"""
Copyright (c) Microsoft Corporation.
Licensed under the MIT license.

UNITER finetuning for VQA
"""
import argparse
import json
import os
from os.path import abspath, dirname, exists, join
from time import time

import torch
from torch.nn import functional as F
from torch.nn.utils import clip_grad_norm_
from torch.utils.data import DataLoader
from torch.optim import Adam, Adamax

from apex import amp
from horovod import torch as hvd

from tqdm import tqdm

from data import (TokenBucketSampler, PrefetchLoader,
                  TxtTokLmdb, ImageLmdbGroup, ConcatDatasetWithLens,
                  VqaDataset, VqaEvalDataset,
                  vqa_collate, vqa_eval_collate)
from model import UniterForVisualQuestionAnswering
from optim import AdamW, get_lr_sched

from utils.logger import LOGGER, TB_LOGGER, RunningMeter, add_log_to_file
from utils.distributed import (all_reduce_and_rescale_tensors, all_gather_list,
                               broadcast_tensors)
from utils.save import ModelSaver, save_training_meta
from utils.misc import NoOp, parse_with_config, set_dropout, set_random_seed
from utils.const import BUCKET_SIZE, IMG_DIM


def build_dataloader(dataset, collate_fn, is_train, opts):
    batch_size = (opts.train_batch_size if is_train
                  else opts.val_batch_size)
    sampler = TokenBucketSampler(dataset.lens, bucket_size=BUCKET_SIZE,
                                 batch_size=batch_size, droplast=is_train)
    dataloader = DataLoader(dataset, batch_sampler=sampler,
                            num_workers=opts.n_workers,
                            pin_memory=opts.pin_mem, collate_fn=collate_fn)
    dataloader = PrefetchLoader(dataloader)
    return dataloader


def build_optimizer(model, opts):
    """ vqa linear may get larger learning rate """
    no_decay = ['bias', 'LayerNorm.bias', 'LayerNorm.weight']
    param_optimizer = [(n, p) for n, p in model.named_parameters()
                       if 'vqa_output' not in n]
    param_top = [(n, p) for n, p in model.named_parameters()
                 if 'vqa_output' in n]
    optimizer_grouped_parameters = [
        {'params': [p for n, p in param_top
                    if not any(nd in n for nd in no_decay)],
         'lr': opts.learning_rate,
         'weight_decay': opts.weight_decay},
        {'params': [p for n, p in param_top
                    if any(nd in n for nd in no_decay)],
         'lr': opts.learning_rate,
         'weight_decay': 0.0},
        {'params': [p for n, p in param_optimizer
                    if not any(nd in n for nd in no_decay)],
         'weight_decay': opts.weight_decay},
        {'params': [p for n, p in param_optimizer
                    if any(nd in n for nd in no_decay)],
         'weight_decay': 0.0}
    ]

    # currently Adam only
    if opts.optim == 'adam':
        OptimCls = Adam
    elif opts.optim == 'adamax':
        OptimCls = Adamax
    elif opts.optim == 'adamw':
        OptimCls = AdamW
    else:
        raise ValueError('invalid optimizer')
    optimizer = OptimCls(optimizer_grouped_parameters,
                         lr=opts.learning_rate, betas=opts.betas)
    return optimizer


def main(opts):
    hvd.init()
    n_gpu = hvd.size()
    device = torch.device("cuda", hvd.local_rank())
    torch.cuda.set_device(hvd.local_rank())
    rank = hvd.rank()
    opts.rank = rank
    LOGGER.info("device: {} n_gpu: {}, rank: {}, "
                "16-bits training: {}".format(
                    device, n_gpu, hvd.rank(), opts.fp16))

    if opts.gradient_accumulation_steps < 1:
        raise ValueError("Invalid gradient_accumulation_steps parameter: {}, "
                         "should be >= 1".format(
                            opts.gradient_accumulation_steps))

    set_random_seed(opts.seed)

    ans2label = json.load(open(f'{dirname(abspath(__file__))}'
                               f'/misc/ans2label.json'))
    label2ans = {label: ans for ans, label in ans2label.items()}

    # load DBs and image dirs
    all_img_dbs = ImageLmdbGroup(opts.conf_th, opts.max_bb, opts.min_bb,
                                 opts.num_bb, opts.compressed_db)
    # train
    LOGGER.info(f"Loading Train Dataset "
                f"{opts.train_txt_dbs}, {opts.train_img_dbs}")
    train_datasets = []
    for txt_path, img_path in zip(opts.train_txt_dbs, opts.train_img_dbs):
        img_db = all_img_dbs[img_path]
        txt_db = TxtTokLmdb(txt_path, opts.max_txt_len)
        train_datasets.append(VqaDataset(len(ans2label), txt_db, img_db))
    train_dataset = ConcatDatasetWithLens(train_datasets)
    train_dataloader = build_dataloader(train_dataset, vqa_collate, True, opts)
    # val
    LOGGER.info(f"Loading Train Dataset {opts.val_txt_db}, {opts.val_img_db}")
    val_img_db = all_img_dbs[opts.val_img_db]
    val_txt_db = TxtTokLmdb(opts.val_txt_db, -1)
    val_dataset = VqaEvalDataset(len(ans2label), val_txt_db, val_img_db)
    val_dataloader = build_dataloader(val_dataset, vqa_eval_collate,
                                      False, opts)

    # Prepare model
    if opts.checkpoint:
        checkpoint = torch.load(opts.checkpoint)
    else:
        checkpoint = {}

    all_dbs = opts.train_txt_dbs + [opts.val_txt_db]
    toker = json.load(open(f'{all_dbs[0]}/meta.json'))['bert']
    assert all(toker == json.load(open(f'{db}/meta.json'))['bert']
               for db in all_dbs)
    model = UniterForVisualQuestionAnswering.from_pretrained(
        opts.model_config, checkpoint,
        img_dim=IMG_DIM, num_answer=len(ans2label))
    model.to(device)
    # make sure every process has same model parameters in the beginning
    broadcast_tensors([p.data for p in model.parameters()], 0)
    set_dropout(model, opts.dropout)

    # Prepare optimizer
    optimizer = build_optimizer(model, opts)
    model, optimizer = amp.initialize(model, optimizer,
                                      enabled=opts.fp16, opt_level='O2')
    global_step = 0
    if rank == 0:
        save_training_meta(opts)
        TB_LOGGER.create(join(opts.output_dir, 'log'))
        pbar = tqdm(total=opts.num_train_steps)
        model_saver = ModelSaver(join(opts.output_dir, 'ckpt'))
        json.dump(ans2label,
                  open(join(opts.output_dir, 'ckpt', 'ans2label.json'), 'w'))
        os.makedirs(join(opts.output_dir, 'results'))  # store VQA predictions
        add_log_to_file(join(opts.output_dir, 'log', 'log.txt'))
    else:
        LOGGER.disabled = True
        pbar = NoOp()
        model_saver = NoOp()

    LOGGER.info(f"***** Running training with {n_gpu} GPUs *****")
    LOGGER.info("  Num examples = %d", len(train_dataset) * hvd.size())
    LOGGER.info("  Batch size = %d", opts.train_batch_size)
    LOGGER.info("  Accumulate steps = %d", opts.gradient_accumulation_steps)
    LOGGER.info("  Num steps = %d", opts.num_train_steps)

    running_loss = RunningMeter('loss')
    model.train()
    n_examples = 0
    n_epoch = 0
    start = time()
    # quick hack for amp delay_unscale bug
    optimizer.zero_grad()
    optimizer.step()
    while True:
        for step, batch in enumerate(train_dataloader):
            n_examples += batch['input_ids'].size(0)

            loss = model(batch, compute_loss=True)
            loss = loss.mean() * batch['targets'].size(1)  # instance-leval bce
            delay_unscale = (step+1) % opts.gradient_accumulation_steps != 0
            with amp.scale_loss(loss, optimizer, delay_unscale=delay_unscale
                                ) as scaled_loss:
                scaled_loss.backward()
                if not delay_unscale:
                    # gather gradients from every processes
                    # do this before unscaling to make sure every process uses
                    # the same gradient scale
                    grads = [p.grad.data for p in model.parameters()
                             if p.requires_grad and p.grad is not None]
                    all_reduce_and_rescale_tensors(grads, float(1))

            running_loss(loss.item())

            if (step + 1) % opts.gradient_accumulation_steps == 0:
                global_step += 1

                # learning rate scheduling
                lr_this_step = get_lr_sched(global_step, opts)
                for i, param_group in enumerate(optimizer.param_groups):
                    if i == 0 or i == 1:
                        param_group['lr'] = lr_this_step * opts.lr_mul
                    elif i == 2 or i == 3:
                        param_group['lr'] = lr_this_step
                    else:
                        raise ValueError()
                TB_LOGGER.add_scalar('lr', lr_this_step, global_step)

                # log loss
                losses = all_gather_list(running_loss)
                running_loss = RunningMeter(
                    'loss', sum(l.val for l in losses)/len(losses))
                TB_LOGGER.add_scalar('loss', running_loss.val, global_step)
                TB_LOGGER.step()

                # update model params
                if opts.grad_norm != -1:
                    grad_norm = clip_grad_norm_(amp.master_params(optimizer),
                                                opts.grad_norm)
                    TB_LOGGER.add_scalar('grad_norm', grad_norm, global_step)
                optimizer.step()
                optimizer.zero_grad()
                pbar.update(1)

                if global_step % 100 == 0:
                    # monitor training throughput
                    LOGGER.info(f'============Step {global_step}=============')
                    tot_ex = sum(all_gather_list(n_examples))
                    ex_per_sec = int(tot_ex / (time()-start))
                    LOGGER.info(f'{tot_ex} examples trained at '
                                f'{ex_per_sec} ex/s')
                    TB_LOGGER.add_scalar('perf/ex_per_s',
                                         ex_per_sec, global_step)
                    LOGGER.info(f'===========================================')

                if global_step % opts.valid_steps == 0:
                    val_log, results = validate(
                        model, val_dataloader, label2ans)
                    with open(f'{opts.output_dir}/results/'
                              f'results_{global_step}_'
                              f'rank{rank}.json', 'w') as f:
                        json.dump(results, f)
                    TB_LOGGER.log_scaler_dict(val_log)
                    model_saver.save(model, global_step)
            if global_step >= opts.num_train_steps:
                break
        if global_step >= opts.num_train_steps:
            break
        n_epoch += 1
        LOGGER.info(f"finished {n_epoch} epochs")
    val_log, results = validate(model, val_dataloader, label2ans)
    with open(f'{opts.output_dir}/results/'
              f'results_{global_step}_'
              f'rank{rank}_final.json', 'w') as f:
        json.dump(results, f)
    TB_LOGGER.log_scaler_dict(val_log)
    model_saver.save(model, f'{global_step}_final')


@torch.no_grad()
def validate(model, val_loader, label2ans):
    LOGGER.info("start running validation...")
    model.eval()
    val_loss = 0
    tot_score = 0
    n_ex = 0
    st = time()
    results = {}
    for i, batch in enumerate(val_loader):
        scores = model(batch, compute_loss=False)
        targets = batch['targets']
        loss = F.binary_cross_entropy_with_logits(
            scores, targets, reduction='sum')
        val_loss += loss.item()
        tot_score += compute_score_with_logits(scores, targets).sum().item()
        answers = [label2ans[i]
                   for i in scores.max(dim=-1, keepdim=False
                                       )[1].cpu().tolist()]
        for qid, answer in zip(batch['qids'], answers):
            results[qid] = answer
        n_ex += len(batch['qids'])
    val_loss = sum(all_gather_list(val_loss))
    tot_score = sum(all_gather_list(tot_score))
    n_ex = sum(all_gather_list(n_ex))
    tot_time = time()-st
    val_loss /= n_ex
    val_acc = tot_score / n_ex
    val_log = {'valid/loss': val_loss,
               'valid/acc': val_acc,
               'valid/ex_per_s': n_ex/tot_time}
    model.train()
    LOGGER.info(f"validation finished in {int(tot_time)} seconds, "
                f"score: {val_acc*100:.2f}")
    return val_log, results


def compute_score_with_logits(logits, labels):
    logits = torch.max(logits, 1)[1]  # argmax
    one_hots = torch.zeros(*labels.size(), device=labels.device)
    one_hots.scatter_(1, logits.view(-1, 1), 1)
    scores = (one_hots * labels)
    return scores


if __name__ == "__main__":
    parser = argparse.ArgumentParser()

    # Required parameters
    # TODO datasets
    parser.add_argument('--compressed_db', action='store_true',
                        help='use compressed LMDB')
    parser.add_argument("--model_config",
                        default=None, type=str,
                        help="json file for model architecture")
    parser.add_argument("--checkpoint",
                        default=None, type=str,
                        help="pretrained model")

    parser.add_argument(
        "--output_dir", default=None, type=str,
        help="The output directory where the model checkpoints will be "
             "written.")

    # Prepro parameters
    parser.add_argument('--max_txt_len', type=int, default=60,
                        help='max number of tokens in text (BERT BPE)')
    parser.add_argument('--conf_th', type=float, default=0.2,
                        help='threshold for dynamic bounding boxes '
                             '(-1 for fixed)')
    parser.add_argument('--max_bb', type=int, default=100,
                        help='max number of bounding boxes')
    parser.add_argument('--min_bb', type=int, default=10,
                        help='min number of bounding boxes')
    parser.add_argument('--num_bb', type=int, default=36,
                        help='static number of bounding boxes')

    # training parameters
    parser.add_argument("--train_batch_size", default=4096, type=int,
                        help="Total batch size for training. "
                             "(batch by tokens)")
    parser.add_argument("--val_batch_size", default=4096, type=int,
                        help="Total batch size for validation. "
                             "(batch by tokens)")
    parser.add_argument('--gradient_accumulation_steps', type=int, default=16,
                        help="Number of updates steps to accumualte before "
                             "performing a backward/update pass.")
    parser.add_argument("--learning_rate", default=3e-5, type=float,
                        help="The initial learning rate for Adam.")
    parser.add_argument("--lr_mul", default=1.0, type=float,
                        help="multiplier for top layer lr")
    parser.add_argument("--valid_steps", default=1000, type=int,
                        help="Run validation every X steps")
    parser.add_argument("--num_train_steps", default=100000, type=int,
                        help="Total number of training updates to perform.")
    parser.add_argument("--optim", default='adam',
                        choices=['adam', 'adamax', 'adamw'],
                        help="optimizer")
    parser.add_argument("--betas", default=[0.9, 0.98], nargs='+',
                        help="beta for adam optimizer")
    parser.add_argument("--decay", default='linear',
                        choices=['linear', 'invsqrt', 'constant', 'vqa'],
                        help="learning rate decay method")
    parser.add_argument("--decay_int", default=2000, type=int,
                        help="interval between VQA lr decy")
    parser.add_argument("--warm_int", default=2000, type=int,
                        help="interval for VQA lr warmup")
    parser.add_argument("--decay_st", default=20000, type=int,
                        help="when to start decay")
    parser.add_argument("--decay_rate", default=0.2, type=float,
                        help="ratio of lr decay")
    parser.add_argument("--dropout", default=0.1, type=float,
                        help="tune dropout regularization")
    parser.add_argument("--weight_decay", default=0.0, type=float,
                        help="weight decay (L2) regularization")
    parser.add_argument("--grad_norm", default=2.0, type=float,
                        help="gradient clipping (-1 for no clipping)")
    parser.add_argument("--warmup_steps", default=4000, type=int,
                        help="Number of training steps to perform linear "
                             "learning rate warmup for. (invsqrt decay)")

    # device parameters
    parser.add_argument('--seed', type=int, default=42,
                        help="random seed for initialization")
    parser.add_argument('--fp16', action='store_true',
                        help="Whether to use 16-bit float precision instead "
                             "of 32-bit")
    parser.add_argument('--n_workers', type=int, default=4,
                        help="number of data workers")
    parser.add_argument('--pin_mem', action='store_true', help="pin memory")

    # can use config files
    parser.add_argument('--config', help='JSON config files')

    args = parse_with_config(parser)

    if exists(args.output_dir) and os.listdir(args.output_dir):
        raise ValueError("Output directory ({}) already exists and is not "
                         "empty.".format(args.output_dir))

    # options safe guard
    # TODO
    if args.conf_th == -1:
        assert args.max_bb + args.max_txt_len + 2 <= 512
    else:
        assert args.num_bb + args.max_txt_len + 2 <= 512

    main(args)
