"""
Bug Reproduction: MultiGrid._empty_mask not updated correctly

This script demonstrates that MultiGrid.place_agent() does not update
the _empty_mask array, causing select_cells(only_empty=True) to return
cells that have agents in them.
"""

from mesa import Agent, Model
from mesa.space import MultiGrid, SingleGrid

class TestAgent(Agent):
    """Simple agent for testing."""
    pass

# Create model and grids
model = Model()
single_grid = SingleGrid(3, 3, torus=False)
multi_grid = MultiGrid(3, 3, torus=False)

# Create agents
agent1 = TestAgent(model)
agent2 = TestAgent(model)

print("=" * 60)
print("TEST 1: Compare _empty_mask after placing agent")
print("=" * 60)

# Place agents at (1,1) on both grids
single_grid.place_agent(agent1, (1, 1))
multi_grid.place_agent(agent2, (1, 1))

print(f"\nAfter placing agent at (1,1):")
print(f"  SingleGrid._empty_mask[1,1] = {single_grid._empty_mask[1,1]}")
print(f"  MultiGrid._empty_mask[1,1]  = {multi_grid._empty_mask[1,1]}")
print(f"\n  Expected: Both should be False (cell is occupied)")

# Verify actual cell state
print(f"\nActual cell state (ground truth):")
print(f"  SingleGrid.is_cell_empty((1,1)) = {single_grid.is_cell_empty((1, 1))}")
print(f"  MultiGrid.is_cell_empty((1,1))  = {multi_grid.is_cell_empty((1, 1))}")

print("\n" + "=" * 60)
print("TEST 2: Impact on select_cells(only_empty=True)")
print("=" * 60)

# Create fresh MultiGrid for this test
model2 = Model()
grid = MultiGrid(3, 3, torus=False)
agent = TestAgent(model2)
grid.place_agent(agent, (1, 1))

empty_cells = grid.select_cells(only_empty=True)

print(f"\nMultiGrid 3x3 with 1 agent at (1,1):")
print(f"  Total cells: 9")
print(f"  Agent at: (1,1)")
print(f"  select_cells(only_empty=True) returns: {len(empty_cells)} cells")
print(f"  Expected: 8 cells")

print(f"\n  Cells returned: {empty_cells}")

if (1, 1) in empty_cells:
    print(f"\n   BUG: (1,1) is in 'empty' list but has an agent!")
else:
    print(f"\n  Correct: (1,1) not in 'empty' list")

print("\n" + "=" * 60)
print("TEST 3: Cross-reference _empties set vs _empty_mask")
print("=" * 60)

# These two data structures should be in sync
model3 = Model()
grid3 = MultiGrid(3, 3, torus=False)
agent3 = TestAgent(model3)

# Force _empties to be built
_ = grid3.empties

print(f"\nBefore placing agent:")
print(f"  (1,1) in _empties: {(1,1) in grid3._empties}")
print(f"  _empty_mask[1,1]:  {grid3._empty_mask[1,1]}")

grid3.place_agent(agent3, (1, 1))

print(f"\nAfter placing agent at (1,1):")
print(f"  (1,1) in _empties: {(1,1) in grid3._empties}")
print(f"  _empty_mask[1,1]:  {grid3._empty_mask[1,1]}")

if (1,1) not in grid3._empties and grid3._empty_mask[1,1] == True:
    print(f"\n   INCONSISTENCY: _empties says occupied, but _empty_mask says empty!")

if self._empties_built:
    self._empties.discard(pos)
self._empty_mask[pos] = False  # OUTSIDE the if block

if self._empties_built:
    self._empties.discard(pos)
    self._empty_mask[agent.pos] = True  # INSIDE the if block!

# MultiGrid.place_agent - move _empty_mask update outside if block:
if self._empties_built:
    self._empties.discard(pos)
self._empty_mask[pos] = False  # Always update, use False for occupied

# MultiGrid.remove_agent - similar fix:
if self._empties_built and self.is_cell_empty(pos):
    self._empties.add(pos)
if self.is_cell_empty(pos):
    self._empty_mask[pos] = True  # Update when cell becomes empty