"""Jetson memory budget evaluator for NFT-LIM-01 (AZ-440 / AC-NEW-13).

Tier-2 only scenario. Runs a 30 s warm-up + 5 min Derkachi replay; the
runner samples memory at 1 Hz from two boundary observers:

* ``/proc/<sut_pid>/status`` ``VmRSS`` (the SUT process resident set);
* ``tegrastats`` (system-level memory used).

Both streams are evaluated against the Plan-A budgets by default
(steady ``p50 ≤ 4.5 GiB``, peak ``max ≤ 5.0 GiB``). Plan B
(``steady ≤ 6.0 GiB``, ``peak ≤ 6.5 GiB``) is gated behind the
``MEMORY_PLAN=B`` env flag — the scenario test passes the active plan
into ``evaluate(...)``; this module exposes both as named ``Plan``
constants and never reads the environment itself.

AC-4 (no OOM kills) is evaluated from a ``Sequence[OomEvent]`` projected
out of ``dmesg --since "<run_start>"`` by the scenario.

Public-boundary discipline: does NOT import any
``src/gps_denied_onboard`` symbol. All inputs are pre-projected typed
records (samples / OOM events).
"""

from __future__ import annotations

import csv
from dataclasses import dataclass, field
from enum import Enum
from math import floor
from pathlib import Path
from typing import Sequence

GIB_BYTES = 1024**3


class Plan(str, Enum):
    """Active memory budget plan per AC-5 (Plan A default, Plan B gated)."""

    PLAN_A = "plan-a"
    PLAN_B = "plan-b"


@dataclass(frozen=True)
class PlanBudgets:
    """A pair (steady, peak) budget in bytes for one Plan."""

    steady_bytes: int
    peak_bytes: int

    @classmethod
    def for_plan(cls, plan: Plan) -> "PlanBudgets":
        if plan is Plan.PLAN_A:
            return cls(
                steady_bytes=int(4.5 * GIB_BYTES),
                peak_bytes=int(5.0 * GIB_BYTES),
            )
        if plan is Plan.PLAN_B:
            return cls(
                steady_bytes=int(6.0 * GIB_BYTES),
                peak_bytes=int(6.5 * GIB_BYTES),
            )
        raise ValueError(f"unknown memory plan: {plan!r}")


@dataclass(frozen=True)
class MemorySample:
    """One memory sample at a monotonic timestamp.

    ``vmrss_bytes`` is the ``/proc/<pid>/status`` ``VmRSS`` value
    converted to bytes; ``tegrastats_used_bytes`` is the system-level
    used-RAM figure parsed from one ``tegrastats`` line. Both are
    captured at the same nominal sample tick — they MAY diverge
    slightly because the two sources poll at different cadences, which
    is why the AC budgets apply to each stream independently.
    """

    monotonic_ms: int
    vmrss_bytes: int
    tegrastats_used_bytes: int


@dataclass(frozen=True)
class OomEvent:
    """One OOM-killer line captured from ``dmesg``.

    ``snippet`` is the matched dmesg line (truncated to ≤200 chars in
    CSV evidence). ``monotonic_ms`` is the runner's projection of the
    kernel timestamp onto the monotonic clock — may be ``None`` if the
    runner could not align it (the verdict still fails AC-4).
    """

    monotonic_ms: int | None
    snippet: str


@dataclass(frozen=True)
class StreamStats:
    """p50 + max for one memory stream over the post-warm-up window."""

    sample_count: int
    p50_bytes: int | None
    max_bytes: int | None

    def passes_steady(self, budget_bytes: int) -> bool:
        return self.p50_bytes is not None and self.p50_bytes <= budget_bytes

    def passes_peak(self, budget_bytes: int) -> bool:
        return self.max_bytes is not None and self.max_bytes <= budget_bytes


@dataclass(frozen=True)
class MemoryBudgetReport:
    """Aggregate NFT-LIM-01 verdict for one Tier-2 run."""

    plan: Plan
    budgets: PlanBudgets
    warm_up_ms: int
    window_end_ms: int
    vmrss: StreamStats
    tegrastats: StreamStats
    oom_events: Sequence[OomEvent] = field(default_factory=tuple)

    @property
    def passes_steady_state(self) -> bool:
        # AC-2 — BOTH streams must satisfy steady budget.
        return self.vmrss.passes_steady(self.budgets.steady_bytes) and (
            self.tegrastats.passes_steady(self.budgets.steady_bytes)
        )

    @property
    def passes_peak(self) -> bool:
        # AC-3 — VmRSS peak ≤ peak budget. tegrastats system-level peak is
        # informational only; AC-3 specifies VmRSS as the gating stream.
        return self.vmrss.passes_peak(self.budgets.peak_bytes)

    @property
    def passes_no_oom(self) -> bool:
        # AC-4 — zero OOM-killer entries since run_start.
        return len(self.oom_events) == 0

    @property
    def passes(self) -> bool:
        return self.passes_steady_state and self.passes_peak and self.passes_no_oom


def _percentile_int(values: Sequence[int], q: float) -> int | None:
    """Linear-interpolation percentile rounded to int bytes.

    Returns ``None`` for empty input so the caller distinguishes the
    no-data case. Accepts any real ``q`` in [0, 100]; outside that range
    is a programmer error.
    """
    if not 0.0 <= q <= 100.0:
        raise ValueError(f"percentile q must be in [0, 100], got {q!r}")
    if not values:
        return None
    ordered = sorted(values)
    if len(ordered) == 1:
        return int(ordered[0])
    rank = (q / 100.0) * (len(ordered) - 1)
    lo = floor(rank)
    hi = min(lo + 1, len(ordered) - 1)
    frac = rank - lo
    return int(round(ordered[lo] + (ordered[hi] - ordered[lo]) * frac))


def _post_warmup_window(
    samples: Sequence[MemorySample], warm_up_ms: int
) -> list[MemorySample]:
    """Drop samples whose timestamp is inside the warm-up window."""
    if warm_up_ms < 0:
        raise ValueError(f"warm_up_ms must be >= 0 (was {warm_up_ms!r})")
    if not samples:
        return []
    first = min(s.monotonic_ms for s in samples)
    cutoff = first + warm_up_ms
    return [s for s in samples if s.monotonic_ms >= cutoff]


def _stream_stats(values: Sequence[int]) -> StreamStats:
    return StreamStats(
        sample_count=len(values),
        p50_bytes=_percentile_int(values, 50.0),
        max_bytes=max(values) if values else None,
    )


def evaluate(
    samples: Sequence[MemorySample],
    oom_events: Sequence[OomEvent],
    *,
    plan: Plan = Plan.PLAN_A,
    warm_up_ms: int = 30_000,
) -> MemoryBudgetReport:
    """Compute NFT-LIM-01 AC-2 + AC-3 + AC-4 verdict for one Tier-2 run."""
    budgets = PlanBudgets.for_plan(plan)
    post_warmup = _post_warmup_window(samples, warm_up_ms)
    vmrss_values = [s.vmrss_bytes for s in post_warmup]
    tegrastats_values = [s.tegrastats_used_bytes for s in post_warmup]
    window_end_ms = max((s.monotonic_ms for s in post_warmup), default=warm_up_ms)
    return MemoryBudgetReport(
        plan=plan,
        budgets=budgets,
        warm_up_ms=warm_up_ms,
        window_end_ms=window_end_ms,
        vmrss=_stream_stats(vmrss_values),
        tegrastats=_stream_stats(tegrastats_values),
        oom_events=tuple(oom_events),
    )


def write_csv_evidence(out_path: Path, report: MemoryBudgetReport) -> Path:
    """One-row evidence file naming the AC-2/3/4 verdict + percentiles."""
    out_path.parent.mkdir(parents=True, exist_ok=True)
    r = report
    with out_path.open("w", newline="") as fh:
        writer = csv.writer(fh)
        writer.writerow(
            [
                "plan",
                "warm_up_ms",
                "window_end_ms",
                "vmrss_sample_count",
                "vmrss_p50_bytes",
                "vmrss_max_bytes",
                "tegrastats_sample_count",
                "tegrastats_p50_bytes",
                "tegrastats_max_bytes",
                "steady_budget_bytes",
                "peak_budget_bytes",
                "ac2_steady_passes",
                "ac3_peak_passes",
                "ac4_no_oom_passes",
                "oom_event_count",
                "passes",
            ]
        )
        writer.writerow(
            [
                r.plan.value,
                r.warm_up_ms,
                r.window_end_ms,
                r.vmrss.sample_count,
                "" if r.vmrss.p50_bytes is None else r.vmrss.p50_bytes,
                "" if r.vmrss.max_bytes is None else r.vmrss.max_bytes,
                r.tegrastats.sample_count,
                "" if r.tegrastats.p50_bytes is None else r.tegrastats.p50_bytes,
                "" if r.tegrastats.max_bytes is None else r.tegrastats.max_bytes,
                r.budgets.steady_bytes,
                r.budgets.peak_bytes,
                "true" if r.passes_steady_state else "false",
                "true" if r.passes_peak else "false",
                "true" if r.passes_no_oom else "false",
                len(r.oom_events),
                "true" if r.passes else "false",
            ]
        )
    return out_path


def write_oom_events_csv(
    out_path: Path, oom_events: Sequence[OomEvent]
) -> Path:
    """Per-OOM-event CSV (one row per event) for evidence."""
    out_path.parent.mkdir(parents=True, exist_ok=True)
    with out_path.open("w", newline="") as fh:
        writer = csv.writer(fh)
        writer.writerow(["index", "monotonic_ms", "snippet"])
        for i, ev in enumerate(oom_events):
            snippet = ev.snippet if len(ev.snippet) <= 200 else ev.snippet[:200]
            writer.writerow(
                [
                    i,
                    "" if ev.monotonic_ms is None else ev.monotonic_ms,
                    snippet,
                ]
            )
    return out_path