import numpy as np
import pytest

from he11lib.modes import LGBasis
from he11lib.phase_retrieval import PhaseRetriever, propagate_angular_spectrum
from he11lib.synthetic import SyntheticBeamGenerator

W0 = 5e-3
Z0 = 0.5
WAVELENGTH = 1.76e-3
PIXEL_SCALE = 3e-4
IMAGE_SHAPE = (121, 121)


def make_basis():
    return LGBasis(w0=W0, z0=Z0, wavelength=WAVELENGTH)


def make_grid():
    coords = (np.arange(IMAGE_SHAPE[0]) - IMAGE_SHAPE[0] // 2) * PIXEL_SCALE
    x, y = np.meshgrid(coords, coords)
    return x, y


def test_propagate_round_trip_recovers_original_field():
    basis = make_basis()
    x, y = make_grid()
    field = basis.field(x, y, Z0, p=0, l=0)

    forward = propagate_angular_spectrum(field, PIXEL_SCALE, dz=0.05, wavelength=WAVELENGTH)
    back = propagate_angular_spectrum(forward, PIXEL_SCALE, dz=-0.05, wavelength=WAVELENGTH)

    np.testing.assert_allclose(back, field, atol=1e-3 * np.max(np.abs(field)))


def test_propagate_matches_lgbasis_analytic_evolution():
    basis = make_basis()
    x, y = make_grid()
    field_at_waist = basis.field(x, y, Z0, p=0, l=0)

    dz = 0.05
    propagated = propagate_angular_spectrum(field_at_waist, PIXEL_SCALE, dz=dz, wavelength=WAVELENGTH)
    analytic = basis.field(x, y, Z0 + dz, p=0, l=0)

    # compare intensity profiles (phase reference/global constant may differ)
    np.testing.assert_allclose(
        np.abs(propagated) ** 2, np.abs(analytic) ** 2, atol=1e-2 * np.max(np.abs(analytic) ** 2)
    )


def test_retrieve_recovers_pure_mode_purity():
    # Keep z distances close to the waist so the (widening) beam stays well
    # within the frame -- otherwise FFT wraparound/clipping at the edges
    # degrades angular-spectrum propagation accuracy.
    basis = make_basis()
    gen = SyntheticBeamGenerator(basis=basis, image_shape=IMAGE_SHAPE, pixel_scale=PIXEL_SCALE)
    z_list = [0.47, 0.5, 0.53]
    planes = gen.generate(coefficients={(0, 0): 1.0 + 0j}, z_list=z_list, noise_std=1e-5, seed=0)

    retriever = PhaseRetriever(wavelength=WAVELENGTH)
    result = retriever.retrieve(planes, viewing_angle_deg=0.0, max_iterations=100)

    coeffs = basis.project(
        result.field, result.x, result.y, PIXEL_SCALE, result.z, modes=[(0, 0), (1, 0), (0, 1)]
    )
    total_power = sum(abs(c) ** 2 for c in coeffs.values())
    purity_00 = abs(coeffs[(0, 0)]) ** 2 / total_power
    assert purity_00 > 0.9


def test_retrieve_estimates_beam_center():
    basis = make_basis()
    gen = SyntheticBeamGenerator(basis=basis, image_shape=IMAGE_SHAPE, pixel_scale=PIXEL_SCALE)
    z_list = [0.47, 0.5, 0.53]
    true_center = (15 * PIXEL_SCALE, -8 * PIXEL_SCALE)
    planes = gen.generate(
        coefficients={(0, 0): 1.0 + 0j}, z_list=z_list, center=true_center, noise_std=1e-5, seed=1
    )

    retriever = PhaseRetriever(wavelength=WAVELENGTH)
    result = retriever.retrieve(planes, viewing_angle_deg=0.0, max_iterations=100)

    assert result.center[0] == pytest.approx(true_center[0], abs=3 * PIXEL_SCALE)
    assert result.center[1] == pytest.approx(true_center[1], abs=3 * PIXEL_SCALE)