Springs.ts

import * as THREE from 'three';

export interface SpringParameters {
    // spring traits
    positionA: THREE.Vector3;
    positionB: THREE.Vector3;

    // internal parameters
    constants: SpringConstants;    

    // visuals
    color: number;
}

export abstract class Spring {

    public positionA: THREE.Vector3;
    public positionB: THREE.Vector3;
    public restingLength: number;

    public line: THREE.Line;

    constructor(params: SpringParameters) {
        this.positionA = params.positionA;
        this.positionB = params.positionB;
        this.restingLength = this.positionA.distanceTo(this.positionB);

        this.line = new THREE.Line(
            new THREE.BufferGeometry().setFromPoints([this.positionA, this.positionB]),
            new THREE.LineBasicMaterial({ color: params.color })
        );
    }

    abstract get springConstant(): number;

    public force(x: number, y: number, z: number): THREE.Vector3 {
        let direction = this.positionB.clone().sub(this.positionA);
        const distance = direction.length();
        direction.normalize();
        const sign = distance / Math.abs(distance);
        const result = direction.multiplyScalar(this.springConstant * (distance - this.restingLength) * sign);

        if (this.positionA === new THREE.Vector3(x, y, z)) {
            return result;
        }

        return result.multiplyScalar(-1);
    }

    public setColor(color: number): void {
        (this.line.material as THREE.LineBasicMaterial).color.set(color);
    }

    notify(): void {
        this.line.geometry.setFromPoints([this.positionA, this.positionB]);
    }
}

export class SpringConstants {
    public structural: number = 1;
    public shear: number = 1;
    public bend: number = 1;
}

export class StructuralSpring extends Spring {

    public constants: SpringConstants;

    constructor(params: SpringParameters) {
        super(params);
        this.constants = params.constants;
    }

    get springConstant(): number {
        return this.constants.structural;
    }
}

export class ShearSpring extends Spring {

    public constants: SpringConstants;

    constructor(params: SpringParameters) {
        super(params);
        this.constants = params.constants;
    }

    get springConstant(): number {
        return this.constants.shear;
    }
}

export class BendingSpring extends Spring {

    public constants: SpringConstants;

    constructor(params: SpringParameters) {
        super(params);
        this.constants = params.constants;
    }

    get springConstant(): number {
        return this.constants.bend;
    }
}