Add support for reading the default model from a config file

This commit adds support for reading the default model from a config file
located at `~/.aichat/config.yml`. If the `model` flag is not specified when
running the program, it will try to read the default model from the config file.
If the config file does not exist or does not contain a `model` field, it will
use the default model `gogpt.GPT3Dot5Turbo`.

aichat.go

@@ -228,7 +228,7 @@ func main() {
 	var listPrompts = false
 	var nonStreaming = false
 	var split = false
-	var model = gogpt.GPT4
+	var model = ""
 	getopt.FlagLong(&temperature, "temperature", 't', "temperature")
 	getopt.FlagLong(&maxTokens, "max-tokens", 0, "max tokens, 0 to use default")
 	getopt.FlagLong(&verbose, "verbose", 'v', "verbose output")
@@ -249,6 +249,21 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
+
+	config, err := ReadConfig()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// if model is not specified, use the default model from the config file
+	if model == "" {
+		if config.Model == "" {
+			model = gogpt.GPT3Dot5Turbo
+		} else {
+			model = config.Model
+		}
+	}
+
 	options := chatOptions{
 		model:        model,
 		temperature:  temperature,

config.go

@@ -0,0 +1,29 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+)
+
+type Config struct {
+	Model string `yaml:"model"`
+}
+
+func ReadConfig() (*Config, error) {
+	config := &Config{}
+	// try to read from ~/.aichat/config.yml
+	homedir, err := os.UserHomeDir()
+	if err != nil {
+		return nil, err
+	}
+	path := filepath.Join(homedir, ".aichat", "config.yml")
+
+	if err := ReadYamlFromFile(path, config); err != nil {
+		// if the file does not exist, return an empty config
+		if os.IsNotExist(err) {
+			return config, nil
+		}
+		return nil, err
+	}
+	return config, nil
+}