<?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.
 *
 * THIS CODE WAS ACTUALLY NEVER TESTED
 * TAKE IT AS A STARTING POINT AND HAVE A LOOK AT THE GENERATOR FOR MYSQL
 */

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

  private $terms = array();

  private $termTableName = "";

  function generate($tqlAST, $terms, $termTableName) {
    $this->terms = $terms;
    $this->termTableName = $termTableName;
    return $tqlAST->accept ($this);
  }

  /*
   * Visitor functions
   */

  function visitIdentifier($tqlIdentifier) {
    $termId = $this->terms[$tqlIdentifier->value];
    if ($termId == -1) {
      // term is not in vocabulary
      return NULL;
    }
    else {
      return "(SELECT DISTINCT nid FROM `$this->termTableName` WHERE tid=$termId)";
    }
  }

  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 ($operand == NULL) {
      // in this case we return the whole universe... :-)
      return "(SELECT DISTINCT nid FROM `$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 ($left == NULL || $right == NULL) {
      return NULL;
    }

    return "($left INTERSECT DISTINCT $right)";
  }

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

    // in this case it's impossible to have any result!
    if ($left == NULL) {
      return $right; // might be NULL as well!
    }
    elseif ($right == NULL) {
      return $left; // might be NULL as well!
    }
    else {
      return "($left UNION DISTINCT $right)";
    }
  }

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

    if ($left == NULL) {
      return $right; // might be NULL as well!
    }
    elseif ($right == NULL) {
      return $left; // might be NULL as well!
    }
    else {
      return "(($left EXCEPT DISTINCT $right) UNION ($right EXCEPT $left))";
    }
  }
}