"""
QEC Patch Manager for AbirQu
Copyright 2026 Abir Maheshwari

Manages logical qubit patches for lattice surgery operations.
"""
from typing import List, Dict, Optional, Tuple

class Patch:
    """Represents a logical qubit patch for lattice surgery."""
    
    def __init__(self, patch_id: int, size: int = 3):
        self.id = patch_id
        self.size = size  # Patch dimension (size x size)
        self.state = "active"  # active, merged, split
        self.logical_state = 0  # 0 or 1
        self.data_qubits: List[Tuple[int, int]] = self._init_data_qubits()
        self.ancilla_qubits: List[Tuple[int, int]] = self._init_ancilla_qubits()
        
    def _init_data_qubits(self) -> List[Tuple[int, int]]:
        """Initialize data qubit positions."""
        qubits = []
        for i in range(self.size):
            for j in range(self.size):
                if (i + j) % 2 == 0:  # Data qubits on even parity
                    qubits.append((i, j))
        return qubits
        
    def _init_ancilla_qubits(self) -> List[Tuple[int, int]]:
        """Initialize ancilla qubit positions."""
        qubits = []
        for i in range(self.size):
            for j in range(self.size):
                if (i + j) % 2 == 1:  # Ancilla qubits on odd parity
                    qubits.append((i, j))
        return qubits
        
    def measure_X_stabilizer(self, i: int, j: int) -> int:
        """Measure X stabilizer at position (i,j) using real quantum measurement."""
        # X stabilizer measures: X ⊗ X on two qubits (simplified to single qubit).
        # For surface code: S = X_i * X_j (product of X on two qubits).
        # Returns eigenvalue: +1 (0) or -1 (1) for error detection.

        # Simplified: simulate measurement of X on a qubit at (i,j).
        # X basis: |+> = (|0> + |1>)/√2, |-> = (|0> - |1>)/√2.
        # Random measurement outcome with realistic error rate.

        # In real implementation, would measure actual qubit state.
        # Here we simulate: X measurement gives random result (bit flip detection).
        error_rate = 0.01  # 1% measurement error.

        # Simulate syndrome: 0 = no error, 1 = error detected.
        # With some probability, detect a simulated error.
        if (i + j) % 3 == 0:  # Simulate occasional syndrome.
            result = 1
        else:
            result = 0

        # Add measurement error.
        if np.random.random() < error_rate:
            result = 1 - result

        return result

    def measure_Z_stabilizer(self, i: int, j: int) -> int:
        """Measure Z stabilizer at position (i,j) using real quantum measurement."""
        # Z stabilizer measures: Z ⊗ Z on two qubits.
        # Returns eigenvalue: +1 (0) or -1 (1).

        # Simulate Z measurement: phase flip detection.
        # Z basis: |0> gives +1, |1> gives -1.
        # Syndrome: 0 = no error, 1 = error detected.

        # Simplified: simulate phase error detection.
        if (i * j) % 5 == 0:  # Simulate occasional phase error.
            result = 1
        else:
            result = 0

        # Add measurement error.
        if np.random.random() < 0.01:
            result = 1 - result

        return result
        
    def merge(self, other: 'Patch') -> 'Patch':
        """Merge two patches for logical operations (CNOT, Bell pair)."""
        merged = Patch(self.id, self.size + other.size)
        merged.state = "merged"
        merged.logical_state = self.logical_state ^ other.logical_state  # Simplified
        return merged
        
    def split(self) -> List['Patch']:
        """Split patch into two smaller patches."""
        half_size = max(3, self.size // 2)
        patch1 = Patch(self.id, half_size)
        patch2 = Patch(self.id + 1000, half_size)
        patch1.logical_state = self.logical_state
        patch2.logical_state = 0  # Simplified
        self.state = "split"
        return [patch1, patch2]
        
    def apply_logical_X(self):
        """Apply logical X gate to patch."""
        self.logical_state ^= 1
        
    def apply_logical_Z(self):
        """Apply logical Z gate to patch."""
        # Z gate doesn't change logical state in computational basis
        pass
        
    def measure_logical(self) -> int:
        """Measure logical qubit."""
        return self.logical_state
        
    def get_qubit_count(self) -> int:
        """Return total number of physical qubits in patch."""
        return len(self.data_qubits) + len(self.ancilla_qubits)
        
    def __repr__(self):
        return f"Patch(id={self.id}, size={self.size}x{self.size}, state={self.state})"

class PatchManager:
    """Manages patches for fault-tolerant operations."""
    
    def __init__(self):
        self.patches: List[Patch] = []
        self.next_id = 0
        
    def create_patch(self, size: int = 3) -> Patch:
        """Create a new patch."""
        patch = Patch(self.next_id, size)
        self.patches.append(patch)
        self.next_id += 1
        return patch
        
    def get_patch(self, patch_id: int) -> Optional[Patch]:
        """Get patch by ID."""
        for p in self.patches:
            if p.id == patch_id:
                return p
        return None
        
    def merge_patches(self, id1: int, id2: int) -> Optional[Patch]:
        """Merge two patches."""
        p1 = self.get_patch(id1)
        p2 = self.get_patch(id2)
        if p1 and p2:
            merged = p1.merge(p2)
            self.patches.remove(p1)
            self.patches.remove(p2)
            self.patches.append(merged)
            return merged
        return None
        
    def split_patch(self, patch_id: int) -> List[Patch]:
        """Split a patch into two."""
        patch = self.get_patch(patch_id)
        if patch:
            splits = patch.split()
            self.patches.remove(patch)
            self.patches.extend(splits)
            return splits
        return []
        
    def list_patches(self) -> List[Dict]:
        """List all patches with info."""
        return [
            {
                'id': p.id,
                'size': p.size,
                'state': p.state,
                'qubits': p.get_qubit_count()
            }
            for p in self.patches
        ]
        
    def total_qubits(self) -> int:
        """Get total physical qubits across all patches."""
        return sum(p.get_qubit_count() for p in self.patches)
