"""Construct our own manifest definition.

Usually you may want to utilize some library layer instead, some standard
program to bundle the layers with your build definition, platform, license,
author etc. Here we demonstrate how to do this by hand instead.

The process is simple. The build tool will pass a file into which it dumps the
hash-based object-identity of all layers that will be part of the bundled
image. In turn, the runner constructs an OCI compatible manifest description
for (part of) these layers. Referencing layers that were not in the file
provided will generally fail. More precisely, only layers mentioned to the
task's timeline as `export-layer` can be utilized.
"""
import json
import hashlib
import sys

with open('layers.json', 'r') as layers:
    layers = json.load(layers)
    layers = [r['layer'] for r in layers['exports']]

print(layers, file=sys.stderr)

with open('oci-config.json', 'wb') as config:
    config_data = json.dumps({
        "architecture":"amd64",
        "os":"linux",
        "rootfs": {
            "type":"layers",
            "diff_ids":[l['digest'] for l in layers],
        }
    }).encode()

    configsize = len(config_data)
    config.write(config_data)
    m = hashlib.sha256()
    m.update(config_data)
    configdigest = m.hexdigest()


with open('manifest.json', 'w') as manifest:
    json.dump({
        "schemaVersion": 2,
        "mediaType": "application/vnd.oci.image.manifest.v1+json",
        "config": {
            "mediaType": "application/vnd.oci.image.config.v1+json",
            "digest": f"sha256:{configdigest}",
            "size": configsize,
        },
        "layers": layers,
    }, manifest, indent=1)