From cfb4e7e874e16491683b48f5ec7e56093a0680bd Mon Sep 17 00:00:00 2001
From: Martin Polden <mpolden@mpolden.no>
Date: Sat, 11 Sep 2021 14:04:11 +0200
Subject: cmd: Print only unique log lines

---
 cmd/unp/main.go         | 11 +++++++++++
 go.mod                  |  4 ++--
 go.sum                  |  5 ++++-
 logutil/logutil.go      | 40 ++++++++++++++++++++++++++++++++++++++++
 logutil/logutil_test.go | 25 +++++++++++++++++++++++++
 5 files changed, 82 insertions(+), 3 deletions(-)
 create mode 100644 logutil/logutil.go
 create mode 100644 logutil/logutil_test.go

diff --git a/cmd/unp/main.go b/cmd/unp/main.go
index 0b08820..f868a8a 100644
--- a/cmd/unp/main.go
+++ b/cmd/unp/main.go
@@ -3,14 +3,25 @@ package main
 import (
 	"flag"
 	"fmt"
+	"io"
 	"log"
+	"os"
 
+	"github.com/mattn/go-isatty"
+	"github.com/mpolden/unp/logutil"
 	"github.com/mpolden/unp/watcher"
 )
 
 func init() {
+	var out io.Writer
+	if stderr := os.Stderr; isatty.IsTerminal(stderr.Fd()) {
+		out = logutil.NewUniqueWriter(stderr)
+	} else {
+		out = stderr
+	}
 	log.SetPrefix("unp: ")
 	log.SetFlags(0)
+	log.SetOutput(out)
 }
 
 func main() {
diff --git a/go.mod b/go.mod
index 05b96fd..0ba9196 100644
--- a/go.mod
+++ b/go.mod
@@ -3,9 +3,9 @@ module github.com/mpolden/unp
 go 1.17
 
 require (
+	github.com/mattn/go-isatty v0.0.14
 	github.com/mpolden/sfv v0.9.0
 	github.com/nwaples/rardecode v1.1.0
 	github.com/rjeczalik/notify v0.9.2
+	golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c // indirect
 )
-
-require golang.org/x/sys v0.0.0-20180926160741-c2ed4eda69e7 // indirect
diff --git a/go.sum b/go.sum
index b558f35..456e6e5 100644
--- a/go.sum
+++ b/go.sum
@@ -1,8 +1,11 @@
+github.com/mattn/go-isatty v0.0.14 h1:yVuAays6BHfxijgZPzw+3Zlu5yQgKGP2/hcQbHb7S9Y=
+github.com/mattn/go-isatty v0.0.14/go.mod h1:7GGIvUiUoEMVVmxf/4nioHXj79iQHKdU27kJ6hsGG94=
 github.com/mpolden/sfv v0.9.0 h1:POHC8Js30xxOgMvgNLUEkJZh2fhOtx5NwK1pj7g9VvQ=
 github.com/mpolden/sfv v0.9.0/go.mod h1:EymWriacbRB9ZKQ21Vj+ahcIV8aq8G0FNluX6UNCcVk=
 github.com/nwaples/rardecode v1.1.0 h1:vSxaY8vQhOcVr4mm5e8XllHWTiM4JF507A0Katqw7MQ=
 github.com/nwaples/rardecode v1.1.0/go.mod h1:5DzqNKiOdpKKBH87u8VlvAnPZMXcGRhxWkRpHbbfGS0=
 github.com/rjeczalik/notify v0.9.2 h1:MiTWrPj55mNDHEiIX5YUSKefw/+lCQVoAFmD6oQm5w8=
 github.com/rjeczalik/notify v0.9.2/go.mod h1:aErll2f0sUX9PXZnVNyeiObbmTlk5jnMoCa4QEjJeqM=
-golang.org/x/sys v0.0.0-20180926160741-c2ed4eda69e7 h1:bit1t3mgdR35yN0cX0G8orgLtOuyL9Wqxa1mccLB0ig=
 golang.org/x/sys v0.0.0-20180926160741-c2ed4eda69e7/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c h1:F1jZWGFhYfh0Ci55sIpILtKKK8p3i2/krTr0H1rg74I=
+golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
diff --git a/logutil/logutil.go b/logutil/logutil.go
new file mode 100644
index 0000000..467e57d
--- /dev/null
+++ b/logutil/logutil.go
@@ -0,0 +1,40 @@
+package logutil
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+)
+
+const (
+	cursorUp = "\033[1A"
+	eraseEOL = "\033[K"
+)
+
+type UniqueWriter struct {
+	w     io.Writer
+	prev  []byte
+	count int64
+}
+
+func NewUniqueWriter(w io.Writer) *UniqueWriter { return &UniqueWriter{w: w} }
+
+func (uw *UniqueWriter) Write(p []byte) (n int, err error) {
+	if len(p) == 0 {
+		return 0, nil
+	}
+	if bytes.Equal(uw.prev, p) {
+		uw.count++
+		if p[len(p)-1] == '\n' {
+			p = p[:len(p)-1]
+		}
+		space := ""
+		if len(p) > 0 {
+			space = " "
+		}
+		return fmt.Fprintf(uw.w, "%s%s%s%s[repeated %d times]\n", cursorUp, eraseEOL, p, space, uw.count)
+	}
+	uw.prev = p
+	uw.count = 1
+	return uw.w.Write(p)
+}
diff --git a/logutil/logutil_test.go b/logutil/logutil_test.go
new file mode 100644
index 0000000..29f8849
--- /dev/null
+++ b/logutil/logutil_test.go
@@ -0,0 +1,25 @@
+package logutil
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestWrite(t *testing.T) {
+	var sb strings.Builder
+	w := NewUniqueWriter(&sb)
+
+	w.Write([]byte("l1\n"))
+	w.Write([]byte("l1\n"))
+	w.Write([]byte("l2\n"))
+	w.Write([]byte("\n"))
+	w.Write([]byte("\n"))
+
+	want := "l1\n" +
+		"\033[1A\033[Kl1 [repeated 2 times]\n" +
+		"l2\n" +
+		"\n\033[1A\033[K[repeated 2 times]\n"
+	if got := sb.String(); got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+}
-- 
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