;;;; -*- Mode: LISP; Syntax: ANSI-Common-Lisp; Base: 10 -*-
;;;; *************************************************************************
;;;;
;;;; $Id$
;;;;
;;;; CLSQL square bracket symbolic query syntax. Functions for
;;;; enabling and disabling the syntax and for building SQL
;;;; expressions using the syntax.
;;;;
;;;; This file is part of CLSQL.
;;;;
;;;; CLSQL users are granted the rights to distribute and use this software
;;;; as governed by the terms of the Lisp Lesser GNU Public License
;;;; (http://opensource.franz.com/preamble.html), also known as the LLGPL.
;;;; *************************************************************************

(in-package #:clsql-sys)

(defvar *original-reader-enter* nil)

(defvar *original-reader-exit* nil)

(defvar *sql-macro-open-char* #\[)

(defvar *sql-macro-close-char* #\])

(defvar *restore-sql-reader-syntax* nil)


;; Exported functions for disabling SQL syntax.

(defmacro disable-sql-reader-syntax ()
  "Turns off the SQL reader syntax setting the syntax state such
that if the syntax is subsequently enabled,
RESTORE-SQL-READER-SYNTAX-STATE will disable it again."
  '(eval-when (:compile-toplevel :load-toplevel :execute)
    (setf *restore-sql-reader-syntax* nil)
    (%disable-sql-reader-syntax)))

(defmacro locally-disable-sql-reader-syntax ()
  "Turns off the SQL reader syntax without changing the syntax
state such that RESTORE-SQL-READER-SYNTAX-STATE will re-establish
the current syntax state."
  '(eval-when (:compile-toplevel :load-toplevel :execute)
    (%disable-sql-reader-syntax)))

(defun %disable-sql-reader-syntax ()
  (when *original-reader-enter*
    (set-macro-character *sql-macro-open-char* *original-reader-enter*))
  (setf *original-reader-enter* nil)
  (values))


;; Exported functions for enabling SQL syntax.

(defmacro enable-sql-reader-syntax ()
  "Turns on the SQL reader syntax setting the syntax state such
that if the syntax is subsequently disabled,
RESTORE-SQL-READER-SYNTAX-STATE will enable it again."
  '(eval-when (:compile-toplevel :load-toplevel :execute)
    (setf *restore-sql-reader-syntax* t)
    (%enable-sql-reader-syntax)))

(defmacro locally-enable-sql-reader-syntax ()
  "Turns on the SQL reader syntax without changing the syntax
state such that RESTORE-SQL-READER-SYNTAX-STATE will re-establish
the current syntax state."
  '(eval-when (:compile-toplevel :load-toplevel :execute)
    (%enable-sql-reader-syntax)))

(defun %enable-sql-reader-syntax ()
  (unless *original-reader-enter*
    (setf *original-reader-enter* (get-macro-character *sql-macro-open-char*)))
  (set-macro-character *sql-macro-open-char* #'sql-reader-open)
  (enable-sql-close-syntax)
  (values))

(defmacro restore-sql-reader-syntax-state ()
  "Enables the SQL reader syntax if ENABLE-SQL-READER-SYNTAX has
been called more recently than DISABLE-SQL-READER-SYNTAX and
otherwise disables the SQL reader syntax. By default, the SQL
reader syntax is disabled."
  '(eval-when (:compile-toplevel :load-toplevel :execute)
    (if *restore-sql-reader-syntax*
        (%enable-sql-reader-syntax)
        (%disable-sql-reader-syntax))))

(defun sql-reader-open (stream char)
  (declare (ignore char))
  (let ((sqllist (read-delimited-list #\] stream t)))
    (cond ((string= (write-to-string (car sqllist)) "||")
           (cons (sql-operator 'concat-op) (cdr sqllist)))
          ((and (= (length sqllist) 1) (eql (car sqllist) '*))
           (apply #'generate-sql-reference sqllist))
          ((sql-operator (car sqllist))
           (cons (sql-operator (car sqllist)) (cdr sqllist)))
          (t (apply #'generate-sql-reference sqllist)))))

(defun disable-sql-close-syntax ()
  "Internal function that disables the close syntax when leaving
  sql context."
  (set-macro-character *sql-macro-close-char* *original-reader-exit*)
  (setf *original-reader-exit* nil))

(defun enable-sql-close-syntax ()
  "Internal function that enables close syntax when entering SQL
  context."
  (setf *original-reader-exit* (get-macro-character *sql-macro-close-char*))
  (set-macro-character *sql-macro-close-char* (get-macro-character #\))))

(defun generate-sql-reference (&rest arglist)
  (cond ((= (length arglist) 1)	; string, table or attribute
	 (if (stringp (car arglist))
	     (sql-expression :string (car arglist))
             (sql-expression :attribute (car arglist))))
	((<= 2 (length arglist))
	 (let ((sqltype (when (keywordp (caddr arglist)) (caddr arglist) nil)))
           (cond
             ((stringp (cadr arglist))
	     (sql-expression :table (car arglist)
			     :alias (cadr arglist)
			     :type sqltype))
	    ((keywordp (cadr arglist))
	     (sql-expression :attribute (car arglist)
			     :type (cadr arglist)))
	    (t
	     (sql-expression :attribute (cadr arglist)
			     :table (car arglist)
			     :type sqltype)))))
	(t
	 (error 'sql-user-error :message "bad expression syntax"))))


;; Exported functions for dealing with SQL syntax 

(defun sql (&rest args)
  "Returns an SQL string generated from the expressions ARGS. The
expressions are translated into SQL strings and then concatenated
with a single space delimiting each expression. An error of type
SQL-USER-ERROR is signalled if any element in ARGS is not of the
supported types (a symbol, string, number or symbolic SQL
expression) or a list or vector containing only these supported
types."
  (format nil "~{~A~^ ~}" (mapcar #'sql-output args)))

(defun sql-expression (&key string table alias attribute type)
  "Returns an SQL expression constructed from the supplied
arguments which may be combined as follows: ATTRIBUTE and TYPE;
ATTRIBUTE; ALIAS or TABLE and ATTRIBUTE and TYPE; ALIAS or TABLE
and ATTRIBUTE; TABLE, ATTRIBUTE and TYPE; TABLE and ATTRIBUTE;
TABLE and ALIAS; TABLE; and STRING. An error of type
SQL-USER-ERROR is signalled if an unsupported combination of
keyword arguments is specified."
  (cond
    (string
     (make-instance 'sql :string string))
    (attribute
     (make-instance 'sql-ident-attribute  :name attribute
                    :qualifier (or table alias)
                    :type type))
    ((and table (not attribute))
     (make-instance 'sql-ident-table :name table
                    :table-alias alias))))

(defun sql-operator (operator)
  "Returns the Lisp symbol corresponding to the SQL operator
  represented by the symbol OPERATOR. If OPERATOR does not
  represent a supported SQL operator or is not a symbol, nil is
  returned."
  (typecase operator
    (string nil)
    (symbol (values (gethash (symbol-name-default-case (symbol-name operator))
                             *sql-op-table*)))))

(defun sql-operation (operator &rest args)
  "Returns an SQL expression constructed from the supplied symbol
OPERATOR representing an SQL operator or function and its
arguments ARGS. An error of type SQL-USER-ERROR is signalled if
OPERATOR is not a symbol representing a supported SQL
operator. If OPERATOR is passed the symbol FUNCTION then the
first value in ARGS must be a string representing a valid SQL
function and the remaining values in ARGS its arguments as
strings."
  (if (sql-operator operator)
      (apply (symbol-function (sql-operator operator)) args)
      (error 'sql-user-error 
             :message 
             (format nil "~A is not a recognized SQL operator." operator))))