#!/usr/bin/env python3
"""
analyze_epoch_tail_csv.py

Compute correct tail proxy statistics from Phase 51/52 epoch CSV.

Input CSV (from scripts/soak_mixed_single_process.sh):
  epoch,iter,throughput_ops_s,rss_mb

Key points:
- Tail in throughput space is the *LOW* tail (p1/p0.1), not p99.
- Tail in latency space is the *HIGH* tail (p99/p999), computed from per-epoch latency values:
    latency_ns = 1e9 / throughput_ops_s
- Do NOT compute latency percentiles as 1e9 / throughput_percentile (nonlinear + order inversion).
"""

from __future__ import annotations

import argparse
import csv
import math
from dataclasses import dataclass
from typing import List, Tuple


def percentile(sorted_vals: List[float], p: float) -> float:
    if not sorted_vals:
        return float("nan")
    if p <= 0:
        return sorted_vals[0]
    if p >= 100:
        return sorted_vals[-1]
    # linear interpolation between closest ranks
    k = (len(sorted_vals) - 1) * (p / 100.0)
    f = math.floor(k)
    c = math.ceil(k)
    if f == c:
        return sorted_vals[int(k)]
    d0 = sorted_vals[f] * (c - k)
    d1 = sorted_vals[c] * (k - f)
    return d0 + d1


@dataclass
class Stats:
    mean: float
    stdev: float
    cv: float
    p50: float
    p90: float
    p99: float
    p999: float
    p10: float
    p1: float
    p01: float
    minv: float
    maxv: float


def compute_stats(vals: List[float]) -> Stats:
    if not vals:
        nan = float("nan")
        return Stats(nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan)
    n = len(vals)
    mean = sum(vals) / n
    var = sum((v - mean) ** 2 for v in vals) / n
    stdev = math.sqrt(var)
    cv = (stdev / mean) if mean != 0 else float("nan")
    s = sorted(vals)
    return Stats(
        mean=mean,
        stdev=stdev,
        cv=cv,
        p50=percentile(s, 50),
        p90=percentile(s, 90),
        p99=percentile(s, 99),
        p999=percentile(s, 99.9),
        p10=percentile(s, 10),
        p1=percentile(s, 1),
        p01=percentile(s, 0.1),
        minv=s[0],
        maxv=s[-1],
    )


def read_csv(path: str) -> Tuple[List[float], List[float]]:
    thr: List[float] = []
    rss: List[float] = []
    with open(path, newline="") as f:
        reader = csv.DictReader(f)
        for row in reader:
            t = row.get("throughput_ops_s", "").strip()
            r = row.get("rss_mb", "").strip()
            if not t:
                continue
            try:
                thr.append(float(t))
            except ValueError:
                continue
            if r:
                try:
                    rss.append(float(r))
                except ValueError:
                    pass
    return thr, rss


def main() -> int:
    ap = argparse.ArgumentParser()
    ap.add_argument("csv", help="epoch CSV (from scripts/soak_mixed_single_process.sh)")
    args = ap.parse_args()

    thr, rss = read_csv(args.csv)
    thr_stats = compute_stats(thr)

    lat = [(1e9 / t) for t in thr if t > 0]
    lat_stats = compute_stats(lat)

    print(f"epochs={len(thr)}")
    print("")
    print("Throughput (ops/s) [NOTE: tail = low throughput]")
    print(f"  mean={thr_stats.mean:,.0f} stdev={thr_stats.stdev:,.0f} cv={thr_stats.cv*100:.2f}%")
    print(f"  p50={thr_stats.p50:,.0f} p10={thr_stats.p10:,.0f} p1={thr_stats.p1:,.0f} p0.1={thr_stats.p01:,.0f}")
    print(f"  min={thr_stats.minv:,.0f} max={thr_stats.maxv:,.0f}")
    print("")
    print("Latency proxy (ns/op) [NOTE: tail = high latency]")
    print(f"  mean={lat_stats.mean:,.2f} stdev={lat_stats.stdev:,.2f} cv={lat_stats.cv*100:.2f}%")
    print(f"  p50={lat_stats.p50:,.2f} p90={lat_stats.p90:,.2f} p99={lat_stats.p99:,.2f} p99.9={lat_stats.p999:,.2f}")
    print(f"  min={lat_stats.minv:,.2f} max={lat_stats.maxv:,.2f}")
    if rss:
        rss_stats = compute_stats(rss)
        print("")
        print("RSS (MB) [peak per epoch sample]")
        print(f"  mean={rss_stats.mean:,.2f} stdev={rss_stats.stdev:,.2f} cv={rss_stats.cv*100:.2f}%")
        print(f"  min={rss_stats.minv:,.2f} max={rss_stats.maxv:,.2f}")
    return 0


if __name__ == "__main__":
    raise SystemExit(main())