quantrs2_device/dynamical_decoupling/

sequences.rs

//! Dynamical decoupling sequence generation and management

use std::collections::HashMap;
use std::f64::consts::PI;

use quantrs2_circuit::prelude::*;
use quantrs2_core::{
    gate::{
        single::{Hadamard, PauliX, PauliY, PauliZ},
        GateOp,
    },
    qubit::QubitId,
};

use super::config::{DDSequenceType, NoiseType};
use crate::DeviceResult;
use scirs2_core::random::prelude::*;

/// Dynamical decoupling sequence representation
#[derive(Debug, Clone)]
pub struct DDSequence {
    /// Sequence type
    pub sequence_type: DDSequenceType,
    /// Target qubits
    pub target_qubits: Vec<QubitId>,
    /// Sequence duration
    pub duration: f64,
    /// Circuit implementation
    pub circuit: Circuit<32>,
    /// Pulse timings
    pub pulse_timings: Vec<f64>,
    /// Pulse phases
    pub pulse_phases: Vec<f64>,
    /// Sequence properties
    pub properties: DDSequenceProperties,
}

/// Properties of a DD sequence
#[derive(Debug, Clone)]
pub struct DDSequenceProperties {
    /// Number of pulses
    pub pulse_count: usize,
    /// Sequence order (cancellation order)
    pub sequence_order: usize,
    /// Periodicity
    pub periodicity: usize,
    /// Symmetry properties
    pub symmetry: SequenceSymmetry,
    /// Noise suppression characteristics
    pub noise_suppression: HashMap<NoiseType, f64>,
    /// Resource requirements
    pub resource_requirements: ResourceRequirements,
}

/// Sequence symmetry properties
#[derive(Debug, Clone)]
pub struct SequenceSymmetry {
    /// Time-reversal symmetry
    pub time_reversal: bool,
    /// Phase symmetry
    pub phase_symmetry: bool,
    /// Rotational symmetry
    pub rotational_symmetry: bool,
    /// Inversion symmetry
    pub inversion_symmetry: bool,
}

/// Resource requirements for a DD sequence
#[derive(Debug, Clone)]
pub struct ResourceRequirements {
    /// Gate count
    pub gate_count: usize,
    /// Circuit depth
    pub circuit_depth: usize,
    /// Required connectivity
    pub required_connectivity: Vec<(QubitId, QubitId)>,
    /// Estimated execution time
    pub execution_time: f64,
    /// Memory requirements
    pub memory_requirements: usize,
}

/// DD sequence generator
pub struct DDSequenceGenerator;

impl DDSequenceGenerator {
    /// Generate a base DD sequence
    pub fn generate_base_sequence(
        sequence_type: &DDSequenceType,
        target_qubits: &[QubitId],
        duration: f64,
    ) -> DeviceResult<DDSequence> {
        // Input validation
        if target_qubits.is_empty() {
            return Err(crate::DeviceError::InvalidInput(
                "Target qubits cannot be empty".to_string(),
            ));
        }

        if duration <= 0.0 {
            return Err(crate::DeviceError::InvalidInput(
                "Duration must be positive".to_string(),
            ));
        }

        if !duration.is_finite() {
            return Err(crate::DeviceError::InvalidInput(
                "Duration must be finite".to_string(),
            ));
        }

        match sequence_type {
            DDSequenceType::CPMG { n_pulses } => {
                Self::generate_cpmg_sequence_with_pulses(target_qubits, duration, *n_pulses)
            }
            DDSequenceType::XY4 => Self::generate_xy4_sequence(target_qubits, duration),
            DDSequenceType::XY8 => Self::generate_xy8_sequence(target_qubits, duration),
            DDSequenceType::XY16 => Self::generate_xy16_sequence(target_qubits, duration),
            DDSequenceType::UDD { n_pulses } => {
                Self::generate_udd_sequence_with_pulses(target_qubits, duration, *n_pulses)
            }
            DDSequenceType::KDD => Self::generate_kdd_sequence(target_qubits, duration),
            DDSequenceType::QDD => Self::generate_qdd_sequence(target_qubits, duration),
            DDSequenceType::CDD => Self::generate_cdd_sequence(target_qubits, duration),
            DDSequenceType::RDD => Self::generate_rdd_sequence(target_qubits, duration),
            DDSequenceType::HahnEcho => Self::generate_hahn_echo_sequence(target_qubits, duration),
            DDSequenceType::CarrPurcell => Self::generate_cp_sequence(target_qubits, duration),
            DDSequenceType::SciRS2Optimized => {
                Self::generate_optimized_sequence(target_qubits, duration)
            }
            DDSequenceType::Custom(name) => {
                Self::generate_custom_sequence(name, target_qubits, duration)
            }
            DDSequenceType::Composite => {
                // Generate base sequences first
                let base_xy4 = Self::generate_xy4_sequence(target_qubits, duration)?;
                let base_cpmg = Self::generate_cpmg_sequence(target_qubits, duration)?;
                let base_sequences = vec![base_xy4, base_cpmg];
                Self::generate_composite_sequence(&base_sequences, CompositionStrategy::Sequential)
            }
            DDSequenceType::MultiQubitCoordinated => {
                // Use XY4 as a fallback for multi-qubit coordinated
                Self::generate_xy4_sequence(target_qubits, duration)
            }
            DDSequenceType::Adaptive => {
                // Use optimized sequence as fallback for adaptive
                Self::generate_optimized_sequence(target_qubits, duration)
            }
        }
    }

    /// Generate Hahn Echo sequence
    fn generate_hahn_echo_sequence(
        target_qubits: &[QubitId],
        duration: f64,
    ) -> DeviceResult<DDSequence> {
        let pulse_spacing = duration / 2.0; // Single π pulse at the center

        let mut circuit = Circuit::<32>::new();
        let mut pulse_timings = Vec::new();
        let mut pulse_phases = Vec::new();

        for qubit in target_qubits {
            pulse_timings.push(pulse_spacing);
            pulse_phases.push(PI); // Y rotation (π pulse)
            circuit.add_gate(PauliY { target: *qubit })?;
        }

        let properties = DDSequenceProperties {
            pulse_count: target_qubits.len(),
            sequence_order: 1,
            periodicity: 1,
            symmetry: SequenceSymmetry {
                time_reversal: true,
                phase_symmetry: true,
                rotational_symmetry: false,
                inversion_symmetry: true,
            },
            noise_suppression: {
                let mut suppression = HashMap::new();
                suppression.insert(NoiseType::PhaseDamping, 0.8);
                suppression.insert(NoiseType::AmplitudeDamping, 0.2);
                suppression
            },
            resource_requirements: ResourceRequirements {
                gate_count: target_qubits.len(),
                circuit_depth: 1,
                required_connectivity: Vec::new(),
                execution_time: duration,
                memory_requirements: target_qubits.len() * 8,
            },
        };

        Ok(DDSequence {
            sequence_type: DDSequenceType::HahnEcho,
            target_qubits: target_qubits.to_vec(),
            duration,
            circuit,
            pulse_timings,
            pulse_phases,
            properties,
        })
    }

    /// Generate CPMG (Carr-Purcell-Meiboom-Gill) sequence
    fn generate_cpmg_sequence_with_pulses(
        target_qubits: &[QubitId],
        duration: f64,
        n_pulses: usize,
    ) -> DeviceResult<DDSequence> {
        let pulse_spacing = duration / (n_pulses + 1) as f64;

        let mut circuit = Circuit::<32>::new();
        let mut pulse_timings = Vec::new();
        let mut pulse_phases = Vec::new();

        for qubit in target_qubits {
            for i in 1..=n_pulses {
                let timing = i as f64 * pulse_spacing;
                pulse_timings.push(timing);
                pulse_phases.push(PI); // Y rotation (π pulse)

                circuit.add_gate(PauliY { target: *qubit })?;
            }
        }

        let properties = DDSequenceProperties {
            pulse_count: n_pulses * target_qubits.len(),
            sequence_order: 1,
            periodicity: n_pulses,
            symmetry: SequenceSymmetry {
                time_reversal: true,
                phase_symmetry: true,
                rotational_symmetry: false,
                inversion_symmetry: true,
            },
            noise_suppression: {
                let mut suppression = HashMap::new();
                suppression.insert(NoiseType::PhaseDamping, 0.9);
                suppression.insert(NoiseType::AmplitudeDamping, 0.3);
                suppression
            },
            resource_requirements: ResourceRequirements {
                gate_count: n_pulses * target_qubits.len(),
                circuit_depth: n_pulses,
                required_connectivity: Vec::new(),
                execution_time: duration,
                memory_requirements: n_pulses * target_qubits.len() * 8,
            },
        };

        Ok(DDSequence {
            sequence_type: DDSequenceType::CPMG { n_pulses },
            target_qubits: target_qubits.to_vec(),
            duration,
            circuit,
            pulse_timings,
            pulse_phases,
            properties,
        })
    }

    /// Generate CPMG sequence with default number of pulses (backward compatibility)
    fn generate_cpmg_sequence(
        target_qubits: &[QubitId],
        duration: f64,
    ) -> DeviceResult<DDSequence> {
        Self::generate_cpmg_sequence_with_pulses(target_qubits, duration, 16)
    }

    /// Generate XY-4 sequence
    fn generate_xy4_sequence(target_qubits: &[QubitId], duration: f64) -> DeviceResult<DDSequence> {
        let base_sequence = vec![PI, PI / 2.0, PI, 3.0 * PI / 2.0]; // X, Y, X, -Y rotations
        let n_repetitions = 4;
        let pulse_spacing = duration / (base_sequence.len() * n_repetitions) as f64;

        let mut circuit = Circuit::<32>::new();
        let mut pulse_timings = Vec::new();
        let mut pulse_phases = Vec::new();

        for qubit in target_qubits {
            for rep in 0..n_repetitions {
                for (i, &phase) in base_sequence.iter().enumerate() {
                    let timing = (rep * base_sequence.len() + i + 1) as f64 * pulse_spacing;
                    pulse_timings.push(timing);
                    pulse_phases.push(phase);

                    match phase {
                        p if (p - PI).abs() < 1e-6 => {
                            circuit.add_gate(PauliX { target: *qubit })?;
                        }
                        p if (p - PI / 2.0).abs() < 1e-6 => {
                            circuit.add_gate(PauliY { target: *qubit })?;
                        }
                        p if (p - 3.0 * PI / 2.0).abs() < 1e-6 => {
                            circuit.add_gate(PauliY { target: *qubit })?;
                            circuit.add_gate(PauliZ { target: *qubit })?;
                            circuit.add_gate(PauliZ { target: *qubit })?;
                        }
                        _ => {
                            circuit.add_gate(PauliX { target: *qubit })?;
                        }
                    }
                }
            }
        }

        let properties = DDSequenceProperties {
            pulse_count: base_sequence.len() * n_repetitions * target_qubits.len(),
            sequence_order: 2,
            periodicity: base_sequence.len(),
            symmetry: SequenceSymmetry {
                time_reversal: true,
                phase_symmetry: true,
                rotational_symmetry: true,
                inversion_symmetry: true,
            },
            noise_suppression: {
                let mut suppression = HashMap::new();
                suppression.insert(NoiseType::PhaseDamping, 0.95);
                suppression.insert(NoiseType::AmplitudeDamping, 0.4);
                suppression.insert(NoiseType::Depolarizing, 0.8);
                suppression
            },
            resource_requirements: ResourceRequirements {
                gate_count: base_sequence.len() * n_repetitions * target_qubits.len(),
                circuit_depth: base_sequence.len() * n_repetitions,
                required_connectivity: Vec::new(),
                execution_time: duration,
                memory_requirements: base_sequence.len() * n_repetitions * target_qubits.len() * 8,
            },
        };

        Ok(DDSequence {
            sequence_type: DDSequenceType::XY4,
            target_qubits: target_qubits.to_vec(),
            duration,
            circuit,
            pulse_timings,
            pulse_phases,
            properties,
        })
    }

    /// Generate XY-8 sequence
    fn generate_xy8_sequence(target_qubits: &[QubitId], duration: f64) -> DeviceResult<DDSequence> {
        let base_sequence = vec![
            PI,
            PI / 2.0,
            PI,
            3.0 * PI / 2.0, // XY4
            3.0 * PI / 2.0,
            PI,
            PI / 2.0,
            PI, // -Y X Y X
        ];
        let n_repetitions = 2;
        let pulse_spacing = duration / (base_sequence.len() * n_repetitions) as f64;

        let mut circuit = Circuit::<32>::new();
        let mut pulse_timings = Vec::new();
        let mut pulse_phases = Vec::new();

        for qubit in target_qubits {
            for rep in 0..n_repetitions {
                for (i, &phase) in base_sequence.iter().enumerate() {
                    let timing = (rep * base_sequence.len() + i + 1) as f64 * pulse_spacing;
                    pulse_timings.push(timing);
                    pulse_phases.push(phase);

                    match phase {
                        p if (p - PI).abs() < 1e-6 => {
                            circuit.add_gate(PauliX { target: *qubit })?;
                        }
                        p if (p - PI / 2.0).abs() < 1e-6 => {
                            circuit.add_gate(PauliY { target: *qubit })?;
                        }
                        p if (p - 3.0 * PI / 2.0).abs() < 1e-6 => {
                            circuit.add_gate(PauliY { target: *qubit })?;
                            circuit.add_gate(PauliZ { target: *qubit })?;
                            circuit.add_gate(PauliZ { target: *qubit })?;
                        }
                        _ => {
                            circuit.add_gate(PauliX { target: *qubit })?;
                        }
                    }
                }
            }
        }

        let properties = DDSequenceProperties {
            pulse_count: base_sequence.len() * n_repetitions * target_qubits.len(),
            sequence_order: 3,
            periodicity: base_sequence.len(),
            symmetry: SequenceSymmetry {
                time_reversal: true,
                phase_symmetry: true,
                rotational_symmetry: true,
                inversion_symmetry: true,
            },
            noise_suppression: {
                let mut suppression = HashMap::new();
                suppression.insert(NoiseType::PhaseDamping, 0.98);
                suppression.insert(NoiseType::AmplitudeDamping, 0.5);
                suppression.insert(NoiseType::Depolarizing, 0.9);
                suppression.insert(NoiseType::CoherentErrors, 0.85);
                suppression
            },
            resource_requirements: ResourceRequirements {
                gate_count: base_sequence.len() * n_repetitions * target_qubits.len(),
                circuit_depth: base_sequence.len() * n_repetitions,
                required_connectivity: Vec::new(),
                execution_time: duration,
                memory_requirements: base_sequence.len() * n_repetitions * target_qubits.len() * 8,
            },
        };

        Ok(DDSequence {
            sequence_type: DDSequenceType::XY8,
            target_qubits: target_qubits.to_vec(),
            duration,
            circuit,
            pulse_timings,
            pulse_phases,
            properties,
        })
    }

    /// Generate XY-16 sequence (placeholder)
    fn generate_xy16_sequence(
        target_qubits: &[QubitId],
        duration: f64,
    ) -> DeviceResult<DDSequence> {
        // For now, use XY8 as base and extend
        let mut xy8_sequence = Self::generate_xy8_sequence(target_qubits, duration)?;
        xy8_sequence.sequence_type = DDSequenceType::XY16;
        xy8_sequence.properties.sequence_order = 4;
        xy8_sequence
            .properties
            .noise_suppression
            .insert(NoiseType::OneOverFNoise, 0.7);
        Ok(xy8_sequence)
    }

    /// Generate Uhrig Dynamical Decoupling (UDD) sequence
    fn generate_udd_sequence_with_pulses(
        target_qubits: &[QubitId],
        duration: f64,
        n_pulses: usize,
    ) -> DeviceResult<DDSequence> {
        let mut pulse_timings = Vec::new();
        let mut pulse_phases = Vec::new();

        // UDD pulse timings: τₖ = T * sin²(πk/(2n+2))
        for k in 1..=n_pulses {
            let timing = duration
                * (PI * k as f64 / (2.0 * n_pulses as f64 + 2.0))
                    .sin()
                    .powi(2);
            pulse_timings.push(timing);
            pulse_phases.push(PI); // X rotations
        }

        let mut circuit = Circuit::<32>::new();
        for qubit in target_qubits {
            for _ in 0..n_pulses {
                circuit.add_gate(PauliX { target: *qubit })?;
            }
        }

        let properties = DDSequenceProperties {
            pulse_count: n_pulses * target_qubits.len(),
            sequence_order: n_pulses,
            periodicity: 1,
            symmetry: SequenceSymmetry {
                time_reversal: false,
                phase_symmetry: false,
                rotational_symmetry: false,
                inversion_symmetry: false,
            },
            noise_suppression: {
                let mut suppression = HashMap::new();
                suppression.insert(NoiseType::PhaseDamping, 0.99);
                suppression.insert(NoiseType::OneOverFNoise, 0.9);
                suppression
            },
            resource_requirements: ResourceRequirements {
                gate_count: n_pulses * target_qubits.len(),
                circuit_depth: n_pulses,
                required_connectivity: Vec::new(),
                execution_time: duration,
                memory_requirements: n_pulses * target_qubits.len() * 8,
            },
        };

        Ok(DDSequence {
            sequence_type: DDSequenceType::UDD { n_pulses },
            target_qubits: target_qubits.to_vec(),
            duration,
            circuit,
            pulse_timings,
            pulse_phases,
            properties,
        })
    }

    /// Generate Knill Dynamical Decoupling (KDD) sequence (placeholder)
    fn generate_kdd_sequence(target_qubits: &[QubitId], duration: f64) -> DeviceResult<DDSequence> {
        // Simplified KDD - use CPMG as base with modifications
        let mut cpmg_sequence = Self::generate_cpmg_sequence(target_qubits, duration)?;
        cpmg_sequence.sequence_type = DDSequenceType::KDD;
        cpmg_sequence
            .properties
            .noise_suppression
            .insert(NoiseType::CoherentErrors, 0.95);
        Ok(cpmg_sequence)
    }

    /// Generate composite DD sequence
    pub fn generate_composite_sequence(
        base_sequences: &[DDSequence],
        composition_strategy: CompositionStrategy,
    ) -> DeviceResult<DDSequence> {
        if base_sequences.is_empty() {
            return Err(crate::DeviceError::InvalidInput(
                "No base sequences provided".to_string(),
            ));
        }

        match composition_strategy {
            CompositionStrategy::Sequential => {
                let mut composite_circuit = Circuit::<32>::new();
                let mut composite_timings = Vec::new();
                let mut composite_phases = Vec::new();
                let mut total_duration = 0.0;
                let mut total_gate_count = 0;
                let target_qubits = base_sequences[0].target_qubits.clone();

                for sequence in base_sequences {
                    // Append sequence to composite
                    for &timing in &sequence.pulse_timings {
                        composite_timings.push(total_duration + timing);
                    }
                    composite_phases.extend(&sequence.pulse_phases);
                    total_duration += sequence.duration;
                    total_gate_count += sequence.properties.pulse_count;

                    // Add gates from sequence circuit (simplified)
                    for qubit in &target_qubits {
                        for _ in 0..sequence.properties.pulse_count / target_qubits.len() {
                            composite_circuit.add_gate(PauliY { target: *qubit })?;
                        }
                    }
                }

                // Combine noise suppression properties
                let mut combined_suppression = HashMap::new();
                for sequence in base_sequences {
                    for (noise_type, suppression) in &sequence.properties.noise_suppression {
                        let current = combined_suppression.get(noise_type).unwrap_or(&0.0);
                        // Use geometric mean for combination
                        combined_suppression
                            .insert(noise_type.clone(), (current * suppression).sqrt());
                    }
                }

                let properties = DDSequenceProperties {
                    pulse_count: composite_timings.len(),
                    sequence_order: base_sequences
                        .iter()
                        .map(|s| s.properties.sequence_order)
                        .max()
                        .unwrap_or(1),
                    periodicity: base_sequences.len(),
                    symmetry: SequenceSymmetry {
                        time_reversal: base_sequences
                            .iter()
                            .all(|s| s.properties.symmetry.time_reversal),
                        phase_symmetry: base_sequences
                            .iter()
                            .all(|s| s.properties.symmetry.phase_symmetry),
                        rotational_symmetry: base_sequences
                            .iter()
                            .any(|s| s.properties.symmetry.rotational_symmetry),
                        inversion_symmetry: base_sequences
                            .iter()
                            .all(|s| s.properties.symmetry.inversion_symmetry),
                    },
                    noise_suppression: combined_suppression,
                    resource_requirements: ResourceRequirements {
                        gate_count: total_gate_count,
                        circuit_depth: base_sequences
                            .iter()
                            .map(|s| s.properties.resource_requirements.circuit_depth)
                            .sum(),
                        required_connectivity: Vec::new(),
                        execution_time: total_duration,
                        memory_requirements: total_gate_count * 8,
                    },
                };

                Ok(DDSequence {
                    sequence_type: DDSequenceType::Composite,
                    target_qubits,
                    duration: total_duration,
                    circuit: composite_circuit,
                    pulse_timings: composite_timings,
                    pulse_phases: composite_phases,
                    properties,
                })
            }
            CompositionStrategy::Interleaved => {
                // Interleave sequences (simplified implementation)
                Self::generate_composite_sequence(base_sequences, CompositionStrategy::Sequential)
            }
            CompositionStrategy::Nested => {
                // Nested composition (simplified implementation)
                Self::generate_composite_sequence(base_sequences, CompositionStrategy::Sequential)
            }
        }
    }

    /// Generate other sequence types (placeholders)
    fn generate_qdd_sequence(target_qubits: &[QubitId], duration: f64) -> DeviceResult<DDSequence> {
        let mut base =
            DDSequenceGenerator::generate_udd_sequence_with_pulses(target_qubits, duration, 8)?;
        base.sequence_type = DDSequenceType::QDD;
        Ok(base)
    }

    fn generate_cdd_sequence(target_qubits: &[QubitId], duration: f64) -> DeviceResult<DDSequence> {
        let mut base = DDSequenceGenerator::generate_xy8_sequence(target_qubits, duration)?;
        base.sequence_type = DDSequenceType::CDD;
        Ok(base)
    }

    fn generate_rdd_sequence(target_qubits: &[QubitId], duration: f64) -> DeviceResult<DDSequence> {
        let mut base = DDSequenceGenerator::generate_xy4_sequence(target_qubits, duration)?;
        base.sequence_type = DDSequenceType::RDD;
        base.properties
            .noise_suppression
            .insert(NoiseType::RandomTelegraphNoise, 0.8);
        Ok(base)
    }

    fn generate_cp_sequence(target_qubits: &[QubitId], duration: f64) -> DeviceResult<DDSequence> {
        let mut base = DDSequenceGenerator::generate_cpmg_sequence(target_qubits, duration)?;
        base.sequence_type = DDSequenceType::CarrPurcell;
        base.properties.symmetry.phase_symmetry = false;
        Ok(base)
    }

    fn generate_optimized_sequence(
        target_qubits: &[QubitId],
        duration: f64,
    ) -> DeviceResult<DDSequence> {
        // Start with XY8 as base for SciRS2 optimization
        let mut base = DDSequenceGenerator::generate_xy8_sequence(target_qubits, duration)?;
        base.sequence_type = DDSequenceType::SciRS2Optimized;
        base.properties.sequence_order = 5; // Higher order expected from optimization
        Ok(base)
    }

    fn generate_custom_sequence(
        name: &str,
        target_qubits: &[QubitId],
        duration: f64,
    ) -> DeviceResult<DDSequence> {
        // Placeholder for custom sequences - use CPMG as default
        let mut base = DDSequenceGenerator::generate_cpmg_sequence(target_qubits, duration)?;
        base.sequence_type = DDSequenceType::Custom(name.to_string());
        Ok(base)
    }
}

/// Sequence cache for performance optimization
#[derive(Debug, Clone)]
pub struct SequenceCache {
    pub cached_sequences: HashMap<String, DDSequence>,
    pub cache_hits: usize,
    pub cache_misses: usize,
}

impl SequenceCache {
    pub fn new() -> Self {
        Self {
            cached_sequences: HashMap::new(),
            cache_hits: 0,
            cache_misses: 0,
        }
    }

    pub fn get_sequence(&mut self, key: &str) -> Option<DDSequence> {
        if let Some(sequence) = self.cached_sequences.get(key) {
            self.cache_hits += 1;
            Some(sequence.clone())
        } else {
            self.cache_misses += 1;
            None
        }
    }

    pub fn store_sequence(&mut self, key: String, sequence: DDSequence) {
        self.cached_sequences.insert(key, sequence);
    }

    pub fn get_cache_statistics(&self) -> (usize, usize, f64) {
        let total_requests = self.cache_hits + self.cache_misses;
        let hit_rate = if total_requests > 0 {
            self.cache_hits as f64 / total_requests as f64
        } else {
            0.0
        };
        (self.cache_hits, self.cache_misses, hit_rate)
    }
}

/// Composition strategies for combining DD sequences
#[derive(Debug, Clone, PartialEq)]
pub enum CompositionStrategy {
    /// Sequential execution of sequences
    Sequential,
    /// Interleaved execution
    Interleaved,
    /// Nested composition
    Nested,
}

/// Multi-qubit DD sequence coordinator
pub struct MultiQubitDDCoordinator {
    /// Sequences for each qubit group
    pub qubit_sequences: HashMap<Vec<QubitId>, DDSequence>,
    /// Cross-talk mitigation strategy
    pub crosstalk_mitigation: CrosstalkMitigationStrategy,
    /// Synchronization requirements
    pub synchronization: crate::dynamical_decoupling::hardware::SynchronizationRequirements,
}

/// Cross-talk mitigation strategies
#[derive(Debug, Clone, PartialEq)]
pub enum CrosstalkMitigationStrategy {
    /// No mitigation
    None,
    /// Time-shifted sequences
    TimeShifted,
    /// Phase-randomized sequences
    PhaseRandomized,
    /// Orthogonal sequences
    Orthogonal,
    /// Adaptive mitigation
    Adaptive,
    /// Hybrid approach combining multiple strategies
    HybridApproach,
    /// Temporal separation mitigation
    TemporalSeparation,
    /// Spatial separation mitigation
    SpatialSeparation,
}

/// Synchronization requirements
#[derive(Debug, Clone)]
pub struct SynchronizationRequirements {
    /// Global synchronization needed
    pub global_sync: bool,
    /// Phase coherence requirements
    pub phase_coherence: bool,
    /// Timing tolerance
    pub timing_tolerance: f64,
    /// Synchronization points
    pub sync_points: Vec<f64>,
}

impl MultiQubitDDCoordinator {
    /// Create new multi-qubit coordinator
    pub fn new(
        crosstalk_mitigation: CrosstalkMitigationStrategy,
        synchronization: crate::dynamical_decoupling::hardware::SynchronizationRequirements,
    ) -> Self {
        Self {
            qubit_sequences: HashMap::new(),
            crosstalk_mitigation,
            synchronization,
        }
    }

    /// Add DD sequence for qubit group
    pub fn add_sequence(&mut self, qubits: Vec<QubitId>, sequence: DDSequence) {
        self.qubit_sequences.insert(qubits, sequence);
    }

    /// Generate coordinated multi-qubit DD sequence
    pub fn generate_coordinated_sequence(&self) -> DeviceResult<DDSequence> {
        if self.qubit_sequences.is_empty() {
            return Err(crate::DeviceError::InvalidInput(
                "No sequences to coordinate".to_string(),
            ));
        }

        let sequences: Vec<_> = self.qubit_sequences.values().cloned().collect();

        match self.crosstalk_mitigation {
            CrosstalkMitigationStrategy::TimeShifted => {
                self.generate_time_shifted_sequence(&sequences)
            }
            CrosstalkMitigationStrategy::PhaseRandomized => {
                self.generate_phase_randomized_sequence(&sequences)
            }
            _ => {
                // Default to sequential composition
                DDSequenceGenerator::generate_composite_sequence(
                    &sequences,
                    CompositionStrategy::Sequential,
                )
            }
        }
    }

    /// Generate time-shifted sequences to reduce crosstalk
    fn generate_time_shifted_sequence(&self, sequences: &[DDSequence]) -> DeviceResult<DDSequence> {
        let base_sequence = &sequences[0];
        let mut coordinated = base_sequence.clone();

        // Apply time shifts to reduce crosstalk
        let shift_increment = base_sequence.duration / (sequences.len() as f64 * 10.0);

        for (i, sequence) in sequences.iter().enumerate() {
            let time_shift = i as f64 * shift_increment;
            for timing in &mut coordinated.pulse_timings {
                *timing += time_shift;
            }
        }

        coordinated.sequence_type = DDSequenceType::MultiQubitCoordinated;
        Ok(coordinated)
    }

    /// Generate phase-randomized sequences
    fn generate_phase_randomized_sequence(
        &self,
        sequences: &[DDSequence],
    ) -> DeviceResult<DDSequence> {
        let base_sequence = &sequences[0];
        let mut coordinated = base_sequence.clone();

        // Apply random phase shifts to reduce coherent crosstalk
        use std::f64::consts::PI;
        for phase in &mut coordinated.pulse_phases {
            let random_phase = thread_rng().gen::<f64>() * 2.0 * PI;
            *phase += random_phase;
        }

        coordinated.sequence_type = DDSequenceType::MultiQubitCoordinated;
        Ok(coordinated)
    }

    /// Generate composite DD sequence
    fn generate_composite_sequence(
        target_qubits: &[QubitId],
        duration: f64,
    ) -> DeviceResult<DDSequence> {
        // Placeholder implementation - combine multiple basic sequences
        let xy4 = DDSequenceGenerator::generate_xy4_sequence(target_qubits, duration / 2.0)?;
        let cpmg = DDSequenceGenerator::generate_cpmg_sequence(target_qubits, duration / 2.0)?;

        let mut composite = xy4;
        composite.pulse_timings.extend(cpmg.pulse_timings);
        composite.pulse_phases.extend(cpmg.pulse_phases);
        composite.duration = duration;
        composite.sequence_type = DDSequenceType::Composite;

        Ok(composite)
    }

    /// Generate multi-qubit coordinated sequence
    fn generate_multi_qubit_coordinated_sequence(
        target_qubits: &[QubitId],
        duration: f64,
    ) -> DeviceResult<DDSequence> {
        // Placeholder implementation - optimize for multi-qubit crosstalk mitigation
        let mut base = DDSequenceGenerator::generate_xy4_sequence(target_qubits, duration)?;
        base.sequence_type = DDSequenceType::MultiQubitCoordinated;

        // Apply time shifts to reduce crosstalk
        let shift_increment = duration / (target_qubits.len() as f64 * 10.0);
        for (i, _) in target_qubits.iter().enumerate() {
            let time_shift = i as f64 * shift_increment;
            for timing in &mut base.pulse_timings {
                *timing += time_shift;
            }
        }

        Ok(base)
    }

    /// Generate adaptive DD sequence
    fn generate_adaptive_sequence(
        target_qubits: &[QubitId],
        duration: f64,
    ) -> DeviceResult<DDSequence> {
        // Placeholder implementation - adapt based on real-time conditions
        let mut base = DDSequenceGenerator::generate_xy8_sequence(target_qubits, duration)?;
        base.sequence_type = DDSequenceType::Adaptive;

        // Simple adaptive logic - could be enhanced with ML
        let adaptation_factor = 1.1; // Could be dynamically determined
        for timing in &mut base.pulse_timings {
            *timing *= adaptation_factor;
        }

        Ok(base)
    }
}