#!/usr/bin/env python
# encoding: utf-8

from generic import Stack
from calculus import isNumber, doMath


class Expression(object):
    """An arithmetic expression"""

    priority = {"*" : 3, "/": 3, "+": 2, "-":2, "(": 1}

    def __init__(self, exp, fix = "infix"):
        """Initiate the expression.

        :param exp: the string representing the expression (infx form by default)
        :param fix: form of the expression infix (default) - postfix - prefix

        """
        if fix == "infix":
            self._exp_infix = exp
            self._token_infix = exp.split(" ")
        elif fix == "postfix":
            self._token_postfix = exp
        else:
            print("Pas encore fait!")

    def infixToPostfix(self):
        """Convert the infix expression into postfix expression.
        """
        #@todo importer les exemples
        opStack = Stack()
        postfixList = []

        for token in self._token_infix:
            if token == "(":
                opStack.push(token)
            elif token == ")":
                topToken = opStack.pop()
                while topToken != "(":
                    postfixList.append(topToken)
                    topToken = opStack.pop()
            elif token in "+-*/":
                while (not opStack.isEmpty()) and (self.priority[opStack.peek()] >= self.priority[token]):
                    postfixList.append(opStack.pop())
                opStack.push(token)
            else:
                postfixList.append(token)

        while not opStack.isEmpty():
            postfixList.append(opStack.pop())

        self._token_postfix = postfixList
        self._exp_postfix = " ".join(postfixList)
        
    def computePostfix(self):
        """Compute a postfix expression like a good student

        :returns: list of steps to reach the result (postfix form)

        """
        tokenList = self._token_postfix.copy()
        tmpTokenList = []
        # on va chercher les motifs du genre A B + pour les calculer
        while len(tokenList) > 2: 
            #print(tokenList[2])
            if isNumber(tokenList[0]) and isNumber(tokenList[1]) and tokenList[2] in "+-*/":
                # S'il y a une opération à faire
                op1 = tokenList[0]
                op2 = tokenList[1]
                token = tokenList[2]
                res = doMath(token, op1, op2)

                tmpTokenList.append(res)

                # Comme on vient de faire le calcul, on peut détruire aussi les deux prochains termes
                del tokenList[0:3]
            else:
                tmpTokenList.append(tokenList[0])

                del tokenList[0]
        tmpTokenList += tokenList

        if len(tmpTokenList) > 1:
            next_steps = Expression(tmpTokenList, fix = "postfix").computePostfix()
        else:
            next_steps = tmpTokenList
        print(self._exp_postfix)
        return [self._exp_postfix] + next_steps


def test(exp):
    """Make various test on an expression

    """
    print("-------------")
    print("Expression ",exp)
    expression = Expression(exp)
    expression.infixToPostfix()
    print(expression.computePostfix())

if __name__ == '__main__':
    exp = "1 + 3 * 5"
    test(exp)

    exp = "2 * 3 * 3 * 5"
    test(exp)

    exp = "2 * 3 + 3 * 5"
    test(exp)

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