"""Tests for Gamma SSM Block."""

import torch
import pytest

from gamma_space_model import GammaSingleBlock


class TestGammaSingleBlockInitialization:
    """Test GammaSingleBlock initialization."""
    
    def test_direct_parameter_init(self):
        """Test GammaSingleBlock with direct parameters (no config)."""
        block = GammaSingleBlock(
            d_model=16,
            hidden_dim=32,
            delta_t=0.1,
            kernel_length=4,
            A_type="tridiagonal",
            prenorm=True,
            residual_scale=1.0,
            dropout=0.0,
        )
        
        assert block.d_model == 16
        assert block.prenorm is True
        assert block.residual_scale == 1.0
        assert block.dropout_p == 0.0
    
    def test_default_parameters(self):
        """Test that default parameters are set correctly."""
        block = GammaSingleBlock(d_model=16, hidden_dim=32)
        
        assert block.d_model == 16
        assert block.prenorm is True
        assert block.residual_scale == 1.0
        assert block.dropout_p == 0.0
        assert block.ssm.delta_t == 0.1
    
    def test_ssm_instantiation(self):
        """Test that SSM block is correctly instantiated."""
        block = GammaSingleBlock(
            d_model=16,
            hidden_dim=32,
            delta_t=0.2,
            A_type="tridiagonal",
        )
        
        assert block.ssm.state_dim == 16
        assert block.ssm.hidden_dim == 32
        assert block.ssm.delta_t == 0.2
        assert block.ssm.A_type == "tridiagonal"


class TestGammaSingleBlockForwardPass:
    """Test GammaSingleBlock forward pass."""
    
    def test_forward_output_shape(self):
        """Test that forward pass produces correct output shape."""
        batch_size, seq_len, d_model = 4, 32, 16
        hidden_dim = 32
        
        block = GammaSingleBlock(d_model=d_model, hidden_dim=hidden_dim)
        x = torch.randn(batch_size, seq_len, d_model)
        
        output, final_state = block(x)
        
        assert output.shape == (batch_size, seq_len, d_model)
        assert final_state.shape == (batch_size, hidden_dim)
    
    def test_forward_with_initial_state(self):
        """Test forward pass with provided initial state."""
        batch_size, seq_len, d_model, hidden_dim = 2, 16, 8, 16
        
        block = GammaSingleBlock(d_model=d_model, hidden_dim=hidden_dim)
        x = torch.randn(batch_size, seq_len, d_model)
        initial_state = torch.zeros(batch_size, hidden_dim)
        
        output1, final_state1 = block(x, state=initial_state)
        output2, final_state2 = block(x, state=None)
        
        # Should produce the same results since initial_state defaults to zeros
        assert torch.allclose(output1, output2, atol=1e-5)


class TestGammaSingleBlockNormalization:
    """Test GammaSingleBlock normalization (prenorm vs postnorm)."""
    
    def test_prenorm_configuration(self):
        """Test prenorm configuration."""
        block = GammaSingleBlock(d_model=16, hidden_dim=32, prenorm=True)
        
        x = torch.randn(2, 10, 16)
        output, _ = block(x)
        
        assert output.shape == (2, 10, 16)
    
    def test_postnorm_configuration(self):
        """Test postnorm configuration."""
        block = GammaSingleBlock(d_model=16, hidden_dim=32, prenorm=False)
        
        x = torch.randn(2, 10, 16)
        output, _ = block(x)
        
        assert output.shape == (2, 10, 16)
    
    def test_prenorm_vs_postnorm_outputs_differ(self):
        """Test that prenorm and postnorm produce different outputs."""
        x = torch.randn(2, 10, 16)
        
        prenorm_block = GammaSingleBlock(d_model=16, hidden_dim=32, prenorm=True)
        postnorm_block = GammaSingleBlock(d_model=16, hidden_dim=32, prenorm=False)
        
        output_pre, _ = prenorm_block(x)
        output_post, _ = postnorm_block(x)
        
        # Outputs should differ but have same shape
        assert output_pre.shape == output_post.shape
        assert not torch.allclose(output_pre, output_post)


class TestGammaSingleBlockResidualConnection:
    """Test GammaSingleBlock residual connection."""
    
    def test_residual_with_scale_1(self):
        """Test residual connection with scale=1.0."""
        block = GammaSingleBlock(
            d_model=16,
            hidden_dim=32,
            residual_scale=1.0,
            prenorm=True,
        )
        
        x = torch.randn(2, 10, 16)
        output, _ = block(x)
        
        # Output should be x + SSM_output (approximately close to x)
        assert torch.allclose(output, x, atol=2.0)
    
    def test_residual_with_scale_0(self):
        """Test residual connection with scale=0.0 (no residual)."""
        block = GammaSingleBlock(
            d_model=16,
            hidden_dim=32,
            residual_scale=0.0,
            prenorm=True,
        )
        
        x = torch.randn(2, 10, 16)
        output, _ = block(x)
        
        # Output should be purely from norm + SSM (not affected by input)
        # It will still be different from x
        assert not torch.allclose(output, x)
    
    def test_residual_scale_effect(self):
        """Test that residual_scale parameter affects output."""
        x = torch.randn(2, 10, 16)
        
        block1 = GammaSingleBlock(
            d_model=16,
            hidden_dim=32,
            residual_scale=0.5,
            prenorm=True,
        )
        block2 = GammaSingleBlock(
            d_model=16,
            hidden_dim=32,
            residual_scale=2.0,
            prenorm=True,
        )
        
        output1, _ = block1(x)
        output2, _ = block2(x)
        
        # Different scales should produce different outputs
        assert not torch.allclose(output1, output2)


class TestGammaSingleBlockDropout:
    """Test GammaSingleBlock dropout."""
    
    def test_dropout_train_mode(self):
        """Test that dropout is applied during training."""
        block = GammaSingleBlock(
            d_model=16,
            hidden_dim=32,
            dropout=0.5,
        )
        block.train()
        
        x = torch.randn(2, 10, 16)
        
        # Multiple forward passes should give different results due to dropout
        output1, _ = block(x)
        output2, _ = block(x)
        
        assert not torch.allclose(output1, output2)
    
    def test_dropout_eval_mode(self):
        """Test that dropout is not applied during evaluation."""
        block = GammaSingleBlock(
            d_model=16,
            hidden_dim=32,
            dropout=0.5,
        )
        block.eval()
        
        x = torch.randn(2, 10, 16)
        
        # Multiple forward passes should give same results in eval mode
        output1, _ = block(x)
        output2, _ = block(x)
        
        assert torch.allclose(output1, output2)
    
    def test_no_dropout_with_zero_dropout_rate(self):
        """Test that no dropout is applied when dropout=0."""
        block = GammaSingleBlock(
            d_model=16,
            hidden_dim=32,
            dropout=0.0,
        )
        
        # Should not have dropout layer
        assert block.dropout is None


class TestGammaSingleBlockMasking:
    """Test GammaSingleBlock masking functionality."""
    
    def test_forward_with_mask(self):
        """Test forward pass with masking."""
        batch_size, seq_len, d_model = 2, 10, 16
        hidden_dim = 32
        
        block = GammaSingleBlock(d_model=d_model, hidden_dim=hidden_dim)
        x = torch.randn(batch_size, seq_len, d_model)
        mask = torch.ones(batch_size, seq_len, dtype=torch.bool)
        mask[1, 5:] = False
        
        output, _ = block(x, mask=mask)
        
        assert output.shape == (batch_size, seq_len, d_model)


class TestGammaSingleBlockGradients:
    """Test gradient flow through GammaSingleBlock."""
    
    def test_backward_pass(self):
        """Test that gradients flow correctly."""
        batch_size, seq_len, d_model = 2, 10, 16
        hidden_dim = 32
        
        block = GammaSingleBlock(d_model=d_model, hidden_dim=hidden_dim)
        x = torch.randn(batch_size, seq_len, d_model, requires_grad=True)
        
        output, _ = block(x)
        loss = output.sum()
        loss.backward()
        
        assert x.grad is not None
        assert x.grad.shape == x.shape
        
        # Check that block parameters have gradients
        for param in block.parameters():
            if param.requires_grad:
                assert param.grad is not None
    
    def test_gradient_flow_prenorm(self):
        """Test gradient flow with prenorm."""
        block = GammaSingleBlock(d_model=16, hidden_dim=32, prenorm=True)
        x = torch.randn(2, 10, 16, requires_grad=True)
        
        output, _ = block(x)
        loss = output.sum()
        loss.backward()
        
        assert x.grad is not None
    
    def test_gradient_flow_postnorm(self):
        """Test gradient flow with postnorm."""
        block = GammaSingleBlock(d_model=16, hidden_dim=32, prenorm=False)
        x = torch.randn(2, 10, 16, requires_grad=True)
        
        output, _ = block(x)
        loss = output.sum()
        loss.backward()
        
        assert x.grad is not None


class TestGammaSingleBlockIntegration:
    """Integration tests for GammaSingleBlock."""
    
    def test_stacked_blocks(self):
        """Test stacking multiple blocks together."""
        d_model, hidden_dim = 16, 32
        num_blocks = 3
        
        blocks = [
            GammaSingleBlock(d_model=d_model, hidden_dim=hidden_dim)
            for _ in range(num_blocks)
        ]
        
        x = torch.randn(2, 10, d_model)
        states = []
        
        # Forward through blocks
        for block in blocks:
            x, state = block(x)
            states.append(state)
        
        assert x.shape == (2, 10, d_model)
        assert len(states) == num_blocks
    
    def test_device_transfer(self):
        """Test that block can be transferred between devices."""
        block = GammaSingleBlock(d_model=16, hidden_dim=32)
        
        # Test on CPU
        x_cpu = torch.randn(2, 10, 16)
        output_cpu, _ = block(x_cpu)
        assert output_cpu.device.type == "cpu"
        
        if torch.cuda.is_available():
            # Transfer to GPU
            block = block.cuda()
            x_gpu = torch.randn(2, 10, 16).cuda()
            output_gpu, _ = block(x_gpu)
            assert output_gpu.device.type == "cuda"
            
            # Transfer back to CPU
            block = block.cpu()
            output_cpu2, _ = block(x_cpu)
            assert output_cpu2.device.type == "cpu"
    
    def test_state_dict_save_load(self):
        """Test saving and loading state dict."""
        block1 = GammaSingleBlock(d_model=16, hidden_dim=32)
        block2 = GammaSingleBlock(d_model=16, hidden_dim=32)
        
        # Save state dict from block1
        state_dict = block1.state_dict()
        
        # Load into block2
        block2.load_state_dict(state_dict)
        
        # They should produce same output
        x = torch.randn(2, 10, 16)
        
        with torch.no_grad():
            out1, _ = block1(x)
            out2, _ = block2(x)
        
        assert torch.allclose(out1, out2, atol=1e-6)
    
    def test_train_eval_mode_switching(self):
        """Test switching between train and eval modes."""
        block = GammaSingleBlock(d_model=16, hidden_dim=32, dropout=0.5)
        
        # Train mode
        block.train()
        assert block.training
        
        # Eval mode
        block.eval()
        assert not block.training
        
        # Train mode again
        block.train()
        assert block.training
    
    def test_different_d_models_and_hidden_dims(self):
        """Test blocks with various dimensions."""
        configs = [
            (8, 16),
            (16, 32),
            (64, 128),
            (256, 512),
        ]
        
        for d_model, hidden_dim in configs:
            block = GammaSingleBlock(d_model=d_model, hidden_dim=hidden_dim)
            x = torch.randn(2, 10, d_model)
            
            output, state = block(x)
            
            assert output.shape == (2, 10, d_model)
            assert state.shape == (2, hidden_dim)


if __name__ == "__main__":
    pytest.main([__file__, "-v"])