package dslog;

import java.io.BufferedInputStream;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.time.Instant;
import java.util.Iterator;
import java.util.NoSuchElementException;

class DseventsReader implements Closeable, Iterator<DseventsReader.Event> {
	public static class Event {
		public Instant time;
		public String message;
	}

	/*============================================================*\
	|| Primitive IO                                               ||
	\*============================================================*/

	private final InputStream reader;
	public DseventsReader(InputStream reader) throws IOException {
		if (!reader.markSupported()) {
			reader = new BufferedInputStream(reader);
		}
		this.reader = reader;
	}

	private boolean atEOF() throws IOException {
		reader.mark(2);
		boolean eof = (reader.read() < 0);
		reader.reset();
		return eof;
	}

	/*============================================================*\
	|| Parsing                                                    ||
	\*============================================================*/

	private int m_version;
	private boolean m_haveVersion = false;
	public int version() throws IOException {
		if (!m_haveVersion) {
			m_version = Read.i32(reader);
			m_haveVersion = true;
		}
		return m_version;
	}

	private Instant m_startTime;
	public Instant startTime() throws IOException {
		if (m_startTime == null) {
			switch (version()) {
			case 0:
				throw new UnsupportedVersionException("DSEVENTS (TODO)", 0);
			case 1:
			case 2:
			case 3: // 2016-now
				m_startTime = Read.LVTimestamp(reader);
				break;
			default:
				throw new UnsupportedVersionException("DSEVENTS", version(), 3);
			}
		}
		return m_startTime;
	}

	public Event readEvent() throws IOException{
		startTime();
		if (atEOF()) {
			return null;
		}
		switch (version()) {
		case 0:
			throw new UnsupportedVersionException("DSEVENTS (TODO)", 0);
		case 1:
		case 2:
		case 3:
			return new Event() {{
				time = Read.LVTimestamp(reader);
				message = Read.LVString(reader);
			}};
		default:
			throw new UnsupportedVersionException("DSEVENTS", version(), 3);
		}
	}

	/*============================================================*\
	|| Interfaces                                                 ||
	\*============================================================*/

	private IOException m_err;
	private Event m_next;
	public boolean hasNext() {
		if (m_next == null) {
			try {
				m_next = readEvent();
			} catch (IOException e) {
				m_err = e;
			}
		}
		return m_next != null;
	}
	public Event next() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		return m_next;
	}
	public IOException err() {
		return m_err;
	}

	public void close() throws IOException {
		reader.close();
	}
}