"""A router's latency is each scrape's own percentile (#5741): the rise in
Traefik's histogram since the last scrape, every label set's buckets summed
per `le`. Read as it stood, the histogram gave a percentile of every
response since Traefik started, which barely moved (nextcloud's flat 100 ms
p95)."""
import pytest

from plugins.traefik.scraper import compute_router_metrics, service_buckets

BUCKET = "traefik_service_request_duration_seconds_bucket"
EDGES = ("0.1", "0.3", "1.2", "5", "+Inf")       # Traefik's default buckets


def _hist(service, code, method, counts):
    """{labels: count} for one label set's cumulative buckets, in EDGES order."""
    return {frozenset({"service": service, "code": code, "method": method, "le": le}.items()): n
            for le, n in zip(EDGES, counts)}


def _scrape(*sets):
    out = {}
    for s in sets:
        out.update(_hist(*s))
    return {BUCKET: out}


def test_latency_reads_the_responses_since_the_last_scrape_not_since_start():
    # A million fast responses since start, then 100 slow ones (all 0.3–1.2 s).
    before = _scrape(("cloud@docker", "200", "GET", (1_000_000, 1_000_000, 1_000_000, 1_000_000, 1_000_000)))
    after = _scrape(("cloud@docker", "200", "GET", (1_000_000, 1_000_000, 1_000_100, 1_000_100, 1_000_100)))
    got = compute_router_metrics(after, before, 60.0)["cloud@docker"]
    assert 300.0 < got["latency_p50_ms"] < 1200.0
    assert got["latency_p95_ms"] == pytest.approx(300.0 + 0.95 * 900.0)


def test_every_label_set_counts_toward_one_histogram():
    # GET answered fast and POST slowly: 90 + 10 responses, so p95 is a POST's.
    before = _scrape(("app@docker", "200", "GET", (0, 0, 0, 0, 0)),
                     ("app@docker", "200", "POST", (0, 0, 0, 0, 0)))
    after = _scrape(("app@docker", "200", "GET", (90, 90, 90, 90, 90)),
                    ("app@docker", "200", "POST", (0, 0, 0, 10, 10)))
    assert service_buckets(after[BUCKET], before[BUCKET], "app@docker") == [
        (0.1, 90.0), (0.3, 90.0), (1.2, 90.0), (5.0, 100.0), (float("inf"), 100.0)]
    got = compute_router_metrics(after, before, 60.0)["app@docker"]
    assert got["latency_p50_ms"] < 100.0
    assert 1200.0 < got["latency_p95_ms"] < 5000.0


def test_an_idle_scrape_and_the_first_scrape_have_no_latency():
    still = _scrape(("idle@docker", "200", "GET", (50, 60, 60, 60, 60)))
    idle = compute_router_metrics(still, still, 60.0)["idle@docker"]
    first = compute_router_metrics(still, None, 60.0)["idle@docker"]
    for got in (idle, first):
        assert got["latency_p50_ms"] is None and got["latency_p95_ms"] is None
        assert got["latency_p99_ms"] is None


def test_a_percentile_past_the_last_edge_reads_as_at_least_that_edge():
    before = _scrape(("ws@docker", "101", "GET", (0, 0, 0, 0, 0)))
    after = _scrape(("ws@docker", "101", "GET", (0, 0, 0, 0, 20)))     # all longer than 5 s
    assert compute_router_metrics(after, before, 60.0)["ws@docker"]["latency_p95_ms"] == 5000.0