#!/usr/bin/env python3
"""Restore byte-exact original files from the transparent text transport package.

From the anc directory, run: python3 restore_files.py
Then run: python3 code/check_all.py
Full enumeration, if desired: python3 code/reproduce.py --output reproduction --workers 4

The transport README is replaced by the preserved original ancillary README.
Part files, the manifest, and this script remain available after restoration.
"""
from __future__ import annotations

import hashlib
import json
import os
from pathlib import Path, PurePosixPath

ROOT = Path(__file__).resolve().parent.parent
MANIFEST = Path(__file__).resolve().parent / 'restoration-manifest.json'


def checked_path(name: str) -> Path:
    rel = PurePosixPath(name)
    if rel.is_absolute() or not rel.parts or any(x in ('', '.', '..') for x in rel.parts):
        raise ValueError(f'Unsafe manifest path: {name!r}')
    result = ROOT.joinpath(*rel.parts)
    if not result.resolve().is_relative_to(ROOT):
        raise ValueError(f'Path leaves package: {name!r}')
    if result.is_symlink():
        raise ValueError(f'Symlink is not an original package file: {name!r}')
    return result


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


def main() -> None:
    manifest = json.loads(MANIFEST.read_text(encoding='utf-8'))
    if manifest['format_version'] != 1:
        raise ValueError('Unsupported restoration manifest version')
    originals = manifest['original_files']
    if len({row['path'] for row in originals}) != len(originals):
        raise ValueError('Duplicate original paths')
    prepared: list[tuple[Path, bytes, dict]] = []
    # Validate every source and every original digest before changing any file.
    for row in originals:
        destination = checked_path(row['path'])
        representation = row['representation']
        kind = representation['kind']
        if kind == 'empty':
            data = b''
        elif kind in ('file', 'concatenate'):
            chunks = []
            for part in representation['parts']:
                source = checked_path(part['path'])
                content = source.read_bytes()
                if len(content) != part['bytes'] or digest(content) != part['sha256']:
                    raise ValueError(f'Transport file verification failed: {part["path"]}')
                chunks.append(content)
            data = b''.join(chunks)
        else:
            raise ValueError(f'Unsupported representation: {kind!r}')
        if len(data) != row['bytes'] or digest(data) != row['sha256']:
            raise ValueError(f'Original file verification failed: {row["path"]}')
        prepared.append((destination, data, row))
    for destination, data, row in prepared:
        if destination.is_file() and digest(destination.read_bytes()) == row['sha256']:
            continue
        destination.parent.mkdir(parents=True, exist_ok=True)
        temporary = destination.with_name(destination.name + '.restore-tmp')
        if temporary.exists() or temporary.is_symlink():
            raise ValueError(f'Temporary path already exists: {temporary}')
        temporary.write_bytes(data)
        os.replace(temporary, destination)
    for destination, _, row in prepared:
        data = destination.read_bytes()
        if len(data) != row['bytes'] or digest(data) != row['sha256']:
            raise ValueError(f'Post-restoration verification failed: {row["path"]}')
    print(f'Restored and SHA-256 verified all {len(originals)} original files.')
    print('From the anc directory, run the supplied checks: python3 code/check_all.py')


if __name__ == '__main__':
    main()