'use client'

/**
 * Ingående saldon (payroll cutover) section on the employee detail page.
 *
 * Mid-year switchers from another payroll system enter per-employee state
 * here: YTD accumulators, vacation balances (incl. sparade dagar per
 * origin year), opening semesterlöneskuld SEK, and the karens adjustment.
 * Locked (read-only) once the employee has a booked salary run; the lock
 * self-releases if that run is corrected.
 */

import { useEffect, useState } from 'react'
import { useTranslations } from 'next-intl'
import { Button } from '@/components/ui/button'
import { formatDate } from '@/lib/utils'
import { DetailSection } from '@/components/ui/detail-section'
import { HelpPopover } from '@/components/ui/help-popover'
import { Skeleton } from '@/components/ui/skeleton'
import { SettingsGroup, SettingsInput, SettingsRow } from '@/components/settings/SettingsRows'
import { useToast } from '@/components/ui/use-toast'
import { getErrorMessage } from '@/lib/errors/get-error-message'
import { useBranding } from '@/lib/branding/brand-context'

interface OpeningBalancesData {
  cutover_date: string
  ytd_gross: number
  ytd_tax: number
  ytd_net: number
  vacation_paid_days_remaining: number
  vacation_days_taken_this_year: number
  vacation_saved_days_by_year: Record<string, number>
  opening_semester_liability: number
  opening_semester_liability_avgifter: number
  karens_periods_adjustment: number
  locked: boolean
  locked_by_run_id: string | null
}

const currentYear = new Date().getFullYear()
/** Sparade dagar origin years: Semesterlagen allows saving max 5 years. */
const SAVED_YEARS = Array.from({ length: 5 }, (_, i) => String(currentYear - 1 - i))

// Numeric and date fields are sized by their content, not by the row.
const FIELD_CLASS = 'max-w-44 flex-none tabular-nums'

interface PanelValues {
  cutoverDate: string
  ytdGross: string
  ytdTax: string
  ytdNet: string
  daysRemaining: string
  daysTaken: string
  savedByYear: Record<string, string>
  liability: string
  liabilityAvgifter: string
  karens: string
}

/**
 * Stable serialization of the panel's field values, used to gate the save
 * button on actual edits. Empty saved-days entries equal absent entries, so
 * typing into a year and clearing it again returns the panel to clean.
 */
function fingerprint(v: PanelValues): string {
  const saved = Object.entries(v.savedByYear)
    .filter(([, days]) => days.trim() !== '')
    .sort(([a], [b]) => a.localeCompare(b))
  return JSON.stringify({ ...v, savedByYear: saved })
}

export function OpeningBalancesPanel({ employeeId, canWrite }: { employeeId: string; canWrite: boolean }) {
  const t = useTranslations('salary_employee')
  const { appName } = useBranding()
  const { toast } = useToast()
  const [loading, setLoading] = useState(true)
  const [saving, setSaving] = useState(false)
  const [locked, setLocked] = useState(false)
  const [hasRow, setHasRow] = useState(false)
  // Collapsed by default: this is a one-time form for switching payroll
  // system, and 14 empty input rows on every employee is clutter. Opens by
  // itself once balances exist, so stored values are never hidden.
  const [expanded, setExpanded] = useState<boolean | null>(null)

  const [cutoverDate, setCutoverDate] = useState(`${currentYear}-01-01`)
  const [ytdGross, setYtdGross] = useState('')
  const [ytdTax, setYtdTax] = useState('')
  const [ytdNet, setYtdNet] = useState('')
  const [daysRemaining, setDaysRemaining] = useState('')
  const [daysTaken, setDaysTaken] = useState('')
  const [savedByYear, setSavedByYear] = useState<Record<string, string>>({})
  const [liability, setLiability] = useState('')
  const [liabilityAvgifter, setLiabilityAvgifter] = useState('')
  const [karens, setKarens] = useState('')
  // Fingerprint of the last loaded/saved values: the save button stays
  // disabled until the fields actually differ from it.
  const [baseline, setBaseline] = useState(() =>
    fingerprint({
      cutoverDate: `${currentYear}-01-01`,
      ytdGross: '',
      ytdTax: '',
      ytdNet: '',
      daysRemaining: '',
      daysTaken: '',
      savedByYear: {},
      liability: '',
      liabilityAvgifter: '',
      karens: '',
    }),
  )

  useEffect(() => {
    async function load() {
      setLoading(true)
      try {
        const res = await fetch(`/api/salary/employees/${employeeId}/opening-balances`)
        if (!res.ok) return
        const { data } = (await res.json()) as { data: OpeningBalancesData | null }
        if (data) {
          const values: PanelValues = {
            cutoverDate: data.cutover_date,
            ytdGross: String(data.ytd_gross),
            ytdTax: String(data.ytd_tax),
            ytdNet: String(data.ytd_net),
            daysRemaining: String(data.vacation_paid_days_remaining),
            daysTaken: String(data.vacation_days_taken_this_year ?? 0),
            savedByYear: Object.fromEntries(
              Object.entries(data.vacation_saved_days_by_year ?? {}).map(([y, d]) => [y, String(d)]),
            ),
            liability: String(data.opening_semester_liability),
            liabilityAvgifter: String(data.opening_semester_liability_avgifter),
            karens: String(data.karens_periods_adjustment),
          }
          setHasRow(true)
          setLocked(data.locked)
          setCutoverDate(values.cutoverDate)
          setYtdGross(values.ytdGross)
          setYtdTax(values.ytdTax)
          setYtdNet(values.ytdNet)
          setDaysRemaining(values.daysRemaining)
          setDaysTaken(values.daysTaken)
          setSavedByYear(values.savedByYear)
          setLiability(values.liability)
          setLiabilityAvgifter(values.liabilityAvgifter)
          setKarens(values.karens)
          setBaseline(fingerprint(values))
        }
      } catch {
        // Network failure: the panel falls back to its empty form rather
        // than holding the skeleton forever; a retry happens on remount.
      } finally {
        setLoading(false)
      }
    }
    load()
  }, [employeeId])

  const currentValues: PanelValues = {
    cutoverDate,
    ytdGross,
    ytdTax,
    ytdNet,
    daysRemaining,
    daysTaken,
    savedByYear,
    liability,
    liabilityAvgifter,
    karens,
  }
  const dirty = fingerprint(currentValues) !== baseline

  async function handleSave() {
    setSaving(true)
    const saved: Record<string, number> = {}
    for (const [year, value] of Object.entries(savedByYear)) {
      const days = parseFloat(value)
      if (Number.isFinite(days) && days > 0) saved[year] = days
    }

    const res = await fetch(`/api/salary/employees/${employeeId}/opening-balances`, {
      method: 'PUT',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({
        cutover_date: cutoverDate,
        ytd_gross: parseFloat(ytdGross) || 0,
        ytd_tax: parseFloat(ytdTax) || 0,
        ytd_net: parseFloat(ytdNet) || 0,
        vacation_paid_days_remaining: parseFloat(daysRemaining) || 0,
        vacation_days_taken_this_year: parseFloat(daysTaken) || 0,
        vacation_saved_days_by_year: saved,
        opening_semester_liability: parseFloat(liability) || 0,
        opening_semester_liability_avgifter: parseFloat(liabilityAvgifter) || 0,
        karens_periods_adjustment: parseInt(karens, 10) || 0,
      }),
    })

    if (res.ok) {
      setHasRow(true)
      setBaseline(fingerprint(currentValues))
      toast({ title: t('opening_balances_saved') })
    } else {
      const result = await res.json()
      toast({
        title: t('opening_balances_save_failed'),
        description: getErrorMessage(result, { statusCode: res.status }),
        variant: 'destructive',
      })
    }
    setSaving(false)
  }

  if (loading) {
    return (
      <DetailSection kicker={t('opening_balances_title')}>
        <div className="space-y-3">
          <Skeleton className="h-4 w-full" />
          <Skeleton className="h-4 w-2/3" />
        </div>
      </DetailSection>
    )
  }

  const readOnly = locked || !canWrite
  const open = expanded ?? hasRow

  return (
    /* Own form: this section is its own save scope. It must never be nested
       inside another form (invalid HTML, and its submit would leak). The
       save button closes the expanded form and is a submit, so Enter in any
       field saves too. */
    <form
      onSubmit={(e) => {
        e.preventDefault()
        handleSave()
      }}
    >
      <DetailSection
        kicker={t('opening_balances_title')}
        help={<HelpPopover>{t('opening_balances_description', { appName })}</HelpPopover>}
        aside={
          <Button
            type="button"
            variant="outline"
            size="sm"
            className="-my-1"
            aria-expanded={open}
            onClick={() => setExpanded(!open)}
          >
            {open ? t('opening_balances_hide') : t('opening_balances_show')}
          </Button>
        }
      >
        {!open ? (
          <p className="text-sm text-muted-foreground">
            {hasRow
              ? t('opening_balances_collapsed_set', { date: formatDate(cutoverDate) })
              : t('opening_balances_collapsed_none')}
          </p>
        ) : (
        <>
        {locked && (
          <p className="mb-3 text-sm text-muted-foreground">{t('opening_balances_locked_notice')}</p>
        )}

        <SettingsRow
          label={t('opening_balances_cutover_date')}
          htmlFor="ob-cutover"
          help={t('opening_balances_cutover_hint', { appName })}
          align="baseline"
        >
          <SettingsInput
            id="ob-cutover"
            type="date"
            value={cutoverDate}
            onChange={(e) => setCutoverDate(e.target.value)}
            disabled={readOnly}
            className={FIELD_CLASS}
          />
        </SettingsRow>
        <SettingsRow
          label={t('opening_balances_karens')}
          htmlFor="ob-karens"
          help={t('opening_balances_karens_hint')}
          align="baseline"
        >
          <SettingsInput
            id="ob-karens"
            type="number"
            min={0}
            max={10}
            step={1}
            value={karens}
            onChange={(e) => setKarens(e.target.value)}
            disabled={readOnly}
            className={FIELD_CLASS}
          />
        </SettingsRow>

        <SettingsGroup label={t('opening_balances_ytd_heading')} className="pt-6">
          <SettingsRow label={t('opening_balances_ytd_gross')} htmlFor="ob-ytd-gross" align="baseline">
            <SettingsInput id="ob-ytd-gross" type="number" min={0} value={ytdGross}
              onChange={(e) => setYtdGross(e.target.value)} disabled={readOnly} className={FIELD_CLASS} />
          </SettingsRow>
          <SettingsRow label={t('opening_balances_ytd_tax')} htmlFor="ob-ytd-tax" align="baseline">
            <SettingsInput id="ob-ytd-tax" type="number" min={0} value={ytdTax}
              onChange={(e) => setYtdTax(e.target.value)} disabled={readOnly} className={FIELD_CLASS} />
          </SettingsRow>
          <SettingsRow label={t('opening_balances_ytd_net')} htmlFor="ob-ytd-net" align="baseline">
            <SettingsInput id="ob-ytd-net" type="number" min={0} value={ytdNet}
              onChange={(e) => setYtdNet(e.target.value)} disabled={readOnly} className={FIELD_CLASS} />
          </SettingsRow>
        </SettingsGroup>

        <SettingsGroup label={t('opening_balances_vacation_heading')} className="pt-6">
          <SettingsRow label={t('opening_balances_days_remaining')} htmlFor="ob-days-remaining" align="baseline">
            <SettingsInput id="ob-days-remaining" type="number" min={0} max={40} step={0.5} value={daysRemaining}
              onChange={(e) => setDaysRemaining(e.target.value)} disabled={readOnly} className={FIELD_CLASS} />
          </SettingsRow>
          <SettingsRow
            label={t('opening_balances_days_taken')}
            htmlFor="ob-days-taken"
            help={t('opening_balances_days_taken_hint')}
            align="baseline"
          >
            <SettingsInput id="ob-days-taken" type="number" min={0} max={40} step={0.5} value={daysTaken}
              onChange={(e) => setDaysTaken(e.target.value)} disabled={readOnly} className={FIELD_CLASS} />
          </SettingsRow>
          <SettingsRow label={t('opening_balances_liability')} htmlFor="ob-liability" align="baseline">
            <SettingsInput id="ob-liability" type="number" min={0} value={liability}
              onChange={(e) => setLiability(e.target.value)} disabled={readOnly} className={FIELD_CLASS} />
          </SettingsRow>
          <SettingsRow label={t('opening_balances_liability_avgifter')} htmlFor="ob-liability-avgifter" align="baseline">
            <SettingsInput id="ob-liability-avgifter" type="number" min={0} value={liabilityAvgifter}
              onChange={(e) => setLiabilityAvgifter(e.target.value)} disabled={readOnly} className={FIELD_CLASS} />
          </SettingsRow>
        </SettingsGroup>

        <SettingsGroup
          label={t('opening_balances_saved_heading')}
          help={t('opening_balances_saved_hint')}
          className="pt-6"
        >
          {SAVED_YEARS.map((year, index) => (
            <SettingsRow
              key={year}
              label={<span className="tabular-nums">{year}</span>}
              htmlFor={`ob-saved-${year}`}
              align="baseline"
              borderless={index === SAVED_YEARS.length - 1}
            >
              <SettingsInput
                id={`ob-saved-${year}`}
                type="number"
                min={0}
                max={40}
                step={0.5}
                value={savedByYear[year] ?? ''}
                onChange={(e) => setSavedByYear((prev) => ({ ...prev, [year]: e.target.value }))}
                disabled={readOnly}
                className={FIELD_CLASS}
              />
            </SettingsRow>
          ))}
        </SettingsGroup>

        {!readOnly && (
          <div className="mt-4 flex justify-end">
            <Button type="submit" size="sm" disabled={saving || !dirty}>
              {saving
                ? t('opening_balances_saving')
                : hasRow
                  ? t('opening_balances_update')
                  : t('opening_balances_save')}
            </Button>
          </div>
        )}
        </>
        )}
      </DetailSection>
    </form>
  )
}