"use client";

import { localeHeader, t } from "./i18n";
import type { Activity, Difficulty, HomeworkMode, HomeworkStep } from "./schemas";
import { API_KEY_HEADER, authHeaders } from "./settings";
import { providerHeaders, providersStore } from "./providers-client";

export type GenerateInput = {
  images?: string[];
  text?: string;
  difficulty: Difficulty;
  count?: number;
  focus?: string;
  language?: string;
  mode?: "create" | "more";
  existing?: { title: string; types: string[]; count: number };
};

export type StreamedDeck = {
  title: string;
  subject?: string;
  summary?: string;
  language?: string;
  sourceText: string;
  difficulty: Difficulty;
  activities: Activity[];
};

export type GenerateProgress = {
  stage: "vision" | "generation" | "done";
  message: string;
};

/** No response at all for this long: the run is stuck, not slow. */
const RESPONSE_GUARD_MS = 45_000;
/** No bytes for this long while streaming: the model stopped talking. The
 *  routes heartbeat every 15s, so 90s of silence really is silence. */
const STREAM_GUARD_MS = 90_000;

type StreamEvent =
  | { type: "stage"; stage: "vision" | "generation" | "done"; message: string }
  | { type: "deck"; deck: StreamedDeck; meta: Record<string, unknown> }
  | { type: "error"; error: string; kind?: string }
  | { type: "ping" };

export class ApiError extends Error {
  kind: string;
  constructor(message: string, kind = "unknown") {
    super(message);
    this.name = "ApiError";
    this.kind = kind;
  }
}

/**
 * Reads an NDJSON response line by line and hands each parsed event to the
 * callback. Malformed lines are skipped (a half-written line must never break
 * the stream), and the trailing buffer is flushed at the end.
 */
export async function consumeNdjson(
  response: Response,
  handleEvent: (event: unknown) => void,
  options: { stallMs?: number } = {},
): Promise<void> {
  if (!response.body) throw new ApiError(t("api.empty"), "bad_response");
  const reader = response.body.getReader();
  const decoder = new TextDecoder();
  let buffer = "";
  const stallMs = options.stallMs ?? 0;
  const flush = (line: string) => {
    if (!line.trim()) return;
    try {
      handleEvent(JSON.parse(line));
    } catch {
      /* ignore malformed lines */
    }
  };
  while (true) {
    let chunk: ReadableStreamReadResult<Uint8Array>;
    let timer: ReturnType<typeof setTimeout> | null = null;
    try {
      if (stallMs > 0) {
        const stalled = new Promise<never>((_, reject) => {
          timer = setTimeout(() => reject(new ApiError(t("api.stalled"), "timeout")), stallMs);
        });
        chunk = await Promise.race([reader.read(), stalled]);
      } else {
        chunk = await reader.read();
      }
    } catch (error) {
      // A connection that dropped mid-run used to leak a raw DOMException, and
      // the wizard answered with its generic "check your Ollama settings"
      // card for what was really a network blip. Classify everything here.
      void reader.cancel().catch(() => {});
      if (error instanceof ApiError) throw error;
      if (error instanceof Error && error.name === "AbortError") {
        throw new ApiError(t("api.cancelled"), "aborted");
      }
      throw new ApiError(t("api.streamLost"), "network");
    } finally {
      if (timer) clearTimeout(timer);
    }
    if (chunk.done) break;
    buffer += decoder.decode(chunk.value, { stream: true });
    let newline = buffer.indexOf("\n");
    while (newline !== -1) {
      flush(buffer.slice(0, newline));
      buffer = buffer.slice(newline + 1);
      newline = buffer.indexOf("\n");
    }
  }
  flush(buffer);
}

/**
 * Calls POST /api/generate and consumes the NDJSON progress stream.
 * Progress events arrive between the vision and generation steps.
 */
export async function generateDeck(
  input: GenerateInput,
  options: { onProgress?: (progress: GenerateProgress) => void; signal?: AbortSignal } = {},
): Promise<{ deck: StreamedDeck; meta: Record<string, unknown> }> {
  // A provider picked in Settings → Providers runs the generation instead of
  // the server's Ollama; its key travels with the request only.
  const generation = providersStore.getSnapshot().generation;
  // A run that goes quiet is worse than one that fails: the wizard used to sit
  // on its loading screen until the server's own 2x deadline (ten minutes by
  // default) when the model hung. The caller's signal is forwarded, and a
  // no-response guard covers the "nothing at all" phase.
  const controller = new AbortController();
  const forwarded = options.signal;
  let headersTimedOut = false;
  if (forwarded) {
    if (forwarded.aborted) controller.abort();
    else forwarded.addEventListener("abort", () => controller.abort(), { once: true });
  }
  const headersTimer = setTimeout(() => {
    headersTimedOut = true;
    controller.abort();
  }, RESPONSE_GUARD_MS);
  let response: Response;
  try {
    response = await fetch("/api/generate", {
      method: "POST",
      headers: { "Content-Type": "application/json", ...authHeaders(), ...providerHeaders(generation?.provider), ...localeHeader() },
      body: JSON.stringify(
        generation ? { ...input, textModel: generation.textModel, visionModel: generation.visionModel } : input,
      ),
      signal: controller.signal,
    });
  } catch {
    if (forwarded?.aborted) throw new ApiError(t("api.cancelled"), "aborted");
    if (headersTimedOut) throw new ApiError(t("api.stalled"), "timeout");
    throw new ApiError(t("api.unreachable"), "network");
  } finally {
    clearTimeout(headersTimer);
  }

  if (!response.ok) {
    const body = (await response.json().catch(() => null)) as { error?: string; kind?: string } | null;
    throw new ApiError(body?.error ?? t("api.httpError", { status: response.status }), body?.kind);
  }

  let deck: StreamedDeck | null = null;
  let meta: Record<string, unknown> = {};
  let streamError: ApiError | null = null;
  let sawDeck = false;

  await consumeNdjson(response, (raw) => {
    const event = raw as StreamEvent;
    if (event.type === "stage") {
      options.onProgress?.({ stage: event.stage, message: event.message });
    } else if (event.type === "deck") {
      deck = event.deck;
      meta = event.meta ?? {};
      sawDeck = true;
      options.onProgress?.({ stage: "done", message: t("api.almost") });
    } else if (event.type === "error") {
      streamError = new ApiError(event.error, event.kind);
    }
  }, { stallMs: STREAM_GUARD_MS });

  if (streamError) throw streamError;
  if (!deck) {
    throw new ApiError(
      sawDeck
        ? t("api.incomplete")
        : t("api.noDeck"),
      "bad_response",
    );
  }

  const valid = (deck as StreamedDeck).activities?.filter(
    (activity) => activity && typeof activity.type === "string" && typeof activity.id === "string",
  );
  if (!valid || valid.length === 0) {
    throw new ApiError(t("api.noActivities"), "bad_response");
  }

  return { deck: { ...(deck as StreamedDeck), activities: valid }, meta };
}

/* ------------------------------------------------------------------ */
/* Make my homework                                                    */
/* ------------------------------------------------------------------ */

export type HomeworkInput = {
  mode: HomeworkMode;
  images?: string[];
  text?: string;
  /** Mode "check": the student's own attempt at the assignment. */
  solution?: string;
  /** Mode "check": photos of the attempt (handwritten work, scanned pages). */
  solutionImages?: string[];
  language?: string;
};

export type HomeworkProgress = {
  stage: "vision" | "generation" | "done";
  message: string;
};

export type StreamedHomework =
  | { mode: "make"; title: string; language?: string; answer: string; sourceText?: string }
  | { mode: "guide"; title: string; language?: string; steps: HomeworkStep[]; sourceText?: string }
  | {
      mode: "check";
      title: string;
      language?: string;
      verdict: string;
      correct: string[];
      wrong: Array<{ issue: string; why: string; fix: string }>;
      corrected: string;
      sourceText?: string;
    };

type HomeworkStreamEvent =
  | { type: "stage"; stage: "vision" | "generation" | "done"; message: string }
  | { type: "homework"; homework: StreamedHomework; meta: Record<string, unknown> }
  | { type: "error"; error: string; kind?: string }
  | { type: "ping" };

/**
 * Calls POST /api/homework and consumes the NDJSON progress stream. Same shape
 * as generateDeck: stage events first, then one final payload.
 */
export async function generateHomework(
  input: HomeworkInput,
  options: { onProgress?: (progress: HomeworkProgress) => void; signal?: AbortSignal } = {},
): Promise<{ homework: StreamedHomework; meta: Record<string, unknown> }> {
  const generation = providersStore.getSnapshot().generation;
  // Same guards as generateDeck: no infinite loading screen on a hung model.
  const controller = new AbortController();
  const forwarded = options.signal;
  let headersTimedOut = false;
  if (forwarded) {
    if (forwarded.aborted) controller.abort();
    else forwarded.addEventListener("abort", () => controller.abort(), { once: true });
  }
  const headersTimer = setTimeout(() => {
    headersTimedOut = true;
    controller.abort();
  }, RESPONSE_GUARD_MS);
  let response: Response;
  try {
    response = await fetch("/api/homework", {
      method: "POST",
      headers: { "Content-Type": "application/json", ...authHeaders(), ...providerHeaders(generation?.provider), ...localeHeader() },
      body: JSON.stringify(
        generation ? { ...input, textModel: generation.textModel, visionModel: generation.visionModel } : input,
      ),
      signal: controller.signal,
    });
  } catch {
    if (forwarded?.aborted) throw new ApiError(t("api.cancelled"), "aborted");
    if (headersTimedOut) throw new ApiError(t("api.stalled"), "timeout");
    throw new ApiError(t("api.unreachable"), "network");
  } finally {
    clearTimeout(headersTimer);
  }

  if (!response.ok) {
    const body = (await response.json().catch(() => null)) as { error?: string; kind?: string } | null;
    throw new ApiError(body?.error ?? t("api.httpError", { status: response.status }), body?.kind);
  }

  let homework: StreamedHomework | null = null;
  let meta: Record<string, unknown> = {};
  let streamError: ApiError | null = null;

  await consumeNdjson(response, (raw) => {
    const event = raw as HomeworkStreamEvent;
    if (event.type === "stage") {
      options.onProgress?.({ stage: event.stage, message: event.message });
    } else if (event.type === "homework") {
      homework = event.homework;
      meta = event.meta ?? {};
      options.onProgress?.({ stage: "done", message: t("api.almost") });
    } else if (event.type === "error") {
      streamError = new ApiError(event.error, event.kind);
    }
  }, { stallMs: STREAM_GUARD_MS });

  if (streamError) throw streamError;
  if (!homework) {
    throw new ApiError(t("api.noHomework"), "bad_response");
  }

  const result = homework as StreamedHomework;
  if (result.mode === "make") {
    if (!result.answer?.trim()) throw new ApiError(t("api.noHomework"), "bad_response");
  } else if (result.mode === "check") {
    if (!result.corrected?.trim() || !result.verdict?.trim()) {
      throw new ApiError(t("api.noHomework"), "bad_response");
    }
  } else {
    const steps = result.steps?.filter((step) => step && typeof step.title === "string");
    if (!steps || steps.length < 2) throw new ApiError(t("api.noHomework"), "bad_response");
    // Checkpoints must look like real activities; drop anything malformed
    // rather than crash the guide.
    const cleaned = steps.map((step) => ({
      ...step,
      checkpoint:
        step.checkpoint && typeof step.checkpoint.type === "string" && typeof step.checkpoint.id === "string"
          ? step.checkpoint
          : undefined,
    }));
    return { homework: { ...result, steps: cleaned }, meta };
  }

  return { homework: result, meta };
}

/** Follow-up on a finished result: shorter, more detail, or explain again. */
export async function refineHomework(input: {
  instruction: "shorter" | "more" | "explain";
  text: string;
  context?: string;
  signal?: AbortSignal;
}): Promise<string> {
  const generation = providersStore.getSnapshot().generation;
  let response: Response;
  try {
    response = await fetch("/api/homework/refine", {
      method: "POST",
      headers: { "Content-Type": "application/json", ...authHeaders(), ...providerHeaders(generation?.provider), ...localeHeader() },
      body: JSON.stringify(
        generation
          ? { instruction: input.instruction, text: input.text, context: input.context, model: generation.textModel }
          : { instruction: input.instruction, text: input.text, context: input.context },
      ),
      signal: input.signal,
    });
  } catch (error) {
    if (error instanceof Error && error.name === "AbortError") {
      throw new ApiError(t("api.cancelled"), "aborted");
    }
    throw new ApiError(t("api.unreachable"), "network");
  }
  const body = (await response.json().catch(() => null)) as { text?: string; error?: string; kind?: string } | null;
  if (!response.ok) {
    throw new ApiError(body?.error ?? t("api.httpError", { status: response.status }), body?.kind);
  }
  if (!body?.text?.trim()) throw new ApiError(t("api.noHomework"), "bad_response");
  return body.text.trim();
}

export async function gradeAnswer(input: {
  question: string;
  referenceAnswer: string;
  keyPoints: string[];
  userAnswer: string;
  language?: string;
  signal?: AbortSignal;
}): Promise<{ correct: boolean; score: number; feedback: string; missing: string[] }> {
  const generation = providersStore.getSnapshot().generation;
  let response: Response;
  try {
    response = await fetch("/api/grade", {
      method: "POST",
      headers: { "Content-Type": "application/json", ...authHeaders(), ...providerHeaders(generation?.provider), ...localeHeader() },
      body: JSON.stringify(generation ? { ...input, model: generation.textModel } : input),
      signal: input.signal,
    });
  } catch (error) {
    if (error instanceof Error && error.name === "AbortError") {
      throw new ApiError(t("api.gradingCancelled"), "aborted");
    }
    throw new ApiError(t("api.unreachableShort"), "network");
  }

  const body = (await response.json().catch(() => null)) as
    | { correct: boolean; score: number; feedback: string; missing?: string[]; error?: string; kind?: string }
    | null;

  if (!response.ok || !body || body.error) {
    throw new ApiError(body?.error ?? t("api.gradingFailed", { status: response.status }), body?.kind);
  }

  return {
    correct: Boolean(body.correct),
    score: Math.max(0, Math.min(100, Math.round(body.score))),
    feedback: body.feedback,
    missing: body.missing ?? [],
  };
}

export type HealthModel = {
  configured: string;
  resolved: string;
  available: boolean | null;
  note?: string;
};

export type HealthChatModel = {
  name: string;
  badge: "text" | "vision" | "both";
  available: boolean | null;
};

export type Health = {
  ok: boolean;
  reachable: boolean;
  mode: "local-daemon" | "direct-cloud";
  authMode: "user-key" | "server" | "local";
  needsKey: boolean;
  keyAccepted: boolean | null;
  baseUrl: string;
  hasApiKey: boolean;
  vision: HealthModel;
  text: HealthModel;
  /** Chat model allowlist; optional so older servers/mocks stay valid. */
  chatModels?: HealthChatModel[];
  latencyMs: number | null;
  modelCount: number | null;
  error: string | null;
  kind?: string;
  checkedAt: string;
};

export async function fetchHealth(): Promise<Health> {
  let response: Response;
  try {
    response = await fetch("/api/health", { cache: "no-store", headers: { ...authHeaders(), ...localeHeader() } });
  } catch {
    throw new ApiError(t("api.unreachableShort"), "network");
  }
  const body = (await response.json().catch(() => null)) as (Partial<Health> & { error?: string; kind?: string }) | null;
  if (!response.ok) {
    throw new ApiError(
      body?.error ?? t("api.healthFailed", { status: response.status }),
      body?.kind ?? "http",
    );
  }
  // Guard against anything that isn't a health payload (e.g. a proxy error
  // page) so consumers can rely on the shape.
  if (!body || typeof body !== "object" || !body.vision || !body.text) {
    throw new ApiError(t("api.healthUnexpected"), "bad_response");
  }
  return body as Health;
}

export type KeyCheck =
  | { result: "valid" }
  | { result: "invalid"; message: string }
  | { result: "offline"; message: string };

/**
 * Checks a *draft* key before it is saved anywhere, by asking our own
 * `/api/health` route (which performs a real one-token chat probe against
 * Ollama — model listings alone prove nothing). The key travels in the
 * request header for this single call and is never stored server-side.
 */
export async function verifyOllamaKey(apiKey: string): Promise<KeyCheck> {
  let response: Response;
  try {
    response = await fetch("/api/health", {
      cache: "no-store",
      headers: { [API_KEY_HEADER]: apiKey, ...localeHeader() },
    });
  } catch {
    return {
      result: "offline",
      message: t("api.unreachable"),
    };
  }

  const body = (await response.json().catch(() => null)) as Health | null;
  if (!response.ok || !body) {
    return {
      result: "offline",
      message: t("api.serverUnexpected"),
    };
  }

  if (body.keyAccepted === false) {
    return {
      result: "invalid",
      message:
        body.error ?? t("api.keyRejected"),
    };
  }
  if (body.keyAccepted === true) return { result: "valid" };

  if (!body.reachable) {
    return {
      result: "offline",
      message:
        body.error ?? t("api.ollamaUnreachable"),
    };
  }

  // Reachable, but the probe was inconclusive (usually a model-availability
  // matter rather than a bad key). Let the user in — Settings shows details.
  return { result: "valid" };
}