import { MatrixClient } from 'matrix-js-sdk';

/**
 * [Gitea #108] User-defined sidebar sections from standard `u.<name>` room
 * tags, so they sync across devices and other clients see the same tags.
 */
export const SECTION_TAG_PREFIX = 'u.';

export type RoomSection = {
  /** Display name ("Raids"). */
  name: string;
  /** Full tag name ("u.Raids"). */
  tag: string;
  /** Member room ids, by the tag's `order` (ascending), then by name. */
  rooms: string[];
};

export type TaggedRoom = {
  roomId: string;
  name: string;
  tags: Record<string, { order?: number | string } | undefined> | undefined;
};

export const sectionTag = (name: string): string => `${SECTION_TAG_PREFIX}${name.trim()}`;
export const isSectionTag = (tag: string): boolean =>
  tag.startsWith(SECTION_TAG_PREFIX) && tag.length > SECTION_TAG_PREFIX.length;
export const sectionName = (tag: string): string => tag.slice(SECTION_TAG_PREFIX.length);

const orderOf = (v: { order?: number | string } | undefined): number => {
  const n = typeof v?.order === 'string' ? parseFloat(v.order) : v?.order;
  return typeof n === 'number' && Number.isFinite(n) ? n : 1;
};

/**
 * Sections (alphabetical by name) with their members ordered by tag `order`
 * then name; `sectioned` is the set of rooms that appear in any section.
 * Empty sections simply don't exist — a section is its members' tags.
 */
export function deriveRoomSections(rooms: TaggedRoom[]): {
  sections: RoomSection[];
  sectioned: Set<string>;
} {
  const byTag = new Map<string, { roomId: string; order: number; name: string }[]>();
  const sectioned = new Set<string>();
  rooms.forEach((room) => {
    Object.entries(room.tags ?? {}).forEach(([tag, value]) => {
      if (!isSectionTag(tag)) return;
      const list = byTag.get(tag) ?? [];
      list.push({ roomId: room.roomId, order: orderOf(value), name: room.name });
      byTag.set(tag, list);
      sectioned.add(room.roomId);
    });
  });
  const sections = [...byTag.entries()]
    .map(([tag, members]) => ({
      tag,
      name: sectionName(tag),
      rooms: members
        .sort((a, b) => a.order - b.order || a.name.localeCompare(b.name))
        .map((m) => m.roomId),
    }))
    .sort((a, b) => a.name.localeCompare(b.name, undefined, { sensitivity: 'base' }));
  return { sections, sectioned };
}

/** Every section name in use across the user's rooms (for the "Add to section" menu). */
export function listSectionNames(mx: MatrixClient): string[] {
  const names = new Set<string>();
  mx.getRooms().forEach((room) => {
    Object.keys(room.tags ?? {}).forEach((tag) => {
      if (isSectionTag(tag)) names.add(sectionName(tag));
    });
  });
  return [...names].sort((a, b) => a.localeCompare(b, undefined, { sensitivity: 'base' }));
}

/** Validate a new section name; returns the error to show, or undefined. */
export const validateSectionName = (raw: string, existing: string[]): string | undefined => {
  const name = raw.trim();
  if (!name) return 'Give the section a name.';
  if (name.length > 40) return 'Keep it under 40 characters.';
  if (name.includes('.')) return 'Dots are not allowed in section names.';
  if (existing.some((e) => e.toLowerCase() === name.toLowerCase()))
    return 'A section with that name already exists.';
  return undefined;
};