import { useState } from 'react';
import { Link } from 'react-router-dom';
import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
import { Plus, Edit, Trash2, ChevronDown, ChevronUp, History, Clock, Bot, User } from 'lucide-react';
import Modal from '../ui/Modal';
import Button from '../ui/Button';
import Input from '../ui/Input';
import Badge from '../ui/Badge';
import { contractHistoryApi } from '../../services/api';
import type { ContractHistoryEntry } from '../../types';

interface ContractHistorySectionProps {
  contractId: number;
  canEdit: boolean;
  // Map: contractNumber → contractId. Wird genutzt um in title/description
  // erwähnte Vertragsnummern als Link auf den jeweiligen Vertrag zu rendern.
  // Aufgebaut aus previousContract + followUpContract des aktuellen Vertrags.
  knownContracts?: Record<string, number>;
}

// Vertragsnummer-Pattern: 3 Großbuchstaben + Bindestrich + Alphanumerisch
// (siehe backend/src/utils/helpers.ts generateContractNumber).
const CONTRACT_NUMBER_REGEX = /\b([A-Z]{3}-[A-Z0-9]{6,})\b/g;

// Rendert einen Text und ersetzt enthaltene Vertragsnummern durch Links,
// falls sie in der knownContracts-Map auflösbar sind. Nicht aufgelöste Nummern
// bleiben als normaler Text.
function renderTextWithContractLinks(
  text: string,
  knownContracts?: Record<string, number>,
): React.ReactNode {
  if (!knownContracts || Object.keys(knownContracts).length === 0) return text;
  const parts: React.ReactNode[] = [];
  let lastIndex = 0;
  let match: RegExpExecArray | null;
  CONTRACT_NUMBER_REGEX.lastIndex = 0;
  while ((match = CONTRACT_NUMBER_REGEX.exec(text)) !== null) {
    const num = match[1];
    const id = knownContracts[num];
    if (match.index > lastIndex) parts.push(text.slice(lastIndex, match.index));
    if (id) {
      parts.push(
        <Link
          key={`${match.index}-${num}`}
          to={`/contracts/${id}`}
          target="_blank"
          rel="noopener noreferrer"
          className="text-blue-600 hover:text-blue-800 hover:underline font-mono"
        >
          {num}
        </Link>,
      );
    } else {
      parts.push(num);
    }
    lastIndex = match.index + num.length;
  }
  if (lastIndex < text.length) parts.push(text.slice(lastIndex));
  return parts.length > 0 ? <>{parts}</> : text;
}

export default function ContractHistorySection({
  contractId,
  canEdit,
  knownContracts,
}: ContractHistorySectionProps) {
  const [isExpanded, setIsExpanded] = useState(false);
  const [showAddModal, setShowAddModal] = useState(false);
  const [editingEntry, setEditingEntry] = useState<ContractHistoryEntry | null>(null);
  const queryClient = useQueryClient();

  const { data, isLoading } = useQuery({
    queryKey: ['contract-history', contractId],
    queryFn: () => contractHistoryApi.getByContract(contractId),
  });

  const deleteEntryMutation = useMutation({
    mutationFn: (entryId: number) => contractHistoryApi.delete(contractId, entryId),
    onSuccess: () => {
      queryClient.invalidateQueries({ queryKey: ['contract-history', contractId] });
    },
  });

  const entries = data?.data || [];

  // Sort entries by date (newest first)
  const sortedEntries = [...entries].sort(
    (a, b) => new Date(b.createdAt).getTime() - new Date(a.createdAt).getTime()
  );

  return (
    <div className="bg-white rounded-lg border p-4">
      <div className="flex items-center justify-between mb-3">
        <div className="flex items-center gap-2">
          <History className="w-4 h-4 text-gray-500" />
          <h4 className="text-sm font-medium text-gray-700">Vertragshistorie</h4>
          <Badge variant="default">{entries.length}</Badge>
        </div>
        <div className="flex items-center gap-2">
          {canEdit && (
            <Button variant="ghost" size="sm" onClick={() => setShowAddModal(true)}>
              <Plus className="w-4 h-4" />
            </Button>
          )}
          {entries.length > 0 && (
            <button
              onClick={() => setIsExpanded(!isExpanded)}
              className="text-gray-500 hover:text-gray-700"
            >
              {isExpanded ? <ChevronUp className="w-4 h-4" /> : <ChevronDown className="w-4 h-4" />}
            </button>
          )}
        </div>
      </div>

      {/* Loading state */}
      {isLoading && (
        <p className="text-sm text-gray-500">Laden...</p>
      )}

      {/* Collapsed view - show latest entry */}
      {!isExpanded && !isLoading && sortedEntries.length > 0 && (
        <div className="text-sm text-gray-600">
          <span className="font-medium">
            {new Date(sortedEntries[0].createdAt).toLocaleString('de-DE', {
              day: '2-digit',
              month: '2-digit',
              year: 'numeric',
              hour: '2-digit',
              minute: '2-digit',
            })}
          </span>
          {' - '}
          {renderTextWithContractLinks(sortedEntries[0].title, knownContracts)}
        </div>
      )}

      {/* Expanded view */}
      {isExpanded && !isLoading && sortedEntries.length > 0 && (
        <div className="space-y-2">
          {sortedEntries.map((entry) => (
            <div
              key={entry.id}
              className="flex items-start justify-between p-3 bg-gray-50 rounded-lg group"
            >
              <div className="flex-1">
                <div className="flex items-center gap-2 mb-1">
                  <span className="text-sm font-medium text-gray-800">
                    {renderTextWithContractLinks(entry.title, knownContracts)}
                  </span>
                  {entry.isAutomatic ? (
                    <span className="flex items-center gap-1 px-1.5 py-0.5 text-xs rounded bg-blue-100 text-blue-700" title="Automatisch erstellt">
                      <Bot className="w-3 h-3" />
                      Auto
                    </span>
                  ) : (
                    <span className="flex items-center gap-1 px-1.5 py-0.5 text-xs rounded bg-gray-100 text-gray-600" title="Manuell erstellt">
                      <User className="w-3 h-3" />
                      Manuell
                    </span>
                  )}
                </div>
                {entry.description && (
                  <p className="text-sm text-gray-600 whitespace-pre-wrap mb-1">
                    {renderTextWithContractLinks(entry.description, knownContracts)}
                  </p>
                )}
                <div className="flex items-center gap-3 text-xs text-gray-400">
                  <span className="flex items-center gap-1">
                    <Clock className="w-3 h-3" />
                    {new Date(entry.createdAt).toLocaleString('de-DE', {
                      day: '2-digit',
                      month: '2-digit',
                      year: 'numeric',
                      hour: '2-digit',
                      minute: '2-digit',
                    })}
                  </span>
                  <span>von {entry.createdBy}</span>
                </div>
              </div>
              {canEdit && !entry.isAutomatic && (
                <div className="flex items-center gap-2 opacity-0 group-hover:opacity-100 ml-3">
                  <button
                    onClick={() => setEditingEntry(entry)}
                    className="text-gray-500 hover:text-blue-600"
                    title="Bearbeiten"
                  >
                    <Edit className="w-4 h-4" />
                  </button>
                  <button
                    onClick={() => {
                      if (confirm('Eintrag wirklich löschen?')) {
                        deleteEntryMutation.mutate(entry.id);
                      }
                    }}
                    className="text-gray-500 hover:text-red-600"
                    title="Löschen"
                  >
                    <Trash2 className="w-4 h-4" />
                  </button>
                </div>
              )}
            </div>
          ))}
        </div>
      )}

      {isExpanded && !isLoading && sortedEntries.length === 0 && (
        <p className="text-sm text-gray-500 italic">Keine Historie vorhanden.</p>
      )}

      {/* Add/Edit Modal */}
      {(showAddModal || editingEntry) && (
        <HistoryEntryModal
          isOpen={true}
          onClose={() => {
            setShowAddModal(false);
            setEditingEntry(null);
          }}
          contractId={contractId}
          entry={editingEntry}
        />
      )}
    </div>
  );
}

// History Entry Modal Component
function HistoryEntryModal({
  isOpen,
  onClose,
  contractId,
  entry,
}: {
  isOpen: boolean;
  onClose: () => void;
  contractId: number;
  entry?: ContractHistoryEntry | null;
}) {
  const queryClient = useQueryClient();
  const isEditing = !!entry;

  const [formData, setFormData] = useState({
    title: entry?.title || '',
    description: entry?.description || '',
  });
  const [error, setError] = useState<string | null>(null);

  const createMutation = useMutation({
    mutationFn: () =>
      contractHistoryApi.create(contractId, {
        title: formData.title,
        description: formData.description || undefined,
      }),
    onSuccess: () => {
      queryClient.invalidateQueries({ queryKey: ['contract-history', contractId] });
      onClose();
    },
    onError: (err: Error) => {
      setError(err.message);
    },
  });

  const updateMutation = useMutation({
    mutationFn: () =>
      contractHistoryApi.update(contractId, entry!.id, {
        title: formData.title,
        description: formData.description || undefined,
      }),
    onSuccess: () => {
      queryClient.invalidateQueries({ queryKey: ['contract-history', contractId] });
      onClose();
    },
    onError: (err: Error) => {
      setError(err.message);
    },
  });

  const handleSubmit = (e: React.FormEvent) => {
    e.preventDefault();
    setError(null);

    if (!formData.title.trim()) {
      setError('Titel ist erforderlich');
      return;
    }

    if (isEditing) {
      updateMutation.mutate();
    } else {
      createMutation.mutate();
    }
  };

  const isPending = createMutation.isPending || updateMutation.isPending;

  return (
    <Modal isOpen={isOpen} onClose={onClose} title={isEditing ? 'Eintrag bearbeiten' : 'Historie-Eintrag hinzufügen'}>
      <form onSubmit={handleSubmit} className="space-y-4">
        {error && (
          <div className="p-3 bg-red-50 border border-red-200 rounded-lg text-red-700 text-sm">
            {error}
          </div>
        )}

        <Input
          label="Titel *"
          value={formData.title}
          onChange={(e) => setFormData({ ...formData, title: e.target.value })}
          placeholder="z.B. kWh auf 18000 erhöht"
          required
        />

        <div>
          <label className="block text-sm font-medium text-gray-700 mb-1">
            Beschreibung (optional)
          </label>
          <textarea
            value={formData.description}
            onChange={(e) => setFormData({ ...formData, description: e.target.value })}
            placeholder="Weitere Details..."
            rows={3}
            className="w-full px-3 py-2 border border-gray-300 rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-blue-500"
          />
        </div>

        <div className="flex justify-end gap-3 pt-4">
          <Button type="button" variant="secondary" onClick={onClose}>
            Abbrechen
          </Button>
          <Button type="submit" disabled={isPending}>
            {isPending ? 'Wird gespeichert...' : isEditing ? 'Speichern' : 'Hinzufügen'}
          </Button>
        </div>
      </form>
    </Modal>
  );
}