feat: download completed docs via api (#1078)

## Description

Allow users to download a completed document via API.

## Testing Performed

Tested the code locally by trying to download both draft and completed
docs. Works as expected.

## Checklist

- [x] I have tested these changes locally and they work as expected.
- [ ] I have added/updated tests that prove the effectiveness of these
changes.
- [ ] I have updated the documentation to reflect these changes, if
applicable.
- [x] I have followed the project's coding style guidelines.
- [ ] I have addressed the code review feedback from the previous
submission, if applicable.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Implemented functionality to download signed documents directly from
the app.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/api/v1/implementation.ts

@@ -23,7 +23,10 @@ import { createDocumentFromTemplate } from '@documenso/lib/server-only/template/
 import { extractNextApiRequestMetadata } from '@documenso/lib/universal/extract-request-metadata';
 import { getFile } from '@documenso/lib/universal/upload/get-file';
 import { putFile } from '@documenso/lib/universal/upload/put-file';
-import { getPresignPostUrl } from '@documenso/lib/universal/upload/server-actions';
+import {
+  getPresignGetUrl,
+  getPresignPostUrl,
+} from '@documenso/lib/universal/upload/server-actions';
 import { DocumentDataType, DocumentStatus, SigningStatus } from '@documenso/prisma/client';
 
 import { ApiContractV1 } from './contract';
@@ -83,6 +86,68 @@ export const ApiContractV1Implementation = createNextRoute(ApiContractV1, {
     }
   }),
 
+  downloadSignedDocument: authenticatedMiddleware(async (args, user, team) => {
+    const { id: documentId } = args.params;
+
+    try {
+      if (process.env.NEXT_PUBLIC_UPLOAD_TRANSPORT !== 's3') {
+        return {
+          status: 500,
+          body: {
+            message: 'Please make sure the storage transport is set to S3.',
+          },
+        };
+      }
+
+      const document = await getDocumentById({
+        id: Number(documentId),
+        userId: user.id,
+        teamId: team?.id,
+      });
+
+      if (!document || !document.documentDataId) {
+        return {
+          status: 404,
+          body: {
+            message: 'Document not found',
+          },
+        };
+      }
+
+      if (DocumentDataType.S3_PATH !== document.documentData.type) {
+        return {
+          status: 400,
+          body: {
+            message: 'Invalid document data type',
+          },
+        };
+      }
+
+      if (document.status !== DocumentStatus.COMPLETED) {
+        return {
+          status: 400,
+          body: {
+            message: 'Document is not completed yet.',
+          },
+        };
+      }
+
+      const { url } = await getPresignGetUrl(document.documentData.data);
+
+      return {
+        status: 200,
+        body: { downloadUrl: url },
+      };
+    } catch (err) {
+      return {
+        status: 500,
+        body: {
+          message: 'Error downloading the document. Please try again.',
+        },
+      };
+    }
+  }),
+
   deleteDocument: authenticatedMiddleware(async (args, user, team) => {
     const { id: documentId } = args.params;