use crate::FunctionCallError;
use crate::ToolName;
use crate::ToolOutput;
use crate::ToolSpec;

/// Controls where a tool is exposed to the model.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum ToolExposure {
    /// Include this tool in the initial model-visible tool list.
    ///
    /// When code mode is enabled, this tool is also available as a nested
    /// code-mode tool.
    Direct,

    /// Register this tool for later discovery, but omit it from the initial
    /// model-visible tool list.
    Deferred,

    /// Include this tool in the initial model-visible tool list only.
    ///
    /// In code-mode-only sessions, this keeps the tool callable as a normal
    /// model tool while excluding it from the nested code-mode tool surface.
    DirectModelOnly,
}

impl ToolExposure {
    pub fn is_direct(self) -> bool {
        matches!(self, Self::Direct | Self::DirectModelOnly)
    }
}

/// Shared runtime contract for model-visible tools.
///
/// Implementations keep the model-visible spec tied to the executable runtime.
/// Host crates can layer routing, hooks, telemetry, or other orchestration on
/// top without reopening the spec/runtime split.
#[async_trait::async_trait]
pub trait ToolExecutor<Invocation>: Send + Sync {
    type Output: ToolOutput + 'static;

    /// The concrete tool name handled by this runtime instance.
    fn tool_name(&self) -> ToolName;

    fn spec(&self) -> Option<ToolSpec> {
        None
    }

    fn exposure(&self) -> ToolExposure {
        ToolExposure::Direct
    }

    fn supports_parallel_tool_calls(&self) -> bool {
        false
    }

    async fn handle(&self, invocation: Invocation) -> Result<Self::Output, FunctionCallError>;
}
