let hInput = document.getElementById("h");
let rInput = document.getElementById("r");
let rsInput = document.getElementById("rs");
let npInput = document.getElementById("np");
let outputdiv = document.getElementById("output");

let height = 0;
let radius = 0;
let spillRadius = 0;
let numberOfPanels = 0;

let multiplier = 1;
let accuracy = 8;

const step = 0.001 * multiplier;
// const offset = 3*10**-15 * multiplier;
const offset = 4*10**-5 * multiplier;

let pointsP = [];
let pointsQ = [];
let distances = [];

let panelPoints = [];

let n = 0;

// maths
function approx(x) {
    return Math.round(x*(10**accuracy))/(10**accuracy);
}

function f(x) {
    res = approx(height * Math.sqrt((1-(Math.pow(x,2)/Math.pow(radius,2)))));
    console.log(`f ${x} ${res}`);
    return res;
}

function fprime(x) {
    res = approx(-1*((Math.pow(height,2)*x)/(Math.pow(radius,2)*f(x))));
    console.log(`fprime ${x} ${res}`);
    return res;
}

function g(x, P) {
    res = approx(fprime(x)*(x-P.x)+P.y);
    console.log(`g ${x} ${P.x} ${P.y} ${res}`);
    return res;
}

function j(A, B) {
    res = approx(A.x*fprime(A.x)-B.x*fprime(B.x)-A.y+B.y)/(fprime(A.x)-fprime(B.x));
    console.log(`j ${A.x} ${A.y} ${B.x} ${B.y} ${res}`);
    return res;
}

function d(A, B) {
    res = approx(Math.sqrt(Math.pow(A.x-B.x,2)+Math.pow(A.y-B.y,2)));
    console.log(`d ${A.x} ${A.y} ${B.x} ${B.y} ${res}`);
    return res;
}

// logic
function getValues() {
    pointsP = [];
    pointsQ = [];
    distances = [];
    panelPoints = [];
    height = /* /* Math.floor */(parseFloat(hInput.value) *multiplier);
    radius = /* Math.floor */(parseFloat(rInput.value) *multiplier);
    spillRadius = /* Math.floor */(parseFloat(rsInput.value) *multiplier);
    numberOfPanels = /* Math.floor */(parseFloat(npInput.value) *multiplier);
    if (isNaN(spillRadius)) {
        spillRadius = /* Math.floor */(0.05*radius);
        rsInput.value = 0.05*radius /multiplier;
    }
    n = ((radius-spillRadius)/(step-offset))-1;
    console.log(`${height}, ${radius}, ${spillRadius}, ${step}, ${offset}`);
}

function getPoints() {
    for (let x = spillRadius; x < radius; x+=step-offset) {
        x=approx(x);
        pointsP.push({
            x: x, 
            y: f(x)
        });
    }
}

function getPointsOfTangentIntersection() {
    for (let i = 0; i < n; i++) {
        console.log(`${i}, ${pointsP[i]}, ${pointsP[i+1]}`);
        pointsQ.push({
            x: j(pointsP[i], pointsP[i+1]),
            y: g(j(pointsP[i], pointsP[i+1]), pointsP[i+1])
        });
    }
}

function getDistancesBetweenIntersections() {
    for (let i = 0; i < n-1; i++) {
        distances.push(d(pointsQ[i], pointsQ[i+1]));
    }
}

function generateCoordinates() {
    let Xi = 0;
    for (let i = 0; i < n-2; i++) {
        Xi+=distances[i];
        Yi=(Math.PI*pointsQ[i].x)/numberOfPanels;
        panelPoints.push({
            x: Xi,
            y: Yi
        });
    }
}

function plotSVG() {
    let maxY = 0;
    panelPoints.forEach((point) => {
        if (maxY < point.y) {
            maxY=point.y
        }
    })
    let pointsA = [];
    let pointsB = [];
    for(let i = 0; i < panelPoints.length; i++) {
        let point = panelPoints[i];
        pointsA.push(`${approx(point.x*10)},${(maxY*10)-approx(point.y*10)}`)
        pointsB.push(`${approx(point.x*10)},${approx((point.y+maxY)*10)}`);
    }
    outputdiv.innerHTML = `
        <svg viewBox="0 0 100 200" xmlns="http://www.w3.org/2000/svg">
            <line x1="${approx(panelPoints[0].x*10)}" x2="${panelPoints[0].x*10}" y1="${maxY*10-approx(panelPoints[0].y*10)}" y2="${approx((panelPoints[0].y+maxY)*10)}" fill="none" stroke="black" stroke-width="0.05" />
            <line x1="${approx(panelPoints[panelPoints.length-1].x*10)}" x2="${panelPoints[panelPoints.length-1].x*10}" y1="${maxY*10-approx(panelPoints[panelPoints.length-1].y*10)}" y2="${approx((panelPoints[panelPoints.length-1].y+maxY)*10)}" fill="none" stroke="black" stroke-width="0.05" />
            <line x1="${approx(panelPoints[0].x*10)}" x2="${panelPoints[panelPoints.length-1].x*10}" y1="${(maxY*10-approx(panelPoints[0].y*10)+approx((panelPoints[0].y+maxY)*10))/2}" y2="${(maxY*10-approx(panelPoints[panelPoints.length-1].y*10)+approx((panelPoints[panelPoints.length-1].y+maxY)*10))/2}" fill="none" stroke="black" stroke-width="0.05" />
            <polyline points="${pointsA}" fill="none" stroke="black" stroke-width="0.05" />
            <polyline points="${pointsB}" fill="none" stroke="black" stroke-width="0.05" />
        </svg>
    `
}


// main func
function generatePanel() {
    getValues();
    getPoints();
    getPointsOfTangentIntersection();
    getDistancesBetweenIntersections();
    generateCoordinates();
    plotSVG();
}