"""
Embedding methods for Transformer models are put here.


Partial implementation uses code from https://github.com/zhouhaoyi/Informer2020/blob/main/models/embed.py
"""

# Created by Wenjie Du <wenjay.du@gmail.com>
# License: BSD-3-Clause


import math

import torch
import torch.fft
import torch.nn as nn


class PositionalEncoding(nn.Module):
    """The original positional-encoding module for Transformer.

    Parameters
    ----------
    d_hid:
        The dimension of the hidden layer.

    n_positions:
        The max number of positions.

    """

    def __init__(self, d_hid: int, n_positions: int = 1000):
        super().__init__()
        pe = torch.zeros(n_positions, d_hid, requires_grad=False).float()
        position = torch.arange(0, n_positions).float().unsqueeze(1)
        div_term = (
            torch.arange(0, d_hid, 2).float()
            * -(torch.log(torch.tensor(10000)) / d_hid)
        ).exp()

        pe[:, 0::2] = torch.sin(position * div_term)
        pe[:, 1::2] = torch.cos(position * div_term)

        pe = pe.unsqueeze(0)
        self.register_buffer("pos_table", pe)

    def forward(self, x: torch.Tensor, return_only_pos: bool = False) -> torch.Tensor:
        """Forward processing of the positional encoding module.

        Parameters
        ----------
        x:
            Input tensor.

        return_only_pos:
            Whether to return only the positional encoding.

        Returns
        -------
        If return_only_pos is True:
            pos_enc:
                The positional encoding.
        else:
            x_with_pos:
                Output tensor, the input tensor with the positional encoding added.
        """
        pos_enc = self.pos_table[:, : x.size(1)].clone().detach()

        if return_only_pos:
            return pos_enc

        x_with_pos = x + pos_enc
        return x_with_pos


class TokenEmbedding(nn.Module):
    def __init__(self, c_in, d_model):
        super().__init__()
        padding = 1 if torch.__version__ >= "1.5.0" else 2
        self.tokenConv = nn.Conv1d(
            in_channels=c_in,
            out_channels=d_model,
            kernel_size=3,
            padding=padding,
            padding_mode="circular",
            bias=False,
        )
        for m in self.modules():
            if isinstance(m, nn.Conv1d):
                nn.init.kaiming_normal_(
                    m.weight, mode="fan_in", nonlinearity="leaky_relu"
                )

    def forward(self, x):
        x = self.tokenConv(x.permute(0, 2, 1)).transpose(1, 2)
        return x


class FixedEmbedding(nn.Module):
    def __init__(self, c_in, d_model):
        super().__init__()

        w = torch.zeros(c_in, d_model).float()
        w.require_grad = False

        position = torch.arange(0, c_in).float().unsqueeze(1)
        div_term = (
            torch.arange(0, d_model, 2).float() * -(math.log(10000.0) / d_model)
        ).exp()

        w[:, 0::2] = torch.sin(position * div_term)
        w[:, 1::2] = torch.cos(position * div_term)

        self.emb = nn.Embedding(c_in, d_model)
        self.emb.weight = nn.Parameter(w, requires_grad=False)

    def forward(self, x):
        return self.emb(x).detach()


class TemporalEmbedding(nn.Module):
    def __init__(self, d_model, embed_type="fixed", freq="h"):
        super().__init__()

        minute_size = 4
        hour_size = 24
        weekday_size = 7
        day_size = 32
        month_size = 13

        Embed = FixedEmbedding if embed_type == "fixed" else nn.Embedding
        if freq == "t":
            self.minute_embed = Embed(minute_size, d_model)
        self.hour_embed = Embed(hour_size, d_model)
        self.weekday_embed = Embed(weekday_size, d_model)
        self.day_embed = Embed(day_size, d_model)
        self.month_embed = Embed(month_size, d_model)

    def forward(self, x):
        x = x.long()
        minute_x = (
            self.minute_embed(x[:, :, 4]) if hasattr(self, "minute_embed") else 0.0
        )
        hour_x = self.hour_embed(x[:, :, 3])
        weekday_x = self.weekday_embed(x[:, :, 2])
        day_x = self.day_embed(x[:, :, 1])
        month_x = self.month_embed(x[:, :, 0])

        return hour_x + weekday_x + day_x + month_x + minute_x


class TimeFeatureEmbedding(nn.Module):
    def __init__(self, d_model, freq="h"):
        super().__init__()

        freq_map = {"h": 4, "t": 5, "s": 6, "m": 1, "a": 1, "w": 2, "d": 3, "b": 3}
        d_inp = freq_map[freq]
        self.embed = nn.Linear(d_inp, d_model, bias=False)

    def forward(self, x):
        return self.embed(x)


class DataEmbedding(nn.Module):
    def __init__(
        self,
        c_in,
        d_model,
        embed_type="fixed",
        freq="h",
        dropout=0.1,
        with_pos=True,
    ):
        super().__init__()

        self.with_pos = with_pos

        self.value_embedding = TokenEmbedding(c_in=c_in, d_model=d_model)
        if with_pos:
            self.position_embedding = PositionalEncoding(d_hid=d_model)
        self.temporal_embedding = (
            TemporalEmbedding(d_model=d_model, embed_type=embed_type, freq=freq)
            if embed_type != "timeF"
            else TimeFeatureEmbedding(d_model=d_model, freq=freq)
        )
        self.dropout = nn.Dropout(p=dropout)

    def forward(self, x, x_timestamp=None):
        if x_timestamp is None:
            x = self.value_embedding(x)
            if self.with_pos:
                x += self.position_embedding(x, return_only_pos=True)
        else:
            x = self.value_embedding(x) + self.temporal_embedding(x_timestamp)
            if self.with_pos:
                x += self.position_embedding(x, return_only_pos=True)
        return self.dropout(x)
