Add JSON-based API under `/api`

This commit provides an unstable JSON API for communication with an
upcoming Dart frontend.

Later it might be part of the public interface for integration into
other services. For this step it has to be ensured the semantics are not
changing a lot in the future which is currently out of scope.

1 files changed, 107 insertions, 0 deletions

diff --git a/view/json.go b/view/json.go
new file mode 100644
index 0000000..deaece2
--- /dev/null
+++ b/view/json.go
@@ -0,0 +1,107 @@
+package view
+
+import (
+	"encoding/json"
+	"io"
+	"net/http"
+	"strconv"
+
+	"xengineering.eu/ceres/model"
+)
+
+func CreateJSON[O model.Object](db *model.DB, constructor func() model.Object) http.Handler {
+	return http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			buf, err := io.ReadAll(r.Body)
+			if err != nil {
+				http.Error(w, "Request body could not be read: "+err.Error(), http.StatusBadRequest)
+				return
+			}
+
+			object := constructor()
+			err = json.Unmarshal(buf, &object)
+			if err != nil {
+				http.Error(w, "JSON could not be parsed: "+err.Error(), http.StatusBadRequest)
+				return
+			}
+
+			err = db.Transaction(object.Create)
+			if err != nil {
+				http.Error(w, "Object could not be saved to database: "+err.Error(), http.StatusBadRequest)
+				return
+			}
+		},
+	)
+}
+
+func ReadJSON[O model.Object](db *model.DB, constructor func() model.Object) http.Handler {
+	return http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			object := constructor()
+
+			id, err := strconv.Atoi(r.PathValue("id"))
+			if err == nil {
+				object.SetID(id)
+			}
+
+			err = db.Transaction(object.Read)
+			if err != nil {
+				http.Error(w, "Object could not be read from database: "+err.Error(), http.StatusBadRequest)
+				return
+			}
+
+			w.Header().Set("Content-Type", "application/json")
+			err = json.NewEncoder(w).Encode(object)
+			if err != nil {
+				http.Error(w, "Object could not be encoded to JSON: "+err.Error(), http.StatusBadRequest)
+				return
+			}
+		},
+	)
+}
+
+func UpdateJSON[O model.Object](db *model.DB, constructor func() model.Object) http.Handler {
+	return http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			buf, err := io.ReadAll(r.Body)
+			if err != nil {
+				http.Error(w, "Request body could not be read: "+err.Error(), http.StatusBadRequest)
+				return
+			}
+
+			object := constructor()
+			err = json.Unmarshal(buf, &object)
+			if err != nil {
+				http.Error(w, "JSON could not be parsed: "+err.Error(), http.StatusBadRequest)
+				return
+			}
+
+			err = db.Transaction(object.Update)
+			if err != nil {
+				http.Error(w, "Object could not be updated in database: "+err.Error(), http.StatusBadRequest)
+				return
+			}
+		},
+	)
+}
+
+func DeleteJSON[O model.Object](db *model.DB, constructor func() model.Object) http.Handler {
+	return http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			object := constructor()
+
+			id, err := strconv.Atoi(r.PathValue("id"))
+			if err != nil {
+				http.Error(w, "ID of object could not be parsed to an integer: "+err.Error(), http.StatusBadRequest)
+				return
+			}
+			object.SetID(id)
+
+			err = db.Transaction(object.Delete)
+			if err != nil {
+				http.Error(w, "Object could not be deleted from database: "+err.Error(), http.StatusBadRequest)
+				return
+			}
+		},
+	)
+}