wip: initial formEngine

src/store/formStore.ts

@@ -0,0 +1,42 @@
+// This is the store that represents a runtime form. It is a writable store that contains the current state of the form
+// and the errors that are present in the form. It is used by the Form component to render the form and to update the
+
+import { Writable, derived, writable, Readable } from "svelte/store";
+type FormStore = { fields: Record<string, { value: string, errors: string[] }>, isValid: boolean };
+const formStore: Writable<FormStore> = writable({ fields: {}, isValid: false });
+
+interface FormEngine {
+    addField: (field: { name: string }) => { field: Writable<string>, errors: Readable<string[]> };
+    subscribe: Readable<FormStore>['subscribe'];
+    isValid: () => boolean;
+}
+
+// TODO: Validate on updates, reactive isValid, dependent fields, handle more than just strings
+export const formEngine: FormEngine = {
+    subscribe: formStore.subscribe,
+    isValid: () => true,
+    addField: (field) => {
+        formStore.update((form) => {
+            return { ...form, fields: { ...form.fields, [field.name]: { value: '', errors: [] } } }
+        });
+        const fieldStore = derived(formStore, ({ fields }) => fields[field.name]);
+        const fieldValueStore: Writable<string> = {
+            subscribe(cb) {
+                return fieldStore.subscribe((value) => cb(value?.value ?? ''));
+            },
+            set(value) {
+                formStore.update((form) => {
+                    return { ...form, fields: { ...form.fields, [field.name]: { value, errors: [] } } }
+                });
+            },
+            update: (updater) => {
+                formStore.update((form) => {
+                    const current = form.fields[field.name];
+                    const newValue = (current?.value && updater(current.value)) ?? ''
+                    return { ...form, fields: { ...form.fields, [field.name]: { value: newValue, errors: [] } } }
+                });
+            },
+        }
+        return { field: fieldValueStore, errors: derived(formStore, ({ fields }) => fields[field.name]?.errors ?? []) };
+    }
+}