pub struct Message {
    pub role: Role,
    pub content: MessageContent,
    pub metadata: Option<MessageMetadata>,
}

pub enum Role {
    User,
    Assistant,
    System,
}

Message::user("Hello")
Message::assistant("Hi there!")
Message::system("You are helpful.")
message.get_text()  // -> Option<&str>

pub enum ContentBlock {
    Text { text: String },
    Image { source: ImageSource, media_type: String },
    ToolUse { id: String, name: String, input: Value },
    ToolResult { tool_use_id: String, content: String, is_error: bool },
    Thinking { thinking: String },
    Document { source: String, media_type: String },
    Opaque(Value),
}

pub struct Usage {
    pub input_tokens: u64,
    pub output_tokens: u64,
    pub cache_creation_input_tokens: u64,
    pub cache_read_input_tokens: u64,
    pub cost_usd: Option<f64>,
}

usage.merge(&other_usage);

pub enum StopReason {
    EndTurn,
    MaxTokens,
    ToolUse,
    StopSequence,
}

pub enum StreamEvent {
    MessageStart { id: String, model: String },
    ContentBlockStart { index: usize, block_type: String, id: Option<String>, name: Option<String> },
    TextDelta { index: usize, text: String },
    InputJsonDelta { index: usize, partial_json: String },
    ThinkingDelta { index: usize, thinking: String },
    ContentBlockStop { index: usize },
    MessageDelta { stop_reason: Option<StopReason>, usage: Option<Usage> },
    MessageStop,
    Ping,
    Error { message: String },
}

pub enum CerseiError {
    Auth(String),
    Provider(String),
    Tool(String),
    Memory(String),
    Http(reqwest::Error),
    Json(serde_json::Error),
    Io(std::io::Error),
    Cancelled,
    Other(anyhow::Error),
}