oxirs-stream 0.2.4

//! # Quantum Entanglement Communication Module
//!
//! Next-generation quantum entanglement-based communication system for ultra-secure
//! and instantaneous data transmission in streaming platforms.
//!
//! **Note**: This is a research implementation exploring quantum computing concepts
//! for future distributed streaming architectures.

use crate::error::{StreamError, StreamResult};
use crate::EventMetadata;
use anyhow::{anyhow, Result};
use serde::{Deserialize, Serialize};
use std::collections::HashMap;
use std::sync::Arc;
use tokio::sync::RwLock;
use tracing::{debug, error, info, warn};

/// Quantum entanglement pair for secure communication
#[derive(Debug, Clone)]
pub struct QuantumPair {
    pub id: String,
    pub particle_a: QuantumParticle,
    pub particle_b: QuantumParticle,
    pub entanglement_strength: f64,
    pub decoherence_time: std::time::Duration,
    pub created_at: std::time::Instant,
}

/// Individual quantum particle state
#[derive(Debug, Clone)]
pub struct QuantumParticle {
    pub id: String,
    pub state: QuantumState,
    pub spin: SpinState,
    pub polarization: PolarizationState,
    pub position: Option<QuantumPosition>,
    pub measured: bool,
}

/// Quantum state representation
#[derive(Debug, Clone, PartialEq)]
pub enum QuantumState {
    Superposition(Vec<QuantumBasis>),
    Collapsed(QuantumBasis),
    Entangled(String), // Reference to entangled particle ID
}

/// Quantum basis states
#[derive(Debug, Clone, PartialEq)]
pub enum QuantumBasis {
    Zero,
    One,
    Plus,
    Minus,
}

/// Spin states for particles
#[derive(Debug, Clone, PartialEq)]
pub enum SpinState {
    Up,
    Down,
    Superposition(f64, f64), // (up_amplitude, down_amplitude)
}

/// Polarization states for photons
#[derive(Debug, Clone, PartialEq)]
pub enum PolarizationState {
    Horizontal,
    Vertical,
    Diagonal,
    AntiDiagonal,
    Circular(CircularPolarization),
}

/// Circular polarization types
#[derive(Debug, Clone, PartialEq)]
pub enum CircularPolarization {
    Left,
    Right,
}

/// Quantum position in 3D space
#[derive(Debug, Clone)]
pub struct QuantumPosition {
    pub x: f64,
    pub y: f64,
    pub z: f64,
    pub uncertainty: f64, // Heisenberg uncertainty
}

/// Quantum communication channel
pub struct QuantumChannel {
    pub id: String,
    pub pairs: Arc<RwLock<HashMap<String, QuantumPair>>>,
    pub error_correction: QuantumErrorCorrection,
    pub key_distribution: QuantumKeyDistribution,
    pub teleportation_protocol: QuantumTeleportation,
}

/// Quantum error correction system
#[derive(Debug, Clone)]
pub struct QuantumErrorCorrection {
    pub code_type: ErrorCorrectionCode,
    pub syndrome_table: HashMap<String, String>,
    pub correction_threshold: f64,
    pub fidelity_target: f64,
}

/// Types of quantum error correction codes
#[derive(Debug, Clone)]
pub enum ErrorCorrectionCode {
    Shor,
    Steane,
    Surface,
    Color,
    TopologicalQubit,
}

/// Quantum key distribution for security
#[derive(Debug, Clone)]
pub struct QuantumKeyDistribution {
    pub protocol: QKDProtocol,
    pub key_length: usize,
    pub security_parameter: f64,
    pub eavesdropping_detection: f64,
}

/// QKD protocols
#[derive(Debug, Clone)]
pub enum QKDProtocol {
    BB84,
    E91,
    SARG04,
    DPS,
    COW,
}

/// Quantum teleportation protocol
#[derive(Debug, Clone)]
pub struct QuantumTeleportation {
    pub bell_state_analyzer: BellStateAnalyzer,
    pub classical_channel: ClassicalChannel,
    pub fidelity_threshold: f64,
}

/// Bell state measurement system
#[derive(Debug, Clone)]
pub struct BellStateAnalyzer {
    pub measurement_basis: Vec<BellState>,
    pub detection_efficiency: f64,
    pub measurement_time: std::time::Duration,
}

/// Bell states for entanglement
#[derive(Debug, Clone, PartialEq)]
pub enum BellState {
    PhiPlus,  // |Φ+⟩ = (|00⟩ + |11⟩)/√2
    PhiMinus, // |Φ-⟩ = (|00⟩ - |11⟩)/√2
    PsiPlus,  // |Ψ+⟩ = (|01⟩ + |10⟩)/√2
    PsiMinus, // |Ψ-⟩ = (|01⟩ - |10⟩)/√2
}

/// Classical communication channel for quantum protocols
#[derive(Debug, Clone)]
pub struct ClassicalChannel {
    pub bandwidth: f64,
    pub latency: std::time::Duration,
    pub error_rate: f64,
    pub authentication: bool,
}

/// Quantum message for streaming
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct QuantumMessage {
    pub id: String,
    pub entanglement_id: String,
    pub data: Vec<u8>,
    pub quantum_signature: QuantumSignature,
    pub timestamp: u64,
    pub priority: QuantumPriority,
}

/// Quantum digital signature
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct QuantumSignature {
    pub signature_states: Vec<QuantumBasis>,
    pub verification_key: String,
    pub security_level: f64,
}

/// Priority levels for quantum messages
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq, PartialOrd, Ord)]
pub enum QuantumPriority {
    Critical,
    High,
    Normal,
    Low,
    Background,
}

impl QuantumChannel {
    /// Create a new quantum communication channel
    pub fn new(id: String) -> Self {
        Self {
            id,
            pairs: Arc::new(RwLock::new(HashMap::new())),
            error_correction: QuantumErrorCorrection::default(),
            key_distribution: QuantumKeyDistribution::default(),
            teleportation_protocol: QuantumTeleportation::default(),
        }
    }

    /// Generate a new entangled pair
    pub async fn create_entangled_pair(&self) -> StreamResult<QuantumPair> {
        let pair_id = uuid::Uuid::new_v4().to_string();
        
        // Generate entangled particles in Bell state |Φ+⟩
        let particle_a = QuantumParticle {
            id: format!("{}_a", pair_id),
            state: QuantumState::Entangled(format!("{}_b", pair_id)),
            spin: SpinState::Superposition(1.0 / 2_f64.sqrt(), 1.0 / 2_f64.sqrt()),
            polarization: PolarizationState::Diagonal,
            position: None,
            measured: false,
        };

        let particle_b = QuantumParticle {
            id: format!("{}_b", pair_id),
            state: QuantumState::Entangled(format!("{}_a", pair_id)),
            spin: SpinState::Superposition(1.0 / 2_f64.sqrt(), -1.0 / 2_f64.sqrt()),
            polarization: PolarizationState::AntiDiagonal,
            position: None,
            measured: false,
        };

        let pair = QuantumPair {
            id: pair_id,
            particle_a,
            particle_b,
            entanglement_strength: 0.99, // Near-perfect entanglement
            decoherence_time: std::time::Duration::from_millis(100), // Realistic decoherence
            created_at: std::time::Instant::now(),
        };

        let mut pairs = self.pairs.write().await;
        pairs.insert(pair.id.clone(), pair.clone());

        info!(
            "Created quantum entangled pair: {} with strength: {:.3}",
            pair.id, pair.entanglement_strength
        );

        Ok(pair)
    }

    /// Perform quantum teleportation of data
    pub async fn teleport_data(&self, data: &[u8], pair_id: &str) -> StreamResult<QuantumMessage> {
        let pairs = self.pairs.read().await;
        let pair = pairs
            .get(pair_id)
            .ok_or_else(|| StreamError::InvalidOperation("Entangled pair not found".to_string()))?;

        // Check if entanglement is still coherent
        if pair.created_at.elapsed() > pair.decoherence_time {
            return Err(StreamError::InvalidOperation(
                "Quantum entanglement has decoherent".to_string(),
            ));
        }

        // Encode data using quantum basis encoding
        let encoded_data = self.encode_classical_data(data)?;

        // Perform Bell state measurement (simplified)
        let bell_measurement = self.measure_bell_state(&pair.particle_a, &pair.particle_b).await?;

        // Create quantum signature
        let quantum_signature = QuantumSignature {
            signature_states: encoded_data.clone(),
            verification_key: pair.id.clone(),
            security_level: pair.entanglement_strength,
        };

        let quantum_msg = QuantumMessage {
            id: uuid::Uuid::new_v4().to_string(),
            entanglement_id: pair_id.to_string(),
            data: data.to_vec(),
            quantum_signature,
            timestamp: chrono::Utc::now().timestamp_millis() as u64,
            priority: QuantumPriority::Normal,
        };

        info!(
            "Quantum teleportation completed for {} bytes using pair {}",
            data.len(),
            pair_id
        );

        Ok(quantum_msg)
    }

    /// Encode classical data into quantum states
    fn encode_classical_data(&self, data: &[u8]) -> StreamResult<Vec<QuantumBasis>> {
        let mut encoded = Vec::new();
        
        for byte in data {
            for bit in 0..8 {
                let bit_value = (byte >> bit) & 1;
                let quantum_state = if bit_value == 0 {
                    QuantumBasis::Zero
                } else {
                    QuantumBasis::One
                };
                encoded.push(quantum_state);
            }
        }

        Ok(encoded)
    }

    /// Measure Bell state (simplified quantum measurement)
    async fn measure_bell_state(
        &self,
        particle_a: &QuantumParticle,
        particle_b: &QuantumParticle,
    ) -> StreamResult<BellState> {
        // Simulate quantum measurement with probabilistic outcomes
        use scirs2_core::random::Random;
        let mut rng = Random::new();

        let measurement_outcome: f64 = rng.uniform_01();
        
        let bell_state = match measurement_outcome {
            x if x < 0.25 => BellState::PhiPlus,
            x if x < 0.50 => BellState::PhiMinus,
            x if x < 0.75 => BellState::PsiPlus,
            _ => BellState::PsiMinus,
        };

        debug!(
            "Bell state measurement: {:?} for particles {} and {}",
            bell_state, particle_a.id, particle_b.id
        );

        Ok(bell_state)
    }

    /// Apply quantum error correction
    pub async fn apply_error_correction(&self, data: &mut [QuantumBasis]) -> StreamResult<f64> {
        // Simplified error correction algorithm
        let mut corrected_errors = 0;
        let total_qubits = data.len();

        for chunk in data.chunks_mut(3) {
            if chunk.len() == 3 {
                // Apply 3-qubit bit flip code
                let syndrome = self.calculate_syndrome(chunk)?;
                if syndrome != "000" {
                    self.apply_correction(chunk, &syndrome)?;
                    corrected_errors += 1;
                }
            }
        }

        let error_rate = corrected_errors as f64 / (total_qubits / 3) as f64;
        
        info!(
            "Quantum error correction applied: {}/{} blocks corrected (error rate: {:.3})",
            corrected_errors,
            total_qubits / 3,
            error_rate
        );

        Ok(error_rate)
    }

    /// Calculate error syndrome for 3-qubit code
    fn calculate_syndrome(&self, qubits: &[QuantumBasis]) -> StreamResult<String> {
        if qubits.len() != 3 {
            return Err(StreamError::InvalidOperation(
                "Syndrome calculation requires exactly 3 qubits".to_string(),
            ));
        }

        // Simplified syndrome calculation
        let s1 = if qubits[0] == qubits[1] { "0" } else { "1" };
        let s2 = if qubits[1] == qubits[2] { "0" } else { "1" };
        let s3 = if qubits[0] == qubits[2] { "0" } else { "1" };

        Ok(format!("{}{}{}", s1, s2, s3))
    }

    /// Apply quantum error correction based on syndrome
    fn apply_correction(&self, qubits: &mut [QuantumBasis], syndrome: &str) -> StreamResult<()> {
        match syndrome {
            "110" => {
                // Error on first qubit
                qubits[0] = match qubits[0] {
                    QuantumBasis::Zero => QuantumBasis::One,
                    QuantumBasis::One => QuantumBasis::Zero,
                    other => other,
                };
            }
            "101" => {
                // Error on second qubit
                qubits[1] = match qubits[1] {
                    QuantumBasis::Zero => QuantumBasis::One,
                    QuantumBasis::One => QuantumBasis::Zero,
                    other => other,
                };
            }
            "011" => {
                // Error on third qubit
                qubits[2] = match qubits[2] {
                    QuantumBasis::Zero => QuantumBasis::One,
                    QuantumBasis::One => QuantumBasis::Zero,
                    other => other,
                };
            }
            _ => {
                // No correction needed or multiple errors detected
            }
        }

        Ok(())
    }

    /// Generate quantum random numbers for cryptographic purposes
    pub async fn generate_quantum_random(&self, length: usize) -> StreamResult<Vec<u8>> {
        let mut random_bytes = Vec::with_capacity(length);
        
        for _ in 0..length {
            // Simulate quantum random number generation
            let pair = self.create_entangled_pair().await?;
            let measurement = self.measure_particle_spin(&pair.particle_a).await?;
            
            let random_byte = match measurement {
                SpinState::Up => 1,
                SpinState::Down => 0,
                SpinState::Superposition(up, _down) => {
                    if up > 0.5 { 1 } else { 0 }
                }
            };
            
            random_bytes.push(random_byte);
        }

        info!("Generated {} quantum random bytes", length);
        Ok(random_bytes)
    }

    /// Measure particle spin state
    async fn measure_particle_spin(&self, particle: &QuantumParticle) -> StreamResult<SpinState> {
        // Simulate quantum measurement collapse
        use scirs2_core::random::Random;
        let mut rng = Random::new();

        match &particle.spin {
            SpinState::Superposition(up_amp, down_amp) => {
                let probability_up = up_amp.powi(2);
                let measurement: f64 = rng.uniform_01();
                
                if measurement < probability_up {
                    Ok(SpinState::Up)
                } else {
                    Ok(SpinState::Down)
                }
            }
            state => Ok(state.clone()),
        }
    }
}

impl Default for QuantumErrorCorrection {
    fn default() -> Self {
        Self {
            code_type: ErrorCorrectionCode::Shor,
            syndrome_table: HashMap::new(),
            correction_threshold: 0.01,
            fidelity_target: 0.99,
        }
    }
}

impl Default for QuantumKeyDistribution {
    fn default() -> Self {
        Self {
            protocol: QKDProtocol::BB84,
            key_length: 256,
            security_parameter: 1e-9,
            eavesdropping_detection: 0.11, // QBER threshold
        }
    }
}

impl Default for QuantumTeleportation {
    fn default() -> Self {
        Self {
            bell_state_analyzer: BellStateAnalyzer {
                measurement_basis: vec![
                    BellState::PhiPlus,
                    BellState::PhiMinus,
                    BellState::PsiPlus,
                    BellState::PsiMinus,
                ],
                detection_efficiency: 0.85,
                measurement_time: std::time::Duration::from_nanos(100),
            },
            classical_channel: ClassicalChannel {
                bandwidth: 1e9, // 1 Gbps
                latency: std::time::Duration::from_micros(1),
                error_rate: 1e-12,
                authentication: true,
            },
            fidelity_threshold: 0.95,
        }
    }
}

/// Quantum computing backend integration
pub struct QuantumBackend {
    pub provider: QuantumProvider,
    pub qubits: usize,
    pub coherence_time: std::time::Duration,
    pub gate_fidelity: f64,
    pub connectivity: QuantumConnectivity,
}

/// Quantum computing providers
#[derive(Debug, Clone)]
pub enum QuantumProvider {
    IBMQuantum {
        backend_name: String,
        access_token: String,
    },
    AWSBraket {
        device_arn: String,
        region: String,
    },
    GoogleQuantumAI {
        processor_id: String,
        project_id: String,
    },
    Simulator {
        noise_model: NoiseModel,
    },
}

/// Quantum device connectivity graph
#[derive(Debug, Clone)]
pub struct QuantumConnectivity {
    pub topology: ConnectivityTopology,
    pub coupling_map: Vec<(usize, usize)>,
    pub gate_times: HashMap<String, std::time::Duration>,
}

/// Connectivity topologies
#[derive(Debug, Clone)]
pub enum ConnectivityTopology {
    Linear,
    Grid,
    Star,
    AllToAll,
    Heavy Hex,
    Custom(Vec<(usize, usize)>),
}

/// Quantum noise models
#[derive(Debug, Clone)]
pub enum NoiseModel {
    Ideal,
    Depolarizing { probability: f64 },
    Amplitude { gamma: f64 },
    Phase { gamma: f64 },
    Thermal { temperature: f64 },
    Realistic { 
        t1: std::time::Duration,
        t2: std::time::Duration,
        gate_error: f64,
    },
}

#[cfg(test)]
mod tests {
    use super::*;

    #[tokio::test]
    async fn test_quantum_entanglement_creation() {
        let channel = QuantumChannel::new("test_channel".to_string());
        let pair = channel.create_entangled_pair().await.unwrap();

        assert!(!pair.id.is_empty());
        assert!(pair.entanglement_strength > 0.5);
        assert!(pair.decoherence_time > std::time::Duration::from_millis(10));
    }

    #[tokio::test]
    async fn test_quantum_teleportation() {
        let channel = QuantumChannel::new("test_teleport".to_string());
        let pair = channel.create_entangled_pair().await.unwrap();
        
        let test_data = b"Hello, Quantum World!";
        let quantum_msg = channel.teleport_data(test_data, &pair.id).await.unwrap();

        assert_eq!(quantum_msg.data, test_data);
        assert_eq!(quantum_msg.entanglement_id, pair.id);
        assert!(quantum_msg.quantum_signature.security_level > 0.5);
    }

    #[tokio::test]
    async fn test_quantum_error_correction() {
        let channel = QuantumChannel::new("test_ecc".to_string());
        let mut data = vec![
            QuantumBasis::Zero,
            QuantumBasis::One,
            QuantumBasis::Zero,
        ];

        let error_rate = channel.apply_error_correction(&mut data).await.unwrap();
        assert!(error_rate >= 0.0 && error_rate <= 1.0);
    }

    #[tokio::test]
    async fn test_quantum_random_generation() {
        let channel = QuantumChannel::new("test_rng".to_string());
        let random_bytes = channel.generate_quantum_random(10).await.unwrap();

        assert_eq!(random_bytes.len(), 10);
        // Test that not all bytes are the same (very unlikely with true randomness)
        let all_same = random_bytes.iter().all(|&x| x == random_bytes[0]);
        assert!(!all_same || random_bytes.len() < 3);
    }
}