Unify error handling and HTTP statuses

Signed-off-by: Sean Du <do4suki@gmail.com>

internal/utils/error.go

@@ -1,6 +1,15 @@
 package honokautils
 
-import "errors"
+import (
+	"errors"
+	"fmt"
+	"net/http"
+	"reflect"
+	"strconv"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+)
 
 type UnimplementedError struct {
 	Kind   string
@@ -35,3 +44,82 @@ func IsUnimplementedError(err error) bool {
 	var target *UnimplementedError
 	return err != nil && errors.As(err, &target)
 }
+
+const maintenanceHeader = "Maintenance"
+
+type ErrorContent struct {
+	Detail    string   `json:"detail,omitempty"`
+	Exception string   `json:"exception,omitempty"`
+	Message   string   `json:"message,omitempty"`
+	Traceback []string `json:"traceback,omitempty"`
+}
+
+func IsMainPHPRequest(path string) bool {
+	return path == "/main.php" || strings.HasPrefix(path, "/main.php/")
+}
+
+func WriteMaintenanceJSON(setHeader func(string, string), writeJSON func(int, any), status int, content any) {
+	setHeader("Content-Type", "application/json; charset=utf-8")
+	setHeader("status_code", strconv.Itoa(status))
+	setHeader(maintenanceHeader, "1")
+	writeJSON(status, content)
+}
+
+func AbortMaintenanceJSON(ctx *gin.Context, status int, content any) {
+	WriteMaintenanceJSON(ctx.Header, ctx.JSON, status, content)
+	ctx.Abort()
+}
+
+func NewDetailContent(detail string) ErrorContent {
+	return ErrorContent{
+		Detail: detail,
+	}
+}
+
+func NewNotFoundContent(path string) ErrorContent {
+	return NewDetailContent(fmt.Sprintf("Endpoint not found: %s", path))
+}
+
+func NewInternalErrorContent(err error) ErrorContent {
+	return ErrorContent{
+		Exception: exceptionName(err),
+		Message:   err.Error(),
+	}
+}
+
+func NewErrorContent(exception, message string) ErrorContent {
+	return ErrorContent{
+		Exception: exception,
+		Message:   message,
+	}
+}
+
+func NewPanicContent(recovered any, stack []byte) ErrorContent {
+	return ErrorContent{
+		Exception: "panic",
+		Message:   fmt.Sprint(recovered),
+		Traceback: splitLines(stack),
+	}
+}
+
+func exceptionName(err error) string {
+	if err == nil {
+		return http.StatusText(http.StatusInternalServerError)
+	}
+
+	typ := reflect.TypeOf(err)
+	if typ.Kind() == reflect.Pointer {
+		typ = typ.Elem()
+	}
+	if name := typ.Name(); name != "" {
+		return name
+	}
+	return typ.String()
+}
+
+func splitLines(stack []byte) []string {
+	if len(stack) == 0 {
+		return nil
+	}
+	return strings.Split(strings.TrimSpace(string(stack)), "\n")
+}