package slangc.parser;

public final class ScanWalker {
	private Scan scan;
	private int index;

	public ScanWalker(Scan scan, int index) {
		reset(scan, index);
	}

    private ScanWalker() {
        
    }
	
	public ScanWalker(Scan scan) {
		reset(scan);
	}

	public Scan getScan() {
		return scan;
	}
	
	public int getIndex() {
		return index;
	}
	
	public void reset(ScanWalker from) {
		reset(from.getScan(), from.getIndex());
	}
	
	public void reset(Scan scan, int index) {
		if (scan.countTokens() < 1) {
			throw new Error("This scan is empty");
		}
		this.scan = scan;
		this.index = index;
        cachedToken = null;
	}
	
	public void reset(Scan scan) {
		reset(scan, 0);
	}
	
	public void reset() {
		reset(scan);
	}
	
    Token cachedToken = null;
	public void advance() {
        cachedToken = null;
		//if (!isAtEnd()) {
			index++;
		//}
	}
	
	public void advance(int n) {
		for (int i = 0; i < n; i++) {
			advance();
		}
	}

    public static ScanWalker[] walkerCache = new ScanWalker[1000];
    public static int walkerCount = 0;

    public static ScanWalker alloc() {
        if (walkerCount > 0) {
            walkerCount--;
            return walkerCache[walkerCount];
        } else {
            return new ScanWalker();
        }
    }

    public static void recycle(ScanWalker w) {
        if (walkerCount < 1000) {
            walkerCache[walkerCount] = w;
            walkerCount++;
        }
    }
	
	public ScanWalker clone() {
        ScanWalker w = alloc();
        w.reset(this);
        return w;
		//return new ScanWalker(scan, index);
	}
	
	public boolean isAtEnd() {
        if (cachedToken == null) {
            return index >= scan.countTokens();
        } else {
            return false;
        }
		//return cachedToken == null && (index < 0 || index >= scan.countTokens());
	}
	
	public Token peek() {
		/*if (isAtEnd()) {
			return null;
		} else {*/
        if (cachedToken == null) {
            return cachedToken = scan.getToken(index);
        }
		return cachedToken;
		//}
	}
	
	public Token peekOffset(int i) {
		/*if (index + i < 0 || index + i >= scan.countTokens()) {
			return null;
		} else {*/
			return scan.getToken(index + i);
		//}
	}
}