/**
 * Execute a JSON-based query using Knex
 *
 * Supported ops:
 * SELECT | INSERT | UPDATE | DELETE
 */
export default function executeJsonQuery(knex, query) {
  const {
    op,
    table,
    columns,
    values,
    where,
    orderBy,
    limit,
    offset
  } = query;

  if (!op || !table) {
    throw new Error('JSON query must include "op" and "table"');
  }

  let qb;

  switch (op) {

    // ----------------------------------
    // SELECT
    // ----------------------------------
    case 'SELECT': {
      qb = knex(table);

      if (Array.isArray(columns) && columns.length > 0) {
        qb.select(columns);
      } else {
        qb.select('*');
      }

      if (where && typeof where === 'object') {
        qb.where(where);
      }

      if (Array.isArray(orderBy)) {
        for (const { column, direction } of orderBy) {
          qb.orderBy(column, direction || 'asc');
        }
      }

      if (Number.isInteger(limit)) {
        qb.limit(limit);
      }

      if (Number.isInteger(offset)) {
        qb.offset(offset);
      }

      return qb;
    }

    // ----------------------------------
    // INSERT
    // ----------------------------------
    case 'INSERT': {
      if (!values || typeof values !== 'object') {
        throw new Error('INSERT requires "values"');
      }

      return knex(table)
        .insert(values)
        .returning(columns || '*');
    }

    // ----------------------------------
    // UPDATE
    // ----------------------------------
    case 'UPDATE': {
      if (!values || typeof values !== 'object') {
        throw new Error('UPDATE requires "values"');
      }

      if (!where || typeof where !== 'object') {
        throw new Error('UPDATE without WHERE is not allowed');
      }

      return knex(table)
        .where(where)
        .update(values)
        .returning(columns || '*');
    }

    // ----------------------------------
    // DELETE
    // ----------------------------------
    case 'DELETE': {
      if (!where || typeof where !== 'object') {
        throw new Error('DELETE without WHERE is not allowed');
      }

      return knex(table)
        .where(where)
        .del();
    }

    default:
      throw new Error(`Unsupported JSON op: ${op}`);
  }
}