"""Bitstring Status List revocation (SLICE-09 TASK-09-03, REQ-NFR-VC-02).

W3C Bitstring Status List v1.0 — one bit per issued credential. bit=1 means
revoked. Persisted in SQLite `status_lists` table. Revocation latency = next
verify call (no cache — status list fetched from SQLite on every verification,
per REQ-NFR-VC-02). Minimum 131072-bit (16KB) list for herd privacy per spec.

Slot allocation is tracked separately from the revocation bitstring (the
revocation bit is 0 for a newly-issued active credential, so it cannot
distinguish "allocated-active" from "never-allocated"). A parallel allocation
bitstring (`{list_id}_alloc`) records which slots have been handed out.
"""

from __future__ import annotations

from db.store import PraxisStore

_MIN_BITS = 131072


class BitstringStatusList:
    def __init__(self, store: PraxisStore, list_id: str = "default") -> None:
        self.store = store
        self.list_id = list_id
        self._alloc_id = f"{list_id}_alloc"

    async def _load(self, list_id: str) -> bytearray:
        row = await self.store.get_status_list(list_id)
        if row is None:
            buf = bytearray(_MIN_BITS // 8)
            await self.store.upsert_status_list(list_id, bytes(buf), _MIN_BITS)
            return buf
        return bytearray(row["bitstring"])

    async def set_status(self, credential_idx: int, revoked: bool) -> None:
        buf = await self._load(self.list_id)
        byte_pos = credential_idx >> 3
        bit_pos = credential_idx & 7
        if revoked:
            buf[byte_pos] |= 1 << bit_pos
        else:
            buf[byte_pos] &= ~(1 << bit_pos)
        size = len(buf) * 8
        await self.store.upsert_status_list(self.list_id, bytes(buf), size)

    async def get_status(self, credential_idx: int) -> bool:
        buf = await self._load(self.list_id)
        byte_pos = credential_idx >> 3
        bit_pos = credential_idx & 7
        if byte_pos >= len(buf):
            return False
        return bool((buf[byte_pos] >> bit_pos) & 1)

    async def allocate_slot(self) -> int:
        buf = await self._load(self._alloc_id)
        for i in range(len(buf) * 8):
            byte_pos = i >> 3
            bit_pos = i & 7
            if not (buf[byte_pos] >> bit_pos) & 1:
                buf[byte_pos] |= 1 << bit_pos
                size = len(buf) * 8
                await self.store.upsert_status_list(
                    self._alloc_id, bytes(buf), size
                )
                return i
        new_size = (len(buf) * 8) * 2
        new_buf = bytearray(new_size // 8)
        new_buf[: len(buf)] = buf
        idx = len(buf) * 8
        new_buf[idx >> 3] |= 1 << (idx & 7)
        await self.store.upsert_status_list(self._alloc_id, bytes(new_buf), new_size)
        return idx


__all__ = ["BitstringStatusList"]