/**
 * 429 response classifier — distinguish rate-limit from quota-exhausted.
 *
 * Most LLM providers return HTTP 429 for two semantically different reasons:
 *
 * 1. **Rate-limit**: short transient back-off ("too many requests in
 *    the last minute"). Fix: wait the Retry-After window and retry.
 * 2. **Quota-exhausted**: long-period cap hit ("daily/monthly limit
 *    reached"). Fix: wait until the period rolls over (could be hours
 *    or days). Retrying every 60s wastes calls and burns alerts.
 *
 * The HTTP status alone cannot disambiguate. This helper inspects the
 * response body and headers to return a `FailureKind` the circuit
 * breaker can use to pick the right cooldown.
 *
 * Companion to OmniRoute issue #2100.
 *
 * @module shared/utils/classify429
 */

export type FailureKind = "rate_limit" | "quota_exhausted" | "transient";

/**
 * Heuristic regexes for "explicit quota exhausted" vs "rate-limited"
 * detection in 429 error bodies. A 429 alone never implies quota
 * exhausted — only an explicit keyword does.
 *
 * Patterns observed across OpenAI, Anthropic, Groq, Cerebras, Mistral,
 * Google Gemini, and OpenRouter free-tier responses.
 */
const QUOTA_PATTERNS: ReadonlyArray<RegExp> = [
  /daily.*limit/i,
  /daily.*quota/i,
  /per.?day.*limit/i,
  /monthly.*limit/i,
  /monthly.*quota/i,
  /per.?month.*limit/i,
  /quota.*exceed/i,
  /exceed.*quota/i,
  /insufficient.*quota/i,
  /billing.*cap/i,
  /credit.*exhaust/i,
  /out of credits/i,
  /hard.?limit/i,
  /plan.*limit/i,

  // Antigravity / Cloud Code quota exhaustion ("Individual quota reached.
  // Contact your administrator to enable overages. Resets in 164h27m24s.").
  // None of the patterns above match it, so the 429 was misclassified as a
  // transient rate-limit and locked for only ~5s instead of the real window.
  // Keep these specific: a bare /quota reached/ would also flag transient
  // per-minute limits like "request quota reached, retry in 60s".
  /individual quota reached/i,
  /enable overages/i,
  /INSUFFICIENT_G1_CREDITS_BALANCE/i,

  // Google APIs return this generic RESOURCE_EXHAUSTED message when a
  // billing-period quota has been consumed. Keep the reset-window qualifier
  // so transient Google rate limits are not treated as long-term exhaustion.
  /resource has been exhausted.*reset after/i,

  // Cloudflare Workers AI daily neuron exhaustion (Issue #6980).
  // Body: "you have used up your daily free allocation of 10,000 neurons,
  //        please upgrade to Cloudflare's Workers Paid plan..."
  // No existing pattern matches "daily free allocation" — without this,
  // the 429 is misclassified as transient rate_limit and retried every
  // ~60s against a budget that only resets at UTC midnight.
  /daily free allocation/i,

  // OmniRoute auth-layer synthetic 429 (Issue #9269).
  // Body: "All antigravity accounts have exhausted their quota (reset after 5m)"
  // Produced by auth.ts line 1477 when every account for a provider has
  // exhausted its quota. Without this pattern, the message is classified as
  // a transient rate-limit and the combo loop burns retries against the
  // same provider instead of falling back to a healthy one.
  /have exhausted their quota/i,

  // Modal-hosted OpenAI-compatible endpoints (e.g. self-hosted Kimi K3).
  // Body: {"error":"usage limit reached"}, no nested "message"/"quota"/
  // "daily" wording. Without this pattern the 429 falls through to
  // "rate_limit" (short cooldown), so combo round-robin's per-conversation
  // session stickiness (#3825) keeps re-targeting the same exhausted
  // connection every turn instead of a long lockout that lets the sticky
  // target fail over to another account.
  //
  // Matches the "error" JSON key with "usage limit reached" as its value.
  // Extra sibling fields (e.g. {"error":"usage limit reached", "code":"..."})
  // still match. A different key like {"detail":"..."} or a qualified value
  // like {"error":"Per-minute usage limit reached"} does NOT match. Bare
  // string bodies without a JSON wrapper also do NOT match.
  // Trailing punctuation/whitespace before the closing quote is tolerated
  // because real API responses may include a period or trailing space.
  /"error"\s*:\s*"usage limit reached[.\s]*"/i,
];

/**
 * Best-effort case-insensitive header lookup.
 */
function getHeader(headers: Record<string, string> | undefined, name: string): string | undefined {
  if (!headers) return undefined;
  const target = name.toLowerCase();
  for (const [k, v] of Object.entries(headers)) {
    if (k.toLowerCase() === target) return v;
  }
  return undefined;
}

/**
 * Coerce a body of unknown shape to a string for keyword scanning.
 * - string: returned as-is
 * - object: JSON-stringified (so nested error.message gets scanned)
 * - undefined/null: empty string
 */
function bodyToText(body: unknown): string {
  if (typeof body === "string") return body;
  if (body == null) return "";
  try {
    return JSON.stringify(body);
  } catch {
    return "";
  }
}

/**
 * Returns true if the body looks like an explicit quota-exhausted
 * error — i.e. the upstream is telling us a long-period cap was hit.
 */
export function looksLikeQuotaExhausted(body: unknown): boolean {
  const text = bodyToText(body);
  if (!text) return false;
  return QUOTA_PATTERNS.some((pat) => pat.test(text));
}

/**
 * A declared upstream retry window at or beyond this is treated as
 * long-period exhaustion. One hour mirrors the circuit breaker's
 * `quota_exhausted` cooldown bucket (`cooldownByKind`, wired in
 * src/sse/handlers/chat.ts, chatHelpers.ts and
 * open-sse/services/accountFallback.ts): the long bucket is only the right
 * lock when the upstream's own window is at least that long.
 */
const QUOTA_SCALE_RETRY_DELAY_SECONDS = 3600;

/**
 * Quota signals that stay terminal no matter what retry hint accompanies
 * them. Credits/billing exhaustion does not clear on a timer, so a short
 * upstream hint must never downgrade these to a 60s retry loop.
 */
const TERMINAL_QUOTA_PATTERNS: ReadonlyArray<RegExp> = [
  /INSUFFICIENT_G1_CREDITS_BALANCE/i,
  /credit.*exhaust/i,
  /out of credits/i,
  /billing.*cap/i,
  /insufficient.*quota/i,
  /individual quota reached/i,
  /enable overages/i,
  /daily free allocation/i,
];

/**
 * Parse an upstream delay string ("38s", "26.66s", "1500ms", "2m", "1h",
 * or a bare number of seconds) into seconds.
 *
 * Deliberately mirrors `parseDelayString` in
 * open-sse/services/retryAfterJson.ts (#7940) rather than importing it:
 * open-sse already imports this module (accountFallback.ts), so the
 * reverse import would close a dependency cycle. Keep the two grammars in
 * step when either changes.
 */
function parseDelaySeconds(value: unknown): number | null {
  if (!value) return null;
  const str = String(value).trim();
  const ms = /^(\d+(?:\.\d+)?)\s*ms$/i.exec(str);
  if (ms) return Number.parseFloat(ms[1]) / 1000;
  const sec = /^(\d+(?:\.\d+)?)\s*s$/i.exec(str);
  if (sec) return Number.parseFloat(sec[1]);
  const min = /^(\d+(?:\.\d+)?)\s*m$/i.exec(str);
  if (min) return Number.parseFloat(min[1]) * 60;
  const hr = /^(\d+(?:\.\d+)?)\s*h$/i.exec(str);
  if (hr) return Number.parseFloat(hr[1]) * 3600;
  const bare = Number.parseFloat(str);
  return Number.isFinite(bare) ? bare : null;
}

/**
 * Upstream-declared retry window in seconds, when the 429 carries one.
 *
 * Google APIs (Gemini `generativelanguage`, Vertex) attach a
 * `google.rpc.RetryInfo` detail whose `retryDelay` Duration states exactly
 * how long the throttle lasts, and repeat the same hint in the human
 * message ("Please retry in 38.922534355s"). Gemini free-tier
 * per-minute/per-token 429s open with the same "You exceeded your current
 * quota, please check your plan and billing details" preamble as genuine
 * long-window exhaustion, so `QUOTA_PATTERNS` cannot tell them apart —
 * even the PerDay-named `quotaId` ships retryDelay values of ~30-50s
 * (#9504). The declared window is the authoritative signal.
 *
 * Both carriers are read because the two live call paths deliver different
 * shapes: `accountFallback` classifies the parsed body (details intact),
 * while `chat.ts` classifies `result.rawMessage`, which
 * `parseUpstreamError` has already reduced to `error.message` text.
 * Structural matching keeps an unrelated `retryDelay` key from triggering
 * the hint; the text form is anchored on Google's exact phrasing, matching
 * the precedent in accountFallback's cooldown parser.
 */
function upstreamRetryDelaySeconds(body: unknown): number | null {
  let root: unknown = body;
  if (typeof body === "string") {
    const phrase = /please retry in (\d+(?:\.\d+)?)\s*s/i.exec(body);
    if (phrase) return Number.parseFloat(phrase[1]);
    try {
      root = JSON.parse(body);
    } catch {
      return null;
    }
  }
  if (root === null || typeof root !== "object") return null;
  const error = (root as { error?: unknown }).error;
  const errorRecord =
    error !== null && typeof error === "object" ? (error as Record<string, unknown>) : {};
  const details = errorRecord.details ?? (root as Record<string, unknown>).details;
  for (const detail of Array.isArray(details) ? details : []) {
    if (detail === null || typeof detail !== "object") continue;
    const entry = detail as Record<string, unknown>;
    if (!String(entry["@type"] ?? "").includes("RetryInfo")) continue;
    const seconds = parseDelaySeconds(entry.retryDelay);
    if (seconds !== null && seconds >= 0) return seconds;
  }
  const message = errorRecord.message;
  if (typeof message === "string") {
    const phrase = /please retry in (\d+(?:\.\d+)?)\s*s/i.exec(message);
    if (phrase) return Number.parseFloat(phrase[1]);
  }
  return null;
}

/**
 * Classify a 429 (or any) response into a `FailureKind`.
 *
 * Decision order:
 * 1. status !== 429 → `"transient"` (don't pretend to know more than
 *    the caller does about non-429 failures).
 * 2. body carries a terminal credits/billing signal → `"quota_exhausted"`
 *    regardless of any retry hint: those do not clear on a timer.
 * 3. body declares a sub-hour retry window → `"rate_limit"` even when
 *    generic quota keywords match: the upstream said the throttle clears
 *    in seconds, so the long lockout bucket would overshoot its own reset
 *    by 60-360x (#9504).
 * 4. body matches a quota keyword → `"quota_exhausted"`.
 * 5. otherwise → `"rate_limit"` (default for 429 — even without
 *    Retry-After, a 429 is per definition a rate-limit signal).
 *
 * @param response - the upstream response with status, optional headers,
 *                   optional body. Headers are looked up
 *                   case-insensitively.
 */
export function classify429(response: {
  status: number;
  headers?: Record<string, string>;
  body?: unknown;
}): FailureKind {
  if (response.status !== 429) return "transient";
  const text = bodyToText(response.body);
  if (text && TERMINAL_QUOTA_PATTERNS.some((pat) => pat.test(text))) {
    return "quota_exhausted";
  }
  const declaredDelay = upstreamRetryDelaySeconds(response.body);
  if (declaredDelay !== null && declaredDelay < QUOTA_SCALE_RETRY_DELAY_SECONDS) {
    return "rate_limit";
  }
  if (looksLikeQuotaExhausted(response.body)) return "quota_exhausted";
  return "rate_limit";
}

/**
 * Parse a `Retry-After` header value into seconds.
 *
 * Accepts:
 * - integer seconds: `"60"`
 * - HTTP date: `"Wed, 08 May 2026 03:00:00 GMT"`
 * - Groq-style relative: `"60s"`, `"5m"`, `"2h"`
 *
 * Returns `null` if unparseable.
 *
 * Note: integer seconds vs Groq relative units are easy to confuse —
 * `parseInt("5m", 10)` returns `5` (parses leading digits and ignores
 * trailing). This helper checks the relative-unit pattern FIRST.
 */
export function parseRetryAfter(headerValue: string | undefined): number | null {
  if (!headerValue) return null;
  const trimmed = headerValue.trim();
  if (!trimmed) return null;

  // Groq-style relative: must check BEFORE plain int parse.
  const relMatch = trimmed.match(/^(\d+)([smh])$/i);
  if (relMatch) {
    const n = Number(relMatch[1]);
    const unit = relMatch[2].toLowerCase();
    if (Number.isFinite(n)) {
      if (unit === "s") return n;
      if (unit === "m") return n * 60;
      if (unit === "h") return n * 3600;
    }
  }

  // Pure integer seconds.
  if (/^\d+$/.test(trimmed)) {
    const n = Number(trimmed);
    return Number.isFinite(n) ? n : null;
  }

  // HTTP date.
  const ts = Date.parse(trimmed);
  if (Number.isFinite(ts)) {
    return Math.max(0, Math.floor((ts - Date.now()) / 1000));
  }

  return null;
}

/**
 * Convenience wrapper: pull the Retry-After from a response's headers
 * and parse it to seconds. Returns null if absent or unparseable.
 */
export function retryAfterFromResponse(response: {
  headers?: Record<string, string>;
}): number | null {
  return parseRetryAfter(getHeader(response.headers, "retry-after"));
}

/**
 * Normalize an unknown headers-like value into a plain `Record<string, string>`.
 * Native `Headers` (from `fetch`) does NOT respond to `Object.entries` — it
 * exposes `.entries()` instead. Without this normalization, `getHeader` would
 * silently miss every header on a Headers instance.
 */
function normalizeHeaders(raw: unknown): Record<string, string> | undefined {
  if (raw === null || typeof raw !== "object") return undefined;
  const maybeIter = (raw as { entries?: unknown }).entries;
  if (typeof maybeIter === "function") {
    try {
      return Object.fromEntries((raw as { entries: () => Iterable<[string, string]> }).entries());
    } catch {
      // fall through to plain-object treatment
    }
  }
  return raw as Record<string, string>;
}

/**
 * Adapter that takes an error thrown by an HTTP client (fetch wrapper, axios,
 * upstream SDK, etc.) and produces a {@link FailureKind} suitable for the
 * `classifyError` option of the circuit breaker.
 *
 * Recognises the common error shapes:
 * - `err.status` + `err.headers` + `err.body` (low-level fetch wrapper)
 * - `err.response.status` + `err.response.headers` + `err.response.data` (axios-style)
 * - `err.message` (last-resort body for keyword scan)
 *
 * Returns `undefined` when the error doesn't carry enough information to
 * classify, so the breaker can decide what to do without a kind tag.
 *
 * Companion to issue #2100 follow-up.
 */
export function classify429FromError(err: unknown): FailureKind | undefined {
  if (err === null || typeof err !== "object") return undefined;
  const e = err as Record<string, unknown>;

  let status: number | undefined;
  let headers: Record<string, string> | undefined;
  let body: unknown;

  if (typeof e.status === "number") {
    status = e.status;
  }
  if (typeof e.statusCode === "number" && status === undefined) {
    status = e.statusCode;
  }

  if (e.response && typeof e.response === "object") {
    const resp = e.response as Record<string, unknown>;
    if (typeof resp.status === "number" && status === undefined) {
      status = resp.status;
    }
    if (resp.headers && typeof resp.headers === "object") {
      headers = normalizeHeaders(resp.headers);
    }
    if (resp.data !== undefined) {
      body = resp.data;
    } else if (typeof resp.body !== "undefined") {
      body = resp.body;
    }
  }

  if (headers === undefined && e.headers && typeof e.headers === "object") {
    headers = normalizeHeaders(e.headers);
  }
  if (body === undefined) {
    if (typeof e.body !== "undefined") {
      body = e.body;
    } else if (typeof e.message === "string") {
      body = e.message;
    }
  }

  if (typeof status !== "number") return undefined;
  return classify429({ status, headers, body });
}