#!/usr/bin/env python3
"""Amdahl sensitivity study only: 0.33.8 measured baseline, 0.34.0 not measured.

No synthetic RPS is described as benchmarked RustProxy throughput. Amdahl uses
RPS_new = RPS_old / (1 - eligible_cost_fraction * fraction_eliminated).
"""
from __future__ import annotations

import argparse
import json
from pathlib import Path

# Verified medians reproduced from the supplied 0.33.8 evidence. Cache OFF.
BASELINE = [
    ("reverse_proxy", 1040, 29334.12, 170610.16, False),
    ("reverse_proxy", 65536, 20735.07, 35393.29, False),
    ("reverse_proxy", 1048576, 4461.19, 2730.23, False),
    ("www", 1040, 24906.20, 351605.13, False),
    ("www", 65536, 20856.67, 203709.91, True),
    ("www", 1048576, 2833.71, 12611.49, True),
]

# WWW scenarios: share of per-request service time due to file copy/read;
# assume sendfile removes HALF of that part, not the full service time.
WWW_SHARES = {"low": 0.20, "middle": 0.40, "high": 0.60}
COPY_COST_REMOVED = 0.50
# Proxy independent optimization: hypothetical reduction in *total* request
# service time, modeling removal of redundant response-frame mutex, nothing else.
PROXY_TIME_SAVED = {"low": 0.01, "middle": 0.03, "high": 0.05}


def run() -> dict:
    items = []
    for kind, payload_bytes, rust_rps, nginx_rps, eligible in BASELINE:
        baseline_ratio = rust_rps / nginx_rps
        row = {
            "kind": kind,
            "bytes": payload_bytes,
            "baseline_version": "0.33.8",
            "baseline_rust_rps": rust_rps,
            "baseline_nginx_rps": nginx_rps,
            "baseline_of_nginx_pct": round(100 * baseline_ratio, 2),
            "factor_to_match_nginx": round(nginx_rps / rust_rps, 2),
            "sendfile_eligible_only_if_plain_linux_http1_1_no_cache_no_compression": eligible,
            "scenarios": {},
        }
        for level in ("low", "middle", "high"):
            if kind == "www" and eligible:
                saved_fraction = WWW_SHARES[level] * COPY_COST_REMOVED
            elif kind == "reverse_proxy":
                saved_fraction = PROXY_TIME_SAVED[level]
            else:
                saved_fraction = 0.0
            simulated_rps = rust_rps / (1.0 - saved_fraction)
            row["scenarios"][level] = {
                "modeled_total_time_saved_pct": round(100 * saved_fraction, 2),
                "simulated_rps": round(simulated_rps),
                "simulated_rps_gain_pct": round(100 * (simulated_rps / rust_rps - 1), 2),
                "simulated_of_nginx_pct": round(100 * simulated_rps / nginx_rps, 2),
                "simulated_remaining_gap_to_nginx_pct_points": round(
                    100 * (1 - simulated_rps / nginx_rps), 2
                ),
            }
        items.append(row)
    return {
        "kind": "HYPOTHETICAL_AMDAHL_SENSITIVITY_NOT_A_BENCHMARK",
        "comparison": "Existing 0.33.8 measurements (5 runs, cache off) vs measured nginx",
        "not_measured": "0.34.0 server performance and sendfile syscall/runtime correctness",
        "conditions": [
            "Identical CPU and network assumptions to supplied 0.33.8 baseline",
            "WWW zero-copy is limited to Linux, cleartext HTTP/1.1, GET >=64KiB, no cache, range, transform, compression or TLS",
            "WWW low/middle/high: file-copy contributes 20%/40%/60% of total request time; modeled sendfile eliminates 50% of that component",
            "Reverse proxy low/middle/high: removing response-frame mutex saves a hypothetical 1%/3%/5% of total service time",
            "These fractions are chosen sensitivity parameters; not measured or inferred from profiling",
            "No change is assumed for WWW 1040B or out-of-scope protocol paths",
            "No network saturation, TLS record processing, queueing, origin latency, filesystem cache misses, CPU contention or concurrency effects modeled",
            "No additional speedup due to cache-retention changes is assumed",
        ],
        "formula": "RPS_sim = RPS_0.33.8 / (1 - fraction_of_total_service_time_eliminated)",
        "entries": items,
    }


def main() -> None:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--output", type=Path, help="write JSON to this file")
    args = parser.parse_args()
    payload = json.dumps(run(), indent=2, ensure_ascii=False) + "\n"
    if args.output:
        args.output.parent.mkdir(parents=True, exist_ok=True)
        args.output.write_text(payload)
        print(f"wrote {args.output}")
    else:
        print(payload)


if __name__ == "__main__":
    main()