Megatest

;;======================================================================
;; Copyright 2017, Matthew Welland.
;; 
;; This file is part of Megatest.
;; 
;;     Megatest is free software: you can redistribute it and/or modify
;;     it under the terms of the GNU General Public License as published by
;;     the Free Software Foundation, either version 3 of the License, or
;;     (at your option) any later version.
;; 
;;     Megatest is distributed in the hope that it will be useful,
;;     but WITHOUT ANY WARRANTY; without even the implied warranty of
;;     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;     GNU General Public License for more details.
;; 
;;     You should have received a copy of the GNU General Public License
;;     along with Megatest.  If not, see <http://www.gnu.org/licenses/>.

;;======================================================================

(declare (unit dbfile))
;; (declare (uses debugprint))
;; (declare (uses commonmod))

(module dbfile
	*
	
(import scheme chicken data-structures extras)
(import (prefix sqlite3 sqlite3:)
	posix typed-records srfi-18
	srfi-69
	stack
	files
	ports

	;; commonmod
	)

;; (import debugprint)

;;======================================================================
;;  R E C O R D S
;;======================================================================

;; a single Megatest area with it's multiple dbs is
;; managed in a dbstruct
;;
(defstruct dbr:dbstruct
  (areapath  #f)
  (homehost  #f)
  (tmppath   #f)
  (read-only #f)
  (subdbs (make-hash-table))
  )

;; NOTE: Need one dbr:subdb per main.db, 1.db ...
;;
(defstruct dbr:subdb
  (dbname      #f) ;; .db/1.db
  (mtdbfile    #f) ;; mtrah/.db/1.db
  (mtdbdat     #f) ;; only need one of these for syncing
  ;; (dbdats      (make-hash-table))  ;; id => dbdat 
  (tmpdbfile   #f) ;; /tmp/.../.db/1.db
  ;; (refndbfile  #f) ;; /tmp/.../.db/1.db_ref
  (dbstack     (make-stack)) ;; stack for tmp dbr:dbdat,
  (homehost    #f) ;; not used yet
  (on-homehost #f) ;; not used yet
  (read-only   #f)
  (last-sync   0)
  (last-write  (current-seconds))
  )                ;; goal is to converge on one struct for an area but for now it is too confusing

;; need to keep dbhandles and cached statements together
(defstruct dbr:dbdat
  (dbfile      #f)
  (dbh         #f)    
  (stmt-cache  (make-hash-table))
  (read-only   #f))

(define *dbstruct-dbs* #f)
(define *db-access-mutex* (make-mutex))
(define *no-sync-db*   #f)

(define (dbfile:run-id->key run-id)
  (or run-id 'main))

(define (db:safely-close-sqlite3-db db stmt-cache #!key (try-num 3))
  (if (<= try-num 0)
      #f
      (handle-exceptions
	  exn
	(begin
	  (print "Attempt to safely close sqlite3 db failed. Trying again. exn=" exn)
	  (thread-sleep! 3)
	  (sqlite3:interrupt! db)
	  (db:safely-close-sqlite3-db db stmt-cache try-num: (- try-num 1)))
	(if (sqlite3:database? db)
	    (let* ((stmts (and stmt-cache (hash-table-ref/default stmt-cache db #f))))
	      (if stmts (map sqlite3:finalize! (hash-table-values stmts)))
	      (sqlite3:finalize! db)
	      #t)
            (begin
             (dbfile:print-err "db:safely-close-sqlite3-db: " db " is not an sqlite3 db")
	     #f
            )
        ))))

;; close all opened run-id dbs
(define (db:close-all dbstruct)
  (if (dbr:dbstruct? dbstruct)
;; (handle-exceptions
;; 	  exn
;; 	  (begin
;; 	    (debug:print 0 *default-log-port* "WARNING: Finalizing failed, "  ((condition-property-accessor 'exn 'message) exn) ", note - exn=" exn)
;; 	    (print-call-chain *default-log-port*))
	;; (db:sync-touched dbstruct 0 force-sync: #t) ;; NO. Do not do this here. Instead we rely on a server to be started when there are writes, even if the server itself is not going to be used as a server.
        (let* ((subdbs     (hash-table-values (dbr:dbstruct-subdbs dbstruct))))
	  (for-each
	   (lambda (subdb)
	     (let* ((tdbs       (stack->list (dbr:subdb-dbstack subdb)))
		    (mtdbdat    (dbr:dbdat-dbh (dbr:subdb-mtdbdat subdb)))
		    #;(rdb        (dbr:dbdat-dbh (dbr:subdb-refndb subdb))))
		    
	       (map (lambda (dbdat)
		      (let* ((stmt-cache (dbr:dbdat-stmt-cache dbdat))
			     (dbh        (dbr:dbdat-dbh        dbdat)))
			(db:safely-close-sqlite3-db dbh stmt-cache)))
		    tdbs)
	       (db:safely-close-sqlite3-db mtdbdat (dbr:dbdat-stmt-cache  (dbr:subdb-mtdbdat subdb))) 
               ;; (if (sqlite3:database? mdb) (sqlite3:finalize! mdb))
	       #;(db:safely-close-sqlite3-db rdb #f))) ;; stmt-cache))))) ;; (if (sqlite3:database? rdb) (sqlite3:finalize! rdb))))))
	   subdbs)
           #t
          )
          #f
  )
)

;; ;; set up a single db (e.g. main.db, 1.db ... etc.)
;; ;;
;; (define (db:setup-db dbstruct areapath run-id)
;;   (let* ((dbname   (db:run-id->dbname run-id))
;; 	 (dbstruct (hash-table-ref/default dbstructs dbname #f)))
;;     (if dbstruct
;; 	dbstruct
;; 	(let* ((dbstruct-new (make-dbr:dbstruct)))
;; 	  (db:open-db dbstruct-new run-id areapath: areapath do-sync: #t)
;; 	  (hash-table-set! dbstructs dbname dbstruct-new)
;; 	  dbstruct-new))))
    
;; ; Returns the dbdat for a particular dbfile inside the area
;; ;;
;; (define (dbr:dbstruct-get-dbdat dbstruct dbfile)
;;   (hash-table-ref/default (dbr:dbstruct-dbdats dbstruct) dbfile #f))
;; 
;; (define (dbr:dbstruct-dbdat-put! dbstruct dbfile db)
;;   (hash-table-set! (dbr:dbstruct-dbdats dbstruct) dbfile db))
;; 
;; (define (db:run-id->first-num run-id)
;;   (let* ((s (number->string run-id))
;; 	 (l (string-length s)))
;;     (substring s (- l 1) l)))

;; 1234 => 4/1234.db
;;   #f => 0/main.db
;;   (abandoned the idea of num/db)
;; 
(define (dbfile:run-id->path apath run-id)
  (conc apath"/"(dbfile:run-id->dbname run-id)))

(define (db:dbname->path apath dbname)
  (conc apath"/"dbname))

(define (dbfile:run-id->dbname run-id)
  (cond
   ((number? run-id) (conc ".db/" (modulo run-id 100) ".db"))
   ((not run-id)     (conc ".db/main.db"))
   (else             run-id)))

;; Make the dbstruct, setup up auxillary db's and call for main db at least once
;;
;; called in http-transport and replicated in rmt.scm for *local* access. 
;;
(define (dbfile:setup do-sync areapath tmppath)
  (cond
   (*dbstruct-dbs* *dbstruct-dbs*);; TODO: when multiple areas are supported, this optimization will be a hazard
   (else ;;(common:on-homehost?)
    (let* ((dbstruct (make-dbr:dbstruct)))
      #;(when (not *toppath*)
        (debug:print-info 0 *default-log-port* "in db:setup, *toppath* not set; calling launch:setup")
        (launch:setup areapath: areapath))
      (set! *dbstruct-dbs* dbstruct)
      (dbr:dbstruct-areapath-set! dbstruct areapath)
      (dbr:dbstruct-tmppath-set!  dbstruct tmppath)
      dbstruct))))

#;(define (dbfile:get-subdb dbstruct run-id)
  (let* ((res (hash-table-ref/default (dbr:dbstruct-subdbs dbstruct) (dbfile:run-id->key run-id) #f)))
    (if res
	res
	(let* ((newsubdb (make-dbr:subdb)))
	  (db:open-db newsubdb run-id areapath: (dbr:dbstruct-areapath dbstruct) do-sync: #t)
	  (hash-table-set! (dbr:dbstruct-subdbs dbstruct) (dbfile:run-id->key run-id) newsubdb)
	  newsubdb))))

(define (dbfile:get-subdb dbstruct run-id)
  (let* ((dbfname (dbfile:run-id->dbname run-id)))
    (hash-table-ref/default (dbr:dbstruct-subdbs dbstruct) dbfname #f)))

(define (dbfile:set-subdb dbstruct run-id subdb)
  (hash-table-set! (dbr:dbstruct-subdbs dbstruct) (dbfile:run-id->dbname run-id) subdb))

;; Get/open a database
;;    if run-id => get run specific db
;;    if #f     => get main db
;;    if run-id is a string treat it as a filename
;;    if db already open - return inmem
;;    if db not open, open inmem, rundb and sync then return inmem
;;    inuse gets set automatically for rundb's
;;
(define (dbfile:get-dbdat dbstruct run-id)
  (let* ((subdb (dbfile:get-subdb dbstruct run-id)))
    (if (stack-empty? (dbr:subdb-dbstack subdb))
	 #f
	(stack-pop! (dbr:subdb-dbstack subdb)))))

;; return a previously opened db handle to the stack of available handles
(define (dbfile:add-dbdat dbstruct run-id dbdat)
  (let* ((subdb (dbfile:get-subdb dbstruct run-id)))
    (stack-push! (dbr:subdb-dbstack subdb) dbdat)))

;; set up a subdb
;;
(define (dbfile:init-subdb dbstruct run-id init-proc)
  (let* ((dbname    (dbfile:run-id->dbname run-id))
	 (areapath  (dbr:dbstruct-areapath dbstruct))
	 (tmppath   (dbr:dbstruct-tmppath  dbstruct))
	 (mtdbpath  (dbfile:run-id->path areapath run-id))
	 (tmpdbpath (dbfile:run-id->path tmppath run-id))
	 (mtdbdat   (dbfile:open-sqlite3-db mtdbpath init-proc))
	 (newsubdb  (make-dbr:subdb dbname:    dbname
				    mtdbfile:  mtdbpath
				    tmpdbfile: tmpdbpath
				    mtdbdat:   mtdbdat)))
    (dbfile:set-subdb dbstruct run-id newsubdb)
    newsubdb)) ;; return the new subdb - but shouldn't really use it

;; returns dbdat with dbh and dbfilepath
;;  1. if needed setup the subdb for the given run-id
;;  2. if there is no existing db handle in the stack
;;     create a new handle and return it (do NOT add
;;     it to the stack).
;;
(define (dbfile:open-db dbstruct run-id init-proc)
  (let* ((subdb (dbfile:get-subdb dbstruct run-id)))
    (if (not subdb) ;; not yet defined
	(begin
	  (dbfile:init-subdb dbstruct run-id init-proc)
	  (dbfile:open-db dbstruct run-id init-proc))
	(let* ((dbdat (dbfile:get-dbdat dbstruct run-id)))
	  (if dbdat
	      dbdat
	      (let* ((tmppath   (dbr:dbstruct-tmppath  dbstruct))
		     (tmpdbpath (dbfile:run-id->path tmppath run-id)))
		(dbfile:open-sqlite3-db tmpdbpath init-proc)))))))

;; COMBINE dbfile:open-sqlite-db and dbfile:lock-create-open
;;

;; Open the classic megatest.db file (defaults to open in toppath)
;;
;;   NOTE: returns a dbdat not a dbstruct!
;;
(define (dbfile:open-sqlite3-db dbpath init-proc)
  (let* ((dbexists     (file-exists? dbpath))
	 (write-access (file-write-access? dbpath))
	 (db           (dbfile:cautious-open-database dbpath init-proc))) #;(sqlite3:open-database dbpath)
    (sqlite3:set-busy-handler! db (sqlite3:make-busy-timeout 10000))
    ;; (init-proc db)
    (make-dbr:dbdat dbfile: dbpath dbh: db read-only: (not write-access))))

(define (dbfile:print-and-exit . params)
  (with-output-to-port
      (current-error-port)
    (lambda ()
      (apply print params)))
  (exit 1))
    
(define (dbfile:print-err . params)
  (with-output-to-port
      (current-error-port)
    (lambda ()
      (apply print params))))
    
;; open an sql database inside a file lock
;; returns: db existed-prior-to-opening
;; RA => Returns a db handler; sets the lock if opened in writable mode
;;
;; (define *db-open-mutex* (make-mutex))
;;
#;(define (dbfile:lock-create-open fname initproc)
  (let* ((parent-dir   (or (pathname-directory fname)(current-directory))) ;; no parent? go local
         (raw-fname    (pathname-file fname))
	 (dir-writable (file-write-access? parent-dir))
	 (file-exists  (file-exists? fname))
	 (file-write   (if file-exists
			   (file-write-access? fname)
			   dir-writable )))
    ;; (mutex-lock! *db-open-mutex*) ;; tried this mutex, not clear it helped.
    (if file-write ;; dir-writable
	(condition-case
         (let* ((lockfname   (conc fname ".lock"))
                (readyfname  (conc parent-dir "/.ready-" raw-fname))
                (readyexists (common:file-exists? readyfname)))
           (if (not readyexists)
               (common:simple-file-lock-and-wait lockfname))
           (let ((db      (sqlite3:open-database fname)))
             (sqlite3:set-busy-handler! db (sqlite3:make-busy-timeout 136000))
             (sqlite3:execute db "PRAGMA synchronous = 0;")
             (if (not file-exists)
                 (initproc db))
             (if (not readyexists)
                 (begin
                   (common:simple-file-release-lock lockfname)
                   (with-output-to-file
                       readyfname
                     (lambda ()
                       (print "Ready at " 
                              (seconds->year-work-week/day-time 
                               (current-seconds)))))))
             db))
         (exn (io-error)  (dbfile:print-and-exit "ERROR: i/o error with " fname ". Check permissions, disk space etc. and try again."))
         (exn (corrupt)   (dbfile:print-and-exit "ERROR: database " fname " is corrupt. Repair it to proceed."))
         (exn (busy)      (dbfile:print-and-exit "ERROR: database " fname " is locked. Try copying to another location, remove original and copy back."))
         (exn (permission)(dbfile:print-and-exit "ERROR: database " fname " has some permissions problem."))
         (exn () (dbfile:print-and-exit "ERROR: Unknown error with database " fname " message: " ((condition-property-accessor 'exn 'message) exn))))
        
	(condition-case
         (begin
           (dbfile:print-err "WARNING: opening db in non-writable dir " fname)
           (let ((db (sqlite3:open-database fname)))
             (sqlite3:set-busy-handler! db (sqlite3:make-busy-timeout 136000))
             (sqlite3:execute db "PRAGMA synchronous = 0;")
	     ;; (mutex-unlock! *db-open-mutex*)
             db))
         (exn (io-error)
	      (dbfile:print-and-exit
	       "ERROR: i/o error with " fname ". Check permissions, disk space etc. and try again."))
         (exn (corrupt)
	      (dbfile:print-and-exit
	       "ERROR: database " fname " is corrupt. Repair it to proceed."))
         (exn (busy)
	      (dbfile:print-and-exit
	       "ERROR: database " fname " is locked. Try copying to another location, remove original and copy back."))
         (exn (permission)
	      (dbfile:print-and-exit
	       "ERROR: database " fname " has some permissions problem."))
         (exn ()
	      (dbfile:print-and-exit
	       "ERROR: Unknown error with database " fname " message: " ((condition-property-accessor 'exn 'message) exn))))
	)))


;; This routine creates the db if not already present. It is only called if the db is not already opened
;;
#;(define (db:init-dbstruct dbstruct run-id init-proc #!key (do-sync #t))
  (let* ((subdb          (dbfile:get-subdb dbstruct run-id))
	 (tmpdb-stack    (dbr:subdb-dbstack subdb)) 
	 (max-stale-tmp  (dbr:dbstruct-max-stale-secs dbstruct));; (configf:lookup-number *configdat* "server" "filling-db-max-stale-seconds" default: 10))
	   (dbpath       (dbr:dbstruct-tmppath dbstruct)) ;;  (db:dbfile-path))      ;; path to tmp db area
	   (dbname       (dbfile:run-id->dbname run-id))
	   (dbexists     (file-exists? dbpath))
	   (areapath     (dbr:dbstruct-areapath dbstruct))
	   (mtdbfname    (conc areapath "/"dbname))
	   (mtdbexists   (file-exists? mtdbfname))
	   (mtdbmodtime  (if mtdbexists (dbfile:lazy-sqlite-db-modification-time mtdbfname)  #f))
	   (mtdb         (db:open-sqlite-db mtdbfname init-proc))
	   ;; the reference db for syncing
	   (refdbfname   (conc dbpath "/"dbname"_ref"))
	   (refndb       (db:open-megatest-db refdbfname))
	   ;; (mtdbpath     (dbr:dbdat-dbfile mtdb))
	   ;; the tmpdb
	   (tmpdbfname   (conc dbpath"/"dbname)) ;; /tmp/<stuff>/.db/[main|1,2...].db 
	   (tmpdb        (db:open-megatest-db tmpdbfname)) ;; lock-create-open dbpath db:initialize-main-db))
	   (dbfexists    (common:file-exists? tmpdbfname))  ;; (conc dbpath "/megatest.db")))
	   (tmpdbmodtime (if dbfexists  (common:lazy-sqlite-db-modification-time tmpdbfname) #f))
	   
	   (write-access (file-write-access? mtdbfname))
	   
	   ;; (mtdbmodtime (if mtdbexists
	   ;; (common:lazy-sqlite-db-modification-time mtdbpath)
	   ;; #f)) ; moving this before db:open-megatest-db is
	   ;; called. if wal mode is on -WAL and -shm file get
	   ;; created with causing the tmpdbmodtime timestamp
	   ;; always greater than mtdbmodtime (tmpdbmodtime (if
	   ;; dbfexists (common:lazy-sqlite-db-modification-time
	   ;; tmpdbfname) #f)) if wal mode is on -WAL and -shm
	   ;; file get created when db:open-megatest-db is
	   ;; called. modtimedelta will always be < 10 so db in
	   ;; tmp not get synced (tmpdbmodtime (if dbfexists
	   ;; (db:get-last-update-time (car tmpdb)) #f)) (fmt
	   ;; (file-modification-time tmpdbfname))
	   
	   (modtimedelta (and mtdbmodtime tmpdbmodtime (- mtdbmodtime tmpdbmodtime))))

    (when write-access
      (sqlite3:execute (dbr:dbdat-dbh mtdb) "drop trigger if exists update_tests_trigger")
      (sqlite3:execute (dbr:dbdat-dbh mtdb) "drop trigger if exists update_runs_trigger"))
    
    ;; (print "mtdbmodtime " mtdbmodtime " tmpdbmodtime " tmpdbmodtime " mtdbpath " mtdbpath " " (conc *toppath* "/megatest.db"))
    ;; (debug:print-info 13 *default-log-port* "db:open-db>> mtdbpath="mtdbpath" mtdbexists="mtdbexists" and write-access="write-access)
    (if (and dbexists (not write-access))
	(begin
	  (set! *db-write-access* #f)
	  (dbr:subdb-read-only-set! subdb #t)))
    (dbr:subdb-mtdb-set!   subdb mtdb)
    (dbr:subdb-tmpdb-set!  subdb tmpdb)
    (dbr:subdb-dbstack-set! subdb (make-stack)) ;; BB: why a stack?  Why would the number of db's be indeterminate?  Is this a legacy of 1.db 2.db .. ?
    (stack-push! (dbr:subdb-dbstack subdb) tmpdb) ;; olddb is already a (cons db path)
    (dbr:subdb-refndb-set! subdb refndb)
    (if (and  (or (not dbfexists)
		  (and modtimedelta
		       (> modtimedelta max-stale-tmp))) ;; if db in tmp is over ten seconds older than the file in MTRA then do a sync back
	      do-sync)
	(begin
	  (dbfile:print-err "filling db " (dbr:dbdat-dbfile tmpdb) " with data \n    from " (dbr:dbdat-dbfile mtdb) " mod time delta: " modtimedelta)
	  (db:sync-tables (db:sync-all-tables-list subdb) #f mtdb refndb tmpdb)
	  ;; touch tmp db to avoid wal mode wierdness  
	  (set! (file-modification-time tmpdbfname) (current-seconds))  
	  (dbfile:print-err "INFO: db:sync-all-tables-list done.")
	  )
	(dbfile:print-err " db, " (dbr:dbdat-dbfile tmpdb) " already exists or fresh enough, not propogating data from\n     " (dbr:dbdat-dbfile mtdb) " mod time delta: " modtimedelta) )
    ;; (db:multi-db-sync subdb 'old2new))  ;; migrate data from megatest.db automatically
    tmpdb))
		
;;======================================================================
;; no-sync.db - small bits of data to be shared between servers
;;======================================================================

;; if we are not a server create a db handle. this is not finalized
;; so watch for problems. I'm still not clear if it is needed to manually
;; finalize sqlite3 dbs with the sqlite3 egg.
;;

(define (dbfile:cautious-open-database fname init-proc #!optional (tries-left 10))
  (let* ((lock-file (conc fname".lock"))
	 (retry (lambda ()
		  (thread-sleep! 1.1)
		  (if (> tries-left 0)
		      (dbfile:cautious-open-database fname init-proc (- tries-left 1))))))
    (assert (>= tries-left 0) (conc "FATAL: Five attempts in dbfile:cautious-open-database of "fname", giving up."))
    (if (and (file-write-access? fname) (not (dbfile:simple-file-lock lock-file)))
	(begin
	  (dbfile:print-err "INFO: dbfile:cautious-open-database: lock file " lock-file " exists, trying again in 1 second.")
	  (thread-sleep! 1)
	  (if (eq? tries-left 2)
	      (begin
		(dbfile:print-err "INFO: stealing the lock "lock-file)
		(delete-file lock-file)))
	  (dbfile:cautious-open-database fname init-proc (- tries-left 1)))
	(let* ((db-exists (file-exists? fname))
	       (result (condition-case
			   (let* ((db (sqlite3:open-database fname)))
			     (if (and init-proc (not db-exists))
				 (init-proc db))
			     db)
			(exn (io-error)
			     (dbfile:print-err exn "ERROR: i/o error with " fname ". Check permissions, disk space etc. and try again.")
			     (retry))
			(exn (corrupt)
			     (dbfile:print-err exn "ERROR: database " fname " is corrupt. Repair it to proceed.")
			     (retry))
			(exn (busy)
			     (dbfile:print-err exn "ERROR: database " fname
					       " is locked. Try copying to another location, remove original and copy back.")
			     (retry))
			(exn (permission)(dbfile:print-err exn "ERROR: database " fname " has some permissions problem.")
			     (retry))
			(exn ()
			     (dbfile:print-err exn "ERROR: Unknown error with database " fname " message: "
					       ((condition-property-accessor 'exn 'message) exn))
			     (retry)))))
          (if (file-write-access? fname)
	    (dbfile:simple-file-release-lock lock-file)
          )
	  result))))


(define (dbfile:open-no-sync-db dbpath)
  (if *no-sync-db*
      *no-sync-db*
      (begin
	(if (not (file-exists? dbpath))
	    (create-directory dbpath #t))
	(let* ((dbname    (conc dbpath "/no-sync.db"))
	       (db-exists (file-exists? dbname))
	       (init-proc (lambda (db)
			    (if (not db-exists)
				(begin
				  (sqlite3:execute db "PRAGMA synchronous = 0;")
				  (sqlite3:execute db "CREATE TABLE IF NOT EXISTS no_sync_metadat (var TEXT,val TEXT, CONSTRAINT no_sync_metadat_constraint UNIQUE (var));"))
				)))
	       (db        (dbfile:cautious-open-database dbname init-proc))) ;; (sqlite3:open-database dbname)))
	  (sqlite3:set-busy-handler! db (sqlite3:make-busy-timeout 136000))
	  ;;(sqlite3:execute db "PRAGMA journal_mode=WAL;")
	  (set! *no-sync-db* db)
	  db))))

(define (db:no-sync-set db var val)
  (sqlite3:execute db "INSERT OR REPLACE INTO no_sync_metadat (var,val) VALUES (?,?);" var val))

(define (db:no-sync-del! db var)
  (sqlite3:execute db "DELETE FROM no_sync_metadat WHERE var=?;" var))

(define (db:no-sync-get/default db var default)
  (let ((res default))
    (sqlite3:for-each-row
     (lambda (val)
       (set! res val))
     db
     "SELECT val FROM no_sync_metadat WHERE var=?;"
     var)
    (if res
        (let ((newres (if (string? res)
			  (string->number res)
			  #f)))
          (if newres
              newres
              res))
        res)))

;; transaction protected lock aquisition
;; either:
;;    fails    returns  (#f . lock-creation-time)
;;    succeeds (returns (#t . lock-creation-time)
;; use (db:no-sync-del! db keyname) to release the lock
;;
(define (db:no-sync-get-lock db keyname)
  (sqlite3:with-transaction
   db
   (lambda ()
     (handle-exceptions
	 exn
	 (let ((lock-time (current-seconds)))
	   ;; (debug:print-info 2 *default-log-port* "db:no-sync-get-lock keyname=" keyname ", lock-time=" lock-time ", exn=" exn)
	   (sqlite3:execute db "INSERT INTO no_sync_metadat (var,val) VALUES(?,?);" keyname lock-time)
	   `(#t . ,lock-time))
       `(#f . ,(sqlite3:first-result db "SELECT val FROM no_sync_metadat WHERE var=?;" keyname))))))


;;======================================================================
;; file utils
;;======================================================================

;;======================================================================
;; lazy-safe get file mod time. on any error (file not existing etc.) return 0
;;
(define (dbfile:lazy-modification-time fpath)
  (handle-exceptions
      exn
    (begin
      (dbfile:print-err "Failed to get modification time for " fpath ", treating it as zero. exn=" exn)
      0)
    (if (file-exists? fpath)
	(file-modification-time fpath)
	0)))

;;======================================================================
;; find timestamp of newest file associated with a sqlite db file
(define (dbfile:lazy-sqlite-db-modification-time fpath)
  (let* ((glob-list (handle-exceptions
			exn
		      (begin
			(dbfile:print-err "Failed to glob " fpath "*, exn=" exn)
			`(,(conc "/no/such/file, message: " ((condition-property-accessor 'exn 'message) exn))))
		      (glob (conc fpath "*"))))
         (file-list (if (eq? 0 (length glob-list))
			'("/no/such/file")
			glob-list)))
  (apply max
	 (map
	  dbfile:lazy-modification-time 
	  file-list))))

;; dot-locking egg seems not to work, using this for now
;; if lock is older than expire-time then remove it and try again
;; to get the lock
;;
(define (dbfile:simple-file-lock fname #!key (expire-time 300))
  (let ((fmod-time (handle-exceptions
		       ext
		     (current-seconds)
		     (file-modification-time fname))))
    (if (file-exists? fname)
	(if (> (- (current-seconds) fmod-time) expire-time)
	    (begin
	      (handle-exceptions exn #f (delete-file* fname))	
	      (dbfile:simple-file-lock fname expire-time: expire-time))
	    #f)
	(let ((key-string (conc (get-host-name) "-" (current-process-id)))
	      (oup        (open-output-file fname)))
	  (with-output-to-port
	      oup
	    (lambda ()
	      (print key-string)))
	  (close-output-port oup)
	  #;(with-output-to-file fname ;; bizarre. with-output-to-file does not seem to be cleaning up after itself.
	    (lambda ()
	  (print key-string)))
	  (thread-sleep! 0.25)
	  (if (file-exists? fname)
	      (handle-exceptions exn
                #f 
                (with-input-from-file fname
	  	  (lambda ()
		    (equal? key-string (read-line)))))
	      #f)
       )
    )
  )
)

(define (dbfile:simple-file-lock-and-wait fname #!key (expire-time 300))
  (let ((end-time (+ expire-time (current-seconds))))
    (let loop ((got-lock (dbfile:simple-file-lock fname expire-time: expire-time)))
      (if got-lock
	  #t
	  (if (> end-time (current-seconds))
	      (begin
		(thread-sleep! 3)
		(loop (dbfile:simple-file-lock fname expire-time: expire-time)))
	      #f)))))

(define (dbfile:simple-file-release-lock fname)
  (handle-exceptions
      exn
      #f ;; I don't really care why this failed (at least for now)
    (delete-file* fname)))


)