import { useState, useEffect, useCallback, useMemo } from 'react'
import { FaFilePdf, FaArrowUpRightFromSquare, FaSpinner, FaRotate, FaPlus } from 'react-icons/fa6'
import { integrationsApi, formatMoney, INVOICE_STATUS, INVOICE_NINJA_PUBLIC_URL } from '../lib/integrationsApi'
import { useFinanceSummary } from '../hooks/useFinanceSummary'
import { useCustomers } from '../hooks/useCustomers'
import { PageHeader, Card, Button, Kpi, EmptyState, Field } from '../components/ui'

export default function FinancePage() {
  const { summary, loading: sumLoading, refresh: refreshSummary } = useFinanceSummary()
  const { customers } = useCustomers()
  const [invoices, setInvoices] = useState([])
  const [loading, setLoading] = useState(true)
  const [error, setError] = useState(null)
  const [filter, setFilter] = useState('all') // all | open | overdue | paid
  const [search, setSearch] = useState('')
  const [openingId, setOpeningId] = useState(null)
  const [showCreate, setShowCreate] = useState(false)

  const load = useCallback(async () => {
    setLoading(true)
    setError(null)
    try {
      const data = await integrationsApi.listInvoices(undefined, 400)
      setInvoices(data.invoices || [])
    } catch (err) {
      setError(err.message)
    } finally {
      setLoading(false)
    }
  }, [])

  useEffect(() => { load() }, [load])

  const today = new Date().toISOString().slice(0, 10)
  const filtered = useMemo(() => {
    return invoices.filter((inv) => {
      const overdue = Number(inv.balance) > 0 && inv.due_date && inv.due_date < today
      if (filter === 'open' && !(Number(inv.balance) > 0)) return false
      if (filter === 'overdue' && !overdue) return false
      if (filter === 'paid' && inv.status_id !== 4) return false
      if (search) {
        const s = search.toLowerCase()
        if (!`${inv.number} ${inv.client_name}`.toLowerCase().includes(s)) return false
      }
      return true
    })
  }, [invoices, filter, search, today])

  const openPdf = async (id) => {
    setOpeningId(id)
    try { await integrationsApi.openInvoicePdf(id) }
    catch (err) { alert('PDF-Fehler: ' + err.message) }
    finally { setOpeningId(null) }
  }

  return (
    <div className="page">
      <PageHeader
        title="Finanzen"
        subtitle="Rechnungen aus InvoiceNinja - Uebersicht, Status und schnelle Aktionen"
        actions={
          <>
            <Button variant="ghost" as="a" href={INVOICE_NINJA_PUBLIC_URL} target="_blank" rel="noopener noreferrer">
              <FaArrowUpRightFromSquare /> InvoiceNinja
            </Button>
            <Button variant="ghost" onClick={() => { load(); refreshSummary() }}><FaRotate /> Aktualisieren</Button>
            <Button variant="primary" onClick={() => setShowCreate((s) => !s)}><FaPlus /> Rechnung erstellen</Button>
          </>
        }
      />

      <div className="kpi-grid">
        <Kpi label="Offener Betrag" value={sumLoading ? '...' : formatMoney(summary?.outstanding)} sub={`${summary?.openCount ?? 0} offene Rechnungen`} accent="var(--warn)" />
        <Kpi label="Ueberfaellig" value={sumLoading ? '...' : formatMoney(summary?.overdue)} sub={`${summary?.overdueCount ?? 0} ueberfaellig`} accent="var(--danger)" />
        <Kpi label="Bezahlt (Monat)" value={sumLoading ? '...' : formatMoney(summary?.paidThisMonth)} accent="var(--ok)" />
        <Kpi label="Rechnungen gesamt" value={sumLoading ? '...' : (summary?.total ?? 0)} accent="var(--info)" />
      </div>

      {showCreate && (
        <div style={{ marginBottom: 16 }}>
          <CreateInvoiceForm customers={customers} onDone={() => { setShowCreate(false); load(); refreshSummary() }} onCancel={() => setShowCreate(false)} />
        </div>
      )}

      <Card pad={false}>
        <div className="ui-card-head">
          <div className="seg">
            {[['all', 'Alle'], ['open', 'Offen'], ['overdue', 'Ueberfaellig'], ['paid', 'Bezahlt']].map(([id, label]) => (
              <button key={id} className={filter === id ? 'active' : ''} onClick={() => setFilter(id)}>{label}</button>
            ))}
          </div>
          <input className="form-control search-input" placeholder="Nummer oder Kunde suchen..." value={search} onChange={(e) => setSearch(e.target.value)} style={{ maxWidth: 280 }} />
        </div>
        <div className="ui-card-body" style={{ padding: 0 }}>
          {loading ? (
            <div className="empty"><FaSpinner className="spinner" /></div>
          ) : error ? (
            <div className="empty text-red">{error}</div>
          ) : filtered.length === 0 ? (
            <EmptyState title="Keine Rechnungen" hint="Keine Rechnungen fuer diesen Filter." />
          ) : (
            <div style={{ overflowX: 'auto' }}>
              <table className="ui-table">
                <thead>
                  <tr><th>Nr.</th><th>Kunde</th><th>Datum</th><th>Faellig</th><th>Betrag</th><th>Offen</th><th>Status</th><th></th></tr>
                </thead>
                <tbody>
                  {filtered.map((inv) => {
                    const st = INVOICE_STATUS[inv.status_id] || { label: '—', color: 'var(--text-muted)' }
                    const overdue = Number(inv.balance) > 0 && inv.due_date && inv.due_date < today
                    return (
                      <tr key={inv.id}>
                        <td className="mono">{inv.number || inv.id?.slice(-6)}</td>
                        <td>{inv.client_name || '-'}</td>
                        <td className="muted">{inv.date || '-'}</td>
                        <td style={{ color: overdue ? 'var(--danger)' : 'var(--text-muted)' }}>{inv.due_date || '-'}</td>
                        <td>{formatMoney(inv.amount)}</td>
                        <td style={{ color: Number(inv.balance) > 0 ? 'var(--warn)' : 'var(--ok)' }}>{formatMoney(inv.balance)}</td>
                        <td><span style={{ color: st.color, fontWeight: 700 }}>{st.label}{overdue ? ' (ueberf.)' : ''}</span></td>
                        <td>
                          <Button size="sm" variant="ghost" disabled={openingId === inv.id} onClick={() => openPdf(inv.id)} title="PDF">
                            {openingId === inv.id ? <FaSpinner className="spinner" /> : <FaFilePdf />}
                          </Button>
                        </td>
                      </tr>
                    )
                  })}
                </tbody>
              </table>
            </div>
          )}
        </div>
      </Card>
    </div>
  )
}

function CreateInvoiceForm({ customers, onDone, onCancel }) {
  const linkable = (customers || []).filter((c) => c.invoiceNinjaClientId)
  const [clientId, setClientId] = useState('')
  const [description, setDescription] = useState('')
  const [cost, setCost] = useState('')
  const [quantity, setQuantity] = useState('1')
  const [busy, setBusy] = useState(false)
  const [error, setError] = useState(null)

  const submit = async (e) => {
    e.preventDefault()
    if (!clientId) { setError('Bitte Kunde waehlen'); return }
    setBusy(true); setError(null)
    try {
      await integrationsApi.createInvoice({
        client_id: clientId,
        public_notes: description,
        line_items: [{ notes: description, cost: Number(cost || 0), quantity: Number(quantity || 1) }],
      })
      onDone()
    } catch (err) { setError(err.message); setBusy(false) }
  }

  return (
    <Card title="Neue Rechnung">
      {linkable.length === 0 ? (
        <p className="muted">Kein Kunde ist mit InvoiceNinja verknuepft. Bitte zuerst im Kunden-Bereich verknuepfen.</p>
      ) : (
        <form onSubmit={submit}>
          <Field label="Kunde">
            <select className="form-control" value={clientId} onChange={(e) => setClientId(e.target.value)} required>
              <option value="">Kunde waehlen...</option>
              {linkable.map((c) => <option key={c.$id} value={c.invoiceNinjaClientId}>{c.name}</option>)}
            </select>
          </Field>
          <Field label="Leistung / Beschreibung">
            <textarea className="form-control" rows={2} value={description} onChange={(e) => setDescription(e.target.value)} required />
          </Field>
          <div className="flex gap-3">
            <Field label="Einzelpreis (EUR)"><input className="form-control" type="number" step="0.01" value={cost} onChange={(e) => setCost(e.target.value)} required /></Field>
            <Field label="Menge"><input className="form-control" type="number" step="1" value={quantity} onChange={(e) => setQuantity(e.target.value)} /></Field>
          </div>
          {error && <div className="text-red" style={{ marginBottom: 8 }}>{error}</div>}
          <div className="flex gap-2">
            <Button variant="primary" type="submit" disabled={busy}>{busy ? <FaSpinner className="spinner" /> : 'Rechnung erstellen'}</Button>
            <Button variant="ghost" type="button" onClick={onCancel}>Abbrechen</Button>
          </div>
        </form>
      )}
    </Card>
  )
}