import torch
import torch.nn.functional as F
from dataclasses import dataclass

import tiktoken

import safetensors.torch

tokenizer = tiktoken.get_encoding("gpt2")

# Define the GPTConfig dataclass
@dataclass
class GPTConfig:
    vocab_size : int = 50304
    n_layer : int = 12
    n_head : int = 6 # head dim 128 suggested by @Grad62304977
    n_embd : int = 768

# Define the Rotary class
class Rotary(torch.nn.Module):

    def __init__(self, dim, base=10000):
        super().__init__()
        self.inv_freq = 1.0 / (base ** (torch.arange(0, dim, 2).float() / dim))
        self.seq_len_cached = None
        self.cos_cached = None
        self.sin_cached = None

    def forward(self, x):
        seq_len = x.shape[1]
        if seq_len!= self.seq_len_cached:
            self.seq_len_cached = seq_len
            t = torch.arange(seq_len, device=x.device).type_as(self.inv_freq)
            freqs = torch.outer(t, self.inv_freq).to(x.device)
            self.cos_cached = freqs.cos().bfloat16()
            self.sin_cached = freqs.sin().bfloat16()
        return self.cos_cached[None, :, None, :], self.sin_cached[None, :, None, :]

def apply_rotary_emb(x, cos, sin):
    assert x.ndim == 4 # multihead attention
    d = x.shape[3]//2
    x1 = x[..., :d]
    x2 = x[..., d:]
    y1 = x1 * cos + x2 * sin
    y2 = x1 * (-sin) + x2 * cos
    return torch.cat([y1, y2], 3).type_as(x)

# Define the CausalSelfAttention class
class CausalSelfAttention(torch.nn.Module):

    def __init__(self, config):
        super().__init__()
        self.n_head = config.n_head
        self.n_embd = config.n_embd
        self.head_dim = self.n_embd // self.n_head
        assert self.n_embd % self.n_head == 0
        self.c_q = torch.nn.Linear(self.n_embd, self.n_embd, bias=False)
        self.c_k = torch.nn.Linear(self.n_embd, self.n_embd, bias=False)
        self.c_v = torch.nn.Linear(self.n_embd, self.n_embd, bias=False)
        # output projection
        self.c_proj = torch.nn.Linear(self.n_embd, self.n_embd, bias=False)
        self.c_proj.weight.data.zero_() # zero init suggested by @Grad62304977
        self.rotary = Rotary(self.head_dim)
        self.lamb = torch.nn.Parameter(torch.tensor(0.5)) # @Grad62304977

    def forward(self, x, v1=None):
        B, T, C = x.size() # batch size, sequence length, embedding dimensionality (n_embd)
        q = self.c_q(x).view(B, T, self.n_head, self.head_dim)
        k = self.c_k(x).view(B, T, self.n_head, self.head_dim)
        v = self.c_v(x).view(B, T, self.n_head, self.head_dim)
        if v1 is None:
            v1 = v # This happens if we are in the first block. v needs to be accessed by subsequent blocks
        v = (1 - self.lamb) * v + self.lamb * v1.view_as(v) # @Grad62304977
        cos, sin = self.rotary(q)
        q, k = F.rms_norm(q, (q.size(-1),)), F.rms_norm(k, (k.size(-1),)) # QK norm suggested by @Grad62304977
        q, k = apply_rotary_emb(q, cos, sin), apply_rotary_emb(k, cos, sin)
        y = F.scaled_dot_product_attention(q.transpose(1, 2), k.transpose(1, 2), v.transpose(1, 2), is_causal=True)
        y = y.transpose(1, 2).contiguous().view_as(x) # re-assemble all head outputs side by side
        y = self.c_proj(y)
        return y, v1

# Define the MLP class
class MLP(torch.nn.Module):

    def __init__(self, config):
        super().__init__()
        self.c_fc    = torch.nn.Linear(config.n_embd, 4 * config.n_embd, bias=False)
        self.c_proj  = torch.nn.Linear(4 * config.n_embd, config.n_embd, bias=False)
        self.c_proj.weight.data.zero_() # zero init suggested by @Grad62304977

    def forward(self, x):
        x = self.c_fc(x)
        x = F.relu(x).square() # https://arxiv.org/abs/2109.08668v2; ~1-2% better than GELU; suggested by @SKYLINEZ007 and @Grad62304977
        x = self.c_proj(x)
        return x

# Define the Block class
class Block(torch.nn.Module):

    def __init__(self, config):
        super().__init__()
        self.attn = CausalSelfAttention(config)
        self.mlp = MLP(config)
        self.lambdas = torch.nn.Parameter(torch.tensor([1., 0.]))

    def forward(self, x, v1, x0):
        x = self.lambdas[0] * x + self.lambdas[1] * x0
        x1, v1 = self.attn(F.rms_norm(x, (x.size(-1),)), v1)
        x = x + x1
        x = x + self.mlp(F.rms_norm(x, (x.size(-1),)))
        return x, v1

# Define the GPT class
class GPT(torch.nn.Module):

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

        self.transformer = torch.nn.ModuleDict(dict(
            wte = torch.nn.Embedding(config.vocab_size, config.n_embd),
            h = torch.nn.ModuleList([Block(config) for _ in range(config.n_layer)]),
        ))
        self.lm_head = torch.nn.Linear(config.n_embd, config.vocab_size, bias=False)
        self.lm_head.weight.data.zero_() # @Grad62304977

    def forward(self, idx, targets=None, return_logits=True):

        # forward the GPT model itself
        x = self.transformer.wte(idx) # token embeddings of shape (b, t, n_embd)
        x = F.rms_norm(x, (x.size(-1),)) # @Grad62304977
        x0 = x
        v1 = None
        for block in self.transformer.h:
            x, v1 = block(x, v1, x0)
        x = F.rms_norm(x, (x.size(-1),))

        if targets is not None:
            # if we are given some desired targets also calculate the loss
            logits = self.lm_head(x)
            logits = 30 * torch.tanh(logits / 30) # @Grad62304977
            logits = logits.float() # use tf32/fp32 for logits
            loss = F.cross_entropy(logits.view(-1, logits.size(-1)), targets.view(-1), ignore_index=-1)
        else:
            # inference-time mini-optimization: only forward the lm_head on the very last position
            logits = self.lm_head(x[:, [-1], :]) # note: using list [-1] to preserve the time dim
            logits = 30 * torch.tanh(logits / 30) # @Grad62304977
            logits = logits.float() # use tf32/fp32 for logits
            loss = None

        # there are performance reasons why not returning logits is prudent, if not needed
        if not return_logits:
            logits = None

        return logits, loss
    
    def generate(self, idx, max_new_tokens, temperature=1.0, top_k=None):
        """
        Take a conditioning sequence of indices idx (LongTensor of shape (b,t)) and complete
        the sequence max_new_tokens times, feeding the predictions back into the model each time.
        Most likely you'll want to make sure to be in model.eval() mode of operation for this.
        """
        for _ in range(max_new_tokens):
            # if the sequence context is growing too long we must crop it at block_size
            #idx_cond = idx if idx.size(1) <= self.config.block_size else idx[:, -self.config.block_size:]
            # forward the model to get the logits for the index in the sequence
            logits, _ = self(idx)
            # pluck the logits at the final step and scale by desired temperature
            logits = logits[:, -1, :] / temperature
            # optionally crop the logits to only the top k options
            if top_k is not None:
                v, _ = torch.topk(logits, min(top_k, logits.size(-1)))
                logits[logits < v[:, [-1]]] = -float('Inf')
            # apply softmax to convert logits to (normalized) probabilities
            probs = F.softmax(logits, dim=-1)
            # sample from the distribution
            idx_next = torch.multinomial(probs, num_samples=1)
            # append sampled index to the running sequence and continue
            idx = torch.cat((idx, idx_next), dim=1)

        return idx

# Load the trained parameters
def load_checkpoint(model, checkpoint_path):
    checkpoint = torch.load(checkpoint_path, map_location=torch.device('cpu'))
    model.load_state_dict(dict([(n.removeprefix("_orig_mod."), p) for n, p in checkpoint['model'].items()]))

# Run LLM inference
def run_inference(model, input_ids):
    input_ids = torch.tensor(input_ids).unsqueeze(0)
    return model.generate(input_ids, 50)

# Main function
def main():
    config = GPTConfig()
    model = GPT(config)
    model_path = 'nanogpt-speedrun-baseline.safetensors'  # replace with your checkpoint path
    missing, unexpected = safetensors.torch.load_model(model, model_path)
    print(missing)
    print(unexpected)
    model.eval()

    prompt = "Once upon a time, in a magical kingdom, "
    input_ids = tokenizer.encode_ordinary(prompt)
    output_ids = run_inference(model, input_ids)
    #print(output_ids)
    tmp = output_ids.squeeze().tolist()
    #print(tmp)
    print(tokenizer.decode(tmp))


if __name__ == '__main__':
    main()