path: root/BJC-Utils2/src/main/java/bjc/utils/parserutils/RuleBasedConfigReader.java

package bjc.utils.parserutils;

import bjc.utils.data.IHolder;
import bjc.utils.data.IPair;
import bjc.utils.data.Identity;
import bjc.utils.data.Pair;
import bjc.utils.exceptions.UnknownPragmaException;
import bjc.utils.funcdata.FunctionalMap;
import bjc.utils.funcdata.FunctionalStringTokenizer;
import bjc.utils.funcdata.IMap;

import java.io.InputStream;
import java.util.InputMismatchException;
import java.util.Scanner;
import java.util.function.BiConsumer;
import java.util.function.Consumer;

/**
 * This class parses a rules based config file, and uses it to drive a provided
 * set of actions
 *
 * @author ben
 *
 * @param <E>
 *                The type of the state object to use
 *
 */
public class RuleBasedConfigReader<E> {
	// Function to execute when starting a rule
	// Takes the tokenizer, and a pair of the read token and application
	// state
	private BiConsumer<FunctionalStringTokenizer, IPair<String, E>> start;

	// Function to use when continuing a rule
	// Takes a tokenizer and application state
	private BiConsumer<FunctionalStringTokenizer, E> continueRule;

	// Function to use when ending a rule
	// Takes an application state
	private Consumer<E> end;

	// Map of pragma names to pragma actions
	// Pragma actions are functions taking a tokenizer and application state
	private IMap<String, BiConsumer<FunctionalStringTokenizer, E>> pragmas;

	/**
	 * Create a new rule-based config reader
	 *
	 * @param start
	 *                The action to fire when starting a rule
	 * @param continueRule
	 *                The action to fire when continuing a rule
	 * @param end
	 *                The action to fire when ending a rule
	 */
	public RuleBasedConfigReader(BiConsumer<FunctionalStringTokenizer, IPair<String, E>> start,
			BiConsumer<FunctionalStringTokenizer, E> continueRule, Consumer<E> end) {
		this.start = start;
		this.continueRule = continueRule;
		this.end = end;

		this.pragmas = new FunctionalMap<>();
	}

	/**
	 * Add a pragma to this reader
	 *
	 * @param name
	 *                The name of the pragma to add
	 * @param action
	 *                The function to execute when this pragma is read
	 */
	public void addPragma(String name, BiConsumer<FunctionalStringTokenizer, E> action) {
		if(name == null)
			throw new NullPointerException("Pragma name must not be null");
		else if(action == null) throw new NullPointerException("Pragma action must not be null");

		pragmas.put(name, action);
	}

	private void continueRule(E state, boolean isRuleOpen, String line) {
		// Make sure our input is correct
		if(isRuleOpen == false)
			throw new InputMismatchException("Cannot continue rule with no rule open");
		else if(continueRule == null)
			throw new InputMismatchException("Rule continuation not supported for current grammar");

		// Accept the rule
		continueRule.accept(new FunctionalStringTokenizer(line.substring(1), " "), state);
	}

	private boolean endRule(E state, boolean isRuleOpen) {
		// Ignore blank line without an open rule
		if(isRuleOpen == false)
			// Do nothing
			return false;
		else {
			// Nothing happens on rule end
			if(end != null) {
				// Process the rule ending
				end.accept(state);
			}

			// Return a closed rule
			return false;
		}
	}

	/**
	 * Run a stream through this reader
	 *
	 * @param input
	 *                The stream to get input
	 * @param initialState
	 *                The initial state of the reader
	 * @return The final state of the reader
	 */
	public E fromStream(InputStream input, E initialState) {
		if(input == null) throw new NullPointerException("Input stream must not be null");

		// Application state: We're giving this back later
		E state = initialState;

		// Prepare our input source
		try(Scanner source = new Scanner(input)) {
			source.useDelimiter("\n");
			// This is true when a rule's open
			IHolder<Boolean> isRuleOpen = new Identity<>(false);

			// Do something for every line of the file
			source.forEachRemaining((line) -> {
				// Skip comment lines
				if(line.startsWith("#") || line.startsWith("//"))
					// It's a comment
					return;
				else if(line.equals("")) {
					// End the rule
					isRuleOpen.replace(endRule(state, isRuleOpen.getValue()));
				} else if(line.startsWith("\t")) {
					// Continue the rule
					continueRule(state, isRuleOpen.getValue(), line);
				} else {
					// Open a rule
					isRuleOpen.replace(startRule(state, isRuleOpen.getValue(), line));
				}
			});
		}

		// Return the state that the user has created
		return state;

	}

	/**
	 * Set the action to execute when continuing a rule
	 *
	 * @param continueRule
	 *                The action to execute on continuation of a rule
	 */
	public void setContinueRule(BiConsumer<FunctionalStringTokenizer, E> continueRule) {
		this.continueRule = continueRule;
	}

	/**
	 * Set the action to execute when ending a rule
	 *
	 * @param end
	 *                The action to execute on ending of a rule
	 */
	public void setEndRule(Consumer<E> end) {
		this.end = end;
	}

	/**
	 * Set the action to execute when starting a rule
	 *
	 * @param start
	 *                The action to execute on starting of a rule
	 */
	public void setStartRule(BiConsumer<FunctionalStringTokenizer, IPair<String, E>> start) {
		if(start == null) throw new NullPointerException("Action on rule start must be non-null");

		this.start = start;
	}

	private boolean startRule(E state, boolean isRuleOpen, String line) {
		// Create the line tokenizer
		FunctionalStringTokenizer tokenizer = new FunctionalStringTokenizer(line, " ");

		// Get the initial token
		String nextToken = tokenizer.nextToken();

		// Handle pragmas
		if(nextToken.equals("pragma")) {
			// Get the pragma name
			String token = tokenizer.nextToken();

			// Handle pragmas
			pragmas.getOrDefault(token, (tokenzer, stat) -> {
				throw new UnknownPragmaException("Unknown pragma " + token);
			}).accept(tokenizer, state);
		} else {
			// Make sure input is correct
			if(isRuleOpen == true)
				throw new InputMismatchException("Nested rules are currently not supported");

			// Start a rule
			start.accept(tokenizer, new Pair<>(nextToken, state));

			isRuleOpen = true;
		}

		return isRuleOpen;
	}
}