'use strict';

const getImageData = require("./get-image-data");
const scanRow = require("./scan-row");

function findEdge(canvas, firstRow, lastRow, step) {
	let imageData = getImageData(canvas).data;
	let valuesPerRow = canvas.width * 4;
	let hitEnd = false;

	if (step === 0) {
		throw new Error("Step cannot be 0");
	}

	let row = firstRow;

	while(!hitEnd) {
		let highestValue = scanRow(imageData, (row * valuesPerRow), canvas.width);

		/* 240 is a somewhat randomly picked value to deal with anti-aliasing. */
		if (highestValue > 240) {
			return row;
		}

		row += step;

		if (step > 0) {
			hitEnd = (row > lastRow);
		} else if (step < 0) {
			hitEnd = (row < lastRow);
		}
	}
}

module.exports = {
	lowest: function findLowestEdge(canvas) {
		return findEdge(canvas, canvas.height - 1, 0, -1);
	},
	highest: function findHighestEdge(canvas) {
		return findEdge(canvas, 0, canvas.height - 1, 1);
	}
};