// CARRY Quantum Simulator Benchmark Suite
// Standard Reference Circuits & Multi-Agent Verification Overhead Benchmark Suite.

use std::time::Instant;
use crate::quantum::core::{Circuit, Gate, QuantumSimulator, SimulationMode, ErrorModel};

/// Benchmark Summary Result.
#[derive(Debug, Clone)]
pub struct BenchmarkReport {
    pub circuit_name: String,
    pub num_qubits: usize,
    pub num_gates: usize,
    pub shots: usize,
    pub execution_time_ms: u128,
    pub verification_overhead_ms: u128,
    pub fidelity: f64,
    pub status: String,
}

pub struct BenchmarkSuite;

impl BenchmarkSuite {
    /// Build Bell state circuit: H(0), CNOT(0, 1)
    pub fn build_bell_circuit() -> Circuit {
        let mut circuit = Circuit::new(2);
        circuit.add_gate(Gate::h(0));
        circuit.add_gate(Gate::cnot(0, 1));
        circuit
    }

    /// Build GHZ state circuit: H(0), CNOT(0, 1), CNOT(1, 2)
    pub fn build_ghz_circuit(num_qubits: usize) -> Circuit {
        let mut circuit = Circuit::new(num_qubits);
        circuit.add_gate(Gate::h(0));
        for i in 0..(num_qubits - 1) {
            circuit.add_gate(Gate::cnot(i, i + 1));
        }
        circuit
    }

    /// Build Quantum Teleportation circuit (3 qubits)
    pub fn build_teleportation_circuit() -> Circuit {
        let mut circuit = Circuit::new(3);
        // Prepare state on q0: H(0)
        circuit.add_gate(Gate::h(0));
        // Entangle Bell pair on q1, q2
        circuit.add_gate(Gate::h(1));
        circuit.add_gate(Gate::cnot(1, 2));
        // Bell measurement on q0, q1
        circuit.add_gate(Gate::cnot(0, 1));
        circuit.add_gate(Gate::h(0));
        // Corrections on q2
        circuit.add_gate(Gate::cnot(1, 2));
        circuit.add_gate(Gate::cz(0, 2));
        circuit
    }

    /// Build Deutsch-Jozsa circuit (2 qubits)
    pub fn build_deutsch_circuit() -> Circuit {
        let mut circuit = Circuit::new(2);
        circuit.add_gate(Gate::x(1));
        circuit.add_gate(Gate::h(0));
        circuit.add_gate(Gate::h(1));
        // Balanced oracle: CNOT(0, 1)
        circuit.add_gate(Gate::cnot(0, 1));
        circuit.add_gate(Gate::h(0));
        circuit
    }

    /// Build Grover 2-qubit search circuit
    pub fn build_grover_circuit() -> Circuit {
        let mut circuit = Circuit::new(2);
        // Equal superposition
        circuit.add_gate(Gate::h(0));
        circuit.add_gate(Gate::h(1));
        // Oracle for |11⟩: CZ(0, 1)
        circuit.add_gate(Gate::cz(0, 1));
        // Diffuser: H, X, CZ, X, H
        circuit.add_gate(Gate::h(0));
        circuit.add_gate(Gate::h(1));
        circuit.add_gate(Gate::x(0));
        circuit.add_gate(Gate::x(1));
        circuit.add_gate(Gate::cz(0, 1));
        circuit.add_gate(Gate::x(0));
        circuit.add_gate(Gate::x(1));
        circuit.add_gate(Gate::h(0));
        circuit.add_gate(Gate::h(1));
        circuit
    }

    /// Build QFT (Quantum Fourier Transform) circuit for n qubits
    pub fn build_qft_circuit(n: usize) -> Circuit {
        let mut circuit = Circuit::new(n);
        for i in 0..n {
            circuit.add_gate(Gate::h(i));
            for j in (i + 1)..n {
                let angle = std::f64::consts::PI / (1 << (j - i)) as f64;
                circuit.add_gate(Gate::rz(j, angle));
                circuit.add_gate(Gate::cz(i, j));
            }
        }
        for i in 0..(n / 2) {
            circuit.add_gate(Gate::swap(i, n - 1 - i));
        }
        circuit
    }

    /// Run full benchmark for a given circuit with execution timing & verification overhead measurement.
    pub fn run_benchmark(name: &str, circuit: &Circuit, shots: usize) -> Result<BenchmarkReport, String> {
        let start_time = Instant::now();
        let mut sim = QuantumSimulator::new(circuit.num_qubits, SimulationMode::StateVector, ErrorModel::None);

        // Execute circuit gates
        for gate in &circuit.gates {
            sim.apply_gate(gate)?;
        }
        let exec_time = start_time.elapsed().as_millis();

        // Verification overhead timing
        let verify_start = Instant::now();
        let _purity = sim.state.purity();
        let _valid = sim.state.is_valid_state();
        let verify_time = verify_start.elapsed().as_millis();

        Ok(BenchmarkReport {
            circuit_name: name.to_string(),
            num_qubits: circuit.num_qubits,
            num_gates: circuit.gates.len(),
            shots,
            execution_time_ms: exec_time,
            verification_overhead_ms: verify_time,
            // WC-3 fix: compute actual fidelity as post-circuit norm validity.
            // 1.0 = state remains normalised; values < 1.0 indicate drift.
            fidelity: if _valid { 1.0 - (_purity - 1.0).abs().min(1.0) } else { 0.0 },
            status: "SUCCESS".to_string(),
        })
    }
}