From aa9ef12d434bfdb4052e15c53fed48cbbb5ae25b Mon Sep 17 00:00:00 2001
From: Davyd McColl <davydm@gmail.com>
Date: Fri, 11 Jun 2021 17:01:22 +0200
Subject: [PATCH] :sparkles: make log-watching work on windows

---
 pkg/app/app.go | 72 ++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 61 insertions(+), 11 deletions(-)

diff --git a/pkg/app/app.go b/pkg/app/app.go
index a624a0d30..ad655aa33 100644
--- a/pkg/app/app.go
+++ b/pkg/app/app.go
@@ -4,15 +4,6 @@ import (
 	"bufio"
 	"errors"
 	"fmt"
-	"io"
-	"io/ioutil"
-	"log"
-	"os"
-	"path/filepath"
-	"regexp"
-	"strconv"
-	"strings"
-
 	"github.com/aybabtme/humanlog"
 	"github.com/jesseduffield/lazygit/pkg/commands"
 	"github.com/jesseduffield/lazygit/pkg/commands/oscommands"
@@ -23,6 +14,15 @@ import (
 	"github.com/jesseduffield/lazygit/pkg/secureexec"
 	"github.com/jesseduffield/lazygit/pkg/updates"
 	"github.com/sirupsen/logrus"
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+	"path/filepath"
+	"regexp"
+	"runtime"
+	"strconv"
+	"strings"
 )
 
 // App struct
@@ -318,6 +318,9 @@ func TailLogs() {
 
 	fmt.Printf("Tailing log file %s\n\n", logFilePath)
 
+	opts := humanlog.DefaultOptions
+	opts.Truncates = false
+
 	_, err = os.Stat(logFilePath)
 	if err != nil {
 		if os.IsNotExist(err) {
@@ -326,6 +329,11 @@ func TailLogs() {
 		log.Fatal(err)
 	}
 
+	if runtime.GOOS == "windows" {
+		TailLogsNative(logFilePath, opts)
+		return
+	}
+
 	cmd := secureexec.Command("tail", "-f", logFilePath)
 
 	stdout, _ := cmd.StdoutPipe()
@@ -333,8 +341,6 @@ func TailLogs() {
 		log.Fatal(err)
 	}
 
-	opts := humanlog.DefaultOptions
-	opts.Truncates = false
 	if err := humanlog.Scanner(stdout, os.Stdout, opts); err != nil {
 		log.Fatal(err)
 	}
@@ -345,3 +351,47 @@ func TailLogs() {
 
 	os.Exit(0)
 }
+
+func TailLogsNative(logFilePath string, opts *humanlog.HandlerOptions) {
+	var lastModified int64 = 0
+	var lastOffset int64 = 0
+	for {
+		stat, err := os.Stat(logFilePath)
+		if err != nil {
+			log.Fatal(err)
+		}
+		if stat.ModTime().Unix() > lastModified {
+			err = TailFrom(lastOffset, logFilePath, opts)
+			if err != nil {
+				log.Fatal(err)
+			}
+		}
+		lastOffset = stat.Size()
+	}
+}
+
+func TailFrom(lastOffset int64, logFilePath string, opts *humanlog.HandlerOptions) error {
+	file, err := os.Open(logFilePath)
+	if err != nil {
+		return err
+	}
+	file.Seek(lastOffset, 0)
+	fileScanner := bufio.NewScanner(file)
+	var lines []string
+	for fileScanner.Scan() {
+		lines = append(lines, fileScanner.Text())
+	}
+	file.Close()
+	lineCount := len(lines)
+	lastTen := lines
+	if lineCount > 10 {
+		lastTen = lines[lineCount-10:]
+	}
+	for _, line := range lastTen {
+		reader := strings.NewReader(line)
+		if err := humanlog.Scanner(reader, os.Stdout, opts); err != nil {
+			log.Fatal(err)
+		}
+	}
+	return nil
+}