/**
 * 从 Claude projects 目录扫描已 /rename（jsonl 含 custom-title）且尚未登记到
 * managed store 的会话，供「导入」候选列表使用。
 */

import { promises as fsp } from 'node:fs'
import * as path from 'node:path'
import { projectsDirFor } from '../cc/sessionWatcher'
import { readManagedSessions } from './managedStore'

export interface ImportableNamedSession {
  id: string
  name: string
  mtimeMs: number
}

/** 从 jsonl 文本提取最后一条 custom-title（trim 后非空），否则 null */
export function extractLastCustomTitle(jsonlText: string): string | null {
  let last: string | null = null
  const lines = jsonlText.split(/\r?\n/)
  for (const line of lines) {
    const trimmed = line.trim()
    if (!trimmed)
      continue
    let parsed: unknown
    try {
      parsed = JSON.parse(trimmed)
    }
    catch {
      continue
    }
    if (!parsed || typeof parsed !== 'object')
      continue
    const rec = parsed as { type?: unknown, customTitle?: unknown }
    if (rec.type !== 'custom-title')
      continue
    if (typeof rec.customTitle !== 'string')
      continue
    const title = rec.customTitle.trim()
    if (!title)
      continue
    last = title
  }
  return last
}

/**
 * 列出可导入命名会话：扫 projectsDir 顶层 *.jsonl，过滤已在 managed 的 id，mtime 降序。
 * `projectsDir` 可选，便于测试注入；默认 `projectsDirFor(workspaceRoot)`。
 */
export async function listImportableNamedSessions(
  workspaceRoot: string,
  projectsDir?: string,
): Promise<ImportableNamedSession[]> {
  const dir = projectsDir ?? projectsDirFor(workspaceRoot)
  let entries: import('node:fs').Dirent[]
  try {
    entries = await fsp.readdir(dir, { withFileTypes: true })
  }
  catch {
    return []
  }

  const managed = await readManagedSessions(workspaceRoot)
  const managedIds = new Set(managed.sessions.map(s => s.id))

  const results: ImportableNamedSession[] = []
  for (const ent of entries) {
    if (!ent.isFile() || !ent.name.endsWith('.jsonl'))
      continue
    const id = ent.name.slice(0, -'.jsonl'.length)
    if (!id || managedIds.has(id))
      continue
    const filePath = path.join(dir, ent.name)
    let text: string
    let mtimeMs: number
    try {
      const [raw, st] = await Promise.all([
        fsp.readFile(filePath, 'utf8'),
        fsp.stat(filePath),
      ])
      text = raw
      mtimeMs = st.mtimeMs
    }
    catch {
      continue
    }
    const name = extractLastCustomTitle(text)
    if (!name)
      continue
    results.push({ id, name, mtimeMs })
  }

  results.sort((a, b) => b.mtimeMs - a.mtimeMs)
  return results
}