fix: sol.go file gen by tpl now pure golang

Makefile

@@ -14,16 +14,4 @@ test:
 .PNONY:new-day
 new-day:
 	@read -p "Enter day number: " num; \
-	folder="./day$$num"; \
-	if test -d "$$folder"; \
-	then echo Folder already exists; \
-	else echo "Creating $$folder"; \
-		mkdir -p "$$folder";  \
-		touch "$$folder/sol.go"; \
-		echo "package day$$num\n\n\
-func Part1(lines []string) int{\n\
-\t//todo: write code here\n\
-\treturn -1\n\
-}\n" >> "./day$$num/sol.go"; \
-	fi
-
+	go run -tags gen ./tpl/. -day $$num

tpl/soltpl.gotext

@@ -0,0 +1,30 @@
+package day{{.Day}}
+
+import "aoc"
+
+/*
+	Note: output arg type of Part1 and Part2 can be freely changed.
+*/
+
+func Part1(lines []string) int {
+	//todo: write code here
+	return -1
+}
+
+func Part2(lines []string) int {
+	//todo: write code here
+	return -1
+}
+
+func init() {
+	// this registers solution to be able to run from ./cmd/main.go,
+	// BUT you must add import like `_ "aoc/day{{.Day}}"` in "main.go" by hands!
+	aoc.RegisterSolution({{.Day}}, aoc.DaySolution{
+		Part1: func(lines []string) interface{} {
+			return Part1(lines)
+		},
+		Part2: func(lines []string) interface{} {
+			return Part2(lines)
+		},
+	})
+}

tpl/tpl.go

@@ -0,0 +1,72 @@
+// +build gen
+
+package main
+
+import (
+	_ "embed"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+	"text/template"
+)
+
+//go:embed soltpl.gotext
+var tpl string
+
+var errLog = log.New(os.Stderr, "ERR ", log.LstdFlags)
+var warnLog = log.New(os.Stderr, "WRN ", log.LstdFlags)
+
+func main() {
+	fmt.Println("Solution file generator")
+
+	t, err := template.New("").Parse(tpl)
+	if err != nil {
+		errLog.Println("template parse:", err)
+		os.Exit(1)
+	}
+
+	var day int
+	flag.IntVar(&day, "day", 0, "day number (ex: 1)")
+	flag.Parse()
+
+	if day <= 0 {
+		errLog.Println("wrong day number")
+	}
+
+	folder := filepath.Join(".", fmt.Sprintf("day%2d", day))
+
+	_, err = os.Stat(folder)
+	if err == nil {
+		warnLog.Println("folder already exists, wrong day?")
+		os.Exit(1)
+	}
+
+	err = os.Mkdir(folder, 0755)
+	if err != nil {
+		errLog.Println(err)
+		os.Exit(1)
+	}
+
+	f, err := os.Create(filepath.Join(folder, "sol.go"))
+	if err != nil {
+		errLog.Println("create solution go-file:", err)
+		os.Exit(1)
+	}
+	defer f.Close()
+
+	type data struct {
+		Day int
+	}
+
+	err = t.Execute(f, data{Day: day})
+	if err != nil {
+		errLog.Println("process template:", err)
+		os.Exit(1)
+	}
+
+	log.Println("folder crated:", folder)
+
+	fmt.Println("Done.")
+}