regex-le 0.1.0

//! `extract_patterns` — the tool **both** servers offer.
//!
//! The npm server (`src/mcp/tools.ts`) and this one are meant to be the
//! same tool, not two similar ones: same schema, same envelope,
//! byte-identical output. `fixtures/mcp-extract-patterns.json` runs
//! against both, so changing one without the other fails a build.
//!
//! It touches no filesystem. An agent already has file-read tools;
//! duplicating them here would add a path-traversal surface for no
//! capability. The tool that needs a filesystem is `regex_le_lint`.

use serde_json::{Value, json};

use crate::detect::extract::extract_patterns;

const DEFAULT_MAX_RESULTS: usize = 500;
const MAX_MAX_RESULTS: usize = 5000;

pub(crate) fn definition() -> Value {
    json!({
        "name": "extract_patterns",
        "description": "Find every regular expression in a document — literals and RegExp \
                        constructors — with 1-based line and column and a ReDoS verdict for \
                        each. Nothing is executed: the verdict comes from the shape of the \
                        pattern text. It flags dangerous shapes and cannot prove a pattern safe.",
        "inputSchema": {
            "type": "object",
            "properties": {
                "content": { "type": "string", "description": "The document text to scan." },
                "maxResults": {
                    "type": "integer",
                    "minimum": 1,
                    "maximum": MAX_MAX_RESULTS,
                    "default": DEFAULT_MAX_RESULTS,
                    "description": format!(
                        "Cap on returned patterns (default {DEFAULT_MAX_RESULTS}). \
                         meta.truncated reports whether any were dropped."
                    ),
                },
            },
            "required": ["content"],
            "additionalProperties": false,
        },
    })
}

pub(crate) fn run(arguments: &Value) -> Result<Value, String> {
    let content = arguments
        .get("content")
        .and_then(Value::as_str)
        .ok_or_else(|| "content is required and must be a string".to_string())?;
    let max_results = read_max_results(arguments)?;

    let (patterns, diagnostics) = match extract_patterns(content) {
        Ok(patterns) => (patterns, Vec::new()),
        // A refusal, not an empty document: reporting no patterns when
        // the scan gave up would have a model conclude the file is
        // clean.
        Err(message) => (
            Vec::new(),
            vec![json!({
                "severity": "error",
                "code": "incomplete",
                "message": message,
            })],
        ),
    };

    let mut values: Vec<Value> = patterns
        .iter()
        .map(|pattern| serde_json::to_value(pattern).expect("a pattern serializes"))
        .collect();

    // The `truncated` flag matters more than the cap: a silently
    // incomplete answer is wrong in the most expensive way.
    let truncated = values.len() > max_results;
    values.truncate(max_results);

    let count = values.len();
    Ok(super::envelope(
        "extract_patterns",
        &json!({ "patterns": values }),
        count,
        &diagnostics,
        truncated,
    ))
}

/// Clamp quietly, reject loudly — the npm server's asymmetry.
fn read_max_results(arguments: &Value) -> Result<usize, String> {
    let Some(raw) = arguments.get("maxResults") else {
        return Ok(DEFAULT_MAX_RESULTS);
    };
    let invalid = "maxResults must be a positive integer".to_string();
    let value = raw.as_u64().ok_or(invalid.clone())?;
    if value < 1 {
        return Err(invalid);
    }
    Ok(usize::try_from(value)
        .unwrap_or(MAX_MAX_RESULTS)
        .min(MAX_MAX_RESULTS))
}

#[cfg(test)]
mod tests {
    use serde::Deserialize;

    use super::*;
    use crate::detect::corpus::document;

    const CASES: &str = include_str!("../../fixtures/mcp-extract-patterns.json");

    #[derive(Debug, Deserialize)]
    struct Case {
        name: String,
        file: Option<String>,
        content: Option<String>,
        arguments: Value,
        expected: Option<Value>,
        #[serde(rename = "expectedError")]
        expected_error: Option<String>,
    }

    #[test]
    fn every_shared_case_answers_identically() {
        let cases: Vec<Case> = serde_json::from_str(CASES).expect("the corpus is valid JSON");
        assert!(!cases.is_empty(), "the corpus is empty");

        for case in cases {
            let mut arguments = case.arguments.clone();
            let content = case
                .file
                .as_deref()
                .map(document)
                .map(str::to_string)
                .or(case.content);
            if let Some(content) = content {
                arguments["content"] = json!(content);
            }

            match (case.expected, case.expected_error) {
                (_, Some(expected)) => {
                    assert_eq!(
                        run(&arguments).expect_err(&case.name),
                        expected,
                        "{}",
                        case.name
                    );
                }
                (Some(expected), None) => {
                    assert_eq!(
                        run(&arguments).expect(&case.name),
                        expected,
                        "{}",
                        case.name
                    );
                }
                (None, None) => panic!("{} pins neither a result nor an error", case.name),
            }
        }
    }

    #[test]
    fn the_tool_name_is_pinned() {
        assert_eq!(definition()["name"], "extract_patterns");
    }

    /// The tester half is not here, and the schema may not imply it is.
    #[test]
    fn the_schema_offers_no_text_to_match_against() {
        let definition = definition();
        let properties = definition["inputSchema"]["properties"]
            .as_object()
            .expect("properties");
        for absent in ["text", "input", "subject", "timeout"] {
            assert!(!properties.contains_key(absent), "{absent} is offered");
        }
    }

    #[test]
    fn a_fractional_cap_is_refused() {
        let error = run(&json!({ "content": "x", "maxResults": 1.5 })).expect_err("a refusal");
        assert_eq!(error, "maxResults must be a positive integer");
    }
}