let uInput = document.getElementById("u");
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 stepInput = document.getElementById("steps");
let lenOutput = document.getElementById("len");

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

let multiplier = 1;
let accuracy = 8;

let 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;
let unit = "px";
let strokeWidth = 1;

// maths
function approx(n) {
    return Math.round(n * (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);
    step = radius / parseInt(stepInput.value);
    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;
    let maxX = 0;
    let minX = 1000;
    panelPoints.forEach((point) => {
        if (maxY < point.y) {
            maxY = point.y;
        }
        if (minX > point.x) {
            minX = point.x;
        }
        if (maxX < point.x) {
            maxX = point.x;
        }
    })
    let pointsA = "";
    let pointsB = "";
    for (let i = 0; i < panelPoints.length; i++) {
        let point = panelPoints[i];
        pointsA += `${approx(point.x)},${(maxY) - approx(point.y)} `;
        pointsB +=`${approx(point.x)},${approx((point.y + maxY))} `;
    }
    outputdiv.innerHTML = `
        <svg    width="297mm"
                height="210mm"
                xmlns="http://www.w3.org/2000/svg">
                <g id="layer1">
                    <line 
                        x1="${approx(panelPoints[0].x)}${unit}" 
                        x2="${panelPoints[0].x}${unit}" 
                        y1="${maxY - approx(panelPoints[0].y)}${unit}" 
                        y2="${approx((panelPoints[0].y + maxY))}${unit}"
                        fill="none" 
                        stroke="black" 
                        stroke-width="${strokeWidth}" 
                    />
                    <line 
                        x1="${approx(panelPoints[panelPoints.length - 1].x)}${unit}" 
                        x2="${panelPoints[panelPoints.length - 1].x}${unit}" 
                        y1="${maxY - approx(panelPoints[panelPoints.length - 1].y)}${unit}" 
                        y2="${approx((panelPoints[panelPoints.length - 1].y + maxY))}${unit}" 
                        fill="none" 
                        stroke="black" 
                        stroke-width="${strokeWidth}" 
                    />
                    <line 
                        x1="${approx(panelPoints[0].x)}${unit}" 
                        x2="${panelPoints[panelPoints.length - 1].x}${unit}" 
                        y1="${(maxY - approx(panelPoints[0].y) + approx((panelPoints[0].y + maxY))) / 2}${unit}" 
                        y2="${(maxY - approx(panelPoints[panelPoints.length - 1].y) + approx((panelPoints[panelPoints.length - 1].y + maxY))) / 2}${unit}" 
                        fill="none" 
                        stroke="black" 
                        stroke-width="${strokeWidth}" 
                    />
                    <polyline 
                        points="${pointsA}" 
                        fill="none" 
                        stroke="black" 
                        stroke-width="${strokeWidth}" 
                    />
                    <polyline 
                        points="${pointsB}" 
                        fill="none" 
                        stroke="black" 
                        stroke-width="${strokeWidth}" 
                    />
            </g>
        </svg>
    `;
    lenOutput.innerText = `Recommended length: ${approx(maxX - minX)} ${unit}`;
}


// main func
function generatePanel() {
    unit=uInput.value;
    getValues();
    getPoints();
    getPointsOfTangentIntersection();
    getDistancesBetweenIntersections();
    generateCoordinates();
    plotSVG();
}