const format = require("pg-format");
const XLSX = require('xlsx');

function deduceType(cells) {
    if (!cells || cells.length === 0) return 'text';

    const nonEmptyCells = cells.filter(cell => cell && cell.v != null);
    if (nonEmptyCells.length === 0) return 'text';

    // Check for dates by looking at both cell type and formatted value
    const isDateCell = cell => cell?.t === 'd' || (cell?.t === 'n' && cell.w && /\d{4}-\d{2}-\d{2}|\d{1,2}\/\d{1,2}\/\d{4}|\d{2}-[A-Za-z]{3}-\d{4}|[A-Za-z]{3}-\d{2}|\d{1,2}-[A-Za-z]{3}/.test(cell.w));

    if (nonEmptyCells.some(isDateCell)) { return 'date'; }

    // Check for booleans
    const allBooleans = nonEmptyCells.every(cell => cell.t === 'b');
    if (allBooleans) { return 'boolean'; }

    // Check for numbers
    const allNumbers = nonEmptyCells.every(cell => cell.t === 'n' || (cell.t === 's' && !isNaN(cell.v.replace(/[,$\s%()]/g, ''))));

    if (allNumbers) {
        const numbers = nonEmptyCells.map(cell => {
            if (cell.t === 'n') return cell.v;
            return parseFloat(cell.v.replace(/[,$\s%()]/g, ''));
        });

        const needsPrecision = numbers.some(num => {
            const str = num.toString();
            return str.includes('e') ||
                   (str.includes('.') && str.split('.')[1].length > 6) ||
                   Math.abs(num) > 1e15;
        });

        return needsPrecision ? 'numeric' : 'double precision';
    }
    return 'text'; // default to string type
}

function parseValue(cell, type) {
    if (!cell || cell.v == null) return null;
    
    switch (type) {
        case 'date':
            if (cell.t === 'd') { return cell.v.toISOString().split('T')[0]; }
            if (cell.t === 'n') {
                const date = new Date((cell.v - 25569) * 86400 * 1000);
                return date.toISOString().split('T')[0];
            }
            return null;

        case 'numeric':
        case 'double precision':
            if (cell.t === 'n') return cell.v;
            if (cell.t === 's') {
                const cleaned = cell.v.replace(/[,$\s%()]/g, '');
                if (!isNaN(cleaned)) return parseFloat(cleaned);
            }
            return null;

        case 'boolean':
            return cell.t === 'b' ? cell.v : null;

        default:
            return String(cell.v);
    }
}

/* create table and load data given a worksheet and a PostgreSQL client */
async function sheet_to_pg_table(client, worksheet, tableName) {
    if (!worksheet['!ref']) return;
    
    const range = XLSX.utils.decode_range(worksheet['!ref']);
    
    /* Extract headers from first row, clean names for PostgreSQL */
    const headers = [];
    for (let col = range.s.c; col <= range.e.c; col++) {
        const cellAddress = XLSX.utils.encode_cell({ r: range.s.r, c: col });
        const cell = worksheet[cellAddress];
        const headerValue = cell ? String(cell.v).replace(/[^a-zA-Z0-9_]/g, '_') : `column_${col + 1}`;
        headers.push(headerValue.toLowerCase());
    }

    /* Group cell values by column for type deduction */
    const columnValues = headers.map(() => []);
    for (let row = range.s.r + 1; row <= range.e.r; row++) {
        for (let col = range.s.c; col <= range.e.c; col++) {
            const cellAddress = XLSX.utils.encode_cell({ r: row, c: col });
            const cell = worksheet[cellAddress];
            columnValues[col].push(cell);
        }
    }

    /* Deduce PostgreSQL type for each column */
    const types = {};
    headers.forEach((header, idx) => {
        types[header] = deduceType(columnValues[idx]);
    });

    /* Delete table if it exists in the DB */
    await client.query(format('DROP TABLE IF EXISTS %I', tableName));
    
    /* Create table */
    const createTableSQL = format(
        'CREATE TABLE %I (%s)',
        tableName,
        headers.map(header => format('%I %s', header, types[header])).join(', ')
    );
    await client.query(createTableSQL);

    /* Insert data row by row */
    for (let row = range.s.r + 1; row <= range.e.r; row++) {
        const values = headers.map((header, col) => {
            const cellAddress = XLSX.utils.encode_cell({ r: row, c: col });
            const cell = worksheet[cellAddress];
            return parseValue(cell, types[header]);
        });

        const insertSQL = format(
            'INSERT INTO %I (%s) VALUES (%s)',
            tableName,
            headers.map(h => format('%I', h)).join(', '),
            values.map(() => '%L').join(', ')
        );
        await client.query(format(insertSQL, ...values));
    }
}

module.exports = { sheet_to_pg_table };