import { mat2, vec2 } from 'gl-matrix';
import { Collidable } from './collision';

const rot90 = mat2.fromValues(
	0, 1,
	-1, 0,
);

export function normal(out: vec2, a: vec2): vec2 {
	return vec2.transformMat2(out, a, rot90);
}

export function crossz(a: vec2, b: vec2): number {
	return a[0] * b[1] - a[1] * b[0];
}

export class Line {
	constructor(
		public readonly p: vec2,
		public readonly v: vec2,
	) {}

	public getNormal(out: vec2): vec2 {
		return normal(out, this.v);
	}

	public projectPointDistance(p2: vec2): number {
		const v2 = vec2.sub(vec2.create(), p2, this.p);
		return vec2.dot(this.v, v2);
	}

	public projectPoint(out: vec2, p2: vec2): vec2 {
		const d = this.projectPointDistance(p2);
		return vec2.scaleAndAdd(out, this.p, this.v, d);
	}

	public distancePoint(p2: vec2): number {
		const v2 = vec2.sub(vec2.create(), p2, this.p);
		return crossz(this.v, v2);
	}

	public intersectLine(out: vec2, l2: Line): vec2 {
		const vp = vec2.sub(vec2.create(), l2.p, this.p);
		const d = crossz(vp, this.v);
		const d2 = d / crossz(this.v, l2.v);
		return vec2.scaleAndAdd(out, l2.p, l2.v, d2);
	}
}

export class Movement {
	public readonly v: vec2;

	constructor(
		public readonly src: vec2,
		public readonly dest: vec2,
	) {
		this.v = vec2.sub(vec2.create(), dest, src);
	}

	public intersectLine(out: vec2, l: Line): vec2 {
		const vp = vec2.sub(vec2.create(), l.p, this.src);
		const d = crossz(vp, this.v);
		const d2 = d / crossz(this.v, l.v);
		return vec2.scaleAndAdd(out, l.p, l.v, d2);
	}

	public passes(p: vec2): boolean {
		const vp = vec2.sub(vec2.create(), p, this.src);
		const d = vec2.dot(this.v, vp);
		return d >= 0 && d <= vec2.sqrLen(this.v);
	}

	public toLineSegment(): LineSegment {
		return LineSegment.fromPoints(this.src, this.dest);
	}

	public translate(t: vec2): Movement {
		const src = vec2.add(vec2.create(), this.src, t);
		const dest = vec2.add(vec2.create(), this.dest, t);
		return new Movement(src, dest);
	}
}

export class LineSegment extends Line implements Collidable {
	public static fromPoints(p1: vec2, p2: vec2): LineSegment {
		const d = vec2.dist(p1, p2);
		const v = vec2.sub(vec2.create(), p2, p1);
		vec2.scale(v, v, 1 / d);

		return new LineSegment(p1, v, d);
	}

	constructor(
		p: vec2,
		v: vec2,
		public readonly l: number,
	) {
		super(p, v);
	}

	public getP2(out: vec2): vec2 {
		return vec2.scaleAndAdd(out, this.p, this.v, this.l);
	}

	public containsPoint(p2: vec2): boolean {
		const d = this.projectPointDistance(p2);
		return (d >= 0 && d <= this.l);
	}

	public collide(out: vec2, move: Movement, r: number): boolean {
		if (this.distancePoint(move.src) < 0)
			return false;

		if (crossz(move.v, this.v) < 0)
			return false;

		const t = this.getNormal(vec2.create());
		vec2.scale(t, t, -r);

		const refMove = move.translate(t);

		if (!this.collideRef(out, refMove))
			return false;

		vec2.sub(out, out, t);
		return true;
	}

	private collideRef(out: vec2, move: Movement): boolean {
		if (this.distancePoint(move.dest) >= 0)
			return false;

		const x = move.intersectLine(vec2.create(), this);
		if (!this.containsPoint(x))
			return false;

		this.projectPoint(out, move.dest);

		return true;
	}
}