"""chat stats

Revision ID: d4a7e2b91f38
Revises: c1f6b3d84a92
Create Date: 2026-08-06 12:30:00.000000

"""

from collections.abc import Sequence

from alembic import op

revision: str = "d4a7e2b91f38"
down_revision: str | None = "c1f6b3d84a92"
branch_labels: str | Sequence[str] | None = None
depends_on: str | Sequence[str] | None = None

_APPLY = """
CREATE FUNCTION chat_stats_apply() RETURNS trigger LANGUAGE plpgsql AS $$
BEGIN
    IF TG_OP = 'INSERT' THEN
        INSERT INTO chat_stats AS cs (account_id, chat_id, message_count,
                                      last_date, last_message_id,
                                      last_text, last_sender_id)
        VALUES (NEW.account_id, NEW.chat_id, 1,
                CASE WHEN NEW.date <= now() + interval '1 day'
                     THEN NEW.date END,
                CASE WHEN NEW.date <= now() + interval '1 day'
                     THEN NEW.message_id END,
                NEW.text, NEW.sender_id)
        ON CONFLICT (account_id, chat_id) DO UPDATE SET
            message_count = cs.message_count + 1,
            last_date = CASE WHEN chat_stats_newer(cs, EXCLUDED)
                        THEN EXCLUDED.last_date ELSE cs.last_date END,
            last_message_id = CASE WHEN chat_stats_newer(cs, EXCLUDED)
                              THEN EXCLUDED.last_message_id
                              ELSE cs.last_message_id END,
            last_text = CASE WHEN chat_stats_newer(cs, EXCLUDED)
                        THEN EXCLUDED.last_text ELSE cs.last_text END,
            last_sender_id = CASE WHEN chat_stats_newer(cs, EXCLUDED)
                             THEN EXCLUDED.last_sender_id
                             ELSE cs.last_sender_id END;
    ELSE
        UPDATE chat_stats
        SET last_text = NEW.text, last_sender_id = NEW.sender_id
        WHERE account_id = NEW.account_id
          AND chat_id = NEW.chat_id
          AND last_message_id = NEW.message_id;
    END IF;
    RETURN NULL;
END;
$$
"""

_NEWER = """
CREATE FUNCTION chat_stats_newer(current chat_stats, incoming chat_stats)
RETURNS boolean LANGUAGE sql IMMUTABLE AS $$
    SELECT incoming.last_date IS NOT NULL
       AND (current.last_date IS NULL
            OR (incoming.last_date, incoming.last_message_id)
               > (current.last_date, current.last_message_id))
$$
"""

_BACKFILL = """
INSERT INTO chat_stats (account_id, chat_id, message_count, last_date,
                        last_message_id, last_text, last_sender_id)
SELECT agg.account_id, agg.chat_id, agg.message_count,
       last.date, last.message_id, last.text, last.sender_id
FROM (
    SELECT account_id, chat_id, count(*) AS message_count
    FROM messages GROUP BY account_id, chat_id
) agg
LEFT JOIN LATERAL (
    SELECT date, message_id, text, sender_id FROM messages m
    WHERE m.account_id = agg.account_id AND m.chat_id = agg.chat_id
      AND m.date <= now() + interval '1 day'
    ORDER BY m.date DESC, m.message_id DESC LIMIT 1
) last ON true
"""


def upgrade() -> None:
    op.execute(
        "CREATE TABLE chat_stats ("
        "account_id integer NOT NULL, "
        "chat_id bigint NOT NULL, "
        "message_count bigint NOT NULL DEFAULT 0, "
        "last_date timestamptz, "
        "last_message_id bigint, "
        "last_text text, "
        "last_sender_id bigint, "
        "PRIMARY KEY (account_id, chat_id))"
    )
    op.execute(_BACKFILL)
    op.execute(
        "CREATE INDEX ix_chat_stats_recent ON chat_stats "
        "(account_id, last_date DESC, chat_id DESC)"
    )
    op.execute(_NEWER)
    op.execute(_APPLY)
    op.execute(
        "CREATE TRIGGER messages_chat_stats_insert AFTER INSERT ON messages "
        "FOR EACH ROW EXECUTE FUNCTION chat_stats_apply()"
    )
    op.execute(
        "CREATE TRIGGER messages_chat_stats_update AFTER UPDATE ON messages "
        "FOR EACH ROW WHEN (OLD.text IS DISTINCT FROM NEW.text "
        "OR OLD.sender_id IS DISTINCT FROM NEW.sender_id) "
        "EXECUTE FUNCTION chat_stats_apply()"
    )


def downgrade() -> None:
    op.execute("DROP TRIGGER IF EXISTS messages_chat_stats_update ON messages")
    op.execute("DROP TRIGGER IF EXISTS messages_chat_stats_insert ON messages")
    op.execute("DROP FUNCTION IF EXISTS chat_stats_apply()")
    op.execute("DROP FUNCTION IF EXISTS chat_stats_newer(chat_stats, chat_stats)")
    op.execute("DROP TABLE IF EXISTS chat_stats")