"""DFT-spread OFDM (SC-FDMA style, localized mapping).

Identical grid/CP structure to OFDM; each data symbol's 48 constellation
symbols are DFT-48 precoded before subcarrier mapping (lower PAPR,
single-carrier-like).  The pilot symbol is sent directly in the frequency
domain (DMRS-style, no spreading).
"""

from __future__ import annotations

import numpy as np

from .ofdm import OFDM


class DFTsOFDM(OFDM):
    name = "dfts_ofdm"

    def _fill_grid(self, s):
        data = s.reshape(s.shape[:-1] + (self.n_sym - 1, self.n_occ))
        data = np.fft.fft(data, axis=-1, norm="ortho")  # DFT spreading
        pil = np.broadcast_to(self.pilots[:, None, :], s.shape[:-1] + (1, self.n_occ))
        return np.concatenate([pil, data], axis=-2)

    def _extract_data(self, grid):
        d = np.fft.ifft(grid[..., 1:, :], axis=-1, norm="ortho")  # de-spread
        return d.reshape(d.shape[:-2] + (self.cfg.n_data,))