const ERROR_PAYLOAD_PREFIX_RE =
  /^(?:error|(?:[a-z][\w-]*\s+)?api\s*error|apierror|openai\s*error|anthropic\s*error|gateway\s*error)(?:\s+\d{3})?[:\s-]+/i;
const HTTP_STATUS_PREFIX_RE = /^(?:http\s*)?(\d{3})\s+(.+)$/i;
const HTTP_STATUS_CODE_PREFIX_RE = /^(?:http\s*)?(\d{3})(?:\s+([\s\S]+))?$/i;
const HTML_ERROR_PREFIX_RE = /^\s*(?:<!doctype\s+html\b|<html\b)/i;
const CLOUDFLARE_HTML_ERROR_CODES = new Set([521, 522, 523, 524, 525, 526, 530]);

type ErrorPayload = Record<string, unknown>;

export type ApiErrorInfo = {
  httpCode?: string;
  type?: string;
  message?: string;
  requestId?: string;
};

function isErrorPayloadObject(payload: unknown): payload is ErrorPayload {
  if (!payload || typeof payload !== "object" || Array.isArray(payload)) {
    return false;
  }
  const record = payload as ErrorPayload;
  if (record.type === "error") {
    return true;
  }
  if (typeof record.request_id === "string" || typeof record.requestId === "string") {
    return true;
  }
  if ("error" in record) {
    const err = record.error;
    if (err && typeof err === "object" && !Array.isArray(err)) {
      const errRecord = err as ErrorPayload;
      if (
        typeof errRecord.message === "string" ||
        typeof errRecord.type === "string" ||
        typeof errRecord.code === "string"
      ) {
        return true;
      }
    }
  }
  return false;
}

export function parseApiErrorPayload(raw?: string): ErrorPayload | null {
  if (!raw) {
    return null;
  }
  const trimmed = raw.trim();
  if (!trimmed) {
    return null;
  }
  const candidates = [trimmed];
  if (ERROR_PAYLOAD_PREFIX_RE.test(trimmed)) {
    candidates.push(trimmed.replace(ERROR_PAYLOAD_PREFIX_RE, "").trim());
  }
  for (const candidate of candidates) {
    if (!candidate.startsWith("{") || !candidate.endsWith("}")) {
      continue;
    }
    try {
      const parsed = JSON.parse(candidate) as unknown;
      if (isErrorPayloadObject(parsed)) {
        return parsed;
      }
    } catch {
      // ignore parse errors
    }
  }
  return null;
}

export function extractLeadingHttpStatus(raw: string): { code: number; rest: string } | null {
  const match = raw.match(HTTP_STATUS_CODE_PREFIX_RE);
  if (!match) {
    return null;
  }
  const code = Number(match[1]);
  if (!Number.isFinite(code)) {
    return null;
  }
  return { code, rest: (match[2] ?? "").trim() };
}

export function isCloudflareOrHtmlErrorPage(raw: string): boolean {
  const trimmed = raw.trim();
  if (!trimmed) {
    return false;
  }

  const status = extractLeadingHttpStatus(trimmed);
  if (!status || status.code < 500) {
    return false;
  }

  if (CLOUDFLARE_HTML_ERROR_CODES.has(status.code)) {
    return true;
  }

  return (
    status.code < 600 && HTML_ERROR_PREFIX_RE.test(status.rest) && /<\/html>/i.test(status.rest)
  );
}

export function parseApiErrorInfo(raw?: string): ApiErrorInfo | null {
  if (!raw) {
    return null;
  }
  const trimmed = raw.trim();
  if (!trimmed) {
    return null;
  }

  let httpCode: string | undefined;
  let candidate = trimmed;

  const httpPrefixMatch = candidate.match(/^(\d{3})\s+(.+)$/s);
  if (httpPrefixMatch) {
    httpCode = httpPrefixMatch[1];
    candidate = httpPrefixMatch[2].trim();
  }

  const payload = parseApiErrorPayload(candidate);
  if (!payload) {
    return null;
  }

  const requestId =
    typeof payload.request_id === "string"
      ? payload.request_id
      : typeof payload.requestId === "string"
        ? payload.requestId
        : undefined;

  const topType = typeof payload.type === "string" ? payload.type : undefined;
  const topMessage = typeof payload.message === "string" ? payload.message : undefined;

  let errType: string | undefined;
  let errMessage: string | undefined;
  if (payload.error && typeof payload.error === "object" && !Array.isArray(payload.error)) {
    const err = payload.error as Record<string, unknown>;
    if (typeof err.type === "string") {
      errType = err.type;
    }
    if (typeof err.code === "string" && !errType) {
      errType = err.code;
    }
    if (typeof err.message === "string") {
      errMessage = err.message;
    }
  }

  return {
    httpCode,
    type: errType ?? topType,
    message: errMessage ?? topMessage,
    requestId,
  };
}

export function formatRawAssistantErrorForUi(raw?: string): string {
  const trimmed = (raw ?? "").trim();
  if (!trimmed) {
    return "LLM request failed with an unknown error.";
  }

  const leadingStatus = extractLeadingHttpStatus(trimmed);
  if (leadingStatus && isCloudflareOrHtmlErrorPage(trimmed)) {
    return `The AI service is temporarily unavailable (HTTP ${leadingStatus.code}). Please try again in a moment.`;
  }

  const httpMatch = trimmed.match(HTTP_STATUS_PREFIX_RE);
  if (httpMatch) {
    const rest = httpMatch[2].trim();
    if (!rest.startsWith("{")) {
      return `HTTP ${httpMatch[1]}: ${rest}`;
    }
  }

  const info = parseApiErrorInfo(trimmed);
  if (info?.message) {
    const prefix = info.httpCode ? `HTTP ${info.httpCode}` : "LLM error";
    const type = info.type ? ` ${info.type}` : "";
    const requestId = info.requestId ? ` (request_id: ${info.requestId})` : "";
    return `${prefix}${type}: ${info.message}${requestId}`;
  }

  return trimmed.length > 600 ? `${trimmed.slice(0, 600)}…` : trimmed;
}