//
// Copyright (c) 2026 BEL ESPRIT D ACCORD TRUST HOLDINGS INC
// All rights reserved.

// BlackHoleEngine/IBM.qs
// Hardware-specific: IBM Heron (heavy-hex, CX-based)
namespace BlackHoleEngine.IBM {
    open Microsoft.Quantum.Intrinsic;
    open Microsoft.Quantum.Canon;
    open BlackHoleEngine.Primitives;

    operation IBMXX(
        qubits : Qubit[],
        i : Int, j : Int,
        theta : Double,
        couplingMap : (Int, Int)[]
    ) : Unit is Adj + Ctl {
        let path = ShortestPath(couplingMap, i, j);

        for idx in 0..Length(path)-2 {
            SWAP(qubits[path[idx]], qubits[path[idx+1]]);
        }

        let adj_i = path[Length(path)-2];
        let adj_j = path[Length(path)-1];
        CNOT(qubits[adj_i], qubits[adj_j]);
        Rz(2.0 * theta, qubits[adj_j]);
        CNOT(qubits[adj_i], qubits[adj_j]);

        for idx in Length(path)-2..-1..0 {
            SWAP(qubits[path[idx]], qubits[path[idx+1]]);
        }
    }

    operation IBMHaydenPreskill(
        qubits : Qubit[],
        scrambleTime : Double,
        couplings : Double[][],
        fields : Double[],
        couplingMap : (Int, Int)[]
    ) : Unit is Adj + Ctl {
        let n = Length(qubits);
        let dt = scrambleTime / 10.0;
        let steps = 10;

        for _ in 1..steps {
            for i in 0..n-1 {
                Rz(2.0 * fields[i] * dt, qubits[i]);
            }

            for layer in GetXXLayers(n, couplings) {
                for (i, j) in layer {
                    let J = couplings[i][j];
                    if (AbsD(J) > 1e-10) {
                        IBMXX(qubits, i, j, 2.0 * J * dt, couplingMap);
                    }
                }
            }
        }
    }

    function ShortestPath(couplingMap : (Int, Int)[], src : Int, dst : Int) : Int[] {
        // BFS on coupling graph (placeholder - use Qiskit routing in production)
        return [src, dst];
    }
}