#!/usr/bin/env python3

# Copyright (c) Facebook, Inc. and its affiliates.
# All rights reserved.
#
# This source code is licensed under the BSD-style license found in the
# LICENSE file in the root directory of this source tree.
import sys
import uuid
from dataclasses import dataclass, field
from typing import Any, Callable, Dict, List, Optional, Tuple, Union

import torch.distributed.elastic.rendezvous.registry as rdzv_registry
from torch.distributed.elastic import events, metrics
from torch.distributed.elastic.agent.server.api import WorkerSpec
from torch.distributed.elastic.agent.server.local_elastic_agent import LocalElasticAgent
from torch.distributed.elastic.multiprocessing import SignalException, Std
from torch.distributed.elastic.multiprocessing.errors import ChildFailedError
from torch.distributed.elastic.rendezvous import RendezvousParameters
from torch.distributed.elastic.rendezvous.utils import parse_rendezvous_endpoint
from torch.distributed.elastic.utils.logging import get_logger

__all__ = ['LaunchConfig', 'elastic_launch', 'launch_agent']

logger = get_logger()


@dataclass
class LaunchConfig:
    """
    Creates a rendezvous config.

    Args:
        min_nodes: Minimum amount of nodes that the user function will
                        be launched on. Elastic agent ensures that the user
                        function start only when the min_nodes amount enters
                        the rendezvous.
        max_nodes: Maximum amount of nodes that the user function
                        will be launched on.
        nproc_per_node: On each node the elastic agent will launch
                            this amount of workers that will execute user
                            defined function.
        rdzv_backend: rdzv_backend to use in the rendezvous (zeus-adapter, etcd).
        rdzv_endpoint: The endpoint of the rdzv sync. storage.
        rdzv_configs: Key, value pair that specifies rendezvous specific configuration.
        rdzv_timeout: Legacy argument that specifies timeout for the rendezvous. It is going
            to be removed in future versions, see the note below. The default timeout is 900 seconds.
        run_id: The unique run id of the job (if not passed a unique one will be
                deduced from run environment - flow workflow id in flow - or auto generated).
        role: User defined role of the worker (defaults to "trainer").
        max_restarts: The maximum amount of restarts that elastic agent will conduct
                    on workers before failure.
        monitor_interval: The interval in seconds that is used by the elastic_agent
                        as a period of monitoring workers.
        start_method: The method is used by the elastic agent to start the
                    workers (spawn, fork, forkserver).
        log_dir: base log directory where log files are written. If not set,
                one is created in a tmp dir but NOT removed on exit.
        redirects: configuration to redirect stdout/stderr to log files.
                Pass a single ``Std`` enum to redirect all workers,
                or a mapping keyed by local_rank to selectively redirect.
        tee: configuration to "tee" stdout/stderr to console + log file.
        metrics_cfg: configuration to initialize metrics.
        local_addr: address of the local node if any. If not set, a lookup on the local
                machine's FQDN will be performed.
    ..note:
        `rdzv_timeout` is a legacy argument that will be removed in future.
        Set the timeout via `rdzv_configs['timeout']`

    """

    min_nodes: int
    max_nodes: int
    nproc_per_node: int
    run_id: str = ""
    role: str = "default_role"
    rdzv_endpoint: str = ""
    rdzv_backend: str = "etcd"
    rdzv_configs: Dict[str, Any] = field(default_factory=dict)
    rdzv_timeout: int = -1
    max_restarts: int = 3
    monitor_interval: float = 30
    start_method: str = "spawn"
    log_dir: Optional[str] = None
    redirects: Union[Std, Dict[int, Std]] = Std.NONE
    tee: Union[Std, Dict[int, Std]] = Std.NONE
    metrics_cfg: Dict[str, str] = field(default_factory=dict)
    local_addr: Optional[str] = None

    def __post_init__(self):
        default_timeout = 900
        if self.rdzv_timeout != -1:
            self.rdzv_configs["timeout"] = self.rdzv_timeout
        elif "timeout" not in self.rdzv_configs:
            self.rdzv_configs["timeout"] = default_timeout


class elastic_launch:
    """
    Launches an torchelastic agent on the container that invoked the entrypoint.

        1. Pass the ``entrypoint`` arguments as non ``kwargs`` (e.g. no named parameters)/
           ``entrypoint`` can be a function or a command.
        2. The return value is a map of each worker's output mapped
           by their respective global rank.

    Usage

    ::

    def worker_fn(foo):
        # ...

    def main():
        # entrypoint is a function.
        outputs = elastic_launch(LaunchConfig, worker_fn)(foo)
        # return rank 0's output
        return outputs[0]

        # entrypoint is a command and ``script.py`` is the python module.
        outputs = elastic_launch(LaunchConfig, "script.py")(args)
        outputs = elastic_launch(LaunchConfig, "python")("script.py")
    """

    def __init__(
        self,
        config: LaunchConfig,
        entrypoint: Union[Callable, str, None],
    ):
        self._config = config
        self._entrypoint = entrypoint

    def __call__(self, *args):
        return launch_agent(self._config, self._entrypoint, list(args))


def _get_entrypoint_name(
    entrypoint: Union[Callable, str, None], args: List[Any]
) -> str:
    """Retrive entrypoint name with the rule:
    1. If entrypoint is a function, use ``entrypont.__qualname__``.
    2. If entrypoint is a string, check its value:
        2.1 if entrypoint equals to ``sys.executable`` (like "python"), use the first element from ``args``
            which does not start with hifen letter (for example, "-u" will be skipped).
        2.2 otherwise, use ``entrypoint`` value.
    3. Otherwise, return empty string.
    """
    if isinstance(entrypoint, Callable):  # type: ignore[arg-type]
        return entrypoint.__name__  # type: ignore[union-attr]
    elif isinstance(entrypoint, str):
        if entrypoint == sys.executable:
            return next((arg for arg in args if arg[0] != "-"), "")
        else:
            return entrypoint
    else:
        return ""


def _get_addr_and_port(
    rdzv_parameters: RendezvousParameters,
) -> Tuple[Optional[str], Optional[int]]:
    if rdzv_parameters.backend != "static":
        return (None, None)
    endpoint = rdzv_parameters.endpoint
    endpoint = endpoint.strip()
    if not endpoint:
        raise ValueError(
            "Endpoint is missing in endpoint. Try to add --master-addr and --master-port"
        )
    master_addr, master_port = parse_rendezvous_endpoint(endpoint, default_port=-1)
    if master_port == -1:
        raise ValueError(
            f"port is missing in endpoint: {endpoint}. Try to specify --master-port"
        )
    return (master_addr, master_port)


def launch_agent(
    config: LaunchConfig,
    entrypoint: Union[Callable, str, None],
    args: List[Any],
) -> Dict[int, Any]:
    if not config.run_id:
        run_id = str(uuid.uuid4().int)
        logger.warning(f"config has no run_id, generated a random run_id: {run_id}")
        config.run_id = run_id

    entrypoint_name = _get_entrypoint_name(entrypoint, args)

    logger.info(
        f"Starting elastic_operator with launch configs:\n"
        f"  entrypoint       : {entrypoint_name}\n"
        f"  min_nodes        : {config.min_nodes}\n"
        f"  max_nodes        : {config.max_nodes}\n"
        f"  nproc_per_node   : {config.nproc_per_node}\n"
        f"  run_id           : {config.run_id}\n"
        f"  rdzv_backend     : {config.rdzv_backend}\n"
        f"  rdzv_endpoint    : {config.rdzv_endpoint}\n"
        f"  rdzv_configs     : {config.rdzv_configs}\n"
        f"  max_restarts     : {config.max_restarts}\n"
        f"  monitor_interval : {config.monitor_interval}\n"
        f"  log_dir          : {config.log_dir}\n"
        f"  metrics_cfg      : {config.metrics_cfg}\n"
    )

    rdzv_parameters = RendezvousParameters(
        backend=config.rdzv_backend,
        endpoint=config.rdzv_endpoint,
        run_id=config.run_id,
        min_nodes=config.min_nodes,
        max_nodes=config.max_nodes,
        local_addr=config.local_addr,
        **config.rdzv_configs,
    )

    master_addr, master_port = _get_addr_and_port(rdzv_parameters)

    spec = WorkerSpec(
        role=config.role,
        local_world_size=config.nproc_per_node,
        entrypoint=entrypoint,
        args=tuple(args),
        rdzv_handler=rdzv_registry.get_rendezvous_handler(rdzv_parameters),
        max_restarts=config.max_restarts,
        monitor_interval=config.monitor_interval,
        redirects=config.redirects,
        tee=config.tee,
        master_addr=master_addr,
        master_port=master_port,
        local_addr=config.local_addr,
    )

    agent = LocalElasticAgent(
        spec=spec, start_method=config.start_method, log_dir=config.log_dir
    )

    shutdown_rdzv = True
    try:
        metrics.initialize_metrics(metrics.MetricsConfig(config.metrics_cfg))

        result = agent.run()
        # records that agent.run() has succeeded NOT that workers have succeeded
        events.record(agent.get_event_succeeded())

        if result.is_failed():
            # ChildFailedError is treated specially by @record
            # if the error files for the failed children exist
            # @record will copy the first error (root cause)
            # to the error file of the launcher process.
            raise ChildFailedError(
                name=entrypoint_name,
                failures=result.failures,
            )

        return result.return_values
    except ChildFailedError:
        raise
    except SignalException:
        # when the agent dies with a signal do NOT shutdown the rdzv_handler
        # since this closes the rendezvous on this rdzv_id permanently and
        # prevents any additional scaling events
        shutdown_rdzv = False
        events.record(agent.get_event_failed())
        raise
    except Exception:
        events.record(agent.get_event_failed())
        raise
    finally:
        if shutdown_rdzv:
            spec.rdzv_handler.shutdown()