"""
The Farm Ver 1.3 (thefarm.py)

featuring...

from the OST Skunkworks:  a Freakish Tractor

generator that moves forward to a boundary reading
current character, writing current marker.  Fuel
might run out.  The send method may be employed to
tank up, redirect, change the marker.  Farm is an
n x m array, presumably smallish, for interactive
console experiments.

  -- Python track, O'Reilly School of Technology
  http://www.facebook.com/oreillyschool
  
"""

import ost

from ost.farmworld import Farm # an ascii canvas

def tractor(thefarm , pos = [0,0], facing="N", marker="O", fuel=10):
    "pos is mutable = current position"
    while True:
        y,x = pos
        
        if fuel > 0:
            
            if facing   == "N":
                if y > 0:
                    y -= 1
                else:
                    return

            elif facing == "S": 
                if y < thefarm.h - 1:
                    y += 1
                else:
                    return
                
            elif facing == "W": 
                if x > 0:
                    x -= 1
                else:
                    return
                
            elif facing == "E": 
                if x < thefarm.w - 1:
                    x += 1
                else:
                    return
                    
            fuel -= 1            
            pos = (y,x)

        else:
            return

        changes = yield (thefarm.field[y][x], pos, fuel)
        thefarm.field[y][x] = marker
            
        if changes:
            facing = changes.get('facing',facing)
            marker = changes.get('marker',marker)
            fuel   = changes.get('fuel',fuel)
            pos    = changes.get('pos',pos)

def _test(n):
    # Agile Programming:  TDD is your friend
    thefarm = Farm(20,20, bg = ".")
    print("Empty field, all is peaceful", thefarm, sep="\n\n")  # frame of film
    t1 = tractor(thefarm, pos=[10,10], marker="O", facing="N")
    t2 = tractor(thefarm, pos=[10,11], marker="X", facing="S")
    thefarm.add(t1)
    thefarm.add(t2)
    print("Showing the tractors in a list: ", thefarm.tractors, "===", sep="\n")
    print("A busy day begins...", thefarm, sep="\n\n")  # frame of film

    for arrow_of_time in range(n):
        thefarm.ticktock()  # much physics involved in terms of what's a realistic throughput
        
    print("After {} ticks of the clock, the tractors have moved...".format(n),
          thefarm, sep="\n\n")  # frame of film

if __name__ == "__main__":
    _test(10)