import type { Category } from './data/types'

export type Project = {
  name: string
  route_path: string
}

type ProjectsPayload = {
  projects?: Project[]
}

const PROJECTS_ENDPOINT = '/api/projects'
const EVENTS_ENDPOINT = '/api/projects/events'
/** 读取服务端扫描出的项目列表。 */
export async function fetchProjects(signal?: AbortSignal): Promise<Project[]> {
  const response = await fetch(PROJECTS_ENDPOINT, {
    signal,
    headers: { Accept: 'application/json' },
  })

  if (!response.ok) {
    throw new Error(`请求 ${PROJECTS_ENDPOINT} 失败：HTTP ${response.status}`)
  }

  const payload = (await response.json()) as ProjectsPayload
  return Array.isArray(payload.projects) ? payload.projects : []
}

export type ProjectEventsHandlers = {
  onProjects: (projects: Project[]) => void
  /** SSE 连接建立 / 断开时回调，浏览器的 EventSource 会自行重连。 */
  onConnectionChange?: (connected: boolean) => void
}

/**
 * 订阅服务端的项目快照推送。
 * 浏览器不支持 SSE 时静默降级为空清理函数，页面仍可用手动刷新。
 */
export function subscribeProjects(handlers: ProjectEventsHandlers): () => void {
  if (typeof EventSource === 'undefined') {
    return () => {}
  }

  const source = new EventSource(EVENTS_ENDPOINT)

  const handleProjects = (event: Event) => {
    try {
      const payload = JSON.parse((event as MessageEvent<string>).data) as ProjectsPayload
      if (Array.isArray(payload.projects)) {
        handlers.onProjects(payload.projects)
      }
    } catch {
      // 单条事件格式异常时保留旧数据，等待下一次推送
    }
  }

  const handleOpen = () => handlers.onConnectionChange?.(true)
  const handleError = () => handlers.onConnectionChange?.(false)

  source.addEventListener('projects', handleProjects)
  source.addEventListener('open', handleOpen)
  source.addEventListener('error', handleError)

  return () => {
    source.removeEventListener('projects', handleProjects)
    source.removeEventListener('open', handleOpen)
    source.removeEventListener('error', handleError)
    source.close()
  }
}

// ---------------------------------------------------------------------------
// 内容目录：数据来自后端的 SQLite 内容库（data/stash.db），不再是前端静态数组
// ---------------------------------------------------------------------------

const CATALOG_ENDPOINT = '/api/catalog'
const CATALOG_EVENTS_ENDPOINT = '/api/catalog/events'

type CatalogPayload = {
  categories?: Category[]
}

/** 内容目录的完整返回；侧栏由这份分类树派生 */
export type Catalog = {
  categories: Category[]
}

/**
 * 拉取完整内容目录。
 *
 * 数据量只有几十 KB，一次全量取回即可；搜索仍然在前端按关键字过滤。
 */
export async function fetchCatalog(signal?: AbortSignal): Promise<Catalog> {
  const response = await fetch(CATALOG_ENDPOINT, {
    signal,
    headers: { Accept: 'application/json' },
  })

  if (!response.ok) {
    throw new Error(`请求 ${CATALOG_ENDPOINT} 失败：HTTP ${response.status}`)
  }

  const payload = (await response.json()) as CatalogPayload

  return {
    categories: Array.isArray(payload.categories) ? payload.categories : [],
  }
}

/**
 * 订阅内容库变更。
 *
 * 服务端用 SQLite 的 data_version 检测「外部工具改了库」，事件里不带数据，
 * 只表示「该重新拉一次了」，避免两套数据结构需要保持同步。
 */
export function subscribeCatalog(onChange: () => void): () => void {
  if (typeof EventSource === 'undefined') {
    return () => {}
  }

  const source = new EventSource(CATALOG_EVENTS_ENDPOINT)
  const handleChange = () => onChange()

  source.addEventListener('catalog', handleChange)

  return () => {
    source.removeEventListener('catalog', handleChange)
    source.close()
  }
}