// 预览区标签的纯操作：打开已有标签只激活，关闭激活标签时选中相邻的一个。

export interface PreviewTab {
  id: string
  name: string
}

export function openPreviewTab(tabs: PreviewTab[], tab: PreviewTab): { tabs: PreviewTab[]; activeId: string } {
  const i = tabs.findIndex(t => t.id === tab.id)
  if (i >= 0) {
    const next = tabs.slice()
    next[i] = { ...next[i], name: tab.name || next[i].name }
    return { tabs: next, activeId: tab.id }
  }
  return { tabs: [...tabs, tab], activeId: tab.id }
}

export function closePreviewTab(
  tabs: PreviewTab[], activeId: string | null, id: string,
): { tabs: PreviewTab[]; activeId: string | null } {
  const i = tabs.findIndex(t => t.id === id)
  if (i < 0) return { tabs, activeId }
  const next = tabs.filter(t => t.id !== id)
  if (activeId !== id) return { tabs: next, activeId }
  const neighbor = next[Math.min(i, next.length - 1)] ?? null
  return { tabs: next, activeId: neighbor?.id ?? null }
}

/** 预览标签的会话键。空态（未选会话）统一落在 '_'：写入（requestPreview）与
 *  渲染（previewOpen/PreviewPane）共用同一口径，空态点开工件才能出现预览区。 */
export function previewTabsKey(currentConvId: string | null | undefined): string {
  return currentConvId ?? '_'
}

/** 进入会话时把空态打开的孤儿标签（'_' 键）并入会话键下；按 id 去重，
 *  会话侧顺序在前，'_' 键清空。无孤儿或目标即 '_' 时原样返回。 */
export function mergeOrphanPreviewTabs(
  tabsByConv: Record<string, PreviewTab[]>,
  convId: string,
): Record<string, PreviewTab[]> {
  const orphan = tabsByConv['_'] ?? []
  if (orphan.length === 0 || convId === '_') return tabsByConv
  const own = tabsByConv[convId] ?? []
  const ids = new Set(own.map(t => t.id))
  const merged = [...own, ...orphan.filter(t => !ids.has(t.id))]
  return { ...tabsByConv, [convId]: merged, '_': [] }
}