'''lecture_27_koch_lsystem.py
Draw a Koch snowflake using an L-system
Oliver W. Layton
CS 151: Computational Thinking: Visual Media
Fall 2020
'''
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)
        if char == '+':
            turt.left(angle)
        if 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`
    '''
    newString = ''
    for char in string:
        if char == findStr:
            newString += repStr
        else:
            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
    baseStr = 'F++F++F'
    findStr = 'F'
    replaceStr = 'F-F++F-F'

    # Set up distance and angle for Koch snowflake
    distance = 100
    angle = 60

    # Apply the L-system replacement rules some number of times (iterations)
    numIterations = 2
    string = baseStr
    for i in range(numIterations):
        string = replace(string, findStr, replaceStr)

    # Draw the L-system
    drawString(turt, string, distance, angle)

    print(string)

    screen.update()
    screen.exitonclick()