class Merge

class Merge extends Query implements ConditionInterface {
    use QueryConditionTrait;
    
    /**
     * Returned by execute() if an INSERT query has been executed.
     */
    const STATUS_INSERT = 1;
    
    /**
     * Returned by execute() if an UPDATE query has been executed.
     */
    const STATUS_UPDATE = 2;
    
    /**
     * The table to be used for INSERT and UPDATE.
     *
     * @var string
     */
    protected $table;
    
    /**
     * The table or subquery to be used for the condition.
     *
     * @var string
     */
    protected $conditionTable;
    
    /**
     * An array of fields on which to insert.
     *
     * @var array
     */
    protected $insertFields = [];
    
    /**
     * An array of fields which should be set to their database-defined defaults.
     *
     * Used on INSERT.
     *
     * @var array
     */
    protected $defaultFields = [];
    
    /**
     * An array of values to be inserted.
     *
     * @var string
     */
    protected $insertValues = [];
    
    /**
     * An array of fields that will be updated.
     *
     * @var array
     */
    protected $updateFields = [];
    
    /**
     * Array of fields to update to an expression in case of a duplicate record.
     *
     * This variable is a nested array in the following format:
     * @code
     * <some field> => [
     *  'condition' => <condition to execute, as a string>,
     *  'arguments' => <array of arguments for condition, or NULL for none>,
     * ];
     * @endcode
     *
     * @var array
     */
    protected $expressionFields = [];
    
    /**
     * Flag indicating whether an UPDATE is necessary.
     *
     * @var bool
     */
    protected $needsUpdate = FALSE;
    
    /**
     * Constructs a Merge object.
     *
     * @param \Drupal\Core\Database\Connection $connection
     *   A Connection object.
     * @param string $table
     *   Name of the table to associate with this query.
     * @param array $options
     *   Array of database options.
     */
    public function __construct(Connection $connection, $table, array $options = []) {
        // @todo Remove $options['return'] in Drupal 11.
        // @see https://www.drupal.org/project/drupal/issues/3256524
        $options['return'] = Database::RETURN_AFFECTED;
        parent::__construct($connection, $options);
        $this->table = $table;
        $this->conditionTable = $table;
        $this->condition = $this->connection
            ->condition('AND');
    }
    
    /**
     * Sets the table or subquery to be used for the condition.
     *
     * @param $table
     *   The table name or the subquery to be used. Use a Select query object to
     *   pass in a subquery.
     *
     * @return $this
     *   The called object.
     */
    protected function conditionTable($table) {
        $this->conditionTable = $table;
        return $this;
    }
    
    /**
     * Adds a set of field->value pairs to be updated.
     *
     * @param $fields
     *   An associative array of fields to write into the database. The array keys
     *   are the field names and the values are the values to which to set them.
     *
     * @return $this
     *   The called object.
     */
    public function updateFields(array $fields) {
        $this->updateFields = $fields;
        $this->needsUpdate = TRUE;
        return $this;
    }
    
    /**
     * Specifies fields to be updated as an expression.
     *
     * Expression fields are cases such as counter = counter + 1. This method
     * takes precedence over MergeQuery::updateFields() and its wrappers,
     * MergeQuery::key() and MergeQuery::fields().
     *
     * @param $field
     *   The field to set.
     * @param $expression
     *   The field will be set to the value of this expression. This parameter
     *   may include named placeholders.
     * @param $arguments
     *   If specified, this is an array of key/value pairs for named placeholders
     *   corresponding to the expression.
     *
     * @return $this
     *   The called object.
     */
    public function expression($field, $expression, ?array $arguments = NULL) {
        $this->expressionFields[$field] = [
            'expression' => $expression,
            'arguments' => $arguments,
        ];
        $this->needsUpdate = TRUE;
        return $this;
    }
    
    /**
     * Adds a set of field->value pairs to be inserted.
     *
     * @param $fields
     *   An array of fields on which to insert. This array may be indexed or
     *   associative. If indexed, the array is taken to be the list of fields.
     *   If associative, the keys of the array are taken to be the fields and
     *   the values are taken to be corresponding values to insert. If a
     *   $values argument is provided, $fields must be indexed.
     * @param $values
     *   An array of fields to insert into the database. The values must be
     *   specified in the same order as the $fields array.
     *
     * @return $this
     *   The called object.
     */
    public function insertFields(array $fields, array $values = []) {
        if ($values) {
            $fields = array_combine($fields, $values);
        }
        $this->insertFields = $fields;
        return $this;
    }
    
    /**
     * Specifies fields for which the database-defaults should be used.
     *
     * If you want to force a given field to use the database-defined default,
     * not NULL or undefined, use this method to instruct the database to use
     * default values explicitly. In most cases this will not be necessary
     * unless you are inserting a row that is all default values, as you cannot
     * specify no values in an INSERT query.
     *
     * Specifying a field both in fields() and in useDefaults() is an error
     * and will not execute.
     *
     * @param $fields
     *   An array of values for which to use the default values
     *   specified in the table definition.
     *
     * @return $this
     *   The called object.
     */
    public function useDefaults(array $fields) {
        $this->defaultFields = $fields;
        return $this;
    }
    
    /**
     * Sets common field-value pairs in the INSERT and UPDATE query parts.
     *
     * This method should only be called once. It may be called either
     * with a single associative array or two indexed arrays. If called
     * with an associative array, the keys are taken to be the fields
     * and the values are taken to be the corresponding values to set.
     * If called with two arrays, the first array is taken as the fields
     * and the second array is taken as the corresponding values.
     *
     * @param $fields
     *   An array of fields to insert, or an associative array of fields and
     *   values. The keys of the array are taken to be the fields and the values
     *   are taken to be corresponding values to insert.
     * @param $values
     *   An array of values to set into the database. The values must be
     *   specified in the same order as the $fields array.
     *
     * @return $this
     *   The called object.
     */
    public function fields(array $fields, array $values = []) {
        if ($values) {
            $fields = array_combine($fields, $values);
        }
        foreach ($fields as $key => $value) {
            $this->insertFields[$key] = $value;
            $this->updateFields[$key] = $value;
        }
        $this->needsUpdate = TRUE;
        return $this;
    }
    
    /**
     * Sets the key fields to be used as conditions for this query.
     *
     * This method should only be called once. It may be called either
     * with a single associative array or two indexed arrays. If called
     * with an associative array, the keys are taken to be the fields
     * and the values are taken to be the corresponding values to set.
     * If called with two arrays, the first array is taken as the fields
     * and the second array is taken as the corresponding values.
     *
     * The fields are copied to the condition of the query and the INSERT part.
     * If no other method is called, the UPDATE will become a no-op.
     *
     * @param $fields
     *   An array of fields to set, or an associative array of fields and values.
     * @param $values
     *   An array of values to set into the database. The values must be
     *   specified in the same order as the $fields array.
     *
     * @return $this
     */
    public function keys(array $fields, array $values = []) {
        if ($values) {
            $fields = array_combine($fields, $values);
        }
        foreach ($fields as $key => $value) {
            $this->insertFields[$key] = $value;
            $this->condition($key, $value);
        }
        return $this;
    }
    
    /**
     * Sets a single key field to be used as condition for this query.
     *
     * Same as \Drupal\Core\Database\Query\Merge::keys() but offering a signature
     * that is more natural for the case of a single key.
     *
     * @param string $field
     *   The name of the field to set.
     * @param mixed $value
     *   The value to set into the database.
     *
     * @return $this
     *
     * @see \Drupal\Core\Database\Query\Merge::keys()
     */
    public function key($field, $value = NULL) {
        // @todo D9: Remove this backwards-compatibility shim.
        if (is_array($field)) {
            @trigger_error("Passing an array to the \$field argument of " . __METHOD__ . '() is deprecated in drupal:10.2.0 and is removed from drupal:11.0.0. See https://www.drupal.org/node/2205327', E_USER_DEPRECATED);
            $this->keys($field, $value ?? []);
        }
        else {
            $this->keys([
                $field => $value,
            ]);
        }
        return $this;
    }
    
    /**
     * Implements PHP magic __toString method to convert the query to a string.
     *
     * In the degenerate case, there is no string-able query as this operation
     * is potentially two queries.
     *
     * @return string
     *   The prepared query statement.
     */
    public function __toString() {
    }
    
    /**
     * Executes the merge database query.
     *
     * @return int|null
     *   One of the following values:
     *   - Merge::STATUS_INSERT: If the entry does not already exist,
     *     and an INSERT query is executed.
     *   - Merge::STATUS_UPDATE: If the entry already exists,
     *     and an UPDATE query is executed.
     *
     * @throws \Drupal\Core\Database\Query\InvalidMergeQueryException
     *   When there are no conditions found to merge.
     */
    public function execute() {
        if (!count($this->condition)) {
            throw new InvalidMergeQueryException('Invalid merge query: no conditions');
        }
        $select = $this->connection
            ->select($this->conditionTable)
            ->condition($this->condition);
        $select->addExpression('1');
        if (!$select->execute()
            ->fetchField()) {
            try {
                $insert = $this->connection
                    ->insert($this->table)
                    ->fields($this->insertFields);
                if ($this->defaultFields) {
                    $insert->useDefaults($this->defaultFields);
                }
                $insert->execute();
                return self::STATUS_INSERT;
            } catch (IntegrityConstraintViolationException $e) {
                // The insert query failed, maybe it's because a racing insert query
                // beat us in inserting the same row. Retry the select query, if it
                // returns a row, ignore the error and continue with the update
                // query below.
                if (!$select->execute()
                    ->fetchField()) {
                    throw $e;
                }
            }
        }
        if ($this->needsUpdate) {
            $update = $this->connection
                ->update($this->table)
                ->fields($this->updateFields)
                ->condition($this->condition);
            if ($this->expressionFields) {
                foreach ($this->expressionFields as $field => $data) {
                    $update->expression($field, $data['expression'], $data['arguments']);
                }
            }
            $update->execute();
            return self::STATUS_UPDATE;
        }
        return NULL;
    }

}