# Copyright 2024 PRIME team and/or its affiliates
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""
FSDP PPO Trainer with Ray-based single controller.
This trainer supports model-agonistic model initialization with huggingface
"""

import os
import statistics
import uuid
from copy import deepcopy
from pprint import pprint

import numpy as np
import torch
from omegaconf import OmegaConf, open_dict

from verl import DataProto
from verl.single_controller.ray import RayWorkerGroup
from verl.trainer.ppo.core_algos import agg_loss
from verl.trainer.ppo.metric_utils import _compute_response_info
from verl.trainer.ppo.ray_trainer import RayPPOTrainer, ResourcePoolManager, Role, WorkerType, _timer
from verl.utils.checkpoint.checkpoint_manager import find_latest_ckpt_path
from verl.utils.dataset.rl_dataset import RLHFDataset, collate_fn
from verl.utils.metric import reduce_metrics

from . import prime_core_algos


def compute_advantage(data: DataProto, adv_estimator, config):
    if adv_estimator == "rloo":
        responses = data.batch["responses"]
        response_length = responses.size(-1)
        attention_mask = data.batch["attention_mask"]
        response_mask = attention_mask[:, -response_length:]
        advantages, returns = prime_core_algos.compute_rloo_advantage_return(data, response_mask, config.actor_rollout_ref.rollout.n, config)
        data.batch["advantages"] = advantages
        data.batch["returns"] = returns
    else:
        raise NotImplementedError
    return data


def compute_data_metrics(batch, use_critic=True):
    advantages = batch.batch["advantages"]
    returns = batch.batch["returns"]

    max_response_length = batch.batch["responses"].shape[-1]

    prompt_mask = batch.batch["attention_mask"][:, :-max_response_length].bool()
    response_mask = batch.batch["attention_mask"][:, -max_response_length:].bool()

    max_prompt_length = prompt_mask.size(-1)

    response_info = _compute_response_info(batch)
    prompt_length = response_info["prompt_length"]
    response_length = response_info["response_length"]

    valid_adv = torch.masked_select(advantages, response_mask)
    valid_returns = torch.masked_select(returns, response_mask)

    if use_critic:
        values = batch.batch["values"]
        valid_values = torch.masked_select(values, response_mask)
        return_diff_var = torch.var(valid_returns - valid_values)
        return_var = torch.var(valid_returns)

    metrics = {
        # adv
        "critic/advantages/mean": torch.mean(valid_adv).detach().item(),
        "critic/advantages/max": torch.max(valid_adv).detach().item(),
        "critic/advantages/min": torch.min(valid_adv).detach().item(),
        # returns
        "critic/returns/mean": torch.mean(valid_returns).detach().item(),
        "critic/returns/max": torch.max(valid_returns).detach().item(),
        "critic/returns/min": torch.min(valid_returns).detach().item(),
        **(
            {
                # values
                "critic/values/mean": torch.mean(valid_values).detach().item(),
                "critic/values/max": torch.max(valid_values).detach().item(),
                "critic/values/min": torch.min(valid_values).detach().item(),
                # vf explained var
                "critic/vf_explained_var": (1.0 - return_diff_var / (return_var + 1e-5)).detach().item(),
            }
            if use_critic
            else {}
        ),
        # response length
        "response_length/mean": torch.mean(response_length).detach().item(),
        "response_length/max": torch.max(response_length).detach().item(),
        "response_length/min": torch.min(response_length).detach().item(),
        "response_length/clip_ratio": torch.mean(torch.eq(response_length, max_response_length).float()).detach().item(),
        # prompt length
        "prompt_length/mean": torch.mean(prompt_length).detach().item(),
        "prompt_length/max": torch.max(prompt_length).detach().item(),
        "prompt_length/min": torch.min(prompt_length).detach().item(),
        "prompt_length/clip_ratio": torch.mean(torch.eq(prompt_length, max_prompt_length).float()).detach().item(),
    }
    return metrics


def compute_response_mask(data: DataProto):
    responses = data.batch["responses"]
    response_length = responses.size(1)
    attention_mask = data.batch["attention_mask"]
    return attention_mask[:, -response_length:]


def compute_timing_metrics(batch, timing_raw):
    response_info = _compute_response_info(batch)
    num_prompt_tokens = torch.sum(response_info["prompt_length"]).item()
    num_response_tokens = torch.sum(response_info["response_length"]).item()
    num_overall_tokens = num_prompt_tokens + num_response_tokens

    num_tokens_of_section = {
        "gen": num_response_tokens,
        **{name: num_overall_tokens for name in ["ref", "values", "adv", "update_critic", "update_actor"]},
    }

    return {
        **{f"timing_s/{name}": value for name, value in timing_raw.items()},
        **{f"timing_per_token_ms/{name}": timing_raw[name] * 1000 / num_tokens_of_section[name] for name in set(num_tokens_of_section.keys()) & set(timing_raw.keys())},
    }


class RayPRIMETrainer(RayPPOTrainer):
    """
    Note that this trainer runs on the driver process on a single CPU/GPU node.
    """

    # TODO: support each role have individual ray_worker_group_cls,
    # i.e., support different backend of different role
    def __init__(
        self,
        config,
        tokenizer,
        role_worker_mapping: dict[Role, WorkerType],
        resource_pool_manager: ResourcePoolManager,
        ray_worker_group_cls: RayWorkerGroup = RayWorkerGroup,
        reward_fn=None,
        val_reward_fn=None,
    ):
        # assert torch.cuda.is_available(), 'cuda must be available on driver'

        super().__init__(
            config,
            tokenizer,
            role_worker_mapping,
            resource_pool_manager,
            ray_worker_group_cls,
            reward_fn,
            val_reward_fn,
        )

        self.use_critic = False

    def _validate_config(self):
        super()._validate_config()
        # TODO: Additional config checks can be added here

    def _create_dataloader(self, *args, **kwargs):
        from torch.utils.data import DataLoader, RandomSampler, SequentialSampler

        # TODO: we have to make sure the batch size is divisible by the dp size
        self.train_dataset = RLHFDataset(data_files=self.config.data.train_files, tokenizer=self.tokenizer, config=self.config.data)
        # use sampler for better ckpt resume
        if self.config.data.shuffle:
            train_dataloader_generator = torch.Generator()
            train_dataloader_generator.manual_seed(self.config.data.get("seed", 1))
            sampler = RandomSampler(data_source=self.train_dataset, generator=train_dataloader_generator)
        else:
            sampler = SequentialSampler(data_source=self.train_dataset)

        self.train_dataloader = DataLoader(
            dataset=self.train_dataset,
            batch_size=int(self.config.data.train_batch_size * self.config.data.oversample_factor),
            drop_last=True,
            collate_fn=collate_fn,
            sampler=sampler,
        )

        self.val_dataset = RLHFDataset(data_files=self.config.data.val_files, tokenizer=self.tokenizer, config=self.config.data)
        self.val_dataloader = DataLoader(
            dataset=self.val_dataset,
            batch_size=len(self.val_dataset),
            shuffle=True,
            drop_last=True,
            collate_fn=collate_fn,
        )

        assert len(self.train_dataloader) >= 1
        assert len(self.val_dataloader) >= 1

        print(f"Size of train dataloader: {len(self.train_dataloader)}")
        print(f"Size of val dataloader: {len(self.val_dataloader)}")

        # inject total_training_steps to actor/critic optim_config. This is hacky.
        total_training_steps = len(self.train_dataloader) * self.config.trainer.total_epochs

        if self.config.trainer.total_training_steps is not None:
            total_training_steps = self.config.trainer.total_training_steps

        self.total_training_steps = total_training_steps
        print(f"Total training steps: {self.total_training_steps}")

        OmegaConf.set_struct(self.config, True)
        with open_dict(self.config):
            self.config.actor_rollout_ref.actor.optim.total_training_steps = total_training_steps
            self.config.critic.optim.total_training_steps = total_training_steps

    def _save_checkpoint(self):
        # path: given_path + `/global_step_{global_steps}` + `/actor`
        local_global_step_folder = os.path.join(self.config.trainer.default_local_dir, f"global_step_{self.global_steps}")
        print(f"local_global_step_folder: {local_global_step_folder}")
        actor_local_path = os.path.join(local_global_step_folder, "actor")

        actor_remote_path = None if self.config.trainer.default_hdfs_dir is None else os.path.join(self.config.trainer.default_hdfs_dir, f"global_step_{self.global_steps}", "actor")
        self.actor_rollout_wg.save_checkpoint(
            actor_local_path,
            actor_remote_path,
            self.global_steps,
        )

        if self.use_rm:
            reward_local_path = os.path.join(local_global_step_folder, "reward")
            reward_remote_path = None if self.config.trainer.default_hdfs_dir is None else os.path.join(self.config.trainer.default_hdfs_dir, f"global_step_{self.global_steps}", "reward")
            self.rm_wg.save_checkpoint(
                reward_local_path,
                reward_remote_path,
                self.global_steps,
            )

        # save dataloader
        dataloader_local_path = os.path.join(local_global_step_folder, "data.pt")
        import dill

        torch.save(self.train_dataloader, dataloader_local_path, pickle_module=dill)

        # latest checkpointed iteration tracker (for atomic usage)
        local_latest_checkpointed_iteration = os.path.join(self.config.trainer.default_local_dir, "latest_checkpointed_iteration.txt")
        with open(local_latest_checkpointed_iteration, "w") as f:
            f.write(str(self.global_steps))

    def _load_checkpoint(self):
        if self.config.trainer.resume_mode == "disable":
            return 0

        # load from hdfs
        if self.config.trainer.default_hdfs_dir is not None:
            NotImplementedError("load from hdfs is not implemented yet")
        else:
            checkpoint_folder = self.config.trainer.default_local_dir  # TODO: check path
            if not os.path.isabs(checkpoint_folder):
                working_dir = os.getcwd()
                checkpoint_folder = os.path.join(working_dir, checkpoint_folder)
            global_step_folder = find_latest_ckpt_path(checkpoint_folder)  # None if no latest

        # find global_step_folder
        if self.config.trainer.resume_mode == "auto":
            if global_step_folder is None:
                print("Training from scratch")
                return 0
        else:
            if self.config.trainer.resume_mode == "resume_path":
                assert isinstance(self.config.trainer.resume_from_path, str), "resume ckpt must be str type"
                assert "global_step_" in self.config.trainer.resume_from_path, "resume ckpt must specify the global_steps"
                global_step_folder = self.config.trainer.resume_from_path
                if not os.path.isabs(global_step_folder):
                    working_dir = os.getcwd()
                    global_step_folder = os.path.join(working_dir, global_step_folder)
        print(f"Load from checkpoint folder: {global_step_folder}")
        # set global step
        self.global_steps = int(global_step_folder.split("global_step_")[-1])

        print(f"Setting global step to {self.global_steps}")
        print(f"Resuming from {global_step_folder}")

        actor_path = os.path.join(global_step_folder, "actor")
        reward_path = os.path.join(global_step_folder, "reward")
        # load actor
        self.actor_rollout_wg.load_checkpoint(actor_path, del_local_after_load=self.config.trainer.del_local_ckpt_after_load)
        # load rm
        if self.use_rm:
            self.rm_wg.load_checkpoint(reward_path, del_local_after_load=self.config.trainer.del_local_ckpt_after_load)

        # load dataloader,
        # TODO: from remote not implemented yet
        dataloader_local_path = os.path.join(global_step_folder, "data.pt")
        self.train_dataloader = torch.load(dataloader_local_path)
        if isinstance(self.train_dataloader.dataset, RLHFDataset):
            self.train_dataloader.dataset.resume_dataset_state()

    def fit(self):
        """
        The training loop of PPO.
        The driver process only need to call the compute functions of the worker group through RPC to
        construct the PPO dataflow. The light-weight advantage computation is done on the driver process.
        """
        from omegaconf import OmegaConf

        from verl.utils.tracking import Tracking

        logger = Tracking(
            project_name=self.config.trainer.project_name,
            experiment_name=self.config.trainer.experiment_name,
            default_backend=self.config.trainer.logger,
            config=OmegaConf.to_container(self.config, resolve=True),
        )

        self.global_steps = 0

        # load checkpoint before doing anything
        self._load_checkpoint()

        # perform validation before training
        # currently, we only support validation using the reward_function.
        if self.val_reward_fn is not None and self.config.trainer.get("val_before_train", True):
            val_metrics = self._validate()
            assert val_metrics, f"{val_metrics=}"
            pprint(f"Initial validation metrics: {val_metrics}")
            logger.log(data=val_metrics, step=self.global_steps)
            if self.config.trainer.get("val_only", False):
                return

        # we start from step 1
        self.global_steps += 1

        for epoch in range(self.config.trainer.total_epochs):
            for batch_dict in self.train_dataloader:
                metrics = {}
                timing_raw = {}

                batch: DataProto = DataProto.from_single_dict(batch_dict)

                # pop those keys for generation
                gen_batch = batch.pop(batch_keys=["input_ids", "attention_mask", "position_ids"])

                with _timer("step", timing_raw):
                    # generate a batch
                    with _timer("gen", timing_raw):
                        gen_batch_output = self.actor_rollout_wg.generate_sequences(gen_batch)
                        timing_raw.update(gen_batch_output.meta_info["timing"])
                        gen_batch_output.meta_info.pop("timing", None)

                    if self.config.algorithm.adv_estimator == "remax":
                        with _timer("gen_max", timing_raw):
                            gen_baseline_batch = deepcopy(gen_batch)
                            gen_baseline_batch.meta_info["do_sample"] = False
                            gen_baseline_output = self.actor_rollout_wg.generate_sequences(gen_baseline_batch)

                            batch = batch.union(gen_baseline_output)
                            reward_baseline_tensor = self.reward_fn(batch)
                            reward_baseline_tensor = reward_baseline_tensor.sum(dim=-1)

                            batch.pop(batch_keys=list(gen_baseline_output.batch.keys()))

                            batch.batch["reward_baselines"] = reward_baseline_tensor

                            del gen_baseline_batch, gen_baseline_output

                    batch.non_tensor_batch["uid"] = np.array([str(uuid.uuid4()) for _ in range(len(batch.batch))], dtype=object)
                    # repeat to align with repeated responses in rollout
                    batch = batch.repeat(repeat_times=self.config.actor_rollout_ref.rollout.n, interleave=True)
                    batch = batch.union(gen_batch_output)

                    # Balance the number of valid tokens across DP ranks.
                    # NOTE: This usually changes the order of data in the `batch`,
                    # which won't affect the advantage calculation (since it's based on uid),
                    # but might affect the loss calculation (due to the change of mini-batching).
                    # TODO: Decouple the DP balancing and mini-batching.
                    if self.config.trainer.balance_batch:
                        self._balance_batch(batch, metrics=metrics)

                    # compute global_valid tokens
                    batch.meta_info["global_token_num"] = torch.sum(batch.batch["attention_mask"], dim=-1).tolist()

                    # verify
                    with _timer("verify", timing_raw):
                        scores = self.reward_fn.verify(batch)
                        metrics["acc"] = statistics.mean(scores)

                    # filter the batch. 1/oversample_factor samples will be kept.
                    # If there is a filter, prompts passing it will be prioritized.

                    batch = self.filter_and_downsample(scores, batch)
                    batch.meta_info["n"] = self.config.actor_rollout_ref.rollout.n
                    n_samples = self.config.actor_rollout_ref.rollout.n

                    # recompute old_log_probs
                    with _timer("old_log_prob", timing_raw):
                        old_log_prob = self.actor_rollout_wg.compute_log_prob(batch)
                        entropys = old_log_prob.batch["entropys"]
                        response_masks = compute_response_mask(batch)
                        loss_agg_mode = self.config.actor_rollout_ref.actor.loss_agg_mode
                        entropy_agg = agg_loss(loss_mat=entropys, loss_mask=response_masks, loss_agg_mode=loss_agg_mode)
                        old_log_prob_metrics = {"actor/entropy": entropy_agg.detach().item()}
                        metrics.update(old_log_prob_metrics)
                        old_log_prob.batch.pop("entropys")
                        batch = batch.union(old_log_prob)

                    if self.use_reference_policy:
                        # compute reference log_prob
                        with _timer("ref", timing_raw):
                            ref_log_prob = self.ref_policy_wg.compute_ref_log_prob(batch)
                            batch = batch.union(ref_log_prob)

                    with _timer("adv", timing_raw):
                        if self.use_rm:
                            update_style = self.config.reward_model.model.get("update", "none")
                            if update_style == "none":  # only run forward
                                reward_output = self.rm_wg.compute_rm_score(batch)
                            elif update_style == "after":  # update and directly return the reward
                                reward_output = self.rm_wg.update_rm(batch)
                            elif update_style == "before":  # update reward model, and then run forward
                                reward_output = self.rm_wg.update_rm(batch)
                                if "metrics" in reward_output.meta_info.keys():
                                    reward_output_metrics = reduce_metrics(reward_output.meta_info["metrics"])
                                    metrics.update(reward_output_metrics)

                                reward_output = self.rm_wg.compute_rm_score(batch)
                            elif update_style == "reverse":  # run forward to calculate statistics, then update reward model
                                reward_output = self.rm_wg.compute_rm_score(batch)
                                # broadcast q and acc tensor to each result
                                bc_td = DataProto.from_dict(
                                    tensors={
                                        "Q_bc": reward_output.batch["q"].sum(dim=-1).view(-1, n_samples).unsqueeze(1).expand(-1, n_samples, -1).reshape(-1, n_samples),
                                        "acc_bc": batch.batch["acc"].view(-1, n_samples).unsqueeze(1).expand(-1, n_samples, -1).reshape(-1, n_samples),
                                    }
                                )
                                batch = batch.union(bc_td)
                                reward_output = self.rm_wg.update_rm(batch)
                            else:
                                raise NotImplementedError
                            batch = batch.union(reward_output)
                            if "metrics" in reward_output.meta_info.keys():
                                reward_output_metrics = reduce_metrics(reward_output.meta_info["metrics"])
                                metrics.update(reward_output_metrics)

                        # compute advantages, executed on the driver process
                        batch = compute_advantage(batch, adv_estimator=self.config.algorithm.adv_estimator, config=self.config)

                    # update actor
                    with _timer("update_actor", timing_raw):
                        actor_output = self.actor_rollout_wg.update_actor(batch)
                    actor_output_metrics = reduce_metrics(actor_output.meta_info["metrics"])
                    metrics.update(actor_output_metrics)

                    # validate
                    if self.val_reward_fn is not None and self.config.trainer.test_freq > 0 and self.global_steps % self.config.trainer.test_freq == 0:
                        with _timer("testing", timing_raw):
                            val_metrics: dict = self._validate()
                        metrics.update(val_metrics)

                    if self.config.trainer.save_freq > 0 and self.global_steps % self.config.trainer.save_freq == 0:
                        with _timer("save_checkpoint", timing_raw):
                            self._save_checkpoint()

                # collect metrics
                metrics.update(compute_data_metrics(batch=batch, use_critic=self.use_critic))
                metrics.update(compute_timing_metrics(batch=batch, timing_raw=timing_raw))

                # TODO: make a canonical logger that supports various backend
                logger.log(data=metrics, step=self.global_steps)

                self.global_steps += 1

                if self.global_steps >= self.total_training_steps:
                    # perform validation after training
                    if self.val_reward_fn is not None:
                        val_metrics = self._validate()
                        pprint(f"Final validation metrics: {val_metrics}")
                        logger.log(data=val_metrics, step=self.global_steps)
                    if self.config.trainer.save_freq > 0 and (self.global_steps - 1) % self.config.trainer.save_freq != 0:
                        with _timer("save_checkpoint", timing_raw):
                            self._save_checkpoint()
                    return

    def filter_and_downsample(self, scores, batch: DataProto):
        """
        downsample the batch according to oversample_factor
        samples passing the filters will be prioritized
        """
        n_samples = int(self.config.actor_rollout_ref.rollout.n)
        reward_matrix = torch.tensor(scores).reshape(-1, n_samples)

        filter_mask = torch.ones((reward_matrix.shape[0]), dtype=torch.bool)

        if self.config.data.filter_accuracy:
            acc_tensor = torch.mean(reward_matrix, dim=-1)
            filter_mask[(acc_tensor > self.config.data.accuracy_upper_bound) | (acc_tensor < self.config.data.accuracy_lower_bound)] = False

        if self.config.data.filter_truncate:
            length_matrix = batch.batch["attention_mask"][:, -batch.batch["responses"].shape[-1] :].sum(dim=-1).reshape(-1, n_samples)
            length_tensor = torch.max(length_matrix, dim=-1)[0]
            filter_mask[length_tensor >= self.config.data.max_response_length - 1] = False

        reorder_index = torch.argsort(filter_mask, descending=True)
        reorder_index = (reorder_index.unsqueeze(-1) * n_samples + torch.arange(0, n_samples).unsqueeze(0)).view(-1)
        batch.reorder(reorder_index[: int(len(batch) // self.config.data.oversample_factor)])  # this operation is inplace

        return batch
