/**
 * 代码问答的存法：每个工作区文件夹一份 `<workspace>/.spx/code-qa.json`，读写的规矩同文件注释（见 pathMap）。
 * 形状是 `{ "相对路径": [{ anchor, entries: [{ id, question, answer, createdAt, sessionId }] }] }`：
 * 一份文件里挂着问答的每一块一项（anchor 见 BlockAnchors），块下面问过的按时间排。
 */

import type { PathMap, PathMapFile } from '../pathMap'

/** 问过的一次：问题、回答（Markdown）、什么时候问的（ISO 时间）、Claude Code 的会话 id。 */
export interface QaEntry {
  id: string
  question: string
  answer: string
  createdAt: string
  sessionId: string
  /** 用哪个 profile 答的（profile 名）；选「默认」时、以前存的没有 */
  profile?: string
}

/** 挂在一块上的问答。 */
export interface QaThread {
  anchor: string
  entries: QaEntry[]
}

export type QaMap = PathMap<QaThread[]>

function isRecord(value: unknown): value is Record<string, unknown> {
  return typeof value === 'object' && value !== null && !Array.isArray(value)
}

function text(value: unknown): string | undefined {
  return typeof value === 'string' && value.trim() !== '' ? value : undefined
}

function parseEntry(value: unknown): QaEntry | undefined {
  if (!isRecord(value))
    return undefined
  const [id, question, answer, createdAt, profile] = [text(value.id), text(value.question), text(value.answer), text(value.createdAt), text(value.profile)]
  if (!id || !question || !answer || !createdAt || Number.isNaN(Date.parse(createdAt)))
    return undefined
  return { id, question, answer, createdAt, sessionId: typeof value.sessionId === 'string' ? value.sessionId : '', ...(profile && { profile }) }
}

/** 同一块的并成一项；块按记号排，问答按时间排：写出来的顺序稳定，git diff 干净。 */
function tidy(threads: QaThread[]): QaThread[] {
  const byAnchor = new Map<string, QaEntry[]>()
  for (const thread of threads)
    byAnchor.set(thread.anchor, [...byAnchor.get(thread.anchor) ?? [], ...thread.entries])
  return [...byAnchor]
    .filter(([, entries]) => entries.length > 0)
    .sort(([a], [b]) => a < b ? -1 : a > b ? 1 : 0)
    .map(([anchor, entries]) => ({
      anchor,
      entries: [...entries].sort((a, b) => Date.parse(a.createdAt) - Date.parse(b.createdAt) || (a.id < b.id ? -1 : a.id > b.id ? 1 : 0)),
    }))
}

/** 一份文件的问答：不是数组、一项都认不出的当没有；认不出的块、问答跳过。 */
function parseThreads(value: unknown): QaThread[] | undefined {
  if (!Array.isArray(value))
    return undefined
  const threads = value.flatMap((item): QaThread[] => {
    const anchor = isRecord(item) ? text(item.anchor) : undefined
    if (!anchor || !isRecord(item) || !Array.isArray(item.entries))
      return []
    return [{ anchor, entries: item.entries.flatMap(entry => parseEntry(entry) ?? []) }]
  })
  const tidied = tidy(threads)
  return tidied.length > 0 ? tidied : undefined
}

export const QA_FILE: PathMapFile<QaThread[]> = {
  path: '.spx/code-qa.json',
  label: '代码问答',
  parse: parseThreads,
}

/** 在 key 这份文件的 anchor 那块下面记一次问答。 */
export function withEntry(map: QaMap, key: string, anchor: string, entry: QaEntry): QaMap {
  return { ...map, [key]: tidy([...map[key] ?? [], { anchor, entries: [entry] }]) }
}

/** 删掉一次问答；块下面删光了这块就不挂了，文件里删光了这份文件就不记了。 */
export function withoutEntry(map: QaMap, key: string, anchor: string, entryId: string): QaMap {
  const threads = tidy((map[key] ?? []).map(thread => thread.anchor === anchor
    ? { anchor, entries: thread.entries.filter(entry => entry.id !== entryId) }
    : thread))
  const next = { ...map }
  delete next[key]
  return threads.length > 0 ? { ...next, [key]: threads } : next
}

/** 再问 anchor 那块时接着的会话：这块最近一次问答的会话 id；没问过、或那次没记会话 id 时没有，重新开会话。 */
export function latestSession(threads: readonly QaThread[] | undefined, anchor: string): string | undefined {
  return threads?.find(thread => thread.anchor === anchor)?.entries.at(-1)?.sessionId || undefined
}