"""add conversation sessions table

Revision ID: add_conversation_sessions_table
Revises: add_kb_chunk_ivfflat_index
Create Date: 2026-03-11
"""

from __future__ import annotations

from alembic import op
import sqlalchemy as sa


revision = "add_conversation_sessions_table"
down_revision = "add_kb_chunk_ivfflat_index"
branch_labels = None
depends_on = None


def _table_exists(bind, table_name: str) -> bool:
    return sa.inspect(bind).has_table(table_name)


def _index_exists(bind, table_name: str, index_name: str) -> bool:
    inspector = sa.inspect(bind)
    if not inspector.has_table(table_name):
        return False
    return any(idx.get("name") == index_name for idx in inspector.get_indexes(table_name))


def _create_index_if_missing(bind, table_name: str, index_name: str, columns: list[str], *, unique: bool = False) -> None:
    if not _index_exists(bind, table_name, index_name):
        op.create_index(index_name, table_name, columns, unique=unique)


def _drop_index_if_exists(bind, table_name: str, index_name: str) -> None:
    if _index_exists(bind, table_name, index_name):
        op.drop_index(index_name, table_name=table_name)


def upgrade() -> None:
    bind = op.get_bind()
    if not _table_exists(bind, "conversation_sessions"):
        op.create_table(
            "conversation_sessions",
            sa.Column("id", sa.Integer(), primary_key=True, autoincrement=True),
            sa.Column("tenant_id", sa.BigInteger(), nullable=False, server_default="1"),
            sa.Column("sender", sa.String(length=128), nullable=False),
            sa.Column("current_project_id", sa.BigInteger(), sa.ForeignKey("projects.id"), nullable=True),
            sa.Column("last_intent", sa.String(length=64), nullable=True),
            sa.Column("last_message_text", sa.String(length=200), nullable=True),
            sa.Column("last_active_at", sa.TIMESTAMP(), nullable=False, server_default=sa.func.now()),
            sa.Column("created_at", sa.TIMESTAMP(), nullable=False, server_default=sa.func.now()),
            sa.Column("updated_at", sa.TIMESTAMP(), nullable=False, server_default=sa.func.now(), onupdate=sa.func.now()),
            sa.UniqueConstraint("tenant_id", "sender", name="uq_conversation_sessions_tenant_sender"),
        )

    _create_index_if_missing(bind, "conversation_sessions", "ix_conversation_sessions_tenant_id", ["tenant_id"])
    _create_index_if_missing(bind, "conversation_sessions", "ix_conversation_sessions_sender", ["sender"])
    _create_index_if_missing(bind, "conversation_sessions", "ix_conversation_sessions_current_project_id", ["current_project_id"])
    _create_index_if_missing(bind, "conversation_sessions", "ix_conversation_sessions_last_intent", ["last_intent"])
    _create_index_if_missing(bind, "conversation_sessions", "ix_conversation_sessions_last_active_at", ["last_active_at"])
    _create_index_if_missing(
        bind,
        "conversation_sessions",
        "ix_conversation_sessions_tenant_sender_last_active",
        ["tenant_id", "sender", "last_active_at"],
    )


def downgrade() -> None:
    bind = op.get_bind()
    if not _table_exists(bind, "conversation_sessions"):
        return

    _drop_index_if_exists(bind, "conversation_sessions", "ix_conversation_sessions_tenant_sender_last_active")
    _drop_index_if_exists(bind, "conversation_sessions", "ix_conversation_sessions_last_active_at")
    _drop_index_if_exists(bind, "conversation_sessions", "ix_conversation_sessions_last_intent")
    _drop_index_if_exists(bind, "conversation_sessions", "ix_conversation_sessions_current_project_id")
    _drop_index_if_exists(bind, "conversation_sessions", "ix_conversation_sessions_sender")
    _drop_index_if_exists(bind, "conversation_sessions", "ix_conversation_sessions_tenant_id")
    op.drop_table("conversation_sessions")