implementation module htmlRefFormlib

// Reference types that allow destructive sharing of model data types.
// These can be guarded by consistency checking functions.
// In addition, it handles version management of the shared data.
// (c) MJP 2006

import StdList, StdString
import htmlExceptions, htmlFormlib

:: Ref2 a					= Ref2 String

instance					== (Ref2 a) where (==) (Ref2 file1) (Ref2 file2) = file1 == file2


invokeRefEditor :: !((InIDataId b) *HSt -> (Form d,*HSt)) !(InIDataId b) !*HSt -> (!Form b,!*HSt)
invokeRefEditor editor (init,formid) hst
# (idata,hst)				= editor (init,formid) hst
= ({idata & value = formid.ival},hst)

//	iData for destructively shared model data:

universalRefEditor :: !Lifespan !(InIDataId (Ref2 a)) !(a -> Judgement) !*HSt -> (!Form a,!*HSt) | iData a
universalRefEditor lifespan (init,formid=:{ival=Ref2 filename}) invariant hst
| filename == ""			= mkEditForm (Init,xtFormId "ure_TEMP" createDefault) hst
# (dbf,hst)					= myDatabase Init filename (0,createDefault) hst				// create / read out current value in file file
# (dbversion,dbvalue)		= dbf.value														// version number and value stored in database
# (versionf,hst)			= myVersion Init filename dbversion hst 						// create / read out version number expected by this application
# version					= versionf.value												// current version number assumed in this application
| init == Init && isMember formid.mode [Display,NoForm]										// we only want to read, no version conflict
	= myEditor Init filename dbvalue hst													// synchronize with latest value 
| dbversion > version																		// we have a version conflict and want to write
	# (_,hst)				= ExceptionStore ((+) (Just (filename, "Ref Your screen data is out of date; I have retrieved the latest data."))) hst
																							// Raise exception
	# (_,hst)				= myVersion Set filename dbversion hst							// synchronize with new version
	= myEditor Set filename dbvalue hst														// return current version stored in database 
# (valuef,hst)				= myEditor Init filename dbvalue hst							// editor is in sync; create / read out current value 
# exception					= invariant valuef.value										// check invariants															// check invariants
| isJust exception																			// we want to write, but invariants don't hold
	# (_,hst)				= ExceptionStore ((+) exception) hst 							// report them 
	= (valuef,hst)																			// return wrong value such that it can be improved
# (versionf,hst)			= myVersion  Set filename (dbversion + 1) hst					// increment version number
# (_,hst)					= myDatabase Set filename (dbversion + 1,valuef.value) hst		// update database file
= ({valuef & changed = True},hst)
where
	myDatabase init filename cntvalue hst													// write the database
							= mkEditForm (init, if (lifespan == TxtFile) xpFormId xdbFormId filename cntvalue) hst
	myVersion  init filename cnt hst														// track version number
							= mkEditForm (init,reuseFormId formid cnt <@ ("vrs_r_" +++ filename) <@ NoForm) hst
	myEditor   init filename value hst														// copy of database information
							= mkShowHideForm (init,reuseFormId formid value <@ "copy_r_" +++ filename) hst