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Copyright 2010,2011. Google Inc.
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modification, are permitted provided that the following conditions are
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    * Redistributions of source code must retain the above copyright
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    * Redistributions in binary form must reproduce the above
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contributors may be used to endorse or promote products derived from
this software without specific prior written permission.

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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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*/

package com.google.refine.grel;

import java.util.LinkedList;
import java.util.List;
import java.util.regex.Pattern;

import com.google.refine.expr.Evaluable;
import com.google.refine.expr.ParsingException;
import com.google.refine.expr.functions.arrays.ArgsToArray;
import com.google.refine.grel.Scanner.NumberToken;
import com.google.refine.grel.Scanner.RegexToken;
import com.google.refine.grel.Scanner.Token;
import com.google.refine.grel.Scanner.TokenType;
import com.google.refine.grel.ast.ControlCallExpr;
import com.google.refine.grel.ast.FieldAccessorExpr;
import com.google.refine.grel.ast.FunctionCallExpr;
import com.google.refine.grel.ast.LiteralExpr;
import com.google.refine.grel.ast.OperatorCallExpr;
import com.google.refine.grel.ast.VariableExpr;

public class Parser {
    protected Scanner   _scanner;
    protected Token     _token;
    protected Evaluable _root;

    public Parser(String s) throws ParsingException {
        this(s, 0, s.length());
    }

    public Parser(String s, int from, int to) throws ParsingException {
        _scanner = new Scanner(s, from, to);
        _token = _scanner.next(true);

        _root = parseExpression();
    }

    public Evaluable getExpression() {
        return _root;
    }

    protected void next(boolean regexPossible) {
        _token = _scanner.next(regexPossible);
    }

    protected ParsingException makeException(String desc) {
        int index = _token != null ? _token.start : _scanner.getIndex();

        return new ParsingException("Parsing error at offset " + index + ": " + desc);
    }

    /**
     *  <expression> := <sub-expression>
     *                | <expression> [ "<" "<=" ">" ">=" "==" "!=" ] <sub-expression>
     */
    protected Evaluable parseExpression() throws ParsingException {
        Evaluable sub = parseSubExpression();

        while (_token != null &&
                _token.type == TokenType.Operator &&
                ">=<==!=".indexOf(_token.text) >= 0) {

            String op = _token.text;

            next(true);

            Evaluable sub2 = parseSubExpression();

            sub = new OperatorCallExpr(new Evaluable[] { sub, sub2 }, op);
        }

        return sub;
    }

    /**
     *  <sub-expression> := <term>
     *                    | <sub-expression> [ "+" "-" ] <term>
     */
    protected Evaluable parseSubExpression() throws ParsingException {
        Evaluable sub = parseTerm();

        while (_token != null &&
                _token.type == TokenType.Operator &&
                "+-".indexOf(_token.text) >= 0) {

            String op = _token.text;

            next(true);

            Evaluable sub2 = parseTerm();

            sub = new OperatorCallExpr(new Evaluable[] { sub, sub2 }, op);
        }

        return sub;
    }

    /**
     *  <term> := <factor>
     *          | <term> [ "*" "/" "%" ] <factor>
     */
    protected Evaluable parseTerm() throws ParsingException {
        Evaluable factor = parseFactor();

        while (_token != null &&
                _token.type == TokenType.Operator &&
                "*/%".indexOf(_token.text) >= 0) {

            String op = _token.text;

            next(true);

            Evaluable factor2 = parseFactor();

            factor = new OperatorCallExpr(new Evaluable[] { factor, factor2 }, op);
        }

        return factor;
    }

    /**
     *  <term> := <term-start> ( <path-segment> )*
     *  <term-start> :=
     *      <string> | <number> | - <number> | <regex> | <identifier> |
     *      <identifier> ( <expression-list> )
     *
     *  <path-segment> := "[" <expression-list> "]"
     *                  | "." <identifier>
     *                  | "." <identifier> "(" <expression-list> ")"
     *
     */
    protected Evaluable parseFactor() throws ParsingException {
        if (_token == null) {
            throw makeException("Expecting something more at end of expression");
        }

        Evaluable eval = null;

        if (_token.type == TokenType.String) {
            eval = new LiteralExpr(_token.text);
            next(false);
        } else if (_token.type == TokenType.Regex) {
            RegexToken t = (RegexToken) _token;

            try {
                Pattern pattern = Pattern.compile(_token.text, t.caseInsensitive ? Pattern.CASE_INSENSITIVE : 0);
                eval = new LiteralExpr(pattern);
                next(false);
            } catch (Exception e) {
                throw makeException("Bad regular expression (" + e.getMessage() + ")");
            }
        } else if (_token.type == TokenType.Number) {
            eval = new LiteralExpr(((NumberToken)_token).value);
            next(false);
        } else if (_token.type == TokenType.Operator && _token.text.equals("-")) { // unary minus?
            next(true);

            if (_token != null && _token.type == TokenType.Number) {
                Number n = ((NumberToken)_token).value;

                eval = new LiteralExpr(n instanceof Long ? -n.longValue() : -n.doubleValue());

                next(false);
            } else {
                throw makeException("Bad negative number");
            }
        } else if (_token.type == TokenType.Identifier) {
            String text = _token.text;
            next(false);

            if (_token == null || _token.type != TokenType.Delimiter || !_token.text.equals("(")) {
                eval = "null".equals(text) ? new LiteralExpr(null) : new VariableExpr(text);
            } else if( "PI".equals(text) ) {
                eval = new LiteralExpr(Math.PI);
                next(false);
            } else {
                Function f = ControlFunctionRegistry.getFunction(text);
                Control c = ControlFunctionRegistry.getControl(text);
                if (f == null && c == null) {
                    throw makeException("Unknown function or control named " + text);
                }

                next(true); // swallow (

                List<Evaluable> args = parseExpressionList(")");

                if (c != null) {
                    Evaluable[] argsA = makeArray(args);
                    String errorMessage = c.checkArguments(argsA);
                    if (errorMessage != null) {
                        throw makeException(errorMessage);
                    }
                    eval = new ControlCallExpr(argsA, c);
                } else {
                    eval = new FunctionCallExpr(makeArray(args), f);
                }
            }
        } else if (_token.type == TokenType.Delimiter && _token.text.equals("(")) {
            next(true);

            eval = parseExpression();

            if (_token != null && _token.type == TokenType.Delimiter && _token.text.equals(")")) {
                next(false);
            } else {
                throw makeException("Missing )");
            }
        } else if (_token.type == TokenType.Delimiter && _token.text.equals("[")) { // [ ... ] array
        	next(true); // swallow [

            List<Evaluable> args = parseExpressionList("]");

            eval = new FunctionCallExpr(makeArray(args), new ArgsToArray());
        } else {
            throw makeException("Missing number, string, identifier, regex, or parenthesized expression");
        }

        while (_token != null) {
            if (_token.type == TokenType.Operator && _token.text.equals(".")) {
                next(false); // swallow .

                if (_token == null || _token.type != TokenType.Identifier) {
                    throw makeException("Missing function name");
                }

                String identifier = _token.text;
                next(false);

                if (_token != null && _token.type == TokenType.Delimiter && _token.text.equals("(")) {
                    next(true); // swallow (

                    Function f = ControlFunctionRegistry.getFunction(identifier);
                    if (f == null) {
                        throw makeException("Unknown function " + identifier);
                    }

                    List<Evaluable> args = parseExpressionList(")");
                    args.add(0, eval);

                    eval = new FunctionCallExpr(makeArray(args), f);
                } else {
                    eval = new FieldAccessorExpr(eval, identifier);
                }
            } else if (_token.type == TokenType.Delimiter && _token.text.equals("[")) {
                next(true); // swallow [

                List<Evaluable> args = parseExpressionList("]");
                args.add(0, eval);

                eval = new FunctionCallExpr(makeArray(args), ControlFunctionRegistry.getFunction("get"));
            } else {
                break;
            }
        }

        return eval;
    }

    /**
     *  <expression-list> := <empty>
     *                     | <expression> ( "," <expression> )*
     *
     */
    protected List<Evaluable> parseExpressionList(String closingDelimiter) throws ParsingException {
        List<Evaluable> l = new LinkedList<Evaluable>();

        if (_token != null &&
            (_token.type != TokenType.Delimiter || !_token.text.equals(closingDelimiter))) {

            while (_token != null) {
                Evaluable eval = parseExpression();

                l.add(eval);

                if (_token != null && _token.type == TokenType.Delimiter && _token.text.equals(",")) {
                    next(true); // swallow comma, loop back for more
                } else {
                    break;
                }
            }
        }

        if (_token != null && _token.type == TokenType.Delimiter && _token.text.equals(closingDelimiter)) {
            next(false); // swallow closing delimiter
        } else {
            throw makeException("Missing " + closingDelimiter);
        }

        return l;
    }

    protected Evaluable[] makeArray(List<Evaluable> l) {
        Evaluable[] a = new Evaluable[l.size()];
        l.toArray(a);

        return a;
    }
}