Add basic filter

source/scripts/services/filter.js.coffee

@@ -0,0 +1,46 @@
+angular.module("sideBySide").service "filter", ['poems', (poems) ->
+	headers = []
+
+	@update = () ->
+		extractHeaders(poems.all)
+
+	@getFilter = () ->
+		for header in headers
+			activeHeaderValues = _.uniq(poems.getActive().map((item) ->
+				item.meta[header]
+			))
+			if (activeHeaderValues.length > 1)
+				continue # header value differs
+
+			inactiveMatching = poems.getInactive().filter((item) ->
+				item.meta[header] == activeHeaderValues[0]
+			)
+			if (inactiveMatching.length > 0)
+				continue # inactive poems have same header value
+
+			ret = {}
+			ret[header] = activeHeaderValues
+			return ret
+
+	extractHeaders = (all) ->
+		fieldLengths = all
+			.map (poem) ->
+				poem.meta
+			.reduce((fields, meta) ->
+				for key, val of meta
+					if typeof val == 'string'
+						if key not of fields
+							fields[key] = 0
+						fields[key] += val.length
+				fields
+			, {})
+
+		headers = _
+			.sortBy((
+				{ 'key': k, 'len': l } for k,l of fieldLengths
+			), 'len')
+			.map (item) ->
+				item.key
+
+	@
+]