const sync_max = 512;

const textarea = document.getElementById ("JNG5U2EX");
const debug_text = document.getElementById ("XDHSIT76");

textarea.innerText = "Loading...";

let page = "";
let offset = 0;

function line_start_before (page, offset) {
	const sync_start = Math.max (sync_max, offset) - sync_max;
	
	for (let i = offset; i >= sync_start; i--) {
		const c = page.charAt (i);
		if (c == '\n') {
			return i + 1;
		}
	}
	
	return null;
}

function line_start_after (page, offset)
{
	for (let i = offset; i < offset + sync_max; i++) {
		const c = page.charAt (i);
		if (c == '\n') {
			return i + 1;
		}
	}
	
	return null;
}

function layout_text (page, offset) {
	const width = 120;
	const height = 24;
	
	const line_start = line_start_before (page, offset) || 0;
	
	// Compute layout
	
	let lines = Array ();
	let line = "";
	
	for (let i = line_start; i < page.length; i++) {
		if (lines.length >= height) {
			break;
		}
		if (line.length >= width) {
			lines.push (line);
			line = "";
		}
		
		const c = page.charAt (i);
		
		if (c == '\n') {
			lines.push (line);
			line = "";
		}
		else {
			line = line + page.charAt (i);
		}
	}
	
	return lines.join ('\n');
}

function repaint (offset) 
{
	textarea.innerText = layout_text (page, offset);
	debug_text.innerText = "Offset: " + offset + "\n";
}

async function async_main () 
{
	let file_length = null;
	
	{
		const resp = await fetch ("log.txt", {
			"method": "HEAD",
		});
		
		file_length = resp.headers.get ("content-length");
	}
	
	const resp = await fetch ("log.txt", {
		"headers": {
			"range": "bytes=0-65535",
		},
	});
	
	page = await resp.text ();
	
	repaint (offset);
}

async_main ().then (
	function (val) {},
	function (err) {}
);

function cursor_left () 
{
	offset = Math.max (1, offset) - 1;
	repaint (offset);
}

function cursor_right () 
{
	offset += 1;
	repaint (offset);
}

function cursor_up () 
{
	offset = line_start_before (page, offset - 2) || 0;
	repaint (offset);
}

function cursor_down () 
{
	offset = line_start_after (page, offset);
	repaint (offset);
}