# Copyright (c) Meta Platforms, Inc. and affiliates.
# This software may be used and distributed according to the terms of the GNU General Public License version 3.

from typing import Optional, Tuple
from dataclasses import dataclass
import math

import torch
from torch import nn
from torch.nn import Embedding, Linear
import torch.nn.functional as F


@dataclass
class ModelArgs:
    dim: int = 512
    n_layers: int = 8
    n_heads: int = 8
    vocab_size: int = -1  # defined later by tokenizer
    multiple_of: int = 256  # make SwiGLU hidden layer size multiple of large power of 2
    norm_eps: float = 1e-5

    max_batch_size: int = 32
    max_seq_len: int = 2048

    w_bias: bool = True # use bias tuning
    w_lora: bool = True # use lora tuning
    lora_rank: int = 16


class RMSNorm(torch.nn.Module):
    def __init__(self, dim: int, eps: float = 1e-6):
        super().__init__()
        self.eps = eps
        self.weight = nn.Parameter(torch.ones(dim))

    def _norm(self, x):
        return x * torch.rsqrt(x.pow(2).mean(-1, keepdim=True) + self.eps)

    def forward(self, x):
        output = self._norm(x.float()).type_as(x)
        return output * self.weight


def precompute_freqs_cis(dim: int, end: int, theta: float = 10000.0):
    freqs = 1.0 / (theta ** (torch.arange(0, dim, 2)[: (dim // 2)].float() / dim))
    t = torch.arange(end, device=freqs.device)  # type: ignore
    freqs = torch.outer(t, freqs).float()  # type: ignore
    freqs_cis = torch.polar(torch.ones_like(freqs), freqs)  # complex64
    return freqs_cis


def reshape_for_broadcast(freqs_cis: torch.Tensor, x: torch.Tensor):
    ndim = x.ndim
    assert 0 <= 1 < ndim
    assert freqs_cis.shape == (x.shape[1], x.shape[-1])
    shape = [d if i == 1 or i == ndim - 1 else 1 for i, d in enumerate(x.shape)]
    return freqs_cis.view(*shape)


def apply_rotary_emb(
    xq: torch.Tensor,
    xk: torch.Tensor,
    freqs_cis: torch.Tensor,
) -> Tuple[torch.Tensor, torch.Tensor]:
    xq_ = torch.view_as_complex(xq.float().reshape(*xq.shape[:-1], -1, 2))
    xk_ = torch.view_as_complex(xk.float().reshape(*xk.shape[:-1], -1, 2))
    freqs_cis = reshape_for_broadcast(freqs_cis, xq_)
    xq_out = torch.view_as_real(xq_ * freqs_cis).flatten(3)
    xk_out = torch.view_as_real(xk_ * freqs_cis).flatten(3)
    return xq_out.type_as(xq), xk_out.type_as(xk)


class Attention(nn.Module):
    def __init__(self, args: ModelArgs):
        super().__init__()
        self.args = args

        self.n_local_heads = args.n_heads
        self.head_dim = args.dim // args.n_heads

        self.wq = Linear(
            args.dim,
            args.n_heads * self.head_dim,
            bias=args.w_bias
        )
        self.wk = Linear(
            args.dim,
            args.n_heads * self.head_dim,
            bias=False
        )
        self.wv = Linear(
            args.dim,
            args.n_heads * self.head_dim,
            bias=False
        )
        self.wo = Linear(
            args.n_heads * self.head_dim,
            args.dim,
            bias=args.w_bias
        )
        if args.w_bias:
            nn.init.constant_(self.wq.bias.data, 0)
            nn.init.constant_(self.wo.bias.data, 0)

        self.w_lora = args.w_lora
        if args.w_lora:
           self.lora_wq_l1 = Linear(args.dim, args.lora_rank, bias=False)
           self.lora_wq_l2 = Linear(args.lora_rank, args.dim, bias=False)

           self.lora_wk_l1 = Linear(args.dim, args.lora_rank, bias=False)
           self.lora_wk_l2 = Linear(args.lora_rank, args.dim, bias=False)

           self.lora_wv_l1 = Linear(args.dim, args.lora_rank, bias=False)
           self.lora_wv_l2 = Linear(args.lora_rank, args.dim, bias=False)

           self.lora_wo_l1 = Linear(args.dim, args.lora_rank, bias=False)
           self.lora_wo_l2 = Linear(args.lora_rank, args.dim, bias=False)
           nn.init.constant_(self.lora_wq_l2.weight.data, 0)
           nn.init.constant_(self.lora_wk_l2.weight.data, 0)
           nn.init.constant_(self.lora_wv_l2.weight.data, 0)
           nn.init.constant_(self.lora_wo_l2.weight.data, 0)

        self.cache_k = None
        self.cache_v = None

        self.gate = torch.nn.Parameter(torch.zeros(1, self.n_local_heads, 1, 1))


    def train(self, mode: bool = True):
        if mode:
            self.cache_k = None
            self.cache_v = None
        else:
            self.cache_k = torch.zeros(
                (self.args.max_batch_size, self.args.max_seq_len, self.n_local_heads, self.head_dim)
            ).cuda()
            self.cache_v = torch.zeros(
                (self.args.max_batch_size, self.args.max_seq_len, self.n_local_heads, self.head_dim)
            ).cuda()
        return super().train(mode)


    def forward(self, x: torch.Tensor, start_pos: int, freqs_cis: torch.Tensor, mask: Optional[torch.Tensor], adapter=None):
        bsz, seqlen, _ = x.shape
        xq, xk, xv = self.wq(x), self.wk(x), self.wv(x)
        if self.w_lora:
           xq = xq + self.lora_wq_l2(self.lora_wq_l1(x))
           xk = xk + self.lora_wk_l2(self.lora_wk_l1(x))
           xv = xv + self.lora_wv_l2(self.lora_wv_l1(x))

        xq = xq.view(bsz, seqlen, self.n_local_heads, self.head_dim)
        xk = xk.view(bsz, seqlen, self.n_local_heads, self.head_dim)
        xv = xv.view(bsz, seqlen, self.n_local_heads, self.head_dim)

        xq, xk = apply_rotary_emb(xq, xk, freqs_cis=freqs_cis)

        if not self.training:
            self.cache_k = self.cache_k.to(xq)
            self.cache_v = self.cache_v.to(xq)

            self.cache_k[:bsz, start_pos : start_pos + seqlen] = xk
            self.cache_v[:bsz, start_pos : start_pos + seqlen] = xv

            keys = self.cache_k[:bsz, : start_pos + seqlen]
            values = self.cache_v[:bsz, : start_pos + seqlen]
        else:
            assert start_pos==0
            keys = xk
            values = xv

        if adapter is not None:
            adapter_len = adapter.shape[1]
            adapter_v = self.wv(adapter).view(bsz, adapter_len, self.n_local_heads, self.head_dim)
            adapter_v = adapter_v.transpose(1, 2)

            if adapter_len > 1:
                adapter_k = self.wk(adapter).view(bsz, adapter_len, self.n_local_heads, self.head_dim)
                adapter_k = adapter_k.transpose(1, 2)


        xq = xq.transpose(1, 2)
        keys = keys.transpose(1, 2)
        values = values.transpose(1, 2)
        scores = torch.matmul(xq, keys.transpose(2, 3)) / math.sqrt(self.head_dim)

        if mask is not None:
            scores = scores + mask  # (bs, n_local_heads, slen, cache_len + slen)

        scores = F.softmax(scores.float(), dim=-1).type_as(xq)
        output = torch.matmul(scores, values)  # (bs, n_local_heads, slen, head_dim)

        if adapter is not None:
            if adapter_len > 1:
                adapter_scores = torch.matmul(xq, adapter_k.transpose(2, 3)) / math.sqrt(self.head_dim)
                adapter_scores = self.gate.tanh() * F.softmax(adapter_scores.float(), dim=-1).type_as(xq)
                output = output + torch.matmul(adapter_scores, adapter_v)
            else:
                output = output + self.gate.tanh() * adapter_v

        output = output.transpose(
            1, 2
        ).contiguous().view(bsz, seqlen, -1)

        if self.w_lora:
           return self.wo(output) + self.lora_wo_l2(self.lora_wo_l1(output))
        else:
           return self.wo(output)


class FeedForward(nn.Module):
    def __init__(
        self,
        dim: int,
        hidden_dim: int,
        multiple_of: int,
        args: ModelArgs
    ):
        super().__init__()
        hidden_dim = int(2 * hidden_dim / 3)
        hidden_dim = multiple_of * ((hidden_dim + multiple_of - 1) // multiple_of)

        self.w1 = Linear(
            dim, hidden_dim, bias=args.w_bias
        )
        self.w2 = Linear(
            hidden_dim, dim, bias=args.w_bias
        )
        self.w3 = Linear(
            dim, hidden_dim, bias=args.w_bias
        )
        if args.w_bias:
            nn.init.constant_(self.w1.bias.data, 0)
            nn.init.constant_(self.w2.bias.data, 0)
            nn.init.constant_(self.w3.bias.data, 0)

        self.w_lora = args.w_lora
        if args.w_lora:
           self.lora_w1_l1 = Linear(dim, args.lora_rank, bias=False)
           self.lora_w1_l2 = Linear(args.lora_rank, hidden_dim, bias=False)
           self.lora_w2_l1 = Linear(hidden_dim, args.lora_rank, bias=False)
           self.lora_w2_l2 = Linear(args.lora_rank, dim, bias=False)
           self.lora_w3_l1 = Linear(dim, args.lora_rank, bias=False)
           self.lora_w3_l2 = Linear(args.lora_rank, hidden_dim, bias=False)
           nn.init.constant_(self.lora_w1_l2.weight.data, 0)
           nn.init.constant_(self.lora_w2_l2.weight.data, 0)
           nn.init.constant_(self.lora_w3_l2.weight.data, 0)

    def forward(self, x):
        if self.w_lora:
           out = F.silu(self.w1(x) + self.lora_w1_l2(self.lora_w1_l1(x))) * (self.w3(x) + self.lora_w3_l2(self.lora_w3_l1(x)))
           return self.w2(out) + self.lora_w2_l2(self.lora_w2_l1(out))
        else:
           return self.w2(F.silu(self.w1(x)) * self.w3(x))


class TransformerBlock(nn.Module):
    def __init__(self, layer_id: int, args: ModelArgs):
        super().__init__()
        self.n_heads = args.n_heads
        self.dim = args.dim
        self.head_dim = args.dim // args.n_heads
        self.attention = Attention(args)
        self.feed_forward = FeedForward(
            dim=args.dim, hidden_dim=4 * args.dim, multiple_of=args.multiple_of, args=args
        )
        self.layer_id = layer_id
        self.attention_norm = RMSNorm(args.dim, eps=args.norm_eps)
        self.ffn_norm = RMSNorm(args.dim, eps=args.norm_eps)

    def forward(self, x: torch.Tensor, start_pos: int, freqs_cis: torch.Tensor, mask: Optional[torch.Tensor], prompt=None):

        h = x + self.attention.forward(self.attention_norm(x), start_pos, freqs_cis, mask, prompt)
        out = h + self.feed_forward.forward(self.ffn_norm(h))
        return out


class Transformer(nn.Module):
    def __init__(self, params: ModelArgs):
        super().__init__()
        self.params = params
        self.vocab_size = params.vocab_size
        self.n_layers = params.n_layers
        self.tok_embeddings = Embedding(
            params.vocab_size, params.dim
        )

        self.layers = torch.nn.ModuleList()
        for layer_id in range(params.n_layers):
            self.layers.append(TransformerBlock(layer_id, params))

        self.norm = RMSNorm(params.dim, eps=params.norm_eps)
        self.output = Linear(
            params.dim, params.vocab_size, bias=False
        )

        self.freqs_cis = precompute_freqs_cis(
            self.params.dim // self.params.n_heads, self.params.max_seq_len * 2
        )

    @torch.inference_mode()
    def forward(self, tokens: torch.Tensor, start_pos: int):
        _bsz, seqlen = tokens.shape
        h = self.tok_embeddings(tokens)
        self.freqs_cis = self.freqs_cis.to(h.device)
        freqs_cis = self.freqs_cis[start_pos : start_pos + seqlen]

        mask = None
        if seqlen > 1:
            mask = torch.full((1, 1, seqlen, seqlen), float("-inf"), device=tokens.device)
            mask = torch.triu(mask, diagonal=start_pos + 1).type_as(h)

        for layer in self.layers:
            h = layer(h, start_pos, freqs_cis, mask)
        h = self.norm(h)
        output = self.output(h[:, -1, :])  # only compute last logits
        return output.float()
