feat: initial TTS support (#528)

* feat: initial TTS support

* chore: lint, omitempty

* chore: dont use pointer in struct

* fix: add mocked server tests to speech_test.go

Co-authored-by: Lachlan Laycock <supagroova@gmail.com>

* chore: update imports

* chore: fix lint

* chore: add an error check

* chore: ignore lint

* chore: add error checks in package

* chore: add test

* chore: fix test

---------

Co-authored-by: Lachlan Laycock <supagroova@gmail.com>

speech.go

@@ -0,0 +1,87 @@
+package openai
+
+import (
+	"context"
+	"errors"
+	"io"
+	"net/http"
+)
+
+type SpeechModel string
+
+const (
+	TTSModel1   SpeechModel = "tts-1"
+	TTsModel1HD SpeechModel = "tts-1-hd"
+)
+
+type SpeechVoice string
+
+const (
+	VoiceAlloy   SpeechVoice = "alloy"
+	VoiceEcho    SpeechVoice = "echo"
+	VoiceFable   SpeechVoice = "fable"
+	VoiceOnyx    SpeechVoice = "onyx"
+	VoiceNova    SpeechVoice = "nova"
+	VoiceShimmer SpeechVoice = "shimmer"
+)
+
+type SpeechResponseFormat string
+
+const (
+	SpeechResponseFormatMp3  SpeechResponseFormat = "mp3"
+	SpeechResponseFormatOpus SpeechResponseFormat = "opus"
+	SpeechResponseFormatAac  SpeechResponseFormat = "aac"
+	SpeechResponseFormatFlac SpeechResponseFormat = "flac"
+)
+
+var (
+	ErrInvalidSpeechModel = errors.New("invalid speech model")
+	ErrInvalidVoice       = errors.New("invalid voice")
+)
+
+type CreateSpeechRequest struct {
+	Model          SpeechModel          `json:"model"`
+	Input          string               `json:"input"`
+	Voice          SpeechVoice          `json:"voice"`
+	ResponseFormat SpeechResponseFormat `json:"response_format,omitempty"` // Optional, default to mp3
+	Speed          float64              `json:"speed,omitempty"`           // Optional, default to 1.0
+}
+
+func contains[T comparable](s []T, e T) bool {
+	for _, v := range s {
+		if v == e {
+			return true
+		}
+	}
+	return false
+}
+
+func isValidSpeechModel(model SpeechModel) bool {
+	return contains([]SpeechModel{TTSModel1, TTsModel1HD}, model)
+}
+
+func isValidVoice(voice SpeechVoice) bool {
+	return contains([]SpeechVoice{VoiceAlloy, VoiceEcho, VoiceFable, VoiceOnyx, VoiceNova, VoiceShimmer}, voice)
+}
+
+func (c *Client) CreateSpeech(ctx context.Context, request CreateSpeechRequest) (response io.ReadCloser, err error) {
+	if !isValidSpeechModel(request.Model) {
+		err = ErrInvalidSpeechModel
+		return
+	}
+	if !isValidVoice(request.Voice) {
+		err = ErrInvalidVoice
+		return
+	}
+	req, err := c.newRequest(ctx, http.MethodPost, c.fullURL("/audio/speech", request.Model),
+		withBody(request),
+		withContentType("application/json; charset=utf-8"),
+	)
+	if err != nil {
+		return
+	}
+
+	response, err = c.sendRequestRaw(req)
+
+	return
+}