#ifndef _scan_h_
#define _scan_h_

#include <stdexcept>
#include <iostream>
#include <string>
#include "util.h"

using namespace std;

/* 
 * Token scanner object for the recursive descent parser.  Breaks the input
 * stream into the tokens described below, essentially identifiers, integer
 * constants, and some operators.
 */

/* A token has a code number and the string it actually represents. */
class Scanner {
public:
	/* These are code numbers for each token type. */
	enum tok_code { 
		tok_id, 	// An identifier, L(L|D)*
		tok_lit, 	// A literal: an unsigned integer number.
		tok_left, 	// A left paren.
		tok_right,  	// A right paren
		tok_splat,  	// An asterisk
		tok_slash, 	// A slash
		tok_plus,  	// A plus sign
		tok_minus,  	// A minus sign or dash
		tok_asst,  	// An assignment symbol, :=
		tok_semi,  	// A semicolon.
		tok_EOF		// END-of-file.
	};

	// The tokens returned by the scanner are of this type.
	class Token: public ParserObject {
	public:
		tok_code code() const { return m_code; }
		string text() const { return m_text; }
		void pr(ostream &s, int indent) const {
			s << spaces(indent) << m_codenames[m_code] 
			  << "(" << m_text << ")"; 
		}
		Token(): m_code(tok_EOF), m_text("Uninitialized") { }
		Token(tok_code c, string t): m_code(c), m_text(t) { }
	private:
		tok_code m_code;
		string m_text;
	};

	/* Get the current token. */
	const Token & curr_tok() const { return m_curr; }

	/* Move forward one token, and return the new current token. */
	const Token & next_tok();

	/* Create the scanner.  Remembers the stream, and reads the
	   first token from it, which can be recovered with curr_token(). */
	Scanner(istream &strm): m_in(strm) { next_tok(); }

private:
	/* Reference to the underlying input stream. */
	istream &m_in;

	/* Current token. */
	Token m_curr;

	/* String names to correspond to the token codes */
	static const char *m_codenames[];
};

// Class for scanner execeptions.
class BadInputCharacter: public runtime_error {
public:
	BadInputCharacter(char ch): 
		runtime_error("Bad input character '" + ch_to_str(ch) + "'") { }
private:
	string ch_to_str(char ch) {
		char ret[2] = { ch, 0 };
		return ret;
	}
};

#endif