feat: add Anthropic API support with custom version header (#934)

* feat: add Anthropic API support with custom version header

* refactor: use switch statement for API type header handling

* refactor: add OpenAI & AzureAD types to be exhaustive

* Update client.go

need explicit fallthrough in empty case statements

* constant for APIVersion; addtl tests

config.go

@@ -11,6 +11,8 @@ const (
 
 	azureAPIPrefix         = "openai"
 	azureDeploymentsPrefix = "deployments"
+
+	AnthropicAPIVersion = "2023-06-01"
 )
 
 type APIType string
@@ -20,6 +22,7 @@ const (
 	APITypeAzure           APIType = "AZURE"
 	APITypeAzureAD         APIType = "AZURE_AD"
 	APITypeCloudflareAzure APIType = "CLOUDFLARE_AZURE"
+	APITypeAnthropic       APIType = "ANTHROPIC"
 )
 
 const AzureAPIKeyHeader = "api-key"
@@ -37,7 +40,7 @@ type ClientConfig struct {
 	BaseURL              string
 	OrgID                string
 	APIType              APIType
-	APIVersion           string // required when APIType is APITypeAzure or APITypeAzureAD
+	APIVersion           string // required when APIType is APITypeAzure or APITypeAzureAD or APITypeAnthropic
 	AssistantVersion     string
 	AzureModelMapperFunc func(model string) string // replace model to azure deployment name func
 	HTTPClient           HTTPDoer
@@ -76,6 +79,23 @@ func DefaultAzureConfig(apiKey, baseURL string) ClientConfig {
 	}
 }
 
+func DefaultAnthropicConfig(apiKey, baseURL string) ClientConfig {
+	if baseURL == "" {
+		baseURL = "https://api.anthropic.com/v1"
+	}
+	return ClientConfig{
+		authToken:  apiKey,
+		BaseURL:    baseURL,
+		OrgID:      "",
+		APIType:    APITypeAnthropic,
+		APIVersion: AnthropicAPIVersion,
+
+		HTTPClient: &http.Client{},
+
+		EmptyMessagesLimit: defaultEmptyMessagesLimit,
+	}
+}
+
 func (ClientConfig) String() string {
 	return "<OpenAI API ClientConfig>"
 }