(function (root, factory) {
  const api = factory();
  if (typeof module === 'object' && module.exports) module.exports = api;
  else root.createTaskOverlayHistory = api;
})(typeof globalThis !== 'undefined' ? globalThis : this, function () {
  'use strict';

  const allowed = new Set(['new', 'find', 'search', 'search-preview', 'plan-today', 'plan-today-preview', 'today-readiness']);

  return function createTaskOverlayHistory({ history, eventTarget, onChange }) {
    let active = allowed.has(history.state?.taskOverlay) ? history.state.taskOverlay : null;
    let started = false;

    function stateKind(state = history.state) {
      return allowed.has(state?.taskOverlay) ? state.taskOverlay : null;
    }

    function apply(state) {
      const next = stateKind(state);
      if (next === active) return;
      const previous = active;
      active = next;
      onChange(next, previous);
    }

    return {
      start() {
        if (started) return;
        started = true;
        eventTarget.addEventListener('popstate', event => apply(event.state));
      },
      open(kind) {
        if (!allowed.has(kind)) return false;
        if (active === kind) return true;
        const previous = active;
        const state = { ...(history.state || {}), taskOverlay: kind };
        history.pushState(state, '');
        active = kind;
        onChange(kind, previous);
        return true;
      },
      close() {
        if (!active) return false;
        history.back();
        return true;
      },
      leave() {
        if (!active) return false;
        const previous = active;
        const state = { ...(history.state || {}) };
        delete state.taskOverlay;
        history.replaceState(state, '');
        active = null;
        onChange(null, previous);
        return true;
      },
      current() { return active; },
    };
  };
});