/**
 * 返回可指定大小的随机二维向量
 * @param {number} magnitude 向量大小
 * @return {p5.Vector} vector 随机二维向量
 */
function randomVector(magnitude) {
    let vector = p5.Vector.random2D();
    return magnitude ? vector.mult(magnitude) : vector;
}

class Vehicle {
    constructor(x, y, color) {
        this.path = [];
        this.color = color;
        this.position = createVector(x, y);
        this.velocity = createVector(0, 0);
        this.heading = this.velocity.heading();
        this.acceleration = createVector(0, 0);
        this.maxVelocity = 6;
        this.maxAcceleration = 0.25;
    }

    seek(target, slowdownDistance = 100) {
        const desired = p5.Vector.sub(target, this.position);
        const distance = desired.mag();
        const magnitude =
            slowdownDistance > 0 && distance <= slowdownDistance
                ? map(distance, 0, slowdownDistance, 0, this.maxVelocity)
                : this.maxVelocity;
        desired.setMag(magnitude);
        const steering = p5.Vector.sub(desired, this.velocity);
        this.acceleration.add(steering);
    }

    flee(target, fleeDistance = 100) {
        const desired = p5.Vector.sub(this.position, target);
        const distance = desired.mag();
        const magnitude =
            !fleeDistance || fleeDistance <= 0
                ? this.maxVelocity
                : distance <= fleeDistance
                ? map(distance, 0, fleeDistance, this.maxVelocity, 0)
                : 0;
        desired.setMag(magnitude);
        const steering = p5.Vector.sub(desired, this.velocity);
        this.acceleration.add(steering);
    }

    wander() {
        const target = this.velocity.copy();
        target.setMag(50).add(this.position);

        // stroke(128);
        // const x1 = target.x + -25 * cos(PI / 2 + this.heading);
        // const y1 = target.y + -25 * sin(PI / 2 + this.heading);
        // const x2 = target.x + 25 * cos(PI / 2 + this.heading);
        // const y2 = target.y + 25 * sin(PI / 2 + this.heading);
        // line(x1, y1, x2, y2);

        const offset = map(noise(Date.now() / 1000), 0, 1, -50, 50);
        const x = offset * cos(PI / 2 + this.heading);
        const y = offset * sin(PI / 2 + this.heading);
        target.add(x, y);

        noStroke();
        fill("#F063A4");
        circle(target.x, target.y, 5);

        const steering = target.sub(this.position);
        this.acceleration.add(steering);
    }

    follow(path, ahead = 50) {
        // find future point of vehicle
        const future = p5.Vector.add(
            this.position,
            this.velocity.copy().mult(ahead)
        );

        // noStroke();
        // fill("#FF0000");
        // circle(future.x, future.y, 5);

        // find project point on the path
        const v1 = p5.Vector.sub(future, path.start);
        const v2 = p5.Vector.sub(path.end, path.start);
        const project = path.start.copy().add(vectorProjection(v1, v2));

        noStroke();
        fill("#00FF00");
        circle(project.x, project.y, 5);

        // find the distance between project point and future point
        const distance = future.dist(project);
        // if the distance larger than path width then seek the project point
        if (distance > path.width) this.seek(project, -1);
    }

    move() {
        this.acceleration.limit(this.maxAcceleration);
        this.velocity.add(this.acceleration);
        if (this.velocity.mag() > 0) this.heading = this.velocity.heading();
        this.velocity.limit(this.maxVelocity);
        this.position.add(this.velocity);
        this.acceleration.set(0, 0);
        this.path.push(this.position.copy());

        // this.acceleration.limit(this.maxAcceleration);
        // // 计算时间差
        // const duration = deltaTime / 1000;
        // // 计算速度及位移
        // const deltaVelocity = this.acceleration.mult(duration);
        // const averageVelocity = deltaVelocity.copy().div(2).add(this.velocity);
        // const movement = averageVelocity.mult(duration);
        // // 更新速度及位置
        // this.velocity.add(deltaVelocity);
        // this.velocity.limit(this.maxVelocity);
        // if (this.velocity.mag() > 0) this.heading = this.velocity.heading();
        // this.position.add(movement);
        // this.acceleration.set(0, 0);
        // this.path.push(this.position.copy());
    }

    turn() {
        let x = this.position.x;
        let y = this.position.y;
        while (x < 0 || x >= width) x = (x + width) % width;
        while (y < 0 || y >= height) y = (y + height) % height;
        const edgeCrossed = x != this.position.x || y != this.position.y;
        this.position.x = x;
        this.position.y = y;
        if (edgeCrossed) {
            this.path.pop();
            this.path.push(null);
        }
        return edgeCrossed;
    }

    // bounce() {
    //     if (this.position.x <= this.size / 2) {
    //         this.position.x = this.size / 2;
    //         this.velocity.x *= -1;
    //         return true;
    //     } else if (this.position.x > canvasWidth - this.size / 2) {
    //         this.position.x = canvasWidth - this.size / 2;
    //         this.velocity.x *= -1;
    //         return true;
    //     }
    //     if (this.position.y <= this.size / 2) {
    //         this.position.y = this.size / 2;
    //         this.velocity.y *= -1;
    //         return true;
    //     } else if (this.position.y >= canvasHeight - this.size / 2) {
    //         this.position.y = canvasHeight - this.size / 2;
    //         this.velocity.y *= -1;
    //         return true;
    //     }
    //     return false;
    // }

    drawPath(length = 1024) {
        push();
        noFill();
        stroke(255, 64);
        strokeWeight(1);
        if (this.path.length >= length) this.path.shift();
        beginShape();
        this.path.forEach((v) => {
            if (!v) {
                endShape();
                beginShape();
            } else {
                vertex(v.x, v.y);
            }
        });
        endShape();
        pop();
    }

    show(mode = "triangle") {
        push();
        translate(this.position.x, this.position.y);
        rotate(this.heading);
        stroke(this.color);
        fill(this.color);
        if (mode == "point") circle(0, 0, 5);
        else triangle(0, 0, -10, 2.5, -10, -2.5);
        pop();
    }
}

class Path {
    constructor(x1, y1, x2, y2, width = 20) {
        this.start = createVector(x1, y1);
        this.end = createVector(x2, y2);
        this.width = width;
    }

    show() {
        push();
        stroke(255, 64);
        strokeWeight(this.width * 2);
        line(this.start.x, this.start.y, this.end.x, this.end.y);
        stroke(255);
        strokeWeight(1);
        line(this.start.x, this.start.y, this.end.x, this.end.y);
        pop();
    }
}

function vectorProjection(v1, v2) {
    const v2n = v2.copy().normalize();
    const sp = v1.dot(v2n);
    return v2n.setMag(sp);
}