"use server";

import { prisma } from "@/lib/db";
import { requireUserId } from "@/lib/auth-helpers";
import { categoryAccessFilter } from "@/lib/access";
import { getAiCredentials, getAiSettingsView, joinApiUrl } from "@/lib/ai-settings";

export interface TodoAiMessage {
  role: "user" | "assistant";
  content: string;
}

export interface TodoAiProposal {
  title: string;
  details?: string;
}

export type TodoAiResult =
  | { action: "ask"; question: string }
  | { action: "finalize"; todos: TodoAiProposal[] }
  | { error: string };

const TITLE_MAX = 20;

// Same "respond with exactly one JSON shape" contract as converseAboutGroup
// (lib/actions/group-ai.ts) -- the AI backend is a user-configured
// OpenAI-compatible endpoint reached over raw fetch, so there's no
// function-calling/JSON-mode to lean on; the format has to be held
// together by the prompt plus defensive parsing below.
const SYSTEM_PROMPT = `You are helping a user create one or more to-dos for a group called "{{GROUP_TITLE}}" in a to-do list app. Have a brief conversation to understand what they need to track. Ask at most one short, specific follow-up question at a time if genuinely needed. A to-do's title is hard-capped at ${TITLE_MAX} characters -- keep every title short and punchy, and put anything else worth remembering in that to-do's own "details" (short markdown notes, optional). Split unrelated tasks into separate to-dos rather than cramming them into one.{{EXISTING_TITLES_CLAUSE}}

You must respond with ONLY a single JSON object and nothing else -- no preamble, no code block, no text before or after it. It must match exactly one of these two shapes:

Still gathering information:
{"action": "ask", "question": "<one short, specific question>"}

Ready to finalize:
{"action": "finalize", "todos": [{"title": "<${TITLE_MAX} characters or fewer>", "details": "<optional short markdown notes, omit or leave empty if none>"}]}

Respond with the raw JSON object only.`;

function extractMessageContent(body: unknown): string | null {
  if (!body || typeof body !== "object") return null;
  const choices = (body as { choices?: unknown }).choices;
  if (!Array.isArray(choices) || !choices[0]) return null;
  const message = (choices[0] as { message?: unknown }).message;
  if (!message || typeof message !== "object") return null;
  const content = (message as { content?: unknown }).content;
  return typeof content === "string" ? content : null;
}

/** Model output sometimes arrives fenced in a ```json code block despite
 * instructions not to -- strip that before parsing rather than failing. */
function stripCodeFence(text: string): string {
  const trimmed = text.trim();
  const fenced = trimmed.match(/^```(?:json)?\s*([\s\S]*?)\s*```$/i);
  return fenced ? fenced[1] : trimmed;
}

function parseTodos(value: unknown): TodoAiProposal[] | null {
  if (!Array.isArray(value)) return null;
  const todos: TodoAiProposal[] = [];
  for (const entry of value) {
    if (!entry || typeof entry !== "object") continue;
    const rawTitle = (entry as { title?: unknown }).title;
    if (typeof rawTitle !== "string") continue;
    const title = rawTitle.trim().slice(0, TITLE_MAX);
    if (!title) continue;
    const rawDetails = (entry as { details?: unknown }).details;
    const details = typeof rawDetails === "string" ? rawDetails.trim() : "";
    todos.push(details ? { title, details } : { title });
  }
  return todos.length > 0 ? todos : null;
}

function parseModelOutput(content: string): TodoAiResult | null {
  let json: unknown;
  try {
    json = JSON.parse(stripCodeFence(content));
  } catch {
    return null;
  }
  if (!json || typeof json !== "object") return null;

  const action = (json as { action?: unknown }).action;
  if (action === "ask") {
    const question = (json as { question?: unknown }).question;
    return typeof question === "string" && question.trim()
      ? { action: "ask", question: question.trim() }
      : null;
  }
  if (action === "finalize") {
    const todos = parseTodos((json as { todos?: unknown }).todos);
    return todos ? { action: "finalize", todos } : null;
  }
  return null;
}

/**
 * Sends the interview's conversation so far to the configured AI provider
 * and returns either a follow-up question or a finalized list of to-do
 * proposals. Reuses the same admin-configured endpoint/key as the group
 * notes "Ask AI" feature (see lib/ai-settings.ts).
 */
export async function converseAboutTodos(
  groupId: string,
  groupTitle: string,
  existingTodoTitles: string[],
  messages: TodoAiMessage[],
  forceFinalize: boolean
): Promise<TodoAiResult> {
  const userId = await requireUserId();

  const group = await prisma.group.findFirst({
    where: { id: groupId, category: categoryAccessFilter(userId) },
    select: { id: true },
  });
  if (!group) return { error: "Group not found." };

  const [{ apiUrl, apiKey }, settings] = await Promise.all([
    getAiCredentials(),
    getAiSettingsView(),
  ]);
  if (!apiUrl || !settings.model) {
    return { error: "AI generation isn't configured yet. Ask an administrator to set it up." };
  }

  let chatUrl: URL;
  try {
    chatUrl = joinApiUrl(apiUrl, "chat/completions");
  } catch {
    return { error: "The configured AI API URL is invalid." };
  }

  const existingTitlesClause =
    existingTodoTitles.length > 0
      ? ` This group already has these to-dos, don't duplicate them: ${existingTodoTitles
          .map((t) => `"${t}"`)
          .join(", ")}.`
      : "";
  let systemPrompt = SYSTEM_PROMPT.replace("{{GROUP_TITLE}}", groupTitle).replace(
    "{{EXISTING_TITLES_CLAUSE}}",
    existingTitlesClause
  );
  if (forceFinalize) {
    systemPrompt +=
      '\n\nThe user has asked you to wrap up now with whatever information you have, even if it feels incomplete. Do not ask another question -- respond with {"action": "finalize", ...} using your best effort.';
  }

  let response: Response;
  try {
    response = await fetch(chatUrl, {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
        ...(apiKey ? { Authorization: `Bearer ${apiKey}` } : {}),
      },
      body: JSON.stringify({
        model: settings.model,
        messages: [{ role: "system", content: systemPrompt }, ...messages],
        temperature: 0.4,
      }),
      signal: AbortSignal.timeout(30_000),
    });
  } catch (error) {
    const message = error instanceof Error ? error.message : "Unknown error";
    return { error: `Couldn't reach the AI provider -- ${message}` };
  }

  if (!response.ok) {
    if (response.status === 401 || response.status === 403) {
      return { error: "The AI provider rejected the configured API key." };
    }
    return { error: `The AI provider responded with ${response.status} ${response.statusText}.` };
  }

  let body: unknown;
  try {
    body = await response.json();
  } catch {
    return { error: "The AI provider didn't return valid JSON." };
  }

  const content = extractMessageContent(body);
  if (!content) return { error: "The AI provider's response was empty." };

  const parsed = parseModelOutput(content);
  // Not every backend reliably follows the "JSON only" instruction --
  // rather than erroring out, treat unparseable output as a follow-up
  // question so the conversation degrades gracefully instead of dying.
  return parsed ?? { action: "ask", question: content.trim() };
}