feat: add OpenAI image generation controls

backend/internal/service/openai_sse_data.go

@@ -0,0 +1,70 @@
+package service
+
+import (
+	"strings"
+
+	"github.com/tidwall/gjson"
+)
+
+type openAISSEDataAccumulator struct {
+	lines []string
+}
+
+func (a *openAISSEDataAccumulator) AddLine(line string, fn func([]byte)) {
+	if fn == nil {
+		return
+	}
+	trimmedLine := strings.TrimRight(line, "\r\n")
+	if data, ok := extractOpenAISSEDataLine(trimmedLine); ok {
+		a.lines = append(a.lines, data)
+		return
+	}
+	if strings.TrimSpace(trimmedLine) == "" {
+		a.Flush(fn)
+	}
+}
+
+func (a *openAISSEDataAccumulator) Flush(fn func([]byte)) {
+	if fn == nil || len(a.lines) == 0 {
+		return
+	}
+	emitOpenAISSEDataPayloads(a.lines, fn)
+	a.lines = a.lines[:0]
+}
+
+func forEachOpenAISSEDataPayload(body string, fn func([]byte)) {
+	if fn == nil || strings.TrimSpace(body) == "" {
+		return
+	}
+	var acc openAISSEDataAccumulator
+	for _, line := range strings.Split(body, "\n") {
+		acc.AddLine(line, fn)
+	}
+	acc.Flush(fn)
+}
+
+func emitOpenAISSEDataPayloads(lines []string, fn func([]byte)) {
+	if fn == nil || len(lines) == 0 {
+		return
+	}
+	if len(lines) == 1 {
+		emitOpenAISSEDataPayload(lines[0], fn)
+		return
+	}
+	joined := strings.Join(lines, "\n")
+	if gjson.Valid(joined) {
+		emitOpenAISSEDataPayload(joined, fn)
+		return
+	}
+	for _, line := range lines {
+		emitOpenAISSEDataPayload(line, fn)
+	}
+}
+
+func emitOpenAISSEDataPayload(data string, fn func([]byte)) {
+	data = strings.TrimSpace(data)
+	if data == "" || data == "[DONE]" {
+		return
+	}
+	fn([]byte(data))
+}