<?php
// $Id$

/**
 * @file
 * Visits an AST and inserts every identifier into the terms array.
 * The key will be the term, the value how many time it occurs in the AST of the query.
 */

class TqlMySqlGenerator extends TqlASTVisitor {
  public $nonExistentTags = array();

  private $terms = array();

  private $termTableName = "";

  private $tableNumber = 0;

  function generate($tqlAST, $terms, $termTableName) {
    $this->terms = $terms;
    $this->termTableName = $termTableName;
    $result = $tqlAST->accept ($this);
    if ($result) {
      return "SELECT * FROM {". $result ."} AS finalTable";
    }
    else {
      return NULL;
    }
  }

/*
 * Visitor functions
 */


  function visitIdentifier($tqlIdentifier) {
    $termIds = $this->terms[$tqlIdentifier->value];
    // in case the term has not been found it was set to 'NULL' by the 'TqlNameToTid' visitor.
    if (is_NULL($termIds)) {
      // term is not in vocabulary
      return NULL;
    }
    else {
      $termList = implode(',', $termIds);
      return "(SELECT DISTINCT nid FROM `$this->termTableName` WHERE tid in ($termList))";
    }
  }

  function visitUnaryOperation($tqlUnaryOperation) {
    // switch to operation visitor
    return $tqlUnaryOperation->acceptOperation($this);
  }

  function visitBinaryOperation($tqlBinaryOperation) {
    // switch to operation visitor
    return $tqlBinaryOperation->acceptOperation($this);
  }

  function visitNot($tqlNot) {
    $operand = $tqlNot->operand->accept($this);

    if (is_NULL($operand)) {
      // in this case we return the whole universe... :-)
      return "(SELECT DISTINCT nid FROM `$this->termTableName`)";
    }
    else {
      return "(SELECT DISTINCT nid FROM `$this->termTableName` WHERE nid not in $operand)";
    }
  }

  function visitAnd($tqlAnd) {
    $left = $tqlAnd->left->accept($this);
    $right = $tqlAnd->right->accept($this);

    // in this case it's impossible to have any result!
    if (is_NULL($left) || is_NULL($right)) {
      return NULL;
    }

    //Original SQL: return "($left INTERSECT DISTINCT $right)";
    $this->tableNumber++;
    return "(SELECT DISTINCT left$this->tableNumber.nid FROM $left AS left$this->tableNumber, $right AS right$this->tableNumber WHERE left$this->tableNumber.nid  = right$this->tableNumber.nid)";
  }

  function visitOr($tqlOr) {
    $left = $tqlOr->left->accept($this);
    $right = $tqlOr->right->accept($this);

    // in this case it's impossible to have any result!
    if (is_NULL($left)) {
      return $right; // might be NULL as well!
    }
    elseif (is_NULL($right)) {
      return $left; // might be NULL as well!
    }
    else {
      //Original SQL: return "($left UNION DISTINCT $right)";
      $this->tableNumber++;
      return "(SELECT * FROM $left AS left$this->tableNumber UNION SELECT * FROM $right AS right$this->tableNumber)";
    }
  }

  function visitXor($tqlXor) {
    $left = $tqlXor->left->accept($this);
    $right = $tqlXor->right->accept($this);

    if (is_NULL($left)) {
      return $right; // might be NULL as well!
    }
    elseif (is_NULL($right)) {
      return $left; // might be NULL as well!
    }
    else {
      //Original SQL: return "(($left EXCEPT DISTINCT $right) UNION ($right EXCEPT $left))";
      $this->tableNumber++;
      return "(SELECT * FROM (SELECT DISTINCT leftXor1.nid FROM (SELECT DISTINCT nid FROM `term_node` WHERE nid not in $left) AS leftXor1, $right AS rightXor1 WHERE leftXor1.nid  = rightXor1.nid) AS leftXor3 UNION SELECT * FROM (SELECT DISTINCT leftXor2.nid FROM (SELECT DISTINCT nid FROM `term_node` WHERE nid not in $right) AS leftXor2, $left AS rightXor2 WHERE leftXor2.nid  = rightXor2.nid) AS rightXor3)";
    }

  }
}