import { getFrame } from '../platform/frame.ts'
import type { ReconcilerTask } from '../core/reconciler-core.ts'

/**
 * dsh-file-viewer open marker. The plugin renders a
 * <section class="dsfv-panel" data-conversation-composer-overlay> as a
 * conversation.view tab next to "对话"/"轨迹" (its own idempotent <style>
 * uses the stable `dsfv-` prefix — no CSS Modules). Detection keys on the
 * panel's own `.dsfv-panel` class, NOT on `data-conversation-composer-overlay`:
 * that attribute is the host conversation.view system's generic overlay flag
 * shared by every view tab (the built-in trajectory tab sets it too), so it
 * would false-positive the marker whenever any overlay is open. The marker
 * only reflects the file-viewer panel existing and serves the compat.css
 * mobile layout rules. Gesture takeover is a separate signal —
 * sidebar-swipe.ts reads the generic overlay attribute directly.
 * Idempotent like the other frame markers; dispose clears it when the tab
 * unmounts or on deactivation.
 * Scoped to the mobile branch because the reconciler only runs when the
 * mobile breakpoint is active (registerReconcileTasks installs it there).
 * (Port of community fork fix 2ff7976, re-scoped per design
 * 2026-09-06-conversation-overlay-takeover-design.md §4.1.)
 */
export function createFileViewerMarkerTask(): ReconcilerTask {
  return {
    name: 'file-viewer-open-marker',
    scopes: ['*'],
    ensure: () => {
      const frame = getFrame()
      if (frame === null) return
      const active = document.querySelector('.dsfv-panel') !== null
      if (active) {
        frame.setAttribute('data-file-viewer-open', '')
      } else if (frame.hasAttribute('data-file-viewer-open')) {
        frame.removeAttribute('data-file-viewer-open')
      }
    },
    dispose: () => {
      getFrame()?.removeAttribute('data-file-viewer-open')
    },
  }
}