'use client'

import { useLocale, useTranslations } from 'next-intl'
import { useCallback, useEffect, useMemo, useState } from 'react'
import { AttnLine } from '@/components/ui/attn-line'
import { Button } from '@/components/ui/button'
import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card'
import { Label } from '@/components/ui/label'
import { Switch } from '@/components/ui/switch'
import { useToast } from '@/components/ui/use-toast'
import { useCompany } from '@/contexts/CompanyContext'
import { Cloud, Download, Info, Loader2 } from 'lucide-react'
import { ENABLED_EXTENSION_IDS } from '@/lib/extensions/_generated/enabled-extensions'
import { getSettingsPanel } from '@/lib/extensions/settings-panel-registry'
import type { FiscalPeriod } from '@/types'
import {
  getErrorMessage as getUserErrorMessage,
  type ErrorLocale,
} from '@/lib/errors/get-error-message'

const CloudBackupPanel = getSettingsPanel('cloud-backup')
const hasCloudBackup = ENABLED_EXTENSION_IDS.has('cloud-backup')

type Scope = 'all' | 'period'

interface EstimateResponse {
  total_bytes: number
  document_bytes: number
  document_count: number
  size_limit_bytes: number
  within_limit: boolean
}

const LAST_DOWNLOAD_STORAGE_KEY = 'Accounted:last-backup-download'

export function BackupDownloadForm() {
  const t = useTranslations('settings_backup_download')
  const errorLocale = useLocale() as ErrorLocale
  const { toast } = useToast()
  const { company } = useCompany()

  const [scope, setScope] = useState<Scope>('all')
  const [includeDocuments, setIncludeDocuments] = useState(true)
  // null = the fiscal years are not known: still loading, or the read failed
  // (periodsError). A failed read must never render the confirmed-empty
  // "Inga räkenskapsår" option: the company usually has fiscal years, the
  // read just did not land. Scope "all" never touches this list, so the full
  // backup keeps working either way.
  const [periods, setPeriods] = useState<FiscalPeriod[] | null>(null)
  // detail === null: transient, so the line carries a retry. A detail sentence
  // means the user has to act (an expired session) and a retry cannot help.
  const [periodsError, setPeriodsError] = useState<{ detail: string | null } | null>(null)
  const [periodsReloadKey, setPeriodsReloadKey] = useState(0)
  const [selectedPeriodId, setSelectedPeriodId] = useState<string>('')
  const [estimate, setEstimate] = useState<EstimateResponse | null>(null)
  const [isLoadingEstimate, setIsLoadingEstimate] = useState(false)
  const [isDownloading, setIsDownloading] = useState(false)
  const [lastDownloadedAt, setLastDownloadedAt] = useState<string | null>(null)

  const storageKey = useMemo(
    () => (company ? `${LAST_DOWNLOAD_STORAGE_KEY}:${company.id}` : null),
    [company]
  )

  useEffect(() => {
    if (!storageKey) return
    setLastDownloadedAt(window.localStorage.getItem(storageKey))
  }, [storageKey])

  useEffect(() => {
    let cancelled = false
    async function loadPeriods() {
      setPeriodsError(null)
      try {
        const res = await fetch('/api/bookkeeping/fiscal-periods')
        if (!res.ok) {
          // Not-JSON bodies (an HTML error page, an empty 502) leave null,
          // and getErrorMessage falls back to the status map.
          const body = await res.json().catch(() => null)
          if (cancelled) return
          const sessionGone = res.status === 401 || res.status === 403
          setPeriods(null)
          setPeriodsError({
            detail: sessionGone
              ? getUserErrorMessage(body, { statusCode: res.status, locale: errorLocale })
              : null,
          })
          return
        }
        // A 200 whose body will not parse throws into the catch below; a 200
        // without the list is a failed read too. Neither may become a
        // fabricated "Inga räkenskapsår".
        const body = await res.json()
        if (cancelled) return
        if (!Array.isArray(body?.data)) {
          setPeriods(null)
          setPeriodsError({ detail: null })
          return
        }
        const sorted = body.data as FiscalPeriod[]
        setPeriods(sorted)
        if (sorted.length > 0) {
          setSelectedPeriodId((prev) => prev || sorted[0].id)
        }
      } catch {
        if (!cancelled) {
          setPeriods(null)
          setPeriodsError({ detail: null })
        }
      }
    }
    void loadPeriods()
    return () => {
      cancelled = true
    }
  }, [periodsReloadKey, errorLocale])

  const estimateUrl = useMemo(() => {
    const params = new URLSearchParams({ estimate: '1', scope })
    if (scope === 'period' && selectedPeriodId) {
      params.set('period_id', selectedPeriodId)
    }
    if (!includeDocuments) {
      params.set('include_documents', 'false')
    }
    return `/api/reports/full-archive?${params.toString()}`
  }, [scope, selectedPeriodId, includeDocuments])

  useEffect(() => {
    if (scope === 'period' && !selectedPeriodId) {
      setEstimate(null)
      return
    }
    let cancelled = false
    setIsLoadingEstimate(true)
    setEstimate(null)
    ;(async () => {
      try {
        const res = await fetch(estimateUrl)
        if (!res.ok) return
        const { data } = (await res.json()) as { data: EstimateResponse }
        if (!cancelled) setEstimate(data)
      } catch {
        // leave estimate null; we still let users attempt the download
      } finally {
        if (!cancelled) setIsLoadingEstimate(false)
      }
    })()
    return () => {
      cancelled = true
    }
  }, [estimateUrl, scope, selectedPeriodId])

  const downloadUrl = useMemo(() => {
    const params = new URLSearchParams({ scope })
    if (scope === 'period' && selectedPeriodId) {
      params.set('period_id', selectedPeriodId)
    }
    if (!includeDocuments) {
      params.set('include_documents', 'false')
    }
    return `/api/reports/full-archive?${params.toString()}`
  }, [scope, selectedPeriodId, includeDocuments])

  const handleDownload = useCallback(async () => {
    if (scope === 'period' && !selectedPeriodId) return

    setIsDownloading(true)
    try {
      const res = await fetch(downloadUrl)
      if (!res.ok) {
        if (res.status === 413) {
          const body = await res.json().catch(() => ({}))
          const sizeMb = body.size_bytes ? Math.round(body.size_bytes / (1024 * 1024)) : null
          toast({
            title: t('toast_too_large_title'),
            description: sizeMb
              ? t('toast_too_large_with_size', { size: sizeMb })
              : t('toast_too_large_generic'),
            variant: 'destructive',
          })
          return
        }
        const body = await res.json().catch(() => ({}))
        throw new Error(body.error || t('error_create_archive'))
      }

      const blob = await res.blob()
      const contentDisposition = res.headers.get('Content-Disposition') || ''
      const match = contentDisposition.match(/filename="?([^";]+)"?/)
      const filename = match?.[1] || 'arkiv.zip'

      const url = window.URL.createObjectURL(blob)
      const link = document.createElement('a')
      link.href = url
      link.download = filename
      document.body.appendChild(link)
      link.click()
      document.body.removeChild(link)
      window.URL.revokeObjectURL(url)

      const now = new Date().toISOString()
      if (storageKey) {
        window.localStorage.setItem(storageKey, now)
        setLastDownloadedAt(now)
      }

      toast({ title: t('toast_backup_created'), description: filename })
    } catch (err) {
      toast({
        title: t('toast_backup_failed'),
        description: err instanceof Error ? getUserErrorMessage(err) : t('toast_try_again'),
        variant: 'destructive',
      })
    } finally {
      setIsDownloading(false)
    }
  }, [downloadUrl, scope, selectedPeriodId, storageKey, toast, t])

  const isOverLimit = !!estimate && !estimate.within_limit && includeDocuments
  const canDownload = !isDownloading && !isOverLimit && (scope === 'all' || !!selectedPeriodId)

  return (
    <div className="space-y-8">
      <Card>
        <CardHeader>
          <CardTitle className="text-base">{t('create_backup_title')}</CardTitle>
        </CardHeader>
        <CardContent className="space-y-6">
          <div className="space-y-2">
            <Label>{t('scope_label')}</Label>
            <div className="flex flex-col gap-2 sm:flex-row">
              <ScopeRadio
                checked={scope === 'all'}
                onChange={() => setScope('all')}
                label={t('scope_all_label')}
                description={t('scope_all_desc')}
                recommendedLabel={t('recommended')}
                recommended
              />
              <ScopeRadio
                checked={scope === 'period'}
                onChange={() => setScope('period')}
                label={t('scope_period_label')}
                description={t('scope_period_desc')}
                recommendedLabel={t('recommended')}
              />
            </div>
            {/* Live region always mounted so the failure is announced when it
                appears, not merely inserted. The full-history scope stays
                fully functional; the line only reports that per-period backup
                cannot be offered until the fiscal years can be read. */}
            <div role="status" aria-live="polite" className="min-w-0">
              {periodsError && (
                <AttnLine
                  action={
                    periodsError.detail
                      ? undefined
                      : {
                          label: t('periods_load_retry'),
                          onClick: () => setPeriodsReloadKey((k) => k + 1),
                        }
                  }
                >
                  {periodsError.detail
                    ? `${t('periods_load_failed')} ${periodsError.detail}`
                    : t('periods_load_failed')}
                </AttnLine>
              )}
            </div>
          </div>

          {scope === 'period' && (
            <div className="space-y-2">
              <Label htmlFor="backup-period">{t('fiscal_year_label')}</Label>
              <select
                id="backup-period"
                value={selectedPeriodId}
                onChange={(e) => setSelectedPeriodId(e.target.value)}
                className="flex h-10 w-full max-w-xs rounded-md border border-input bg-background px-3 py-2 text-sm ring-offset-background focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2"
                disabled={periods === null || periods.length === 0}
              >
                {/* The confirmed-empty option only after a confirmed empty
                    read; an unknown list renders an empty disabled select. */}
                {periods !== null && periods.length === 0 && (
                  <option value="">{t('no_fiscal_years')}</option>
                )}
                {(periods ?? []).map((p) => (
                  <option key={p.id} value={p.id}>
                    {p.period_start}: {p.period_end}
                  </option>
                ))}
              </select>
            </div>
          )}

          <div className="flex items-start justify-between gap-4">
            <div className="space-y-1">
              <Label htmlFor="include-documents">{t('include_docs_label')}</Label>
              <p className="text-xs text-muted-foreground max-w-prose">
                {t('include_docs_help')}
              </p>
            </div>
            <Switch
              id="include-documents"
              checked={includeDocuments}
              onCheckedChange={setIncludeDocuments}
            />
          </div>

          <div className="rounded-md border border-border bg-muted/30 p-3 text-sm">
            <div className="flex items-center gap-2 text-muted-foreground">
              <Info className="h-3.5 w-3.5" />
              {isLoadingEstimate ? (
                <span>{t('calculating_size')}</span>
              ) : estimate ? (
                <span>
                  {t('estimated_size')} <strong className="text-foreground">{formatBytes(estimate.total_bytes)}</strong>
                  {' '}({estimate.document_count} {estimate.document_count === 1 ? t('attachment_singular') : t('attachment_plural')})
                </span>
              ) : (
                <span>{t('size_will_calculate')}</span>
              )}
            </div>
            {isOverLimit && (
              <p className="mt-2 text-xs text-destructive">
                {t('over_limit_message', { limit: formatBytes(estimate!.size_limit_bytes) })}
              </p>
            )}
          </div>

          <div className="flex flex-col gap-3 sm:flex-row sm:items-center sm:justify-between">
            <Button onClick={handleDownload} disabled={!canDownload}>
              {isDownloading ? (
                <>
                  <Loader2 className="mr-2 h-4 w-4 animate-spin" />
                  {t('creating_backup')}
                </>
              ) : (
                <>
                  <Download className="mr-2 h-4 w-4" />
                  {t('create_and_download')}
                </>
              )}
            </Button>
            {lastDownloadedAt && (
              <p className="text-xs text-muted-foreground">
                {t('last_download')}: {formatDate(lastDownloadedAt)}
              </p>
            )}
          </div>
        </CardContent>
      </Card>

      {hasCloudBackup && CloudBackupPanel ? (
        <CloudBackupPanel />
      ) : (
        <Card className="border-dashed">
          <CardHeader>
            <CardTitle className="flex items-center gap-2 text-base">
              <Cloud className="h-4 w-4 text-muted-foreground" />
              {t('cloud_sync_title')}
            </CardTitle>
          </CardHeader>
          <CardContent>
            <p className="text-sm text-muted-foreground max-w-prose">
              {t('cloud_sync_disabled_help')}
            </p>
          </CardContent>
        </Card>
      )}
    </div>
  )
}

interface ScopeRadioProps {
  checked: boolean
  onChange: () => void
  label: string
  description: string
  recommended?: boolean
  recommendedLabel: string
}

function ScopeRadio({ checked, onChange, label, description, recommended, recommendedLabel }: ScopeRadioProps) {
  return (
    <button
      type="button"
      onClick={onChange}
      className={`flex-1 rounded-lg border-2 p-3 text-left transition-colors ${
        checked ? 'border-primary bg-primary/5' : 'border-border hover:border-primary/40'
      }`}
    >
      <div className="flex items-center gap-2">
        <span className="font-medium text-sm">{label}</span>
        {recommended && (
          <span className="text-[10px] font-medium uppercase tracking-wider text-primary">
            {recommendedLabel}
          </span>
        )}
      </div>
      <p className="mt-0.5 text-xs text-muted-foreground">{description}</p>
    </button>
  )
}

function formatBytes(bytes: number): string {
  if (bytes < 1024) return `${bytes} B`
  const kb = bytes / 1024
  if (kb < 1024) return `${kb.toFixed(1)} kB`
  const mb = kb / 1024
  if (mb < 1024) return `${mb.toFixed(1)} MB`
  return `${(mb / 1024).toFixed(2)} GB`
}

function formatDate(iso: string): string {
  const d = new Date(iso)
  return d.toLocaleString('sv-SE', {
    year: 'numeric',
    month: '2-digit',
    day: '2-digit',
    hour: '2-digit',
    minute: '2-digit',
  })
}