// Copyright IBM Corp. 2015,2016. All Rights Reserved.
  // Node module: loopback-connector
  // This file is licensed under the MIT License.
  // License text available at https://opensource.org/licenses/MIT
  
  var assert = require('assert');
  var PLACEHOLDER = '?';
  
  module.exports = ParameterizedSQL;
  
  /**
   * A class for parameterized SQL clauses
   * @param {String|Object} sql The SQL clause. If the value is a string, treat
   * it as the template using `?` as the placeholder, for example, `(?,?)`. If
   * the value is an object, treat it as {sql: '...', params: [...]}
   * @param {*[]} params An array of parameter values. The length should match the
   * number of placeholders in the template
   * @returns {ParameterizedSQL} A new instance of ParameterizedSQL
   * @constructor
   */
  function ParameterizedSQL(sql, params) {
    if (!(this instanceof ParameterizedSQL)) {
      return new ParameterizedSQL(sql, params);
    }
    sql = sql || '';
    if (arguments.length === 1 && typeof sql === 'object') {
      this.sql = sql.sql;
      this.params = sql.params || [];
    } else {
      this.sql = sql;
      this.params = params || [];
    }
    assert(typeof this.sql === 'string', 'sql must be a string');
    assert(Array.isArray(this.params), 'params must be an array');
  
    var parts = this.sql.split(PLACEHOLDER);
    assert(parts.length - 1 === this.params.length,
      'The number of ? (' + (parts.length - 1) +
      ') in the sql (' + this.sql + ') must match the number of params (' +
      this.params.length +
      ') ' + this.params);
  }
  
  /**
   * Merge the parameterized sqls into the current instance
   * @param {Object|Object[]} ps A parametered SQL or an array of parameterized
   * SQLs
   * @param {String} [separator] Separator, default to ` `
   * @returns {ParameterizedSQL} The current instance
   */
  ParameterizedSQL.prototype.merge = function(ps, separator) {
    if (Array.isArray(ps)) {
      return this.constructor.append(this,
        this.constructor.join(ps, separator), separator);
    } else {
      return this.constructor.append(this, ps, separator);
    }
  };
  
  ParameterizedSQL.prototype.toJSON = function() {
    return {
      sql: this.sql,
      params: this.params,
    };
  };
  
  /**
   * Append the statement into the current statement
   * @param {Object} currentStmt The current SQL statement
   * @param {Object} stmt The statement to be appended
   * @param {String} [separator] Separator, default to ` `
   * @returns {*} The merged statement
   */
  ParameterizedSQL.append = function(currentStmt, stmt, separator) {
    currentStmt = (currentStmt instanceof ParameterizedSQL) ?
      currentStmt : new ParameterizedSQL(currentStmt);
    stmt = (stmt instanceof ParameterizedSQL) ? stmt :
      new ParameterizedSQL(stmt);
    separator = typeof separator === 'string' ? separator : ' ';
    if (currentStmt.sql) {
      currentStmt.sql += separator;
    }
    if (stmt.sql) {
      currentStmt.sql += stmt.sql;
    }
    currentStmt.params = currentStmt.params.concat(stmt.params);
    return currentStmt;
  };
  
  /**
   * Join multiple parameterized SQLs into one
   * @param {Object[]} sqls An array of parameterized SQLs
   * @param {String} [separator] Separator, default to ` `
   * @returns {ParameterizedSQL}
   */
  ParameterizedSQL.join = function(sqls, separator) {
    assert(Array.isArray(sqls), 'sqls must be an array');
    var ps = new ParameterizedSQL('', []);
    for (var i = 0, n = sqls.length; i < n; i++) {
      this.append(ps, sqls[i], separator);
    }
    return ps;
  };
  
  ParameterizedSQL.PLACEHOLDER = PLACEHOLDER;