#!/usr/bin/env python3
"""Apply the reviewed public static overlay with per-file backups and readback."""
import hashlib
import json
import os
from pathlib import Path, PurePosixPath
import shutil
import socket
import stat
import subprocess
import tempfile

STAGE = Path('/var/lib/framebridge-release-publication/20261028-r2')
ORIGIN = Path('/srv/geranas-services/framebridge-public')
MANIFEST_SHA = '6bbdcacd9745af413546074b80619590a3b0982119c4fbf5586ff9e806794289'
COMMIT = 'a52625219e5d7eeadcc0c91d1d0fd92108e6b51a'
JOURNAL = STAGE / 'ACTIVATION-RECEIPT.json'
BACKUP = STAGE / 'pre-activation-backup'

def require(value, message):
    if not value:
        raise ValueError(message)

def digest(path):
    h = hashlib.sha256()
    with path.open('rb') as stream:
        for chunk in iter(lambda: stream.read(1024 * 1024), b''):
            h.update(chunk)
    return h.hexdigest()

def path_safe(path):
    require(path.is_absolute(), 'Absolute path required')
    for parent in (path, *path.parents):
        if parent.exists() or parent.is_symlink():
            s = parent.lstat()
            require(not stat.S_ISLNK(s.st_mode), 'Symlink path rejected')
            require(s.st_uid == 0 and not s.st_mode & 0o022, 'Untrusted writable path')

def verify(path, record):
    require(path.is_file() and not path.is_symlink(), 'Expected regular public file')
    require(path.stat().st_size == record['bytes'] and digest(path) == record['sha256'],
            'Public file content mismatch: ' + str(path))

def save(state):
    temporary = JOURNAL.with_suffix('.partial')
    with temporary.open('x') as stream:
        json.dump(state, stream, sort_keys=True, indent=2)
        stream.write('\n')
        stream.flush()
        os.fsync(stream.fileno())
    temporary.replace(JOURNAL)

def priority(name):
    if name.startswith('debian/dists/') and name.endswith(('/InRelease', '/Release', '/Release.gpg')):
        return 2
    if name.startswith('debian/dists/'):
        return 1
    if name.startswith('site/'):
        return 3
    return 0

def main():
    require(os.geteuid() == 0 and socket.gethostname().lower() == 'geranas', 'GERANAS root context required')
    os.umask(0o077)
    for path in (STAGE, ORIGIN):
        path_safe(path)
    manifest_path = STAGE / 'PUBLIC-OVERLAY-MANIFEST.json'
    require(digest(manifest_path) == MANIFEST_SHA, 'Reviewed manifest changed')
    manifest = json.loads(manifest_path.read_text())
    require(manifest['source_commit'] == COMMIT and manifest['version'] == '0.3.3', 'Wrong release')
    require(len(manifest['files']) == 70, 'Unexpected overlay inventory')
    require(not JOURNAL.exists() and not BACKUP.exists(), 'Existing transaction; inspect before replay')
    entries = {}
    for name, record in manifest['files'].items():
        p = PurePosixPath(name)
        require(not p.is_absolute() and '..' not in p.parts and p.parts[0] in ('site','downloads','debian'), 'Unsafe manifest path')
        source, destination = STAGE / 'overlay-files' / name, ORIGIN / name
        path_safe(source)
        path_safe(destination)
        verify(source, record)
        entries[name] = {'new': record, 'old': None}
        if destination.exists():
            require(destination.is_file(), 'Non-file destination')
            s = destination.stat()
            entries[name]['old'] = {'bytes': s.st_size, 'sha256': digest(destination),
                                    'uid': s.st_uid, 'gid': s.st_gid, 'mode': stat.S_IMODE(s.st_mode)}
    for name, record in manifest['preserve_required'].items():
        verify(ORIGIN / name, record)
    master = subprocess.run(['systemctl','show','framebridge-web.service','--property=MainPID','--value'],
                            check=True, capture_output=True, text=True).stdout.strip()
    state = {'schema': 1, 'phase': 'PREPARED', 'source_commit': COMMIT, 'version': '0.3.3',
             'manifest_sha256': MANIFEST_SHA, 'entries': entries, 'applied': [], 'master_pid': master,
             'backup_directory': str(BACKUP), 'other_services_changed': False}
    descriptor = os.open(JOURNAL, os.O_WRONLY | os.O_CREAT | os.O_EXCL | os.O_NOFOLLOW, 0o600)
    os.close(descriptor)
    save(state)
    BACKUP.mkdir(mode=0o700)
    for name, entry in entries.items():
        if entry['old'] is not None:
            backup = BACKUP / name
            backup.parent.mkdir(parents=True, exist_ok=True, mode=0o700)
            shutil.copy2(ORIGIN / name, backup)
            verify(backup, entry['old'])
    state['phase'] = 'BACKUP_VERIFIED'
    save(state)
    for name in sorted(entries, key=lambda n:(priority(n),n)):
        source, destination = STAGE / 'overlay-files' / name, ORIGIN / name
        old = entries[name]['old']
        if old is not None:
            verify(destination, old)
        else:
            require(not destination.exists(), 'Destination created since guard')
        missing = []
        parent = destination.parent
        while not parent.exists():
            missing.append(parent)
            parent = parent.parent
        for directory in reversed(missing):
            directory.mkdir(mode=0o755)
            directory.chmod(0o755)
        fd, temporary = tempfile.mkstemp(prefix='.fb-release-', dir=destination.parent)
        try:
            with os.fdopen(fd, 'wb') as stream, source.open('rb') as inp:
                shutil.copyfileobj(inp, stream)
                stream.flush()
                os.fsync(stream.fileno())
            os.chmod(temporary, old['mode'] if old else 0o644)
            if old:
                os.chown(temporary, old['uid'], old['gid'])
            verify(Path(temporary), entries[name]['new'])
            os.replace(temporary, destination)
            state['applied'].append(name)
            state['phase'] = 'APPLYING'
            save(state)
        finally:
            if os.path.exists(temporary):
                os.unlink(temporary)
    for name, entry in entries.items():
        verify(ORIGIN / name, entry['new'])
    for name, record in manifest['preserve_required'].items():
        verify(ORIGIN / name, record)
    after = subprocess.run(['systemctl','show','framebridge-web.service','--property=MainPID','--value'],
                           check=True, capture_output=True, text=True).stdout.strip()
    require(master == after, 'Unexpected web master change')
    state.update(phase='COMPLETE', files_verified=70, dependency_sources_preserved=True,
                 web_master_preserved=True, old_release_files_removed=False)
    save(state)
    print(json.dumps({k:v for k,v in state.items() if k not in ('entries','applied')}, sort_keys=True))

if __name__ == '__main__':
    main()