# @Time   : 2020/6/25
# @Author : Shanlei Mu
# @Email  : slmu@ruc.edu.cn

# UPDATE:
# @Time   : 2020/9/16
# @Author : Shanlei Mu
# @Email  : slmu@ruc.edu.cn

r"""BPR
################################################
Reference:
    Steffen Rendle et al. "BPR: Bayesian Personalized Ranking from Implicit Feedback." in UAI 2009.
"""

import torch
from torch import nn

from hopwise.model.abstract_recommender import GeneralRecommender
from hopwise.model.init import xavier_normal_initialization
from hopwise.model.loss import BPRLoss
from hopwise.utils import InputType


class BPR(GeneralRecommender):
    r"""BPR is a basic matrix factorization model that be trained in the pairwise way."""

    input_type = InputType.PAIRWISE

    def __init__(self, config, dataset):
        super().__init__(config, dataset)

        # load parameters info
        self.embedding_size = config["embedding_size"]

        # define layers and loss
        self.user_embedding = nn.Embedding(self.n_users, self.embedding_size)
        self.item_embedding = nn.Embedding(self.n_items, self.embedding_size)
        self.loss = BPRLoss()

        # parameters initialization
        self.apply(xavier_normal_initialization)

    def get_user_embedding(self, user):
        r"""Get a batch of user embedding tensor according to input user's id.

        Args:
            user (torch.LongTensor): The input tensor that contains user's id, shape: [batch_size, ]

        Returns:
            torch.FloatTensor: The embedding tensor of a batch of user, shape: [batch_size, embedding_size]
        """
        return self.user_embedding(user)

    def get_item_embedding(self, item):
        r"""Get a batch of item embedding tensor according to input item's id.

        Args:
            item (torch.LongTensor): The input tensor that contains item's id, shape: [batch_size, ]

        Returns:
            torch.FloatTensor: The embedding tensor of a batch of item, shape: [batch_size, embedding_size]
        """
        return self.item_embedding(item)

    def forward(self, user, item):
        user_e = self.get_user_embedding(user)
        item_e = self.get_item_embedding(item)
        return user_e, item_e

    def calculate_loss(self, interaction):
        user = interaction[self.USER_ID]
        pos_item = interaction[self.ITEM_ID]
        neg_item = interaction[self.NEG_ITEM_ID]

        user_e, pos_e = self.forward(user, pos_item)
        neg_e = self.get_item_embedding(neg_item)
        pos_item_score, neg_item_score = (
            torch.mul(user_e, pos_e).sum(dim=1),
            torch.mul(user_e, neg_e).sum(dim=1),
        )
        loss = self.loss(pos_item_score, neg_item_score)
        return loss

    def predict(self, interaction):
        user = interaction[self.USER_ID]
        item = interaction[self.ITEM_ID]
        user_e, item_e = self.forward(user, item)
        return torch.mul(user_e, item_e).sum(dim=1)

    def full_sort_predict(self, interaction):
        user = interaction[self.USER_ID]
        user_e = self.get_user_embedding(user)
        all_item_e = self.item_embedding.weight
        score = torch.matmul(user_e, all_item_e.transpose(0, 1))
        return score.view(-1)
