fix #2: add --create-config to create a default config file

cmd/config.go

@@ -1,5 +1,5 @@
 /*
-Copyright © 2025 Thomas von Dein
+Copyright © 2025-2026 Thomas von Dein
 
 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
@@ -27,6 +27,7 @@ import (
 	"github.com/knadh/koanf/parsers/toml"
 	"github.com/knadh/koanf/providers/file"
 	"github.com/knadh/koanf/providers/posflag"
+	"github.com/knadh/koanf/providers/structs"
 	"github.com/knadh/koanf/v2"
 	flag "github.com/spf13/pflag"
 )
@@ -42,6 +43,7 @@ Options:
 -s --store-progress      remember reading position
 -n --line-numbers        add line numbers
 -c --config <file>       use config <file>
+   --create-config       create a default config file
 -i --cover-image         display cover image
 -t --txt                 dump readable content to STDOUT
 -x --xml                 dump source xml to STDOUT
@@ -51,6 +53,31 @@ Options:
 -v --version             show program version`
 )
 
+var (
+	DefaultDark = ColorSetting{
+		Title:   "#ff4500",
+		Chapter: "#ff4500",
+		Body:    "#cdb79e",
+	}
+
+	DefaultLight = ColorSetting{
+		Title:   "#ff0000",
+		Chapter: "#8b0000",
+		Body:    "#696969",
+	}
+)
+
+// used for config writing, it's a subset of the Config struct
+// add fields as you add user configurable fields to Config
+type UserConfig struct {
+	StoreProgress bool         `koanf:"store-progress"`
+	Darkmode      bool         `koanf:"dark"`
+	LineNumbers   bool         `koanf:"line-numbers"`
+	NoColor       bool         `koanf:"no-color"`
+	ColorDark     ColorSetting `koanf:"colordark"`
+	ColorLight    ColorSetting `koanf:"colorlight"`
+}
+
 type Config struct {
 	Showversion     bool         `koanf:"version"`        // -v
 	Debug           bool         `koanf:"debug"`          // -d
@@ -64,13 +91,15 @@ type Config struct {
 	ColorDark       ColorSetting `koanf:"colordark"`      // comes from config file only
 	ColorLight      ColorSetting `koanf:"colorlight"`     // comes from config file only
 	ShowHelp        bool         `koanf:"help"`
-	ShowCover       bool         `koanf:"cover-image"` // -i
+	ShowCover       bool         `koanf:"cover-image"`   // -i
+	CreateConfig    bool         `koanf:"create-config"` // --create-config
 	Colors          Colors       // generated from user config file or internal defaults, respects dark mode
 	Document        string
 	InitialProgress int // lines
 }
 
 func InitConfig(output io.Writer) (*Config, error) {
+	conf := &Config{}
 	var kloader = koanf.New(".")
 
 	// setup custom usage
@@ -93,6 +122,7 @@ func InitConfig(output io.Writer) (*Config, error) {
 	flagset.BoolP("no-color", "N", false, "disable colors")
 	flagset.BoolP("cover-image", "i", false, "show cover image")
 	flagset.BoolP("help", "h", false, "show help")
+	flagset.BoolP("create-config", "", false, "create a config file with default settings")
 	flagset.StringP("config", "c", "", "read config from file")
 
 	if err := flagset.Parse(os.Args[1:]); err != nil {
@@ -104,14 +134,13 @@ func InitConfig(output io.Writer) (*Config, error) {
 	var configfiles []string
 
 	configfile, _ := flagset.GetString("config")
-	home, _ := os.UserHomeDir()
 
 	if configfile != "" {
 		configfiles = []string{configfile}
 	} else {
 		configfiles = []string{
 			"/etc/epuppy.toml", "/usr/local/etc/epuppy.toml", // unix variants
-			filepath.Join(home, ".config", "epuppy", "config.toml"),
+			filepath.Join(conf.GetConfigDir(), "config.toml"),
 		}
 	}
 
@@ -132,7 +161,6 @@ func InitConfig(output io.Writer) (*Config, error) {
 	}
 
 	// fetch values
-	conf := &Config{}
 	if err := kloader.Unmarshal("", &conf); err != nil {
 		return nil, fmt.Errorf("error unmarshalling: %w", err)
 	}
@@ -141,7 +169,7 @@ func InitConfig(output io.Writer) (*Config, error) {
 	if len(flagset.Args()) > 0 {
 		conf.Document = flagset.Args()[0]
 	} else {
-		if !conf.Showversion && !conf.ShowHelp {
+		if !conf.Showversion && !conf.ShowHelp && !conf.CreateConfig {
 			flagset.Usage()
 			os.Exit(1)
 		}
@@ -152,18 +180,7 @@ func InitConfig(output io.Writer) (*Config, error) {
 	}
 
 	// setup color config
-	conf.Colors = SetColorconfig(
-		ColorSetting{ // Dark
-			Title:   "#ff4500",
-			Chapter: "#ff4500",
-			Body:    "#cdb79e",
-		},
-		ColorSetting{ // Light
-			Title:   "#ff0000",
-			Chapter: "#8b0000",
-			Body:    "#696969",
-		},
-		conf)
+	conf.Colors = SetColorconfig(DefaultDark, DefaultLight, conf)
 
 	// disable colors if requested by command line
 	if conf.NoColor {
@@ -173,7 +190,41 @@ func InitConfig(output io.Writer) (*Config, error) {
 	return conf, nil
 }
 
-func (c *Config) GetConfigDir() string {
+func (conf *Config) GetConfigDir() string {
 	home, _ := os.UserHomeDir()
 	return filepath.Join(home, ".config", "epuppy")
 }
+
+func (conf *Config) WriteConfigFile() (string, error) {
+	cfgfile := filepath.Join(conf.GetConfigDir(), "config.toml")
+
+	if FileExists(cfgfile) {
+		return "", fmt.Errorf("config file %s already exists.", cfgfile)
+	}
+
+	var kloader = koanf.New(".")
+
+	userconf := UserConfig{
+		StoreProgress: conf.StoreProgress,
+		Darkmode:      conf.Darkmode,
+		LineNumbers:   conf.LineNumbers,
+		NoColor:       conf.NoColor,
+		ColorDark:     DefaultDark,
+		ColorLight:    DefaultLight,
+	}
+
+	if err := kloader.Load(structs.Provider(userconf, "koanf"), nil); err != nil {
+		return "", fmt.Errorf("error loading config struct: %w", err)
+	}
+
+	toml, err := kloader.Marshal(toml.Parser())
+	if err != nil {
+		return "", fmt.Errorf("error unmarshalling config: %w", err)
+	}
+
+	if err := WriteFile(cfgfile, toml); err != nil {
+		return "", fmt.Errorf("error writing config file %s: %w", cfgfile, err)
+	}
+
+	return fmt.Sprintf("new config file %s created.", cfgfile), nil
+}