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.

5 files changed, 142 insertions, 3 deletions

diff --git a/model/object.go b/model/object.go
index 63ef419..0b1919b 100644
--- a/model/object.go
+++ b/model/object.go
@@ -9,4 +9,5 @@ type Object interface {
 	Read(tx *sql.Tx) error
 	Update(tx *sql.Tx) error
 	Delete(tx *sql.Tx) error
+	SetID(id int)
 }
diff --git a/model/recipe.go b/model/recipe.go
index 684b158..adcafa1 100644
--- a/model/recipe.go
+++ b/model/recipe.go
@@ -5,6 +5,8 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"log"
+	"strconv"
 )
 
 type Recipe struct {
@@ -19,11 +21,23 @@ type Recipe struct {
 	IsFavorite  bool   `json:"is_favorite"`
 }
 
+func NewRecipe() Object {
+	return &Recipe{}
+}
+
 func (r Recipe) String() string {
 	b, _ := json.MarshalIndent(r, "", "    ")
 	return string(b)
 }
 
+func (r *Recipe) SetID(id int) {
+	if r == nil {
+		log.Println("Got nil as recipe!")
+	}
+
+	r.Id = strconv.Itoa(id)
+}
+
 func (r *Recipe) Validate() error {
 	var err error
 
diff --git a/model/recipes.go b/model/recipes.go
index e4fd1b8..09b51e7 100644
--- a/model/recipes.go
+++ b/model/recipes.go
@@ -7,13 +7,21 @@ import (
 )
 
 type RecipesElement struct {
-	Id         int64 // TODO change to string
-	Title      string
-	IsFavorite bool
+	Id         int64  `json:"id"` // TODO change to string
+	Title      string `json:"title"`
+	IsFavorite bool   `json:"is_favorite"`
 }
 
 type Recipes []RecipesElement
 
+func NewRecipes() Object {
+	return &Recipes{}
+}
+
+func (r *Recipes) SetID(id int) {
+	// singleton object, ignoring ID
+}
+
 func (r *Recipes) Create(tx *sql.Tx) error {
 	return fmt.Errorf("Impossible to create a recipe list")
 }
diff --git a/server.go b/server.go
index 3b17227..03c8251 100644
--- a/server.go
+++ b/server.go
@@ -26,12 +26,21 @@ func NewServer(addr string, db *model.DB) *Server {
 
 	mux.Handle("GET /version", view.VersionRead(version))
 
+	mux.Handle("GET /api/recipes", view.ReadJSON[*model.Recipes](db, model.NewRecipes))
 	mux.Handle("GET /recipes", view.RecipesRead(db))
 
 	mux.Handle("GET /recipe/create", view.RecipeCreate())
+
+	mux.Handle("POST /api/recipe", view.CreateJSON[*model.Recipe](db, model.NewRecipe))
 	mux.Handle("POST /recipe", controller.RecipeCreate(db))
+
+	mux.Handle("GET /api/recipe/{id}", view.ReadJSON[*model.Recipe](db, model.NewRecipe))
 	mux.Handle("GET /recipe/{id}", view.RecipeRead(db))
+
+	mux.Handle("POST /api/recipe/{id}", view.UpdateJSON[*model.Recipe](db, model.NewRecipe))
 	mux.Handle("POST /recipe/{id}", controller.RecipeUpdate(db))
+
+	mux.Handle("DELETE /api/recipe/{id}", view.DeleteJSON[*model.Recipe](db, model.NewRecipe))
 	mux.Handle("DELETE /recipe/{id}", controller.RecipeDelete(db))
 
 	mux.Handle("GET /favicon.ico", view.FaviconRead())
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
+			}
+		},
+	)
+}