#!/usr/bin/env python3
"""Verify a complete MindView dataset snapshot; optionally extract its listed assets.

Standard library only. Does not access credentials, networks, or model runtimes.
Use a trusted, pinned snapshot and a destination not modified by other processes.
"""
from __future__ import annotations

import argparse
import hashlib
import json
import os
from pathlib import Path, PurePosixPath
import re
import stat
import sys
import tarfile
import tempfile

CHUNK = 8 * 1024 * 1024
SOURCES = {"scannet", "scannetpp", "arkitscenes"}
SHA = re.compile(r"[0-9a-f]{64}\Z")


class VerificationError(Exception):
    """Invalid package or unsafe extraction request."""


def relative(value: object, label: str) -> str:
    if not isinstance(value, str) or not value or "\\" in value or any(ord(char) < 32 or ord(char) == 127 for char in value):
        raise VerificationError(f"Invalid {label}: {value!r}")
    parts = value.split("/")
    if value.startswith("/") or any(p in {"", ".", ".."} for p in parts):
        raise VerificationError(f"Unsafe {label}: {value!r}")
    if ":" in parts[0] or str(PurePosixPath(value)) != value:
        raise VerificationError(f"Noncanonical {label}: {value!r}")
    return value


def digest_value(value: object, label: str) -> str:
    if not isinstance(value, str) or SHA.fullmatch(value) is None:
        raise VerificationError(f"Invalid SHA256 for {label}")
    return value


def size_value(value: object, label: str) -> int:
    if type(value) is not int or value < 0:
        raise VerificationError(f"Invalid byte size for {label}")
    return value


def check_ancestors(path: Path, *, missing_ok: bool = False) -> None:
    """Reject symlinks and non-directories in every existing parent component."""
    absolute = path.absolute()
    current = Path(absolute.anchor)
    for part in absolute.parts[1:]:
        current = current / part
        try:
            status = current.lstat()
        except FileNotFoundError:
            if missing_ok:
                return
            raise VerificationError(f"Missing directory: {current}") from None
        if stat.S_ISLNK(status.st_mode) or not stat.S_ISDIR(status.st_mode):
            raise VerificationError(f"Expected a real directory, found unsafe component: {current}")


def input_file(repo: Path, name: str) -> Path:
    path = repo / relative(name, "repository path")
    check_ancestors(path.parent)
    try:
        mode = path.lstat().st_mode
    except FileNotFoundError:
        raise VerificationError(f"Missing package file: {name}") from None
    if not stat.S_ISREG(mode):
        raise VerificationError(f"Package file is not a regular file: {name}")
    return path


def open_regular(path: Path):
    flags = os.O_RDONLY | getattr(os, "O_NOFOLLOW", 0)
    fd = os.open(path, flags)
    if not stat.S_ISREG(os.fstat(fd).st_mode):
        os.close(fd)
        raise VerificationError(f"Not a regular file: {path}")
    return os.fdopen(fd, "rb")


def hash_stream(stream) -> tuple[str, int]:
    digest = hashlib.sha256()
    total = 0
    while True:
        block = stream.read(CHUNK)
        if not block:
            return digest.hexdigest(), total
        digest.update(block)
        total += len(block)


def file_hash(path: Path) -> tuple[str, int]:
    with open_regular(path) as stream:
        return hash_stream(stream)


def checksum_inventory(repo: Path) -> dict[str, str]:
    checks = {}
    inventory = input_file(repo, "SHA256SUMS")
    with inventory.open("r", encoding="utf-8") as stream:
        for number, line in enumerate(stream, 1):
            line = line.rstrip("\n")
            match = re.fullmatch(r"([0-9a-f]{64}) [ *](.+)", line)
            if match is None:
                raise VerificationError(f"Malformed SHA256SUMS line {number}")
            expected, name = match.groups()
            relative(name, "checksum path")
            if name == "SHA256SUMS" or name in checks:
                raise VerificationError(f"Duplicate/self-referential checksum path: {name}")
            checks[name] = expected
    if not checks:
        raise VerificationError("Empty SHA256SUMS inventory")
    for name, expected in checks.items():
        actual, _ = file_hash(input_file(repo, name))
        if actual != expected:
            raise VerificationError(f"Checksum mismatch: {name}")
    return checks


def read_manifest(repo: Path, checks: dict[str, str]):
    index_name = "manifests/asset_archives.json"
    assets_name = "manifests/assets.jsonl"
    for name in (index_name, assets_name):
        if name not in checks:
            raise VerificationError(f"Missing checksum entry: {name}")
    with input_file(repo, index_name).open("r", encoding="utf-8") as stream:
        index = json.load(stream)
    if not isinstance(index, dict) or not isinstance(index.get("archives"), list):
        raise VerificationError("Archive index must contain an archives list")
    archives = {}
    members = {}
    destinations = set()
    for entry in index["archives"]:
        if not isinstance(entry, dict):
            raise VerificationError("Archive entry must be an object")
        name = relative(entry.get("path"), "archive path")
        if not name.startswith("assets/") or not name.endswith(".tar"):
            raise VerificationError(f"Expected an assets/*.tar archive: {name}")
        if name in archives:
            raise VerificationError(f"Duplicate archive: {name}")
        source = entry.get("dataset")
        if not isinstance(source, str) or source not in SOURCES:
            raise VerificationError(f"Unknown source dataset: {source!r}")
        size_value(entry.get("bytes"), name)
        digest_value(entry.get("sha256"), name)
        if checks.get(name) != entry["sha256"]:
            raise VerificationError(f"Archive hash absent/inconsistent in SHA256SUMS: {name}")
        if input_file(repo, name).stat().st_size != entry["bytes"]:
            raise VerificationError(f"Archive size mismatch: {name}")
        archives[name] = entry
        members[name] = {}
    with input_file(repo, assets_name).open("r", encoding="utf-8") as stream:
        for number, line in enumerate(stream, 1):
            try:
                row = json.loads(line)
            except json.JSONDecodeError as exc:
                raise VerificationError(f"Malformed assets.jsonl line {number}: {exc}") from None
            if not isinstance(row, dict):
                raise VerificationError(f"Asset row {number} is not an object")
            shard = relative(row.get("shard"), "asset shard")
            member = relative(row.get("member"), "TAR member")
            source_path = relative(row.get("relative_path"), "asset source path")
            if shard not in archives:
                raise VerificationError(f"Asset points to an unlisted archive: {shard}")
            if row.get("dataset") != archives[shard]["dataset"]:
                raise VerificationError(f"Dataset mismatch for {shard}:{member}")
            if member != source_path:
                raise VerificationError(f"Member/source path mismatch: {shard}:{member}")
            size_value(row.get("bytes"), member)
            digest_value(row.get("sha256"), member)
            destination = f"{row['dataset']}/{source_path}"
            if member in members[shard] or destination in destinations:
                raise VerificationError(f"Duplicate asset destination: {destination}")
            destinations.add(destination)
            members[shard][member] = row
    ordered_destinations = sorted(destinations)
    for first, second in zip(ordered_destinations, ordered_destinations[1:]):
        if second.startswith(first + "/"):
            raise VerificationError(f"Overlapping asset destinations: {first} and {second}")
    if not destinations or not archives:
        raise VerificationError("Empty asset/archive inventory")
    for name, entries in members.items():
        if not entries:
            raise VerificationError(f"Archive has no listed assets: {name}")
        declared = archives[name].get("num_assets")
        if declared is not None and declared != len(entries):
            raise VerificationError(f"Archive member count mismatch: {name}")
        declared_bytes = archives[name].get("uncompressed_bytes")
        if declared_bytes is not None and declared_bytes != sum(r["bytes"] for r in entries.values()):
            raise VerificationError(f"Archive uncompressed byte count mismatch: {name}")
    return archives, members


def checked_members(repo: Path, name: str, expected: dict):
    """Yield regular, listed members only; the caller must consume all members."""
    seen = set()
    with open_regular(input_file(repo, name)) as stream:
        with tarfile.open(fileobj=stream, mode="r:") as archive:
            for member in archive:
                relative(member.name, "TAR member")
                if not member.isfile() or member.issparse():
                    raise VerificationError(f"Non-regular/sparse TAR member: {name}:{member.name}")
                if member.name in seen or member.name not in expected:
                    raise VerificationError(f"Duplicate/unlisted TAR member: {name}:{member.name}")
                seen.add(member.name)
                row = expected[member.name]
                if member.size != row["bytes"]:
                    raise VerificationError(f"Member size mismatch: {name}:{member.name}")
                payload = archive.extractfile(member)
                if payload is None:
                    raise VerificationError(f"Cannot read TAR member: {name}:{member.name}")
                with payload:
                    yield row, payload
    if seen != set(expected):
        missing = sorted(set(expected) - seen)
        raise VerificationError(f"Missing TAR members in {name}: {missing[:3]}")


def verify_members(repo: Path, members: dict) -> None:
    for name, entries in members.items():
        for row, payload in checked_members(repo, name, entries):
            digest, length = hash_stream(payload)
            if digest != row["sha256"] or length != row["bytes"]:
                raise VerificationError(f"Member checksum mismatch: {name}:{row['member']}")


def output_file(output: Path, row: dict) -> Path:
    path = output / row["dataset"] / row["relative_path"]
    check_ancestors(path.parent, missing_ok=True)
    try:
        mode = path.lstat().st_mode
    except FileNotFoundError:
        return path
    if not stat.S_ISREG(mode):
        raise VerificationError(f"Existing output is not a regular file: {path}")
    actual, length = file_hash(path)
    if actual != row["sha256"] or length != row["bytes"]:
        raise VerificationError(f"Refusing to overwrite a conflicting output: {path}")
    return path


def extract(repo: Path, output: Path, members: dict) -> tuple[int, int]:
    # Preflight every destination before any writes; identical files are reusable.
    for entries in members.values():
        for row in entries.values():
            output_file(output, row)
    extracted = reused = 0
    for name, entries in members.items():
        for row, payload in checked_members(repo, name, entries):
            path = output_file(output, row)
            if path.exists():
                reused += 1
                # Ensure the second archive traversal still consumes payload safely.
                digest, length = hash_stream(payload)
                if digest != row["sha256"] or length != row["bytes"]:
                    raise VerificationError(f"Archive changed after verification: {name}:{row['member']}")
                continue
            path.parent.mkdir(parents=True, exist_ok=True)
            check_ancestors(path.parent)
            descriptor, temporary = tempfile.mkstemp(prefix=".mindview-", dir=path.parent)
            try:
                digest = hashlib.sha256()
                length = 0
                with os.fdopen(descriptor, "wb") as target:
                    while True:
                        block = payload.read(CHUNK)
                        if not block:
                            break
                        target.write(block)
                        digest.update(block)
                        length += len(block)
                    target.flush()
                    os.fsync(target.fileno())
                if digest.hexdigest() != row["sha256"] or length != row["bytes"]:
                    raise VerificationError(f"Archive changed after verification: {name}:{row['member']}")
                os.chmod(temporary, 0o644)
                # A hard-link install is atomic and refuses to replace an existing path.
                try:
                    os.link(temporary, path, follow_symlinks=False)
                except FileExistsError:
                    output_file(output, row)
                    reused += 1
                else:
                    extracted += 1
            finally:
                Path(temporary).unlink(missing_ok=True)
    return extracted, reused


def main(argv=None) -> int:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--repo", type=Path, default=Path(__file__).resolve().parents[1], help="Complete downloaded dataset repository")
    group = parser.add_mutually_exclusive_group(required=True)
    group.add_argument("--verify-only", action="store_true", help="Verify all package files and TAR members; write no assets")
    group.add_argument("--output", type=Path, help="Extract under OUTPUT/<source-dataset>/")
    args = parser.parse_args(argv)
    repo = Path(os.path.abspath(args.repo))
    check_ancestors(repo)
    checks = checksum_inventory(repo)
    archives, members = read_manifest(repo, checks)
    verify_members(repo, members)
    result = {"status": "pass", "checksum_files": len(checks), "archives": len(archives), "assets": sum(map(len, members.values())), "mode": "verify-only"}
    if args.output is not None:
        output = Path(os.path.abspath(args.output))
        check_ancestors(output, missing_ok=True)
        if output == repo or repo in output.parents or output in repo.parents:
            raise VerificationError("Extraction directory and package directory must not contain one another")
        created, reused = extract(repo, output, members)
        result.update(mode="verified-extraction", extracted=created, reused=reused)
    print(json.dumps(result, indent=2))
    return 0


if __name__ == "__main__":
    try:
        raise SystemExit(main())
    except (VerificationError, OSError, ValueError, tarfile.TarError) as exc:
        print(f"ERROR: {exc}", file=sys.stderr)
        raise SystemExit(1)