import logging
from collections.abc import Awaitable, Callable
from dataclasses import dataclass, field

from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.audit.log import write_audit_log
from app.db.base import begin_immediate
from app.db.models import PendingTransaction, PendingTransactionTxid, RoundConfig, UtxoEvent
from app.rounds.events import broadcaster
from app.wallet.balance import recompute_balance
from app.wallet.psbt_builder import DUST_LIMIT_SATS

logger = logging.getLogger(__name__)

# B-82 (DEP-03): confirmations a coinbase output needs before it can be spent, PLM's
# COINBASE_MATURITY (palladiumcore/src/consensus/consensus.h). A coinbase paying a user's
# address is credited no earlier than this, whatever deposit_confirmations says.
COINBASE_MATURITY = 120

# Confirmations an output created by a transaction of the platform itself — the change of
# a bet or a withdrawal, a payout — needs: the platform built it, nobody else could have
# double-spent its inputs (DEP-03).
PLATFORM_TRANSACTION_CONFIRMATIONS = 1

# Default of round_config.deposit_confirmations, used only when the config row does not
# exist yet (get_round_config creates it with the same value).
DEFAULT_DEPOSIT_CONFIRMATIONS = 6


async def find_new_credit_candidates(session: AsyncSession, user_id: int, entries: list[dict]) -> list[dict]:
    """The subset of `entries` that would actually credit something: confirmed
    (height > 0, per the Electrum convention where <= 0 means mempool) and not
    already recorded, and not dust (B-75: below DUST_LIMIT_SATS nothing is credited).

    Split out from credit_confirmed_utxos so the caller
    (electrum/listener.py:refresh_user) can corroborate each *new* outpoint
    against the other configured servers before any of it is written (B-59) —
    the mirror image of what B-29 already required before a balance may go
    *down*. Only new ones: corroborating outpoints already credited would open a
    connection to every other server on every refresh, for an answer that can no
    longer change what we hold.
    """
    existing_keys = {
        (txid, vout)
        for txid, vout in (
            await session.execute(select(UtxoEvent.txid, UtxoEvent.vout).where(UtxoEvent.user_id == user_id))
        ).all()
    }
    return [
        entry
        for entry in entries
        if entry["height"] > 0
        and entry["value"] >= DUST_LIMIT_SATS  # B-75 (DEP-01)
        and (entry["tx_hash"], entry["tx_pos"]) not in existing_keys
    ]


@dataclass
class DepositPolicy:
    """What decides how many confirmations an incoming output needs (DEP-03), read from the
    database before any network call: the configured deposit threshold and which of the
    transactions involved are the platform's own."""

    deposit_confirmations: int = DEFAULT_DEPOSIT_CONFIRMATIONS
    platform_txids: set[str] = field(default_factory=set)


async def read_deposit_policy(session: AsyncSession, txids: set[str]) -> DepositPolicy:
    """The deposit threshold and, among `txids`, the ones created by a platform transaction:
    any txid of a `pending_transactions` row, replaced RBF versions included (B-77)."""
    configured = await session.scalar(select(RoundConfig.deposit_confirmations))
    platform: set[str] = set()
    if txids:
        platform |= set(
            (await session.scalars(select(PendingTransactionTxid.txid).where(PendingTransactionTxid.txid.in_(txids))))
        )
        platform |= set(
            (await session.scalars(select(PendingTransaction.current_txid).where(PendingTransaction.current_txid.in_(txids))))
        )
    return DepositPolicy(
        deposit_confirmations=configured if configured else DEFAULT_DEPOSIT_CONFIRMATIONS, platform_txids=platform
    )


async def classify_new_deposits(
    new_entries: list[dict],
    tip_height: int,
    policy: DepositPolicy,
    is_coinbase: Callable[[str], Awaitable[bool | None]],
) -> tuple[list[tuple[dict, int]], list[dict]]:
    """Split the new, confirmed, non-dust entries of `find_new_credit_candidates` into the
    ones that may now be credited — as `(entry, required_confirmations)`, the number the
    quorum is then asked to confirm (ELC-17) — and the ones still **waiting** for
    confirmations (B-82, DEP-03, DEP-14).

    Confirmations are `tip_height - height + 1`. The threshold is 1 for an output of a
    platform transaction, 120 (`COINBASE_MATURITY`) for a coinbase output, and
    `deposit_confirmations` for anything else; a coinbase is only looked for once the plain
    threshold is met, since below it the output waits anyway. `is_coinbase` answers from the
    raw transaction (hash-checked by the caller) and may return None when it cannot tell, in
    which case the output waits and is asked again at the next refresh. No database session
    is involved: this runs between the read and the write phases, where the network is used.
    """
    candidates: list[tuple[dict, int]] = []
    waiting: list[dict] = []
    for entry in new_entries:
        confirmations = tip_height - entry["height"] + 1
        if entry["tx_hash"] in policy.platform_txids:
            required = PLATFORM_TRANSACTION_CONFIRMATIONS
        else:
            required = policy.deposit_confirmations
            if required <= confirmations < COINBASE_MATURITY:
                # Plain threshold met, maturity not: only now is it worth knowing whether
                # this is a coinbase output (which would still be immature).
                coinbase = await is_coinbase(entry["tx_hash"])
                if coinbase is None or coinbase:
                    waiting.append(entry)
                    continue
        if confirmations < required:
            waiting.append(entry)
            continue
        candidates.append((entry, required))
    return candidates, waiting


async def credit_confirmed_utxos(session: AsyncSession, user_id: int, entries: list[dict]) -> int:
    """Insert utxo_events for newly-confirmed entries from an Electrum
    `listunspent` response (idempotent on txid+vout), refresh the user's cached
    balance. Returns the number of newly-credited UTXOs.

    entries: [{"tx_hash": ..., "tx_pos": ..., "height": ..., "value": ...}, ...]
    height <= 0 means unconfirmed (mempool) per the Electrum protocol convention —
    skipped, since the spec requires 1 confirmation before crediting.

    B-88: opens with BEGIN IMMEDIATE, so the "already recorded?" read and the inserts
    it guards are one transaction — the unique (txid, vout) constraint stays the
    backstop, not the mechanism.
    """
    await begin_immediate(session)
    existing_keys = {
        (txid, vout)
        for txid, vout in (
            await session.execute(select(UtxoEvent.txid, UtxoEvent.vout).where(UtxoEvent.user_id == user_id))
        ).all()
    }

    newly_credited = 0
    for entry in entries:
        if entry["height"] <= 0:
            continue
        if entry["value"] < DUST_LIMIT_SATS:
            # B-75 (DEP-01): anyone can send dust to a public address; crediting it would
            # make every later refresh of this user's address do more work, for coins
            # that cost more to spend than they are worth.
            continue
        key = (entry["tx_hash"], entry["tx_pos"])
        if key in existing_keys:
            continue
        session.add(
            UtxoEvent(
                user_id=user_id,
                txid=entry["tx_hash"],
                vout=entry["tx_pos"],
                amount_sats=entry["value"],
                confirmed_height=entry["height"],
            )
        )
        await write_audit_log(
            session,
            "deposit_credited",
            {"txid": entry["tx_hash"], "vout": entry["tx_pos"], "amount_sats": entry["value"]},
            user_id=user_id,
        )
        newly_credited += 1

    if newly_credited:
        await session.flush()
        await recompute_balance(session, user_id)
        await session.commit()
        broadcaster.publish()  # nudges this user's dashboard to refetch its balance instantly

    return newly_credited


_EXTERNAL_SPEND_SENTINEL = "external-spend"


async def find_reinstate_candidates(session: AsyncSession, user_id: int, entries: list[dict]) -> list[dict]:
    """Outpoints flagged as spent outside the platform that this refresh's `listunspent`
    lists again, confirmed and for the amount we recorded — the *candidates* for
    reinstatement (B-83, DEP-02, DEP-08). Read-only: like a new credit (B-59) and a
    candidate external spend (B-29), a reinstatement moves a balance, so the caller
    (electrum/listener.py:refresh_user) must have the other servers corroborate each
    candidate before reinstate_reappeared_utxos writes it. An entry whose amount differs
    from our record is not a candidate: it is not the coin we wrote off."""
    flagged = (
        await session.scalars(
            select(UtxoEvent).where(UtxoEvent.user_id == user_id, UtxoEvent.spent_txid == _EXTERNAL_SPEND_SENTINEL)
        )
    ).all()
    amounts = {(row.txid, row.vout): row.amount_sats for row in flagged}
    return [
        entry
        for entry in entries
        if amounts.get((entry["tx_hash"], entry["tx_pos"])) == entry.get("value") and (entry.get("height") or 0) > 0
    ]


async def reinstate_reappeared_utxos(session: AsyncSession, user_id: int, entries: list[dict]) -> int:
    """The reverse of a mark applied by find_utxos_missing_from/
    mark_utxos_spent_externally (B-29): if an outpoint we'd previously flagged as
    spent outside the platform reappears as unspent in a later listunspent, undo
    the mark instead of leaving it permanent no matter what the chain says
    afterwards.

    Persistence only, for entries the caller has **already corroborated** against the
    other servers (B-83, ELC-25) — it used to run on the active server's word alone, so a
    hostile one could put a spent coin back into a balance. Re-checks, under the write
    lock, that each row still carries the mark before clearing it (DEP-08).
    """
    current_keys = {(entry["tx_hash"], entry["tx_pos"]) for entry in entries}

    # B-88: the lock is only worth taking when there is something to write, and this
    # runs on every refresh — so look first (plain columns), then take it and read the
    # rows again under it.
    flagged = (
        await session.execute(
            select(UtxoEvent.txid, UtxoEvent.vout).where(
                UtxoEvent.user_id == user_id, UtxoEvent.spent_txid == _EXTERNAL_SPEND_SENTINEL
            )
        )
    ).all()
    if not any((txid, vout) in current_keys for txid, vout in flagged):
        return 0
    await begin_immediate(session)

    marked_rows = (
        await session.scalars(
            select(UtxoEvent).where(
                UtxoEvent.user_id == user_id, UtxoEvent.spent_txid == _EXTERNAL_SPEND_SENTINEL
            )
        )
    ).all()

    reinstated = 0
    for row in marked_rows:
        if (row.txid, row.vout) not in current_keys:
            continue
        row.spent_txid = None
        await write_audit_log(
            session,
            "utxo_external_spend_reinstated",
            {"txid": row.txid, "vout": row.vout, "amount_sats": row.amount_sats},
            user_id=user_id,
        )
        reinstated += 1

    if reinstated:
        await session.flush()
        await recompute_balance(session, user_id)
        await session.commit()
        broadcaster.publish()

    return reinstated


async def find_utxos_missing_from(session: AsyncSession, user_id: int, entries: list[dict]) -> list[UtxoEvent]:
    """Candidates for an external spend (B-29): unspent UTXOs the DB believes this
    user still holds that are absent from `entries`, this address's current
    listunspent. Everything the platform itself spends (bets, withdrawals,
    payouts) sets spent_txid at broadcast time, before the tx ever reaches the
    chain — so an outpoint still marked unspent in our own DB that Electrum no
    longer reports as unspent was never on our own radar.

    Returning a row here is *not* proof it was actually spent — only that this one
    server's reply no longer lists it. A single broken, behind, or malicious
    server could otherwise zero a user's balance on one bad reply, which is why
    the caller (electrum/listener.py:refresh_user) must independently
    corroborate each candidate against other configured servers before treating
    it as genuine, rather than this function marking anything itself.

    An entirely empty `entries` for an address the DB believes is funded returns
    no candidates at all: it would otherwise flag every one of this user's UTXOs
    as missing from a single reply, which is a strong sign of an incomplete or
    broken response rather than N independent spends landing in the same refresh.
    """
    current_keys = {(entry["tx_hash"], entry["tx_pos"]) for entry in entries}

    unspent_rows = (
        await session.scalars(
            select(UtxoEvent).where(UtxoEvent.user_id == user_id, UtxoEvent.spent_txid.is_(None))
        )
    ).all()

    if not entries and unspent_rows:
        logger.warning(
            "listunspent for user_id=%s returned no entries at all while %s UTXO(s) are still recorded "
            "unspent — treating this as an incomplete response rather than a full external sweep",
            user_id,
            len(unspent_rows),
        )
        return []

    return [row for row in unspent_rows if (row.txid, row.vout) not in current_keys]


async def mark_utxos_spent_externally(session: AsyncSession, user_id: int, utxo_ids: list[int]) -> int:
    """Applies the external-spend sentinel to UTXOs the caller has already
    corroborated against other servers (B-29) — this function does no
    verification of its own, only persistence, so it never runs with a session
    held open across the network calls that verification needs.

    Re-checks each row is still unspent before applying the mark: something else
    may have resolved it (a legitimate platform spend, or a prior refresh) between
    when the caller read the candidate list and finished corroborating it.
    """
    await begin_immediate(session)  # B-88: that re-check and the mark are one transaction
    marked = 0
    for utxo_id in utxo_ids:
        row = await session.get(UtxoEvent, utxo_id)
        if row is None or row.spent_txid is not None:
            continue
        row.spent_txid = _EXTERNAL_SPEND_SENTINEL
        await write_audit_log(
            session,
            "utxo_spent_externally",
            {"txid": row.txid, "vout": row.vout, "amount_sats": row.amount_sats},
            user_id=user_id,
        )
        marked += 1

    if marked:
        await session.flush()
        await recompute_balance(session, user_id)
        await session.commit()
        broadcaster.publish()

    return marked