made a start on mutating the AST

src/features/editor/ast.ts

@@ -0,0 +1,93 @@
+import type { Node, Text, Element, ElementContent, Parent, RootContent } from 'hast';
+import { find } from 'unist-util-find';
+import { visit } from 'unist-util-visit';
+import { deepCopy } from '~/utilities';
+
+/**
+ * 
+ * Given
+ * root
+ * |- element
+ * |  |- text [0, 6]
+ * |  |- element
+ * |  |  |- text [7, 18]
+ * |  |- text [19, 25]
+ * |- element
+ *    |- text [26, 40]
+ *    |- element
+ *    |  |- text [41, 53]
+ *    |- text [54, 60]
+ * 
+ * split at 10
+ * 
+ * root
+ * |- element
+ * |  |- text [0, 6]
+ * |  |- element
+ * |  |  |- text [7, 9]
+ * 
+ * root
+ * |- element
+ * |  |- element
+ * |  |  |- text [10, 18]
+ * |  |- text [19, 25]
+ * |- element
+ *    |- text [26, 40]
+ *    |- element
+ *    |  |- text [41, 53]
+ *    |- text [54, 60]
+ */
+
+export const splitAt = (tree: Parent, node: Text, offset: number): [RootContent[], RootContent[]] => {
+    const index = tree.children.findIndex(c => find(c, { ...node }));
+
+    if (index === -1) {
+        throw new Error('The tree does not contain the given node');
+    }
+
+    const left = tree.children.slice(0, index);
+    const right = tree.children.slice(index + 1);
+
+    if (offset === 0) {
+        right.unshift(tree.children[index]);
+    }
+    else if (offset === node.value.length) {
+        left.push(tree.children[index]);
+    }
+    else {
+        const targetLeft = deepCopy(tree.children[index]);
+        const targetRight = tree.children[index];
+
+        left.push(targetLeft);
+        right.unshift(targetRight);
+
+        visit(targetLeft, (n): n is Text => equals(n, node), n => {
+            n.value = n.value.slice(0, offset);
+        })
+
+        visit(targetRight, (n): n is Text => equals(n, node), n => {
+            n.value = n.value.slice(offset);
+        })
+    }
+
+    return [left, right];
+};
+
+const splitNode = (node: Node, offset: number) => {
+
+}
+
+const equals = (a: Node, b: Node): boolean => {
+    if (a === b) {
+        return true;
+    }
+
+    if (a.type !== b.type) {
+        return false;
+    }
+
+    // This is the nasty version of deep object checking, 
+    // but I hope this is safe to do in this case because
+    // we are working with a html-ast and not just any type of object.
+    return JSON.stringify(a) === JSON.stringify(b);
+};