const express = require('express');
const router = express.Router();
const { Pool } = require('pg'); // Assuming pg driver

// --- Configuration & Helpers ---

const DEFAULT_PAGE_LIMIT = 50;
const MAX_PAGE_LIMIT = 200; // Prevent excessive data requests

/**
 * Maps user-friendly query parameter keys (camelCase) to database column names.
 * Also validates if the column is safe for sorting or filtering.
 * Add ALL columns from product_metrics that should be filterable/sortable.
 */
const COLUMN_MAP = {
    // Product Info
    pid: { dbCol: 'pm.pid', type: 'number' },
    sku: { dbCol: 'pm.sku', type: 'string' },
    title: { dbCol: 'pm.title', type: 'string' },
    brand: { dbCol: 'pm.brand', type: 'string' },
    vendor: { dbCol: 'pm.vendor', type: 'string' },
    imageUrl: { dbCol: 'pm.image_url', type: 'string' },
    isVisible: { dbCol: 'pm.is_visible', type: 'boolean' },
    isReplenishable: { dbCol: 'pm.is_replenishable', type: 'boolean' },
    // Current Status
    currentPrice: { dbCol: 'pm.current_price', type: 'number' },
    currentRegularPrice: { dbCol: 'pm.current_regular_price', type: 'number' },
    currentCostPrice: { dbCol: 'pm.current_cost_price', type: 'number' },
    currentLandingCostPrice: { dbCol: 'pm.current_landing_cost_price', type: 'number' },
    currentStock: { dbCol: 'pm.current_stock', type: 'number' },
    currentStockCost: { dbCol: 'pm.current_stock_cost', type: 'number' },
    currentStockRetail: { dbCol: 'pm.current_stock_retail', type: 'number' },
    currentStockGross: { dbCol: 'pm.current_stock_gross', type: 'number' },
    onOrderQty: { dbCol: 'pm.on_order_qty', type: 'number' },
    onOrderCost: { dbCol: 'pm.on_order_cost', type: 'number' },
    onOrderRetail: { dbCol: 'pm.on_order_retail', type: 'number' },
    earliestExpectedDate: { dbCol: 'pm.earliest_expected_date', type: 'date' },
    // Historical Dates
    dateCreated: { dbCol: 'pm.date_created', type: 'date' },
    dateFirstReceived: { dbCol: 'pm.date_first_received', type: 'date' },
    dateLastReceived: { dbCol: 'pm.date_last_received', type: 'date' },
    dateFirstSold: { dbCol: 'pm.date_first_sold', type: 'date' },
    dateLastSold: { dbCol: 'pm.date_last_sold', type: 'date' },
    ageDays: { dbCol: 'pm.age_days', type: 'number' },
    // Rolling Period Metrics
    sales7d: { dbCol: 'pm.sales_7d', type: 'number' }, revenue7d: { dbCol: 'pm.revenue_7d', type: 'number' },
    sales14d: { dbCol: 'pm.sales_14d', type: 'number' }, revenue14d: { dbCol: 'pm.revenue_14d', type: 'number' },
    sales30d: { dbCol: 'pm.sales_30d', type: 'number' }, revenue30d: { dbCol: 'pm.revenue_30d', type: 'number' },
    cogs30d: { dbCol: 'pm.cogs_30d', type: 'number' }, profit30d: { dbCol: 'pm.profit_30d', type: 'number' },
    returnsUnits30d: { dbCol: 'pm.returns_units_30d', type: 'number' }, returnsRevenue30d: { dbCol: 'pm.returns_revenue_30d', type: 'number' },
    discounts30d: { dbCol: 'pm.discounts_30d', type: 'number' }, grossRevenue30d: { dbCol: 'pm.gross_revenue_30d', type: 'number' },
    grossRegularRevenue30d: { dbCol: 'pm.gross_regular_revenue_30d', type: 'number' },
    stockoutDays30d: { dbCol: 'pm.stockout_days_30d', type: 'number' },
    sales365d: { dbCol: 'pm.sales_365d', type: 'number' }, revenue365d: { dbCol: 'pm.revenue_365d', type: 'number' },
    avgStockUnits30d: { dbCol: 'pm.avg_stock_units_30d', type: 'number' }, avgStockCost30d: { dbCol: 'pm.avg_stock_cost_30d', type: 'number' },
    avgStockRetail30d: { dbCol: 'pm.avg_stock_retail_30d', type: 'number' }, avgStockGross30d: { dbCol: 'pm.avg_stock_gross_30d', type: 'number' },
    receivedQty30d: { dbCol: 'pm.received_qty_30d', type: 'number' }, receivedCost30d: { dbCol: 'pm.received_cost_30d', type: 'number' },
    // Lifetime Metrics
    lifetimeSales: { dbCol: 'pm.lifetime_sales', type: 'number' }, lifetimeRevenue: { dbCol: 'pm.lifetime_revenue', type: 'number' },
    // First Period Metrics
    first7DaysSales: { dbCol: 'pm.first_7_days_sales', type: 'number' }, first7DaysRevenue: { dbCol: 'pm.first_7_days_revenue', type: 'number' },
    first30DaysSales: { dbCol: 'pm.first_30_days_sales', type: 'number' }, first30DaysRevenue: { dbCol: 'pm.first_30_days_revenue', type: 'number' },
    first60DaysSales: { dbCol: 'pm.first_60_days_sales', type: 'number' }, first60DaysRevenue: { dbCol: 'pm.first_60_days_revenue', type: 'number' },
    first90DaysSales: { dbCol: 'pm.first_90_days_sales', type: 'number' }, first90DaysRevenue: { dbCol: 'pm.first_90_days_revenue', type: 'number' },
    // Calculated KPIs
    asp30d: { dbCol: 'pm.asp_30d', type: 'number' }, acp30d: { dbCol: 'pm.acp_30d', type: 'number' }, avgRos30d: { dbCol: 'pm.avg_ros_30d', type: 'number' },
    avgSalesPerDay30d: { dbCol: 'pm.avg_sales_per_day_30d', type: 'number' }, avgSalesPerMonth30d: { dbCol: 'pm.avg_sales_per_month_30d', type: 'number' },
    margin30d: { dbCol: 'pm.margin_30d', type: 'number' }, markup30d: { dbCol: 'pm.markup_30d', type: 'number' }, gmroi30d: { dbCol: 'pm.gmroi_30d', type: 'number' },
    stockturn30d: { dbCol: 'pm.stockturn_30d', type: 'number' }, returnRate30d: { dbCol: 'pm.return_rate_30d', type: 'number' },
    discountRate30d: { dbCol: 'pm.discount_rate_30d', type: 'number' }, stockoutRate30d: { dbCol: 'pm.stockout_rate_30d', type: 'number' },
    markdown30d: { dbCol: 'pm.markdown_30d', type: 'number' }, markdownRate30d: { dbCol: 'pm.markdown_rate_30d', type: 'number' },
    sellThrough30d: { dbCol: 'pm.sell_through_30d', type: 'number' }, avgLeadTimeDays: { dbCol: 'pm.avg_lead_time_days', type: 'number' },
    // Forecasting & Replenishment
    abcClass: { dbCol: 'pm.abc_class', type: 'string' }, salesVelocityDaily: { dbCol: 'pm.sales_velocity_daily', type: 'number' },
    configLeadTime: { dbCol: 'pm.config_lead_time', type: 'number' }, configDaysOfStock: { dbCol: 'pm.config_days_of_stock', type: 'number' },
    configSafetyStock: { dbCol: 'pm.config_safety_stock', type: 'number' }, planningPeriodDays: { dbCol: 'pm.planning_period_days', type: 'number' },
    leadTimeForecastUnits: { dbCol: 'pm.lead_time_forecast_units', type: 'number' }, daysOfStockForecastUnits: { dbCol: 'pm.days_of_stock_forecast_units', type: 'number' },
    planningPeriodForecastUnits: { dbCol: 'pm.planning_period_forecast_units', type: 'number' }, leadTimeClosingStock: { dbCol: 'pm.lead_time_closing_stock', type: 'number' },
    daysOfStockClosingStock: { dbCol: 'pm.days_of_stock_closing_stock', type: 'number' }, replenishmentNeededRaw: { dbCol: 'pm.replenishment_needed_raw', type: 'number' },
    replenishmentUnits: { dbCol: 'pm.replenishment_units', type: 'number' }, replenishmentCost: { dbCol: 'pm.replenishment_cost', type: 'number' },
    replenishmentRetail: { dbCol: 'pm.replenishment_retail', type: 'number' }, replenishmentProfit: { dbCol: 'pm.replenishment_profit', type: 'number' },
    toOrderUnits: { dbCol: 'pm.to_order_units', type: 'number' }, forecastLostSalesUnits: { dbCol: 'pm.forecast_lost_sales_units', type: 'number' },
    forecastLostRevenue: { dbCol: 'pm.forecast_lost_revenue', type: 'number' }, stockCoverInDays: { dbCol: 'pm.stock_cover_in_days', type: 'number' },
    poCoverInDays: { dbCol: 'pm.po_cover_in_days', type: 'number' }, sellsOutInDays: { dbCol: 'pm.sells_out_in_days', type: 'number' },
    replenishDate: { dbCol: 'pm.replenish_date', type: 'date' }, overstockedUnits: { dbCol: 'pm.overstocked_units', type: 'number' },
    overstockedCost: { dbCol: 'pm.overstocked_cost', type: 'number' }, overstockedRetail: { dbCol: 'pm.overstocked_retail', type: 'number' },
    isOldStock: { dbCol: 'pm.is_old_stock', type: 'boolean' },
    // Yesterday
    yesterdaySales: { dbCol: 'pm.yesterday_sales', type: 'number' },
};

function getSafeColumnInfo(queryParamKey) {
    return COLUMN_MAP[queryParamKey] || null;
}

// --- Route Handlers ---

// GET /metrics/filter-options - Provide distinct values for filter dropdowns
router.get('/filter-options', async (req, res) => {
    const pool = req.app.locals.pool;
    console.log('GET /metrics/filter-options');
    try {
        const [vendorRes, brandRes, abcClassRes] = await Promise.all([
            pool.query(`SELECT DISTINCT vendor FROM public.product_metrics WHERE vendor IS NOT NULL AND vendor <> '' ORDER BY vendor`),
            pool.query(`SELECT DISTINCT COALESCE(brand, 'Unbranded') as brand FROM public.product_metrics WHERE brand IS NOT NULL AND brand <> '' ORDER BY brand`),
            pool.query(`SELECT DISTINCT abc_class FROM public.product_metrics WHERE abc_class IS NOT NULL ORDER BY abc_class`)
            // Add queries for other distinct options if needed (e.g., categories if stored on pm)
        ]);

        res.json({
            vendors: vendorRes.rows.map(r => r.vendor),
            brands: brandRes.rows.map(r => r.brand),
            abcClasses: abcClassRes.rows.map(r => r.abc_class),
        });
    } catch (error) {
        console.error('Error fetching filter options:', error);
        res.status(500).json({ error: 'Failed to fetch filter options' });
    }
});


// GET /metrics/ - List all product metrics with filtering, sorting, pagination
router.get('/', async (req, res) => {
    const pool = req.app.locals.pool; // Get pool from app instance
    console.log('GET /metrics received query:', req.query);

    try {
        // --- Pagination ---
        let page = parseInt(req.query.page, 10);
        let limit = parseInt(req.query.limit, 10);
        if (isNaN(page) || page < 1) page = 1;
        if (isNaN(limit) || limit < 1) limit = DEFAULT_PAGE_LIMIT;
        limit = Math.min(limit, MAX_PAGE_LIMIT); // Cap the limit
        const offset = (page - 1) * limit;

        // --- Sorting ---
        const sortQueryKey = req.query.sort || 'title'; // Default sort field key
        const sortColumnInfo = getSafeColumnInfo(sortQueryKey);
        const sortColumn = sortColumnInfo ? sortColumnInfo.dbCol : 'pm.title'; // Default DB column
        const sortDirection = req.query.order?.toLowerCase() === 'desc' ? 'DESC' : 'ASC';
        const nullsOrder = (sortDirection === 'ASC' ? 'NULLS FIRST' : 'NULLS LAST'); // Consistent null handling

        // --- Filtering ---
        const conditions = [];
        const params = [];
        let paramCounter = 1;

        // Add default visibility/replenishable filters unless overridden
        if (req.query.showInvisible !== 'true') conditions.push(`pm.is_visible = true`);
        if (req.query.showNonReplenishable !== 'true') conditions.push(`pm.is_replenishable = true`);

        // Process other filters from query parameters
        for (const key in req.query) {
            if (['page', 'limit', 'sort', 'order', 'showInvisible', 'showNonReplenishable'].includes(key)) continue; // Skip control params

            let filterKey = key;
            let operator = '='; // Default operator
            let value = req.query[key];

            // Check for operator suffixes (e.g., sales30d_gt, title_like)
            const operatorMatch = key.match(/^(.*)_(eq|ne|gt|gte|lt|lte|like|ilike|between|in)$/);
            if (operatorMatch) {
                filterKey = operatorMatch[1]; // e.g., "sales30d"
                operator = operatorMatch[2]; // e.g., "gt"
            }

            const columnInfo = getSafeColumnInfo(filterKey);
            if (!columnInfo) {
                console.warn(`Invalid filter key ignored: ${key}`);
                continue; // Skip if the key doesn't map to a known column
            }

            const dbColumn = columnInfo.dbCol;
            const valueType = columnInfo.type;

            // --- Build WHERE clause fragment ---
            try {
                let conditionFragment = '';
                let needsParam = true; // Most operators need a parameter

                switch (operator.toLowerCase()) {
                    case 'eq': operator = '='; break;
                    case 'ne': operator = '<>'; break;
                    case 'gt': operator = '>'; break;
                    case 'gte': operator = '>='; break;
                    case 'lt': operator = '<'; break;
                    case 'lte': operator = '<='; break;
                    case 'like': operator = 'LIKE'; value = `%${value}%`; break; // Add wildcards for LIKE
                    case 'ilike': operator = 'ILIKE'; value = `%${value}%`; break; // Add wildcards for ILIKE
                    case 'between':
                        const [val1, val2] = String(value).split(',');
                        if (val1 !== undefined && val2 !== undefined) {
                             conditionFragment = `${dbColumn} BETWEEN $${paramCounter++} AND $${paramCounter++}`;
                             params.push(parseValue(val1, valueType), parseValue(val2, valueType));
                             needsParam = false; // Params added manually
                        } else {
                             console.warn(`Invalid 'between' value for ${key}: ${value}`);
                             continue; // Skip this filter
                        }
                        break;
                    case 'in':
                        const inValues = String(value).split(',');
                        if (inValues.length > 0) {
                            const placeholders = inValues.map(() => `$${paramCounter++}`).join(', ');
                            conditionFragment = `${dbColumn} IN (${placeholders})`;
                            params.push(...inValues.map(v => parseValue(v, valueType))); // Add all parsed values
                             needsParam = false; // Params added manually
                        } else {
                             console.warn(`Invalid 'in' value for ${key}: ${value}`);
                             continue; // Skip this filter
                        }
                        break;
                    // Add other operators as needed (IS NULL, IS NOT NULL, etc.)
                    case '=': // Keep default '='
                    default: operator = '='; break; // Ensure default is handled
                }

                if (needsParam) {
                    conditionFragment = `${dbColumn} ${operator} $${paramCounter++}`;
                    params.push(parseValue(value, valueType));
                }

                if (conditionFragment) {
                    conditions.push(`(${conditionFragment})`); // Wrap condition in parentheses
                }

            } catch (parseError) {
                 console.warn(`Skipping filter for key "${key}" due to parsing error: ${parseError.message}`);
                 // Decrement counter if param wasn't actually used due to error
                 if (needsParam) paramCounter--;
            }
        }

        // --- Construct and Execute Queries ---
        const whereClause = conditions.length > 0 ? `WHERE ${conditions.join(' AND ')}` : '';

        // Count Query
        const countSql = `SELECT COUNT(*) AS total FROM public.product_metrics pm ${whereClause}`;
        console.log('Executing Count Query:', countSql, params);
        const countPromise = pool.query(countSql, params);

        // Data Query (Select all columns from metrics table for now)
        const dataSql = `
            SELECT pm.*
            FROM public.product_metrics pm
            ${whereClause}
            ORDER BY ${sortColumn} ${sortDirection} ${nullsOrder}
            LIMIT $${paramCounter} OFFSET $${paramCounter + 1}
        `;
        const dataParams = [...params, limit, offset];
        console.log('Executing Data Query:', dataSql, dataParams);
        const dataPromise = pool.query(dataSql, dataParams);

        // Execute queries in parallel
        const [countResult, dataResult] = await Promise.all([countPromise, dataPromise]);

        const total = parseInt(countResult.rows[0].total, 10);
        const metrics = dataResult.rows;
        console.log(`Total: ${total}, Fetched: ${metrics.length} for page ${page}`);

        // --- Respond ---
        res.json({
            metrics,
            pagination: {
                total,
                pages: Math.ceil(total / limit),
                currentPage: page,
                limit,
            },
            // Optionally include applied filters/sort for frontend confirmation
             appliedQuery: {
                 filters: req.query, // Send back raw query filters
                 sort: sortQueryKey,
                 order: sortDirection.toLowerCase()
             }
        });

    } catch (error) {
        console.error('Error fetching metrics list:', error);
        res.status(500).json({ error: 'Failed to fetch product metrics list.' });
    }
});

// GET /metrics/:pid - Get metrics for a single product
router.get('/:pid', async (req, res) => {
    const pool = req.app.locals.pool;
    const pid = parseInt(req.params.pid, 10);

    if (isNaN(pid)) {
        return res.status(400).json({ error: 'Invalid Product ID.' });
    }

    console.log(`GET /metrics/${pid}`);
    try {
        const { rows } = await pool.query(
            `SELECT * FROM public.product_metrics WHERE pid = $1`,
            [pid]
        );

        if (rows.length === 0) {
            console.log(`Metrics not found for PID: ${pid}`);
            return res.status(404).json({ error: 'Metrics not found for this product.' });
        }

        console.log(`Metrics found for PID: ${pid}`);
        // Data is pre-calculated, return the first (only) row
        res.json(rows[0]);

    } catch (error) {
        console.error(`Error fetching metrics for PID ${pid}:`, error);
        res.status(500).json({ error: 'Failed to fetch product metrics.' });
    }
});


/**
 * Parses a value based on its expected type.
 * Throws error for invalid formats.
 */
function parseValue(value, type) {
    if (value === null || value === undefined || value === '') return null; // Allow empty strings? Or handle differently?

    switch (type) {
        case 'number':
            const num = parseFloat(value);
            if (isNaN(num)) throw new Error(`Invalid number format: "${value}"`);
            return num;
        case 'boolean':
            if (String(value).toLowerCase() === 'true') return true;
            if (String(value).toLowerCase() === 'false') return false;
            throw new Error(`Invalid boolean format: "${value}"`);
        case 'date':
            // Basic validation, rely on DB to handle actual date conversion
            if (!String(value).match(/^\d{4}-\d{2}-\d{2}$/)) {
               // Allow full timestamps too? Adjust regex if needed
               // console.warn(`Potentially invalid date format: "${value}"`); // Warn instead of throwing?
            }
            return String(value); // Send as string, let DB handle it
        case 'string':
        default:
            return String(value);
    }
}

module.exports = router;