"""
Optional memory diagnostics for long-running training (CPU RSS, worker tree, CUDA, tracemalloc).

YAML (all optional except interval to enable):
  memory_debug_interval: 2000          # 0 = disabled
  memory_debug_tracemalloc: false     # true = on RSS spike, diff Python allocs (heavier)
  memory_debug_growth_mb: 50          # RSS delta since last tick → tracemalloc diff (if enabled)
  memory_debug_include_children: true  # sum DataLoader worker RSS; pip install psutil

When RSS keeps climbing, set memory_debug_interval: 1000–5000 and memory_debug_tracemalloc: true;
logs will show file:line growth (often lists, caches, or Arrow/Python conversions).
"""

from __future__ import annotations

import gc
import logging
import sys
import tracemalloc

logger = logging.getLogger(__name__)


def current_rss_mb() -> float:
    """Resident set size in MiB for this process."""
    try:
        with open("/proc/self/status", encoding="utf-8") as f:
            for line in f:
                if line.startswith("VmRSS:"):
                    parts = line.split()
                    return float(parts[1]) / 1024.0  # KiB → MiB
    except OSError:
        pass
    try:
        import psutil

        return psutil.Process().memory_info().rss / (1024.0 * 1024.0)
    except ImportError:
        import resource

        rss = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
        if sys.platform == "darwin":
            return float(rss) / (1024.0 * 1024.0)
        return float(rss) / 1024.0


def current_rss_mb_with_children() -> float:
    """This process plus all descendants (e.g. DataLoader workers)."""
    total = current_rss_mb()
    try:
        import psutil

        p = psutil.Process()
        for c in p.children(recursive=True):
            try:
                total += c.memory_info().rss / (1024.0 * 1024.0)
            except (psutil.NoSuchProcess, psutil.AccessDenied):
                pass
        return total
    except ImportError:
        return total


def cuda_mem_mb() -> tuple[float, float]:
    """Allocated and reserved CUDA memory (MiB) for current device."""
    try:
        import torch

        if not torch.cuda.is_available():
            return 0.0, 0.0
        return (
            torch.cuda.memory_allocated() / (1024.0 * 1024.0),
            torch.cuda.memory_reserved() / (1024.0 * 1024.0),
        )
    except Exception:
        return 0.0, 0.0


class MemoryDebugSession:
    """RSS / CUDA logging; optional tracemalloc diff only when RSS jumps (cheap steady state)."""

    def __init__(
        self,
        rank: int,
        use_tracemalloc: bool = False,
        growth_alert_mb: float = 50.0,
        include_children: bool = True,
    ):
        self.rank = rank
        self.use_tracemalloc = use_tracemalloc
        self.growth_alert_mb = growth_alert_mb
        self.include_children = include_children
        self._prev_snapshot: tracemalloc.Snapshot | None = None
        self._prev_rss_mb: float | None = None
        self._started = False

    def _rss(self) -> float:
        if self.include_children:
            return current_rss_mb_with_children()
        return current_rss_mb()

    def start(self) -> None:
        if self._started:
            return
        self._started = True
        if self.use_tracemalloc:
            try:
                tracemalloc.start(25)
            except RuntimeError:
                logger.warning("[memdbg] tracemalloc was already started; continuing")
            self._prev_snapshot = tracemalloc.take_snapshot()
        self._prev_rss_mb = self._rss()

    def tick(self, step: int, force_tracemalloc_diff: bool = False) -> None:
        if not self._started:
            self.start()

        rss = self._rss()
        alloc_mb, res_mb = cuda_mem_mb()
        delta_rss = None if self._prev_rss_mb is None else rss - self._prev_rss_mb

        scope = "rss_tree_mib" if self.include_children else "rss_self_mib"
        if delta_rss is not None:
            logger.info(
                f"[memdbg rank={self.rank}] step={step} {scope}={rss:.1f} "
                f"delta_since_last_tick_mib={delta_rss:+.1f} "
                f"cuda_alloc_mib={alloc_mb:.1f} cuda_reserved_mib={res_mb:.1f}"
            )
        else:
            logger.info(
                f"[memdbg rank={self.rank}] step={step} {scope}={rss:.1f} "
                f"cuda_alloc_mib={alloc_mb:.1f} cuda_reserved_mib={res_mb:.1f}"
            )
        self._prev_rss_mb = rss

        if not self.use_tracemalloc:
            gc.collect()
            return

        growth = delta_rss is not None and delta_rss >= self.growth_alert_mb
        if growth or force_tracemalloc_diff:
            snap = tracemalloc.take_snapshot()
            if self._prev_snapshot is not None:
                stats = snap.compare_to(self._prev_snapshot, "lineno", cumulative=True)
                lines = [f"[memdbg rank={self.rank}] tracemalloc top growth (since last snapshot):"]
                for i, st in enumerate(stats[:25], 1):
                    lines.append(f"  {i}. {st}")
                logger.warning("\n".join(lines))
            self._prev_snapshot = snap

        gc.collect()