CREATE TABLE IF NOT EXISTS sessions (
    id           UUID PRIMARY KEY,
    user_id      UUID NOT NULL,
    title        VARCHAR(100) NOT NULL DEFAULT '新对话',
    config       JSONB NOT NULL DEFAULT '{}',
    created_at   TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at   TIMESTAMPTZ NOT NULL DEFAULT NOW(),

    CONSTRAINT check_title_length CHECK (char_length(title) >= 1 AND char_length(title) <= 100)
);

CREATE INDEX IF NOT EXISTS idx_sessions_user_id ON sessions (user_id);
CREATE INDEX IF NOT EXISTS idx_sessions_user_updated ON sessions (user_id, updated_at DESC);

-- 表和列注释
COMMENT ON TABLE sessions IS '会话表，存储用户的对话会话信息';
COMMENT ON COLUMN sessions.id IS '会话唯一标识符 (UUID)';
COMMENT ON COLUMN sessions.user_id IS '所属用户 ID，关联 users 表';
COMMENT ON COLUMN sessions.title IS '会话标题，默认为"新对话"，长度 1-100 字符';
COMMENT ON COLUMN sessions.config IS '会话配置 (JSONB)，包含: tts_enabled (布尔), detail_level (''low''/''high''), language (语言代码), scenario (情景 ID)';
COMMENT ON COLUMN sessions.created_at IS '会话创建时间';
COMMENT ON COLUMN sessions.updated_at IS '会话最后更新时间';