feat: Implement file upload structure and API for file retrieval

src/app/api/files/[fileId]/route.js

@@ -1,8 +1,58 @@
 import { NextResponse } from "next/server";
+import { readFile } from "fs/promises";
+import { existsSync } from "fs";
 import { unlink } from "fs/promises";
 import path from "path";
 import db from "@/lib/db";
 
+export async function GET(request, { params }) {
+	try {
+		const fileId = params.fileId;
+
+		// Get file info from database
+		const file = db.prepare(`
+			SELECT * FROM file_attachments WHERE file_id = ?
+		`).get(parseInt(fileId));
+
+		if (!file) {
+			return NextResponse.json(
+				{ error: "File not found" },
+				{ status: 404 }
+			);
+		}
+
+		// Construct the full file path
+		const fullPath = path.join(process.cwd(), "public", file.file_path);
+
+		// Check if file exists
+		if (!existsSync(fullPath)) {
+			return NextResponse.json(
+				{ error: "File not found on disk" },
+				{ status: 404 }
+			);
+		}
+
+		// Read the file
+		const fileBuffer = await readFile(fullPath);
+
+		// Return the file with appropriate headers
+		return new NextResponse(fileBuffer, {
+			headers: {
+				"Content-Type": file.mime_type || "application/octet-stream",
+				"Content-Disposition": `attachment; filename="${encodeURIComponent(file.original_filename)}"`,
+				"Content-Length": fileBuffer.length.toString(),
+			},
+		});
+
+	} catch (error) {
+		console.error("Error downloading file:", error);
+		return NextResponse.json(
+			{ error: "Failed to download file" },
+			{ status: 500 }
+		);
+	}
+}
+
 export async function DELETE(request, { params }) {
 	try {
 		const fileId = params.fileId;