export interface TimeSeriesFinancialDto {
  symbol: string;
  metric_name: string;
  period_date: string;
  value: number;
  source?: string;
}

export interface FinancialTableRow {
  metric: string;
  [year: string]: string | number | undefined;
}

export interface FinancialTableData {
  headers: string[]; // Sorted years
  rows: FinancialTableRow[];
}

/**
 * Transforms a flat list of TimeSeriesFinancialDto into a pivoted table structure.
 * 
 * Input: 
 * [
 *   { metric_name: "Revenue", period_date: "2023-12-31", value: 100, source: "tushare" },
 *   { metric_name: "Revenue", period_date: "2022-12-31", value: 90, source: "tushare" },
 * ]
 * 
 * Output:
 * {
 *   headers: ["2023", "2022"],
 *   rows: [
 *     { metric: "Revenue", "2023": 100, "2022": 90 }
 *   ]
 * }
 */
export function transformFinancialData(data: TimeSeriesFinancialDto[]): FinancialTableData {
  if (!data || data.length === 0) {
    return { headers: [], rows: [] };
  }

  // 1. Collect all unique years (from period_date)
  const yearsSet = new Set<string>();
  // 2. Group by metric name
  const metricMap = new Map<string, Record<string, number | string>>();

  data.forEach(item => {
    if (!item.period_date) return;
    // Extract year from "YYYY-MM-DD"
    const year = item.period_date.substring(0, 4);
    yearsSet.add(year);

    if (!metricMap.has(item.metric_name)) {
      metricMap.set(item.metric_name, { metric: item.metric_name });
    }
    
    const row = metricMap.get(item.metric_name)!;
    
    // Handle potential conflicts: 
    // If multiple sources provide data, we currently just overwrite or keep the last one.
    // A better approach might be to append source info or average, but for a table view, single value is cleaner.
    // Maybe prioritize sources? Tushare > YFinance > AlphaVantage?
    // For now, we just use the value. 
    // We could format it with source: "100 (Tushare)" but that breaks numeric sorting/formatting.
    row[year] = item.value; 
  });

  // Sort years descending (newest first)
  const headers = Array.from(yearsSet).sort((a, b) => Number(b) - Number(a));

  // Create rows
  const rows = Array.from(metricMap.values()).map(row => {
    // Ensure all header keys exist (fill with undefined/null if needed)
    return row as FinancialTableRow;
  });

  return { headers, rows };
}