#!/usr/bin/env python3
"""Writes a minimal one-layer OCI Image Layout tar to the path given as argv[1].

Used by meson.build to produce a fixture for the `meson test` smoke test.
"""

import gzip
import hashlib
import io
import json
import sys
import tarfile


def sha256_hex(data: bytes) -> str:
    return hashlib.sha256(data).hexdigest()


def add_bytes(tar: tarfile.TarFile, name: str, data: bytes) -> None:
    info = tarfile.TarInfo(name=name)
    info.size = len(data)
    tar.addfile(info, io.BytesIO(data))


def main() -> None:
    out_path = sys.argv[1]

    # Uncompressed layer content: a tiny tar with a single file.
    layer_tar_buf = io.BytesIO()
    with tarfile.open(fileobj=layer_tar_buf, mode="w") as layer_tar:
        add_bytes(layer_tar, "hello.txt", b"hello from slocker-lite fixture\n")
    layer_tar_bytes = layer_tar_buf.getvalue()
    diff_id = sha256_hex(layer_tar_bytes)

    layer_gz_bytes = gzip.compress(layer_tar_bytes)
    layer_digest = sha256_hex(layer_gz_bytes)

    config = {
        "architecture": "amd64",
        "os": "linux",
        "config": {},
        "rootfs": {"type": "layers", "diff_ids": [f"sha256:{diff_id}"]},
    }
    config_bytes = json.dumps(config).encode()
    config_digest = sha256_hex(config_bytes)

    manifest = {
        "schemaVersion": 2,
        "mediaType": "application/vnd.oci.image.manifest.v1+json",
        "config": {
            "mediaType": "application/vnd.oci.image.config.v1+json",
            "digest": f"sha256:{config_digest}",
            "size": len(config_bytes),
        },
        "layers": [
            {
                "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
                "digest": f"sha256:{layer_digest}",
                "size": len(layer_gz_bytes),
            }
        ],
    }
    manifest_bytes = json.dumps(manifest).encode()
    manifest_digest = sha256_hex(manifest_bytes)

    index = {
        "schemaVersion": 2,
        "manifests": [
            {
                "mediaType": "application/vnd.oci.image.manifest.v1+json",
                "digest": f"sha256:{manifest_digest}",
                "size": len(manifest_bytes),
            }
        ],
    }
    index_bytes = json.dumps(index).encode()

    oci_layout_bytes = json.dumps({"imageLayoutVersion": "1.0.0"}).encode()

    with tarfile.open(out_path, mode="w") as tar:
        add_bytes(tar, "oci-layout", oci_layout_bytes)
        add_bytes(tar, "index.json", index_bytes)
        add_bytes(tar, f"blobs/sha256/{config_digest}", config_bytes)
        add_bytes(tar, f"blobs/sha256/{manifest_digest}", manifest_bytes)
        add_bytes(tar, f"blobs/sha256/{layer_digest}", layer_gz_bytes)


if __name__ == "__main__":
    main()