import torch


class Rotary(torch.nn.Module):
    def __init__(self, dim, base=10_000):
        super().__init__()
        inv_freq = 1.0 / (base ** (torch.arange(0, dim, 2).float() / dim))
        self.register_buffer("inv_freq", inv_freq)
        self.seq_len_cached = None
        self.cos_cached = None
        self.sin_cached = None

    def forward(self, x, seq_dim=1):
        seq_len = x.shape[seq_dim]
        if seq_len != self.seq_len_cached:
            self.seq_len_cached = seq_len
            t = torch.arange(x.shape[seq_dim], device=x.device).type_as(self.inv_freq)
            freqs = torch.einsum("i,j->ij", t, self.inv_freq.clone())
            emb = torch.cat((freqs, freqs), dim=-1).to(x.device)
            # dims are: batch, seq_len, qkv, head, dim
            self.cos_cached = emb.cos()[None, :, None, None, :].repeat(1, 1, 3, 1, 1)
            self.sin_cached = emb.sin()[None, :, None, None, :].repeat(1, 1, 3, 1, 1)
            # This makes the transformation on v an identity.
            self.cos_cached[:, :, 2, :, :].fill_(1.0)
            self.sin_cached[:, :, 2, :, :].fill_(0.0)

        return self.cos_cached, self.sin_cached


def rotate_half(x):
    x1, x2 = x[..., : x.shape[-1] // 2], x[..., x.shape[-1] // 2 :]
    return torch.cat((-x2, x1), dim=-1)


def _apply_rotary_pos_emb_native(qkv, cos, sin):
    """Native PyTorch implementation without JIT compilation"""
    return (qkv * cos) + (rotate_half(qkv) * sin)


@torch.jit.script
def _apply_rotary_pos_emb_torchscript(qkv, cos, sin):
    return (qkv * cos) + (rotate_half(qkv) * sin)


def apply_rotary_pos_emb(qkv, cos, sin):
    try:
        import flash_attn.layers.rotary

        cos_flash = cos[0, :, 0, 0, : cos.shape[-1] // 2]
        sin_flash = sin[0, :, 0, 0, : sin.shape[-1] // 2]
        return flash_attn.layers.rotary.apply_rotary_emb_qkv_(qkv, cos_flash, sin_flash)
    except (ImportError, AttributeError, RuntimeError):
        # Use native implementation without TorchScript due to compatibility issues
        return _apply_rotary_pos_emb_native(qkv, cos, sin)