cypok/gist:8c1a3df1f8dc1548c855403c76356103

## gistfile1.txt
import com.sun.net.httpserver.HttpExchange;
import com.sun.net.httpserver.HttpHandler;
import com.sun.net.httpserver.HttpServer;

import java.io.*;
import java.net.InetSocketAddress;
import java.nio.charset.StandardCharsets;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.*;

public class HearTheTennisBackend implements HttpHandler {

    private static final String COLOR_FREE = "#b1fc99";
    private static final String COLOR_BUSY = "#f3d3d9";

    private static final String DATA_FILE = "data.csv";
    private static final SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    private final ArrayList<Tick> ticks = new ArrayList<>();

    public static void main(String[] args) throws IOException, ParseException {
        HttpHandler handler = new HearTheTennisBackend();

        HttpServer server = HttpServer.create(new InetSocketAddress(8008), 0);
        server.createContext("/", handler);
        server.createContext("/put", handler);
        server.setExecutor(java.util.concurrent.Executors.newCachedThreadPool());
        server.start();
    }

    public HearTheTennisBackend() throws IOException, ParseException {
        readTicksFromDisk();
        writeTicksToDisk();
    }

    @Override
    public void handle(HttpExchange t) throws IOException {
        final String responseBody;
        final int responseCode;
        System.out.println(t.getRequestURI().toString());
        switch (t.getRequestMethod()) {
            case "GET":
                if (!t.getRequestURI().toString().equals("/")) {
                    responseCode = 404;
                    responseBody = "unexpected request";
                } else {
                    responseCode = 200;
                    responseBody = renderMainPage();
                }
                break;

            case "POST":
                if (!t.getRequestURI().toString().startsWith("/put?")) {
                    responseCode = 404;
                    responseBody = "unexpected request";
                } else {
                    final Map<String, String> params = queryToMap(t.getRequestURI().getQuery());
                    final String business = params.get("business");
                    final Tick tick = addNewTick(business);
                    responseCode = 200;
                    responseBody = tick.toString();
                }
                break;

            default:
                responseCode = 400;
                responseBody = "unexpected method " + t.getRequestMethod();
                break;
        }

        final OutputStream responseOS = t.getResponseBody();
        final byte[] responseBytes = responseBody.getBytes(StandardCharsets.US_ASCII);
        t.sendResponseHeaders(responseCode, responseBytes.length);
        responseOS.write(responseBytes);
        responseOS.close();
    }

    private Tick addNewTick(String business) throws IOException {
        final State state = State.byName(business);
        Tick tick = new Tick(new Date(), state);
        System.out.println(tick);

        ticks.add(tick);

        writeTicksToDisk();
        return tick;
    }

    private String renderMainPage() {
        final StringBuilder sb = new StringBuilder();
        sb.append("<html><body>Last states:<br/>");
        for (int i = ticks.size() - 1; i >= 0; i--) {
            Tick tick = ticks.get(i);

            final String color;
            switch (tick.state) {
                case FREE:
                    color = COLOR_FREE;
                    break;
                case BUSY:
                    color = COLOR_BUSY;
                    break;
                case NODATA:
                    color = null;
                    break;

                default:
                    throw new IllegalStateException("Unexpected value: " + tick.state);
            }

            if (i != ticks.size() - 1) {
                sb.append("<br/>");
            }
            String s = DATE_FORMAT.format(tick.time);
            if (color != null) {
                sb.append("<span style='background-color:").append(color).append("'>").append(s).append("</span>");
            } else {
                sb.append(s);
            }
        }
        sb.append("</body></html>");
        return sb.toString();
    }


    public static Map<String, String> queryToMap(String query) {
        if (query == null) {
            return null;
        }
        Map<String, String> result = new HashMap<>();
        for (String param : query.split("&")) {
            String[] entry = param.split("=");
            if (entry.length > 1) {
                result.put(entry[0], entry[1]);
            } else {
                result.put(entry[0], "");
            }
        }
        return result;
    }

    private void readTicksFromDisk() throws IOException, ParseException {
        ticks.clear();

        try (FileReader fr = new FileReader(DATA_FILE);
             BufferedReader br = new BufferedReader(fr)) {

            String line;
            while ((line = br.readLine()) != null) {
                String[] parts = line.split(",");
                if (parts.length != 2) {
                    continue;
                }

                String date = parts[0];
                String state = parts[1];
                Tick tick = new Tick(DATE_FORMAT.parse(date), State.byName(state));
                ticks.add(tick);
            }
        } catch (FileNotFoundException e) {
            // ignore it, we will create it
        }
    }

    private void writeTicksToDisk() throws IOException {
        try (FileWriter fw = new FileWriter(DATA_FILE);
             BufferedWriter bw = new BufferedWriter(fw)) {

            for (Tick tick : ticks) {
                bw.write(DATE_FORMAT.format(tick.time) + "," + tick.state + "\n");
            }
        }
    }

}

class Tick {
    final Date time;
    final State state;

    Tick(Date time, State state) {
        this.time = time;
        this.state = state;
    }

    @Override
    public String toString() {
        return "{" + time + ", " + state + "}";
    }
}

enum State {
    NODATA,
    FREE,
    BUSY,
    ;

    public static State byName(String s) {
        return valueOf(s.toUpperCase(Locale.ROOT));
    }

    public String toString() {
        return name().toLowerCase(Locale.ROOT);
    }

}

## gistfile2.txt
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Hear the Tennis</title>
    <style>
        .curstate {
            width: 10em;
            height: 2em;
            line-height: 2em;
            border: 1px;
            text-align: center;
        }

        .free {
            background-color: #b1fc99;
            padding: 5px;
        }

        .busy {
            background-color: #f3d3d9;
        }

        .last-update {
            font-size: small;
        }

    </style>
</head>
<body>

    <iframe src="https://giphy.com/embed/ECwTCTrHPVqKI" width="400" height="300" frameBorder="0" class="giphy-embed"></iframe>

<!--    <iframe src="https://giphy.com/embed/g01ZnwAUvutuK8GIQn" width="533" height="300" frameBorder="0" class="giphy-embed"></iframe>-->

<!--    <iframe src="https://giphy.com/embed/l0NwvUd7IEjn1764U" width="533" height="300" frameBorder="0" class="giphy-embed"></iframe>-->


    <p>
        Table tennis room is <span class="free">free</span> for the last 23 minutes.
    </p>

    <p>
        No information for the last 48 minutes, sorry. Contact guys at 817.
    </p>


    <p>
        <span class="last-update">Last update: 2021-10-11 11:18:02.</span>
    </p>


</body>
</html>
	import com.sun.net.httpserver.HttpExchange;
	import com.sun.net.httpserver.HttpHandler;
	import com.sun.net.httpserver.HttpServer;

	import java.io.*;
	import java.net.InetSocketAddress;
	import java.nio.charset.StandardCharsets;
	import java.text.ParseException;
	import java.text.SimpleDateFormat;
	import java.util.*;

	public class HearTheTennisBackend implements HttpHandler {

	private static final String COLOR_FREE = "#b1fc99";
	private static final String COLOR_BUSY = "#f3d3d9";

	private static final String DATA_FILE = "data.csv";
	private static final SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

	private final ArrayList<Tick> ticks = new ArrayList<>();

	public static void main(String[] args) throws IOException, ParseException {
	HttpHandler handler = new HearTheTennisBackend();

	HttpServer server = HttpServer.create(new InetSocketAddress(8008), 0);
	server.createContext("/", handler);
	server.createContext("/put", handler);
	server.setExecutor(java.util.concurrent.Executors.newCachedThreadPool());
	server.start();
	}

	public HearTheTennisBackend() throws IOException, ParseException {
	readTicksFromDisk();
	writeTicksToDisk();
	}

	@Override
	public void handle(HttpExchange t) throws IOException {
	final String responseBody;
	final int responseCode;
	System.out.println(t.getRequestURI().toString());
	switch (t.getRequestMethod()) {
	case "GET":
	if (!t.getRequestURI().toString().equals("/")) {
	responseCode = 404;
	responseBody = "unexpected request";
	} else {
	responseCode = 200;
	responseBody = renderMainPage();
	}
	break;

	case "POST":
	if (!t.getRequestURI().toString().startsWith("/put?")) {
	responseCode = 404;
	responseBody = "unexpected request";
	} else {
	final Map<String, String> params = queryToMap(t.getRequestURI().getQuery());
	final String business = params.get("business");
	final Tick tick = addNewTick(business);
	responseCode = 200;
	responseBody = tick.toString();
	}
	break;

	default:
	responseCode = 400;
	responseBody = "unexpected method " + t.getRequestMethod();
	break;
	}

	final OutputStream responseOS = t.getResponseBody();
	final byte[] responseBytes = responseBody.getBytes(StandardCharsets.US_ASCII);
	t.sendResponseHeaders(responseCode, responseBytes.length);
	responseOS.write(responseBytes);
	responseOS.close();
	}

	private Tick addNewTick(String business) throws IOException {
	final State state = State.byName(business);
	Tick tick = new Tick(new Date(), state);
	System.out.println(tick);

	ticks.add(tick);

	writeTicksToDisk();
	return tick;
	}

	private String renderMainPage() {
	final StringBuilder sb = new StringBuilder();
	sb.append("<html><body>Last states:<br/>");
	for (int i = ticks.size() - 1; i >= 0; i--) {
	Tick tick = ticks.get(i);

	final String color;
	switch (tick.state) {
	case FREE:
	color = COLOR_FREE;
	break;
	case BUSY:
	color = COLOR_BUSY;
	break;
	case NODATA:
	color = null;
	break;

	default:
	throw new IllegalStateException("Unexpected value: " + tick.state);
	}

	if (i != ticks.size() - 1) {
	sb.append("<br/>");
	}
	String s = DATE_FORMAT.format(tick.time);
	if (color != null) {
	sb.append("<span style='background-color:").append(color).append("'>").append(s).append("</span>");
	} else {
	sb.append(s);
	}
	}
	sb.append("</body></html>");
	return sb.toString();
	}


	public static Map<String, String> queryToMap(String query) {
	if (query == null) {
	return null;
	}
	Map<String, String> result = new HashMap<>();
	for (String param : query.split("&")) {
	String[] entry = param.split("=");
	if (entry.length > 1) {
	result.put(entry[0], entry[1]);
	} else {
	result.put(entry[0], "");
	}
	}
	return result;
	}

	private void readTicksFromDisk() throws IOException, ParseException {
	ticks.clear();

	try (FileReader fr = new FileReader(DATA_FILE);
	BufferedReader br = new BufferedReader(fr)) {

	String line;
	while ((line = br.readLine()) != null) {
	String[] parts = line.split(",");
	if (parts.length != 2) {
	continue;
	}

	String date = parts[0];
	String state = parts[1];
	Tick tick = new Tick(DATE_FORMAT.parse(date), State.byName(state));
	ticks.add(tick);
	}
	} catch (FileNotFoundException e) {
	// ignore it, we will create it
	}
	}

	private void writeTicksToDisk() throws IOException {
	try (FileWriter fw = new FileWriter(DATA_FILE);
	BufferedWriter bw = new BufferedWriter(fw)) {

	for (Tick tick : ticks) {
	bw.write(DATE_FORMAT.format(tick.time) + "," + tick.state + "\n");
	}
	}
	}

	}

	class Tick {
	final Date time;
	final State state;

	Tick(Date time, State state) {
	this.time = time;
	this.state = state;
	}

	@Override
	public String toString() {
	return "{" + time + ", " + state + "}";
	}
	}

	enum State {
	NODATA,
	FREE,
	BUSY,
	;

	public static State byName(String s) {
	return valueOf(s.toUpperCase(Locale.ROOT));
	}

	public String toString() {
	return name().toLowerCase(Locale.ROOT);
	}

	}
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<title>Hear the Tennis</title>
	<style>
	.curstate {
	width: 10em;
	height: 2em;
	line-height: 2em;
	border: 1px;
	text-align: center;
	}

	.free {
	background-color: #b1fc99;
	padding: 5px;
	}

	.busy {
	background-color: #f3d3d9;
	}

	.last-update {
	font-size: small;
	}

	</style>
	</head>
	<body>

	<iframe src="https://giphy.com/embed/ECwTCTrHPVqKI" width="400" height="300" frameBorder="0" class="giphy-embed"></iframe>

	<!-- <iframe src="https://giphy.com/embed/g01ZnwAUvutuK8GIQn" width="533" height="300" frameBorder="0" class="giphy-embed"></iframe>-->

	<!-- <iframe src="https://giphy.com/embed/l0NwvUd7IEjn1764U" width="533" height="300" frameBorder="0" class="giphy-embed"></iframe>-->


	<p>
	Table tennis room is <span class="free">free</span> for the last 23 minutes.
	</p>

	<p>
	No information for the last 48 minutes, sorry. Contact guys at 817.
	</p>



	<p>
	<span class="last-update">Last update: 2021-10-11 11:18:02.</span>
	</p>


	</body>
	</html>