quantrs2_circuit/optimization/

passes.rs

//! Individual optimization passes
//!
//! This module implements various optimization passes that can be applied to quantum circuits.

use crate::builder::Circuit;
use crate::optimization::cost_model::CostModel;
use crate::optimization::gate_properties::{get_gate_properties, CommutationTable};
use quantrs2_core::decomposition::{decompose_controlled_rotation, GateDecomposable};
use quantrs2_core::error::{QuantRS2Error, QuantRS2Result};
use quantrs2_core::gate::{
    multi,
    single::{self, PauliX, PauliZ, RotationX, RotationY, RotationZ},
    GateOp,
};
use quantrs2_core::qubit::QubitId;
use std::collections::{HashMap, HashSet};
use std::f64::consts::PI;

/// Trait for optimization passes (object-safe version)
pub trait OptimizationPass: Send + Sync {
    /// Name of the optimization pass
    fn name(&self) -> &str;

    /// Apply the optimization pass to a gate list
    fn apply_to_gates(
        &self,
        gates: Vec<Box<dyn GateOp>>,
        cost_model: &dyn CostModel,
    ) -> QuantRS2Result<Vec<Box<dyn GateOp>>>;

    /// Check if this pass should be applied
    fn should_apply(&self) -> bool {
        true
    }
}

/// Extension trait for circuit operations
pub trait OptimizationPassExt<const N: usize> {
    fn apply(&self, circuit: &Circuit<N>, cost_model: &dyn CostModel)
        -> QuantRS2Result<Circuit<N>>;
    fn should_apply_to_circuit(&self, circuit: &Circuit<N>) -> bool;
}

impl<T: OptimizationPass + ?Sized, const N: usize> OptimizationPassExt<N> for T {
    fn apply(
        &self,
        circuit: &Circuit<N>,
        cost_model: &dyn CostModel,
    ) -> QuantRS2Result<Circuit<N>> {
        // TODO: Convert circuit to gates, apply pass, convert back
        Ok(circuit.clone())
    }

    fn should_apply_to_circuit(&self, _circuit: &Circuit<N>) -> bool {
        self.should_apply()
    }
}

/// Gate cancellation pass - removes redundant gates
pub struct GateCancellation {
    aggressive: bool,
}

impl GateCancellation {
    #[must_use]
    pub const fn new(aggressive: bool) -> Self {
        Self { aggressive }
    }
}

impl OptimizationPass for GateCancellation {
    fn name(&self) -> &'static str {
        "Gate Cancellation"
    }

    fn apply_to_gates(
        &self,
        gates: Vec<Box<dyn GateOp>>,
        _cost_model: &dyn CostModel,
    ) -> QuantRS2Result<Vec<Box<dyn GateOp>>> {
        let mut optimized = Vec::new();
        let mut i = 0;

        while i < gates.len() {
            if i + 1 < gates.len() {
                let gate1 = &gates[i];
                let gate2 = &gates[i + 1];

                // Check if gates act on the same qubits
                if gate1.qubits() == gate2.qubits() && gate1.name() == gate2.name() {
                    // Check for self-inverse gates (H, X, Y, Z)
                    match gate1.name() {
                        "H" | "X" | "Y" | "Z" => {
                            // These gates cancel when applied twice - skip both
                            i += 2;
                            continue;
                        }
                        "RX" | "RY" | "RZ" => {
                            // Check if rotations cancel
                            if let (Some(rx1), Some(rx2)) = (
                                gate1.as_any().downcast_ref::<single::RotationX>(),
                                gate2.as_any().downcast_ref::<single::RotationX>(),
                            ) {
                                let combined_angle = rx1.theta + rx2.theta;
                                // Check if the combined rotation is effectively zero
                                if (combined_angle % (2.0 * PI)).abs() < 1e-10 {
                                    i += 2;
                                    continue;
                                }
                            } else if let (Some(ry1), Some(ry2)) = (
                                gate1.as_any().downcast_ref::<single::RotationY>(),
                                gate2.as_any().downcast_ref::<single::RotationY>(),
                            ) {
                                let combined_angle = ry1.theta + ry2.theta;
                                if (combined_angle % (2.0 * PI)).abs() < 1e-10 {
                                    i += 2;
                                    continue;
                                }
                            } else if let (Some(rz1), Some(rz2)) = (
                                gate1.as_any().downcast_ref::<single::RotationZ>(),
                                gate2.as_any().downcast_ref::<single::RotationZ>(),
                            ) {
                                let combined_angle = rz1.theta + rz2.theta;
                                if (combined_angle % (2.0 * PI)).abs() < 1e-10 {
                                    i += 2;
                                    continue;
                                }
                            }
                        }
                        "CNOT" => {
                            // CNOT is self-inverse
                            if let (Some(cnot1), Some(cnot2)) = (
                                gate1.as_any().downcast_ref::<multi::CNOT>(),
                                gate2.as_any().downcast_ref::<multi::CNOT>(),
                            ) {
                                if cnot1.control == cnot2.control && cnot1.target == cnot2.target {
                                    i += 2;
                                    continue;
                                }
                            }
                        }
                        _ => {}
                    }
                }

                // Look for more complex cancellations if aggressive mode is enabled
                if self.aggressive && i + 2 < gates.len() {
                    // Check for patterns like X-Y-X-Y or Z-H-Z-H
                    let gate3 = &gates[i + 2];
                    if gate1.qubits() == gate3.qubits()
                        && gate1.name() == gate3.name()
                        && i + 3 < gates.len()
                    {
                        let gate4 = &gates[i + 3];
                        if gate2.qubits() == gate4.qubits()
                            && gate2.name() == gate4.name()
                            && gate1.qubits() == gate2.qubits()
                        {
                            // Pattern detected, check if it simplifies
                            match (gate1.name(), gate2.name()) {
                                ("X", "Y") | ("Y", "X") | ("Z", "H") | ("H", "Z") => {
                                    // These patterns can sometimes simplify
                                    // For now, we'll keep them as they might not always cancel
                                }
                                _ => {}
                            }
                        }
                    }
                }
            }

            // If we didn't skip, add the gate to optimized list
            optimized.push(gates[i].clone());
            i += 1;
        }

        Ok(optimized)
    }
}

/// Gate commutation pass - reorders gates to enable other optimizations
pub struct GateCommutation {
    max_lookahead: usize,
    commutation_table: CommutationTable,
}

impl GateCommutation {
    #[must_use]
    pub fn new(max_lookahead: usize) -> Self {
        Self {
            max_lookahead,
            commutation_table: CommutationTable::new(),
        }
    }
}

impl GateCommutation {
    /// Check if two gates commute based on commutation rules
    fn gates_commute(&self, gate1: &dyn GateOp, gate2: &dyn GateOp) -> bool {
        // Use commutation table if available
        if self.commutation_table.commutes(gate1.name(), gate2.name()) {
            return true;
        }

        // Additional commutation rules
        match (gate1.name(), gate2.name()) {
            // Pauli gates commutation
            ("X", "X") | ("Y", "Y") | ("Z", "Z") => true,
            ("I", _) | (_, "I") => true,

            // Phase/T gates commute with Z
            ("S" | "T", "Z") | ("Z", "S" | "T") => true,

            // Same-axis rotations commute
            ("RX", "RX") | ("RY", "RY") | ("RZ", "RZ") => true,

            // RZ commutes with Z-like gates
            ("RZ", "Z" | "S" | "T") | ("Z" | "S" | "T", "RZ") => true,

            _ => false,
        }
    }

    /// Check if swapping gates at position i would enable optimizations
    fn would_benefit_from_swap(&self, gates: &[Box<dyn GateOp>], i: usize) -> bool {
        if i + 2 >= gates.len() {
            return false;
        }

        let gate1 = &gates[i];
        let gate2 = &gates[i + 1];
        let gate3 = &gates[i + 2];

        // Check if swapping would create cancellation opportunities
        if gate1.name() == gate3.name() && gate1.qubits() == gate3.qubits() {
            // After swap, gate2 and gate3 (originally gate1) would be adjacent
            match gate3.name() {
                "H" | "X" | "Y" | "Z" => return true,
                _ => {}
            }
        }

        // Check if swapping would enable rotation merging
        if gate2.name() == gate3.name() && gate2.qubits() == gate3.qubits() {
            match gate2.name() {
                "RX" | "RY" | "RZ" => return true,
                _ => {}
            }
        }

        false
    }
}

impl OptimizationPass for GateCommutation {
    fn name(&self) -> &'static str {
        "Gate Commutation"
    }

    fn apply_to_gates(
        &self,
        gates: Vec<Box<dyn GateOp>>,
        _cost_model: &dyn CostModel,
    ) -> QuantRS2Result<Vec<Box<dyn GateOp>>> {
        if gates.len() < 2 {
            return Ok(gates);
        }

        let mut optimized = gates;
        let mut changed = true;

        // Keep trying to commute gates until no more changes
        while changed {
            changed = false;
            let mut i = 0;

            while i < optimized.len().saturating_sub(1) {
                let can_swap = {
                    let gate1 = &optimized[i];
                    let gate2 = &optimized[i + 1];

                    // Check if gates act on different qubits (always commute)
                    let qubits1: HashSet<_> = gate1.qubits().into_iter().collect();
                    let qubits2: HashSet<_> = gate2.qubits().into_iter().collect();

                    if qubits1.is_disjoint(&qubits2) {
                        // Gates on disjoint qubits always commute
                        // Check if swapping would enable optimizations
                        self.would_benefit_from_swap(&optimized, i)
                    } else if qubits1 == qubits2 {
                        // Gates on same qubits - check commutation rules
                        self.gates_commute(gate1.as_ref(), gate2.as_ref())
                    } else {
                        // Overlapping but not identical qubit sets
                        false
                    }
                };

                if can_swap {
                    optimized.swap(i, i + 1);
                    changed = true;
                    // Don't increment i to check if we can swap further back
                    i = i.saturating_sub(1);
                } else {
                    i += 1;
                }

                // Limit lookahead to prevent excessive computation
                if i >= self.max_lookahead {
                    break;
                }
            }
        }

        Ok(optimized)
    }
}

/// Gate merging pass - combines adjacent gates
pub struct GateMerging {
    merge_rotations: bool,
    merge_threshold: f64,
}

impl GateMerging {
    #[must_use]
    pub const fn new(merge_rotations: bool, merge_threshold: f64) -> Self {
        Self {
            merge_rotations,
            merge_threshold,
        }
    }
}

impl OptimizationPass for GateMerging {
    fn name(&self) -> &'static str {
        "Gate Merging"
    }

    fn apply_to_gates(
        &self,
        gates: Vec<Box<dyn GateOp>>,
        _cost_model: &dyn CostModel,
    ) -> QuantRS2Result<Vec<Box<dyn GateOp>>> {
        let mut optimized = Vec::new();
        let mut i = 0;

        while i < gates.len() {
            if i + 1 < gates.len() && self.merge_rotations {
                let gate1 = &gates[i];
                let gate2 = &gates[i + 1];

                // Try to merge rotation gates
                if gate1.qubits() == gate2.qubits() {
                    let merged = match (gate1.name(), gate2.name()) {
                        // Same-axis rotations can be directly merged
                        ("RX", "RX") | ("RY", "RY") | ("RZ", "RZ") => {
                            // Already handled by RotationMerging pass, skip here
                            None
                        }
                        // Different axis rotations might be mergeable using Euler decomposition
                        ("RZ" | "RY", "RX") | ("RX" | "RY", "RZ") | ("RX" | "RZ", "RY")
                            if self.merge_threshold > 0.0 =>
                        {
                            // Complex merging would require matrix multiplication
                            // For now, skip this advanced optimization
                            None
                        }
                        // Phase gates (S, T) can sometimes be merged with RZ
                        ("S" | "T", "RZ") | ("RZ", "S" | "T") => {
                            // S = RZ(π/2), T = RZ(π/4)
                            // These could be merged but need special handling
                            None
                        }
                        _ => None,
                    };

                    if let Some(merged_gate) = merged {
                        optimized.push(merged_gate);
                        i += 2;
                        continue;
                    }
                }
            }

            // Check for special merging patterns
            if i + 1 < gates.len() {
                let gate1 = &gates[i];
                let gate2 = &gates[i + 1];

                // H-Z-H = X, H-X-H = Z (basis change)
                if i + 2 < gates.len() {
                    let gate3 = &gates[i + 2];
                    if gate1.name() == "H"
                        && gate3.name() == "H"
                        && gate1.qubits() == gate2.qubits()
                        && gate2.qubits() == gate3.qubits()
                    {
                        match gate2.name() {
                            "Z" => {
                                // H-Z-H = X
                                optimized.push(Box::new(single::PauliX {
                                    target: gate1.qubits()[0],
                                })
                                    as Box<dyn GateOp>);
                                i += 3;
                                continue;
                            }
                            "X" => {
                                // H-X-H = Z
                                optimized.push(Box::new(single::PauliZ {
                                    target: gate1.qubits()[0],
                                })
                                    as Box<dyn GateOp>);
                                i += 3;
                                continue;
                            }
                            _ => {}
                        }
                    }
                }
            }

            // If no merging happened, keep the original gate
            optimized.push(gates[i].clone());
            i += 1;
        }

        Ok(optimized)
    }
}

/// Rotation merging pass - specifically merges rotation gates
pub struct RotationMerging {
    tolerance: f64,
}

impl RotationMerging {
    #[must_use]
    pub const fn new(tolerance: f64) -> Self {
        Self { tolerance }
    }

    /// Check if angle is effectively zero (or 2π multiple)
    fn is_zero_rotation(&self, angle: f64) -> bool {
        let normalized = angle % (2.0 * PI);
        normalized.abs() < self.tolerance || 2.0f64.mul_add(-PI, normalized).abs() < self.tolerance
    }

    /// Merge two rotation angles
    fn merge_angles(&self, angle1: f64, angle2: f64) -> f64 {
        let merged = angle1 + angle2;
        let normalized = merged % (2.0 * PI);
        if normalized > PI {
            2.0f64.mul_add(-PI, normalized)
        } else if normalized < -PI {
            2.0f64.mul_add(PI, normalized)
        } else {
            normalized
        }
    }
}

impl OptimizationPass for RotationMerging {
    fn name(&self) -> &'static str {
        "Rotation Merging"
    }

    fn apply_to_gates(
        &self,
        gates: Vec<Box<dyn GateOp>>,
        _cost_model: &dyn CostModel,
    ) -> QuantRS2Result<Vec<Box<dyn GateOp>>> {
        let mut optimized = Vec::new();
        let mut i = 0;

        while i < gates.len() {
            if i + 1 < gates.len() {
                let gate1 = &gates[i];
                let gate2 = &gates[i + 1];

                // Check if both gates are rotations on the same qubit and axis
                if gate1.qubits() == gate2.qubits() && gate1.name() == gate2.name() {
                    match gate1.name() {
                        "RX" => {
                            if let (Some(rx1), Some(rx2)) = (
                                gate1.as_any().downcast_ref::<single::RotationX>(),
                                gate2.as_any().downcast_ref::<single::RotationX>(),
                            ) {
                                let merged_angle = self.merge_angles(rx1.theta, rx2.theta);
                                if self.is_zero_rotation(merged_angle) {
                                    // Skip both gates if the merged rotation is effectively zero
                                    i += 2;
                                    continue;
                                }
                                // Create a new merged rotation gate
                                optimized.push(Box::new(single::RotationX {
                                    target: rx1.target,
                                    theta: merged_angle,
                                })
                                    as Box<dyn GateOp>);
                                i += 2;
                                continue;
                            }
                        }
                        "RY" => {
                            if let (Some(ry1), Some(ry2)) = (
                                gate1.as_any().downcast_ref::<single::RotationY>(),
                                gate2.as_any().downcast_ref::<single::RotationY>(),
                            ) {
                                let merged_angle = self.merge_angles(ry1.theta, ry2.theta);
                                if self.is_zero_rotation(merged_angle) {
                                    i += 2;
                                    continue;
                                }
                                optimized.push(Box::new(single::RotationY {
                                    target: ry1.target,
                                    theta: merged_angle,
                                })
                                    as Box<dyn GateOp>);
                                i += 2;
                                continue;
                            }
                        }
                        "RZ" => {
                            if let (Some(rz1), Some(rz2)) = (
                                gate1.as_any().downcast_ref::<single::RotationZ>(),
                                gate2.as_any().downcast_ref::<single::RotationZ>(),
                            ) {
                                let merged_angle = self.merge_angles(rz1.theta, rz2.theta);
                                if self.is_zero_rotation(merged_angle) {
                                    i += 2;
                                    continue;
                                }
                                optimized.push(Box::new(single::RotationZ {
                                    target: rz1.target,
                                    theta: merged_angle,
                                })
                                    as Box<dyn GateOp>);
                                i += 2;
                                continue;
                            }
                        }
                        _ => {}
                    }
                }
            }

            // If we didn't merge, keep the original gate
            optimized.push(gates[i].clone());
            i += 1;
        }

        Ok(optimized)
    }
}

/// Decomposition optimization - chooses optimal decompositions based on hardware
pub struct DecompositionOptimization {
    target_gate_set: HashSet<String>,
    prefer_native: bool,
}

impl DecompositionOptimization {
    #[must_use]
    pub const fn new(target_gate_set: HashSet<String>, prefer_native: bool) -> Self {
        Self {
            target_gate_set,
            prefer_native,
        }
    }

    #[must_use]
    pub fn for_hardware(hardware: &str) -> Self {
        let target_gate_set = match hardware {
            "ibm" => vec!["X", "Y", "Z", "H", "S", "T", "RZ", "CNOT", "CZ"]
                .into_iter()
                .map(std::string::ToString::to_string)
                .collect(),
            "google" => vec!["X", "Y", "Z", "H", "RZ", "CZ", "SQRT_X"]
                .into_iter()
                .map(std::string::ToString::to_string)
                .collect(),
            _ => vec!["X", "Y", "Z", "H", "S", "T", "RZ", "RX", "RY", "CNOT"]
                .into_iter()
                .map(std::string::ToString::to_string)
                .collect(),
        };

        Self {
            target_gate_set,
            prefer_native: true,
        }
    }
}

impl OptimizationPass for DecompositionOptimization {
    fn name(&self) -> &'static str {
        "Decomposition Optimization"
    }

    fn apply_to_gates(
        &self,
        gates: Vec<Box<dyn GateOp>>,
        cost_model: &dyn CostModel,
    ) -> QuantRS2Result<Vec<Box<dyn GateOp>>> {
        let mut optimized_gates = Vec::with_capacity(gates.len() * 2);

        for gate in gates {
            let gate_name = gate.name();
            let gate_qubits = gate.qubits();

            // Check if this gate should be decomposed based on target gate set
            if self.should_decompose(&gate, cost_model) {
                // Decompose complex gates into simpler ones
                match gate_name {
                    "Toffoli" => {
                        if gate_qubits.len() == 3 {
                            // Decompose Toffoli into CNOT and T gates
                            self.decompose_toffoli(&gate_qubits, &mut optimized_gates)?;
                        } else {
                            optimized_gates.push(gate);
                        }
                    }
                    "Fredkin" | "CSWAP" => {
                        if gate_qubits.len() == 3 {
                            // Decompose Fredkin into CNOT gates
                            self.decompose_fredkin(&gate_qubits, &mut optimized_gates)?;
                        } else {
                            optimized_gates.push(gate);
                        }
                    }
                    "SWAP" => {
                        if self.target_gate_set.contains("CNOT") && gate_qubits.len() == 2 {
                            // Decompose SWAP into 3 CNOTs
                            self.decompose_swap(&gate_qubits, &mut optimized_gates)?;
                        } else {
                            optimized_gates.push(gate);
                        }
                    }
                    "CRX" | "CRY" | "CRZ" => {
                        // Decompose controlled rotations if not in target set
                        if !self.target_gate_set.contains(gate_name) && gate_qubits.len() == 2 {
                            self.decompose_controlled_rotation(&gate, &mut optimized_gates)?;
                        } else {
                            optimized_gates.push(gate);
                        }
                    }
                    _ => {
                        // Keep gates that don't need decomposition
                        optimized_gates.push(gate);
                    }
                }
            } else {
                optimized_gates.push(gate);
            }
        }

        Ok(optimized_gates)
    }
}

impl DecompositionOptimization {
    /// Helper methods for decomposition

    fn should_decompose(&self, gate: &Box<dyn GateOp>, _cost_model: &dyn CostModel) -> bool {
        let gate_name = gate.name();

        // Always decompose if gate is not in target set
        if self.target_gate_set.contains(gate_name) {
            false
        } else {
            // Only decompose gates we know how to decompose
            matches!(
                gate_name,
                "Toffoli" | "Fredkin" | "CSWAP" | "SWAP" | "CRX" | "CRY" | "CRZ"
            )
        }
    }

    fn decompose_toffoli(
        &self,
        qubits: &[QubitId],
        gates: &mut Vec<Box<dyn GateOp>>,
    ) -> QuantRS2Result<()> {
        if qubits.len() != 3 {
            return Err(quantrs2_core::error::QuantRS2Error::InvalidInput(
                "Toffoli gate requires exactly 3 qubits".to_string(),
            ));
        }

        let c1 = qubits[0];
        let c2 = qubits[1];
        let target = qubits[2];

        // Standard Toffoli decomposition using CNOT and T gates
        use quantrs2_core::gate::{
            multi::CNOT,
            single::{Hadamard, TDagger, T},
        };

        gates.push(Box::new(Hadamard { target }));
        gates.push(Box::new(CNOT {
            control: c2,
            target,
        }));
        gates.push(Box::new(TDagger { target }));
        gates.push(Box::new(CNOT {
            control: c1,
            target,
        }));
        gates.push(Box::new(T { target }));
        gates.push(Box::new(CNOT {
            control: c2,
            target,
        }));
        gates.push(Box::new(TDagger { target }));
        gates.push(Box::new(CNOT {
            control: c1,
            target,
        }));
        gates.push(Box::new(T { target: c2 }));
        gates.push(Box::new(T { target }));
        gates.push(Box::new(CNOT {
            control: c1,
            target: c2,
        }));
        gates.push(Box::new(Hadamard { target }));
        gates.push(Box::new(T { target: c1 }));
        gates.push(Box::new(TDagger { target: c2 }));
        gates.push(Box::new(CNOT {
            control: c1,
            target: c2,
        }));

        Ok(())
    }

    fn decompose_fredkin(
        &self,
        qubits: &[QubitId],
        gates: &mut Vec<Box<dyn GateOp>>,
    ) -> QuantRS2Result<()> {
        if qubits.len() != 3 {
            return Err(quantrs2_core::error::QuantRS2Error::InvalidInput(
                "Fredkin gate requires exactly 3 qubits".to_string(),
            ));
        }

        let control = qubits[0];
        let target1 = qubits[1];
        let target2 = qubits[2];

        // Fredkin decomposition using CNOT gates
        use quantrs2_core::gate::multi::CNOT;

        gates.push(Box::new(CNOT {
            control: target2,
            target: target1,
        }));
        gates.push(Box::new(CNOT {
            control,
            target: target1,
        }));
        gates.push(Box::new(CNOT {
            control: target1,
            target: target2,
        }));
        gates.push(Box::new(CNOT {
            control,
            target: target1,
        }));
        gates.push(Box::new(CNOT {
            control: target2,
            target: target1,
        }));

        Ok(())
    }

    fn decompose_swap(
        &self,
        qubits: &[QubitId],
        gates: &mut Vec<Box<dyn GateOp>>,
    ) -> QuantRS2Result<()> {
        if qubits.len() != 2 {
            return Err(quantrs2_core::error::QuantRS2Error::InvalidInput(
                "SWAP gate requires exactly 2 qubits".to_string(),
            ));
        }

        let q1 = qubits[0];
        let q2 = qubits[1];

        // SWAP decomposition using 3 CNOT gates
        use quantrs2_core::gate::multi::CNOT;

        gates.push(Box::new(CNOT {
            control: q1,
            target: q2,
        }));
        gates.push(Box::new(CNOT {
            control: q2,
            target: q1,
        }));
        gates.push(Box::new(CNOT {
            control: q1,
            target: q2,
        }));

        Ok(())
    }

    fn decompose_controlled_rotation(
        &self,
        gate: &Box<dyn GateOp>,
        gates: &mut Vec<Box<dyn GateOp>>,
    ) -> QuantRS2Result<()> {
        let qubits = gate.qubits();
        if qubits.len() != 2 {
            return Err(quantrs2_core::error::QuantRS2Error::InvalidInput(
                "Controlled rotation requires exactly 2 qubits".to_string(),
            ));
        }

        let control = qubits[0];
        let target = qubits[1];

        // Simplified decomposition - in reality, we'd extract the angle parameter
        // For now, we'll use a generic decomposition with placeholder angles
        use quantrs2_core::gate::{
            multi::CNOT,
            single::{RotationX, RotationY, RotationZ},
        };

        match gate.name() {
            "CRX" => {
                gates.push(Box::new(RotationX {
                    target,
                    theta: std::f64::consts::PI / 4.0,
                }));
                gates.push(Box::new(CNOT { control, target }));
                gates.push(Box::new(RotationX {
                    target,
                    theta: -std::f64::consts::PI / 4.0,
                }));
                gates.push(Box::new(CNOT { control, target }));
            }
            "CRY" => {
                gates.push(Box::new(RotationY {
                    target,
                    theta: std::f64::consts::PI / 4.0,
                }));
                gates.push(Box::new(CNOT { control, target }));
                gates.push(Box::new(RotationY {
                    target,
                    theta: -std::f64::consts::PI / 4.0,
                }));
                gates.push(Box::new(CNOT { control, target }));
            }
            "CRZ" => {
                gates.push(Box::new(RotationZ {
                    target,
                    theta: std::f64::consts::PI / 4.0,
                }));
                gates.push(Box::new(CNOT { control, target }));
                gates.push(Box::new(RotationZ {
                    target,
                    theta: -std::f64::consts::PI / 4.0,
                }));
                gates.push(Box::new(CNOT { control, target }));
            }
            _ => {
                return Err(quantrs2_core::error::QuantRS2Error::UnsupportedOperation(
                    format!("Unknown controlled rotation gate: {}", gate.name()),
                ));
            }
        }

        Ok(())
    }
}

/// Cost-based optimization - minimizes gate count, depth, or error
pub struct CostBasedOptimization {
    optimization_target: CostTarget,
    max_iterations: usize,
}

#[derive(Debug, Clone, Copy)]
pub enum CostTarget {
    GateCount,
    CircuitDepth,
    TotalError,
    ExecutionTime,
    Balanced,
}

impl CostBasedOptimization {
    #[must_use]
    pub const fn new(target: CostTarget, max_iterations: usize) -> Self {
        Self {
            optimization_target: target,
            max_iterations,
        }
    }
}

impl OptimizationPass for CostBasedOptimization {
    fn name(&self) -> &'static str {
        "Cost-Based Optimization"
    }

    fn apply_to_gates(
        &self,
        gates: Vec<Box<dyn GateOp>>,
        cost_model: &dyn CostModel,
    ) -> QuantRS2Result<Vec<Box<dyn GateOp>>> {
        let mut best_gates = gates.clone();
        let mut best_cost = self.calculate_cost(&best_gates, cost_model);

        for iteration in 0..self.max_iterations {
            let candidate_gates = self.generate_candidate_solution(&best_gates, iteration)?;
            let candidate_cost = self.calculate_cost(&candidate_gates, cost_model);

            if candidate_cost < best_cost {
                best_gates = candidate_gates;
                best_cost = candidate_cost;
            }
        }

        Ok(best_gates)
    }
}

impl CostBasedOptimization {
    /// Helper methods for cost-based optimization

    fn calculate_cost(&self, gates: &[Box<dyn GateOp>], cost_model: &dyn CostModel) -> f64 {
        match self.optimization_target {
            CostTarget::GateCount => gates.len() as f64,
            CostTarget::CircuitDepth => self.calculate_depth(gates) as f64,
            CostTarget::TotalError => self.calculate_total_error(gates),
            CostTarget::ExecutionTime => self.calculate_execution_time(gates),
            CostTarget::Balanced => {
                // Weighted combination of all metrics
                let gate_count = gates.len() as f64;
                let depth = self.calculate_depth(gates) as f64;
                let error = self.calculate_total_error(gates);
                let time = self.calculate_execution_time(gates);

                (0.2 * error).mul_add(1000.0, 0.3f64.mul_add(gate_count, 0.3 * depth))
                    + 0.2 * time / 1000.0
            }
        }
    }

    fn generate_candidate_solution(
        &self,
        gates: &[Box<dyn GateOp>],
        iteration: usize,
    ) -> QuantRS2Result<Vec<Box<dyn GateOp>>> {
        let mut candidate = gates.to_vec();

        // Apply different optimization strategies based on target
        match self.optimization_target {
            CostTarget::GateCount => {
                // Try to cancel adjacent inverse gates
                self.cancel_inverse_gates(&mut candidate);
            }
            CostTarget::CircuitDepth => {
                // Try to parallelize gates that don't conflict
                self.parallelize_gates(&mut candidate);
            }
            CostTarget::TotalError => {
                // Try to replace high-error gates with lower-error equivalents
                self.reduce_error_gates(&candidate)?;
            }
            CostTarget::ExecutionTime => {
                // Try to replace slow gates with faster equivalents
                self.optimize_for_speed(&candidate)?;
            }
            CostTarget::Balanced => {
                // Apply a mix of strategies
                match iteration % 4 {
                    0 => self.cancel_inverse_gates(&mut candidate),
                    1 => self.parallelize_gates(&mut candidate),
                    2 => self.reduce_error_gates(&candidate)?,
                    3 => self.optimize_for_speed(&candidate)?,
                    _ => unreachable!(),
                }
            }
        }

        Ok(candidate)
    }

    fn calculate_depth(&self, gates: &[Box<dyn GateOp>]) -> usize {
        // Simple depth calculation - track when each qubit is last used
        let mut qubit_depths = std::collections::HashMap::new();
        let mut max_depth = 0;

        for gate in gates {
            let gate_qubits = gate.qubits();
            let gate_start_depth = gate_qubits
                .iter()
                .map(|q| qubit_depths.get(&q.id()).copied().unwrap_or(0))
                .max()
                .unwrap_or(0);

            let gate_end_depth = gate_start_depth + 1;

            for qubit in gate_qubits {
                qubit_depths.insert(qubit.id(), gate_end_depth);
            }

            max_depth = max_depth.max(gate_end_depth);
        }

        max_depth
    }

    fn calculate_total_error(&self, gates: &[Box<dyn GateOp>]) -> f64 {
        gates
            .iter()
            .map(|gate| self.estimate_gate_error(gate.name()))
            .sum()
    }

    fn calculate_execution_time(&self, gates: &[Box<dyn GateOp>]) -> f64 {
        gates
            .iter()
            .map(|gate| self.estimate_gate_time(gate.name()))
            .sum()
    }

    fn estimate_gate_error(&self, gate_name: &str) -> f64 {
        match gate_name {
            "H" | "X" | "Y" | "Z" | "S" | "T" => 0.0001,
            "RX" | "RY" | "RZ" => 0.0005,
            "CNOT" | "CX" | "CZ" | "CY" => 0.01,
            "SWAP" | "CRX" | "CRY" | "CRZ" => 0.015,
            "Toffoli" | "Fredkin" => 0.05,
            _ => 0.01,
        }
    }

    fn estimate_gate_time(&self, gate_name: &str) -> f64 {
        match gate_name {
            "H" | "X" | "Y" | "Z" | "S" | "T" | "RX" | "RY" | "RZ" => 50.0,
            "CNOT" | "CX" | "CZ" | "CY" | "SWAP" | "CRX" | "CRY" | "CRZ" => 200.0,
            "Toffoli" | "Fredkin" => 500.0,
            _ => 100.0,
        }
    }

    fn cancel_inverse_gates(&self, gates: &mut Vec<Box<dyn GateOp>>) {
        let mut i = 0;
        while i + 1 < gates.len() {
            if self.are_inverse_gates(&gates[i], &gates[i + 1]) {
                gates.remove(i + 1);
                gates.remove(i);
                i = i.saturating_sub(1);
            } else {
                i += 1;
            }
        }
    }

    fn are_inverse_gates(&self, gate1: &Box<dyn GateOp>, gate2: &Box<dyn GateOp>) -> bool {
        if gate1.qubits() != gate2.qubits() {
            return false;
        }

        match (gate1.name(), gate2.name()) {
            ("H", "H") | ("X", "X") | ("Y", "Y") | ("Z", "Z") => true,
            ("S", "SDG") | ("SDG", "S") => true,
            ("T", "TDG") | ("TDG", "T") => true,
            ("CNOT", "CNOT") | ("CX", "CX") => true,
            _ => false,
        }
    }

    fn parallelize_gates(&self, _gates: &mut Vec<Box<dyn GateOp>>) {
        // For now, just a stub - real parallelization would reorder gates
        // to minimize depth while preserving correctness
    }

    fn reduce_error_gates(&self, gates: &[Box<dyn GateOp>]) -> QuantRS2Result<()> {
        // Replace high-error gates with lower-error alternatives where possible
        for i in 0..gates.len() {
            if gates[i].name() == "Toffoli" {
                // Could decompose Toffoli to reduce error in some cases
                // (would need to check if total error is actually lower)
            } else {
                // Keep other gates as-is for now
            }
        }
        Ok(())
    }

    fn optimize_for_speed(&self, gates: &[Box<dyn GateOp>]) -> QuantRS2Result<()> {
        // Replace slow gates with faster alternatives where possible
        for i in 0..gates.len() {
            if gates[i].name() == "Toffoli" {
                // Could use a faster Toffoli implementation if available
            } else {
                // Keep other gates as-is for now
            }
        }
        Ok(())
    }
}

/// Two-qubit gate optimization
pub struct TwoQubitOptimization {
    use_kak_decomposition: bool,
    optimize_cnots: bool,
}

impl TwoQubitOptimization {
    #[must_use]
    pub const fn new(use_kak_decomposition: bool, optimize_cnots: bool) -> Self {
        Self {
            use_kak_decomposition,
            optimize_cnots,
        }
    }
}

impl OptimizationPass for TwoQubitOptimization {
    fn name(&self) -> &'static str {
        "Two-Qubit Optimization"
    }

    fn apply_to_gates(
        &self,
        gates: Vec<Box<dyn GateOp>>,
        _cost_model: &dyn CostModel,
    ) -> QuantRS2Result<Vec<Box<dyn GateOp>>> {
        // TODO: Implement two-qubit optimization
        Ok(gates)
    }
}

/// Peephole optimization - looks at small windows of gates for local optimizations
pub struct PeepholeOptimization {
    window_size: usize,
    patterns: Vec<PeepholePattern>,
}

#[derive(Clone)]
pub struct PeepholePattern {
    name: String,
    window_size: usize,
    matcher: fn(&[Box<dyn GateOp>]) -> Option<Vec<Box<dyn GateOp>>>,
}

impl PeepholeOptimization {
    #[must_use]
    pub fn new(window_size: usize) -> Self {
        let patterns = vec![
            // Pattern: X-Y-X = -Y
            PeepholePattern {
                name: "X-Y-X to -Y".to_string(),
                window_size: 3,
                matcher: |gates| {
                    if gates.len() >= 3 {
                        let g0 = &gates[0];
                        let g1 = &gates[1];
                        let g2 = &gates[2];

                        if g0.name() == "X"
                            && g2.name() == "X"
                            && g1.name() == "Y"
                            && g0.qubits() == g1.qubits()
                            && g1.qubits() == g2.qubits()
                        {
                            // X-Y-X = -Y, we can return Y with a phase
                            return Some(vec![g1.clone()]);
                        }
                    }
                    None
                },
            },
            // Pattern: H-S-H = X·RZ(π/2)·X
            PeepholePattern {
                name: "H-S-H simplification".to_string(),
                window_size: 3,
                matcher: |gates| {
                    if gates.len() >= 3 {
                        let g0 = &gates[0];
                        let g1 = &gates[1];
                        let g2 = &gates[2];

                        if g0.name() == "H"
                            && g2.name() == "H"
                            && g1.name() == "S"
                            && g0.qubits() == g1.qubits()
                            && g1.qubits() == g2.qubits()
                        {
                            let target = g0.qubits()[0];
                            return Some(vec![
                                Box::new(single::PauliX { target }) as Box<dyn GateOp>,
                                Box::new(single::RotationZ {
                                    target,
                                    theta: PI / 2.0,
                                }) as Box<dyn GateOp>,
                                Box::new(single::PauliX { target }) as Box<dyn GateOp>,
                            ]);
                        }
                    }
                    None
                },
            },
            // Pattern: RZ-RX-RZ (Euler decomposition check)
            PeepholePattern {
                name: "Euler angle optimization".to_string(),
                window_size: 3,
                matcher: |gates| {
                    if gates.len() >= 3 {
                        let g0 = &gates[0];
                        let g1 = &gates[1];
                        let g2 = &gates[2];

                        if g0.name() == "RZ"
                            && g1.name() == "RX"
                            && g2.name() == "RZ"
                            && g0.qubits() == g1.qubits()
                            && g1.qubits() == g2.qubits()
                        {
                            // Check if this is an inefficient decomposition
                            if let (Some(rz1), Some(rx), Some(rz2)) = (
                                g0.as_any().downcast_ref::<single::RotationZ>(),
                                g1.as_any().downcast_ref::<single::RotationX>(),
                                g2.as_any().downcast_ref::<single::RotationZ>(),
                            ) {
                                // If middle rotation is small, might be numerical error
                                if rx.theta.abs() < 1e-10 {
                                    // Combine the two RZ rotations
                                    let combined_angle = rz1.theta + rz2.theta;
                                    if combined_angle.abs() < 1e-10 {
                                        return Some(vec![]); // Identity
                                    }
                                    return Some(vec![Box::new(single::RotationZ {
                                        target: rz1.target,
                                        theta: combined_angle,
                                    })
                                        as Box<dyn GateOp>]);
                                }
                            }
                        }
                    }
                    None
                },
            },
            // Pattern: CNOT-RZ-CNOT (phase gadget)
            PeepholePattern {
                name: "Phase gadget optimization".to_string(),
                window_size: 3,
                matcher: |gates| {
                    if gates.len() >= 3 {
                        let g0 = &gates[0];
                        let g1 = &gates[1];
                        let g2 = &gates[2];

                        if g0.name() == "CNOT" && g2.name() == "CNOT" && g1.name() == "RZ" {
                            if let (Some(cnot1), Some(rz), Some(cnot2)) = (
                                g0.as_any().downcast_ref::<multi::CNOT>(),
                                g1.as_any().downcast_ref::<single::RotationZ>(),
                                g2.as_any().downcast_ref::<multi::CNOT>(),
                            ) {
                                // Check if it's the same CNOT structure
                                if cnot1.control == cnot2.control
                                    && cnot1.target == cnot2.target
                                    && rz.target == cnot1.target
                                {
                                    // This is a controlled-RZ, keep as is for now
                                    // In future, could replace with native CRZ if available
                                    return None;
                                }
                            }
                        }
                    }
                    None
                },
            },
            // Pattern: Hadamard ladder reduction
            PeepholePattern {
                name: "Hadamard ladder".to_string(),
                window_size: 4,
                matcher: |gates| {
                    if gates.len() >= 4 {
                        // H-CNOT-H-CNOT pattern
                        if gates[0].name() == "H"
                            && gates[1].name() == "CNOT"
                            && gates[2].name() == "H"
                            && gates[3].name() == "CNOT"
                        {
                            // Check qubit connectivity
                            let h1_target = gates[0].qubits()[0];
                            let h2_target = gates[2].qubits()[0];

                            if let (Some(cnot1), Some(cnot2)) = (
                                gates[1].as_any().downcast_ref::<multi::CNOT>(),
                                gates[3].as_any().downcast_ref::<multi::CNOT>(),
                            ) {
                                if h1_target == cnot1.control
                                    && h2_target == cnot2.control
                                    && cnot1.target == cnot2.target
                                {
                                    // Can sometimes be simplified
                                    return None; // Keep for now, needs deeper analysis
                                }
                            }
                        }
                    }
                    None
                },
            },
        ];

        Self {
            window_size,
            patterns,
        }
    }

    /// Apply patterns to a window of gates
    fn apply_patterns(&self, window: &[Box<dyn GateOp>]) -> Option<Vec<Box<dyn GateOp>>> {
        for pattern in &self.patterns {
            if window.len() >= pattern.window_size {
                if let Some(replacement) = (pattern.matcher)(window) {
                    return Some(replacement);
                }
            }
        }
        None
    }
}

impl OptimizationPass for PeepholeOptimization {
    fn name(&self) -> &'static str {
        "Peephole Optimization"
    }

    fn apply_to_gates(
        &self,
        gates: Vec<Box<dyn GateOp>>,
        _cost_model: &dyn CostModel,
    ) -> QuantRS2Result<Vec<Box<dyn GateOp>>> {
        let mut optimized = Vec::new();
        let mut i = 0;

        while i < gates.len() {
            // Try to match patterns starting at position i
            let mut matched = false;

            // Try different window sizes up to the configured maximum
            for window_size in (2..=self.window_size).rev() {
                if i + window_size <= gates.len() {
                    let window = &gates[i..i + window_size];

                    if let Some(replacement) = self.apply_patterns(window) {
                        // Apply the optimization
                        optimized.extend(replacement);
                        i += window_size;
                        matched = true;
                        break;
                    }
                }
            }

            // If no pattern matched, keep the original gate
            if !matched {
                optimized.push(gates[i].clone());
                i += 1;
            }
        }

        Ok(optimized)
    }
}

/// Template matching optimization
pub struct TemplateMatching {
    templates: Vec<CircuitTemplate>,
}

#[derive(Clone)]
pub struct CircuitTemplate {
    name: String,
    pattern: Vec<String>, // Simplified representation
    replacement: Vec<String>,
    cost_reduction: f64,
}

impl TemplateMatching {
    #[must_use]
    pub fn new() -> Self {
        let templates = vec![
            CircuitTemplate {
                name: "H-X-H to Z".to_string(),
                pattern: vec!["H".to_string(), "X".to_string(), "H".to_string()],
                replacement: vec!["Z".to_string()],
                cost_reduction: 2.0,
            },
            CircuitTemplate {
                name: "CNOT-H-CNOT to CZ".to_string(),
                pattern: vec!["CNOT".to_string(), "H".to_string(), "CNOT".to_string()],
                replacement: vec!["CZ".to_string()],
                cost_reduction: 1.5,
            },
            CircuitTemplate {
                name: "Double CNOT elimination".to_string(),
                pattern: vec!["CNOT".to_string(), "CNOT".to_string()],
                replacement: vec![],
                cost_reduction: 2.0,
            },
        ];

        Self { templates }
    }

    #[must_use]
    pub const fn with_templates(templates: Vec<CircuitTemplate>) -> Self {
        Self { templates }
    }
}

impl OptimizationPass for TemplateMatching {
    fn name(&self) -> &'static str {
        "Template Matching"
    }

    fn apply_to_gates(
        &self,
        gates: Vec<Box<dyn GateOp>>,
        cost_model: &dyn CostModel,
    ) -> QuantRS2Result<Vec<Box<dyn GateOp>>> {
        let mut optimized = gates;
        let mut changed = true;

        while changed {
            changed = false;
            let original_cost = cost_model.gates_cost(&optimized);

            for template in &self.templates {
                let result = self.apply_template(template, optimized.clone())?;
                let new_cost = cost_model.gates_cost(&result);

                if new_cost < original_cost {
                    optimized = result;
                    changed = true;
                    break;
                }
            }
        }

        Ok(optimized)
    }
}

impl TemplateMatching {
    /// Apply a single template to the gates
    fn apply_template(
        &self,
        template: &CircuitTemplate,
        gates: Vec<Box<dyn GateOp>>,
    ) -> QuantRS2Result<Vec<Box<dyn GateOp>>> {
        let mut result = Vec::new();
        let mut i = 0;

        while i < gates.len() {
            if let Some(replacement) = self.match_pattern_at_position(template, &gates, i)? {
                // Add replacement gates
                result.extend(replacement);
                i += template.pattern.len();
            } else {
                // Keep original gate
                result.push(gates[i].clone());
                i += 1;
            }
        }

        Ok(result)
    }

    /// Try to match a pattern starting at a specific position
    fn match_pattern_at_position(
        &self,
        template: &CircuitTemplate,
        gates: &[Box<dyn GateOp>],
        start: usize,
    ) -> QuantRS2Result<Option<Vec<Box<dyn GateOp>>>> {
        if start + template.pattern.len() > gates.len() {
            return Ok(None);
        }

        // Check if pattern matches and collect qubits
        let mut qubit_mapping = HashMap::new();
        let mut all_qubits = Vec::new();
        let mut is_match = true;

        for (i, pattern_gate) in template.pattern.iter().enumerate() {
            let gate = &gates[start + i];

            // Check if the gate name matches
            if !self.gate_matches_pattern(gate.as_ref(), pattern_gate, &qubit_mapping) {
                is_match = false;
                break;
            }

            // Collect qubits from this gate
            for qubit in gate.qubits() {
                if !all_qubits.contains(&qubit) {
                    all_qubits.push(qubit);
                }
            }
        }

        if !is_match {
            return Ok(None);
        }

        // Check if all gates operate on the same qubit(s) for single-qubit patterns
        if template
            .pattern
            .iter()
            .all(|p| p == "H" || p == "X" || p == "Y" || p == "Z" || p == "S" || p == "T")
        {
            // For single-qubit gates, check they all operate on the same qubit
            let first_qubit = gates[start].qubits();
            if first_qubit.len() != 1 {
                return Ok(None);
            }

            for i in 1..template.pattern.len() {
                let gate_qubits = gates[start + i].qubits();
                if gate_qubits != first_qubit {
                    return Ok(None);
                }
            }
        }

        // Store qubits in mapping for replacement generation
        qubit_mapping.insert("qubits".to_string(), all_qubits);

        // Generate replacement gates
        self.generate_replacement_gates(template, &qubit_mapping)
    }

    /// Check if a gate matches a pattern element
    fn gate_matches_pattern(
        &self,
        gate: &dyn GateOp,
        pattern: &str,
        qubit_mapping: &HashMap<String, Vec<QubitId>>,
    ) -> bool {
        // For now, use simple name matching
        // Later we can add more sophisticated pattern matching
        gate.name() == pattern
    }

    /// Parse a pattern string like "H(q0)" or "CNOT(q0,q1)"
    fn parse_pattern(&self, pattern: &str) -> Option<(String, String)> {
        if let Some(open_paren) = pattern.find('(') {
            if let Some(close_paren) = pattern.find(')') {
                let gate_name = pattern[..open_paren].to_string();
                let qubit_pattern = pattern[open_paren + 1..close_paren].to_string();
                return Some((gate_name, qubit_pattern));
            }
        }
        None
    }

    /// Generate replacement gates based on the template and qubit mapping
    fn generate_replacement_gates(
        &self,
        template: &CircuitTemplate,
        qubit_mapping: &HashMap<String, Vec<QubitId>>,
    ) -> QuantRS2Result<Option<Vec<Box<dyn GateOp>>>> {
        let mut replacement_gates = Vec::new();

        // For simple patterns, just use the first qubit found in the mapping
        let qubits: Vec<QubitId> = qubit_mapping
            .values()
            .flat_map(|v| v.iter().copied())
            .collect();
        let mut unique_qubits: Vec<QubitId> = Vec::new();
        for qubit in qubits {
            if !unique_qubits.contains(&qubit) {
                unique_qubits.push(qubit);
            }
        }

        for replacement_pattern in &template.replacement {
            if let Some(gate) = self.create_simple_gate(replacement_pattern, &unique_qubits)? {
                replacement_gates.push(gate);
            }
        }

        Ok(Some(replacement_gates))
    }

    /// Create a simple gate from pattern and available qubits
    fn create_simple_gate(
        &self,
        pattern: &str,
        qubits: &[QubitId],
    ) -> QuantRS2Result<Option<Box<dyn GateOp>>> {
        if qubits.is_empty() {
            return Ok(None);
        }

        match pattern {
            "H" => Ok(Some(Box::new(single::Hadamard { target: qubits[0] }))),
            "X" => Ok(Some(Box::new(single::PauliX { target: qubits[0] }))),
            "Y" => Ok(Some(Box::new(single::PauliY { target: qubits[0] }))),
            "Z" => Ok(Some(Box::new(single::PauliZ { target: qubits[0] }))),
            "S" => Ok(Some(Box::new(single::Phase { target: qubits[0] }))),
            "T" => Ok(Some(Box::new(single::T { target: qubits[0] }))),
            "CNOT" if qubits.len() >= 2 => Ok(Some(Box::new(multi::CNOT {
                control: qubits[0],
                target: qubits[1],
            }))),
            "CZ" if qubits.len() >= 2 => Ok(Some(Box::new(multi::CZ {
                control: qubits[0],
                target: qubits[1],
            }))),
            "SWAP" if qubits.len() >= 2 => Ok(Some(Box::new(multi::SWAP {
                qubit1: qubits[0],
                qubit2: qubits[1],
            }))),
            _ => Ok(None),
        }
    }

    /// Create a gate from a pattern string and qubit mapping
    fn create_gate_from_pattern(
        &self,
        pattern: &str,
        qubit_mapping: &HashMap<String, Vec<QubitId>>,
    ) -> QuantRS2Result<Option<Box<dyn GateOp>>> {
        if let Some((gate_name, qubit_pattern)) = self.parse_pattern(pattern) {
            if let Some(qubits) = qubit_mapping.get(&qubit_pattern) {
                return Ok(Some(self.create_gate(&gate_name, qubits)?));
            }
        } else {
            // Try to find any single qubit for simple patterns
            if let Some((_, qubits)) = qubit_mapping.iter().next() {
                if !qubits.is_empty() {
                    return Ok(Some(self.create_gate(pattern, &[qubits[0]])?));
                }
            }
        }

        Ok(None)
    }

    /// Create a gate instance from name and qubits
    fn create_gate(&self, gate_name: &str, qubits: &[QubitId]) -> QuantRS2Result<Box<dyn GateOp>> {
        match (gate_name, qubits.len()) {
            ("H", 1) => Ok(Box::new(single::Hadamard { target: qubits[0] })),
            ("X", 1) => Ok(Box::new(single::PauliX { target: qubits[0] })),
            ("Y", 1) => Ok(Box::new(single::PauliY { target: qubits[0] })),
            ("Z", 1) => Ok(Box::new(single::PauliZ { target: qubits[0] })),
            ("S", 1) => Ok(Box::new(single::Phase { target: qubits[0] })),
            ("T", 1) => Ok(Box::new(single::T { target: qubits[0] })),
            ("CNOT", 2) => Ok(Box::new(multi::CNOT {
                control: qubits[0],
                target: qubits[1],
            })),
            ("CZ", 2) => Ok(Box::new(multi::CZ {
                control: qubits[0],
                target: qubits[1],
            })),
            ("SWAP", 2) => Ok(Box::new(multi::SWAP {
                qubit1: qubits[0],
                qubit2: qubits[1],
            })),
            _ => Err(QuantRS2Error::UnsupportedOperation(format!(
                "Cannot create gate {} with {} qubits",
                gate_name,
                qubits.len()
            ))),
        }
    }

    /// Create an advanced template matcher with more sophisticated patterns
    #[must_use]
    pub fn with_advanced_templates() -> Self {
        let templates = vec![
            // Basis change patterns
            CircuitTemplate {
                name: "H-Z-H to X".to_string(),
                pattern: vec!["H".to_string(), "Z".to_string(), "H".to_string()],
                replacement: vec!["X".to_string()],
                cost_reduction: 2.0,
            },
            CircuitTemplate {
                name: "H-X-H to Z".to_string(),
                pattern: vec!["H".to_string(), "X".to_string(), "H".to_string()],
                replacement: vec!["Z".to_string()],
                cost_reduction: 2.0,
            },
            // CNOT patterns
            CircuitTemplate {
                name: "CNOT-CNOT elimination".to_string(),
                pattern: vec!["CNOT".to_string(), "CNOT".to_string()],
                replacement: vec![],
                cost_reduction: 2.0,
            },
            // Phase gate optimizations
            CircuitTemplate {
                name: "S-S to Z".to_string(),
                pattern: vec!["S".to_string(), "S".to_string()],
                replacement: vec!["Z".to_string()],
                cost_reduction: 1.0,
            },
            CircuitTemplate {
                name: "T-T-T-T to Identity".to_string(),
                pattern: vec![
                    "T".to_string(),
                    "T".to_string(),
                    "T".to_string(),
                    "T".to_string(),
                ],
                replacement: vec![],
                cost_reduction: 4.0,
            },
            // Two-qubit patterns
            CircuitTemplate {
                name: "CNOT-H-CNOT to CZ".to_string(),
                pattern: vec!["CNOT".to_string(), "H".to_string(), "CNOT".to_string()],
                replacement: vec!["CZ".to_string()],
                cost_reduction: 1.0,
            },
            // Fredkin decomposition optimization
            CircuitTemplate {
                name: "SWAP via 3 CNOTs".to_string(),
                pattern: vec!["CNOT".to_string(), "CNOT".to_string(), "CNOT".to_string()],
                replacement: vec!["SWAP".to_string()],
                cost_reduction: 0.5, // SWAP might be native on some hardware
            },
        ];

        Self { templates }
    }

    /// Create a template matcher for specific hardware
    #[must_use]
    pub fn for_hardware(hardware: &str) -> Self {
        let templates = match hardware {
            "ibm" => vec![
                CircuitTemplate {
                    name: "H-Z-H to X".to_string(),
                    pattern: vec!["H".to_string(), "Z".to_string(), "H".to_string()],
                    replacement: vec!["X".to_string()],
                    cost_reduction: 2.0,
                },
                CircuitTemplate {
                    name: "CNOT-CNOT elimination".to_string(),
                    pattern: vec!["CNOT".to_string(), "CNOT".to_string()],
                    replacement: vec![],
                    cost_reduction: 2.0,
                },
            ],
            "google" => vec![CircuitTemplate {
                name: "CNOT to CZ with Hadamards".to_string(),
                pattern: vec!["CNOT".to_string()],
                replacement: vec!["H".to_string(), "CZ".to_string(), "H".to_string()],
                cost_reduction: -0.5, // CZ might be more native
            }],
            _ => Self::new().templates,
        };

        Self { templates }
    }
}

impl Default for TemplateMatching {
    fn default() -> Self {
        Self::new()
    }
}

/// Circuit rewriting using equivalence rules
pub struct CircuitRewriting {
    rules: Vec<RewriteRule>,
    max_rewrites: usize,
}

#[derive(Clone)]
pub struct RewriteRule {
    name: String,
    condition: fn(&[Box<dyn GateOp>]) -> bool,
    rewrite: fn(&[Box<dyn GateOp>]) -> Vec<Box<dyn GateOp>>,
}

impl CircuitRewriting {
    #[must_use]
    pub const fn new(max_rewrites: usize) -> Self {
        let rules = vec![
            // Add rewrite rules here
        ];

        Self {
            rules,
            max_rewrites,
        }
    }
}

impl OptimizationPass for CircuitRewriting {
    fn name(&self) -> &'static str {
        "Circuit Rewriting"
    }

    fn apply_to_gates(
        &self,
        gates: Vec<Box<dyn GateOp>>,
        _cost_model: &dyn CostModel,
    ) -> QuantRS2Result<Vec<Box<dyn GateOp>>> {
        // TODO: Implement circuit rewriting
        Ok(gates)
    }
}

/// Helper functions for optimization passes
pub mod utils {
    use super::{get_gate_properties, GateOp, HashMap, OptimizationPass};

    /// Check if two gates cancel each other
    pub fn gates_cancel(gate1: &dyn GateOp, gate2: &dyn GateOp) -> bool {
        if gate1.name() != gate2.name() || gate1.qubits() != gate2.qubits() {
            return false;
        }

        let props = get_gate_properties(gate1);
        props.is_self_inverse
    }

    /// Check if a gate is effectively identity
    pub fn is_identity_gate(gate: &dyn GateOp, tolerance: f64) -> bool {
        match gate.name() {
            "RX" | "RY" | "RZ" => {
                // Check if rotation angle is effectively 0
                if let Ok(matrix) = gate.matrix() {
                    // Check diagonal elements are close to 1
                    (matrix[0].re - 1.0).abs() < tolerance && matrix[0].im.abs() < tolerance
                } else {
                    false
                }
            }
            _ => false,
        }
    }

    /// Calculate circuit depth
    #[must_use]
    pub fn calculate_depth(gates: &[Box<dyn GateOp>]) -> usize {
        let mut qubit_depths: HashMap<u32, usize> = HashMap::new();
        let mut max_depth = 0;

        for gate in gates {
            let gate_qubits = gate.qubits();
            let current_depth = gate_qubits
                .iter()
                .map(|q| qubit_depths.get(&q.id()).copied().unwrap_or(0))
                .max()
                .unwrap_or(0);

            let new_depth = current_depth + 1;
            for qubit in gate_qubits {
                qubit_depths.insert(qubit.id(), new_depth);
            }

            max_depth = max_depth.max(new_depth);
        }

        max_depth
    }
}