package bjc.dicelang.expr;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/**
 * Contains per-instance state for token parsing.
 *
 * @author EVE
 *
 */
public class Tokens {
	/*
	 * Contains mappings from variable references to string names.
	 */
	private final Map<Integer, String> symTab;
	/*
	 * Reverse index into the symbol table.
	 */
	private final Map<String, Integer> revSymTab;

	/**
	 * Read-only view on the symbol table.
	 */
	public final Map<Integer, String> symbolTable;

	/*
	 * Next index into the symbol table
	 */
	private int nextSym;

	/*
	 * Mapping from literal tokens to token types.
	 */
	private final Map<String, TokenType> litTokens;

	/**
	 * Create a new set of tokens.
	 */
	public Tokens() {
		symTab = new HashMap<>();
		revSymTab = new HashMap<>();

		symbolTable = Collections.unmodifiableMap(symTab);

		nextSym = 0;

		litTokens = new HashMap<>();

		litTokens.put("+", TokenType.ADD);
		litTokens.put("-", TokenType.SUBTRACT);
		litTokens.put("*", TokenType.MULTIPLY);
		litTokens.put("/", TokenType.DIVIDE);
		litTokens.put("(", TokenType.OPAREN);
		litTokens.put(")", TokenType.CPAREN);
	}

	/**
	 * Convert the string representation of a token into a token.
	 *
	 * @param tok
	 *                The string repr. of the token.
	 * @param raw
	 *                The original string the token came from.
	 *
	 * @return The token the string represents.
	 */
	public Token lexToken(String tok, String raw) {
		if(litTokens.containsKey(tok))
			return new Token(litTokens.get(tok), raw, this);
		else
			return parseVRef(tok, raw);
	}

	/*
	 * Parse a variable reference.
	 */
	private Token parseVRef(String tok, String raw) {
		Token tk = new Token(TokenType.VREF, raw, this);

		if(revSymTab.containsKey(tok)) {
			/*
			 * Reuse the entry if it exists.
			 */
			tk.intValue = revSymTab.get(tok);
		} else {
			/*
			 * Create a new entry.
			 */
			tk.intValue = nextSym;

			symTab.put(nextSym, tok);
			revSymTab.put(tok, nextSym);

			nextSym += 1;
		}

		return tk;
	}
}