Add different data providers and improve docs

This adds support for switching between in-memory, local filesystem, s3
or sqlite.

handlers/api/documents.go

@@ -0,0 +1,48 @@
+package documents
+
+import (
+	"bytes"
+	"excalidraw-complete/core"
+	"io"
+	"net/http"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/go-chi/render"
+)
+
+type (
+	DocumentCreateResponse struct {
+		ID string `json:"id"`
+	}
+)
+
+func HandleCreate(documentStore core.DocumentStore) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		data := new(bytes.Buffer)
+		_, err := io.Copy(data, r.Body)
+		if err != nil {
+			http.Error(w, "Failed to copy", http.StatusInternalServerError)
+			return
+		}
+		id, err := documentStore.Create(r.Context(), &core.Document{Data: *data})
+		if err != nil {
+			http.Error(w, "Failed to save", http.StatusInternalServerError)
+			return
+		}
+
+		render.JSON(w, r, DocumentCreateResponse{ID: id})
+		render.Status(r, http.StatusOK)
+	}
+}
+
+func HandleGet(documentStore core.DocumentStore) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		id := chi.URLParam(r, "id")
+		document, err := documentStore.FindID(r.Context(), id)
+		if err != nil {
+			http.Error(w, "not found", http.StatusNotFound)
+			return
+		}
+		w.Write(document.Data.Bytes())
+	}
+}