import { apiPost, getApiBaseUrl } from "@/lib/api/client";
import { getAuthToken } from "@/lib/auth/auth-client";

export const CHAT_ORIGIN_PAGES = [
  "home",
  "tuition",
  "learn-anything",
  "study-chat",
  "classes",
  "notes",
  "quizzes",
  "pyq-analyzer",
  "progress",
  "bookmarks",
  "notifications",
  "settings",
  "workspace",
] as const;

export type ChatOriginPage = (typeof CHAT_ORIGIN_PAGES)[number];

export type StudyChatAcademicContext = {
  origin?: string | null;
  subject?: string | null;
  chapter?: string | null;
  topic?: string | null;
  objective?: string | null;
  current_step?: string | null;
  relevant_context?: string | null;
  source_id?: string | null;
  source_ref?: string | null;
  source_label?: string | null;
  activity_type?: string | null;
  question_id?: string | null;
  question_label?: string | null;
  return_href?: string | null;
  captured_at?: string | null;
};

export function isChatOriginPage(value: string | null): value is ChatOriginPage {
  return CHAT_ORIGIN_PAGES.some((page) => page === value);
}

export type ChatRequest = {
  message: string;
  intent?: string;
  source_ids?: string[];
  subject?: string;
  language?: string;
  origin_page?: ChatOriginPage;
  academic_context?: StudyChatAcademicContext;
  mode?: StudyChatMode;
  correction_question?: string;
  student_answer?: string;
  marks?: number;
  session_id?: string;
  idempotency_key?: string;
};

export type StudyChatMode =
  | "general_explanation"
  | "selected_sources"
  | "pyq_verified"
  | "pyq_style"
  | "answer_correction";

export type SourceCitation = {
  source_id: string;
  source_title: string;
  source_version: string;
  chunk_id: string;
  chunk_index: number;
  page_number?: number | null;
  heading?: string | null;
  excerpt: string;
  confidence: number;
  availability?: "live" | "snapshot";
};

export type VerifiedPyqAnalysis = {
  available: boolean;
  status: "available" | "unavailable" | "awaiting_verification";
  message: string;
  disclaimer: string;
  repeated_topics: Array<{ topic: string; chapter: string; count: number; years: number[] }>;
  marks_distribution: Array<{ marks: number; count: number; percentage: number }>;
  data_coverage: { papers: number; questions: number; years: number[] };
  source_count: number;
};

export type StudyChatEvidence = {
  mode: StudyChatMode;
  trust_state:
    | "general_knowledge"
    | "source_grounded"
    | "verified_pyq"
    | "pyq_style_only"
    | "deterministic_correction"
    | "web_grounded"
    | "web_unavailable";
  evidence_scope: string;
  source_ids: string[];
  citations: SourceCitation[];
  pyq_classification: "verified_pyq" | "pyq_style" | "not_pyq";
  pyq_analysis?: VerifiedPyqAnalysis | null;
};

export type WebSource = {
  title: string;
  url: string;
  publisher: string;
  published_date?: string | null;
  author?: string | null;
  snippet?: string | null;
  is_official: boolean;
};

export type ChatApiResponse = {
  answer: string;
  intent_detected: string;
  model_used: string;
  evidence_label?: string | null;
  web_sources: WebSource[];
  evidence: StudyChatEvidence;
  correction?: Record<string, unknown> | null;
};

export async function sendChatMessage(
  payload: ChatRequest,
  options?: { signal?: AbortSignal; timeoutMs?: number },
): Promise<ChatApiResponse> {
  return apiPost<ChatApiResponse, ChatRequest>("/chat", payload, {
    signal: options?.signal,
    timeoutMs: options?.timeoutMs ?? 25000,
  });
}

/**
 * Stream chat tokens from DocDoe via SSE.
 * Calls onDelta for each token, onDone when stream ends, onError on failure.
 */
export async function streamChatMessage(
  payload: ChatRequest,
  callbacks: {
    onDelta: (token: string) => void;
    onDone: (meta: {
      intent: string;
      model: string;
      evidenceLabel: string | null;
      webSources: WebSource[];
      evidence: StudyChatEvidence;
      correction: Record<string, unknown> | null;
    }) => void;
    onError: (message: string) => void;
  },
  signal?: AbortSignal,
): Promise<void> {
  const authToken = getAuthToken();
  const streamSignal = AbortSignal.any([
    AbortSignal.timeout(120_000), ...(signal ? [signal] : []),
  ]);

  let response: Response;
  try {
    response = await fetch(`${getApiBaseUrl()}/chat/stream`, {
      method: "POST",
      signal: streamSignal,
      headers: {
        "Content-Type": "application/json",
        Accept: "text/event-stream",
        ...(authToken ? { Authorization: `Bearer ${authToken}` } : {}),
      },
      body: JSON.stringify(payload),
    });
  } catch {
    if (streamSignal.aborted) {
      callbacks.onError(signal?.aborted ? "Response stopped." : "The response timed out. Please retry.");
      return;
    }
    callbacks.onError("DocDoe backend is offline or unreachable.");
    return;
  }

  if (!response.ok) {
    // Forward the real backend reason so quota/limit/auth errors are classified
    // correctly downstream instead of all looking like "AI service offline".
    let detail = "";
    try {
      const body = (await response.clone().json()) as { error?: { message?: string }; detail?: unknown; message?: string };
      detail =
        body?.error?.message ||
        (typeof body?.detail === "string" ? body.detail : "") ||
        (body?.detail && typeof body.detail === "object" && "message" in body.detail
          ? String((body.detail as { message?: unknown }).message ?? "")
          : "") ||
        body?.message ||
        "";
    } catch {
      detail = "";
    }
    if (response.status === 402) {
      callbacks.onError(detail || "You've reached your plan limit. Try again later or upgrade.");
    } else if (response.status === 429) {
      callbacks.onError("Too many requests. Wait a few seconds and try again.");
    } else if (response.status === 401 || response.status === 403) {
      callbacks.onError("Your session expired. Please sign in again to continue.");
    } else {
      callbacks.onError(detail || "DocDoe could not reach the AI service. Please try again.");
    }
    return;
  }

  const reader = response.body?.getReader();
  if (!reader) {
    callbacks.onError("Streaming not supported. Please try again.");
    return;
  }

  const decoder = new TextDecoder();
  let buffer = "";

  try {
    while (true) {
      const { done, value } = await reader.read();
      if (done) {
        callbacks.onError("The response ended before it was complete. Please retry.");
        return;
      }

      buffer += decoder.decode(value, { stream: true });
      const lines = buffer.split("\n");
      buffer = lines.pop() ?? "";

      for (const line of lines) {
        if (!line.startsWith("data: ")) continue;
        const raw = line.slice(6).trim();
        if (!raw) continue;

        try {
          const event = JSON.parse(raw) as Record<string, unknown>;
          if (event.error) {
            callbacks.onError(String(event.error));
            return;
          }
          if (event.delta) {
            callbacks.onDelta(String(event.delta));
          }
          if (event.done) {
            callbacks.onDone({
              intent: String(event.intent ?? ""),
              model: String(event.model ?? ""),
              evidenceLabel:
                typeof event.evidence_label === "string"
                  ? event.evidence_label
                  : null,
              webSources: Array.isArray(event.web_sources)
                ? (event.web_sources as WebSource[])
                : [],
              evidence: event.evidence as StudyChatEvidence,
              correction:
                event.correction && typeof event.correction === "object"
                  ? (event.correction as Record<string, unknown>)
                  : null,
            });
            return;
          }
        } catch {
          // malformed SSE line — skip
        }
      }
    }
  } catch {
    if (streamSignal.aborted) {
      callbacks.onError(signal?.aborted ? "Response stopped." : "The response timed out. Please retry.");
      return;
    }
    callbacks.onError("Connection lost. Please try again.");
  } finally {
    await reader.cancel().catch(() => undefined);
    reader.releaseLock();
  }
}