import { GoogleGenAI } from "@google/genai";
import { AggregatedData } from "../types";

const SYSTEM_INSTRUCTION = `
You are an expert Data Analyst Assistant for "Craze Analytix".
You have access to a structured dataset of sales performance including Revenue (Sell Out), Units, Product Lines, and Seasonality.

Your Capabilities:
1. **Analyze Trends**: Use the provided Seasonality and Yearly Breakdown data.
2. **Perform Calculations**: You have access to detailed Product Line totals. You MUST calculate growth percentages, market shares, and sums dynamically if the user asks.
3. **Compare**: Compare performance between years (e.g., 2024 vs 2025).

Rules:
- If the user asks for a calculation (e.g., "What is the % share of Line X?"), perform the math using the provided numbers.
- Always format currency as € (e.g., €1,200) and units with 'u' or 'units' (e.g., 500 units).
- Be concise but insightful. Point out significant growth or decline.
- If data is missing for a specific query, state clearly that it is not in the current filtered view.
`;

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

export const queryGemini = async (
  apiKey: string,
  question: string, 
  context: AggregatedData, 
  filteredRecordCount: number
): Promise<string> => {
  
  if (!apiKey) {
    return "Please provide your Gemini API Key in the settings to enable the AI assistant.";
  }

  try {
    // Ensure the key is clean of whitespace
    const ai = new GoogleGenAI({ apiKey: apiKey.trim() });

    // --- 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])) // Descending years
        .map(([year, data]) => `  - ${year}: ${formatCurrency(data.sellOut)} | ${formatUnits(data.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. Growth/Decline
    const growthSummary = context.topMovers.slice(0, 10).map(m => 
        `  - ${m.line}: +€${m.sellOutGrowthValue.toLocaleString()} (${m.sellOutGrowthPercentage.toFixed(1)}%)`
    ).join('\n');

    const declineSummary = context.bottomMovers.slice(0, 10).map(m => 
        `  - ${m.line}: -€${Math.abs(m.sellOutGrowthValue).toLocaleString()} (${m.sellOutGrowthPercentage.toFixed(1)}%)`
    ).join('\n');

    // 4. DETAILED BREAKDOWN (For Calculations)
    // We provide a JSON-like structure of ALL top product lines so the AI can compute shares/totals.
    // We limit this to top 100 to avoid token limits, which covers most relevant data.
    const detailedLines = context.byLine.slice(0, 100).map(l => ({
        name: l.name,
        revenue: l.value,
        units: l.units
    }));

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

YEARLY TOTALS:
${yearlySummary}

MONTHLY TRENDS (Seasonality):
${seasonalitySummary}

TOP PERFORMERS (Growth YoY):
${growthSummary}

WORST PERFORMERS (Decline YoY):
${declineSummary}

DETAILED PRODUCT LINE DATA (Use this for specific calculations):
${JSON.stringify(detailedLines, null, 2)}
`;

    const response = await ai.models.generateContent({
      model: 'gemini-3-pro-preview', // Updated to the latest capable model for complex reasoning
      contents: [
        {
          role: 'user',
          parts: [{ text: `Context Data:\n${fullReport}\n\nUser Question: ${question}` }]
        }
      ],
      config: {
        systemInstruction: SYSTEM_INSTRUCTION,
      }
    });

    return response.text || "I couldn't generate a response based on the data provided.";
  } catch (error: any) {
    console.error("Gemini API Error:", error);
    
    if (error.message && error.message.includes("403")) {
       return "Error 403: Invalid API Key. Please check your key in the settings.";
    }
    if (error.message && error.message.includes("429")) {
        return "Error 429: Quota exceeded. You are sending too many requests.";
    }

    return `Error: ${error.message || "An unexpected error occurred while analyzing the data."}`;
  }
};