const path = require('path');
const fs = require('fs');
const progress = require('./utils/progress'); // Assuming progress utils are here
const { getConnection, closePool } = require('./utils/db'); // Assuming db utils are here
const os = require('os'); // For detecting number of CPU cores

// --- Configuration ---
const BATCH_SIZE_DAYS = 1; // Process 1 day per database function call
const SQL_FUNCTION_FILE = path.resolve(__dirname, 'backfill_historical_snapshots.sql'); // Correct path
const LOG_PROGRESS_INTERVAL_MS = 5000; // Update console progress roughly every 5 seconds
const HISTORY_TYPE = 'backfill_snapshots'; // Identifier for history table
const MAX_WORKERS = Math.max(1, Math.floor(os.cpus().length / 2)); // Use half of available CPU cores
const USE_PARALLEL = false; // Set to true to enable parallel processing
const PG_STATEMENT_TIMEOUT_MS = 1800000; // 30 minutes max per query

// --- Cancellation Handling ---
let isCancelled = false;
let runningQueryPromise = null; // To potentially track the active query

function requestCancellation() {
    if (!isCancelled) {
        isCancelled = true;
        console.warn('\nCancellation requested. Finishing current batch then stopping...');
        // Note: We are NOT forcefully cancelling the backend query anymore.
    }
}

process.on('SIGINT', requestCancellation); // Handle Ctrl+C
process.on('SIGTERM', requestCancellation); // Handle termination signals

// --- Main Backfill Function ---
async function backfillSnapshots(cmdStartDate, cmdEndDate, cmdStartBatch = 1) {
    let connection;
    const overallStartTime = Date.now();
    let calculateHistoryId = null;
    let processedDaysTotal = 0; // Track total days processed across all batches executed in this run
    let currentBatchNum = cmdStartBatch > 0 ? cmdStartBatch : 1;
    let totalBatches = 0; // Initialize totalBatches
    let totalDays = 0; // Initialize totalDays

    console.log(`Starting snapshot backfill process...`);
    console.log(`SQL Function definition file: ${SQL_FUNCTION_FILE}`);
    if (!fs.existsSync(SQL_FUNCTION_FILE)) {
         console.error(`FATAL: SQL file not found at ${SQL_FUNCTION_FILE}`);
         process.exit(1); // Exit early if file doesn't exist
    }

    try {
        // Set up a connection with higher memory limits
        connection = await getConnection({
            // Add performance-related settings
            application_name: 'backfill_snapshots',
            statement_timeout: PG_STATEMENT_TIMEOUT_MS, // 30 min timeout per statement
            // These parameters may need to be configured in your database:
            // work_mem: '1GB',
            // maintenance_work_mem: '2GB',
            // temp_buffers: '1GB',
        });
        
        console.log('Database connection acquired.');

        // --- Ensure Function Exists ---
        console.log('Ensuring database function is up-to-date...');
        try {
            const sqlFunctionDef = fs.readFileSync(SQL_FUNCTION_FILE, 'utf8');
            if (!sqlFunctionDef.includes('CREATE OR REPLACE FUNCTION backfill_daily_snapshots_range_final')) {
                throw new Error(`SQL file ${SQL_FUNCTION_FILE} does not seem to contain the function definition.`);
            }
            await connection.query(sqlFunctionDef); // Execute the whole file
            console.log('Database function `backfill_daily_snapshots_range_final` created/updated.');
            
            // Add performance query hints to the database
            await connection.query(`
                -- Analyze tables for better query planning
                ANALYZE public.products;
                ANALYZE public.imported_daily_inventory;
                ANALYZE public.imported_product_stat_history;
                ANALYZE public.daily_product_snapshots;
                ANALYZE public.imported_product_current_prices;
            `).catch(err => {
                // Non-fatal if analyze fails
                console.warn('Failed to analyze tables (non-fatal):', err.message);
            });
            
        } catch (err) {
            console.error(`Error processing SQL function file ${SQL_FUNCTION_FILE}:`, err);
            throw new Error(`Failed to create or replace DB function: ${err.message}`);
        }

        // --- Prepare History Record ---
        console.log('Preparing calculation history record...');
         // Ensure history table exists (optional, could be done elsewhere)
         await connection.query(`
            CREATE TABLE IF NOT EXISTS public.calculate_history (
                id SERIAL PRIMARY KEY,
                start_time TIMESTAMPTZ NOT NULL DEFAULT NOW(),
                end_time TIMESTAMPTZ,
                duration_seconds INTEGER,
                status VARCHAR(20) NOT NULL, -- e.g., 'running', 'completed', 'failed', 'cancelled'
                error_message TEXT,
                additional_info JSONB -- Store type, file, batch info etc.
            );
         `);
        // Mark previous runs of this type as potentially failed if they were left 'running'
        await connection.query(`
            UPDATE public.calculate_history
            SET status = 'failed', error_message = 'Interrupted by new run.'
            WHERE status = 'running' AND additional_info->>'type' = $1;
        `, [HISTORY_TYPE]);

        // Create new history record
        const historyResult = await connection.query(`
            INSERT INTO public.calculate_history (start_time, status, additional_info)
            VALUES (NOW(), 'running', jsonb_build_object('type', $1::text, 'sql_file', $2::text, 'start_batch', $3::integer))
            RETURNING id;
        `, [HISTORY_TYPE, path.basename(SQL_FUNCTION_FILE), cmdStartBatch]);
        calculateHistoryId = historyResult.rows[0].id;
        console.log(`Calculation history record created with ID: ${calculateHistoryId}`);


        // --- Determine Date Range ---
        console.log('Determining date range...');
        let effectiveStartDate, effectiveEndDate;

        // Use command-line dates if provided, otherwise query DB
        if (cmdStartDate) {
             effectiveStartDate = cmdStartDate;
        } else {
             const minDateResult = await connection.query(`
                SELECT LEAST(
                    COALESCE((SELECT MIN(date) FROM public.imported_daily_inventory WHERE date > '1970-01-01'), CURRENT_DATE),
                    COALESCE((SELECT MIN(date) FROM public.imported_product_stat_history WHERE date > '1970-01-01'), CURRENT_DATE)
                )::date as min_date;
            `);
             effectiveStartDate = minDateResult.rows[0]?.min_date || new Date().toISOString().split('T')[0]; // Fallback
             console.log(`Auto-detected start date: ${effectiveStartDate}`);
        }

        if (cmdEndDate) {
            effectiveEndDate = cmdEndDate;
        } else {
             const maxDateResult = await connection.query(`
                 SELECT GREATEST(
                    COALESCE((SELECT MAX(date) FROM public.imported_daily_inventory WHERE date < CURRENT_DATE), '1970-01-01'::date),
                    COALESCE((SELECT MAX(date) FROM public.imported_product_stat_history WHERE date < CURRENT_DATE), '1970-01-01'::date)
                )::date as max_date;
             `);
             // Ensure end date is not today or in the future
             effectiveEndDate = maxDateResult.rows[0]?.max_date || new Date(Date.now() - 86400000).toISOString().split('T')[0]; // Default yesterday
             if (new Date(effectiveEndDate) >= new Date(new Date().toISOString().split('T')[0])) {
                 effectiveEndDate = new Date(Date.now() - 86400000).toISOString().split('T')[0]; // Set to yesterday if >= today
             }
             console.log(`Auto-detected end date: ${effectiveEndDate}`);
        }

         // Validate dates
         const dStart = new Date(effectiveStartDate);
         const dEnd = new Date(effectiveEndDate);
         if (isNaN(dStart.getTime()) || isNaN(dEnd.getTime()) || dStart > dEnd) {
             throw new Error(`Invalid date range: Start "${effectiveStartDate}", End "${effectiveEndDate}"`);
         }

        // --- Batch Processing ---
        totalDays = Math.ceil((dEnd - dStart) / (1000 * 60 * 60 * 24)) + 1; // Inclusive
        totalBatches = Math.ceil(totalDays / BATCH_SIZE_DAYS);

        console.log(`Target Date Range: ${effectiveStartDate} to ${effectiveEndDate} (${totalDays} days)`);
        console.log(`Total Batches: ${totalBatches} (Batch Size: ${BATCH_SIZE_DAYS} days)`);
        console.log(`Starting from Batch: ${currentBatchNum}`);

        // Initial progress update
        progress.outputProgress({ 
            status: 'running', 
            operation: 'Starting Batch Processing',
            currentBatch: currentBatchNum, 
            totalBatches: totalBatches, 
            totalDays: totalDays,
            elapsed: '0s', 
            remaining: 'Calculating...', 
            rate: 0,
            historyId: calculateHistoryId // Include history ID in the object
        });

        while (currentBatchNum <= totalBatches && !isCancelled) {
            const batchOffset = (currentBatchNum - 1) * BATCH_SIZE_DAYS;
            const batchStartDate = new Date(dStart);
            batchStartDate.setDate(dStart.getDate() + batchOffset);

            const batchEndDate = new Date(batchStartDate);
            batchEndDate.setDate(batchStartDate.getDate() + BATCH_SIZE_DAYS - 1);

            // Clamp batch end date to the overall effective end date
            if (batchEndDate > dEnd) {
                batchEndDate.setTime(dEnd.getTime());
            }

            const batchStartDateStr = batchStartDate.toISOString().split('T')[0];
            const batchEndDateStr = batchEndDate.toISOString().split('T')[0];
            const batchStartTime = Date.now();

            console.log(`\n--- Processing Batch ${currentBatchNum} / ${totalBatches} ---`);
            console.log(`    Dates: ${batchStartDateStr} to ${batchEndDateStr}`);

            // Execute the function for the batch
             try {
                progress.outputProgress({
                     status: 'running', 
                     operation: `Executing DB function for batch ${currentBatchNum}...`,
                     currentBatch: currentBatchNum, 
                     totalBatches: totalBatches, 
                     totalDays: totalDays,
                     elapsed: progress.formatElapsedTime(overallStartTime), 
                     remaining: 'Executing...', 
                     rate: 0,
                     historyId: calculateHistoryId
                 });

                // Performance improvement: Add batch processing hint
                await connection.query('SET LOCAL enable_parallel_append = on; SET LOCAL enable_parallel_hash = on; SET LOCAL max_parallel_workers_per_gather = 4;');

                // Store promise in case we need to try and cancel (though not implemented forcefully)
                runningQueryPromise = connection.query(
                    `SELECT backfill_daily_snapshots_range_final($1::date, $2::date);`,
                    [batchStartDateStr, batchEndDateStr]
                );
                await runningQueryPromise; // Wait for the function call to complete
                runningQueryPromise = null; // Clear the promise

                const batchDurationMs = Date.now() - batchStartTime;
                const daysInThisBatch = Math.ceil((batchEndDate - batchStartDate) / (1000 * 60 * 60 * 24)) + 1;
                processedDaysTotal += daysInThisBatch;

                console.log(`    Batch ${currentBatchNum} completed in ${progress.formatElapsedTime(batchStartTime)}.`);

                // --- Update Progress & History ---
                const overallElapsedSec = Math.round((Date.now() - overallStartTime) / 1000);
                progress.outputProgress({
                    status: 'running', 
                    operation: `Completed batch ${currentBatchNum}`,
                    currentBatch: currentBatchNum, 
                    totalBatches: totalBatches, 
                    totalDays: totalDays,
                    processedDays: processedDaysTotal,
                    elapsed: progress.formatElapsedTime(overallStartTime),
                    remaining: progress.estimateRemaining(overallStartTime, processedDaysTotal, totalDays),
                    rate: progress.calculateRate(overallStartTime, processedDaysTotal),
                    batchDuration: progress.formatElapsedTime(batchStartTime),
                    historyId: calculateHistoryId
                });

                // Save checkpoint in history
                await connection.query(`
                    UPDATE public.calculate_history
                    SET additional_info = jsonb_set(additional_info, '{last_completed_batch}', $1::jsonb)
                                        || jsonb_build_object('last_processed_date', $2::text)
                    WHERE id = $3::integer;
                `, [JSON.stringify(currentBatchNum), batchEndDateStr, calculateHistoryId]);


             } catch (batchError) {
                 console.error(`\n--- ERROR in Batch ${currentBatchNum} (${batchStartDateStr} to ${batchEndDateStr}) ---`);
                 console.error('    Database Error:', batchError.message);
                 console.error('    DB Error Code:', batchError.code);
                 // Log detailed error to history and re-throw to stop the process
                 await connection.query(`
                    UPDATE public.calculate_history
                    SET status = 'failed',
                        end_time = NOW(),
                        duration_seconds = $1::integer,
                        error_message = $2::text,
                        additional_info = additional_info || jsonb_build_object('failed_batch', $3::integer, 'failed_date_range', $4::text)
                    WHERE id = $5::integer;
                 `, [
                     Math.round((Date.now() - overallStartTime) / 1000),
                     `Batch ${currentBatchNum} failed: ${batchError.message} (Code: ${batchError.code || 'N/A'})`,
                     currentBatchNum,
                     `${batchStartDateStr} to ${batchEndDateStr}`,
                     calculateHistoryId
                 ]);
                 throw batchError; // Stop execution
             }

            currentBatchNum++;
            // Optional delay between batches
            // await new Promise(resolve => setTimeout(resolve, 500));

        } // End while loop

        // --- Final Outcome ---
        const finalStatus = isCancelled ? 'cancelled' : 'completed';
        const finalMessage = isCancelled ? `Calculation stopped after completing batch ${currentBatchNum - 1}.` : 'Historical snapshots backfill completed successfully.';
        const finalDurationSec = Math.round((Date.now() - overallStartTime) / 1000);

        console.log(`\n--- Backfill ${finalStatus.toUpperCase()} ---`);
        console.log(finalMessage);
        console.log(`Total duration: ${progress.formatElapsedTime(overallStartTime)}`);

        // Update history record
        await connection.query(`
            UPDATE public.calculate_history SET status = $1::calculation_status, end_time = NOW(), duration_seconds = $2::integer, error_message = $3
            WHERE id = $4::integer;
        `, [finalStatus, finalDurationSec, (isCancelled ? 'User cancelled' : null), calculateHistoryId]);

        if (!isCancelled) {
            progress.clearProgress(); // Clear progress state only on successful completion
        } else {
             progress.outputProgress({ // Final cancelled status update
                status: 'cancelled', 
                operation: finalMessage,
                currentBatch: currentBatchNum - 1, 
                totalBatches: totalBatches, 
                totalDays: totalDays,
                processedDays: processedDaysTotal,
                elapsed: progress.formatElapsedTime(overallStartTime), 
                remaining: 'Cancelled', 
                rate: 0,
                historyId: calculateHistoryId
             });
        }

        return { success: true, status: finalStatus, message: finalMessage, duration: finalDurationSec };

    } catch (error) {
        console.error('\n--- Backfill encountered an unrecoverable error ---');
        console.error(error.message);
        const finalDurationSec = Math.round((Date.now() - overallStartTime) / 1000);

        // Update history if possible
        if (connection && calculateHistoryId) {
             try {
                 await connection.query(`
                    UPDATE public.calculate_history
                    SET status = $1::calculation_status, end_time = NOW(), duration_seconds = $2::integer, error_message = $3::text
                    WHERE id = $4::integer;
                 `, [
                     isCancelled ? 'cancelled' : 'failed',
                     finalDurationSec,
                     error.message,
                     calculateHistoryId
                 ]);
             } catch (histError) {
                 console.error("Failed to update history record with error state:", histError);
             }
        } else {
            console.error("Could not update history record (no ID or connection).");
        }

        // FIX: Use initialized value or a default if loop never started
        const batchNumForError = currentBatchNum > cmdStartBatch ? currentBatchNum - 1 : cmdStartBatch - 1;
        
        // Update progress.outputProgress call to match actual function signature
        try {
            // Create progress data object
            const progressData = {
                status: 'failed',
                operation: 'Backfill failed',
                message: error.message,
                currentBatch: batchNumForError,
                totalBatches: totalBatches,
                totalDays: totalDays,
                processedDays: processedDaysTotal,
                elapsed: progress.formatElapsedTime(overallStartTime),
                remaining: 'Failed',
                rate: 0,
                // Include history ID in progress data if needed
                historyId: calculateHistoryId
            };
            
            // Call with single object parameter (not separate historyId)
            progress.outputProgress(progressData);
        } catch (progressError) {
            console.error('Failed to report progress:', progressError);
        }

        return { success: false, status: 'failed', error: error.message, duration: finalDurationSec };

    } finally {
        if (connection) {
            console.log('Releasing database connection.');
            connection.release();
        }
        // Close pool only if this script is meant to be standalone
        // If part of a larger app, the app should manage pool closure
        // console.log('Closing database pool.');
        // await closePool();
    }
}

// --- Script Execution ---

// Parse command-line arguments
const args = process.argv.slice(2);
let cmdStartDateArg, cmdEndDateArg, cmdStartBatchArg = 1; // Default start batch is 1

for (let i = 0; i < args.length; i++) {
    if (args[i] === '--start-date' && args[i+1]) cmdStartDateArg = args[++i];
    else if (args[i] === '--end-date' && args[i+1]) cmdEndDateArg = args[++i];
    else if (args[i] === '--start-batch' && args[i+1]) cmdStartBatchArg = parseInt(args[++i], 10);
}

if (isNaN(cmdStartBatchArg) || cmdStartBatchArg < 1) {
    console.warn(`Invalid --start-batch value. Defaulting to 1.`);
    cmdStartBatchArg = 1;
}

// Run the backfill process
backfillSnapshots(cmdStartDateArg, cmdEndDateArg, cmdStartBatchArg)
    .then(result => {
        if (result.success) {
            console.log(`\n✅ ${result.message} (Duration: ${result.duration}s)`);
            process.exitCode = 0; // Success
        } else {
            console.error(`\n❌ Backfill failed: ${result.error || 'Unknown error'} (Duration: ${result.duration}s)`);
            process.exitCode = 1; // Failure
        }
    })
    .catch(err => {
        console.error('\n❌ Unexpected error during backfill execution:', err);
        process.exitCode = 1; // Failure
    })
    .finally(async () => {
        // Ensure pool is closed if run standalone
         console.log('Backfill script finished. Closing pool.');
         await closePool(); // Make sure closePool exists and works in your db utils
         process.exit(process.exitCode); // Exit with appropriate code
    });