/**
 * Mappings Routes
 * Manage value mappings
 */

const express = require('express');
const multer = require('multer');
const { parse } = require('csv-parse/sync');

const upload = multer({ storage: multer.memoryStorage() });

const SYSTEM_COLS = new Set(['source_name', 'rule_name', 'input_value', 'record_count', 'sample']);

module.exports = (pool) => {
    const router = express.Router();

    // List all mappings for a source
    router.get('/source/:source_name', async (req, res, next) => {
        try {
            const { rule_name } = req.query;

            let query = 'SELECT * FROM mappings WHERE source_name = $1';
            const params = [req.params.source_name];

            if (rule_name) {
                query += ' AND rule_name = $2';
                params.push(rule_name);
            }

            query += ' ORDER BY rule_name, input_value';

            const result = await pool.query(query, params);
            res.json(result.rows);
        } catch (err) {
            next(err);
        }
    });

    // Get unmapped values
    router.get('/source/:source_name/unmapped', async (req, res, next) => {
        try {
            const { rule_name } = req.query;

            const result = await pool.query(
                'SELECT * FROM get_unmapped_values($1, $2)',
                [req.params.source_name, rule_name || null]
            );

            res.json(result.rows);
        } catch (err) {
            next(err);
        }
    });

    // Export unmapped values + existing mappings as TSV
    // Columns: source_name, rule_name, input_value, record_count, <output keys...>, sample
    // sample is always last and is discarded on import
    router.get('/source/:source_name/export.tsv', async (req, res, next) => {
        try {
            const { rule_name } = req.query;
            const source_name = req.params.source_name;

            const [unmappedResult, mappedResult] = await Promise.all([
                pool.query('SELECT * FROM get_unmapped_values($1, $2)', [source_name, rule_name || null]),
                pool.query(
                    'SELECT * FROM mappings WHERE source_name = $1' + (rule_name ? ' AND rule_name = $2' : '') + ' ORDER BY rule_name, input_value',
                    rule_name ? [source_name, rule_name] : [source_name]
                )
            ]);

            // Collect output keys from existing mappings
            const outputKeys = [];
            for (const row of mappedResult.rows) {
                for (const key of Object.keys(row.output || {})) {
                    if (!outputKeys.includes(key)) outputKeys.push(key);
                }
            }

            const escape = (val) => String(val ?? '').replace(/\t/g, ' ');

            // sample is always last
            const allCols = ['source_name', 'rule_name', 'input_value', 'record_count', ...outputKeys, 'sample'];

            const dataRows = [];

            for (const row of unmappedResult.rows) {
                const r = {
                    source_name,
                    rule_name: row.rule_name,
                    input_value: Array.isArray(row.extracted_value) ? JSON.stringify(row.extracted_value) : String(row.extracted_value ?? ''),
                    record_count: row.record_count,
                    sample: Array.isArray(row.sample) ? row.sample.join(' | ') : String(row.sample ?? '')
                };
                for (const key of outputKeys) r[key] = '';
                dataRows.push(r);
            }

            for (const row of mappedResult.rows) {
                const r = {
                    source_name: row.source_name,
                    rule_name: row.rule_name,
                    input_value: Array.isArray(row.input_value) ? JSON.stringify(row.input_value) : String(row.input_value ?? ''),
                    record_count: '',
                    sample: ''
                };
                for (const key of outputKeys) r[key] = row.output?.[key] ?? '';
                dataRows.push(r);
            }

            const tsv = [
                allCols.map(escape).join('\t'),
                ...dataRows.map(r => allCols.map(c => escape(r[c])).join('\t'))
            ].join('\n');

            res.setHeader('Content-Type', 'text/tab-separated-values');
            res.setHeader('Content-Disposition', `attachment; filename="mappings_${source_name}.tsv"`);
            res.send(tsv);
        } catch (err) {
            next(err);
        }
    });

    // Import mappings from uploaded TSV
    // Any column that isn't a system field (source_name, rule_name, input_value, record_count, sample)
    // is treated as an output key. sample is discarded wherever it appears.
    router.post('/source/:source_name/import-csv', upload.single('file'), async (req, res, next) => {
        const client = await pool.connect();
        try {
            if (!req.file) {
                return res.status(400).json({ error: 'No file uploaded. Send TSV as multipart field named "file".' });
            }

            const records = parse(req.file.buffer, { columns: true, skip_empty_lines: true, trim: true, delimiter: '\t' });

            if (records.length === 0) {
                return res.status(400).json({ error: 'File is empty.' });
            }

            const outputKeys = Object.keys(records[0]).filter(k => !SYSTEM_COLS.has(k));

            const mappings = [];
            for (const row of records) {
                const { source_name, rule_name, input_value } = row;

                const output = {};
                for (const key of outputKeys) {
                    if (row[key] && row[key].trim() !== '') output[key] = row[key].trim();
                }
                if (Object.keys(output).length === 0) continue;

                let parsedInput;
                try { parsedInput = JSON.parse(input_value); } catch { parsedInput = input_value; }

                mappings.push({ source_name, rule_name, input_value: parsedInput, output });
            }

            if (mappings.length === 0) {
                return res.status(400).json({ error: 'No rows with output values filled in.' });
            }

            await client.query('BEGIN');
            const results = [];
            for (const { source_name, rule_name, input_value, output } of mappings) {
                const result = await client.query(
                    `INSERT INTO mappings (source_name, rule_name, input_value, output)
                     VALUES ($1, $2, $3, $4)
                     ON CONFLICT (source_name, rule_name, input_value)
                     DO UPDATE SET output = EXCLUDED.output
                     RETURNING *`,
                    [source_name, rule_name, JSON.stringify(input_value), JSON.stringify(output)]
                );
                results.push(result.rows[0]);
            }
            await client.query('COMMIT');

            res.status(201).json({ count: results.length, mappings: results });
        } catch (err) {
            await client.query('ROLLBACK');
            next(err);
        } finally {
            client.release();
        }
    });

    // Get single mapping
    router.get('/:id', async (req, res, next) => {
        try {
            const result = await pool.query(
                'SELECT * FROM mappings WHERE id = $1',
                [req.params.id]
            );

            if (result.rows.length === 0) {
                return res.status(404).json({ error: 'Mapping not found' });
            }

            res.json(result.rows[0]);
        } catch (err) {
            next(err);
        }
    });

    // Create mapping
    router.post('/', async (req, res, next) => {
        try {
            const { source_name, rule_name, input_value, output } = req.body;

            if (!source_name || !rule_name || !input_value || !output) {
                return res.status(400).json({
                    error: 'Missing required fields: source_name, rule_name, input_value, output'
                });
            }

            const result = await pool.query(
                `INSERT INTO mappings (source_name, rule_name, input_value, output)
                 VALUES ($1, $2, $3, $4)
                 RETURNING *`,
                [source_name, rule_name, JSON.stringify(input_value), JSON.stringify(output)]
            );

            res.status(201).json(result.rows[0]);
        } catch (err) {
            if (err.code === '23505') {  // Unique violation
                return res.status(409).json({ error: 'Mapping already exists' });
            }
            if (err.code === '23503') {  // Foreign key violation
                return res.status(404).json({ error: 'Source or rule not found' });
            }
            next(err);
        }
    });

    // Bulk create mappings
    router.post('/bulk', async (req, res, next) => {
        const client = await pool.connect();
        try {
            const { mappings } = req.body;

            if (!Array.isArray(mappings)) {
                return res.status(400).json({ error: 'Expected array of mappings' });
            }

            await client.query('BEGIN');

            const results = [];
            for (const mapping of mappings) {
                const { source_name, rule_name, input_value, output } = mapping;

                const result = await client.query(
                    `INSERT INTO mappings (source_name, rule_name, input_value, output)
                     VALUES ($1, $2, $3, $4)
                     ON CONFLICT (source_name, rule_name, input_value)
                     DO UPDATE SET output = EXCLUDED.output
                     RETURNING *`,
                    [source_name, rule_name, JSON.stringify(input_value), JSON.stringify(output)]
                );

                results.push(result.rows[0]);
            }

            await client.query('COMMIT');
            res.status(201).json({ count: results.length, mappings: results });
        } catch (err) {
            await client.query('ROLLBACK');
            next(err);
        } finally {
            client.release();
        }
    });

    // Update mapping
    router.put('/:id', async (req, res, next) => {
        try {
            const { input_value, output } = req.body;

            const result = await pool.query(
                `UPDATE mappings
                 SET input_value = COALESCE($2, input_value),
                     output = COALESCE($3, output)
                 WHERE id = $1
                 RETURNING *`,
                [req.params.id, input_value, output ? JSON.stringify(output) : null]
            );

            if (result.rows.length === 0) {
                return res.status(404).json({ error: 'Mapping not found' });
            }

            res.json(result.rows[0]);
        } catch (err) {
            next(err);
        }
    });

    // Delete mapping
    router.delete('/:id', async (req, res, next) => {
        try {
            const result = await pool.query(
                'DELETE FROM mappings WHERE id = $1 RETURNING id',
                [req.params.id]
            );

            if (result.rows.length === 0) {
                return res.status(404).json({ error: 'Mapping not found' });
            }

            res.json({ success: true, deleted: result.rows[0].id });
        } catch (err) {
            next(err);
        }
    });

    return router;
};