from cs1graphics import *
#from file import *

# this module/function reads the information from a file
# and stores it in a list, where every element is a tuple
# of integer values
def readData():
    while True:
        filename=raw_input('Please, input the filename:')
        try:
            fname=file(filename)
            break
        except IOError:
            print 'Cannot open the file. Try again, please'

    listLines=fname.readlines()
    print 'read from file:', listLines

    fname.close()
    print 'File is closed'

    n=len(listLines)
    data=[]
    
    for i in range(n):
        pair=listLines[i].split()
        print pair
        data.append((int(pair[0]),int(pair[1])))

    print data
    return data

# this module/function draws the rectangular coordinate system on the screen
# and displays all the points provided by data variable
def display(data,paper):

    n=len(data) # getting number of points
  
    xAxis=Path(Point(0,300),Point(700,300)) # creating x-axis
    yAxis=Path(Point(350,0),Point(350,600)) # creating y-axis

    paper.add(xAxis) # drawing x-axis
    paper.add(yAxis) # drawing y-axis

    for i in range(n):
        print data[i][0]+350
        print (-1)*data[i][1]+300
        point=Point(data[i][0]+350,(-1)*data[i][1]+300)
        p=Circle(1,point)
        paper.add(p)

def findRegression(data):

    n=len(data)

    sumxy, sumx, sumy, sumx2 = 0,0,0,0
    
    for i in range(n):
        sumxy += data[i][0]*data[i][1]
        sumx += data[i][0]
        sumx2 += data[i][0]**2
        sumy += data[i][1]

    print 'sum_x=%d, sum_y=%d, sum_xy=%d, sum_x^2=%d'%(sumx,sumy,sumxy,sumx2)

    # calculate the slope,m and the y-intercept,b
    m = (n*sumxy-sumx*sumy)/float(n*sumx2 - sumx**2)
    b=(sumy-m*sumx)/float(n)

    # round off b to two decimal places
    b=round(b,2)
    print 'b=',b

    # round off m to two decimal places
    m=round(m,2)
    print 'm=',m

    return m,b

def draw_reg(m,b,paper):

    x1=-100
    y1=x1*m+b
    point=Point(x1+350,(-1)*y1+300)
    print 'x1=%f, y1=%f'%(x1,y1)
    print 'x1_=%f, y1_=%f'%(x1+350,(-1)*y1+300)

    x2=100
    y2=x2*m+b
    point2=Point(x2+350,(-1)*y2+300)
    print 'x2=%f, y2=%f'%(x2,y2)
    print 'x2_=%f, y2_=%f'%(x2+350,(-1)*y2+300)

    regline=Path(point,point2)
    paper.add(regline)

def dispEq(m,b,paper):
    text='y='+str(m)+'x + ' + str(b)
    t=Text(text,12)
    t.move(100,550)
    paper.add(t)
    

def main():

    # read data from the input file
    data=readData()

    paper=Canvas(700,600,'light yellow','Regression Line')

    # display data on the screen
    display(data,paper)
    
    # find regression
    m,b=findRegression(data)

    # draw regression line
    draw_reg(m,b,paper)

    # display the equation of the regression line
    dispEq(m,b,paper)

main()