"""Add the conversation table already specified by docs/02 section 8.1.

Only CREATE TABLE; existing tables and columns are unchanged.
"""
from alembic import op

revision = "20260909_session"
down_revision = "20260909_outbox_delivery"
branch_labels = None
depends_on = None

SESSION_DDL = """CREATE TABLE svc_conversation_session (
  id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
  session_id VARCHAR(64) NOT NULL,
  user_id BIGINT UNSIGNED NOT NULL,
  portal VARCHAR(32) NOT NULL,
  agent_type VARCHAR(32) NULL,
  status VARCHAR(16) NOT NULL DEFAULT 'active',
  clarification_round TINYINT UNSIGNED NOT NULL DEFAULT 0,
  message_count INT UNSIGNED NOT NULL DEFAULT 0,
  last_intent VARCHAR(32) NULL,
  config_version VARCHAR(64) NULL,
  started_at DATETIME(6) NOT NULL DEFAULT CURRENT_TIMESTAMP(6),
  last_active_at DATETIME(6) NOT NULL DEFAULT CURRENT_TIMESTAMP(6),
  ended_at DATETIME(6) NULL,
  created_at DATETIME(6) NOT NULL DEFAULT CURRENT_TIMESTAMP(6),
  updated_at DATETIME(6) NOT NULL DEFAULT CURRENT_TIMESTAMP(6)
    ON UPDATE CURRENT_TIMESTAMP(6),
  PRIMARY KEY (id),
  UNIQUE KEY uk_session_id (session_id),
  KEY idx_session_user_active (user_id, last_active_at),
  KEY idx_session_status_active (status, last_active_at),
  CONSTRAINT fk_session_user FOREIGN KEY (user_id) REFERENCES sys_user(id),
  CONSTRAINT chk_session_status
    CHECK (status IN ('active', 'ended', 'transferred', 'expired')),
  CONSTRAINT chk_session_clarification CHECK (clarification_round <= 10)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
  COMMENT='Agent会话状态与澄清轮次';"""


def upgrade() -> None:
    op.execute(SESSION_DDL)


def downgrade() -> None:
    raise RuntimeError("会话数据禁止自动删除，请使用受控的前向兼容迁移")