[fix] reorganize the typing files

lib/post-process.ts

@@ -1,25 +1,25 @@
 import fs from "fs";
 import path from "path";
 import { PostFilesDirectory } from "@/consts/consts";
-import type { TFrontmatter } from "@/types/frontmatter.type";
-import type { TPostListItem, TPostsByTag } from "@/types/post-list";
+import type { TPostFrontmatter } from "@/types/frontmatter.type";
+import type { TPostListItem, TPostsByTag } from "@/types/docs.type";
 import { serialize } from "next-mdx-remote/serialize";
 import { titleCase } from "title-case";
 import { isEmptyString, nullifyEmptyArray, nullifyEmptyString } from "./utils";
 
-async function extractFrontmatters(filepath: string): Promise<TFrontmatter> {
+async function extractFrontmatters(filepath: string): Promise<TPostFrontmatter> {
   const source = fs.readFileSync(filepath, "utf-8");
   const mdxSource = await serialize(source, {
     parseFrontmatter: true,
     mdxOptions: { format: "md" },
   });
-  const frontmatter = mdxSource.frontmatter as TFrontmatter;
+  const frontmatter = mdxSource.frontmatter as TPostFrontmatter;
 
   const normalizedTags = frontmatter.tags
     ?.filter((tagname) => !isEmptyString(tagname))
     .map((tagname) => tagname.toUpperCase());
 
-  const normalizedResult: TFrontmatter = {
+  const normalizedResult: TPostFrontmatter = {
     title: titleCase(frontmatter.title),
     subtitle: nullifyEmptyString(frontmatter.subtitle),
     coverURL: nullifyEmptyString(frontmatter.coverURL),

lib/toc.ts

@@ -1,4 +1,4 @@
-import type { TTOCItem } from "@/types/toc.type";
+import type { TTOCItem } from "@/types/docs.type";
 import { JSDOM } from "jsdom";
 
 /**

lib/utils.ts

@@ -1,4 +1,3 @@
-import type { NonEmptyArray } from "@/types/utils.type";
 import { type ClassValue, clsx } from "clsx";
 import { twMerge } from "tailwind-merge";
 
@@ -84,11 +83,11 @@ export function isEmptyArray(value: any[] | null | undefined): boolean {
  * @param value - The array value to be nullified if empty.
  * @returns The nullified array if it is empty, otherwise returns the original array.
  */
-export function nullifyEmptyArray<T>(value: T[] | null | undefined): NonEmptyArray<T> | null {
+export function nullifyEmptyArray<T>(value: T[] | null | undefined): T[] | null {
   if (isEmptyArray(value)) {
     return null;
   }
-  return value as NonEmptyArray<T>;
+  return value!;
 }
 
 /**