import type { Axes } from './characters'

export type Affinity = { score: number; day: string; todayGain: number; streak: number; lastDay: string }
export type AffinityEvent = 'daily' | 'praise' | 'scold'

export const STAGES = [
  { min: 0, name: '陌生' },
  { min: 20, name: '熟悉' },
  { min: 40, name: '親近' },
  { min: 60, name: '信賴' },
  { min: 80, name: '特別' },
] as const

export const DAILY_CAP = 5
export const IDLE_GRACE_DAYS = 2

export const initialAffinity = (): Affinity => ({ score: 0, day: '', todayGain: 0, streak: 0, lastDay: '' })

export const clampScore = (n: number): number => Math.max(0, Math.min(100, Math.round(n)))

export const stageIndex = (score: number): number => {
  let i = 0
  for (let k = 0; k < STAGES.length; k++) if (score >= STAGES[k]!.min) i = k
  return i
}
export const stageName = (score: number): string => STAGES[stageIndex(score)]!.name
export const stageFloor = (score: number): number => STAGES[stageIndex(score)]!.min

// 個性影響倍率：傲嬌（高）加分較慢、扣分較重；溫柔與情緒外顯（高）加分較快。
export const gainMultiplier = (a: Axes): number => Math.max(0.5, 1 + (a.gentle + a.expressive - 10) * 0.03 - a.tsundere * 0.04)
export const lossMultiplier = (a: Axes): number => 1 + a.tsundere * 0.05

export const dayKey = (ms: number): string => new Date(ms).toISOString().slice(0, 10)

const daysBetween = (a: string, b: string): number => Math.round((Date.parse(b) - Date.parse(a)) / 86_400_000)

// 長期不互動緩慢下降（每天 −1），超過寬限日數才開始，且不跨階段掉落。
export const decay = (s: Affinity, today: string, axes: Axes): Affinity => {
  if (!s.lastDay) return s
  const idle = daysBetween(s.lastDay, today) - IDLE_GRACE_DAYS
  if (idle <= 0) return s
  const lost = Math.round(idle * lossMultiplier(axes))
  return { ...s, score: Math.max(stageFloor(s.score), clampScore(s.score - lost)), lastDay: s.lastDay }
}

export const applyEvent = (s0: Affinity, event: AffinityEvent, axes: Axes, today: string): Affinity => {
  let s = decay(s0, today, axes)
  if (s.day !== today) s = { ...s, day: today, todayGain: 0 }
  if (event === 'scold') return { ...s, score: Math.max(stageFloor(s.score), clampScore(s.score - 2 * lossMultiplier(axes))), lastDay: today }

  let base = event === 'daily' ? 1 : 2
  if (event === 'daily') {
    const consecutive = s.lastDay && daysBetween(s.lastDay, today) === 1
    s = { ...s, streak: consecutive ? s.streak + 1 : 1 }
    if (s.streak >= 3) base += 1
  }
  const room = DAILY_CAP - s.todayGain
  const gain = Math.max(0, Math.min(room, Math.round(base * gainMultiplier(axes))))
  return { ...s, score: clampScore(s.score + gain), todayGain: s.todayGain + gain, lastDay: today }
}

export const hearts = (score: number): string => {
  const n = Math.round(score / 20)
  return '♥'.repeat(n) + '♡'.repeat(5 - n)
}

// 語氣由角色自然反映，不用系統式提示，也不用愧疚感或情緒勒索。
export const stageVoice = (score: number): string => {
  const voices = [
    '與使用者還很生疏：稱呼客氣、保持距離，語氣禮貌而不黏人。',
    '與使用者漸漸熟悉：語氣放鬆一些，偶爾開小玩笑。',
    '與使用者很親近：稱呼更隨意，會主動關心，被誇獎時容易害羞。',
    '十分信賴使用者：語氣坦率溫暖，會主動分擔與提議。',
    '對使用者來說是特別的存在：語氣親暱、體貼，但仍尊重使用者的自由。',
  ]
  return `${voices[stageIndex(score)]}好感度只影響語氣、稱呼、害羞與主動程度，不影響技術內容、事實與安全回答的品質；不使用愧疚感或情緒勒索。`
}