#Assignment 2 solution
import math

def numericInput(prompt):
    """Gets user input repeating until they enter a number"""
    accepted = False

    while not accepted:
        text = raw_input(prompt)
        try:
            #if the conversion fails, this will error before it returns
            return float(text)
        except:
            print "Please enter a number"


def equationText(coefs):
    """Returns a string containing the equation written out
       For example, equationText([1,0,1]) returns "1*x^2 + 0*x + 1" """
    output = ""

    output = str(coefs[0]) + "*x^2 "
    if coefs[1] < 0:
        output += "- "
    else:
        output += "+ "
        
    output += str(abs(coefs[1])) + "*x "
    
    if coefs[2] < 0:
        output += "- "
    else:
        output += "+ "
        
    output += str(abs(coefs[2]))

    return output


def evaluateEquation(coefs, x):
    """Evaluates the equation defined by coefs and returns the value at x"""
    ans = coefs[0] * x**2
    ans += coefs[1] * x
    ans += coefs[2]

    return ans

    
def readEquation():
    """Reads in the coefficients for an equation"""
    print "A*x^2 + B*x + C"
    coefs=[0,0,0]
    coefs[0] = numericInput("A=")
    coefs[1] = numericInput("B=")
    coefs[2] = numericInput("C=")
    return coefs


def printGraphRow(coefs1,coefs2,y):
    """returns the row of the graph for the given value of y"""
    output = str(y) + "\t"

    for i in range(41):
        x = -10 + .5*i

        mark1 = abs(evaluateEquation(coefs1,x)-y) < .5
        mark2 = abs(evaluateEquation(coefs2,x)-y) < .5
        
        if mark1 and mark2:
            output+="@"
        elif mark1:
            output+="1"
        elif mark2:
            output+="2"
        else:
            if x == 0:
                output+="|"
            elif y == 0:
                output+="-"
            else:
                output += " "
            
    print output



def printGraph(coefs1,coefs2):
    """prints the graph of the 2 equations given as input"""
    print
    y = 10
    while y >= -10:
        printGraphRow(coefs1,coefs2,y)
        y = y - 1

    print "\t   -8  -6  -4  -2   0   2   4   6   8"
    return


option = 0
print "Enter Equation-1 Coefficients"
firstEqCoefs = readEquation()
print "\nEnter Equation-2 Coefficients"    
secondEqCoefs = readEquation()


#repeat until user decides to exit
while option != 5:
    print "\nEquation-1: " + equationText(firstEqCoefs)
    print "Equation-2: " + equationText(secondEqCoefs)
    print "\n1. Re-enter Equation-1 Coefficients"
    print "2. Re-enter Equation-2 Coefficients"
    print "3. Evaluate equations for given x"
    print "4. Print Graph of the equations"
    print "5. Exit"
    print "----------------------------------"
    
    option = numericInput("Select an option: ")

    if option == 1:
        print "\nEnter Equation-1 Coefficients"
        firstEqCoefs = readEquation()
    elif option == 2:
        print "\nEnter Equation-2 Coefficients"
        secondEqCoefs = readEquation()
    elif option == 3:
        print
        x = numericInput("Enter a value for x: ")

        print "Equation-1 evaluates to",evaluateEquation(firstEqCoefs,x)
        print "Equation-2 evaluates to",evaluateEquation(secondEqCoefs,x)
        
    elif option == 4:
        printGraph(firstEqCoefs,secondEqCoefs)
    elif option == 5:
        print "Exiting"
    else:
        print "Please make a valid selection."