"""
Copyright (c) Facebook, Inc. and its affiliates.
Copyright (c) Microsoft Corporation.
Licensed under the MIT License.
Adapted from https://github.com/FAIR-Chem/fairchem/blob/main/src/fairchem/core/models/gemnet/utils.py.
"""

import json
from typing import Any, Dict, Optional, Tuple

import torch
from torch_scatter import segment_csr


def read_json(path: str) -> Dict:
    """"""
    if not path.endswith(".json"):
        raise UserWarning(f"Path {path} is not a json-path.")

    with open(path, "r") as f:
        content = json.load(f)
    return content


def update_json(path: str, data: Dict):
    """"""
    if not path.endswith(".json"):
        raise UserWarning(f"Path {path} is not a json-path.")

    content = read_json(path)
    content.update(data)
    write_json(path, content)


def write_json(path: str, data: Dict):
    """"""
    if not path.endswith(".json"):
        raise UserWarning(f"Path {path} is not a json-path.")

    with open(path, "w", encoding="utf-8") as f:
        json.dump(data, f, ensure_ascii=False, indent=4)


def read_value_json(path: str, key: str) -> Optional[Any]:
    """"""
    content = read_json(path)

    if key in content.keys():
        return content[key]
    else:
        return None


def ragged_range(sizes: torch.Tensor) -> torch.Tensor:
    """Multiple concatenated ranges.

    Examples
    --------
        sizes = [1 4 2 3]
        Return: [0  0 1 2 3  0 1  0 1 2]
    """
    assert sizes.dim() == 1
    if sizes.sum() == 0:
        return sizes.new_empty(0)

    # Remove 0 sizes
    sizes_nonzero = sizes > 0
    if not torch.all(sizes_nonzero):
        sizes = torch.masked_select(sizes, sizes_nonzero)

    # Initialize indexing array with ones as we need to setup incremental indexing
    # within each group when cumulatively summed at the final stage.
    id_steps = torch.ones(sizes.sum(), dtype=torch.long, device=sizes.device)
    id_steps[0] = 0
    insert_index = sizes[:-1].cumsum(0)
    insert_val = (1 - sizes)[:-1]

    # Assign index-offsetting values
    id_steps[insert_index] = insert_val

    # Finally index into input array for the group repeated o/p
    res = id_steps.cumsum(0)
    return res


def repeat_blocks(
    sizes: torch.Tensor,
    repeats: torch.Tensor,
    continuous_indexing: bool = True,
    start_idx: int = 0,
    block_inc: int = 0,
    repeat_inc: int = 0,
) -> torch.Tensor:
    """Repeat blocks of indices.
    Adapted from https://stackoverflow.com/questions/51154989/numpy-vectorized-function-to-repeat-blocks-of-consecutive-elements

    continuous_indexing: Whether to keep increasing the index after each block
    start_idx: Starting index
    block_inc: Number to increment by after each block,
               either global or per block. Shape: len(sizes) - 1
    repeat_inc: Number to increment by after each repetition,
                either global or per block

    Examples
    --------
        sizes = [1,3,2] ; repeats = [3,2,3] ; continuous_indexing = False
        Return: [0 0 0  0 1 2 0 1 2  0 1 0 1 0 1]
        sizes = [1,3,2] ; repeats = [3,2,3] ; continuous_indexing = True
        Return: [0 0 0  1 2 3 1 2 3  4 5 4 5 4 5]
        sizes = [1,3,2] ; repeats = [3,2,3] ; continuous_indexing = True ;
        repeat_inc = 4
        Return: [0 4 8  1 2 3 5 6 7  4 5 8 9 12 13]
        sizes = [1,3,2] ; repeats = [3,2,3] ; continuous_indexing = True ;
        start_idx = 5
        Return: [5 5 5  6 7 8 6 7 8  9 10 9 10 9 10]
        sizes = [1,3,2] ; repeats = [3,2,3] ; continuous_indexing = True ;
        block_inc = 1
        Return: [0 0 0  2 3 4 2 3 4  6 7 6 7 6 7]
        sizes = [0,3,2] ; repeats = [3,2,3] ; continuous_indexing = True
        Return: [0 1 2 0 1 2  3 4 3 4 3 4]
        sizes = [2,3,2] ; repeats = [2,0,2] ; continuous_indexing = True
        Return: [0 1 0 1  5 6 5 6]
    """
    assert sizes.dim() == 1
    assert all(sizes >= 0)

    # Remove 0 sizes
    sizes_nonzero = sizes > 0
    if not torch.all(sizes_nonzero):
        assert block_inc == 0  # Implementing this is not worth the effort
        sizes = torch.masked_select(sizes, sizes_nonzero)
        if isinstance(repeats, torch.Tensor):
            repeats = torch.masked_select(repeats, sizes_nonzero)
        if isinstance(repeat_inc, torch.Tensor):
            repeat_inc = torch.masked_select(repeat_inc, sizes_nonzero)

    if isinstance(repeats, torch.Tensor):
        assert all(repeats >= 0)
        insert_dummy = repeats[0] == 0
        if insert_dummy:
            one = sizes.new_ones(1)
            zero = sizes.new_zeros(1)
            sizes = torch.cat((one, sizes))
            repeats = torch.cat((one, repeats))
            if isinstance(block_inc, torch.Tensor):
                block_inc = torch.cat((zero, block_inc))
            if isinstance(repeat_inc, torch.Tensor):
                repeat_inc = torch.cat((zero, repeat_inc))
    else:
        assert repeats >= 0
        insert_dummy = False

    # Get repeats for each group using group lengths/sizes
    r1 = torch.repeat_interleave(torch.arange(len(sizes), device=sizes.device), repeats)

    # Get total size of output array, as needed to initialize output indexing array
    N = (sizes * repeats).sum()

    # Initialize indexing array with ones as we need to setup incremental indexing
    # within each group when cumulatively summed at the final stage.
    # Two steps here:
    # 1. Within each group, we have multiple sequences, so setup the offsetting
    # at each sequence lengths by the seq. lengths preceding those.
    id_ar = torch.ones(N, dtype=torch.long, device=sizes.device)
    id_ar[0] = 0
    insert_index = sizes[r1[:-1]].cumsum(0)
    insert_val = (1 - sizes)[r1[:-1]]

    if isinstance(repeats, torch.Tensor) and torch.any(repeats == 0):
        diffs = r1[1:] - r1[:-1]
        indptr = torch.cat((sizes.new_zeros(1), diffs.cumsum(0)))
        if continuous_indexing:
            # If a group was skipped (repeats=0) we need to add its size
            insert_val += segment_csr(sizes[: r1[-1]], indptr, reduce="sum")

        # Add block increments
        if isinstance(block_inc, torch.Tensor):
            insert_val += segment_csr(block_inc[: r1[-1]], indptr, reduce="sum")
        else:
            insert_val += block_inc * (indptr[1:] - indptr[:-1])
            if insert_dummy:
                insert_val[0] -= block_inc
    else:
        idx = r1[1:] != r1[:-1]
        if continuous_indexing:
            # 2. For each group, make sure the indexing starts from the next group's
            # first element. So, simply assign 1s there.
            insert_val[idx] = 1

        # Add block increments
        insert_val[idx] += block_inc

    # Add repeat_inc within each group
    if isinstance(repeat_inc, torch.Tensor):
        insert_val += repeat_inc[r1[:-1]]
        if isinstance(repeats, torch.Tensor):
            repeat_inc_inner = repeat_inc[repeats > 0][:-1]
        else:
            repeat_inc_inner = repeat_inc[:-1]
    else:
        insert_val += repeat_inc
        repeat_inc_inner = repeat_inc

    # Subtract the increments between groups
    if isinstance(repeats, torch.Tensor):
        repeats_inner = repeats[repeats > 0][:-1]
    else:
        repeats_inner = repeats
    insert_val[r1[1:] != r1[:-1]] -= repeat_inc_inner * repeats_inner

    # Assign index-offsetting values
    id_ar[insert_index] = insert_val

    if insert_dummy:
        id_ar = id_ar[1:]
        if continuous_indexing:
            id_ar[0] -= 1

    # Set start index now, in case of insertion due to leading repeats=0
    id_ar[0] += start_idx

    # Finally index into input array for the group repeated o/p
    res = id_ar.cumsum(0)
    return res


def calculate_interatomic_vectors(
    R: torch.Tensor, id_s: torch.Tensor, id_t: torch.Tensor, offsets_st: torch.Tensor
) -> Tuple[torch.Tensor, torch.Tensor]:
    """
    Calculate the vectors connecting the given atom pairs,
    considering offsets from periodic boundary conditions (PBC).

    Parameters
    ----------
        R: Tensor, shape = (nAtoms, 3)
            Atom positions.
        id_s: Tensor, shape = (nEdges,)
            Indices of the source atom of the edges.
        id_t: Tensor, shape = (nEdges,)
            Indices of the target atom of the edges.
        offsets_st: Tensor, shape = (nEdges,)
            PBC offsets of the edges.
            Subtract this from the correct direction.

    Returns
    -------
        (D_st, V_st): tuple
            D_st: Tensor, shape = (nEdges,)
                Distance from atom t to s.
            V_st: Tensor, shape = (nEdges,)
                Unit direction from atom t to s.
    """
    Rs = R[id_s]
    Rt = R[id_t]
    # ReLU prevents negative numbers in sqrt
    if offsets_st is None:
        V_st = Rt - Rs  # s -> t
    else:
        V_st = Rt - Rs + offsets_st  # s -> t
    D_st = torch.sqrt(torch.sum(V_st**2, dim=1))
    V_st = V_st / D_st[..., None]
    return D_st, V_st


def inner_product_normalized(x: torch.Tensor, y: torch.Tensor) -> torch.Tensor:
    """
    Calculate the inner product between the given normalized vectors,
    giving a result between -1 and 1.
    """
    return torch.sum(x * y, dim=-1).clamp(min=-1, max=1)


def mask_neighbors(neighbors: torch.Tensor, edge_mask: torch.Tensor) -> torch.Tensor:
    neighbors_old_indptr = torch.cat([neighbors.new_zeros(1), neighbors])
    neighbors_old_indptr = torch.cumsum(neighbors_old_indptr, dim=0)
    neighbors = segment_csr(edge_mask.long(), neighbors_old_indptr)
    return neighbors


def get_k_index_product_set(
    num_k_x: torch.LongTensor, num_k_y: torch.LongTensor, num_k_z: torch.LongTensor
) -> tuple[torch.FloatTensor, int]:
    # Get a box of k-lattice indices around (0,0,0)
    k_index_sets = (
        torch.arange(-num_k_x, num_k_x + 1, dtype=torch.float),
        torch.arange(-num_k_y, num_k_y + 1, dtype=torch.float),
        torch.arange(-num_k_z, num_k_z + 1, dtype=torch.float),
    )
    k_index_product_set = torch.cartesian_prod(*k_index_sets)
    # Because our "signal" is real-valued, for the Fourier transform it holds that
    # F(omega) = F*(-omega) (where F* is the complex conjugate of F). Thus, we only
    # need to consider the positive half of the Fourier space.
    k_index_product_set = k_index_product_set[k_index_product_set.shape[0] // 2 + 1 :]

    # Amount of k-points
    num_k_degrees_of_freedom = k_index_product_set.shape[0]

    return k_index_product_set, num_k_degrees_of_freedom