# Copyright 2010 Hakan Kjellerstrand hakank@gmail.com
#
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#
# Unless required by applicable law or agreed to in writing, software
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and

"""

Traffic lights problem in Google CP Solver.

CSPLib problem 16
http://www.csplib.org/Problems/prob016
'''
Specification:
Consider a four way traffic junction with eight traffic lights. Four of the traffic
lights are for the vehicles and can be represented by the variables V1 to V4 with domains
{r,ry,g,y} (for red, red-yellow, green and yellow). The other four traffic lights are
for the pedestrians and can be represented by the variables P1 to P4 with domains {r,g}.

The constraints on these variables can be modelled by quaternary constraints on
(Vi, Pi, Vj, Pj ) for 1<=i<=4, j=(1+i)mod 4 which allow just the tuples
{(r,r,g,g), (ry,r,y,r), (g,g,r,r), (y,r,ry,r)}.

It would be interesting to consider other types of junction (e.g. five roads
intersecting) as well as modelling the evolution over time of the traffic light sequence.
...

Results
Only 2^2 out of the 2^12 possible assignments are solutions.

(V1,P1,V2,P2,V3,P3,V4,P4) =
{(r,r,g,g,r,r,g,g), (ry,r,y,r,ry,r,y,r), (g,g,r,r,g,g,r,r), (y,r,ry,r,y,r,ry,r)}
[(1,1,3,3,1,1,3,3), ( 2,1,4,1, 2,1,4,1), (3,3,1,1,3,3,1,1), (4,1, 2,1,4,1, 2,1)}

The problem has relative few constraints, but each is very tight. Local propagation
appears to be rather ineffective on this problem.

'''

Note: In this model we use only the constraint solver.AllowedAssignments().

Compare with these models:
* MiniZinc: http://www.hakank.org/minizinc/traffic_lights.mzn
* Comet   : http://www.hakank.org/comet/traffic_lights.co
* ECLiPSe : http://www.hakank.org/eclipse/traffic_lights.ecl
* Gecode  : http://hakank.org/gecode/traffic_lights.cpp
* SICStus : http://hakank.org/sicstus/traffic_lights.pl

This model was created by Hakan Kjellerstrand (hakank@gmail.com)

"""

import string, sys

from constraint_solver import pywrapcp

def main(base=10, start=1, len1=1, len2=4):

# Create the solver.
solver = pywrapcp.Solver('Traffic lights')

#
# data
#
n = 4
r, ry, g, y = range(n)
lights = ["r", "ry", "g", "y"]

# The allowed combinations
allowed = pywrapcp.IntTupleSet(4)
allowed.InsertAll([(r,r,g,g),
(ry,r,y,r),
(g,g,r,r),
(y,r,ry,r)])

#
# declare variables
#
V = [solver.IntVar(0, n-1, 'V[%i]' % i) for i in range(n)]
P = [solver.IntVar(0, n-1, 'P[%i]' % i) for i in range(n)]

#
# constraints
#
for i in range(n):
for j in range(n):
if j == (1+i) % n:

#
# Search and result
#
db = solver.Phase(V + P,
solver.INT_VAR_SIMPLE,
solver.INT_VALUE_DEFAULT)

solver.NewSearch(db)
num_solutions = 0
while solver.NextSolution():
for i in range(n):
print "%+2s %+2s" % (lights[V[i].Value()], lights[P[i].Value()]),
print
num_solutions += 1

solver.EndSearch()

print
print "num_solutions:", num_solutions
print "failures:", solver.Failures()
print "branches:", solver.Branches()
print "WallTime:", solver.WallTime()
print

if __name__ == '__main__':
main()