ai_tokenopt 0.5.9

//! Dynamic tool selector
//!
//! Selects the most relevant tools for a given query using keyword
//! overlap scoring. Reduces the number of tool definitions sent to
//! the LLM.

use crate::types::ToolDefinition;

/// Select the most relevant tools for a query.
///
/// Scores tools by keyword overlap with the query and returns the
/// top-N most relevant. Tools explicitly mentioned by name in the
/// query are always included.
#[must_use]
pub fn select_tools(
    query: &str,
    tools: &[ToolDefinition],
    max_tools: usize,
) -> Vec<ToolDefinition> {
    if tools.len() <= max_tools {
        return tools.to_vec();
    }

    let query_lower = query.to_lowercase();
    let query_words: std::collections::HashSet<&str> = query_lower.split_whitespace().collect();

    let mut scored: Vec<(usize, f64)> = tools
        .iter()
        .enumerate()
        .map(|(i, tool)| {
            let score = score_tool(&query_lower, &query_words, tool);
            (i, score)
        })
        .collect();

    // Sort by score descending
    scored.sort_by(|a, b| b.1.partial_cmp(&a.1).unwrap_or(std::cmp::Ordering::Equal));

    // Take top-N, but always include explicitly mentioned tools
    let mut selected_indices: Vec<usize> = Vec::with_capacity(max_tools);

    // First pass: tools explicitly mentioned by name
    for (i, tool) in tools.iter().enumerate() {
        if query_lower.contains(&tool.name.to_lowercase()) && !selected_indices.contains(&i) {
            selected_indices.push(i);
        }
    }

    // Second pass: fill remaining slots from scored list
    for (i, _score) in &scored {
        if selected_indices.len() >= max_tools {
            break;
        }
        if !selected_indices.contains(i) {
            selected_indices.push(*i);
        }
    }

    // Preserve original order
    selected_indices.sort_unstable();

    selected_indices
        .into_iter()
        .map(|i| tools[i].clone())
        .collect()
}

/// Score a tool's relevance to a query.
fn score_tool(
    query_lower: &str,
    query_words: &std::collections::HashSet<&str>,
    tool: &ToolDefinition,
) -> f64 {
    let mut score = 0.0;

    // Exact name mention in query is highest signal
    if query_lower.contains(&tool.name.to_lowercase()) {
        score += 10.0;
    }

    // Word overlap with tool name (split on underscores)
    let name_words: Vec<&str> = tool.name.split('_').collect();
    for name_word in &name_words {
        if query_words.contains(name_word.to_lowercase().as_str()) {
            score += 3.0;
        }
    }

    // Word overlap with description
    let desc_lower = tool.description.to_lowercase();
    let desc_words: std::collections::HashSet<&str> = desc_lower.split_whitespace().collect();
    let overlap = query_words.intersection(&desc_words).count();
    #[allow(clippy::cast_precision_loss)]
    {
        score += overlap as f64;
    }

    // Boost for parameter name matches
    for param_name in tool.parameters.properties.keys() {
        if query_words.contains(param_name.to_lowercase().as_str()) {
            score += 2.0;
        }
    }

    score
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::types::ToolParameters;
    use std::collections::HashMap;

    fn make_tool(name: &str, desc: &str) -> ToolDefinition {
        ToolDefinition {
            name: name.to_string(),
            description: desc.to_string(),
            parameters: ToolParameters {
                schema_type: "object".to_string(),
                properties: HashMap::new(),
                required: vec![],
            },
            icon: None,
        }
    }

    #[test]
    fn returns_all_when_under_limit() {
        let tools = vec![make_tool("a", "Tool A"), make_tool("b", "Tool B")];
        let result = select_tools("hello", &tools, 5);
        assert_eq!(result.len(), 2);
    }

    #[test]
    fn selects_mentioned_tool() {
        let tools = vec![
            make_tool("get_weather", "Get weather forecast"),
            make_tool("search_web", "Search the web"),
            make_tool("get_calendar", "Get calendar events"),
        ];
        let result = select_tools("What's the weather today?", &tools, 2);
        assert!(result.iter().any(|t| t.name == "get_weather"));
    }

    #[test]
    fn respects_max_tools_limit() {
        let tools: Vec<_> = (0..10)
            .map(|i| make_tool(&format!("tool_{i}"), "desc"))
            .collect();
        let result = select_tools("query", &tools, 3);
        assert_eq!(result.len(), 3);
    }

    #[test]
    fn explicitly_named_tool_always_included() {
        let tools = vec![
            make_tool("irrelevant_1", "Not relevant"),
            make_tool("irrelevant_2", "Not relevant"),
            make_tool("search_web", "Search the web"),
            make_tool("irrelevant_3", "Not relevant"),
        ];
        let result = select_tools("use search_web to find something", &tools, 2);
        assert!(result.iter().any(|t| t.name == "search_web"));
    }
}