"""Replica store and takeover primitives for hosted Group Chat rooms.

Non-authority gateways keep a durable local copy of the room log (``ingest_page()``: idempotent,
gap- and epoch-regression-safe) plus fenced primitives to continue the room when the authority host
dies: ``promote_replica()`` resumes locally at ``epoch + 1`` with a lineage-proving ``authority.claimed``
event; ``demote_room()`` records ``authority.lost`` when a returning stale authority is shown a newer
epoch. Storage primitives only: the caller decides *when* takeover is safe.
"""

from __future__ import annotations

import json
import sqlite3
from contextlib import closing, contextmanager
from functools import partial
from typing import Any, Iterator

from gateway.hosted_rooms import (
    MAX_ACTOR_ID_CHARS, HostedRoomError, RoomConflictError, _actor_json, _connect, _payload_json, _room_id,
    _transaction, _validate_identifier, _validate_members, _validate_room_name, local_authority_gateway_id)
from gateway.hosted_rooms_common import DbPath, bounded_int, clock, utf8_len

MAX_REPLICA_ROOMS = 256
MAX_REPLICA_EVENT_BYTES = 256 * 1024 * 1024
_SYSTEM_ACTOR = {"kind": "system", "id": "authority-control"}
_EVENT_COLUMNS = "(room_id, seq, event_id, kind, actor_json, authority_epoch, payload_json, created_at)"
_INSERT_ROOM_EVENT = f"INSERT INTO hosted_room_events {_EVENT_COLUMNS} VALUES (?, ?, ?, ?, ?, ?, ?, ?)"
_INSERT_REPLICA_EVENT = f"INSERT INTO hosted_room_replica_events {_EVENT_COLUMNS} VALUES (?, ?, ?, ?, ?, ?, ?, ?)"
_SELECT_REPLICA = "SELECT * FROM hosted_room_replicas WHERE room_id=?"


class ReplicaError(HostedRoomError): """Base class for invalid or conflicting replica operations."""
class ReplicaGapError(ReplicaError): """A page does not start at the replica's next expected sequence."""
class ReplicaEpochRegressionError(ReplicaError): """A page or demotion carries an older authority epoch than stored."""


def _initialize_replica_schema(conn: sqlite3.Connection) -> None:
    conn.execute("""CREATE TABLE IF NOT EXISTS hosted_room_replicas (
            room_id TEXT PRIMARY KEY, name TEXT NOT NULL, members_json TEXT NOT NULL,
            authority_gateway_id TEXT NOT NULL,
            authority_epoch INTEGER NOT NULL CHECK (authority_epoch >= 1),
            last_seq INTEGER NOT NULL DEFAULT 0 CHECK (last_seq >= 0),
            latest_seq INTEGER NOT NULL DEFAULT 0, event_bytes INTEGER NOT NULL DEFAULT 0,
            created_at REAL NOT NULL, updated_at REAL NOT NULL
        )""")
    conn.execute("""CREATE TABLE IF NOT EXISTS hosted_room_replica_events (
            room_id TEXT NOT NULL, seq INTEGER NOT NULL CHECK (seq >= 1), event_id TEXT NOT NULL,
            kind TEXT NOT NULL, actor_json TEXT NOT NULL, authority_epoch INTEGER,
            payload_json TEXT NOT NULL, created_at REAL NOT NULL,
            PRIMARY KEY (room_id, seq)
        )""")


@contextmanager
def _replica_transaction(db_path: DbPath) -> Iterator[sqlite3.Connection]:
    """Ensure the replica schema (own autocommit connection), then open an IMMEDIATE transaction. The DDL is
    deliberately re-run inside the transaction: that double init is the established statement order."""
    with closing(_connect(db_path)) as conn, conn:
        _initialize_replica_schema(conn)
    with _transaction(db_path, immediate=True) as conn:
        _initialize_replica_schema(conn)
        yield conn


_positive_int = partial(bounded_int, error=ReplicaError, low=1)


def _control_event(kind: str, epoch: int, payload: dict[str, Any]) -> tuple[str, str, str, str]:
    """(event_id, kind, actor_json, payload_json) of the system ``authority.<kind>`` control event for ``epoch``."""
    return f"system:authority-{kind}:{epoch}", f"authority.{kind}", _actor_json(_SYSTEM_ACTOR), _payload_json(payload)


def _append_control_event(
    conn: sqlite3.Connection, room_id: str, seq: int, epoch: int, event: tuple[str, str, str, str], now: float
) -> None:
    event_id, kind, actor_json, payload_json = event
    conn.execute(_INSERT_ROOM_EVENT, (room_id, seq, event_id, kind, actor_json, epoch, payload_json, now))


def _event_bytes(event: dict[str, Any]) -> int:
    return utf8_len(
        str(event["event_id"]), str(event["kind"]),
        json.dumps(event["actor"], ensure_ascii=False, separators=(",", ":")),
        json.dumps(event["payload"], ensure_ascii=False, separators=(",", ":")))


def _validate_page(page: Any) -> tuple[list[dict[str, Any]], dict[str, Any]]:
    if not isinstance(page, dict):
        raise ReplicaError("page must be an object")
    events, authority = page.get("events"), page.get("authority")
    if not isinstance(events, list):
        raise ReplicaError("page.events must be a list")
    if not isinstance(authority, dict):
        raise ReplicaError("page.authority is required for replication")
    gateway_id = _validate_identifier(
        authority.get("gateway_id"), label="page.authority.gateway_id", max_chars=MAX_ACTOR_ID_CHARS)
    epoch = _positive_int(authority.get("epoch"), message="page.authority.epoch must be a positive integer")
    previous_seq: int | None = None
    for event in events:
        if not isinstance(event, dict):
            raise ReplicaError("page events must be objects")
        seq = _positive_int(event.get("seq"), message="event.seq must be a positive integer")
        if previous_seq is not None and seq != previous_seq + 1:
            raise ReplicaGapError("page events must be contiguous")
        previous_seq = seq
        for field in ("event_id", "kind"):
            if not isinstance(event.get(field), str) or not event[field]:
                raise ReplicaError(f"event.{field} must be a non-empty string")
        if not isinstance(event.get("actor"), dict):
            raise ReplicaError("event.actor must be an object")
        if "payload" not in event:
            raise ReplicaError("event.payload is required")
    return events, {"gateway_id": gateway_id, "epoch": epoch}


def _replica_row_state(conn: sqlite3.Connection, room_id: str) -> tuple[sqlite3.Row | None, int, int, int]:
    """Return (row, stored_epoch, last_seq, stored_bytes); a new room is admitted only under the room cap."""
    row = conn.execute("""SELECT authority_gateway_id, authority_epoch, last_seq, latest_seq, event_bytes
             FROM hosted_room_replicas WHERE room_id=?""", (room_id,)).fetchone()
    if row is None:
        count = conn.execute("SELECT COUNT(*) FROM hosted_room_replicas").fetchone()[0]
        if int(count) >= MAX_REPLICA_ROOMS:
            raise ReplicaError("replica room capacity exhausted")
        return None, 0, 0, 0
    return row, int(row["authority_epoch"]), int(row["last_seq"]), int(row["event_bytes"])


def _store_replica(
    conn: sqlite3.Connection, *, is_new: bool, room_id: str, room_name: str, members_json: str,
    authority: dict[str, Any], new_last: int, latest_seq: int, added_bytes: int, now: float) -> None:
    """INSERT the replica row for a new room, else UPDATE it (event_bytes accumulates)."""
    values = (room_name, members_json, authority["gateway_id"], authority["epoch"], new_last, max(latest_seq, new_last))
    if is_new:
        conn.execute("""INSERT INTO hosted_room_replicas (room_id, name, members_json,
                authority_gateway_id, authority_epoch, last_seq, latest_seq, event_bytes,
                created_at, updated_at) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)""",
            (room_id, *values, added_bytes, now, now))
    else:
        conn.execute("""UPDATE hosted_room_replicas SET name=?, members_json=?, authority_gateway_id=?,
                authority_epoch=?, last_seq=?, latest_seq=?, event_bytes=event_bytes+?,
                updated_at=? WHERE room_id=?""", (*values, added_bytes, now, room_id))


def ingest_page(
    db_path: DbPath, *, room_id: Any, room_name: Any, members: Any, page: Any, now: float | None = None
) -> dict[str, Any]:
    """Persist one verbatim ``read_events()`` page idempotently; refuses seq gaps and epoch regressions."""
    room_id = _room_id(room_id)
    room_name = _validate_room_name(room_name)
    _, members_json = _validate_members(members)
    events, authority = _validate_page(page)
    now = clock(now)
    with _replica_transaction(db_path) as conn:
        row, stored_epoch, last_seq, stored_bytes = _replica_row_state(conn, room_id)
        if authority["epoch"] < stored_epoch:
            raise ReplicaEpochRegressionError("page authority epoch is older than the stored replica epoch")
        new_events = [e for e in events if int(e["seq"]) > last_seq]
        if new_events and int(new_events[0]["seq"]) != last_seq + 1:
            raise ReplicaGapError("page skips sequences the replica has not stored")
        added_bytes = 0
        for event in new_events:
            size = _event_bytes(event)
            if stored_bytes + added_bytes + size > MAX_REPLICA_EVENT_BYTES:
                raise ReplicaError("replica event storage exhausted")
            conn.execute(
                _INSERT_REPLICA_EVENT,
                (
                    room_id, int(event["seq"]), event["event_id"], event["kind"], _actor_json(event["actor"]),
                    event.get("authority_epoch"), _payload_json(event["payload"]),
                    float(event.get("created_at") or now)))
            added_bytes += size
        new_last = int(new_events[-1]["seq"]) if new_events else last_seq
        latest_seq = page.get("latest_seq")
        if isinstance(latest_seq, bool) or not isinstance(latest_seq, int):
            latest_seq = new_last
        _store_replica(
            conn, is_new=row is None, room_id=room_id, room_name=room_name, members_json=members_json,
            authority=authority, new_last=new_last, latest_seq=latest_seq, added_bytes=added_bytes, now=now)
    return {
        "room_id": room_id, "stored_seq": new_last, "ingested": len(new_events), "authority": authority,
        "caught_up": new_last >= max(latest_seq, new_last)}


def replica_state(db_path: DbPath, *, room_id: Any) -> dict[str, Any]:
    """Return the stored replica's coverage and authority lineage."""
    room_id = _room_id(room_id)
    with _replica_transaction(db_path) as conn:
        row = conn.execute(_SELECT_REPLICA, (room_id,)).fetchone()
    if row is None:
        raise ReplicaError("replica not found")
    return {
        "room_id": row["room_id"], "name": row["name"], "members": json.loads(row["members_json"]),
        "authority": {"gateway_id": row["authority_gateway_id"], "epoch": int(row["authority_epoch"])},
        "last_seq": int(row["last_seq"]), "latest_seq": int(row["latest_seq"]), "event_bytes": int(row["event_bytes"]),
        "created_at": float(row["created_at"]), "updated_at": float(row["updated_at"])}


def promote_replica(
    db_path: DbPath, *, room_id: Any, reason: Any = "authority-unreachable", now: float | None = None
) -> dict[str, Any]:
    """Continue a replicated room on THIS gateway at ``epoch + 1``.

    Copies the replica log into the authoritative store and appends a lineage-proving ``authority.claimed``
    event, so wherever the claim replicates the old epoch is stale and every fenced primitive rejects it.
    The caller decides takeover is safe; this makes it atomic and provable.
    """
    room_id = _room_id(room_id)
    if not isinstance(reason, str) or not reason or len(reason) > 200:
        raise ReplicaError("reason must be a non-empty string of at most 200 chars")
    now = clock(now)
    local_gateway = local_authority_gateway_id()
    with _replica_transaction(db_path) as conn:
        replica = conn.execute(_SELECT_REPLICA, (room_id,)).fetchone()
        if replica is None:
            raise ReplicaError("replica not found")
        if replica["authority_gateway_id"] == local_gateway:
            raise ReplicaError("this gateway already holds the room authority")
        if conn.execute("SELECT 1 FROM hosted_rooms WHERE room_id=?", (room_id,)).fetchone():
            raise RoomConflictError("room_id already exists in the local authoritative store")
        if conn.execute("SELECT 1 FROM hosted_room_retired_ids WHERE room_id=?", (room_id,)).fetchone():
            raise RoomConflictError("room_id belongs to a disbanded room")
        previous_gateway, previous_epoch = str(replica["authority_gateway_id"]), int(replica["authority_epoch"])
        target_epoch, claim_seq = previous_epoch + 1, int(replica["last_seq"]) + 1
        claim = _control_event("claimed", target_epoch, {
            "previous_gateway_id": previous_gateway, "authority_gateway_id": local_gateway,
            "authority_epoch": target_epoch, "promoted_from_replica": True, "reason": reason})
        conn.execute("""INSERT INTO hosted_rooms
               (room_id, name, members_json, authority_gateway_id, authority_epoch, next_seq, event_bytes,
                revision, created_at, updated_at, disbanded_at)
               VALUES (?, ?, ?, ?, ?, ?, ?, 1, ?, ?, NULL)""",
            (
                room_id, replica["name"], replica["members_json"], local_gateway, target_epoch, claim_seq + 1,
                int(replica["event_bytes"]) + utf8_len(*claim), now, now))
        conn.execute(
            f"""INSERT INTO hosted_room_events {_EVENT_COLUMNS}
               SELECT room_id, seq, event_id, kind, actor_json, authority_epoch, payload_json, created_at
                 FROM hosted_room_replica_events WHERE room_id=?""", (room_id,))
        _append_control_event(conn, room_id, claim_seq, target_epoch, claim, now)
        conn.execute("DELETE FROM hosted_room_replica_events WHERE room_id=?", (room_id,))
        conn.execute("DELETE FROM hosted_room_replicas WHERE room_id=?", (room_id,))
    return {
        "room_id": room_id, "authority_gateway_id": local_gateway, "authority_epoch": target_epoch,
        "previous_gateway_id": previous_gateway, "previous_epoch": previous_epoch, "claim_seq": claim_seq,
        "latest_seq": claim_seq}


def demote_room(
    db_path: DbPath, *, room_id: Any, observed_gateway_id: Any, observed_epoch: Any, now: float | None = None
) -> dict[str, Any]:
    """Fence THIS gateway's stale room authority against a proven newer epoch.

    When a returning gateway observes (replicated ``authority.claimed`` or a transport rejection) that another
    gateway owns the room at a higher epoch, append ``authority.lost`` and adopt the observed lineage so no
    local send can commit at the stale epoch. Idempotent per lineage.
    """
    room_id = _room_id(room_id)
    observed_gateway_id = _validate_identifier(
        observed_gateway_id, label="observed_gateway_id", max_chars=MAX_ACTOR_ID_CHARS)
    observed_epoch = _positive_int(observed_epoch, message="observed_epoch must be a positive integer")
    now = clock(now)
    local_gateway = local_authority_gateway_id()
    with _transaction(db_path, immediate=True) as conn:
        row = conn.execute("""SELECT authority_gateway_id, authority_epoch, next_seq
                 FROM hosted_rooms WHERE room_id=? AND disbanded_at IS NULL""", (room_id,)).fetchone()
        if row is None:
            raise ReplicaError("room not found in the local authoritative store")
        current_gateway, current_epoch = str(row["authority_gateway_id"]), int(row["authority_epoch"])
        if current_gateway == observed_gateway_id and current_epoch == observed_epoch:
            return {
                "room_id": room_id, "authority_gateway_id": current_gateway, "authority_epoch": current_epoch,
                "idempotent": True}
        if observed_epoch <= current_epoch:
            raise ReplicaEpochRegressionError("observed epoch does not supersede the stored authority")
        if current_gateway != local_gateway:
            raise ReplicaError("room is not locally authoritative; nothing to demote")
        lost = _control_event("lost", observed_epoch, {
            "previous_gateway_id": current_gateway, "authority_gateway_id": observed_gateway_id,
            "authority_epoch": observed_epoch})
        _append_control_event(conn, room_id, int(row["next_seq"]), observed_epoch, lost, now)
        conn.execute("""UPDATE hosted_rooms
                  SET authority_gateway_id=?, authority_epoch=?, next_seq=next_seq+1, revision=revision+1, updated_at=?
                WHERE room_id=?""",
            (observed_gateway_id, observed_epoch, now, room_id))
    return {
        "room_id": room_id, "authority_gateway_id": observed_gateway_id, "authority_epoch": observed_epoch,
        "idempotent": False}