Move filter method to entity stream

index.js

@@ -1,12 +1,11 @@
 const program = require('./lib/program')()
 const entityReader = require('./lib/entity_reader')
 const entityWriter = require('./lib/entity_writer')
-const filter = require('./lib/filter')
 const wikidataFilter = require('./lib/wikidata_filter')(program)
 const handleErrors = require('./lib/handle_errors')
 
 entityReader(process.stdin)
-.pipe(filter(wikidataFilter))
-.pipe(filter(entityWriter))
+.filter(wikidataFilter)
+.filter(entityWriter)
 .pipe(process.stdout)
 .on('error', handleErrors)

lib/entity_reader.js

@@ -3,9 +3,17 @@ const filter = require('./filter')
 const parseLine = require('./parse_line')
 
 module.exports = function (stream) {
-  return stream.pipe(split()).pipe(filter((line) => {
+  const reader = stream.pipe(split()).pipe(filter((line) => {
     const entity = parseLine(line)
     if (!entity) return null
     return entity
   }))
+  return withFilterMethod(reader)
+}
+
+function withFilterMethod (stream) {
+  stream.filter = function (test) {
+    return withFilterMethod(this.pipe(filter(test)))
+  }
+  return stream
 }