'''lecture_28_koch_lsystem.py
Draw a Koch snowflake using an L-system
Oliver W. Layton
CS 151: Computational Thinking: Visual Media
Spring 2021
'''
import turtle


def drawString(turt, string, dist, angle):
    '''Have `turt` draw the L-system string, where `turt` moves forward with a distance `dist` and
    turns at an angle `angle` degrees
    '''
    for char in string:
        if char == 'F':
            turt.forward(dist)
        elif char == '+':
            turt.left(angle)
        elif char == '-':
            turt.right(angle)


def replace(string, findStr, repStr):
    '''Make a new string that applies the L-system replacement rules:
    Replace each occurence of `findStr` in `string` with `repStr`

    Returns:
    ---------
    The new string with the replacement rules applied to `string`
    '''
    # findStr: 'F'
    # repStr: 'F-F++F-F'
    newString = ''
    for char in string:
        # first time around, char = 'F'
        if char == findStr:  # findStr is 'F' here
            # if findStr matches currString
            newString = newString + repStr
        else:
            # otherwise copy over current char to our result as-is
            newString = newString + char
    return newString


if __name__ == '__main__':
    # Make a screen, turn off animations so snowflake draws fast
    screen = turtle.Screen()
    screen.setup(600, 600)
    screen.tracer(False)

    # Make a turtle
    turt = turtle.Turtle()

    # Set up L-system rules
    baseString = 'F++F++F'
    findString = 'F'
    replaceString = 'F-F++F-F'

    # Set up distance and angle for Koch snowflake
    d = 0.4
    theta = 60

    # Apply the L-system replacement rules some number of times (iterations)
    lSysString = baseString  # start with initial shape (triangle)
    nIter = 7
    for i in range(nIter):
        lSysString = replace(lSysString, findString, replaceString)

    # print('l sys string:', lSysString)
    print('l sys string (length):', len(lSysString))

    # Draw the L-system
    drawString(turt, lSysString, d, theta)

    screen.update()
    screen.exitonclick()