/**
 * CSV Export Utilities
 * 
 * Client-side CSV generation for policy settings export.
 * 
 * Features:
 * - RFC 4180 compliant CSV formatting
 * - Proper escaping (commas, quotes, newlines)
 * - UTF-8 BOM for Excel compatibility
 * - Efficient string building
 */

import type { PolicySettingRow } from '@/lib/types/policy-table';

/**
 * Escape a CSV field value according to RFC 4180
 * - Wrap in quotes if contains comma, quote, or newline
 * - Double any quotes inside the value
 */
function escapeCsvField(value: string | null | undefined): string {
  if (value === null || value === undefined) {
    return '';
  }

  const stringValue = String(value);

  // Check if escaping is needed
  const needsEscaping = stringValue.includes(',') || 
                        stringValue.includes('"') || 
                        stringValue.includes('\n') || 
                        stringValue.includes('\r');

  if (!needsEscaping) {
    return stringValue;
  }

  // Double any quotes and wrap in quotes
  const escaped = stringValue.replace(/"/g, '""');
  return `"${escaped}"`;
}

/**
 * Generate CSV content from policy settings
 * @param rows Array of policy settings to export
 * @param columns Optional array of column keys to include (default: all)
 * @returns CSV content as string with UTF-8 BOM
 */
export function generatePolicySettingsCsv(
  rows: PolicySettingRow[],
  columns?: Array<keyof PolicySettingRow>
): string {
  // Default columns in preferred order
  const defaultColumns: Array<keyof PolicySettingRow> = [
    'settingName',
    'settingValue',
    'policyName',
    'policyType',
    'graphPolicyId',
    'lastSyncedAt',
  ];

  const columnsToExport = columns || defaultColumns;

  // Column headers (human-readable)
  const headers: Record<keyof PolicySettingRow, string> = {
    id: 'ID',
    tenantId: 'Tenant ID',
    settingName: 'Setting Name',
    settingValue: 'Setting Value',
    policyName: 'Policy Name',
    policyType: 'Policy Type',
    graphPolicyId: 'Graph Policy ID',
    lastSyncedAt: 'Last Synced',
    createdAt: 'Created At',
  };

  // Build CSV rows
  const csvLines: string[] = [];

  // Header row
  const headerRow = columnsToExport.map(col => escapeCsvField(headers[col])).join(',');
  csvLines.push(headerRow);

  // Data rows
  for (const row of rows) {
    const dataRow = columnsToExport.map(col => {
      const value = row[col];

      // Format dates
      if (value instanceof Date) {
        return escapeCsvField(value.toISOString());
      }

      // Format other values
      return escapeCsvField(String(value));
    }).join(',');

    csvLines.push(dataRow);
  }

  // Join with newlines and add UTF-8 BOM for Excel compatibility
  const csvContent = csvLines.join('\n');
  const utf8Bom = '\uFEFF';
  return utf8Bom + csvContent;
}

/**
 * Trigger browser download of CSV content
 * @param csvContent CSV content string
 * @param filename Suggested filename (e.g., "policy-settings.csv")
 */
export function downloadCsv(csvContent: string, filename: string): void {
  // Create blob with proper MIME type
  const blob = new Blob([csvContent], { type: 'text/csv;charset=utf-8;' });

  // Create download link
  const url = URL.createObjectURL(blob);
  const link = document.createElement('a');
  link.href = url;
  link.download = filename;

  // Trigger download
  document.body.appendChild(link);
  link.click();

  // Cleanup
  document.body.removeChild(link);
  URL.revokeObjectURL(url);
}

/**
 * Generate filename with timestamp
 * @param prefix Filename prefix (e.g., "policy-settings")
 * @param selectedCount Optional count of selected rows
 * @returns Filename with timestamp (e.g., "policy-settings-2025-12-10.csv")
 */
export function generateCsvFilename(prefix: string, selectedCount?: number): string {
  const date = new Date().toISOString().split('T')[0]; // YYYY-MM-DD
  const suffix = selectedCount ? `-selected-${selectedCount}` : '';
  return `${prefix}${suffix}-${date}.csv`;
}