export type ModelName = 'haiku' | 'sonnet' | 'opus'
export type Effort = 'low' | 'medium' | 'high'
export type Tone = 'neutral' | 'praise' | 'scold'
export type Route = { difficulty: number; model: ModelName; effort: Effort; tone: Tone; ack: string; work: boolean }

export const LADDER: readonly ModelName[] = ['haiku', 'sonnet', 'opus']

export const FALLBACK_ROUTE: Route = { difficulty: 5, model: 'sonnet', effort: 'medium', tone: 'neutral', ack: '', work: false }

export const CLASSIFY_PROMPT =
  '你是路由器。讀下面使用者輸入，只回傳一行 JSON：' +
  '{"difficulty":1-10,"model":"haiku|sonnet|opus","effort":"low|medium|high","tone":"neutral|praise|scold","ack":"角色以口吻立刻回應的一句話","work":true|false}。work 為 true 表示需要動手做事（讀寫檔、執行指令、搜尋、改程式）；純閒聊或一句話可答的問題為 false。' +
  'difficulty 低用 haiku，中用 sonnet，高或需深入推理用 opus；tone 是使用者對角色的態度（誇獎／感謝為 praise，責罵為 scold）。\n\n使用者輸入：\n'

const isModel = (v: unknown): v is ModelName => v === 'haiku' || v === 'sonnet' || v === 'opus'
const isEffort = (v: unknown): v is Effort => v === 'low' || v === 'medium' || v === 'high'
const isTone = (v: unknown): v is Tone => v === 'neutral' || v === 'praise' || v === 'scold'

export const parseRoute = (text: string): Route => {
  const m = /\{[\s\S]*\}/.exec(text)
  if (!m) return FALLBACK_ROUTE
  try {
    const j = JSON.parse(m[0]) as Record<string, unknown>
    return {
      difficulty: typeof j.difficulty === 'number' ? j.difficulty : FALLBACK_ROUTE.difficulty,
      model: isModel(j.model) ? j.model : FALLBACK_ROUTE.model,
      effort: isEffort(j.effort) ? j.effort : FALLBACK_ROUTE.effort,
      tone: isTone(j.tone) ? j.tone : 'neutral',
      ack: typeof j.ack === 'string' ? j.ack.slice(0, 200) : '',
      work: j.work === true,
    }
  } catch {
    return FALLBACK_ROUTE
  }
}

export type ChooseOptions = {
  candidates: readonly ModelName[]
  lockModel?: ModelName
  lockEffort?: Effort
  /** 最緊的額度剩餘百分比；低於 downgradeAt 就降一級。 */
  quotaRemain?: number
  downgradeAt: number
}

export const choose = (r: Route, o: ChooseOptions): { model: ModelName; effort: Effort; downgraded: boolean } => {
  const effort = o.lockEffort ?? r.effort
  if (o.lockModel) return { model: o.lockModel, effort, downgraded: false }
  const allowed = LADDER.filter(m => o.candidates.includes(m))
  const pool = allowed.length ? allowed : LADDER
  let idx = Math.max(0, pool.indexOf(r.model))
  if (!pool.includes(r.model)) idx = pool.length - 1 // 選到不在候選內的模型時取候選最強者
  let downgraded = false
  if (o.quotaRemain !== undefined && o.quotaRemain < o.downgradeAt && idx > 0) {
    idx -= 1
    downgraded = true
  }
  return { model: pool[idx]!, effort, downgraded }
}