/**
 * Function-name autocomplete for a formula editor (see FormulaBar.vue and
 * TableGrid.vue's in-cell editor, which both wire this in the same way).
 *
 * Unlike useTheme.ts/useToasts.ts (module-level singletons), this factory
 * creates fresh, independent state per call -- each formula editor gets its
 * own dropdown/selection, since two editors are never showing suggestions
 * for the same formula at once.
 */
import { ref } from 'vue';
import { currentIdentifierAtCaret } from '../engine';
import { useDocument } from '../store/document';
import type { FnSuggestion } from '../store/types';

export function useFormulaAutocomplete() {
  const store = useDocument();
  const suggestions = ref<FnSuggestion[]>([]);
  const activeIndex = ref(0);

  /** Recompute the dropdown for the current buffer + caret -- call this
   *  after every edit to the text (an `input` handler). */
  function update(text: string, caret: number) {
    const hit = currentIdentifierAtCaret(text, caret);
    suggestions.value = hit && hit.text ? store.functionSuggestions(hit.text) : [];
    activeIndex.value = 0;
  }
  function close() {
    suggestions.value = [];
  }
  /** Move the highlighted suggestion by `delta` (wraps). No-op while closed. */
  function move(delta: number) {
    const n = suggestions.value.length;
    if (!n) return;
    activeIndex.value = (activeIndex.value + delta + n) % n;
  }
  /** The replacement the caller should apply via its own `replace(start, end,
   *  value)` (the same one point-mode already uses) to accept the currently
   *  highlighted suggestion -- `null` when no dropdown is open, so the
   *  caller falls through to its normal Tab/Enter handling. Appends "(" ,
   *  ready for arguments, same as Excel/Sheets' own autocomplete. */
  function accept(text: string, caret: number): { start: number; end: number; value: string } | null {
    if (!suggestions.value.length) return null;
    const hit = currentIdentifierAtCaret(text, caret);
    if (!hit) return null;
    return { start: hit.start, end: caret, value: suggestions.value[activeIndex.value].name + '(' };
  }

  return { suggestions, activeIndex, update, close, move, accept };
}