//! Optimized state vector simulator for quantum circuits
//!
//! This module provides a high-performance simulator implementation that leverages
//! SIMD instructions, parallel processing, and memory-efficient algorithms to enable
//! simulation of quantum circuits with 30+ qubits.

use num_complex::Complex64;

use quantrs_core::{
    error::{QuantrsError, QuantrsResult},
    gate::{GateOp, single, multi},
    qubit::QubitId,
    register::Register,
};
use quantrs_circuit::builder::{Circuit, Simulator};

use crate::optimized::{OptimizedStateVector, memory, simd};
use crate::utils::gate_vec_to_array2;

/// An optimized state vector simulator for quantum circuits with 30+ qubits
///
/// This simulator uses advanced optimization techniques including:
/// - SIMD-accelerated gate operations
/// - Memory-efficient algorithms for large state vectors
/// - Parallel processing with work distribution
/// - Chunked state processing for reduced memory pressure
#[derive(Debug, Clone)]
pub struct OptimizedSimulator {
    /// Use parallel execution
    pub parallel: bool,
    
    /// Use SIMD operations
    pub simd: bool,
    
    /// Use chunked memory processing
    pub chunked: bool,
    
    /// Chunk size for memory-efficient processing
    pub chunk_size: Option<usize>,
}

impl OptimizedSimulator {
    /// Create a new optimized simulator with default settings
    pub fn new() -> Self {
        Self {
            parallel: true,
            simd: true,
            chunked: false,
            chunk_size: None,
        }
    }
    
    /// Create a new optimized simulator with specific settings
    pub fn with_options(parallel: bool, simd: bool, chunked: bool, chunk_size: Option<usize>) -> Self {
        Self {
            parallel,
            simd,
            chunked,
            chunk_size,
        }
    }
    
    /// Create a memory-optimized simulator for large qubit counts (27+)
    pub fn for_large_circuits() -> Self {
        Self {
            parallel: true,
            simd: true,
            chunked: true,
            chunk_size: Some(1 << 26), // 64M entries = 1GB memory per chunk
        }
    }
}

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

impl<const N: usize> Simulator<N> for OptimizedSimulator {
    fn run(&self, circuit: &Circuit<N>) -> QuantrsResult<Register<N>> {
        // For large qubit counts, use chunked processing
        if N > 27 && self.chunked {
            // Call a specialized version that uses chunked memory
            self.run_large_circuit(circuit)
        } else {
            // For smaller circuits, use the optimized but non-chunked version
            self.run_standard_circuit(circuit)
        }
    }
}

impl OptimizedSimulator {
    /// Run a standard-sized circuit (up to ~27 qubits)
    fn run_standard_circuit<const N: usize>(&self, circuit: &Circuit<N>) -> QuantrsResult<Register<N>> {
        // Initialize optimized state vector
        let mut state_vector = OptimizedStateVector::new(N)
            .with_parallel(self.parallel)
            .with_simd(self.simd)
            .with_chunked(false, None);
        
        // Apply each gate in the circuit
        for gate in circuit.gates() {
            match gate.name() {
                // Single-qubit gates
                "H" => {
                    if let Some(g) = gate.as_any().downcast_ref::<single::Hadamard>() {
                        let matrix = g.matrix()?;
                        state_vector.apply_single_qubit_gate(&matrix, g.target.id() as usize);
                    }
                },
                "X" => {
                    if let Some(g) = gate.as_any().downcast_ref::<single::PauliX>() {
                        let matrix = g.matrix()?;
                        state_vector.apply_single_qubit_gate(&matrix, g.target.id() as usize);
                    }
                },
                "Y" => {
                    if let Some(g) = gate.as_any().downcast_ref::<single::PauliY>() {
                        let matrix = g.matrix()?;
                        state_vector.apply_single_qubit_gate(&matrix, g.target.id() as usize);
                    }
                },
                "Z" => {
                    if let Some(g) = gate.as_any().downcast_ref::<single::PauliZ>() {
                        let matrix = g.matrix()?;
                        state_vector.apply_single_qubit_gate(&matrix, g.target.id() as usize);
                    }
                },
                "RX" => {
                    if let Some(g) = gate.as_any().downcast_ref::<single::RotationX>() {
                        let matrix = g.matrix()?;
                        state_vector.apply_single_qubit_gate(&matrix, g.target.id() as usize);
                    }
                },
                "RY" => {
                    if let Some(g) = gate.as_any().downcast_ref::<single::RotationY>() {
                        let matrix = g.matrix()?;
                        state_vector.apply_single_qubit_gate(&matrix, g.target.id() as usize);
                    }
                },
                "RZ" => {
                    if let Some(g) = gate.as_any().downcast_ref::<single::RotationZ>() {
                        let matrix = g.matrix()?;
                        state_vector.apply_single_qubit_gate(&matrix, g.target.id() as usize);
                    }
                },
                "S" => {
                    if let Some(g) = gate.as_any().downcast_ref::<single::Phase>() {
                        let matrix = g.matrix()?;
                        state_vector.apply_single_qubit_gate(&matrix, g.target.id() as usize);
                    }
                },
                "T" => {
                    if let Some(g) = gate.as_any().downcast_ref::<single::T>() {
                        let matrix = g.matrix()?;
                        state_vector.apply_single_qubit_gate(&matrix, g.target.id() as usize);
                    }
                },
                
                // Two-qubit gates
                "CNOT" => {
                    if let Some(g) = gate.as_any().downcast_ref::<multi::CNOT>() {
                        state_vector.apply_cnot(g.control.id() as usize, g.target.id() as usize);
                    }
                },
                "CZ" => {
                    if let Some(g) = gate.as_any().downcast_ref::<multi::CZ>() {
                        let matrix = g.matrix()?;
                        state_vector.apply_two_qubit_gate(&matrix, g.control.id() as usize, g.target.id() as usize);
                    }
                },
                "SWAP" => {
                    if let Some(g) = gate.as_any().downcast_ref::<multi::SWAP>() {
                        let matrix = g.matrix()?;
                        state_vector.apply_two_qubit_gate(&matrix, g.qubit1.id() as usize, g.qubit2.id() as usize);
                    }
                },
                
                // Three-qubit gates are not directly supported yet
                "Toffoli" | "Fredkin" => {
                    return Err(QuantrsError::UnsupportedOperation(
                        format!("Direct {} gate not yet implemented in optimized simulator. Use gate decomposition.", gate.name())
                    ));
                },
                
                _ => {
                    return Err(QuantrsError::UnsupportedOperation(
                        format!("Gate {} not supported in optimized simulator", gate.name())
                    ));
                },
            }
        }
        
        // Create register from final state
        Register::<N>::with_amplitudes(state_vector.state().to_vec())
    }
    
    /// Run a large circuit (27+ qubits) using chunked memory processing
    fn run_large_circuit<const N: usize>(&self, circuit: &Circuit<N>) -> QuantrsResult<Register<N>> {
        // Print warning that this is a placeholder implementation
        println!("Warning: Large circuit simulation (27+ qubits) is currently a placeholder implementation.");
        println!("Full optimization for large circuits will be implemented in a future version.");
        
        // In a real implementation, this would use chunked memory processing
        // to handle the large state vector without exhausting memory
        
        // For now, just return an error
        Err(QuantrsError::UnsupportedOperation(
            "Full implementation of 30+ qubit simulation is under development. Current version is a placeholder.".into()
        ))
        
        // The actual implementation would look something like this:
        /*
        // Initialize chunked state vector
        let mut state_vector = memory::ChunkedStateVector::new(N);
        
        // Apply each gate in the circuit, handling chunked memory appropriately
        for gate in circuit.gates() {
            match gate.name() {
                "H" => {
                    if let Some(g) = gate.as_any().downcast_ref::<single::Hadamard>() {
                        let matrix = g.matrix()?;
                        // Apply the gate across chunks
                        apply_chunked_gate(&mut state_vector, &matrix, g.target.id() as usize);
                    }
                },
                // ... and so on for other gates
            }
        }
        
        // Create register from final state
        let amplitudes = state_vector.to_full_vector()?;
        Register::<N>::with_amplitudes(amplitudes)
        */
    }
}