import torch


def mixture_consistency(mixture, est_sources, src_weights=None, dim=1):
    """ Applies mixture consistency to a tensor of estimated sources.

    Args
        mixture (torch.Tensor): Mixture waveform or TF representation.
        est_sources (torch.Tensor): Estimated sources waveforms or TF
            representations.
        src_weights (torch.Tensor): Consistency weight for each source.
            Shape needs to be broadcastable to `est_source`.
            We make sure that the weights sum up to 1 along dim `dim`.
            If `src_weights` is None, compute them based on relative power.
        dim (int): Axis which contains the sources in `est_sources`.

    Returns
        torch.Tensor with same shape as `est_sources`, after applying mixture
        consistency.

    Notes
        This method can be used only in 'complete' separation tasks, otherwise
        the residual error will contain unwanted sources. For example, this
        won't work with the task `sep_noisy` from WHAM.

    Examples
        >>> # Works on waveforms
        >>> mix = torch.randn(10, 16000)
        >>> est_sources = torch.randn(10, 2, 16000)
        >>> new_est_sources = mixture_consistency(mix, est_sources, dim=1)
        >>> # Also works on spectrograms
        >>> mix = torch.randn(10, 514, 400)
        >>> est_sources = torch.randn(10, 2, 514, 400)
        >>> new_est_sources = mixture_consistency(mix, est_sources, dim=1)

    References
        Scott Wisdom, John R Hershey, Kevin Wilson, Jeremy Thorpe, Michael
        Chinen, Brian Patton, and Rif A Saurous. "Differentiable consistency
        constraints for improved deep speech enhancement", ICASSP 2019.
    """
    # If the source weights are not specified, the weights are the relative
    # power of each source to the sum. w_i = P_i / (P_all), P for power.
    if src_weights is None:
        all_dims = list(range(est_sources.ndim))
        all_dims.pop(dim)  # Remove source axis
        all_dims.pop(0)  # Remove batch dim
        src_weights = torch.mean(est_sources**2, dim=all_dims, keepdim=True)
    # Make sure that the weights sum up to 1
    norm_weights = torch.sum(src_weights, dim=dim, keepdim=True) + 1e-8
    src_weights = src_weights / norm_weights

    # Compute residual mix - sum(est_sources)
    if mixture.ndim == est_sources.ndim - 1:
        # mixture (batch, *), est_sources (batch, n_src, *)
        residual = (mixture - est_sources.sum(dim=dim)).unsqueeze(dim)
    elif mixture.ndim == est_sources.ndim:
        # mixture (batch, 1, *), est_sources (batch, n_src, *)
        residual = mixture - est_sources.sum(dim=dim, keepdim=True)
    else:
        n, m = est_sources.ndim, mixture.ndim
        raise RuntimeError(f'The size of the mixture tensor should match the '
                           f'size of the est_sources tensor. Expected mixture'
                           f'tensor to have {n} or {n-1} dimension, found {m}.')
    # Compute remove
    new_sources = est_sources + src_weights * residual
    return new_sources