/**
 * Mention autocomplete — the `@` trigger that opens an entity picker and
 * inserts a `CharacterMention` node.
 *
 * The editor package owns the low-level mechanics (detecting `@query`,
 * positioning the picker, inserting the mention atom). The *data* — which
 * entities to search — is injected by the app through a `MentionProvider`, so
 * this package never imports the app's entity store.
 *
 * The picker is a React component (`MentionPicker`) that reads a small
 * module-level `mentionPickerState` object shared with this extension. The
 * extension exposes an `insertMention` command; the picker calls it on Enter.
 */
import { Extension, type Editor, type RawCommands } from "@tiptap/core";
import type { Node } from "@tiptap/pm/model";
import { CHARACTER_MENTION } from "./constants.js";

/** A single entity option shown in the autocomplete picker. */
export interface MentionEntity {
  id: string;
  label: string;
  /** Optional subtitle (role / one-line bio) shown under the name. */
  subtitle?: string;
}

/**
 * The search provider the app injects. Given a query, return matching
 * entities sorted by relevance (best first). An empty query should return the
 * full list (or a capped prefix) so the picker shows candidates immediately.
 */
export interface MentionProvider {
  search: (query: string) => MentionEntity[];
}

/**
 * Shared picker state between the extension and the React picker. Kept at module
 * scope because the TipTap extension is a singleton and the picker is rendered
 * by the app alongside the editor — there is no cleaner channel between them.
 */
export interface MentionPickerState {
  open: boolean;
  query: string;
  /** Doc position of the `@` trigger (where the mention will be inserted). */
  atPos: number;
  /** Cursor position (end of the query). */
  from: number;
  /** Currently highlighted result index. */
  selectedIndex: number;
}

export const mentionPickerState: MentionPickerState = {
  open: false,
  query: "",
  atPos: 0,
  from: 0,
  selectedIndex: 0,
};

/**
 * Walk backwards from `from` over the doc text looking for the `@` trigger.
 * Returns the trigger position, or `-1` when the text before the cursor is not
 * a live mention query (no `@`, or a space/newline interrupts it).
 */
export function findMentionTrigger(doc: Node, from: number): number {
  let atPos = from;
  while (atPos > 0) {
    const ch = doc.textBetween(atPos - 1, atPos) ?? "";
    if (ch === "@") return atPos - 1;
    if (ch === " " || ch === "\n" || ch === "\t") return -1;
    atPos -= 1;
  }
  return -1;
}

/**
 * The autocomplete extension. Adds the `insertMention` command used by the
 * picker and (optionally) a keyboard shortcut to open the picker manually.
 */
export const MentionAutocomplete = Extension.create({
  name: "mentionAutocomplete",

  addOptions() {
    return {
      /** The trigger character. */
      trigger: "@",
    };
  },

  addCommands() {
    return {
      /**
       * Insert a `CharacterMention` atom at the current trigger, replacing the
       * `@query` text between the trigger and the cursor.
       */
      insertMention:
        (id: string, label: string) =>
        ({ editor }: { editor: Editor }) => {
          const { state, schema } = editor;
          const { from } = state.selection;
          const atPos = findMentionTrigger(state.doc, from);
          if (atPos < 0) return false;

          const nodeType = schema.nodes[CHARACTER_MENTION];
          if (!nodeType) return false;

          const mention = nodeType.create({ entityId: id, label });
          const tr = state.tr.deleteRange(atPos, from).insert(atPos, mention);
          editor.view.dispatch(tr);
          return true;
        },
    } as unknown as Partial<RawCommands>;
  },
});

export default MentionAutocomplete;