feat: synchronize recipe completion controls

Fixes #5\nRefs #1, #2

test/recipe-progress.test.js

@@ -0,0 +1,25 @@
+const test = require("node:test");
+const assert = require("node:assert/strict");
+const { flattenInstructions, updateProgress } = require("../lib/recipe-progress");
+
+const recipe = {
+  recipeIngredient: ["1 cup flour", "1 egg"],
+  recipeInstructions: ["Mix", { itemListElement: [{ text: "Bake" }] }]
+};
+
+test("flattens nested recipe instructions", () => {
+  assert.deepEqual(flattenInstructions(recipe.recipeInstructions), ["Mix", "Bake"]);
+});
+
+test("updates and validates cooking progress", () => {
+  const ingredientProgress = updateProgress(recipe, {}, {
+    kind: "ingredient", index: 1, completed: true
+  });
+  assert.deepEqual(ingredientProgress, { completedIngredients: [1], completedSteps: [] });
+  assert.deepEqual(updateProgress(recipe, ingredientProgress, {
+    kind: "ingredient", index: 1, completed: false
+  }), { completedIngredients: [], completedSteps: [] });
+  assert.throws(() => updateProgress(recipe, {}, {
+    kind: "step", index: 2, completed: true
+  }), /does not exist/);
+});