"""Register staged endpoint agent builds as installable Applications.

The endpoint update_app push resolves an install source from the applications
table alone - it has no knowledge of the agent version store. Without a row
there, a build can be staged and current in agentstore and still be impossible
to push, which is exactly the gap found in the fleet: no application row existed
for the agent at all.

This module bridges the two by making the UPLOAD the single source of truth.
Staging a build repackages the current agent (plus tray) and rewrites the
application row's installpath and installersha256 in the same request, so the
row cannot describe a build that is no longer current. Nothing here is
hand-maintained; an operator never edits these rows.
"""

import os

from shopdb.api import Application, application_package_location, db

from . import agentstore

# Reserved appname for the managed agent bundle. appname is unique, which is
# what makes the upsert idempotent: repeated uploads update one row rather than
# accumulating a row per build. Changing this string strands the existing row,
# so it is a constant rather than anything configurable.
AGENT_APPNAME = 'ShopDB Endpoint Agent'

AGENT_PACKAGE_FILENAME = 'shopdb-endpoint-agent.zip'

_AGENT_DESCRIPTION = (
    'Managed ShopDB endpoint agent bundle. Created and kept current '
    'automatically when an agent build is staged - do not edit by hand.'
)


def _package_path(appid):
    directory, _prefix = application_package_location()
    return os.path.join(directory, str(appid), AGENT_PACKAGE_FILENAME)


def _get_or_create_app():
    """Return the reserved agent Application row, creating it when absent.

    Does not commit: the caller commits once, after the package is written, so
    a failed write cannot leave a row advertising an installer that is not
    there.
    """
    app = Application.query.filter_by(appname=AGENT_APPNAME).first()
    if app:
        return app, False

    app = Application(
        appname=AGENT_APPNAME,
        appdescription=_AGENT_DESCRIPTION,
        # Installable so it can be pushed; hidden so a machine-managed row does
        # not surface in the software catalogue alongside real licensed apps.
        isinstallable=True,
        ishidden=True,
    )
    db.session.add(app)
    # Flush rather than commit: the row needs its appid to build the package
    # path, but the transaction stays open so the whole registration is atomic.
    db.session.flush()
    return app, True


def register_current_agent_package():
    """Repackage the current agent build and point the agent app row at it.

    Returns a dict describing what was registered, or None when there is no
    current agent build to package. Safe to call on every upload: it is an
    upsert keyed on the reserved appname, and it rewrites the package file in
    place.
    """
    payload, manifest = agentstore.build_current_package()
    if payload is None:
        return None

    app, created = _get_or_create_app()

    path = _package_path(app.appid)
    os.makedirs(os.path.dirname(path), exist_ok=True)
    # Write to a temp name and replace, so an interrupted write cannot leave a
    # truncated archive at the path the row already advertises. os.replace is
    # atomic within a filesystem.
    temppath = path + '.tmp'
    with open(temppath, 'wb') as handle:
        handle.write(payload)
    os.replace(temppath, path)

    _directory, urlprefix = application_package_location()
    app.installpath = '{}{}/{}'.format(
        urlprefix, app.appid, AGENT_PACKAGE_FILENAME)
    # The digest of the ARCHIVE, which is what the agent downloads and verifies.
    # The per-binary digests inside the manifest are for the install script to
    # check its unpacked contents, and are not interchangeable with this one.
    app.installersha256 = manifest['sha256']
    db.session.commit()

    return {
        'appid': app.appid,
        'appname': app.appname,
        'created': created,
        'installpath': app.installpath,
        'sha256': manifest['sha256'],
        'size': manifest['size'],
        'agentversion': manifest['agentversion'],
        'contents': manifest['contents'],
    }