#!/usr/bin/env python3
"""Generate deterministic real EROFS Bloom fixtures for B19b."""

from __future__ import annotations

import argparse
import hashlib
import json
import os
from pathlib import Path
import shutil
import struct
import subprocess


SUPER = 1024
MAGIC = 0xE0F5E1E2
CRC32C_POLY = 0x82F63B78


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


def write_json(path: Path, value: object) -> None:
    path.write_text(json.dumps(value, indent=2, sort_keys=True) + "\n", encoding="ascii")


def crc32c(data: bytes | bytearray, seed: int = 0xFFFFFFFF) -> int:
    value = seed
    for byte in data:
        value ^= byte
        for _ in range(8):
            value = (value >> 1) ^ (CRC32C_POLY if value & 1 else 0)
    return value & 0xFFFFFFFF


def load_spec(path: Path) -> dict:
    spec = json.loads(path.read_text(encoding="ascii"))
    if spec.get("schema") != 1 or spec.get("batch") != "B19b" or spec.get("candidate") != "P15-021":
        raise SystemExit("invalid B19b fixture spec identity")
    return spec


class Image:
    def __init__(self, data: bytes | bytearray):
        self.data = bytearray(data)
        if len(self.data) < SUPER + 144 or self.u32(SUPER) != MAGIC:
            raise ValueError("invalid EROFS image")
        self.block_bits = self.data[SUPER + 12]
        self.block_size = 1 << self.block_bits
        self.blocks = self.u32(SUPER + 36)
        self.limit = self.blocks << self.block_bits
        self.meta_blkaddr = self.u32(SUPER + 40)
        self.root_nid = self.u16(SUPER + 14)
        if self.limit > len(self.data):
            raise ValueError("EROFS image is truncated")

    @classmethod
    def load(cls, path: Path) -> "Image":
        return cls(path.read_bytes())

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

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

    def put_u32(self, offset: int, value: int) -> None:
        struct.pack_into("<I", self.data, offset, value)

    def inode(self, nid: int) -> dict[str, int]:
        offset = (self.meta_blkaddr << self.block_bits) + (nid << 5)
        inode_format = self.u16(offset)
        inode_size = 64 if inode_format & 1 else 32
        xattr_count = self.u16(offset + 2)
        xattr_size = 0 if xattr_count == 0 else 12 + 4 * (xattr_count - 1)
        size = struct.unpack_from("<Q" if inode_size == 64 else "<I", self.data, offset + 8)[0]
        return {
            "nid": nid,
            "offset": offset,
            "inode_size": inode_size,
            "xattr_size": xattr_size,
            "layout": (inode_format >> 1) & 7,
            "size": size,
            "start_block": self.u32(offset + 16),
        }

    def inode_data(self, inode: dict[str, int], logical: int, length: int) -> bytes:
        if inode["layout"] == 2:
            physical = inode["offset"] + inode["inode_size"] + inode["xattr_size"] + logical
        elif inode["layout"] == 0:
            physical = (inode["start_block"] << self.block_bits) + logical
        else:
            raise ValueError("fixture directory has an unsupported layout")
        if physical > self.limit or length > self.limit - physical:
            raise ValueError("fixture directory is out of bounds")
        return bytes(self.data[physical:physical + length])

    def directory_entries(self, inode: dict[str, int]) -> list[tuple[bytes, int]]:
        result = []
        logical = 0
        while logical < inode["size"]:
            length = min(self.block_size, inode["size"] - logical)
            data = self.inode_data(inode, logical, length)
            if len(data) < 12:
                raise ValueError("fixture directory block is short")
            first_name = struct.unpack_from("<H", data, 8)[0]
            if first_name == 0 or first_name % 12 or first_name > len(data):
                raise ValueError("fixture directory name offset is invalid")
            count = first_name // 12
            for index in range(count):
                entry = index * 12
                nid = struct.unpack_from("<Q", data, entry)[0]
                start = struct.unpack_from("<H", data, entry + 8)[0]
                end = struct.unpack_from("<H", data, entry + 20)[0] if index + 1 < count else len(data)
                if start > end or end > len(data):
                    raise ValueError("fixture directory name is out of bounds")
                result.append((data[start:end].split(b"\0", 1)[0], nid))
            logical += length
        return result

    def resolve(self, path: str) -> dict[str, int]:
        inode = self.inode(self.root_nid)
        for component in path.strip("/").encode().split(b"/"):
            matches = [nid for name, nid in self.directory_entries(inode) if name == component]
            if len(matches) != 1:
                raise ValueError(f"fixture path is absent or ambiguous: {path}")
            inode = self.inode(matches[0])
        return inode

    def update_checksum(self) -> None:
        compat = self.u32(SUPER + 8)
        if compat & 1:
            self.put_u32(SUPER + 4, 0)
            self.put_u32(SUPER + 4, crc32c(self.data[SUPER:self.block_size]))

    def write(self, path: Path) -> None:
        path.write_bytes(self.data)


def create_source(path: Path, spec: dict) -> None:
    path.mkdir(parents=True)
    path.chmod(0o755)
    files = [path / f"peer-{index:03d}.bin" for index in range(spec["fixture"]["peer_count"])]
    files.append(path / "target.bin")
    for entry in files:
        entry.write_bytes(b"P15-021\n")
        entry.chmod(0o644)
        for index in range(spec["fixture"]["attribute_count"]):
            name = f"user.attr{index:02d}".encode()
            prefix = f"value-{index:02d}-".encode()
            length = spec["fixture"]["attribute_value_bytes"]
            value = (prefix * (length // len(prefix) + 1))[:length]
            os.setxattr(entry, name, value)
        os.utime(entry, (0, 0), follow_symlinks=False)
    os.utime(path, (0, 0), follow_symlinks=False)


def build_valid(output: Path, source: Path, spec: dict) -> list[str]:
    mkfs = shutil.which("mkfs.erofs")
    if mkfs is None:
        raise SystemExit("mkfs.erofs is required")
    command = [
        mkfs,
        "-d0",
        "-T0",
        "--all-time",
        "--all-root",
        "--workers=1",
        "--sort=path",
        f"-U{spec['fixture']['uuid']}",
        "-x2",
        "-Exattr-name-filter,force-inode-extended",
        str(output),
        str(source),
    ]
    completed = subprocess.run(command, check=False, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    if completed.returncode != 0:
        raise SystemExit(f"mkfs.erofs failed: {completed.stdout.decode('utf-8', 'replace')}")
    return command


def mutate(valid: Path, output: Path, mutation: str, spec: dict) -> None:
    image = Image.load(valid)
    target = image.resolve(spec["fixture"]["target"])
    body = target["offset"] + target["inode_size"]
    if mutation == "unknown-filter":
        image.data[SUPER + 104] = 1
    elif mutation == "feature-off":
        image.put_u32(SUPER + 8, image.u32(SUPER + 8) & ~spec["format"]["feature_compat"])
    elif mutation == "corrupt-shared-count":
        image.data[body + 4] = 255
    elif mutation == "corrupt-shared-id":
        if image.data[body + 4] == 0:
            raise SystemExit("valid fixture has no shared IDs")
        image.put_u32(body + 12, 0xFFFFFFFF)
    else:
        raise SystemExit(f"unknown mutation: {mutation}")
    image.update_checksum()
    image.write(output)


def generate(output: Path, work: Path, spec: dict) -> None:
    if output.exists():
        raise SystemExit(f"refusing existing output: {output}")
    if work.exists():
        raise SystemExit(f"refusing existing work directory: {work}")
    output.mkdir(parents=True)
    work.mkdir(parents=True)
    source = work / "source"
    create_source(source, spec)
    valid = output / "valid.erofs"
    command = build_valid(valid, source, spec)
    for mutation in ("unknown-filter", "feature-off", "corrupt-shared-count", "corrupt-shared-id"):
        mutate(valid, output / f"{mutation}.erofs", mutation, spec)
    hashes = {path.name: sha256(path) for path in sorted(output.glob("*.erofs"))}
    if hashes != spec["fixture_sha256"]:
        raise SystemExit(f"B19b generated fixture hashes differ: {hashes}")
    fsck = shutil.which("fsck.erofs")
    if fsck is None:
        raise SystemExit("fsck.erofs is required")
    for name in ("valid.erofs", "unknown-filter.erofs", "feature-off.erofs"):
        completed = subprocess.run([fsck, str(output / name)], check=False, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
        if completed.returncode != 0:
            raise SystemExit(f"fsck.erofs rejected legal fixture {name}")
    sums = "".join(f"{digest}  {name}\n" for name, digest in sorted(hashes.items()))
    (output / "SHA256SUMS").write_text(sums, encoding="ascii")
    write_json(output / "manifest.json", {
        "command": [*command[:-2], "OUTPUT/valid.erofs", "WORK/source"],
        "fixture_sha256": hashes,
        "schema": 1,
        "status": "PASS",
    })
    print(json.dumps({"fixture_sha256": hashes, "status": "PASS"}, sort_keys=True))


def main() -> None:
    parser = argparse.ArgumentParser()
    parser.add_argument("generate", choices=("generate",))
    parser.add_argument("--output", type=Path, required=True)
    parser.add_argument("--work", type=Path, required=True)
    parser.add_argument("--spec", type=Path, required=True)
    args = parser.parse_args()
    generate(args.output, args.work, load_spec(args.spec))


if __name__ == "__main__":
    main()