import type { Session, SessionSummary } from '../types';

export const DEFAULT_CHAT_TITLE = 'New Chat';

function isGeneratedSessionName(name: string): boolean {
  return /^20\d{6}(?:[_-]\d+)?$/.test(name.trim());
}

function isDefaultSessionName(name: string): boolean {
  const trimmed = name.trim();
  return !trimmed || trimmed === DEFAULT_CHAT_TITLE || trimmed === '新对话' || isGeneratedSessionName(trimmed);
}

export function shouldShowNewChatTitle(session: SessionSummary): boolean {
  if (session.recipe) return false;
  return !session.user_set_name && session.message_count === 0 && isDefaultSessionName(session.name);
}

export function sortAndTrim<T extends SessionSummary>(sessions: T[]): T[] {
  return [...sessions]
    .sort((a, b) => {
      const aTime = new Date(a.updated_at ?? a.created_at ?? 0).getTime();
      const bTime = new Date(b.updated_at ?? b.created_at ?? 0).getTime();
      return bTime - aTime;
    });
}

export function hasMeaningfulSessionTitle(session: SessionSummary): boolean {
  if (session.user_set_name) return Boolean(session.name.trim());
  if (session.recipe?.title?.trim()) return true;
  return !isDefaultSessionName(session.name);
}

export function toSessionSummary(session: Session | SessionSummary): SessionSummary {
  return {
    id: session.id,
    name: session.name,
    message_count: session.message_count,
    created_at: session.created_at,
    updated_at: session.updated_at,
    user_set_name: session.user_set_name,
    recipe: session.recipe ?? null,
  };
}

export function mergeSessionRecord(
  existing: SessionSummary | undefined,
  incoming: SessionSummary,
): SessionSummary {
  if (!existing) return incoming;

  const keepExistingTitle =
    hasMeaningfulSessionTitle(existing) && !hasMeaningfulSessionTitle(incoming);
  if (!keepExistingTitle) return { ...existing, ...incoming, id: incoming.id };

  return {
    ...existing,
    ...incoming,
    id: incoming.id,
    name: existing.name,
    user_set_name: existing.user_set_name,
    recipe: existing.recipe ?? incoming.recipe,
  };
}

export function mergeSessionLists(prev: SessionSummary[], incoming: SessionSummary[]): SessionSummary[] {
  const previousById = new Map(prev.map((item) => [item.id, item]));
  return sortAndTrim(incoming.map((item) => mergeSessionRecord(previousById.get(item.id), item)));
}

export function appendSessionLists(prev: SessionSummary[], incoming: SessionSummary[]): SessionSummary[] {
  const previousById = new Map(prev.map((item) => [item.id, item]));
  const mergedIncoming = incoming.map((item) => mergeSessionRecord(previousById.get(item.id), item));
  const incomingIds = new Set(mergedIncoming.map((item) => item.id));
  return sortAndTrim([
    ...prev.filter((item) => !incomingIds.has(item.id)),
    ...mergedIncoming,
  ]);
}

export function prependUnique(prev: SessionSummary[], session: SessionSummary): SessionSummary[] {
  return sortAndTrim([
    mergeSessionRecord(prev.find((s) => s.id === session.id), session),
    ...prev.filter((s) => s.id !== session.id),
  ]);
}

export function touchSession(
  sessions: SessionSummary[],
  sessionId: string,
  messageDelta = 0,
): SessionSummary[] {
  const now = new Date().toISOString();
  return sortAndTrim(
    sessions.map((s) =>
      s.id === sessionId
        ? {
            ...s,
            updated_at: now,
            message_count: Math.max(0, s.message_count + messageDelta),
          }
        : s,
    ),
  );
}

export function getSessionDisplayName(session: SessionSummary): string {
  if (session.user_set_name) return session.name;
  if (session.recipe?.title) return session.recipe.title;
  if (shouldShowNewChatTitle(session)) return DEFAULT_CHAT_TITLE;
  return session.name;
}

function sameLocalDay(a: Date, b: Date): boolean {
  return (
    a.getFullYear() === b.getFullYear() &&
    a.getMonth() === b.getMonth() &&
    a.getDate() === b.getDate()
  );
}

export function getSessionDateKey(session: SessionSummary): string {
  const iso = session.updated_at ?? session.created_at;
  if (!iso) return '';
  const date = new Date(iso);
  if (Number.isNaN(date.getTime())) return '';
  return `${date.getFullYear()}-${date.getMonth()}-${date.getDate()}`;
}

export function formatSessionDateLabel(session: SessionSummary): string {
  const iso = session.updated_at ?? session.created_at;
  if (!iso) return '';
  const date = new Date(iso);
  if (Number.isNaN(date.getTime())) return '';

  const now = new Date();
  if (sameLocalDay(date, now)) return '今天';

  const yesterday = new Date(now);
  yesterday.setDate(yesterday.getDate() - 1);
  if (sameLocalDay(date, yesterday)) return '昨天';

  if (date.getFullYear() === now.getFullYear()) {
    return `${date.getMonth() + 1}月${date.getDate()}日`;
  }

  return `${date.getFullYear()}年${date.getMonth() + 1}月${date.getDate()}日`;
}

export type SessionDateGroup = {
  dateKey: string;
  label: string;
  sessions: SessionSummary[];
};

export function groupSessionsByDate(sessions: SessionSummary[]): SessionDateGroup[] {
  const groups: SessionDateGroup[] = [];
  for (const session of sessions) {
    const dateKey = getSessionDateKey(session);
    const label = formatSessionDateLabel(session) || '未知日期';
    const last = groups[groups.length - 1];
    if (last && last.dateKey === dateKey) {
      last.sessions.push(session);
    } else {
      groups.push({ dateKey, label, sessions: [session] });
    }
  }
  return groups;
}

const DEFAULT_SESSION_NAMES = new Set([DEFAULT_CHAT_TITLE, '新对话']);

export function getSessionListLabel(session: SessionSummary): string {
  const displayName = getSessionDisplayName(session).trim();
  if (displayName && !DEFAULT_SESSION_NAMES.has(displayName) && !isGeneratedSessionName(displayName)) {
    return displayName;
  }
  if (session.message_count > 0) {
    return `对话 · ${session.message_count} 条消息`;
  }
  return `会话 ${session.id.slice(0, 8)}`;
}