import React, { useCallback, useRef, useState } from 'react';
import { useTranslation } from 'react-i18next';
import {
  AlertCircle,
  CheckCircle,
  FileText,
  Loader2,
  Upload,
  RotateCcw,
  ArrowLeft,
  Eye,
  Play,
} from 'lucide-react';
import clsx from 'clsx';
import { Card } from '@/components/ui/Card';
import { Button } from '@/components/ui/Button';
import { Select } from '@/components/ui/Select';
import { Badge } from '@/components/ui/Badge';
import { useToast } from '@/components/ui/Toast';
import { importCsv, type ImportResult } from '@/api/importExport';

// ─── Constants ──────────────────────────────────────────────────────────────

const MAX_FILE_SIZE = 10 * 1024 * 1024; // 10 MB
const ACCEPTED_EXTENSIONS = ['.csv'];

const ENTITY_OPTIONS = [
  { value: 'contacts', label: 'Kontakte' },
  { value: 'companies', label: 'Firmen' },
];

type WizardStep = 'upload' | 'preview' | 'review' | 'result';

// ─── Component ──────────────────────────────────────────────────────────────

export function ImportWizard() {
  const { t } = useTranslation();
  const toast = useToast();

  const [step, setStep] = useState<WizardStep>('upload');
  const [file, setFile] = useState<File | null>(null);
  const [entityType, setEntityType] = useState<string>('contacts');
  const [previewResult, setPreviewResult] = useState<ImportResult | null>(null);
  const [importResult, setImportResult] = useState<ImportResult | null>(null);
  const [previewConfirmed, setPreviewConfirmed] = useState(false);
  const [isDragOver, setIsDragOver] = useState(false);
  const [isLoadingPreview, setIsLoadingPreview] = useState(false);
  const [isLoadingImport, setIsLoadingImport] = useState(false);
  const [fileError, setFileError] = useState<string | null>(null);
  const inputRef = useRef<HTMLInputElement>(null);

  // ─── File validation ────────────────────────────────────────────────────

  const validateFile = useCallback((f: File): string | null => {
    const ext = f.name.toLowerCase().substring(f.name.lastIndexOf('.'));
    if (!ACCEPTED_EXTENSIONS.includes(ext)) {
      return t('importExport.onlyCsvAllowed', 'Nur CSV-Dateien sind erlaubt');
    }
    if (f.size > MAX_FILE_SIZE) {
      return t('importExport.fileTooLarge', 'Datei ist größer als 10 MB');
    }
    return null;
  }, [t]);

  const handleFileSelect = useCallback((f: File | null) => {
    if (!f) return;
    const error = validateFile(f);
    if (error) {
      setFileError(error);
      setFile(null);
      return;
    }
    setFileError(null);
    setFile(f);
  }, [validateFile]);

  const handleDrop = useCallback((e: React.DragEvent) => {
    e.preventDefault();
    setIsDragOver(false);
    const droppedFile = e.dataTransfer.files?.[0];
    if (droppedFile) handleFileSelect(droppedFile);
  }, [handleFileSelect]);

  const handleDragOver = useCallback((e: React.DragEvent) => {
    e.preventDefault();
    setIsDragOver(true);
  }, []);

  const handleDragLeave = useCallback((e: React.DragEvent) => {
    e.preventDefault();
    setIsDragOver(false);
  }, []);

  const handleFileInputChange = useCallback((e: React.ChangeEvent<HTMLInputElement>) => {
    const selected = e.target.files?.[0] ?? null;
    handleFileSelect(selected);
  }, [handleFileSelect]);

  // ─── Preview ────────────────────────────────────────────────────────────

  const handlePreview = async () => {
    if (!file) return;
    setIsLoadingPreview(true);
    try {
      const result = await importCsv(file, entityType, true);
      setPreviewResult(result);
      setStep('preview');
    } catch (err: any) {
      toast.error(err?.message || t('importExport.previewFailed', 'Vorschau fehlgeschlagen'));
    } finally {
      setIsLoadingPreview(false);
    }
  };

  // ─── Import ─────────────────────────────────────────────────────────────

  const handleImport = async () => {
    if (!file) return;
    setIsLoadingImport(true);
    try {
      const result = await importCsv(file, entityType, false);
      setImportResult(result);
      setStep('result');
      toast.success(t('importExport.importSuccess', 'Import erfolgreich abgeschlossen'));
    } catch (err: any) {
      setImportResult({
        errors: [err?.message || t('importExport.importFailed', 'Import fehlgeschlagen')],
      });
      setStep('result');
    } finally {
      setIsLoadingImport(false);
    }
  };

  // ─── Reset ──────────────────────────────────────────────────────────────

  const handleReset = () => {
    setStep('upload');
    setFile(null);
    setPreviewResult(null);
    setImportResult(null);
    setPreviewConfirmed(false);
    setFileError(null);
    if (inputRef.current) inputRef.current.value = '';
  };

  const handleBack = () => {
    if (step === 'preview') setStep('upload');
    else if (step === 'review') setStep('preview');
  };

  // ─── Step indicator ─────────────────────────────────────────────────────

  const steps: { key: WizardStep; label: string }[] = [
    { key: 'upload', label: t('importExport.stepUpload', 'Datei hochladen') },
    { key: 'preview', label: t('importExport.stepPreview', 'Vorschau') },
    { key: 'review', label: t('importExport.stepReview', 'Überprüfung') },
    { key: 'result', label: t('importExport.stepResult', 'Ergebnis') },
  ];
  const currentStepIndex = steps.findIndex((s) => s.key === step);

  // ─── Render ─────────────────────────────────────────────────────────────

  return (
    <div className="space-y-6">
      {/* Step indicator */}
      <div className="flex items-center justify-between max-w-2xl">
        {steps.map((s, idx) => (
          <React.Fragment key={s.key}>
            <div className="flex items-center gap-2">
              <span
                className={clsx(
                  'flex items-center justify-center w-8 h-8 rounded-full text-sm font-medium transition-colors',
                  idx <= currentStepIndex
                    ? 'bg-primary-600 text-white'
                    : 'bg-secondary-200 text-secondary-500'
                )}
              >
                {idx < currentStepIndex ? (
                  <CheckCircle className="w-4 h-4" />
                ) : (
                  idx + 1
                )}
              </span>
              <span
                className={clsx(
                  'text-sm font-medium hidden sm:inline',
                  idx <= currentStepIndex ? 'text-secondary-900' : 'text-secondary-400'
                )}
              >
                {s.label}
              </span>
            </div>
            {idx < steps.length - 1 && (
              <div
                className={clsx(
                  'flex-1 h-0.5 mx-2 transition-colors',
                  idx < currentStepIndex ? 'bg-primary-600' : 'bg-secondary-200'
                )}
              />
            )}
          </React.Fragment>
        ))}
      </div>

      {/* Step: Upload */}
      {step === 'upload' && (
        <Card
          title={t('importExport.uploadTitle', 'Datei hochladen')}
          description={t('importExport.uploadDescription', 'Wählen Sie eine CSV-Datei und den Entitätstyp für den Import')}
        >
          <div className="space-y-4">
            {/* Entity type */}
            <Select
              label={t('importExport.entityType', 'Entitätstyp')}
              options={ENTITY_OPTIONS}
              value={entityType}
              onChange={(e) => setEntityType(e.target.value)}
              required
            />

            {/* Drag & drop zone */}
            <div
              onDrop={handleDrop}
              onDragOver={handleDragOver}
              onDragLeave={handleDragLeave}
              onClick={() => inputRef.current?.click()}
              className={clsx(
                'border-2 border-dashed rounded-lg p-8 text-center cursor-pointer transition-colors',
                isDragOver
                  ? 'border-primary-500 bg-primary-50'
                  : 'border-secondary-300 hover:border-secondary-400 bg-secondary-50'
              )}
            >
              <input
                ref={inputRef}
                type="file"
                accept=".csv"
                onChange={handleFileInputChange}
                className="hidden"
              />
              {file ? (
                <div className="flex flex-col items-center gap-2">
                  <FileText className="w-10 h-10 text-primary-600" />
                  <p className="text-sm font-medium text-secondary-900">{file.name}</p>
                  <p className="text-xs text-secondary-500">
                    {(file.size / 1024).toFixed(1)} KB
                  </p>
                </div>
              ) : (
                <div className="flex flex-col items-center gap-2">
                  <Upload className="w-10 h-10 text-secondary-400" />
                  <p className="text-sm font-medium text-secondary-700">
                    {t('importExport.dropFileHere', 'CSV-Datei hierher ziehen oder klicken zum Auswählen')}
                  </p>
                  <p className="text-xs text-secondary-500">
                    {t('importExport.fileConstraints', 'Max. 10 MB, nur .csv')}
                  </p>
                </div>
              )}
            </div>

            {fileError && (
              <div className="flex items-center gap-2 text-sm text-danger-600">
                <AlertCircle className="w-4 h-4 flex-shrink-0" />
                <span>{fileError}</span>
              </div>
            )}

            {/* Action */}
            <div className="flex justify-end">
              <Button
                onClick={handlePreview}
                disabled={!file || isLoadingPreview}
                isLoading={isLoadingPreview}
                icon={!isLoadingPreview ? <Eye className="w-4 h-4" /> : undefined}
              >
                {t('importExport.preview', 'Vorschau')}
              </Button>
            </div>
          </div>
        </Card>
      )}

      {/* Step: Preview */}
      {step === 'preview' && previewResult && (
        <Card
          title={t('importExport.previewTitle', 'Vorschau der Daten')}
          description={t('importExport.previewDescription', 'Überprüfen Sie das Ergebnis des Dry-Run-Imports')}
          actions={
            <Button variant="ghost" size="sm" onClick={handleBack} icon={<ArrowLeft className="w-4 h-4" />}>
              {t('common.back', 'Zurück')}
            </Button>
          }
        >
          <div className="space-y-4">
            {/* Summary stats */}
            <div className="grid grid-cols-2 sm:grid-cols-3 gap-4">
              <StatBox
                label={t('importExport.totalRows', 'Gesamtzeilen')}
                value={previewResult.total ?? 0}
                icon={<FileText className="w-5 h-5 text-secondary-400" />}
              />
              <StatBox
                label={t('importExport.created', 'Neu')}
                value={previewResult.created ?? 0}
                icon={<CheckCircle className="w-5 h-5 text-success-500" />}
              />
              <StatBox
                label={t('importExport.updated', 'Aktualisiert')}
                value={previewResult.updated ?? 0}
                icon={<RotateCcw className="w-5 h-5 text-accent-500" />}
              />
            </div>

            {/* Errors */}
            {previewResult.errors && previewResult.errors.length > 0 && (
              <div className="space-y-2">
                <div className="flex items-center gap-2">
                  <AlertCircle className="w-5 h-5 text-danger-500" />
                  <h4 className="text-sm font-semibold text-danger-700">
                    {t('importExport.errors', 'Fehler')} ({previewResult.errors.length})
                  </h4>
                </div>
                <ul className="space-y-1 max-h-48 overflow-y-auto">
                  {previewResult.errors.map((err, idx) => (
                    <li key={idx} className="text-sm text-danger-600 bg-danger-50 rounded px-3 py-1.5">
                      {err}
                    </li>
                  ))}
                </ul>
              </div>
            )}

            {/* Warnings */}
            {previewResult.warnings && previewResult.warnings.length > 0 && (
              <div className="space-y-2">
                <div className="flex items-center gap-2">
                  <AlertCircle className="w-5 h-5 text-warning-500" />
                  <h4 className="text-sm font-semibold text-warning-700">
                    {t('importExport.warnings', 'Warnungen')} ({previewResult.warnings.length})
                  </h4>
                </div>
                <ul className="space-y-1 max-h-48 overflow-y-auto">
                  {previewResult.warnings.map((warn, idx) => (
                    <li key={idx} className="text-sm text-warning-700 bg-warning-50 rounded px-3 py-1.5">
                      {warn}
                    </li>
                  ))}
                </ul>
              </div>
            )}

            {/* Preview rows */}
            {previewResult.rows && previewResult.rows.length > 0 && (
              <div className="space-y-2">
                <h4 className="text-sm font-semibold text-secondary-700">
                  {t('importExport.previewRows', 'Vorschau der ersten Zeilen')}
                </h4>
                <div className="overflow-x-auto border border-secondary-200 rounded-lg">
                  <table className="min-w-full divide-y divide-secondary-200">
                    <thead className="bg-secondary-50">
                      <tr>
                        {Object.keys(previewResult.rows[0]).slice(0, 6).map((key) => (
                          <th key={key} className="px-3 py-2 text-left text-xs font-medium text-secondary-500 uppercase tracking-wider">
                            {key}
                          </th>
                        ))}
                      </tr>
                    </thead>
                    <tbody className="bg-white divide-y divide-secondary-200">
                      {previewResult.rows.slice(0, 5).map((row, idx) => (
                        <tr key={idx}>
                          {Object.values(row).slice(0, 6).map((val, vidx) => (
                            <td key={vidx} className="px-3 py-2 text-sm text-secondary-900 whitespace-nowrap">
                              {String(val ?? '')}
                            </td>
                          ))}
                        </tr>
                      ))}
                    </tbody>
                  </table>
                </div>
              </div>
            )}

            {/* Action */}
            <div className="flex justify-end">
              <Button onClick={() => setStep('review')} icon={<CheckCircle className="w-4 h-4" />}>
                {t('importExport.continue', 'Weiter')}
              </Button>
            </div>
          </div>
        </Card>
      )}

      {/* Step: Review */}
      {step === 'review' && (
        <Card
          title={t('importExport.reviewTitle', 'Überprüfung')}
          description={t('importExport.reviewDescription', 'Bestätigen Sie, dass Sie die Vorschau geprüft haben')}
          actions={
            <Button variant="ghost" size="sm" onClick={handleBack} icon={<ArrowLeft className="w-4 h-4" />}>
              {t('common.back', 'Zurück')}
            </Button>
          }
        >
          <div className="space-y-4">
            {/* Summary */}
            <div className="bg-secondary-50 rounded-lg p-4 space-y-2">
              <div className="flex items-center justify-between">
                <span className="text-sm text-secondary-600">{t('importExport.entityType', 'Entitätstyp')}</span>
                <Badge variant="primary">
                  {entityType === 'contacts' ? 'Kontakte' : 'Firmen'}
                </Badge>
              </div>
              <div className="flex items-center justify-between">
                <span className="text-sm text-secondary-600">{t('importExport.file', 'Datei')}</span>
                <span className="text-sm font-medium text-secondary-900">{file?.name}</span>
              </div>
              {previewResult && (
                <>
                  <div className="flex items-center justify-between">
                    <span className="text-sm text-secondary-600">{t('importExport.totalRows', 'Gesamtzeilen')}</span>
                    <span className="text-sm font-medium text-secondary-900">{previewResult.total ?? 0}</span>
                  </div>
                  <div className="flex items-center justify-between">
                    <span className="text-sm text-secondary-600">{t('importExport.created', 'Neu')}</span>
                    <span className="text-sm font-medium text-success-600">{previewResult.created ?? 0}</span>
                  </div>
                  <div className="flex items-center justify-between">
                    <span className="text-sm text-secondary-600">{t('importExport.updated', 'Aktualisiert')}</span>
                    <span className="text-sm font-medium text-accent-600">{previewResult.updated ?? 0}</span>
                  </div>
                  {previewResult.errors && previewResult.errors.length > 0 && (
                    <div className="flex items-center justify-between">
                      <span className="text-sm text-secondary-600">{t('importExport.errors', 'Fehler')}</span>
                      <Badge variant="danger">{previewResult.errors.length}</Badge>
                    </div>
                  )}
                  {previewResult.warnings && previewResult.warnings.length > 0 && (
                    <div className="flex items-center justify-between">
                      <span className="text-sm text-secondary-600">{t('importExport.warnings', 'Warnungen')}</span>
                      <Badge variant="warning">{previewResult.warnings.length}</Badge>
                    </div>
                  )}
                </>
              )}
            </div>

            {/* Confirmation checkbox */}
            <label className="flex items-start gap-3 cursor-pointer">
              <input
                type="checkbox"
                checked={previewConfirmed}
                onChange={(e) => setPreviewConfirmed(e.target.checked)}
                className="mt-1 w-4 h-4 rounded border-secondary-300 text-primary-600 focus:ring-primary-500"
              />
              <span className="text-sm text-secondary-700">
                {t('importExport.confirmPreview', 'Ich habe die Vorschau geprüft und bin mir der Folgen bewusst')}
              </span>
            </label>

            {/* Actions */}
            <div className="flex justify-between">
              <Button variant="ghost" onClick={handleReset} icon={<RotateCcw className="w-4 h-4" />}>
                {t('importExport.restart', 'Neu starten')}
              </Button>
              <Button
                onClick={handleImport}
                disabled={!previewConfirmed || isLoadingImport}
                isLoading={isLoadingImport}
                icon={!isLoadingImport ? <Play className="w-4 h-4" /> : undefined}
              >
                {t('importExport.executeImport', 'Import ausführen')}
              </Button>
            </div>
          </div>
        </Card>
      )}

      {/* Step: Result */}
      {step === 'result' && importResult && (
        <Card
          title={t('importExport.resultTitle', 'Import-Ergebnis')}
          actions={
            <Button variant="ghost" size="sm" onClick={handleReset} icon={<RotateCcw className="w-4 h-4" />}>
              {t('importExport.newImport', 'Neuer Import')}
            </Button>
          }
        >
          <div className="space-y-4">
            {/* Success / Error indicator */}
            {importResult.errors && importResult.errors.length > 0 && !importResult.created && !importResult.updated ? (
              <div className="flex items-center gap-3 bg-danger-50 rounded-lg p-4">
                <AlertCircle className="w-6 h-6 text-danger-600" />
                <span className="text-sm font-medium text-danger-700">
                  {t('importExport.importFailed', 'Import fehlgeschlagen')}
                </span>
              </div>
            ) : (
              <div className="flex items-center gap-3 bg-success-50 rounded-lg p-4">
                <CheckCircle className="w-6 h-6 text-success-600" />
                <span className="text-sm font-medium text-success-700">
                  {t('importExport.importSuccess', 'Import erfolgreich abgeschlossen')}
                </span>
              </div>
            )}

            {/* Stats */}
            {(importResult.created !== undefined || importResult.updated !== undefined || importResult.total !== undefined) && (
              <div className="grid grid-cols-2 sm:grid-cols-3 gap-4">
                {importResult.total !== undefined && (
                  <StatBox
                    label={t('importExport.totalRows', 'Gesamtzeilen')}
                    value={importResult.total}
                    icon={<FileText className="w-5 h-5 text-secondary-400" />}
                  />
                )}
                {importResult.created !== undefined && (
                  <StatBox
                    label={t('importExport.created', 'Neu')}
                    value={importResult.created}
                    icon={<CheckCircle className="w-5 h-5 text-success-500" />}
                  />
                )}
                {importResult.updated !== undefined && (
                  <StatBox
                    label={t('importExport.updated', 'Aktualisiert')}
                    value={importResult.updated}
                    icon={<RotateCcw className="w-5 h-5 text-accent-500" />}
                  />
                )}
              </div>
            )}

            {/* Errors */}
            {importResult.errors && importResult.errors.length > 0 && (
              <div className="space-y-2">
                <div className="flex items-center gap-2">
                  <AlertCircle className="w-5 h-5 text-danger-500" />
                  <h4 className="text-sm font-semibold text-danger-700">
                    {t('importExport.errors', 'Fehler')} ({importResult.errors.length})
                  </h4>
                </div>
                <ul className="space-y-1 max-h-48 overflow-y-auto">
                  {importResult.errors.map((err, idx) => (
                    <li key={idx} className="text-sm text-danger-600 bg-danger-50 rounded px-3 py-1.5">
                      {err}
                    </li>
                  ))}
                </ul>
              </div>
            )}

            {/* Warnings */}
            {importResult.warnings && importResult.warnings.length > 0 && (
              <div className="space-y-2">
                <div className="flex items-center gap-2">
                  <AlertCircle className="w-5 h-5 text-warning-500" />
                  <h4 className="text-sm font-semibold text-warning-700">
                    {t('importExport.warnings', 'Warnungen')} ({importResult.warnings.length})
                  </h4>
                </div>
                <ul className="space-y-1 max-h-48 overflow-y-auto">
                  {importResult.warnings.map((warn, idx) => (
                    <li key={idx} className="text-sm text-warning-700 bg-warning-50 rounded px-3 py-1.5">
                      {warn}
                    </li>
                  ))}
                </ul>
              </div>
            )}
          </div>
        </Card>
      )}
    </div>
  );
}

// ─── Helper sub-component ───────────────────────────────────────────────────

function StatBox({ label, value, icon }: { label: string; value: number; icon: React.ReactNode }) {
  return (
    <div className="bg-secondary-50 rounded-lg p-4 flex items-center gap-3">
      {icon}
      <div>
        <p className="text-xs text-secondary-500">{label}</p>
        <p className="text-lg font-semibold text-secondary-900">{value}</p>
      </div>
    </div>
  );
}