"""
Turns the ops list produced by the graphical (drag-and-drop) circuit
builder component into dense_evolution's own (name, *qubits[, param])
gate tuples -- the same format dashboard_core.engine already runs on the
real dense_evolution DenseSVSimulator (via dashboard_core.qasm_library.
gate_tuples_to_qasm for the QASM round-trip). No separate execution path
for graphically-built circuits, and no Qiskit QuantumCircuit ever built
here: they go through the exact same engine as typed OpenQASM.
"""

import numpy as np

__all__ = ['GATE_PALETTE', 'ops_to_native_tuples']

# Palette offered by the drag-and-drop grid (dashboard_core.circuit_builder_component).
# kind:
#   'single'  -- dropped directly on one qubit's cell
#   'control' -- the (.) end of a 2-qubit gate; pairs with a 'target' in the same column
#   'target'  -- the other end of a 2-qubit gate, carries which gate (x/y/z -> cx/cy/cz)
#   'swap'    -- two 'swap' markers in the same column form a SWAP
GATE_PALETTE = [
    {"id": "h", "label": "H", "kind": "single", "gate": "h"},
    {"id": "x", "label": "X", "kind": "single", "gate": "x"},
    {"id": "y", "label": "Y", "kind": "single", "gate": "y"},
    {"id": "z", "label": "Z", "kind": "single", "gate": "z"},
    {"id": "s", "label": "S", "kind": "single", "gate": "s"},
    {"id": "sdg", "label": "S†", "kind": "single", "gate": "sdg"},
    {"id": "t", "label": "T", "kind": "single", "gate": "t"},
    {"id": "tdg", "label": "T†", "kind": "single", "gate": "tdg"},
    {"id": "sx", "label": "√X", "kind": "single", "gate": "sx"},
    {"id": "rx", "label": "Rx(π/2)", "kind": "single", "gate": "rx"},
    {"id": "ry", "label": "Ry(π/2)", "kind": "single", "gate": "ry"},
    {"id": "rz", "label": "Rz(π/2)", "kind": "single", "gate": "rz"},
    {"id": "ctrl", "label": "●", "kind": "control", "gate": None},
    {"id": "tgt_x", "label": "⊕", "kind": "target", "gate": "x"},
    {"id": "tgt_z", "label": "● Z", "kind": "target", "gate": "z"},
    {"id": "tgt_y", "label": "⊗ Y", "kind": "target", "gate": "y"},
    {"id": "swap", "label": "×", "kind": "swap", "gate": None},
]

_SINGLE_QUBIT_METHODS = {"h", "x", "y", "z", "s", "sdg", "t", "tdg", "sx"}
_ROTATION_METHODS = {"rx", "ry", "rz"}

# Fixed rotation angle for graphically-placed Rx/Ry/Rz -- the grid has no
# angle-entry UI yet (out of scope for this pass), so these place a real,
# working pi/2 rotation rather than a fake/placeholder gate.
_DEFAULT_ROTATION_ANGLE = np.pi / 2


def ops_to_native_tuples(n_qubits: int, ops: list) -> list:
    """Build dense_evolution's own (name, *qubits[, param]) gate tuples
    from the builder's op list -- the same shape dashboard_core.engine's
    QASMParser-based pipeline and qasm_library.gate_tuples_to_qasm both
    already accept, and the same validation the old QuantumCircuit-based
    version did (qubit range, unknown gate name), just performed by hand
    instead of relying on Qiskit's own checks.

    Parameters
    ----------
    n_qubits : int
    ops : list[dict]
        Each dict has 'gate' (one of the GATE_PALETTE gate ids: h/x/y/z/s/t/
        rx/ry/rz/cx/cy/cz/swap) and 'qubits' (list[int]).

    Returns
    -------
    list[tuple]
        Pass to qasm_library.gate_tuples_to_qasm(tuples, n_qubits) for the
        QASM text the rest of the Composer already runs on (measure_all
        equivalent included there by default).
    """
    if n_qubits < 1:
        raise ValueError("circuit must have at least 1 qubit")

    tuples = []
    for op in ops:
        gate = op.get("gate")
        qubits = op.get("qubits", [])
        for q in qubits:
            if not (0 <= q < n_qubits):
                raise ValueError(f"qubit index {q} out of range for {n_qubits}-qubit circuit")

        if gate in _SINGLE_QUBIT_METHODS:
            (q,) = qubits
            tuples.append((gate, q))
        elif gate in _ROTATION_METHODS:
            (q,) = qubits
            tuples.append((gate, q, _DEFAULT_ROTATION_ANGLE))
        elif gate == "swap":
            a, b = qubits
            tuples.append(("swap", a, b))
        elif gate in ("cx", "cy", "cz"):
            control, target = qubits
            tuples.append((gate, control, target))
        else:
            raise ValueError(f"unknown gate from circuit builder: {gate!r}")

    return tuples