Add support for custom OpenAI API base URL

Author: ammario

README.md

@@ -83,4 +83,14 @@ determine the style guide. It is optional, but if it exists, it will be followed
 even if the rules there diverge from the norm.
 
 If there is no repo style guide, `aicommit` will look for a user style guide
-in `~/COMMITS.md`.
+in `~/COMMITS.md`.
+
+## Other Providers
+
+You may set `OPENAI_BASE_URL` to use other OpenAI compatible APIs with `aicommit`.
+So far, I've tested it with [LiteLLM](https://github.com/BerriAI/litellm) across
+local models (via ollama) and Anthropic. I have yet to find a local model
+that is well-steered by the prompt design here, but the Anthropic Claude 3.5
+commit messages are on par with 4o. My theory for why local models don't work well
+is (even the "Instruct" fine-tuned models) have much worse instruction
+fine-tuning than the flagship commercial models.

cmd/aicommit/main.go

@@ -193,12 +193,13 @@ func run(inv *serpent.Invocation, opts runOptions) error {
 }
 
 type runOptions struct {
-	client  *openai.Client
-	model   string
-	dryRun  bool
-	amend   bool
-	ref     string
-	context []string
+	client        *openai.Client
+	openAIBaseURL string
+	model         string
+	dryRun        bool
+	amend         bool
+	ref           string
+	context       []string
 }
 
 func main() {
@@ -253,7 +254,9 @@ func main() {
 				return nil
 			}
 
-			client := openai.NewClient(openAIKey)
+			oaiConfig := openai.DefaultConfig(openAIKey)
+			oaiConfig.BaseURL = opts.openAIBaseURL
+			client := openai.NewClientWithConfig(oaiConfig)
 			opts.client = client
 			if len(inv.Args) > 0 {
 				opts.ref = inv.Args[0]
@@ -268,6 +271,14 @@ func main() {
 				Flag:        "openai-key",
 				Value:       serpent.StringOf(&cliOpenAIKey),
 			},
+			{
+				Name:        "openai-base-url",
+				Description: "The base URL to use for the OpenAI API.",
+				Env:         "OPENAI_BASE_URL",
+				Flag:        "openai-base-url",
+				Value:       serpent.StringOf(&opts.openAIBaseURL),
+				Default:     "https://api.openai.com/v1",
+			},
 			{
 				Name:          "model",
 				Description:   "The model to use, e.g. gpt-4o or gpt-4o-mini.",