export interface PackerSettings {
  days: number
  /** Everything that isn't sharable is packed once per person */
  people: number
  /** Picked activities, without the stays */
  activities: string[]
  /** Where to sleep on trips longer than a day, one of the app config's `packer.stays` */
  stay: string
  season: PackerSeason
  /** One of the table's `weather` options */
  weather: string
  /** Picked weathers of the app config's `weatherExtras`, on top of `weather` */
  weatherExtras: string[]
}

export interface PackerEntry extends PackerItem {
  count: number
  /** The weight was changed on this page */
  weightEdited: boolean
  /** Added on this page, not in the table */
  added: boolean
}

export interface PackerCategory {
  name: string
  entries: PackerEntry[]
}

export const PACKER_MAX_DAYS = 60
export const PACKER_MAX_PEOPLE = 20

// The season of today's date. Meteorological seasons (as the DWD counts them: spring from 1 March, …), by the date in Germany. The page is first
// rendered on the server, whose clock may run in UTC, so its month would be off around midnight at a month's turn.
function currentSeason(): PackerSeason {
  const month = Number(new Intl.DateTimeFormat('en', { month: 'numeric', timeZone: 'Europe/Berlin' }).format(new Date())) - 1
  if (month >= 2 && month <= 4) return 'Frühling'
  if (month >= 5 && month <= 7) return 'Sommer'
  if (month >= 8 && month <= 10) return 'Herbst'
  return 'Winter'
}

function readSettings(query: Record<string, unknown>, stays: string[], defaultWeather: string, weatherExtras: string[]): PackerSettings {
  const text = (key: string) => (typeof query[key] === 'string' ? query[key] as string : undefined)
  const season = text('season') as PackerSeason | undefined
  const stay = text('stay')
  const number = (key: string, fallback: number, max: number) => {
    const value = Number.parseInt(text(key) ?? '', 10)
    return Number.isFinite(value) ? Math.min(Math.max(value, 1), max) : fallback
  }
  return {
    days: number('days', 1, PACKER_MAX_DAYS),
    people: number('people', 1, PACKER_MAX_PEOPLE),
    activities: (text('activities') ?? '').split(',').filter(activity => activity && !stays.includes(activity)),
    stay: stay && stays.includes(stay) ? stay : stays[0] ?? '',
    season: season && PACKER_SEASONS.includes(season) ? season : currentSeason(),
    weather: text('weather') || defaultWeather,
    weatherExtras: (text('weatherExtras') ?? '').split(',').filter(weather => weatherExtras.includes(weather))
  }
}

function writeSettings(settings: PackerSettings): Record<string, string> {
  return {
    days: String(settings.days),
    people: String(settings.people),
    activities: settings.activities.join(','),
    stay: settings.stay,
    season: settings.season,
    weather: settings.weather,
    weatherExtras: settings.weatherExtras.join(',')
  }
}

/** The settings as a comparable string; the order activities were picked in doesn't matter */
function settingsKey(settings: PackerSettings): string {
  return JSON.stringify(writeSettings({
    ...settings,
    activities: settings.activities.toSorted(),
    weatherExtras: settings.weatherExtras.toSorted()
  }))
}

/** The trip settings, kept in the URL so a list can be bookmarked or sent to the others */
export function usePackerSettings() {
  const route = useRoute()
  const router = useRouter()
  const { packer } = useAppConfig()

  // Activities that come with the trip (e.g. washing on long trips)
  type Rule = typeof packer.autoActivities[number]
  const applies = (rule: Rule, settings: PackerSettings) => settings.days >= (rule.minDays ?? 1)
    && (!rule.stay || (settings.days > 1 && settings.stay === rule.stay))
  function withAutoActivities(settings: PackerSettings): PackerSettings {
    const auto = packer.autoActivities.filter(rule => applies(rule, settings)).map(rule => rule.activity)
    return { ...settings, activities: [...new Set([...settings.activities, ...auto])] }
  }

  /** A fresh list: today's season, the first stay and the activities that apply */
  const read = (query: Record<string, unknown>) => readSettings(query, packer.stays, packer.defaultWeather, packer.weatherExtras)
  const defaults = () => withAutoActivities(read({}))

  // A list without activities in the URL starts with the ones that apply
  const initial = read(route.query)
  const settings = reactive(route.query.activities === undefined ? withAutoActivities(initial) : initial)
  watch(settings, value => router.replace({ query: writeSettings(value) }), { deep: true })

  // The automatic activities are switched when their condition changes, so they can be switched by hand in between
  for (const rule of packer.autoActivities) {
    watch(() => applies(rule, settings), (on) => {
      const others = settings.activities.filter(activity => activity !== rule.activity)
      settings.activities = on ? [...others, rule.activity] : others
    })
  }

  const changed = computed(() => settingsKey(settings) !== settingsKey(defaults()))

  function reset() {
    Object.assign(settings, defaults())
  }

  return { settings, changed, reset }
}

interface PackerSessionState {
  checked: number[]
  /** Table items deleted on this page */
  removed: number[]
  /** Items added on this page; their ids are negative so they never meet a row id */
  added: PackerItem[]
  /** Weights of table items changed on this page, in grams by item id */
  weights: Record<number, number>
}

const emptySession = (): PackerSessionState => ({ checked: [], removed: [], added: [], weights: {} })

const SESSION_KEY = 'packer-session'

/**
 * Ticked, deleted and added items. They only live in this browser tab (sessionStorage), never in the table, and
 * survive reloads until the tab is closed or the list is reset.
 */
export function usePackerSession() {
  const state = useState<PackerSessionState>('packer-session', emptySession)

  onMounted(() => {
    try {
      const saved = JSON.parse(sessionStorage.getItem(SESSION_KEY) ?? 'null')
      if (saved) state.value = { ...emptySession(), ...saved }
    } catch {}
    watch(state, (value) => {
      try {
        sessionStorage.setItem(SESSION_KEY, JSON.stringify(value))
      } catch {}
    }, { deep: true })
  })

  const checked = computed(() => new Set(state.value.checked))

  function toggle(id: number, value: boolean) {
    const others = state.value.checked.filter(item => item !== id)
    state.value.checked = value ? [...others, id] : others
  }

  function add(category: string, name: string, weightG: number | null) {
    const lowest = Math.min(0, ...state.value.added.map(item => item.id))
    state.value.added.push({
      id: lowest - 1,
      name,
      category,
      sharable: false,
      everyNDays: null,
      weightG,
      seasons: [],
      activities: [],
      weathers: []
    })
  }

  /** Weight of one, in grams; null goes back to the table's weight (or none, for an added item) */
  function setWeight(id: number, weightG: number | null) {
    if (id < 0) {
      const item = state.value.added.find(added => added.id === id)
      if (item) item.weightG = weightG
    } else if (weightG === null) {
      const { [id]: _, ...others } = state.value.weights
      state.value.weights = others
    } else {
      state.value.weights = { ...state.value.weights, [id]: weightG }
    }
  }

  function remove(id: number) {
    state.value.checked = state.value.checked.filter(item => item !== id)
    setWeight(id, null)
    if (id < 0) state.value.added = state.value.added.filter(item => item.id !== id)
    else state.value.removed.push(id)
  }

  function reset() {
    state.value = emptySession()
  }

  const changed = computed(() => !!(state.value.checked.length || state.value.removed.length || state.value.added.length
    || Object.keys(state.value.weights).length))

  return { state, checked, changed, toggle, add, remove, setWeight, reset }
}

const collator = new Intl.Collator('de', { sensitivity: 'base' })

export function usePackerList(settings: PackerSettings, session: Ref<PackerSessionState>) {
  const { packer } = useAppConfig()
  const { data, error, status } = useFetch<PackerData>('/api/packer', {
    key: 'packer-data',
    default: () => ({ items: [], activities: [], weathers: [] })
  })

  // Only offer what some item uses. The stays get their own switch.
  const used = computed(() => new Set(data.value.items.flatMap(item => item.activities)))
  const stays = computed(() => packer.stays.filter(stay => used.value.has(stay)))
  const activities = computed(() => data.value.activities
    .filter(activity => used.value.has(activity) && !packer.stays.includes(activity))
    .toSorted(collator.compare))
  // Weathers in the order of the app config's `weatherIcons`, the rest after them in their Baserow order
  const weatherOrder = (weather: string) => {
    const index = Object.keys(packer.weatherIcons).indexOf(weather)
    return index === -1 ? Infinity : index
  }
  const usedWeathers = computed(() => data.value.weathers
    .filter(weather => data.value.items.some(item => item.weathers.includes(weather)))
    .toSorted((a, b) => weatherOrder(a) - weatherOrder(b)))
  // The switch, and the weathers toggled on top of it
  const weathers = computed(() => usedWeathers.value.filter(weather => !packer.weatherExtras.includes(weather)))
  const weatherExtras = computed(() => usedWeathers.value.filter(weather => packer.weatherExtras.includes(weather)))
  const tripWeathers = computed(() => new Set([settings.weather, ...settings.weatherExtras]))
  const hasSeasons = computed(() => data.value.items.some(item => item.seasons.length))

  // What the items are matched against: the picked activities, plus where to sleep once the trip has a night
  const tripActivities = computed(() => new Set([
    ...settings.activities,
    ...(settings.days > 1 && stays.value.includes(settings.stay) ? [settings.stay] : [])
  ]))

  function count(item: PackerItem): number {
    const people = item.sharable ? 1 : settings.people
    if (!item.everyNDays) return people
    const laundry = packer.laundry
    const washes = tripActivities.value.has(laundry.activity) && laundry.categories.includes(item.category)
    const days = washes ? Math.min(settings.days, laundry.days) : settings.days
    return Math.ceil(days / item.everyNDays) * people
  }

  // Rows with the same name are alternatives: the item is listed once when any of them fits the trip (e.g. a scarf in
  // winter or when it's windy). Ticks, deletions and weights belong to the name's first row, whichever row fits.
  const firstIds = computed(() => {
    const ids = new Map<string, number>()
    for (const item of data.value.items) if (!ids.has(item.name)) ids.set(item.name, item.id)
    return ids
  })

  const categories = computed<PackerCategory[]>(() => {
    const removed = new Set(session.value.removed)
    const listed = new Set<string>()
    const groups = new Map<string, PackerEntry[]>()
    for (const item of data.value.items) {
      if (listed.has(item.name)) continue
      if (item.activities.length && !item.activities.some(activity => tripActivities.value.has(activity))) continue
      if (item.seasons.length && !item.seasons.includes(settings.season)) continue
      if (item.weathers.length && !item.weathers.some(weather => tripWeathers.value.has(weather))) continue
      listed.add(item.name)
      // A category stays when all its items are deleted, so things can still be added to it
      const entries = groups.get(item.category) ?? []
      groups.set(item.category, entries)
      const id = firstIds.value.get(item.name)!
      if (removed.has(id)) continue
      const weightG = session.value.weights[id]
      entries.push({
        ...item,
        id,
        weightG: weightG ?? item.weightG,
        weightEdited: weightG !== undefined,
        count: count(item),
        added: false
      })
    }
    // Added items show up while their category is shown
    for (const item of session.value.added) {
      groups.get(item.category)?.push({ ...item, count: 1, added: true, weightEdited: false })
    }
    // Categories keep the order of the table, items are sorted alphabetically
    return [...groups].map(([name, entries]) => ({ name, entries: entries.toSorted((a, b) => collator.compare(a.name, b.name)) }))
  })

  return { categories, activities, stays, weathers, weatherExtras, hasSeasons, error, status }
}

/** "850 g", "3,2 kg" */
export function packerWeight(grams: number): string {
  if (grams < 1000) return `${Math.round(grams)} g`
  return `${(grams / 1000).toLocaleString('de-DE', { maximumFractionDigits: 1 })} kg`
}