const canvas = document.getElementById("polyCanvas");
const ctx = canvas.getContext("2d");

const X_data = [1, 2, 3, 4, 5];
const y_data = [3, 8, 15, 24, 35];

function toCanvasX(x, xScale, padding) {
    return padding + x * xScale;
}

function toCanvasY(y, yScale, padding, canvasHeight) {
    return canvasHeight - padding - y * yScale;
}

function setupAndDraw(predX = null, predY = null) {
    const padding = 50;
    const canvasWidth = canvas.width = canvas.clientWidth;
    const canvasHeight = canvas.height = canvas.clientHeight;

    const xMax = 6;
    const yMax = 40;

    const xScale = (canvasWidth - 2 * padding) / xMax;
    const yScale = (canvasHeight - 2 * padding) / yMax;

    // Clear
    ctx.clearRect(0, 0, canvasWidth, canvasHeight);

    // Axes
    ctx.beginPath();
    ctx.moveTo(padding, toCanvasY(0, yScale, padding, canvasHeight));
    ctx.lineTo(canvasWidth - padding, toCanvasY(0, yScale, padding, canvasHeight));
    ctx.moveTo(toCanvasX(0, xScale, padding), padding);
    ctx.lineTo(toCanvasX(0, xScale, padding), canvasHeight - padding);
    ctx.strokeStyle = "#475569";
    ctx.stroke();

    // Points
    ctx.fillStyle = "#3b82f6";
    X_data.forEach((x, i) => {
        ctx.beginPath();
        ctx.arc(toCanvasX(x, xScale, padding), toCanvasY(y_data[i], yScale, padding, canvasHeight), 5, 0, 2 * Math.PI);
        ctx.fill();
    });

    // Curve
    ctx.beginPath();
    ctx.moveTo(toCanvasX(0, xScale, padding), toCanvasY(0, yScale, padding, canvasHeight));
    for (let x = 0; x <= xMax; x += 0.1) {
        const y = x * x + 2 * x;  // match your data (x^2 + 2x)
        ctx.lineTo(toCanvasX(x, xScale, padding), toCanvasY(y, yScale, padding, canvasHeight));
    }
    ctx.strokeStyle = "#ef4444";
    ctx.lineWidth = 2;
    ctx.stroke();

    // Predicted point
    if (predX !== null && predY !== null) {
        ctx.fillStyle = "#22c55e";
        ctx.beginPath();
        ctx.arc(toCanvasX(predX, xScale, padding), toCanvasY(predY, yScale, padding, canvasHeight), 6, 0, 2 * Math.PI);
        ctx.fill();
    }
}

// Prediction handler
function predict() {
    const hours = parseFloat(document.getElementById("hoursInput").value);
    fetch("/predict_poly", {
        method: "POST",
        body: JSON.stringify({ hours }),
        headers: {
            "Content-Type": "application/json"
        }
    })
    .then(res => res.json())
    .then(data => {
        const score = data.prediction;
        document.getElementById("predictedScore").textContent = score;
        document.getElementById("predictionOutput").classList.remove("hidden");
        setupAndDraw(hours, score);
    });
}

window.onload = () => setupAndDraw();