import http from "k6/http";
import { check, sleep } from "k6";
import { Counter, Rate, Trend } from "k6/metrics";

const BASE_URL = (__ENV.BASE_URL || "http://host.docker.internal").replace(
  /\/$/,
  "",
);
const API_URL = `${BASE_URL}/api/v1`;
const FLAG_KEY = __ENV.FLAG_KEY || "";
const SUBJECT_PREFIX = __ENV.SUBJECT_PREFIX || "k6_subject";
const SUBJECT_COUNTRY = __ENV.SUBJECT_COUNTRY || "US";
const SUBJECT_POOL = Number(__ENV.SUBJECT_POOL || "20000");
const THINK_TIME_SECONDS = Number(__ENV.THINK_TIME_SECONDS || "0");

const START_RATE = Number(__ENV.START_RPS || "20");
const RAMP_UP_RATE = Number(__ENV.RAMP_UP_RPS || "200");
const HOLD_RATE = Number(__ENV.HOLD_RPS || "200");
const PRE_ALLOCATED_VUS = Number(__ENV.PRE_ALLOCATED_VUS || "100");
const MAX_VUS = Number(__ENV.MAX_VUS || "600");

const RAMP_UP_DURATION = __ENV.RAMP_UP_DURATION || "30s";
const HOLD_DURATION = __ENV.HOLD_DURATION || "2m";
const RAMP_DOWN_DURATION = __ENV.RAMP_DOWN_DURATION || "20s";

const THRESHOLD_ERROR_RATE = __ENV.THRESHOLD_ERROR_RATE || "0.01";
const THRESHOLD_P95_MS = __ENV.THRESHOLD_P95_MS || "250";
const THRESHOLD_P99_MS = __ENV.THRESHOLD_P99_MS || "500";

if (!FLAG_KEY) {
  throw new Error("FLAG_KEY is required");
}

export const options = {
  scenarios: {
    decide_hot_path: {
      executor: "ramping-arrival-rate",
      startRate: START_RATE,
      timeUnit: "1s",
      preAllocatedVUs: PRE_ALLOCATED_VUS,
      maxVUs: MAX_VUS,
      stages: [
        { target: RAMP_UP_RATE, duration: RAMP_UP_DURATION },
        { target: HOLD_RATE, duration: HOLD_DURATION },
        { target: 0, duration: RAMP_DOWN_DURATION },
      ],
    },
  },
  thresholds: {
    http_req_failed: [`rate<${THRESHOLD_ERROR_RATE}`],
    http_req_duration: [
      `p(95)<${THRESHOLD_P95_MS}`,
      `p(99)<${THRESHOLD_P99_MS}`,
    ],
    decide_status_200_rate: ["rate>0.99"],
  },
  summaryTrendStats: [
    "avg",
    "min",
    "med",
    "p(90)",
    "p(95)",
    "p(99)",
    "max",
  ],
};

const decideStatus200Rate = new Rate("decide_status_200_rate");
const decideAssignedRate = new Rate("decide_experiment_assigned_rate");
const decideRequests = new Counter("decide_requests_total");
const decideDuration = new Trend("decide_request_duration_ms", true);

function buildSubjectId() {
  const idx = ((__ITER * 104729 + __VU * 8191) % SUBJECT_POOL) + 1;
  return `${SUBJECT_PREFIX}_${idx}`;
}

function buildPayload() {
  return JSON.stringify({
    subject_id: buildSubjectId(),
    subject_attributes: { country: SUBJECT_COUNTRY },
    flags: [FLAG_KEY],
  });
}

export default function () {
  const response = http.post(`${API_URL}/decide`, buildPayload(), {
    headers: { "Content-Type": "application/json" },
    tags: { endpoint: "decide" },
  });

  decideRequests.add(1);
  decideDuration.add(response.timings.duration);
  decideStatus200Rate.add(response.status === 200);

  let reason = "";
  if (response.status === 200) {
    const body = response.json();
    if (body && body.decisions && body.decisions.length > 0) {
      reason = String(body.decisions[0].reason || "");
    }
  }
  decideAssignedRate.add(reason === "experiment_assigned");

  check(response, {
    "status is 200": (r) => r.status === 200,
    "has one decision": (r) => {
      const body = r.json();
      return (
        body !== null &&
        typeof body === "object" &&
        Array.isArray(body.decisions) &&
        body.decisions.length === 1
      );
    },
  });

  if (THINK_TIME_SECONDS > 0) {
    sleep(THINK_TIME_SECONDS);
  }
}