import torch
import numpy as np
import math


class TriangularCausalMask:
    def __init__(self, B, L, device="cpu"):
        mask_shape = [B, 1, L, L]
        with torch.no_grad():
            self._mask = torch.triu(
                torch.ones(mask_shape, dtype=torch.bool), diagonal=1
            ).to(device)

    @property
    def mask(self):
        return self._mask

class QuestionMask:
    def __init__(self, B, L, device="cpu"):
        mask_shape = [B, 1, L, L]
        with torch.no_grad():
            self._mask = torch.zeros(mask_shape, dtype=torch.bool).to(device)
            self._mask[:,:,:-1,-1] = True

    @property
    def mask(self):
        return self._mask


class ProbMask:
    def __init__(self, B, H, L, index, scores, device="cpu"):
        _mask = torch.ones(L, scores.shape[-1], dtype=torch.bool).to(device).triu(1)
        _mask_ex = _mask[None, None, :].expand(B, H, L, scores.shape[-1])
        indicator = _mask_ex[
            torch.arange(B)[:, None, None], torch.arange(H)[None, :, None], index, :
        ].to(device)
        self._mask = indicator.view(scores.shape).to(device)

    @property
    def mask(self):
        return self._mask


class LocalMask:
    def __init__(self, B, L, S, device="cpu"):
        mask_shape = [B, 1, L, S]
        with torch.no_grad():
            self.len = math.ceil(np.log2(L))
            self._mask1 = torch.triu(
                torch.ones(mask_shape, dtype=torch.bool), diagonal=1
            ).to(device)
            self._mask2 = ~torch.triu(
                torch.ones(mask_shape, dtype=torch.bool), diagonal=-self.len
            ).to(device)
            self._mask = self._mask1 + self._mask2

    @property
    def mask(self):
        return self._mask