#!/usr/bin/env python3
"""Independently verify B23 explicit-extent images and expectations."""

from __future__ import annotations

import argparse
import hashlib
import json
import math
from pathlib import Path
import struct


SUPER = 1024
MAGIC = 0xE0F5E1E2
FEATURE_COMPAT_SB_CHKSUM = 0x00000001
METABOX_NID_BIT = 1 << 63
BLOCK_SIZE = 4096
CRC32C_POLYNOMIAL = 0x82F63B78


class OracleError(RuntimeError):
    pass


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


def crc32c(data: bytes | bytearray) -> int:
    checksum = 0xFFFFFFFF
    for byte in data:
        checksum ^= byte
        for _ in range(8):
            checksum = (checksum >> 1) ^ (
                CRC32C_POLYNOMIAL if checksum & 1 else 0
            )
    return checksum & 0xFFFFFFFF


def u16(data: bytes, offset: int) -> int:
    return struct.unpack_from("<H", data, offset)[0]


def u32(data: bytes, offset: int) -> int:
    return struct.unpack_from("<I", data, offset)[0]


def u64(data: bytes, offset: int) -> int:
    return struct.unpack_from("<Q", data, offset)[0]


def verify_super(data: bytes) -> tuple[int, int]:
    if len(data) < SUPER + 144 or u32(data, SUPER) != MAGIC:
        raise OracleError("invalid EROFS superblock")
    block_bits = data[SUPER + 12]
    if block_bits != 12:
        raise OracleError("B23 image block size changed")
    declared_size = u32(data, SUPER + 36) << block_bits
    if declared_size > len(data):
        raise OracleError("declared image exceeds provider")
    if u32(data, SUPER + 8) & FEATURE_COMPAT_SB_CHKSUM:
        window = bytearray(data[SUPER : 1 << block_bits])
        expected = u32(window, 4)
        struct.pack_into("<I", window, 4, 0)
        if crc32c(window) != expected:
            raise OracleError("superblock checksum mismatch")
    return 1 << block_bits, declared_size


def expected_payload() -> bytes:
    return bytes((index * 37 + 11) & 0xFF for index in range(BLOCK_SIZE))


def changed_offsets(left: bytes, right: bytes) -> list[int]:
    if len(left) != len(right):
        raise OracleError("negative and baseline provider sizes differ")
    return [index for index, pair in enumerate(zip(left, right)) if pair[0] != pair[1]]


def verify_mutation(directory: Path, image: bytes, case: dict[str, object]) -> None:
    mutation = case.get("mutation")
    baseline_name = case.get("baseline")
    if mutation is None:
        if baseline_name is not None:
            raise OracleError("positive case unexpectedly names a baseline")
        return
    if not isinstance(mutation, dict) or not isinstance(baseline_name, str):
        raise OracleError("negative case lacks mutation evidence")
    baseline = (directory / baseline_name).read_bytes()
    differences = changed_offsets(image, baseline)
    start = int(mutation["offset"])
    end = start + int(mutation["size"])
    if not differences or any(offset < start or offset >= end for offset in differences):
        raise OracleError(f"mutation is not confined to {mutation['field']}")


def record_values(
    image: bytes, case: dict[str, object]
) -> tuple[list[int], list[int], list[int]]:
    record_size = int(case["record_size"])
    record_offset = int(case["record_image_offset"])
    stored_count = int(case["stored_count"])
    payload_offset = int(case["payload_offset"])
    plens: list[int] = []
    pstarts: list[int] = []
    lstarts: list[int] = []
    physical = u64(image, int(case["header_image_offset"]) + 8) if record_size == 4 else 0
    for index in range(stored_count):
        offset = record_offset + index * record_size
        if offset + record_size > len(image):
            raise OracleError("stored record exceeds provider bytes")
        plen = u32(image, offset)
        if record_size == 4:
            pstart = physical
            physical += plen & ((2 * 1024 * 1024) - 1)
            lstart = index * BLOCK_SIZE
        else:
            pstart = u32(image, offset + 4)
            if record_size >= 16:
                pstart |= u32(image, offset + 8) << 32
                lstart = u32(image, offset + 12)
                if record_size == 32:
                    lstart |= u32(image, offset + 16) << 32
            else:
                lstart = index * BLOCK_SIZE
        plens.append(plen)
        pstarts.append(pstart)
        lstarts.append(lstart)
    if any(plen != BLOCK_SIZE for plen in plens):
        raise OracleError("mapped shifted extent length changed")
    if any(pstart != payload_offset for pstart in pstarts):
        raise OracleError("mapped shifted extent physical offset changed")
    return plens, pstarts, lstarts


def verify_case(
    directory: Path,
    spec_case: dict[str, object],
    case: dict[str, object],
    chunk_size: int,
) -> dict[str, object]:
    image_path = directory / str(case["image"])
    image = image_path.read_bytes()
    block_size, declared_size = verify_super(image)
    if sha256(image) != case["image_sha256"]:
        raise OracleError(f"image hash mismatch: {image_path.name}")
    if image[int(case["payload_offset"]) : int(case["payload_offset"]) + block_size] != expected_payload():
        raise OracleError(f"payload block mismatch: {image_path.name}")
    verify_mutation(directory, image, case)

    if u64(image, int(case["target_dirent_offset"])) != int(case["target_nid"]):
        raise OracleError("target dirent NID changed")
    if case["backing"] == "metabox":
        if not int(case["target_nid"]) & METABOX_NID_BIT:
            raise OracleError("metabox target lacks bit-63 NID")
    elif int(case["target_nid"]) & METABOX_NID_BIT:
        raise OracleError("primary target unexpectedly has bit-63 NID")

    inode = int(case["inode_image_offset"])
    inode_format = u16(image, inode)
    if inode_format != 3 or u16(image, inode + 4) != 0o100444:
        raise OracleError("synthetic inode format or mode changed")
    if u64(image, inode + 8) != int(case["file_size"]):
        raise OracleError("synthetic inode size changed")
    header = int(case["header_image_offset"])
    advise = u16(image, header + 4)
    observed_record_size = 4 << ((advise >> 1) & 3)
    if not advise & 1 or observed_record_size != int(case["record_size"]):
        raise OracleError("explicit extent advise changed")
    declared_count = u32(image, header) | (u16(image, header + 6) << 32)
    if int(case["record_size"]) >= 16 and declared_count != int(case["declared_count"]):
        raise OracleError("explicit extent count changed")

    _, _, observed_lstarts = record_values(image, case)
    if observed_lstarts != case["lstarts"]:
        raise OracleError("little-endian lstart decode differs from the manifest")
    outcome = str(spec_case["outcome"])
    violations = [
        index for index in range(1, len(observed_lstarts))
        if observed_lstarts[index] <= observed_lstarts[index - 1]
    ]
    if spec_case.get("mutation") == "descending-lstart":
        if violations != [2]:
            raise OracleError("ordering negative lacks its single violation")
    elif violations:
        raise OracleError("non-ordering case has unordered logical starts")

    if outcome == "PASS":
        if int(case["expected_errno"]) != 0:
            raise OracleError("positive case has an errno")
        if int(case["record_size"]) <= 8:
            expected_calls = 1
        else:
            expected_calls = math.ceil(
                int(case["stored_count"]) * int(case["record_size"]) / chunk_size
            )
        if int(case["expected_scan_calls"]) != expected_calls:
            raise OracleError("bounded scan call count changed")
        if int(case["stored_count"]) >= 4096 and expected_calls >= int(case["stored_count"]):
            raise OracleError("large table regressed to per-record I/O")
    elif int(case["expected_errno"]) != 97:
        raise OracleError("corruption case does not use positive EINTEGRITY")

    mutation = spec_case.get("mutation")
    if mutation == "missing-tail":
        requested_end = int(case["record_logical_offset"]) + 2 * int(case["record_size"])
        if requested_end <= declared_size:
            raise OracleError("primary missing-tail request remains provider-backed")
    elif mutation == "tail-minus-one":
        if int(case["carrier_size"]) != int(case["table_end_logical"]):
            raise OracleError("metabox baseline does not end at the final record")
        if u64(image, int(case["carrier_inode_offset"]) + 8) + 1 != int(case["table_end_logical"]):
            raise OracleError("metabox tail is not exactly one byte short")
    elif mutation == "huge-count":
        if int(case["declared_count"]) <= (1 << 32):
            raise OracleError("huge-count fixture does not exercise 48-bit count decode")

    return {
        "backing": case["backing"],
        "expected_scan_calls": case["expected_scan_calls"],
        "name": spec_case["name"],
        "outcome": outcome,
        "record_size": case["record_size"],
        "stored_count": case["stored_count"],
        "target_marker": case["target_marker"],
    }


def verify(spec_path: Path, directory: Path, report_path: Path) -> None:
    spec = json.loads(spec_path.read_text(encoding="ascii"))
    manifest = json.loads((directory / "fixture-manifest.json").read_text(encoding="ascii"))
    if (
        spec.get("schema") != 1
        or spec.get("batch") != "B23"
        or spec.get("test") != "TC171-explicit-extents"
        or spec.get("candidates") != ["P15-060", "P15-085"]
    ):
        raise OracleError("B23 spec identity changed")
    if (
        manifest.get("schema") != 1
        or manifest.get("batch") != "B23"
        or manifest.get("test") != spec["test"]
        or manifest.get("chunk_size") != spec["chunk_size"]
    ):
        raise OracleError("B23 manifest identity changed")
    if spec.get("errno") != {
        "corruption": 97,
        "provider_io": "unchanged",
        "sign": "positive",
    }:
        raise OracleError("B23 errno contract changed")

    cases = manifest.get("cases")
    if not isinstance(cases, dict) or set(cases) != {
        str(case["name"]) for case in spec["cases"]
    }:
        raise OracleError("B23 case set changed")
    decoded = []
    markers = set()
    for spec_case in spec["cases"]:
        name = str(spec_case["name"])
        case = cases[name]
        if case["target_marker"] != spec_case["target_marker"]:
            raise OracleError("target marker changed")
        markers.add(str(case["target_marker"]))
        decoded.append(
            verify_case(directory, spec_case, case, int(spec["chunk_size"]))
        )
    if len(markers) != len(spec["cases"]):
        raise OracleError("target markers are not unique")
    if {int(case["record_size"]) for case in decoded} != {4, 8, 16, 32}:
        raise OracleError("record-size coverage is incomplete")
    if {str(case["backing"]) for case in decoded} != {"primary", "metabox"}:
        raise OracleError("backing coverage is incomplete")

    report = {
        "batch": "B23",
        "case_count": len(decoded),
        "cases": decoded,
        "chunk_size": spec["chunk_size"],
        "large_scan_calls": {
            str(case["name"]): case["expected_scan_calls"]
            for case in decoded if int(case["stored_count"]) >= 4096
        },
        "status": "PASS",
        "test": spec["test"],
    }
    report_path.write_text(
        json.dumps(report, ensure_ascii=True, indent=2, sort_keys=True) + "\n",
        encoding="ascii",
    )
    print(
        f"B23 independent oracle PASS cases={len(decoded)} "
        f"markers={len(markers)}"
    )


def parse_args() -> argparse.Namespace:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--spec", required=True, type=Path)
    parser.add_argument("--fixtures", required=True, type=Path)
    parser.add_argument("--report", required=True, type=Path)
    return parser.parse_args()


def main() -> None:
    args = parse_args()
    verify(args.spec, args.fixtures, args.report)


if __name__ == "__main__":
    try:
        main()
    except (OracleError, OSError, ValueError, KeyError, struct.error) as error:
        raise SystemExit(f"B23 oracle failed: {error}") from error