import { AggregatedData } from '../types';

const formatCurrency = (val: number) => `€${val.toLocaleString('de-DE', { minimumFractionDigits: 0, maximumFractionDigits: 0 })}`;
const formatUnits = (val: number) => `${val.toLocaleString('de-DE')} units`;

export const queryGemini = async (
  question: string,
  context: AggregatedData,
  filteredRecordCount: number
): Promise<string> => {

  try {
    // --- CONTEXT GENERATION ---
    // We construct a structured report mirroring the dashboard charts

    // 1. Totals by Year (KPI Cards)
    const yearlySummary = Object.entries(context.totalsByYear)
      .sort((a, b) => parseInt(b[0]) - parseInt(a[0]))
      .map(([year, data]) => `  - ${year}: ${formatCurrency((data as any).sellOut)} | ${formatUnits((data as any).units)}`)
      .join('\n');

    // 2. Seasonality (Line Chart Data)
    const seasonalitySummary = context.seasonality.map(p => {
      const yearValues = context.availableYears.map(y => `${y}: ${formatCurrency(p[y] as number || 0)}`).join(', ');
      return `  - ${p.name}: [${yearValues}]`;
    }).join('\n');

    // 3. Top Movers (Growth Table) - Limit to Top 10
    const growthSummary = context.topMovers.slice(0, 10).map(m =>
      `  - ${m.line}: +€${m.sellOutGrowthValue.toLocaleString('de-DE')} (${m.sellOutGrowthPercentage.toFixed(1)}%)`
    ).join('\n');

    // 4. Declining Movers (Decline Table) - Limit to Top 10
    const declineSummary = context.bottomMovers.slice(0, 10).map(m =>
      `  - ${m.line}: -€${Math.abs(m.sellOutGrowthValue).toLocaleString('de-DE')} (${m.sellOutGrowthPercentage.toFixed(1)}%)`
    ).join('\n');

    // 5. Product Lines Overview (Bar Charts) - Limit to Top 50
    const topLinesSummary = context.byLine.slice(0, 50).map((l, i) =>
      `  ${i + 1}. ${l.name}: ${formatCurrency(l.value)} | ${formatUnits(l.units)}`
    ).join('\n');

    // 6. Customer Distribution (Customer Chart)
    const customerSummary = context.byCustomer.map(c =>
      `  - ${c.name}: ${formatCurrency(c.value)}`
    ).join('\n');

    const fullReport = `
REPORT CONTEXT:
----------------
GLOBAL TOTALS:
Total Sell Out: ${formatCurrency(context.totalSellOut)}
Total Units: ${formatUnits(context.totalUnits)}
Records Analyzed: ${filteredRecordCount}
Years Available: ${context.availableYears.join(', ')}

YEARLY BREAKDOWN:
${yearlySummary}

MONTHLY SEASONALITY (Revenue Trends):
${seasonalitySummary}

FASTEST GROWING LINES (Year-over-Year):
${growthSummary}

DECLINING LINES (Year-over-Year):
${declineSummary}

TOP PRODUCT LINES (Revenue & Units):
${topLinesSummary}

PERFORMANCE BY CUSTOMER:
${customerSummary}
`;

    // Call our serverless API endpoint (key is safe server-side)
    const response = await fetch('/api/ask-gemini', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ question, context: fullReport })
    });

    if (!response.ok) {
      const errorData = await response.json().catch(() => ({ error: 'Unknown error' }));
      throw new Error(errorData.error || `Server error: ${response.status}`);
    }

    const data = await response.json();
    return data.response || "I couldn't generate a response based on the data provided.";
  } catch (error: any) {
    console.error("Gemini API Error:", error);
    return `Error: ${error.message || "An unexpected error occurred while analyzing the data."}`;
  }
};