//! Quantum mechanics invariants: any valid circuit must preserve unitarity and normalisation.

use proptest::prelude::*;
use quantum_bridge_mcp::executor::{CanExecute, LocalSimulator};
use quantum_bridge_mcp::types::{CircuitSource, ShotCount};

proptest! {
    /// Normalisation: shot counts always sum to exactly the requested number of shots.
    #[test]
    fn shot_counts_always_sum_to_requested_shots(
        shots in 1u32..=1_000u32
    ) {
        let circuit = r#"OPENQASM 3.0;
include "stdgates.inc";
qubit[2] q;
bit[2] c;
h q[0];
cx q[0], q[1];
c = measure q;"#;
        let sim = LocalSimulator::new();
        let result = sim
            .run(&CircuitSource(circuit.to_string()), ShotCount(shots), false)
            .unwrap();
        let total: u64 = result.counts.values().sum();
        prop_assert_eq!(total, shots as u64);
    }

    /// Statevector norm is always 1.0 within floating-point tolerance.
    #[test]
    fn statevector_norm_is_one(
        angle in -std::f64::consts::PI..=std::f64::consts::PI
    ) {
        let circuit = format!(
            "OPENQASM 3.0;\ninclude \"stdgates.inc\";\nqubit[1] q;\nbit[1] c;\nrx({angle}) q[0];\nc = measure q;"
        );
        let sim = LocalSimulator::new();
        let result = sim
            .run(&CircuitSource(circuit), ShotCount(1), true)
            .unwrap();
        let sv = result.statevector.unwrap();
        let norm: f64 = sv.iter().map(|(r, i)| r * r + i * i).sum();
        prop_assert!((norm - 1.0).abs() < 1e-9, "norm={norm}");
    }

    /// Bitstrings in counts have correct length (= number of qubits).
    #[test]
    fn count_bitstrings_have_correct_length(
        n_qubits in 1usize..=5usize,
        shots in 10u32..=100u32
    ) {
        let qubit_decls: String = (0..n_qubits).map(|i| format!("h q[{i}];\n")).collect();
        let circuit = format!(
            "OPENQASM 3.0;\ninclude \"stdgates.inc\";\nqubit[{n_qubits}] q;\nbit[{n_qubits}] c;\n{qubit_decls}c = measure q;\n"
        );
        let sim = LocalSimulator::new();
        let result = sim
            .run(&CircuitSource(circuit), ShotCount(shots), false)
            .unwrap();
        for key in result.counts.keys() {
            prop_assert_eq!(
                key.len(), n_qubits,
                "bitstring '{}' has wrong length for {}-qubit circuit",
                key, n_qubits
            );
        }
    }
}