Update Document types design

- Use Zod for scheme validation
- Add an explanation of how markdowndb validates document types

DESIGN.md

@@ -1,50 +1,36 @@
-### Define Your Schema
+### Define Your Schema with Zod Scheming
 
-To define the schema, you can use MarkdownDB's flexible schema definition syntax. Below is an example for a blog post with a mandatory `date` field:
+MarkdownDB leverages the powerful Zod library for schema definition, allowing you to specify the structure and validation rules for your Markdown content. Below is an example configuration demonstrating the usage of Zod to define a schema for a blog post with a mandatory `date` field.
 
 ```javascript
 // markdowndb.config.js
+import { z } from "zod";
 
 module.exports = {
-  schemas: {
+  schemas: z.object({
     post: {
-      date: {
-        type: "string",
-        required: true,
-        validate: (fileObject) => {
-          const dateFormat = /\d{4}-\d{2}-\d{2}/; // YYYY-MM-DD
-          if (!dateFormat.test(fileObject.date)) {
-            return {
-              status: false,
-              message: "Invalid date format. Please use YYYY-MM-DD.",
-            };
-          }
-          return {
-            status: true,
-          };
-        },
-        compute(fileObject, ast) {
-          // this function returns the first date in a file
-          const nodes = selectAll("*", ast);
-          nodes.map((node: any) => {
-            if (node.type === "text") {
-              const dateFormat = /\d{4}-\d{2}-\d{2}/;
-              if (!node.value.test(fileObject.date)) {
-                return node.value;
-              }
-            }
-          });
-        },
-      },
-      // Add more fields as needed
+      date: z.string().refine((value) => /\d{4}-\d{2}-\d{2}/.test(value), {
+        message: "Invalid date format. Please use YYYY-MM-DD.",
+      }),
+      // Add more fields as needed, each with its own validation rules
+      // Example:
+      // title: z.string().min(1, "Title must have at least 1 character"),
+      // content: z.string(),
     },
-    // Define additional schemas if necessary
-  },
+    // Define additional schemas for different content types
+    // Example:
+    // page: {
+    //   author: z.string(),
+    //   text: z.string(),
+    // },
+  }),
 };
 ```
 
-In this example, the `date` field is defined as a required string. It also includes custom validation logic to ensure that the date follows the format YYYY-MM-DD.
+In this example, the `post` schema is defined using Zod's `object` method, specifying the structure of the content. The `date` field is required and must adhere to the specified date format using Zod's `string` and `refine` methods for custom validation.
 
 ### How Validation Works
 
-When you load a Markdown file, MarkdownDB will validate it against the specified schema. If the validation fails, MarkdownDB will throw an error, providing detailed error messages to help you identify and fix the issues.
+When you load a Markdown file using MarkdownDB, it automatically validates the content against the defined schema using Zod. If the validation fails for any field, MarkdownDB will throw an error, providing detailed error messages. This helps you quickly identify and rectify issues, ensuring your Markdown content adheres to the specified structure and validation rules.
+
+Feel free to extend the schema by adding more fields and their respective validation rules as needed for your specific use case. This flexibility allows you to define complex structures and ensure the integrity of your data.