/**
 * Tests for the `quak backup` logic, now built on the library API (issue #51).
 *
 * `lib.backup({ downloadDirectory })` refreshes the library, fetches each
 * pending file's original through the content cache/pools, and materialises the
 * unchanged on-disk layout:
 *
 *     <downloadDirectory>/
 *         originals/
 *             <fileID>.<ext>          the decrypted bytes ("present means complete")
 *             <fileID>.json           per-file metadata sidecar (rebuilt each run)
 *         collections/
 *             <name>/<title>          symlink into ../originals (rebuilt each run)
 *             <name>.json             per-collection metadata (rebuilt each run)
 *         failures.json               durable ledger of unresolved failures
 *
 * The properties that distinguish backup from a naive download loop, and that
 * these tests lock down:
 *
 * 1. Present-means-complete: an original already on disk is not re-fetched, so
 *    runs are idempotent and interrupted runs resume.
 * 2. Per-file resilience: a download failure or a symlink failure is recorded
 *    and the run continues (issue #8); the derived symlink/JSON views are
 *    rebuilt from the model every run.
 * 3. A durable `failures.json` records each unresolved failure's classification,
 *    attempt count, and last-tried time; the exit code (result.failed) is
 *    non-zero while any failure remains and clears once every one is resolved.
 *
 * The cache and download layers are covered elsewhere (content.test.ts,
 * download tests); here a mock library client and a stand-in content source
 * drive the backup logic with no crypto and no network.
 */

import {
    existsSync,
    lstatSync,
    mkdirSync,
    mkdtempSync,
    readFileSync,
    readlinkSync,
    rmSync,
    writeFileSync,
} from "node:fs";
import { join } from "node:path";
import { tmpdir } from "node:os";
import { describe, it, expect, beforeEach, afterEach } from "vitest";

import { Library } from "../../src/library/index.js";
import type { ContentSource } from "../../src/library/content.js";
import type { CollectionsPage, FilesPage } from "../../src/client.js";
import type { Collection, EnteFile } from "../../src/model/types.js";

const USER_ID = 42;

// Decrypted-byte length each stub original writes, keyed by fileID.
const SIZE_BY_ID: Record<number, number> = { 100: 3000, 101: 2000, 200: 1500 };

const collection = (id: number, name: string): Collection => ({
    id,
    ownerID: USER_ID,
    key: new Uint8Array([id & 0xff]),
    name,
    type: "album",
    updationTime: 1,
    isShared: false,
});

const file = (id: number, collectionID: number, title: string): EnteFile => ({
    id,
    collectionID,
    ownerID: USER_ID,
    key: new Uint8Array([id & 0xff]),
    metadata: {
        title,
        fileType: "image",
        creationTime: 1,
        modificationTime: 1,
    },
    file: { decryptionHeader: "aGVhZGVy" },
    thumbnail: { decryptionHeader: "dGh1bWI=" },
    updationTime: 1,
});

// A metadata-only client: two albums, three files, served once. No ML.
class MockClient {
    private served = false;
    whoami(): { email: string; userID: number } {
        return { email: "backup@example.com", userID: USER_ID };
    }
    async collectionsSince(): Promise<CollectionsPage> {
        if (this.served) return { collections: [], deleted: [], cursor: 1 };
        this.served = true;
        return {
            collections: [collection(1, "Vacation"), collection(2, "Work")],
            deleted: [],
            cursor: 1,
        };
    }
    async filesSince(args: { collectionID: number }): Promise<FilesPage> {
        const files =
            args.collectionID === 1
                ? [file(100, 1, "beach.jpg"), file(101, 1, "sunset.jpg")]
                : args.collectionID === 2
                  ? [file(200, 2, "diagram.png")]
                  : [];
        return { files, deleted: [], cursor: 1 };
    }
}

// A content source that writes byte buffers of the expected length and can be
// told to fail one fileID's original, to exercise per-file resilience.
interface StubSource extends ContentSource {
    failID?: number;
    originalCalls: number;
}

const stubSource = (): StubSource => {
    const s: StubSource = {
        originalCalls: 0,
        original: async ({ file: f, destination }) => {
            s.originalCalls++;
            if (s.failID === f.id) throw new Error("HTTP 500 from server");
            const size = SIZE_BY_ID[f.id] ?? 10;
            writeFileSync(destination, Buffer.alloc(size));
            return { bytesWritten: size };
        },
        thumbnail: async ({ destination }) => {
            writeFileSync(destination, Buffer.alloc(5));
            return { bytesWritten: 5 };
        },
    };
    return s;
};

let root: string;

const openLibrary = (source: ContentSource): Promise<Library> =>
    Library.open({
        client: new MockClient(),
        cacheDirectory: join(root, "cache"),
        contentSource: source,
        refreshIntervalSeconds: 3600,
    });

const readLedger = (
    outDir: string,
): { files: Record<string, Record<string, unknown>> } =>
    JSON.parse(readFileSync(join(outDir, "failures.json"), "utf-8"));

// Write a durable ledger holding one prior failure, to exercise pruning of
// entries the current run cannot resolve.
const seedLedger = (outDir: string, fileID: number, title: string): void => {
    mkdirSync(outDir, { recursive: true });
    writeFileSync(
        join(outDir, "failures.json"),
        JSON.stringify({
            version: 1,
            files: {
                [String(fileID)]: {
                    fileID,
                    title,
                    classification: "transient",
                    attempts: 1,
                    lastTriedAt: Date.now(),
                    error: "HTTP 500 from server",
                },
            },
        }),
    );
};

beforeEach(() => {
    root = mkdtempSync(join(tmpdir(), "quak-backup-test-"));
});

afterEach(() => {
    if (root && existsSync(root))
        rmSync(root, { recursive: true, force: true });
});

describe("lib.backup", () => {
    it("throws before any network when no downloadDirectory is given", async () => {
        const source = stubSource();
        const lib = await openLibrary(source);
        await expect(lib.backup()).rejects.toThrow(/downloadDirectory/i);
        expect(source.originalCalls).toBe(0);
        lib.close();
    });

    it("writes the expected on-disk layout for every file", async () => {
        const source = stubSource();
        const lib = await openLibrary(source);
        const outDir = join(root, "backup");

        const result = await lib.backup({ downloadDirectory: outDir });

        expect(result.totalFiles).toBe(3);
        expect(result.downloaded).toBe(3);
        expect(result.skipped).toBe(0);
        expect(result.failed).toBe(0);
        expect(result.errors).toEqual([]);

        // Originals under originals/<fileID>.<ext>.
        expect(readFileSync(join(outDir, "originals", "100.jpg")).length).toBe(
            3000,
        );
        expect(readFileSync(join(outDir, "originals", "101.jpg")).length).toBe(
            2000,
        );
        expect(readFileSync(join(outDir, "originals", "200.png")).length).toBe(
            1500,
        );

        // Per-file metadata sidecar.
        const sidecar = JSON.parse(
            readFileSync(join(outDir, "originals", "100.json"), "utf-8"),
        );
        expect(sidecar.id).toBe(100);
        expect(sidecar.metadata.title).toBe("beach.jpg");

        // Collection dirs contain symlinks into ../originals.
        const beach = join(outDir, "collections", "Vacation", "beach.jpg");
        expect(lstatSync(beach).isSymbolicLink()).toBe(true);
        expect(readlinkSync(beach)).toContain("originals");
        expect(readFileSync(beach).length).toBe(3000);

        // Per-collection metadata JSON.
        const vacation = JSON.parse(
            readFileSync(join(outDir, "collections", "Vacation.json"), "utf-8"),
        );
        expect(vacation.name).toBe("Vacation");
        expect(vacation.files.length).toBe(2);
        expect(vacation.files[0].metadata.title).toBeDefined();

        // A clean run leaves no failure ledger behind.
        expect(existsSync(join(outDir, "failures.json"))).toBe(false);
        lib.close();
    });

    it("is an idempotent no-op when every original is already present", async () => {
        const source = stubSource();
        const lib = await openLibrary(source);
        const outDir = join(root, "backup");

        const first = await lib.backup({ downloadDirectory: outDir });
        expect(first.downloaded).toBe(3);
        const callsAfterFirst = source.originalCalls;

        const second = await lib.backup({ downloadDirectory: outDir });
        expect(second.downloaded).toBe(0);
        expect(second.skipped).toBe(3);
        expect(second.failed).toBe(0);
        // A present original is neither fetched nor copied again.
        expect(source.originalCalls).toBe(callsAfterFirst);
        lib.close();
    });

    it("continues past a download failure and records it in failures.json", async () => {
        const source = stubSource();
        source.failID = 101;
        const lib = await openLibrary(source);
        const outDir = join(root, "backup");

        const result = await lib.backup({ downloadDirectory: outDir });

        expect(result.totalFiles).toBe(3);
        expect(result.downloaded).toBe(2);
        expect(result.failed).toBe(1);
        expect(result.errors.length).toBe(1);
        expect(result.errors[0]!.fileID).toBe(101);
        expect(result.errors[0]!.title).toBe("sunset.jpg");

        // The two good files are on disk; the failed one is not.
        expect(existsSync(join(outDir, "originals", "100.jpg"))).toBe(true);
        expect(existsSync(join(outDir, "originals", "200.png"))).toBe(true);
        expect(existsSync(join(outDir, "originals", "101.jpg"))).toBe(false);
        expect(
            existsSync(join(outDir, "collections", "Vacation", "sunset.jpg")),
        ).toBe(false);

        // Durable ledger with classification, attempts, last-tried.
        const ledger = readLedger(outDir);
        const entry = ledger.files["101"]!;
        expect(entry.attempts).toBe(1);
        expect(entry.classification).toBeDefined();
        expect(typeof entry.lastTriedAt).toBe("number");
        lib.close();
    });

    it("increments the attempt count across runs and clears the ledger once resolved", async () => {
        const source = stubSource();
        source.failID = 101;
        const lib = await openLibrary(source);
        const outDir = join(root, "backup");

        const r1 = await lib.backup({ downloadDirectory: outDir });
        expect(r1.failed).toBe(1);
        expect(readLedger(outDir).files["101"]!.attempts).toBe(1);

        // Second run: the two good files are present, only 101 is retried.
        const r2 = await lib.backup({ downloadDirectory: outDir });
        expect(r2.failed).toBe(1);
        expect(r2.skipped).toBe(2);
        expect(readLedger(outDir).files["101"]!.attempts).toBe(2);

        // Resume with a healthy source: 101 downloads, the rest are skipped.
        source.failID = undefined;
        const r3 = await lib.backup({ downloadDirectory: outDir });
        expect(r3.failed).toBe(0);
        expect(r3.skipped).toBe(2);
        expect(existsSync(join(outDir, "originals", "101.jpg"))).toBe(true);
        // A ledger with no remaining failures is removed.
        expect(existsSync(join(outDir, "failures.json"))).toBe(false);
        lib.close();
    });

    it("does not abort when a symlink cannot be created (issue #8)", async () => {
        const source = stubSource();
        const lib = await openLibrary(source);
        const outDir = join(root, "backup");

        // Occupy beach.jpg's symlink path with a directory so symlink creation
        // fails for that one file.
        mkdirSync(join(outDir, "collections", "Vacation", "beach.jpg"), {
            recursive: true,
        });

        const result = await lib.backup({ downloadDirectory: outDir });

        // Every original still downloads despite the symlink failure.
        expect(existsSync(join(outDir, "originals", "100.jpg"))).toBe(true);
        expect(existsSync(join(outDir, "originals", "200.png"))).toBe(true);
        // The other symlinks are still built.
        expect(
            lstatSync(
                join(outDir, "collections", "Vacation", "sunset.jpg"),
            ).isSymbolicLink(),
        ).toBe(true);
        expect(
            lstatSync(
                join(outDir, "collections", "Work", "diagram.png"),
            ).isSymbolicLink(),
        ).toBe(true);

        // The symlink failure is recorded, not thrown.
        expect(result.failed).toBeGreaterThanOrEqual(1);
        const err = result.errors.find((e) => e.fileID === 100);
        expect(err).toBeDefined();
        expect(err!.collection).toBe("Vacation");
        expect(readLedger(outDir).files["100"]).toBeDefined();
        lib.close();
    });

    it("rebuilds a stale sidecar and a missing symlink on a later run", async () => {
        const source = stubSource();
        const lib = await openLibrary(source);
        const outDir = join(root, "backup");

        await lib.backup({ downloadDirectory: outDir });

        // Corrupt a sidecar and delete a symlink between runs.
        writeFileSync(join(outDir, "originals", "100.json"), "not json");
        rmSync(join(outDir, "collections", "Vacation", "beach.jpg"));

        const result = await lib.backup({ downloadDirectory: outDir });
        expect(result.failed).toBe(0);

        // The derived views are repaired from the model.
        const sidecar = JSON.parse(
            readFileSync(join(outDir, "originals", "100.json"), "utf-8"),
        );
        expect(sidecar.metadata.title).toBe("beach.jpg");
        expect(
            lstatSync(
                join(outDir, "collections", "Vacation", "beach.jpg"),
            ).isSymbolicLink(),
        ).toBe(true);
        lib.close();
    });

    it("backs up only the named albums when onlyAlbumNames is given", async () => {
        const source = stubSource();
        const lib = await openLibrary(source);
        const outDir = join(root, "backup");

        const result = await lib.backup({
            downloadDirectory: outDir,
            onlyAlbumNames: ["Work"],
        });

        expect(result.totalFiles).toBe(1);
        expect(result.downloaded).toBe(1);
        expect(existsSync(join(outDir, "originals", "200.png"))).toBe(true);
        expect(existsSync(join(outDir, "originals", "100.jpg"))).toBe(false);
        expect(existsSync(join(outDir, "collections", "Work.json"))).toBe(true);
        expect(existsSync(join(outDir, "collections", "Vacation.json"))).toBe(
            false,
        );
        lib.close();
    });

    it("prunes a ledger entry for a file no longer in the library and exits zero", async () => {
        const source = stubSource();
        const lib = await openLibrary(source);
        const outDir = join(root, "backup");

        // A prior failure for a file that has since left the library (deleted
        // from the account). This run has no way to resolve it, so it must not
        // keep the exit code non-zero forever.
        seedLedger(outDir, 999, "gone.jpg");

        const result = await lib.backup({ downloadDirectory: outDir });

        // Everything still present is backed up cleanly, and the stale entry is
        // dropped rather than counted.
        expect(result.downloaded).toBe(3);
        expect(result.failed).toBe(0);
        expect(existsSync(join(outDir, "failures.json"))).toBe(false);
        lib.close();
    });

    it("prunes an out-of-scope ledger entry on a scoped run and exits zero", async () => {
        const source = stubSource();
        const lib = await openLibrary(source);
        const outDir = join(root, "backup");

        // A prior failure for a Vacation file; this run is scoped to Work and
        // never attempts it, so it must not poison the scoped run's exit code.
        seedLedger(outDir, 100, "beach.jpg");

        const result = await lib.backup({
            downloadDirectory: outDir,
            onlyAlbumNames: ["Work"],
        });

        expect(result.totalFiles).toBe(1);
        expect(result.failed).toBe(0);
        expect(existsSync(join(outDir, "originals", "200.png"))).toBe(true);
        expect(existsSync(join(outDir, "failures.json"))).toBe(false);
        lib.close();
    });

    it("also stores thumbnails when includeThumbnails is set", async () => {
        const source = stubSource();
        const lib = await openLibrary(source);
        const outDir = join(root, "backup");

        await lib.backup({
            downloadDirectory: outDir,
            includeThumbnails: true,
        });

        expect(existsSync(join(outDir, "thumbnails", "100.jpg"))).toBe(true);
        expect(existsSync(join(outDir, "thumbnails", "200.jpg"))).toBe(true);
        lib.close();
    });
});