"""Resolve a sender's email domain to the Dropbox client-folder name.

Used for routing Purchase Order and Invoice attachments under a per-client
subfolder. Unknown domains route to `_unmatched` and are surfaced in the
daily brief so ops can add a mapping without a redeploy.

The mapping table is seeded via `scripts/seed_client_domains.py` and can
be edited at runtime by inserting rows directly into the `client_domains`
table (no server restart needed — lookups happen per request).
"""
from __future__ import annotations

import logging
import re
from typing import Optional

import aiosqlite

logger = logging.getLogger(__name__)


# Conservative domain extraction. We accept lowercase letters, digits, dot,
# and hyphen — the standard DNS character set. Anything else gets rejected
# so we don't pollute the table with junk like "foo@bar baz.com".
_DOMAIN_RE = re.compile(r"^[a-z0-9.\-]+$")


def _extract_domain(sender_email: str) -> Optional[str]:
    """Return the lowercased, validated domain portion of an email, or None.

    Strips angle brackets and surrounding whitespace; accepts "<a@b.com>",
    "  a@b.com  ", "FOO@BAR.COM". Rejects malformed addresses outright.
    """
    if not sender_email:
        return None
    s = sender_email.strip().strip("<>").lower()
    if "@" not in s:
        return None
    _local, _, domain = s.rpartition("@")
    domain = domain.strip()
    if not domain or not _DOMAIN_RE.match(domain):
        return None
    return domain


async def resolve_client_name(
    conn: aiosqlite.Connection,
    sender_email: str,
) -> Optional[str]:
    """Look up the client-folder name for a sender's email domain.

    Returns the client name string if a mapping exists, otherwise None.
    Updates `last_seen_at` on the matched row so ops can see which mappings
    are actively being used.

    The conn is expected to be opened with `aiosqlite.Row` as row factory
    (the standard `get_db` context manager in app.database does this).
    """
    domain = _extract_domain(sender_email)
    if domain is None:
        logger.debug("resolve_client_name: rejected sender %r", sender_email)
        return None

    cursor = await conn.execute(
        "SELECT client_name FROM client_domains WHERE domain = ?",
        (domain,),
    )
    row = await cursor.fetchone()
    if row is None:
        return None

    # Touch last_seen_at so ops can see mapping activity.
    await conn.execute(
        "UPDATE client_domains SET last_seen_at = datetime('now') WHERE domain = ?",
        (domain,),
    )
    await conn.commit()

    return row["client_name"]


async def add_or_update_client_domain(
    conn: aiosqlite.Connection,
    domain: str,
    client_name: str,
    notes: Optional[str] = None,
) -> None:
    """Upsert a domain→client mapping.

    Used by the seed script and by any future admin tool. `domain` is
    normalized lowercase; `client_name` is stored as-is (so case can be
    preserved in the Dropbox folder name, e.g. "Westlake").
    """
    domain_norm = (domain or "").strip().lower()
    if not _DOMAIN_RE.match(domain_norm):
        raise ValueError(f"Invalid domain: {domain!r}")

    await conn.execute(
        """
        INSERT INTO client_domains (domain, client_name, notes)
        VALUES (?, ?, ?)
        ON CONFLICT(domain) DO UPDATE SET
            client_name = excluded.client_name,
            notes       = excluded.notes
        """,
        (domain_norm, client_name.strip(), notes),
    )
    await conn.commit()