Update the draft Downloader implementation to actually download dis…

…covered new files

1. Add a new `FileCopier` class with a `copy` method encapsulating the logic to:
    - automatically create necessary directories at the destination
    - actually attempt copying the file
    - identify and handle the edge case when the specified target file already exists
      using a provided `FileCopyEventsHandler` implementation
2. Update the `Downloader` class to:
    1. Create and configure a `FileCopier` instance with a simple `FileCopyEventsHandler` implementation
       to automatically skip copying over existing files.
    2. Update the `downloadNewFilesFromDir` method to call the `FileCopier.copy` method
       from the `newFiles` loop.

src/downloader/downloader.ts

@@ -1,3 +1,4 @@
+import path from "node:path";
 import { SequentialNamingScanner } from "../scanner";
 import { readDirectoryCursor, saveDirectoryCursor } from "../source-cursor";
 import {
@@ -6,10 +7,22 @@ import {
     findAllSupportedSourceDirs,
     readAutoDownloadConfiguration,
 } from "./configuration";
+import { FileCopier } from "./file-copier";
 import { GroupByDatePlacementStrategy, TargetPlacementStrategy } from "./placement-strategy";
 
 export class Downloader {
     private readonly configurationPromise: Promise<DriveDownloadConfiguration> = readAutoDownloadConfiguration();
+    private readonly fileCopier: FileCopier = new FileCopier({
+        async onTargetAlreadyExists(sourceFile, targetFile) {
+            console.warn(
+                "%s already exists in %s: skip copying %s",
+                path.basename(targetFile),
+                path.dirname(targetFile),
+                sourceFile
+            );
+            return { action: "skip" };
+        },
+    });
 
     /**
      * Download all new files from all supported directories in the specified 'drive' directory.
@@ -54,12 +67,13 @@ export class Downloader {
         });
 
         if (newFiles.length > 0) {
-            console.info("[%s] Found %i new files", sourceDir, newFiles.length);
+            console.info("[%s] Found %i new files in total (in this source directory)", sourceDir, newFiles.length);
 
             const placementStrategy = this.resolveTargetPlacementStrategy(configuration.target);
-            for (const file of newFiles) {
-                const targetFilePath = await placementStrategy.resolveTargetPath(`${sourceDir}/${file}`);
-                console.log("[%s] Copy %s to %s", sourceDir, file, targetFilePath);
+            for (const fileRelativePath of newFiles) {
+                const targetFilePath = await placementStrategy.resolveTargetPath(`${sourceDir}/${fileRelativePath}`);
+                console.log("[%s] Copy %s to %s", sourceDir, fileRelativePath, targetFilePath);
+                await this.fileCopier.copy(`${sourceDir}/${fileRelativePath}`, targetFilePath);
             }
 
             const lastProcessedFile = newFiles[newFiles.length - 1];

src/downloader/file-copier.ts

@@ -0,0 +1,39 @@
+import * as fs from "node:fs/promises";
+import path from "node:path";
+
+export class FileCopier {
+    private readonly createdDirsCache: Set<string> = new Set();
+
+    public constructor(private readonly handlers: FileCopyEventsHandler = {}) {}
+
+    public async copy(sourceFile: string, targetFile: string) {
+        const targetDir = path.dirname(targetFile);
+        if (!this.createdDirsCache.has(targetDir)) {
+            await fs.mkdir(targetDir, { recursive: true });
+            this.createdDirsCache.add(targetDir);
+        }
+
+        try {
+            await fs.copyFile(sourceFile, targetFile, fs.constants.COPYFILE_EXCL);
+        } catch (e) {
+            if ((e as NodeJS.ErrnoException)?.code === "EEXIST" && !!this.handlers?.onTargetAlreadyExists) {
+                const result = await this.handlers.onTargetAlreadyExists(sourceFile, targetFile);
+                if (result.action === "overwrite") {
+                    await fs.copyFile(sourceFile, targetFile);
+                } else if (result.action === "rename") {
+                    await this.copy(sourceFile, result.to);
+                }
+            } else {
+                throw e;
+            }
+        }
+    }
+}
+
+export type OnTargetAlreadyExistsAction =
+    | { readonly action: "overwrite" | "skip" }
+    | { readonly action: "rename"; readonly to: string };
+
+export type FileCopyEventsHandler = {
+    onTargetAlreadyExists?: (sourceFile: string, targetFile: string) => Promise<OnTargetAlreadyExistsAction>;
+};

test/downloader/.resources/dummy-drive-2/DCIM/IMG001.ARW

@@ -0,0 +1 @@
+Test file content

test/downloader/file-copier.spec.ts

@@ -0,0 +1,117 @@
+import * as fs from "node:fs/promises";
+import * as os from "node:os";
+import { FileCopier } from "../../src/downloader/file-copier";
+
+jest.mock("node:fs/promises");
+
+const realFs: typeof fs = jest.requireActual("node:fs/promises");
+
+describe("FileCopier", () => {
+    describe("Given a single file to copy", () => {
+        const sourceFile = `${__dirname}/.resources/dummy-drive-2/DCIM/IMG001.ARW`;
+
+        async function createTestTarget() {
+            const targetRoot = await realFs.mkdtemp(`${os.tmpdir()}/dummy-target-`);
+
+            const targetFileDir = `${targetRoot}/subdir01`;
+            const targetFile = `${targetFileDir}/IMG001.ARW`;
+
+            return { targetRoot, targetFileDir, targetFile };
+        }
+
+        function replaceFsMocksWithSpies() {
+            const mkdir = jest.mocked(fs.mkdir);
+            mkdir.mockImplementation(realFs.mkdir);
+            const copyFile = jest.mocked(fs.copyFile);
+            copyFile.mockImplementation(realFs.copyFile);
+
+            return { mkdir, copyFile };
+        }
+
+        describe("And the target directory does not exist", () => {
+            it("Should create the target directory and copy the file", async () => {
+                const { mkdir, copyFile } = replaceFsMocksWithSpies();
+
+                const { targetFileDir, targetFile } = await createTestTarget();
+
+                const copier = new FileCopier();
+
+                await copier.copy(sourceFile, targetFile);
+
+                expect(mkdir).toHaveBeenCalledWith(targetFileDir, { recursive: true });
+                expect(copyFile).toHaveBeenCalledWith(sourceFile, targetFile, fs.constants.COPYFILE_EXCL);
+            });
+        });
+
+        describe("And the target directory already exists", () => {
+            describe("When attempting to create the target directory", () => {
+                it("Should not fail", async () => {
+                    const { mkdir, copyFile } = replaceFsMocksWithSpies();
+
+                    const { targetFileDir, targetFile } = await createTestTarget();
+                    await realFs.mkdir(targetFileDir);
+
+                    const copier = new FileCopier();
+
+                    await copier.copy(sourceFile, targetFile);
+
+                    // Verify that `FileCopier` attempted to create the directory anyway.
+                    expect(mkdir).toHaveBeenCalledWith(targetFileDir, { recursive: true });
+                    expect(copyFile).toHaveBeenCalledWith(sourceFile, targetFile, fs.constants.COPYFILE_EXCL);
+                });
+            });
+        });
+
+        describe("And the target file already exists", () => {
+            describe("And copy events handler is not provided", () => {
+                it("Should refuse", async () => {
+                    const { copyFile } = replaceFsMocksWithSpies();
+
+                    const copier = new FileCopier();
+
+                    const { targetFileDir, targetFile } = await createTestTarget();
+                    await realFs.mkdir(targetFileDir);
+                    await realFs.writeFile(targetFile, "Original test file content");
+
+                    await expect(() => copier.copy(sourceFile, targetFile)).rejects.toThrow(/.?file already exists.?/);
+
+                    expect(copyFile).toHaveBeenCalledWith(sourceFile, targetFile, fs.constants.COPYFILE_EXCL);
+                    // Verify that the file was not corrupted despite making the `fs.copyFile` unconditionally.
+                    expect(await realFs.readFile(targetFile, { encoding: "utf8" })).toStrictEqual(
+                        "Original test file content"
+                    );
+                });
+            });
+        });
+    });
+
+    describe("Given multiple requests to copy files", () => {
+        it("Should create each target directory once", async () => {
+            const mockMkdir = jest.mocked(fs.mkdir);
+
+            const copier = new FileCopier();
+
+            await copier.copy("/tmp/dummy-file-1", "/tmp/dummy-target/dir01/file01");
+            await copier.copy("/tmp/dummy-file-2", "/tmp/dummy-target/dir01/file02");
+            await copier.copy("/tmp/dummy-file-3", "/tmp/dummy-target/dir01/file03");
+
+            expect(mockMkdir.mock.calls).toStrictEqual([["/tmp/dummy-target/dir01", { recursive: true }]]);
+
+            await copier.copy("/tmp/dummy-file-4", "/tmp/dummy-target/dir02/file04");
+
+            expect(mockMkdir.mock.calls).toStrictEqual([
+                ["/tmp/dummy-target/dir01", { recursive: true }],
+                ["/tmp/dummy-target/dir02", { recursive: true }],
+            ]);
+
+            await copier.copy("/tmp/dummy-file-5", "/tmp/dummy-target/dir03/file05");
+            await copier.copy("/tmp/dummy-file-6", "/tmp/dummy-target/dir03/file06");
+
+            expect(mockMkdir.mock.calls).toStrictEqual([
+                ["/tmp/dummy-target/dir01", { recursive: true }],
+                ["/tmp/dummy-target/dir02", { recursive: true }],
+                ["/tmp/dummy-target/dir03", { recursive: true }],
+            ]);
+        });
+    });
+});