splice state management into ResourceStateManager

app/coffee/ResourceStateManager.coffee

@@ -0,0 +1,46 @@
+Path = require "path"
+fs = require "fs"
+mkdirp = require "mkdirp"
+logger = require "logger-sharelatex"
+settings = require("settings-sharelatex")
+Errors = require "./Errors"
+
+module.exports = ResourceStateManager =
+
+	# The sync state is an identifier which must match for an
+	# incremental update to be allowed.
+	#
+	# The initial value is passed in and stored on a full
+	# compile.
+	#
+	# Subsequent incremental compiles must come with the same value - if
+	# not they will be rejected with a 409 Conflict response.
+	#
+	# An incremental compile can only update existing files with new
+	# content.  The sync state identifier must change if any docs or
+	# files are moved, added, deleted or renamed.
+
+	SYNC_STATE_FILE: ".project-sync-state"
+
+	saveProjectStateHash: (state, basePath, callback) ->
+		stateFile = Path.join(basePath, @SYNC_STATE_FILE)
+		if not state? # remove the file if no state passed in
+			logger.log state:state, basePath:basePath, "clearing sync state"
+			fs.unlink stateFile, (err) ->
+				if err? and err.code isnt 'ENOENT'
+					return callback(err)
+				else
+					return callback()
+		else
+			logger.log state:state, basePath:basePath, "writing sync state"
+			fs.writeFile stateFile, state, {encoding: 'ascii'}, callback
+
+	checkProjectStateHashMatches: (state, basePath, callback) ->
+		stateFile = Path.join(basePath, @SYNC_STATE_FILE)
+		fs.readFile stateFile, {encoding:'ascii'}, (err, oldState) ->
+			if err? and err.code isnt 'ENOENT'
+				return callback(err)
+			else if state isnt oldState
+				return callback new Errors.FilesOutOfSyncError("invalid state for incremental update")
+			else if state is oldState
+				callback(null)