Straightened out the configuration file processing and introduced command-line argument processing

config/config.go

@@ -12,10 +12,31 @@ package config
 
 import (
 	_ "embed"
+	"fmt"
+	"os"
 
+	argparse "github.com/alexflint/go-arg"
 	"gopkg.in/yaml.v3"
 )
 
+// AMSTERDAM_VERSION contains the version number of Amsterdam.
+const AMSTERDAM_VERSION = "0.0.1"
+
+// AmCLI is the command-line interface arguments structure.
+type AmCLI struct {
+	ConfigFile string `arg:"-C,--config" help:"Location of the configuration file."`
+}
+
+// Description (from argparse.Described) returns the description string for the application.
+func (*AmCLI) Description() string {
+	return "Amsterdam Web Communities System Server"
+}
+
+// Version (from argparse.Versioned) returns the version number string for the application.
+func (*AmCLI) Version() string {
+	return "Amsterdam " + AMSTERDAM_VERSION
+}
+
 // AmConfig holds the configuration of the application as read from YAML.
 type AmConfig struct {
 	Site struct {
@@ -29,6 +50,9 @@ type AmConfig struct {
 //go:embed default.yaml
 var defaultConfigData []byte
 
+// defaultConfig holds the default configuration data.
+var defaultConfig AmConfig
+
 // GlobalConfig holds the global configuration.
 var GlobalConfig AmConfig
 
@@ -40,3 +64,49 @@ func init() {
 	}
 	GlobalConfig = defaultConfig
 }
+
+/* overlayString is a helper that takes a loaded or defaulted string and returns it.
+ * Parameters:
+ *     loaded - The string loaded from a configuration file.
+ *     defaulted - The default value of this string.
+ * Returns:
+ *     loaded if it's not empty, otherwise defaulted.
+ */
+func overlayString(loaded string, defaulted string) string {
+	if loaded == "" {
+		return defaulted
+	}
+	return loaded
+}
+
+/* overlayConfig takes two configuration structures and overlays them to create the third.
+ * Parameters:
+ *     dest - Points to the destination copnfiguration structure.
+ *     loaded - Points to the loaded configuration structure.
+ *     defaults - Points to the default configuration structure.
+ */
+func overlayConfig(dest *AmConfig, loaded *AmConfig, defaults *AmConfig) {
+	dest.Site.Title = overlayString(loaded.Site.Title, defaults.Site.Title)
+	dest.Rendering.TemplateDir = overlayString(loaded.Rendering.TemplateDir, defaults.Rendering.TemplateDir)
+}
+
+// SetupConfig loads the command line arguments, loads the config file, and prepares GlobalConfig.
+func SetupConfig() {
+	var args AmCLI
+	argparse.MustParse(&args)
+
+	if args.ConfigFile != "" {
+		// load the data and use it to unmarshal the loaded configuration
+		data, err := os.ReadFile(args.ConfigFile)
+		if err != nil {
+			panic(fmt.Sprintf("unable to load configuration file %s: %v", args.ConfigFile, err))
+		}
+		var loadedConfig AmConfig
+		if err = yaml.Unmarshal(data, &loadedConfig); err != nil {
+			panic(fmt.Sprintf("unable to load configuration file %s: %v", args.ConfigFile, err))
+		}
+		overlayConfig(&GlobalConfig, &loadedConfig, &defaultConfig)
+	} else {
+		GlobalConfig = defaultConfig // just copy over the defaults
+	}
+}