"""Inbox change-feed envelopes (docs/inbox-change-feed-contract.md, v1)."""
from __future__ import annotations

import re
from datetime import datetime
from typing import Any, Literal

from pydantic import BaseModel

CONTRACT = "statehub.inbox-feed.v1"
CURSOR_VERSION = "v1"

_CURSOR_RE = re.compile(r"^(v\d+):(\d+)$")


class CursorError(ValueError):
    """Malformed cursor (400)."""


class ForeignCursorError(ValueError):
    """Cursor of another contract version (409)."""


def encode_cursor(revision: int) -> str:
    return f"{CURSOR_VERSION}:{int(revision)}"


def decode_cursor(cursor: str) -> int:
    match = _CURSOR_RE.match(cursor or "")
    if match is None:
        raise CursorError(f"malformed cursor {cursor!r}")
    if match.group(1) != CURSOR_VERSION:
        raise ForeignCursorError(
            f"cursor {cursor!r} belongs to another contract version; re-snapshot"
        )
    return int(match.group(2))


class FeedChange(BaseModel):
    revision: int
    entity: Literal["message", "receipt", "tombstone"]
    key: str
    op: Literal["upsert", "delete"]
    state: dict[str, Any]


class FeedPage(BaseModel):
    contract: str = CONTRACT
    source_instance: str | None
    source_time: datetime
    high_water: str
    next_cursor: str
    has_more: bool
    compacted_before: str
    changes: list[FeedChange]


class FeedSnapshot(BaseModel):
    contract: str = CONTRACT
    source_instance: str | None
    source_time: datetime
    cursor: str
    compacted_before: str
    messages: list[dict[str, Any]]
    receipts: list[dict[str, Any]]
    tombstones: list[dict[str, Any]]
    count: int
    content_hash: str