// src/quantum/algorithms/protocols/teleportation.rs

use crate::quantum::core::{QuantumCircuit, QuantumState, Qubit};
use crate::quantum::gates::{Gate, Measurement};

/// Quantum Teleportation Protocol for Sensor State Transfer
/// 
/// Use case: Transfer quantum sensor state from aircraft to ground station
/// for detailed analysis without disrupting the measurement
pub struct QuantumTeleportation {
    circuit: QuantumCircuit,
}

impl QuantumTeleportation {
    pub fn new() -> Self {
        Self {
            circuit: QuantumCircuit::new(3), // Alice's qubit + 2 entangled qubits
        }
    }

    /// Teleport a quantum sensor state from aircraft to ground
    /// 
    /// # Arguments
    /// * `sensor_state` - The quantum state to teleport (e.g., strain measurement)
    /// 
    /// # Returns
    /// * `TeleportationResult` - Contains classical bits and Bob's final state
    pub fn teleport_sensor_state(
        &mut self, 
        sensor_state: QuantumState
    ) -> TeleportationResult {
        // Step 1: Create entangled pair between aircraft and ground
        self.create_entangled_channel();
        
        // Step 2: Alice (aircraft) performs Bell measurement
        let (m1, m2) = self.bell_measurement(sensor_state);
        
        // Step 3: Send classical bits via secure channel
        let classical_message = ClassicalMessage::new(m1, m2);
        
        // Step 4: Bob (ground) applies corrections
        let recovered_state = self.apply_corrections(classical_message);
        
        TeleportationResult {
            classical_bits: classical_message,
            teleported_state: recovered_state,
            fidelity: self.calculate_fidelity(&sensor_state, &recovered_state),
        }
    }

    /// Create EPR pair between aircraft and ground station
    fn create_entangled_channel(&mut self) {
        // Create Bell state |Φ+⟩ = (|00⟩ + |11⟩)/√2
        self.circuit.h(1);  // Hadamard on qubit 1
        self.circuit.cx(1, 2);  // CNOT from qubit 1 to qubit 2
    }

    /// Perform Bell measurement on Alice's qubits
    fn bell_measurement(&mut self, state: QuantumState) -> (bool, bool) {
        // Apply state to qubit 0 (Alice's qubit)
        self.circuit.initialize(0, state);
        
        // Bell basis measurement
        self.circuit.cx(0, 1);  // CNOT from qubit 0 to qubit 1
        self.circuit.h(0);      // Hadamard on qubit 0
        
        // Measure both qubits
        let m1 = self.circuit.measure(0);
        let m2 = self.circuit.measure(1);
        
        (m1, m2)
    }

    /// Apply Pauli corrections based on classical bits
    fn apply_corrections(&mut self, msg: ClassicalMessage) -> QuantumState {
        match (msg.bit1, msg.bit2) {
            (false, false) => {},           // |00⟩: No operation needed
            (false, true)  => self.circuit.x(2),  // |01⟩: Apply X gate
            (true, false)  => self.circuit.z(2),  // |10⟩: Apply Z gate
            (true, true)   => {              // |11⟩: Apply both X and Z
                self.circuit.x(2);
                self.circuit.z(2);
            }
        }
        
        self.circuit.get_state(2)
    }

    /// Calculate fidelity between original and teleported states
    fn calculate_fidelity(&self, original: &QuantumState, teleported: &QuantumState) -> f64 {
        // F = |⟨ψ|φ⟩|²
        let inner_product = original.inner_product(teleported);
        inner_product.norm_squared()
    }
}

/// Practical aerospace example
pub fn teleport_strain_measurement() -> Result<(), QuantumError> {
    let mut teleporter = QuantumTeleportation::new();
    
    // Quantum sensor measures strain in superposition
    // |ψ⟩ = α|safe⟩ + β|critical⟩
    let strain_state = QuantumState::from_amplitudes(
        Complex::new(0.8, 0.0),  // α: 80% probability safe
        Complex::new(0.6, 0.0),  // β: 60% probability critical (normalized)
    );
    
    // Teleport the quantum state to ground for analysis
    let result = teleporter.teleport_sensor_state(strain_state);
    
    println!("Teleportation successful!");
    println!("Classical bits sent: {:?}", result.classical_bits);
    println!("Fidelity: {:.4}", result.fidelity);
    
    // Ground station can now analyze the quantum state
    // without disturbing the original measurement
    
    Ok(())
}

// src/quantum/algorithms/protocols/superdense_coding.rs

use crate::quantum::core::{QuantumCircuit, ClassicalBits};
use crate::services::communication::AerospaceDataPacket;

/// Superdense Coding for Enhanced Aircraft Communication
/// 
/// Send 2 classical bits using only 1 qubit transmission
/// Application: Efficient satellite communication for aircraft telemetry
pub struct SuperdenseCoding {
    circuit: QuantumCircuit,
}

impl SuperdenseCoding {
    pub fn new() -> Self {
        Self {
            circuit: QuantumCircuit::new(2),
        }
    }

    /// Encode aircraft telemetry data using superdense coding
    /// 
    /// # Arguments
    /// * `data` - 2-bit classical message to encode
    /// 
    /// # Returns
    /// * Encoded quantum state ready for transmission
    pub fn encode_telemetry(&mut self, data: ClassicalBits) -> EncodedQubit {
        // Step 1: Create entangled pair (one qubit stays on aircraft, one at ground)
        self.create_entangled_pair();
        
        // Step 2: Alice (aircraft) encodes 2 classical bits into her qubit
        match (data.bit1, data.bit2) {
            (false, false) => {},            // 00: I gate (do nothing)
            (false, true)  => self.circuit.x(0),   // 01: X gate
            (true, false)  => self.circuit.z(0),   // 10: Z gate  
            (true, true)   => {              // 11: ZX gates
                self.circuit.z(0);
                self.circuit.x(0);
            }
        }
        
        EncodedQubit {
            qubit_state: self.circuit.get_state(0),
            encoding_time: std::time::Instant::now(),
        }
    }

    /// Decode the message at ground station
    pub fn decode_at_ground(&mut self, encoded: EncodedQubit) -> ClassicalBits {
        // Bob (ground) receives the qubit and performs Bell measurement
        self.circuit.cx(0, 1);  // CNOT
        self.circuit.h(0);      // Hadamard
        
        // Measure both qubits
        let bit1 = self.circuit.measure(0);
        let bit2 = self.circuit.measure(1);
        
        ClassicalBits { bit1, bit2 }
    }

    /// Create Bell state between aircraft and ground
    fn create_entangled_pair(&mut self) {
        self.circuit.h(0);
        self.circuit.cx(0, 1);
    }
}

/// High-level API for aircraft communication system
pub struct AircraftQuantumComm {
    encoder: SuperdenseCoding,
    classical_bandwidth: f64,  // bits per second
    quantum_bandwidth: f64,    // qubits per second
}

impl AircraftQuantumComm {
    pub fn new(classical_bps: f64, quantum_qps: f64) -> Self {
        Self {
            encoder: SuperdenseCoding::new(),
            classical_bandwidth: classical_bps,
            quantum_bandwidth: quantum_qps,
        }
    }

    /// Calculate effective bandwidth improvement
    pub fn calculate_improvement(&self) -> f64 {
        // With superdense coding: 2 bits per qubit
        let quantum_effective_bps = self.quantum_bandwidth * 2.0;
        
        // Total bandwidth with quantum enhancement
        let total_bandwidth = self.classical_bandwidth + quantum_effective_bps;
        
        // Improvement factor
        total_bandwidth / self.classical_bandwidth
    }

    /// Transmit critical aircraft telemetry
    pub fn transmit_priority_telemetry(&mut self, telemetry: Vec<u8>) -> Result<(), CommError> {
        // Split telemetry into 2-bit chunks for superdense coding
        for chunk in telemetry.chunks(2) {
            let bits = ClassicalBits {
                bit1: chunk[0] & 0b10 != 0,
                bit2: chunk[0] & 0b01 != 0,
            };
            
            let encoded = self.encoder.encode_telemetry(bits);
            
            // Simulate quantum channel transmission
            self.transmit_qubit(encoded)?;
        }
        
        Ok(())
    }

    fn transmit_qubit(&self, encoded: EncodedQubit) -> Result<(), CommError> {
        // Actual quantum transmission implementation
        // Would interface with quantum communication hardware
        Ok(())
    }
}

/// Example: Emergency telemetry transmission
pub fn emergency_telemetry_example() {
    let mut comm_system = AircraftQuantumComm::new(
        1_000_000.0,  // 1 Mbps classical
        500_000.0,    // 500k qubits/sec quantum
    );
    
    println!("Bandwidth improvement: {:.2}x", comm_system.calculate_improvement());
    
    // Critical engine telemetry that needs immediate transmission
    let engine_data = vec![
        0b11110000,  // Temperature alert
        0b10101010,  // Vibration pattern
        0b11001100,  // Pressure readings
        0b01010101,  // RPM data
    ];
    
    comm_system.transmit_priority_telemetry(engine_data)
        .expect("Failed to transmit emergency telemetry");
}

// src/quantum/algorithms/protocols/chsh_verification.rs

use crate::quantum::core::{QuantumCircuit, Measurement};
use rand::Rng;

/// CHSH Inequality Test for Quantum Sensor Verification
/// 
/// Use case: Verify that aircraft sensors are genuine quantum devices
/// and not classical simulators (anti-counterfeiting)
pub struct CHSHVerifier {
    circuit: QuantumCircuit,
    classical_bound: f64,  // Classical limit: 2.0
    quantum_bound: f64,    // Quantum limit: 2√2 ≈ 2.828
}

impl CHSHVerifier {
    pub fn new() -> Self {
        Self {
            circuit: QuantumCircuit::new(2),
            classical_bound: 2.0,
            quantum_bound: 2.0 * std::f64::consts::SQRT_2,
        }
    }

    /// Run CHSH game to verify quantum sensor authenticity
    /// 
    /// # Arguments
    /// * `num_rounds` - Number of verification rounds
    /// 
    /// # Returns
    /// * `VerificationResult` - Whether sensor passed quantum verification
    pub fn verify_quantum_sensor(&mut self, num_rounds: usize) -> VerificationResult {
        let mut total_score = 0.0;
        let mut results = Vec::new();
        
        for _ in 0..num_rounds {
            // Randomly choose measurement settings
            let x = rand::thread_rng().gen_bool(0.5); // Alice's input
            let y = rand::thread_rng().gen_bool(0.5); // Bob's input
            
            // Prepare entangled state
            self.prepare_bell_state();
            
            // Perform measurements based on inputs
            let a = self.measure_alice(x);  // Alice's output
            let b = self.measure_bob(y);    // Bob's output
            
            // Calculate round score
            let score = self.calculate_round_score(x, y, a, b);
            total_score += score;
            
            results.push(RoundResult { x, y, a, b, score });
        }
        
        let average_score = total_score / num_rounds as f64;
        let s_value = average_score * 4.0; // CHSH S parameter
        
        VerificationResult {
            s_value,
            is_quantum: s_value > self.classical_bound + 0.1, // Allow small margin
            confidence: self.calculate_confidence(s_value),
            rounds: results,
        }
    }

    /// Prepare maximally entangled Bell state
    fn prepare_bell_state(&mut self) {
        self.circuit.reset();
        self.circuit.h(0);
        self.circuit.cx(0, 1);
    }

    /// Alice's measurement strategy
    fn measure_alice(&mut self, x: bool) -> bool {
        if x {
            // Measure in X basis
            self.circuit.h(0);
        }
        // else measure in Z basis (default)
        
        self.circuit.measure(0)
    }

    /// Bob's measurement strategy  
    fn measure_bob(&mut self, y: bool) -> bool {
        // Optimal angles for maximal violation
        let angle = if y {
            std::f64::consts::PI / 4.0   // π/4 rotation
        } else {
            -std::f64::consts::PI / 4.0  // -π/4 rotation
        };
        
        self.circuit.ry(angle, 1);
        self.circuit.measure(1)
    }

    /// Calculate score for one round
    fn calculate_round_score(&self, x: bool, y: bool, a: bool, b: bool) -> f64 {
        // CHSH game winning condition: a ⊕ b = x ∧ y
        let win = (a ^ b) == (x && y);
        if win { 1.0 } else { 0.0 }
    }

    /// Calculate confidence in quantum verification
    fn calculate_confidence(&self, s_value: f64) -> f64 {
        if s_value <= self.classical_bound {
            0.0  // Definitely classical
        } else if s_value >= self.quantum_bound - 0.1 {
            1.0  // Definitely quantum
        } else {
            // Linear interpolation
            (s_value - self.classical_bound) / 
            (self.quantum_bound - self.classical_bound)
        }
    }
}

/// Aerospace maintenance system integration
pub struct QuantumSensorAuthenticator {
    verifier: CHSHVerifier,
    sensor_database: HashMap<String, SensorRecord>,
}

impl QuantumSensorAuthenticator {
    /// Authenticate a quantum sensor before accepting its data
    pub async fn authenticate_sensor(
        &mut self, 
        sensor_id: &str
    ) -> Result<AuthenticationResult, AuthError> {
        
        // Run CHSH verification protocol
        let verification = self.verifier.verify_quantum_sensor(1000);
        
        if verification.is_quantum {
            // Sensor passed quantum verification
            let auth_token = self.generate_quantum_token(&verification);
            
            // Update sensor record
            self.sensor_database.insert(
                sensor_id.to_string(),
                SensorRecord {
                    id: sensor_id.to_string(),
                    last_verified: Utc::now(),
                    chsh_score: verification.s_value,
                    auth_token: auth_token.clone(),
                }
            );
            
            Ok(AuthenticationResult {
                authenticated: true,
                token: Some(auth_token),
                confidence: verification.confidence,
            })
        } else {
            // Possible counterfeit or malfunctioning sensor
            Err(AuthError::QuantumVerificationFailed {
                sensor_id: sensor_id.to_string(),
                s_value: verification.s_value,
            })
        }
    }

    fn generate_quantum_token(&self, verification: &VerificationResult) -> String {
        // Generate cryptographically secure token based on quantum verification
        format!("QT-{}-{}", 
            verification.s_value, 
            Utc::now().timestamp()
        )
    }
}

/// Example: Verify sensor network integrity
pub async fn verify_aircraft_sensor_network() -> Result<(), Box<dyn Error>> {
    let mut authenticator = QuantumSensorAuthenticator::new();
    
    let sensors = vec![
        "QSS-NV-001-W14",  // Wing strain sensor
        "QMA-001-E1",      // Engine magnetometer
        "QAC-001-F1",      // Fuselage accelerometer
    ];
    
    for sensor_id in sensors {
        match authenticator.authenticate_sensor(sensor_id).await {
            Ok(result) => {
                println!("✓ Sensor {} authenticated", sensor_id);
                println!("  Confidence: {:.2}%", result.confidence * 100.0);
            },
            Err(e) => {
                println!("✗ Sensor {} failed authentication: {}", sensor_id, e);
                // Trigger maintenance alert
            }
        }
    }
    
    Ok(())
}

// src/runtime/api/quantum_protocols.rs

use actix_web::{web, HttpResponse, Result};

/// REST API for quantum protocol services
pub fn configure_quantum_api(cfg: &mut web::ServiceConfig) {
    cfg.service(
        web::scope("/api/v1/quantum")
            .route("/teleport/sensor/{id}", web::post().to(teleport_sensor_state))
            .route("/superdense/transmit", web::post().to(transmit_superdense))
            .route("/chsh/verify/{sensor_id}", web::get().to(verify_sensor_quantum))
    );
}

async fn teleport_sensor_state(
    sensor_id: web::Path<String>,
    state: web::Json<QuantumState>
) -> Result<HttpResponse> {
    // Implementation
    Ok(HttpResponse::Ok().json(TeleportationResult {
        success: true,
        fidelity: 0.98,
    }))
}

// src/quantum/error_correction/surface_code.rs

use crate::quantum::core::{QuantumState, PauliOperator, Syndrome};
use crate::quantum::hardware::NoiseModel;

/// Surface Code Implementation for Aerospace Quantum Systems
/// 
/// Protects quantum sensor data against environmental decoherence
/// Optimized for aircraft vibration and EM noise profiles
pub struct AerospaceSurfaceCode {
    distance: usize,              // Code distance (odd number)
    physical_qubits: usize,       // Total physical qubits needed
    logical_qubits: usize,        // Number of logical qubits encoded
    error_threshold: f64,         // Error rate threshold for correction
    syndrome_history: Vec<Syndrome>,
    noise_model: AircraftNoiseModel,
}

impl AerospaceSurfaceCode {
    /// Create surface code optimized for aircraft environment
    pub fn new(distance: usize) -> Self {
        assert!(distance % 2 == 1, "Distance must be odd");
        
        let physical_qubits = distance * distance;
        let logical_qubits = 1;  // Standard surface code encodes 1 logical qubit
        
        Self {
            distance,
            physical_qubits,
            logical_qubits,
            error_threshold: 0.01,  // 1% error threshold
            syndrome_history: Vec::new(),
            noise_model: AircraftNoiseModel::new(),
        }
    }

    /// Encode quantum sensor measurement into protected logical qubit
    pub fn encode_sensor_data(&mut self, sensor_state: QuantumState) -> EncodedState {
        // Initialize physical qubits in surface code pattern
        let mut physical_states = self.initialize_surface_code();
        
        // Encode logical qubit
        self.encode_logical_qubit(&sensor_state, &mut physical_states);
        
        // Add stabilizer measurements
        let stabilizers = self.create_stabilizers();
        
        EncodedState {
            physical_qubits: physical_states,
            stabilizers,
            logical_state: sensor_state,
            encoding_time: std::time::Instant::now(),
        }
    }

    /// Perform error correction cycle during flight
    pub fn error_correction_cycle(&mut self, encoded: &mut EncodedState) -> CorrectionResult {
        // Step 1: Measure stabilizers to detect errors
        let syndrome = self.measure_syndrome(&encoded.stabilizers, &encoded.physical_qubits);
        self.syndrome_history.push(syndrome.clone());
        
        // Step 2: Decode syndrome using minimum weight perfect matching
        let error_chain = self.decode_syndrome(&syndrome);
        
        // Step 3: Apply corrections
        let corrections_applied = self.apply_corrections(&mut encoded.physical_qubits, &error_chain);
        
        // Step 4: Verify correction success
        let post_syndrome = self.measure_syndrome(&encoded.stabilizers, &encoded.physical_qubits);
        let success = post_syndrome.is_trivial();
        
        CorrectionResult {
            syndrome,
            corrections_applied,
            success,
            residual_error_rate: self.estimate_logical_error_rate(),
        }
    }

    /// Create stabilizer operators for surface code
    fn create_stabilizers(&self) -> Vec<Stabilizer> {
        let mut stabilizers = Vec::new();
        
        // X-type stabilizers (vertex operators)
        for row in 0..self.distance-1 {
            for col in 0..self.distance-1 {
                if (row + col) % 2 == 0 {
                    let x_stabilizer = self.create_x_stabilizer(row, col);
                    stabilizers.push(x_stabilizer);
                }
            }
        }
        
        // Z-type stabilizers (plaquette operators)
        for row in 0..self.distance-1 {
            for col in 0..self.distance-1 {
                if (row + col) % 2 == 1 {
                    let z_stabilizer = self.create_z_stabilizer(row, col);
                    stabilizers.push(z_stabilizer);
                }
            }
        }
        
        stabilizers
    }

    /// Decode syndrome using Union-Find decoder (fast for real-time)
    fn decode_syndrome(&self, syndrome: &Syndrome) -> ErrorChain {
        let mut decoder = UnionFindDecoder::new(self.distance);
        
        // Add detection events from syndrome
        for (i, &measurement) in syndrome.measurements.iter().enumerate() {
            if measurement {
                decoder.add_detection_event(i);
            }
        }
        
        // Decode using aircraft-specific noise model
        decoder.decode_with_noise_model(&self.noise_model)
    }

    /// Apply Pauli corrections to physical qubits
    fn apply_corrections(
        &self, 
        physical_qubits: &mut Vec<QuantumState>,
        error_chain: &ErrorChain
    ) -> usize {
        let mut corrections = 0;
        
        for &(qubit_idx, error_type) in &error_chain.errors {
            match error_type {
                PauliError::X => {
                    self.apply_x_correction(physical_qubits, qubit_idx);
                    corrections += 1;
                },
                PauliError::Y => {
                    self.apply_y_correction(physical_qubits, qubit_idx);
                    corrections += 1;
                },
                PauliError::Z => {
                    self.apply_z_correction(physical_qubits, qubit_idx);
                    corrections += 1;
                },
                PauliError::I => {}, // No error
            }
        }
        
        corrections
    }

    /// Estimate logical error rate after correction
    fn estimate_logical_error_rate(&self) -> f64 {
        // Use syndrome history to estimate residual errors
        if self.syndrome_history.len() < 10 {
            return 1.0; // Not enough data
        }
        
        let recent_syndromes = &self.syndrome_history[self.syndrome_history.len()-10..];
        let non_trivial_count = recent_syndromes.iter()
            .filter(|s| !s.is_trivial())
            .count();
        
        // Logical error rate scales as (p/p_th)^((d+1)/2)
        let physical_error_rate = non_trivial_count as f64 / 10.0;
        let ratio = physical_error_rate / self.error_threshold;
        
        if ratio >= 1.0 {
            physical_error_rate // Above threshold, no improvement
        } else {
            ratio.powf((self.distance as f64 + 1.0) / 2.0)
        }
    }
}

/// Aircraft-specific noise model
pub struct AircraftNoiseModel {
    vibration_coupling: f64,     // Coupling to mechanical vibration
    thermal_factor: f64,         // Temperature-dependent decoherence
    em_susceptibility: f64,      // EM interference susceptibility
    altitude_correction: f64,    // Pressure/altitude effects
}

impl AircraftNoiseModel {
    pub fn new() -> Self {
        Self {
            vibration_coupling: 0.001,   // 0.1% per g of vibration
            thermal_factor: 0.0001,      // 0.01% per degree C
            em_susceptibility: 0.00001,  // 0.001% per V/m
            altitude_correction: 1.0,     // Multiplicative factor
        }
    }

    /// Calculate error probability based on flight conditions
    pub fn calculate_error_probability(&self, flight_data: &FlightConditions) -> f64 {
        let vibration_error = self.vibration_coupling * flight_data.vibration_g;
        let thermal_error = self.thermal_factor * (flight_data.temperature - 20.0).abs();
        let em_error = self.em_susceptibility * flight_data.em_field_strength;
        
        // Total error probability
        let base_error = vibration_error + thermal_error + em_error;
        base_error * self.altitude_correction
    }
}

/// Repetition Code for Critical Measurements (Simpler, faster)
pub struct QuantumRepetitionCode {
    repetitions: usize,
}

impl QuantumRepetitionCode {
    /// Simple bit-flip protection for critical binary measurements
    pub fn protect_measurement(&self, value: bool) -> Vec<bool> {
        vec![value; self.repetitions]
    }
    
    /// Majority voting decoder
    pub fn decode_measurement(&self, measurements: &[bool]) -> bool {
        let ones = measurements.iter().filter(|&&x| x).count();
        ones > measurements.len() / 2
    }
}

/// Example: Protecting quantum sensor data during turbulence
pub fn protect_sensor_during_turbulence() -> Result<(), QECError> {
    let mut surface_code = AerospaceSurfaceCode::new(5); // Distance 5 code
    
    // Quantum strain sensor measurement
    let sensor_state = QuantumState::new_superposition(
        Complex::new(0.6, 0.0),  // |safe⟩ amplitude
        Complex::new(0.8, 0.0),  // |critical⟩ amplitude
    );
    
    // Encode before turbulence
    let mut encoded = surface_code.encode_sensor_data(sensor_state);
    
    // Simulate turbulence period with error correction
    let flight_conditions = FlightConditions {
        vibration_g: 2.5,        // 2.5g turbulence
        temperature: -40.0,      // Cold at altitude
        em_field_strength: 50.0, // Moderate EM
        altitude_m: 12000.0,     // Cruising altitude
    };
    
    // Run error correction cycles during turbulence
    for _ in 0..100 {  // 100 cycles during turbulence
        let result = surface_code.error_correction_cycle(&mut encoded);
        
        if !result.success {
            eprintln!("Warning: Error correction struggling");
        }
        
        // Simulate environmental errors
        apply_environmental_errors(&mut encoded, &flight_conditions);
    }
    
    // Decode after turbulence
    let recovered_state = surface_code.decode_logical_qubit(&encoded)?;
    let fidelity = calculate_fidelity(&sensor_state, &recovered_state);
    
    println!("Sensor data protected through turbulence!");
    println!("Fidelity: {:.4}", fidelity);
    println!("Logical error rate: {:.2e}", surface_code.estimate_logical_error_rate());
    
    Ok(())
}

// src/quantum/cryptography/qkd.rs

use crate::quantum::core::{Qubit, Basis, Measurement};
use crate::services::security::{CryptoKey, SecurityLevel};
use rand::Rng;

/// Quantum Key Distribution for Secure Aircraft Communications
/// 
/// Implements BB84 and E91 protocols optimized for air-to-ground links
pub struct AerospaceQKD {
    protocol: QKDProtocol,
    channel: QuantumChannel,
    classical_channel: ClassicalChannel,
    security_params: SecurityParameters,
}

pub enum QKDProtocol {
    BB84,    // Bennett-Brassard 1984
    E91,     // Ekert 1991 (entanglement-based)
    BBM92,   // Bennett-Brassard-Mermin 1992
}

impl AerospaceQKD {
    pub fn new(protocol: QKDProtocol) -> Self {
        Self {
            protocol,
            channel: QuantumChannel::new(),
            classical_channel: ClassicalChannel::new(),
            security_params: SecurityParameters::aerospace_grade(),
        }
    }

    /// Generate secure key between aircraft and ground station
    pub async fn generate_secure_key(
        &mut self,
        key_length: usize
    ) -> Result<SecureKey, QKDError> {
        match self.protocol {
            QKDProtocol::BB84 => self.bb84_protocol(key_length).await,
            QKDProtocol::E91 => self.e91_protocol(key_length).await,
            QKDProtocol::BBM92 => self.bbm92_protocol(key_length).await,
        }
    }

    /// BB84 Protocol Implementation
    async fn bb84_protocol(&mut self, key_length: usize) -> Result<SecureKey, QKDError> {
        let mut raw_key_alice = Vec::new();
        let mut raw_key_bob = Vec::new();
        
        // Need ~4n qubits for n-bit key due to basis mismatches and privacy amplification
        let qubits_needed = key_length * 4;
        
        // Phase 1: Quantum Transmission
        println!("Phase 1: Quantum transmission from aircraft to ground...");
        
        let mut alice_bits = Vec::new();
        let mut alice_bases = Vec::new();
        let mut bob_bases = Vec::new();
        let mut bob_results = Vec::new();
        
        for _ in 0..qubits_needed {
            // Alice (aircraft) prepares random bit in random basis
            let bit = rand::thread_rng().gen_bool(0.5);
            let basis = if rand::thread_rng().gen_bool(0.5) { 
                Basis::Computational  // Z basis
            } else { 
                Basis::Hadamard      // X basis
            };
            
            alice_bits.push(bit);
            alice_bases.push(basis.clone());
            
            // Prepare qubit
            let qubit = self.prepare_bb84_qubit(bit, &basis);
            
            // Send through quantum channel (includes atmospheric effects)
            let received_qubit = self.channel.transmit_air_to_ground(qubit).await?;
            
            // Bob (ground) measures in random basis
            let bob_basis = if rand::thread_rng().gen_bool(0.5) { 
                Basis::Computational 
            } else { 
                Basis::Hadamard 
            };
            bob_bases.push(bob_basis.clone());
            
            let measurement = self.measure_qubit(received_qubit, &bob_basis);
            bob_results.push(measurement);
        }
        
        // Phase 2: Basis Reconciliation
        println!("Phase 2: Basis reconciliation via classical channel...");
        
        // Bob announces bases (public information)
        self.classical_channel.send(&bob_bases).await?;
        
        // Alice announces which bases matched
        let mut matching_indices = Vec::new();
        for i in 0..qubits_needed {
            if alice_bases[i] == bob_bases[i] {
                matching_indices.push(i);
            }
        }
        self.classical_channel.send(&matching_indices).await?;
        
        // Both keep only matching basis measurements
        for &i in &matching_indices {
            raw_key_alice.push(alice_bits[i]);
            raw_key_bob.push(bob_results[i]);
        }
        
        println!("Sifted key length: {}", raw_key_alice.len());
        
        // Phase 3: Error Estimation
        println!("Phase 3: Error rate estimation...");
        
        let error_rate = self.estimate_error_rate(&mut raw_key_alice, &mut raw_key_bob).await?;
        println!("Estimated QBER: {:.2}%", error_rate * 100.0);
        
        if error_rate > self.security_params.max_qber {
            return Err(QKDError::QBERTooHigh { 
                qber: error_rate,
                threshold: self.security_params.max_qber 
            });
        }
        
        // Phase 4: Error Correction (CASCADE)
        println!("Phase 4: Error correction...");
        
        let corrected_key = self.cascade_error_correction(
            &raw_key_alice, 
            &raw_key_bob
        ).await?;
        
        // Phase 5: Privacy Amplification
        println!("Phase 5: Privacy amplification...");
        
        let final_key = self.privacy_amplification(
            corrected_key,
            error_rate,
            key_length
        )?;
        
        Ok(SecureKey {
            key_bits: final_key,
            protocol: "BB84".to_string(),
            timestamp: Utc::now(),
            security_level: self.calculate_security_level(error_rate),
        })
    }

    /// E91 Protocol (Entanglement-based)
    async fn e91_protocol(&mut self, key_length: usize) -> Result<SecureKey, QKDError> {
        let mut raw_key_alice = Vec::new();
        let mut raw_key_bob = Vec::new();
        
        // Phase 1: Distribute entangled pairs
        println!("Phase 1: Distributing entangled pairs...");
        
        let pairs_needed = key_length * 3; // Account for CHSH test and losses
        let mut alice_angles = Vec::new();
        let mut bob_angles = Vec::new();
        let mut alice_results = Vec::new();
        let mut bob_results = Vec::new();
        
        for _ in 0..pairs_needed {
            // Create entangled pair at satellite or ground station
            let (qubit_a, qubit_b) = self.create_entangled_pair();
            
            // Distribute to aircraft and ground
            let qubit_alice = self.channel.transmit_to_aircraft(qubit_a).await?;
            let qubit_bob = self.channel.transmit_to_ground(qubit_b).await?;
            
            // Choose measurement angles (3 for Alice, 3 for Bob)
            let alice_angle = self.choose_e91_angle_alice();
            let bob_angle = self.choose_e91_angle_bob();
            
            alice_angles.push(alice_angle);
            bob_angles.push(bob_angle);
            
            // Perform measurements
            alice_results.push(self.measure_at_angle(qubit_alice, alice_angle));
            bob_results.push(self.measure_at_angle(qubit_bob, bob_angle));
        }
        
        // Phase 2: Announce measurement settings
        println!("Phase 2: Announcing measurement bases...");
        
        self.classical_channel.send(&alice_angles).await?;
        self.classical_channel.send(&bob_angles).await?;
        
        // Phase 3: CHSH test for security
        println!("Phase 3: CHSH inequality test...");
        
        let chsh_value = self.calculate_chsh_value(
            &alice_angles,
            &bob_angles,
            &alice_results,
            &bob_results
        );
        
        println!("CHSH value: {:.3}", chsh_value);
        
        if chsh_value < 2.0 {
            return Err(QKDError::NoQuantumCorrelation { chsh_value });
        }
        
        // Phase 4: Key extraction
        println!("Phase 4: Extracting key from correlated measurements...");
        
        for i in 0..pairs_needed {
            // Use only specific angle combinations for key
            if self.is_key_generation_angle(alice_angles[i], bob_angles[i]) {
                raw_key_alice.push(alice_results[i]);
                raw_key_bob.push(bob_results[i]);
            }
        }
        
        // Phases 5-6: Error correction and privacy amplification (same as BB84)
        let error_rate = self.estimate_error_rate(&mut raw_key_alice, &mut raw_key_bob).await?;
        let corrected_key = self.cascade_error_correction(&raw_key_alice, &raw_key_bob).await?;
        let final_key = self.privacy_amplification(corrected_key, error_rate, key_length)?;
        
        Ok(SecureKey {
            key_bits: final_key,
            protocol: "E91".to_string(),
            timestamp: Utc::now(),
            security_level: self.calculate_security_level(error_rate),
        })
    }

    /// CASCADE error correction algorithm
    async fn cascade_error_correction(
        &mut self,
        alice_key: &[bool],
        bob_key: &[bool]
    ) -> Result<Vec<bool>, QKDError> {
        let mut alice_blocks = alice_key.to_vec();
        let mut bob_blocks = bob_key.to_vec();
        
        // Multiple passes with increasing block sizes
        let block_sizes = [8, 16, 32, 64, 128];
        
        for &block_size in &block_sizes {
            let mut corrections = 0;
            
            // Shuffle and divide into blocks
            let permutation = self.generate_permutation(alice_blocks.len());
            self.apply_permutation(&mut alice_blocks, &permutation);
            self.apply_permutation(&mut bob_blocks, &permutation);
            
            // Check parity of each block
            for chunk_idx in (0..alice_blocks.len()).step_by(block_size) {
                let end = (chunk_idx + block_size).min(alice_blocks.len());
                
                let alice_parity = self.calculate_parity(&alice_blocks[chunk_idx..end]);
                let bob_parity = self.calculate_parity(&bob_blocks[chunk_idx..end]);
                
                if alice_parity != bob_parity {
                    // Binary search for error
                    let error_pos = self.binary_search_error(
                        &alice_blocks[chunk_idx..end],
                        &bob_blocks[chunk_idx..end]
                    ).await?;
                    
                    // Correct error
                    bob_blocks[chunk_idx + error_pos] = !bob_blocks[chunk_idx + error_pos];
                    corrections += 1;
                }
            }
            
            // Inverse permutation
            let inv_permutation = self.invert_permutation(&permutation);
            self.apply_permutation(&mut alice_blocks, &inv_permutation);
            self.apply_permutation(&mut bob_blocks, &inv_permutation);
            
            println!("Pass with block size {}: {} corrections", block_size, corrections);
            
            if corrections == 0 {
                break; // No more errors found
            }
        }
        
        Ok(bob_blocks)
    }

    /// Privacy amplification using Toeplitz hashing
    fn privacy_amplification(
        &self,
        corrected_key: Vec<bool>,
        error_rate: f64,
        desired_length: usize
    ) -> Result<Vec<bool>, QKDError> {
        // Calculate how much key material to sacrifice
        let eve_information = self.calculate_eve_information(error_rate);
        let safe_length = ((corrected_key.len() as f64) * (1.0 - eve_information)) as usize;
        let final_length = safe_length.min(desired_length);
        
        // Generate random Toeplitz matrix
        let matrix = self.generate_toeplitz_matrix(corrected_key.len(), final_length);
        
        // Hash the key
        let mut final_key = vec![false; final_length];
        for i in 0..final_length {
            let mut bit = false;
            for j in 0..corrected_key.len() {
                if matrix[i][j] && corrected_key[j] {
                    bit = !bit;
                }
            }
            final_key[i] = bit;
        }
        
        Ok(final_key)
    }
}

/// Quantum channel model for aerospace
pub struct QuantumChannel {
    atmospheric_loss: f64,
    turbulence_factor: f64,
    background_noise: f64,
}

impl QuantumChannel {
    /// Transmit qubit through atmosphere with realistic losses
    pub async fn transmit_air_to_ground(&self, qubit: Qubit) -> Result<Qubit, QKDError> {
        // Model atmospheric effects
        let transmission_prob = (-self.atmospheric_loss).exp();
        
        if rand::thread_rng().gen::<f64>() > transmission_prob {
            return Err(QKDError::QubitLost);
        }
        
        // Add noise from turbulence
        let noisy_qubit = self.apply_turbulence_noise(qubit);
        
        Ok(noisy_qubit)
    }
    
    fn apply_turbulence_noise(&self, mut qubit: Qubit) -> Qubit {
        // Simplified noise model
        let error_prob = self.turbulence_factor;
        
        if rand::thread_rng().gen::<f64>() < error_prob {
            // Random Pauli error
            match rand::thread_rng().gen_range(0..3) {
                0 => qubit.apply_x(),
                1 => qubit.apply_y(),
                2 => qubit.apply_z(),
                _ => unreachable!(),
            }
        }
        
        qubit
    }
}

/// Example: Secure key generation for maintenance data
pub async fn secure_maintenance_communication() -> Result<(), Box<dyn Error>> {
    // Initialize QKD system on aircraft
    let mut qkd_system = AerospaceQKD::new(QKDProtocol::BB84);
    
    // Generate 256-bit AES key
    let secure_key = qkd_system.generate_secure_key(256).await?;
    
    println!("Quantum key established!");
    println!("Protocol: {}", secure_key.protocol);
    println!("Security level: {:?}", secure_key.security_level);
    println!("Key entropy: {} bits", secure_key.key_bits.len());
    
    // Use key to encrypt maintenance data
    let maintenance_data = MaintenanceReport {
        aircraft_id: "AMPEL-001",
        sensor_readings: vec![/* quantum sensor data */],
        timestamp: Utc::now(),
        critical_alerts: vec!["Engine vibration anomaly detected"],
    };
    
    let encrypted_data = encrypt_with_quantum_key(&maintenance_data, &secure_key)?;
    
    // Transmit encrypted data over classical channel
    transmit_encrypted_data(encrypted_data).await?;
    
    Ok(())
}