Added book-export endpoints to the API

app/Http/Controllers/Api/BooksExportApiController.php

@@ -0,0 +1,55 @@
+<?php namespace BookStack\Http\Controllers\Api;
+
+use BookStack\Entities\Book;
+use BookStack\Entities\ExportService;
+use BookStack\Entities\Repos\BookRepo;
+use Throwable;
+
+class BooksExportApiController extends ApiController
+{
+
+    protected $bookRepo;
+    protected $exportService;
+
+    /**
+     * BookExportController constructor.
+     */
+    public function __construct(BookRepo $bookRepo, ExportService $exportService)
+    {
+        $this->bookRepo = $bookRepo;
+        $this->exportService = $exportService;
+        parent::__construct();
+    }
+
+    /**
+     * Export a book as a PDF file.
+     * @throws Throwable
+     */
+    public function exportPdf(int $id)
+    {
+        $book = Book::visible()->findOrFail($id);
+        $pdfContent = $this->exportService->bookToPdf($book);
+        return $this->downloadResponse($pdfContent, $book->slug . '.pdf');
+    }
+
+    /**
+     * Export a book as a contained HTML file.
+     * @throws Throwable
+     */
+    public function exportHtml(int $id)
+    {
+        $book = Book::visible()->findOrFail($id);
+        $htmlContent = $this->exportService->bookToContainedHtml($book);
+        return $this->downloadResponse($htmlContent, $book->slug . '.html');
+    }
+
+    /**
+     * Export a book as a plain text file.
+     */
+    public function exportPlainText(int $id)
+    {
+        $book = Book::visible()->findOrFail($id);
+        $textContent = $this->exportService->bookToPlainText($book);
+        return $this->downloadResponse($textContent, $book->slug . '.txt');
+    }
+}