From 8027144b27a787f9f5e28362de84c0fbdceb76ca Mon Sep 17 00:00:00 2001
From: Dean Jackson <deanishe@deanishe.net>
Date: Sat, 27 Jan 2018 17:52:43 +0100
Subject: [PATCH] Add filter middleware for simpler logic

---
 filter.go      | 36 +++++++++++++++++++++
 filter_test.go | 87 ++++++++++++++++++++++++++++++++++++++++++++++++++
 scan.go        | 24 +++++++-------
 3 files changed, 136 insertions(+), 11 deletions(-)
 create mode 100644 filter.go
 create mode 100644 filter_test.go

diff --git a/filter.go b/filter.go
new file mode 100644
index 0000000..d8b917f
--- /dev/null
+++ b/filter.go
@@ -0,0 +1,36 @@
+//
+// Copyright (c) 2018 Dean Jackson <deanishe@deanishe.net>
+//
+// MIT Licence. See http://opensource.org/licenses/MIT
+//
+// Created on 2018-01-27
+//
+
+package main
+
+// Filterer passes selectively passes through strings
+type Filterer func(in <-chan string) <-chan string
+
+// Filter is a chain of Filterers
+type Filter struct {
+	Funcs []Filterer
+}
+
+// Use adds a Filterer to the stack
+func (f *Filter) Use(fn Filterer) {
+	f.Funcs = append(f.Funcs, fn)
+}
+
+// Apply runs the filter on a channel.
+func (f *Filter) Apply(in <-chan string) <-chan string {
+
+	var out = make(<-chan string)
+
+	// Make stack of handlers
+	out = f.Funcs[len(f.Funcs)-1](in)
+	for i := len(f.Funcs) - 2; i >= 0; i-- {
+		out = f.Funcs[i](out)
+	}
+
+	return out
+}
diff --git a/filter_test.go b/filter_test.go
new file mode 100644
index 0000000..5a64898
--- /dev/null
+++ b/filter_test.go
@@ -0,0 +1,87 @@
+//
+// Copyright (c) 2018 Dean Jackson <deanishe@deanishe.net>
+//
+// MIT Licence. See http://opensource.org/licenses/MIT
+//
+// Created on 2018-01-27
+//
+
+package main
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+func TestFilter(t *testing.T) {
+	data := []struct {
+		in, out []string
+	}{
+		{[]string{""}, []string{}},
+		{[]string{"file", "file.txt"}, []string{"file.txt"}},
+		{[]string{"file.txt", "file.pdf"}, []string{"file.txt", "file.pdf"}},
+		{[]string{"file.mp4", "file.pdf"}, []string{"file.pdf"}},
+	}
+
+	for _, td := range data {
+
+		var in = make(chan string)
+
+		// Generate input
+		go func(c chan string, data []string) {
+
+			for _, s := range data {
+				if s == "" {
+					continue
+				}
+				x := filepath.Ext(s)
+				if x == ".mp4" || x == "" {
+					continue
+				}
+				c <- s
+			}
+			close(in)
+		}(in, td.in)
+
+		f := Filter{}
+		f.Use(func(in <-chan string) <-chan string {
+			var out = make(chan string)
+
+			go func() {
+				defer close(out)
+
+				for s := range in {
+					out <- s
+				}
+
+			}()
+
+			return out
+		})
+
+		out := f.Apply(in)
+		res := []string{}
+		for s := range out {
+			res = append(res, s)
+		}
+
+		if !strSlicesEqual(res, td.out) {
+			t.Errorf("Bad Filter. Expected=%#v, Got=%#v", td.out, res)
+		}
+	}
+
+}
+
+func strSlicesEqual(s1, s2 []string) bool {
+	if len(s1) != len(s2) {
+		return false
+	}
+
+	for i, s := range s1 {
+		if s != s2[i] {
+			return false
+		}
+	}
+
+	return true
+}
diff --git a/scan.go b/scan.go
index 2609825..0ab92db 100644
--- a/scan.go
+++ b/scan.go
@@ -53,6 +53,7 @@ func scan() <-chan Project {
 	var (
 		ins []<-chan string
 		out = make(<-chan Project)
+		f   = &Filter{}
 	)
 
 	for name, scanner := range scanners {
@@ -71,17 +72,12 @@ func scan() <-chan Project {
 	}
 
 	// real programs have middleware
-	out = resultToProject(
-		filterExcludes(
-			filterNotExist(
-				filterDupes(
-					filterNotProject(
-						merge(ins...),
-					),
-				),
-			),
-			conf.Excludes),
-	)
+	f.Use(makeFilterExcludes(conf.Excludes))
+	f.Use(filterNotExist)
+	f.Use(filterDupes)
+	f.Use(filterNotProject)
+
+	out = resultToProject(f.Apply(merge(ins...)))
 
 	return out
 }
@@ -271,6 +267,12 @@ func lineCommand(cmd *exec.Cmd, name string) (chan string, error) {
 	return out, err
 }
 
+func makeFilterExcludes(patterns []string) Filterer {
+	return func(in <-chan string) <-chan string {
+		return filterExcludes(in, patterns)
+	}
+}
+
 // Filter files that match any of the glob patterns.
 func filterExcludes(in <-chan string, patterns []string) <-chan string {
 	var globs []glob.Glob