# Copyright 2021 AlQuraishi Laboratory
# Copyright 2021 DeepMind Technologies Limited
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from functools import partial
import torch
import torch.nn as nn


def permute_final_dims(tensor, *inds):
    zero_index = -1 * len(inds)
    first_inds = range(len(tensor.shape[:zero_index]))
    return tensor.permute(*first_inds, *[zero_index + i for i in inds])


def flatten_final_dims(tensor, no_dims):
    return tensor.reshape(*tensor.shape[:-no_dims], -1)


def masked_mean(mask, value, dim, eps=1e-10):
    mask = mask.expand(*value.shape)
    return torch.sum(mask * value, dim=dim) / (eps + torch.sum(mask, dim=dim))


def pts_to_distogram(pts, min_bin=2.3125, max_bin=21.6875, no_bins=64):
    boundaries = torch.linspace(
        min_bin, max_bin, no_bins - 1, device=pts.device
    )
    dists = torch.sqrt(
        torch.sum((pts.unsqueeze(-2) - pts.unsqueeze(-3)) ** 2, dim=-1)
    )
    return torch.bucketize(dists, boundaries)


def dict_multimap(fn, dicts):
    first = dicts[0]
    new_dict = {}
    for k, v in first.items():
        all_v = [d[k] for d in dicts]
        if(type(v) is dict):
            new_dict[k] = dict_multimap(fn, all_v)
        else:
            new_dict[k] = fn(all_v)
    
    return new_dict


def stack_tensor_dicts(dicts):
    first = dicts[0]
    new_dict = {}
    for k, v in first.items():
        all_v = [d[k] for d in dicts]
        if(type(v) is dict):
            new_dict[k] = stack_tensor_dicts(all_v)
        else:
            new_dict[k] = torch.stack(all_v)

    return new_dict


def one_hot(x, v_bins):
    reshaped_bins = v_bins.view(*((1,) * len(x.shape) + (len(v_bins),)))
    diffs = x[..., None] - reshaped_bins
    am = torch.argmin(torch.abs(diffs), dim=-1)
    return nn.functional.one_hot(am, num_classes=len(v_bins)).float()


def batched_gather(data, inds, dim=0, no_batch_dims=0):
    ranges = []
    for i, s in enumerate(data.shape[:no_batch_dims]):
        r = torch.arange(s)
        r = r.view(*(*((1,) * i), -1, *((1,) * (len(inds.shape) - i - 1))))
        ranges.append(r)

    remaining_dims = [
        slice(None) for _ in range(len(data.shape) - no_batch_dims)
    ]
    remaining_dims[dim - no_batch_dims if dim >= 0 else dim] = inds
    ranges.extend(remaining_dims)
    return data[ranges]


# With tree_map, a poor man's JAX tree_map
def dict_map(fn, dic, leaf_type):
    new_dict = {}
    for k, v in dic.items():
        if(type(v) is dict):
            new_dict[k] = dict_map(fn, v, leaf_type)
        else:
            new_dict[k] = tree_map(fn, v, leaf_type)

    return new_dict


def tree_map(fn, tree, leaf_type):
    tree_type = type(tree)
    if(tree_type is dict):
        return dict_map(fn, tree, leaf_type)
    elif(tree_type is list):
        return [tree_map(fn, x, leaf_type) for x in tree]
    elif(tree_type is tuple):
        return tuple([tree_map(fn, x, leaf_type) for x in tree])
    elif(tree_type is leaf_type):
        return fn(tree)
    else:
        raise ValueError("Not supported")

tensor_tree_map = partial(tree_map, leaf_type=torch.Tensor)

def chunk_layer(layer, inputs, chunk_size, no_batch_dims):
    """
        Implements the "chunking" procedure described in section 1.11.8.

        Layer outputs and inputs are assumed to be simple "pytrees," 
        consisting only of (arbitrarily nested) lists, tuples, and dicts with 
        torch.Tensor leaves.

        Args:
            layer:
                The layer to be applied chunk-wise
            inputs:
                A (nested) dictionary of keyworded inputs. All leaves must be 
                tensors and must share the same batch dimensions.
            chunk_size:
                The number of sub-batches per chunk. If multiple batch
                dimensions are specified, a "sub-batch" is defined as a single
                indexing of all batch dimensions simultaneously (s.t. the 
                number of sub-batches is the product of the batch dimensions).
            no_batch_dims:
                How many of the initial dimensions of each input tensor can
                be considered batch dimensions.
        Returns:
            The reassembled output of the layer on the inputs.
    """
        
    if(not (len(inputs) > 0)):
        raise ValueError("Must provide at least one input")

    def fetch_dims(tree):
        shapes = []
        tree_type = type(tree)
        if(tree_type is dict):
            for v in tree.values():
                shapes.extend(fetch_dims(v))
        elif(tree_type is list or tree_type is tuple):
            for t in tree:
                shapes.extend(fetch_dims(t))
        elif(tree_type is torch.Tensor):
            shapes.append(tree.shape)
        else:
            raise ValueError("Not supported")

        return shapes
 
    initial_dims = [shape[:no_batch_dims] for shape in fetch_dims(inputs)]
    orig_batch_dims = [max(s) for s in zip(*initial_dims)]

    def prep_inputs(t):
        # TODO: make this more memory efficient. This sucks
        if(not sum(t.shape[:no_batch_dims]) == no_batch_dims):
            t = t.expand(*orig_batch_dims, *t.shape[no_batch_dims:])
        t = t.reshape(-1, *t.shape[no_batch_dims:])
        return t

    flattened_inputs = tensor_tree_map(prep_inputs, inputs)

    flat_batch_dim = 1
    for d in orig_batch_dims:
        flat_batch_dim *= d

    no_chunks = (
        flat_batch_dim // chunk_size + (flat_batch_dim % chunk_size != 0)
    )

    i = 0
    out = None
    for _ in range(no_chunks):
        # Chunk the input
        select_chunk = lambda t: t[i:i+chunk_size] if t.shape[0] != 1 else t
        chunks = tensor_tree_map(select_chunk, flattened_inputs)

        # Run the layer on the chunk
        output_chunk = layer(**chunks)

        # Allocate space for the output
        if(out is None):
            allocate = lambda t: t.new_zeros(flat_batch_dim, *t.shape[1:])
            out = tensor_tree_map(allocate, output_chunk)

        # Put the chunk in its pre-allocated space
        out_type = type(output_chunk)
        if(out_type is dict):
            def assign(d1, d2):
                for k,v in d1.items():
                    if(type(v) is dict):
                        assign(v, d2[k])
                    else:
                        v[i:i+chunk_size] = d2[k]
            assign(out, output_chunk)
        elif(out_type is tuple):
            for x1, x2 in zip(out, output_chunk):
                x1[i:i+chunk_size] = x2
        elif(out_type is torch.Tensor):
            out[i:i+chunk_size] = output_chunk
        else:
            raise ValueError("Not supported")

        i += chunk_size

    reshape = lambda t: t.reshape(*orig_batch_dims, *t.shape[1:])
    out = tensor_tree_map(reshape, out)

    return out    
