"""Timeout-resilient, method-priority job queue for the training Space.

Why a queue
-----------
Training calls are gated by ``@spaces.GPU``: the GPU is only attached while a
call runs. If several training requests arrive at once — or a client times out
mid-training — the requests must not be lost. They are held in this queue and
processed later, in method-priority order, as the GPU becomes available.

Ordering (the requested behaviour)
---------------------------------
* **Method priority:** all **SFT** jobs run first, then all **DPO**, then all
  **KTO**.  If 5 SFT and 6 DPO requests arrive, every SFT job is drained
  before any DPO job starts.
* **FIFO within a method:** earlier requests of the same method run first.
* **Timeout-resilient:** the queue lives in RAM (and, optionally, mirrored to
  the bucket), so a *client-side* timeout does not drop a request — the worker
  keeps it queued and trains it when the GPU is next available.

Persistence
----------
The raw training *data* is not persisted to the bucket by default (per the
Space's "no data persistence" design). The queue is held in RAM, which
survives a client timeout (the Space process keeps running while a client
waits/abandons). Set ``QUEUE_PERSIST=true`` to also mirror queued jobs to the
bucket so they survive a Space *restart* too.
"""

from __future__ import annotations

import itertools
import time
from dataclasses import dataclass, field
from typing import Optional

# Method priority: lower runs first. SFT first, then DPO, then KTO. Unknown
# methods sort last.
METHOD_PRIORITY = {"sft": 0, "dpo": 1, "kto": 2}

# A monotonic submission counter, used for stable FIFO ordering within a method.
_seq = itertools.count(1)

# A module-level lock: the RAM queue is shared between the (fast) submit
# callback and the (slow, GPU) worker callback, which Gradio runs in separate
# threads.
import threading

_lock = threading.Lock()


@dataclass
class Job:
    """A single queued training request: a method + the raw uploaded rows."""

    method: str
    rows: list
    submitted_at: float = field(default_factory=time.time)
    seq: int = 0
    job_id: str = ""

    def __post_init__(self) -> None:
        self.seq = next(_seq)
        self.job_id = f"j{self.seq:06d}"
        self.method = self.method.lower()

    def as_dict(self) -> dict:
        return {
            "job_id": self.job_id,
            "method": self.method,
            "submitted_at": self.submitted_at,
            "n_examples": len(self.rows),
        }


class JobQueue:
    """An in-RAM, method-priority, FIFO-within-method job queue.

    Optional bucket persistence (``QUEUE_PERSIST=true`` + a ``BUCKET_ID``)
    mirrors the queue to the bucket so it survives a Space restart.
    """

    def __init__(self, bucket_id: str = "", persist: bool = False):
        self._bucket_id = bucket_id
        self._persist = bool(persist and bucket_id)
        self._jobs: list[Job] = []

    # -- submission ------------------------------------------------------- #
    def submit(self, method: str, rows: list) -> Job:
        """Enqueue a request and return its handle. Fast — no GPU, no
        training; this is what makes a client timeout harmless (the request is
        already cached before the call returns)."""
        job = Job(method=method.lower(), rows=list(rows))
        with _lock:
            self._jobs.append(job)
        if self._persist:
            self._mirror(job, add=True)
        return job

    # -- draining --------------------------------------------------------- #
    def pop(self) -> Optional[Job]:
        """Pop and return the highest-priority pending job (method priority,
        then FIFO), or ``None`` if the queue is empty."""
        with _lock:
            if not self._jobs:
                return None
            job = self._sorted()[0]
            self._jobs.remove(job)
        if self._persist:
            self._mirror(job, add=False)
        return job

    def drain(self, max_jobs: int = 0):
        """Yield pending jobs in execution order (method priority, then FIFO),
        up to ``max_jobs`` (0 = no cap). Each yielded job is removed from the
        queue as it is popped, so the queue is drained as the worker runs."""
        n = 0
        while True:
            job = self.pop()
            if job is None:
                break
            yield job
            n += 1
            if max_jobs and n >= max_jobs:
                return

    # -- inspection ------------------------------------------------------- #
    def pending_count(self) -> int:
        with _lock:
            return len(self._jobs)

    def status(self) -> dict:
        with _lock:
            order = self._sorted()
            counts: dict = {}
            for j in self._jobs:
                counts[j.method] = counts.get(j.method, 0) + 1
            return {
                "pending": len(self._jobs),
                "by_method": counts,
                "persisted": self._persist,
                "next": (f"{order[0].method} · {order[0].job_id}" if order else None),
                "order": [f"{j.method}·{j.job_id}" for j in order[:12]],
            }

    # -- helpers ---------------------------------------------------------- #
    def _sorted(self) -> list[Job]:
        """Order the current queue by method priority, then FIFO (seq)."""
        return sorted(
            self._jobs,
            key=lambda j: (METHOD_PRIORITY.get(j.method, 99), j.seq),
        )

    def _mirror(self, job: Job, add: bool) -> None:
        """Best-effort bucket mirror (opt-in). Never raises into the caller."""
        try:
            from store import delete_job, save_job

            if add:
                save_job(self._bucket_id, job)
            else:
                delete_job(self._bucket_id, job.job_id)
        except Exception:  # pragma: no cover
            pass


# A module-level queue instance shared by the Space. It is (re)configured
# from the env on first use via ``init_queue``.
_QUEUE: Optional[JobQueue] = None


def init_queue(bucket_id: str = "", persist: bool = False) -> JobQueue:
    """(Re)create the module-level queue. Called once at Space startup."""
    global _QUEUE
    _QUEUE = JobQueue(bucket_id=bucket_id, persist=persist)
    return _QUEUE


def get_queue() -> JobQueue:
    """Return the module-level queue, creating it lazily if needed."""
    global _QUEUE
    if _QUEUE is None:
        import os

        bucket_id = (os.environ.get("BUCKET_ID") or "").strip()
        persist = (os.environ.get("QUEUE_PERSIST") or "").lower() in ("1", "true", "yes")
        _QUEUE = JobQueue(bucket_id=bucket_id, persist=persist)
    return _QUEUE