From ef8261752f73f0901082dbd3c433b7e90cfa7fd1 Mon Sep 17 00:00:00 2001
From: "Gustavo \"Guz\" L de Mello" <contact@guz.one>
Date: Tue, 25 Feb 2025 14:30:14 -0300
Subject: [PATCH] feat(smalltrip,exceptions): use a JSON handler if none is
 provided via the context

---
 smalltrip/exceptions/exceptions.go |  7 +++
 smalltrip/exceptions/middleware.go | 71 ++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+)
 create mode 100644 smalltrip/exceptions/middleware.go

diff --git a/smalltrip/exceptions/exceptions.go b/smalltrip/exceptions/exceptions.go
index 3e79943..f8b396d 100644
--- a/smalltrip/exceptions/exceptions.go
+++ b/smalltrip/exceptions/exceptions.go
@@ -12,6 +12,11 @@ type Exception struct {
 	Message  string   `json:"message"`         // User friendly message
 	Err      error    `json:"error,omitempty"` // Go error
 	Severity Severity `json:"severity"`        // Exception level
+
+	// Handler to be used. This is normally provided by a middleware via the
+	// request context. Setting this field overrides any provided by the middleware
+	// and can be used to add a handler when using a middleware is not possible.
+	handler HandlerFunc `json:"-"`
 }
 
 var (
@@ -33,6 +38,8 @@ func (e Exception) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		e.handler(e, w, r)
 	}
 
+	e.handler = HandlerJSON(HandlerText)
+
 	handler, ok := r.Context().Value(handlerFuncCtxKey).(HandlerFunc)
 	if !ok {
 		e.handler(e, w, r)
diff --git a/smalltrip/exceptions/middleware.go b/smalltrip/exceptions/middleware.go
new file mode 100644
index 0000000..7d487a6
--- /dev/null
+++ b/smalltrip/exceptions/middleware.go
@@ -0,0 +1,71 @@
+package exceptions
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+)
+
+func HandlerJSON(fallback HandlerFunc) HandlerFunc {
+	return func(e Exception, w http.ResponseWriter, r *http.Request) {
+		j, err := json.Marshal(e)
+		if err != nil {
+			e.Err = errors.Join(fmt.Errorf("marshalling Exception struct: %s", e.Error()), e.Err)
+
+			fallback(e, w, r)
+			return
+		}
+
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(e.Status)
+
+		_, err = w.Write(j)
+		if err != nil {
+			e.Err = errors.Join(fmt.Errorf("writing JSON response to body: %s", e.Error()), e.Err)
+
+			HandlerText(e, w, r)
+			return
+		}
+	}
+}
+
+var _ HandlerFunc = HandlerJSON(HandlerText)
+
+func HandlerText(e Exception, w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "text/plain")
+	w.WriteHeader(e.Status)
+
+	_, err := w.Write([]byte(fmt.Sprintf(
+		"Status: %3d\n"+
+			"Code: %s"+
+			"Message: %s\n"+
+			"Err: %s\n"+
+			"Severity: %s\n\n"+
+			"%+v\n\n"+
+			"%#v",
+		e.Status,
+		e.Code,
+		e.Message,
+		e.Err,
+		e.Severity,
+
+		e, e,
+	)))
+	if err != nil {
+		_, _ = w.Write([]byte(fmt.Sprintf(
+			"Ok, what should we do at this point? You fucked up so bad that this message " +
+				"shouldn't even be able to be sent in the first place. If you are a normal user I'm " +
+				"so sorry for you to be reading this. If you're a developer, go fix your ResponseWriter " +
+				"implementation, because this should never happen in any normal codebase. " +
+				"I hope for the life of anyone you love you don't use this message in some " +
+				"error checking or any sort of API-contract, because there will be no more hope " +
+				"for you or your project. May God or any other or any other divinity that you may " +
+				"or may not believe be with you when trying to fix this mistake, you will need it.",
+			// If someone use this as part of the API-contract I'll not even be surprised.
+			// So any change to this message is still considered a breaking change.
+		)))
+	}
+}
+
+var _ HandlerFunc = HandlerText