feat: add structured error response helpers

internal/server/respond.go

@@ -0,0 +1,43 @@
+package server
+
+import (
+	"mal/internal/observability"
+	"net/http"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+)
+
+type ErrorResponse struct {
+	Error string `json:"error"`
+}
+
+func RespondHTMLOrJSONError(c *gin.Context, status int, message string) {
+	if acceptsHTML(c) {
+		c.String(status, message)
+		c.Abort()
+		return
+	}
+	c.JSON(status, ErrorResponse{Error: message})
+	c.Abort()
+}
+
+func RespondError(c *gin.Context, status int, event string, component string, message string, fields map[string]any, err error) {
+	level := observability.LogLevelWarn
+	if status >= http.StatusInternalServerError {
+		level = observability.LogLevelError
+	}
+	observability.LogJSON(level, event, component, "", fields, err)
+	RespondHTMLOrJSONError(c, status, message)
+}
+
+func acceptsHTML(c *gin.Context) bool {
+	if strings.Contains(c.GetHeader("Accept"), "text/html") {
+		return true
+	}
+	if strings.EqualFold(strings.TrimSpace(c.GetHeader("HX-Request")), "true") {
+		return true
+	}
+	return false
+}
+