import torch, time
from accelerate import Accelerator
from accelerate.utils import gather_object
from transformers import AutoModelForCausalLM, AutoTokenizer



accelerator = Accelerator()


def write_pretty_json(file_path, data):
    import json
    with open(file_path, "w") as write_file:
        json.dump(data, write_file, indent=4)


# 10*10 Prompts. Source: https://www.penguin.co.uk/articles/2022/04/best-first-lines-in-books
prompts_all=[
    "The King is dead. Long live the Queen.",
    "Once there were four children whose names were Peter, Susan, Edmund, and Lucy.",
    "The story so far: in the beginning, the universe was created.",
    "It was a bright cold day in April, and the clocks were striking thirteen.",
    "It is a truth universally acknowledged, that a single man in possession of a good fortune, must be in want of a wife.",
    "The sweat wis lashing oafay Sick Boy; he wis trembling.",
    "124 was spiteful. Full of Baby's venom.",
    "As Gregor Samsa awoke one morning from uneasy dreams he found himself transformed in his bed into a gigantic insect.",
    "I write this sitting in the kitchen sink.",
    "We were somewhere around Barstow on the edge of the desert when the drugs began to take hold.",
] * 10

# load a base model and tokenizer
model_path = "meta-llama/Llama-2-13b-hf"
model = AutoModelForCausalLM.from_pretrained(
    model_path,    
    device_map={"": accelerator.process_index},
    torch_dtype=torch.bfloat16,
)
tokenizer = AutoTokenizer.from_pretrained(model_path)   
tokenizer.pad_token = tokenizer.eos_token

# batch, left pad (for inference), and tokenize
def prepare_prompts(prompts, tokenizer, batch_size=16):
    batches=[prompts[i:i + batch_size] for i in range(0, len(prompts), batch_size)]  
    batches_tok=[]
    tokenizer.padding_side="left"     
    for prompt_batch in batches:
        batches_tok.append(
            tokenizer(
                prompt_batch, 
                return_tensors="pt", 
                padding='longest', 
                truncation=False, 
                pad_to_multiple_of=8,
                add_special_tokens=False).to("cuda") 
            )
    tokenizer.padding_side="right"
    return batches_tok

# sync GPUs and start the timer
accelerator.wait_for_everyone()    
start=time.time()

# divide the prompt list onto the available GPUs 
with accelerator.split_between_processes(prompts_all) as prompts:
    results=dict(outputs=[], num_tokens=0)

    # have each GPU do inference in batches
    prompt_batches=prepare_prompts(prompts, tokenizer, batch_size=16)

    for prompts_tokenized in prompt_batches:
        outputs_tokenized=model.generate(**prompts_tokenized, max_new_tokens=200)

        # remove prompt from gen. tokens
        outputs_tokenized=[ tok_out[len(tok_in):] 
            for tok_in, tok_out in zip(prompts_tokenized["input_ids"], outputs_tokenized) ] 

        # count and decode gen. tokens 
        num_tokens=sum([ len(t) for t in outputs_tokenized ])
        outputs=tokenizer.batch_decode(outputs_tokenized)

        # store in results{} to be gathered by accelerate
        results["outputs"].extend(outputs)
        results["num_tokens"] += num_tokens

    results=[ results ] # transform to list, otherwise gather_object() will not collect correctly

# collect results from all the GPUs
results_gathered=gather_object(results)

if accelerator.is_main_process:
    timediff=time.time()-start
    num_tokens=sum([r["num_tokens"] for r in results_gathered ])

    print(f"tokens/sec: {num_tokens//timediff}, time elapsed: {timediff}, num_tokens {num_tokens}")