# Copyright (c) 2022-2024, The ORBIT Project Developers.
# All rights reserved.
#
# SPDX-License-Identifier: BSD-3-Clause

"""Reward manager for computing reward signals for a given world."""

from __future__ import annotations

import torch
from prettytable import PrettyTable
from typing import TYPE_CHECKING, Sequence

from .manager_base import ManagerBase, ManagerTermBase
from .manager_term_cfg import RewardTermCfg

if TYPE_CHECKING:
    from omni.isaac.orbit.envs import RLTaskEnv


class RewardManager(ManagerBase):
    """Manager for computing reward signals for a given world.

    The reward manager computes the total reward as a sum of the weighted reward terms. The reward
    terms are parsed from a nested config class containing the reward manger's settings and reward
    terms configuration.

    The reward terms are parsed from a config class containing the manager's settings and each term's
    parameters. Each reward term should instantiate the :class:`RewardTermCfg` class.

    .. note::

        The reward manager multiplies the reward term's ``weight``  with the time-step interval ``dt``
        of the environment. This is done to ensure that the computed reward terms are balanced with
        respect to the chosen time-step interval in the environment.

    """

    _env: RLTaskEnv
    """The environment instance."""

    def __init__(self, cfg: object, env: RLTaskEnv):
        """Initialize the reward manager.

        Args:
            cfg: The configuration object or dictionary (``dict[str, RewardTermCfg]``).
            env: The environment instance.
        """
        super().__init__(cfg, env)
        # prepare extra info to store individual reward term information
        self._episode_sums = dict()
        for term_name in self._term_names:
            self._episode_sums[term_name] = torch.zeros(self.num_envs, dtype=torch.float, device=self.device)
        # create buffer for managing reward per environment
        self._reward_buf = torch.zeros(self.num_envs, dtype=torch.float, device=self.device)

    def __str__(self) -> str:
        """Returns: A string representation for reward manager."""
        msg = f"<RewardManager> contains {len(self._term_names)} active terms.\n"

        # create table for term information
        table = PrettyTable()
        table.title = "Active Reward Terms"
        table.field_names = ["Index", "Name", "Weight"]
        # set alignment of table columns
        table.align["Name"] = "l"
        table.align["Weight"] = "r"
        # add info on each term
        for index, (name, term_cfg) in enumerate(zip(self._term_names, self._term_cfgs)):
            table.add_row([index, name, term_cfg.weight])
        # convert table to string
        msg += table.get_string()
        msg += "\n"

        return msg

    """
    Properties.
    """

    @property
    def active_terms(self) -> list[str]:
        """Name of active reward terms."""
        return self._term_names

    """
    Operations.
    """

    def reset(self, env_ids: Sequence[int] | None = None) -> dict[str, torch.Tensor]:
        """Returns the episodic sum of individual reward terms.

        Args:
            env_ids: The environment ids for which the episodic sum of
                individual reward terms is to be returned. Defaults to all the environment ids.

        Returns:
            Dictionary of episodic sum of individual reward terms.
        """
        # resolve environment ids
        if env_ids is None:
            env_ids = slice(None)
        # store information
        extras = {}
        for key in self._episode_sums.keys():
            # store information
            # r_1 + r_2 + ... + r_n
            episodic_sum_avg = torch.mean(self._episode_sums[key][env_ids])
            extras["Episode Reward/" + key] = episodic_sum_avg / self._env.max_episode_length_s
            # reset episodic sum
            self._episode_sums[key][env_ids] = 0.0
        # reset all the reward terms
        for term_cfg in self._class_term_cfgs:
            term_cfg.func.reset(env_ids=env_ids)
        # return logged information
        return extras

    def compute(self, dt: float) -> torch.Tensor:
        """Computes the reward signal as a weighted sum of individual terms.

        This function calls each reward term managed by the class and adds them to compute the net
        reward signal. It also updates the episodic sums corresponding to individual reward terms.

        Args:
            dt: The time-step interval of the environment.

        Returns:
            The net reward signal of shape (num_envs,).
        """
        # reset computation
        self._reward_buf[:] = 0.0
        # iterate over all the reward terms
        for name, term_cfg in zip(self._term_names, self._term_cfgs):
            # skip if weight is zero (kind of a micro-optimization)
            if term_cfg.weight == 0.0:
                continue
            # compute term's value
            value = term_cfg.func(self._env, **term_cfg.params) * term_cfg.weight * dt
            # update total reward
            self._reward_buf += value
            # update episodic sum
            self._episode_sums[name] += value

        return self._reward_buf

    """
    Operations - Term settings.
    """

    def set_term_cfg(self, term_name: str, cfg: RewardTermCfg):
        """Sets the configuration of the specified term into the manager.

        Args:
            term_name: The name of the reward term.
            cfg: The configuration for the reward term.

        Raises:
            ValueError: If the term name is not found.
        """
        if term_name not in self._term_names:
            raise ValueError(f"Reward term '{term_name}' not found.")
        # set the configuration
        self._term_cfgs[self._term_names.index(term_name)] = cfg

    def get_term_cfg(self, term_name: str) -> RewardTermCfg:
        """Gets the configuration for the specified term.

        Args:
            term_name: The name of the reward term.

        Returns:
            The configuration of the reward term.

        Raises:
            ValueError: If the term name is not found.
        """
        if term_name not in self._term_names:
            raise ValueError(f"Reward term '{term_name}' not found.")
        # return the configuration
        return self._term_cfgs[self._term_names.index(term_name)]

    """
    Helper functions.
    """

    def _prepare_terms(self):
        """Prepares a list of reward functions."""
        # parse remaining reward terms and decimate their information
        self._term_names: list[str] = list()
        self._term_cfgs: list[RewardTermCfg] = list()
        self._class_term_cfgs: list[RewardTermCfg] = list()

        # check if config is dict already
        if isinstance(self.cfg, dict):
            cfg_items = self.cfg.items()
        else:
            cfg_items = self.cfg.__dict__.items()
        # iterate over all the terms
        for term_name, term_cfg in cfg_items:
            # check for non config
            if term_cfg is None:
                continue
            # check for valid config type
            if not isinstance(term_cfg, RewardTermCfg):
                raise TypeError(
                    f"Configuration for the term '{term_name}' is not of type RewardTermCfg."
                    f" Received: '{type(term_cfg)}'."
                )
            # check for valid weight type
            if not isinstance(term_cfg.weight, (float, int)):
                raise TypeError(
                    f"Weight for the term '{term_name}' is not of type float or int."
                    f" Received: '{type(term_cfg.weight)}'."
                )
            # resolve common parameters
            self._resolve_common_term_cfg(term_name, term_cfg, min_argc=1)
            # add function to list
            self._term_names.append(term_name)
            self._term_cfgs.append(term_cfg)
            # check if the term is a class
            if isinstance(term_cfg.func, ManagerTermBase):
                self._class_term_cfgs.append(term_cfg)
