
    }
  };

  private drawFrame(): void {
    const canvas = this.canvasRef?.nativeElement;
    const ctx = this.ctx;

    if (!canvas || !ctx) {
      return;
    }

    const { width, height } = canvas;
    ctx.clearRect(0, 0, width, height);

    for (const dot of this.dots) {
      const dx = dot.x - this.mouse.x;
      const dy = dot.y - this.mouse.y;
      const dist = Math.sqrt(dx * dx + dy * dy);

      if (dist != 0 && dist < this.MOUSE_RADIUS) {
        const force = (this.MOUSE_RADIUS - dist) / this.MOUSE_RADIUS;
        dot.vx += (dx / dist) * force * 0.5;
        dot.vy += (dy / dist) * force * 0.5;
      }

      dot.x += dot.vx;
      dot.y += dot.vy;

      const speed = Math.sqrt(dot.vx * dot.vx + dot.vy * dot.vy);
      if (speed > 0.3) {
        dot.vx *= 0.98;
        dot.vy *= 0.98;
      } else if (speed <= 0.3) {
        dot.vx *= 1.02;
        dot.vy *= 1.02;
      } else if (speed === 0) {
        dot.vx = Math.random() * 0.2 - 0.1;
        dot.vy = Math.random() * 0.2 - 0.1;
      }

      if (dot.x < dot.radius || dot.x > width - dot.radius) {
        dot.vx *= -1;
      }
      if (dot.y < dot.radius || dot.y > height - dot.radius) {
        dot.vy *= -1;
      }

      dot.x = Math.max(dot.radius, Math.min(width - dot.radius, dot.x));
      dot.y = Math.max(dot.radius, Math.min(height - dot.radius, dot.y));

      const gradient = ctx.createRadialGradient(dot.x, dot.y, 0, dot.x, dot.y, dot.radius);
      gradient.addColorStop(0, dot.color + '40');
      gradient.addColorStop(1, 'transparent');

      ctx.beginPath();
      ctx.arc(dot.x, dot.y, dot.radius, 0, Math.PI * 2);
      ctx.fillStyle = gradient;
      ctx.fill();
    }
  }
}