numbers-le 0.2.1

//! The agent surface: the same extraction over the Model Context
//! Protocol on stdio, so a model can ask for the URLs rather than be
//! handed the files and pattern-match them itself.
//!
//! Two rules the family's MCP surfaces established:
//!
//! - **An empty answer is not an error.** A document with no URLs comes
//!   back as an ordinary result carrying `ok: true` — the scan ran.
//!   Only a malformed question is a protocol error.
//! - **Refusals speak the caller's vocabulary.** An MCP caller has no
//!   command line, so no message here mentions a flag.
//!
//! Read-only by construction: nothing on this surface writes, so unlike
//! pixelactions there is no consent gate to design.

pub(crate) mod extract;

use std::io::{BufRead, Write};
use std::path::PathBuf;
use std::process::ExitCode;

use serde::Serialize;
use serde_json::value::{RawValue, to_raw_value};
use serde_json::{Value, json};

use crate::extract::{Options, resolve_format};
use crate::scan::{self, ScanOptions};
use crate::walk::{self, WalkOptions};

const PROTOCOL_VERSION: &str = "2025-06-18";

/// JSON-RPC error codes, from the spec.
const INVALID_PARAMS: i64 = -32602;
const METHOD_NOT_FOUND: i64 = -32601;

/// One JSON-RPC reply, serialized through serde rather than assembled
/// as a `Value`.
///
/// **That is not a style choice.** A number's JSON *token* is the
/// contract this server shares with the npm one, and
/// `serde_json::to_value` re-parses a raw token with `serde_json`'s own
/// float reader — the reader `json.rs` documents as not correctly
/// rounded. Routing a reply through a `Value` tree turned
/// `123456789012345680000` into a different double *and* a different
/// token, on the one surface where the two servers must agree byte for
/// byte. A `RawValue` reaches stdout intact only if nothing on the way
/// there parses it.
#[derive(Serialize)]
struct Response<'a> {
    jsonrpc: &'a str,
    id: &'a Value,
    #[serde(skip_serializing_if = "Option::is_none")]
    result: Option<&'a RawValue>,
    #[serde(skip_serializing_if = "Option::is_none")]
    error: Option<Failure>,
}

#[derive(Serialize)]
struct Failure {
    code: i64,
    message: String,
}

/// A `Value` with no raw tokens in it, wrapped for the reply.
fn raw(value: &Value) -> Box<RawValue> {
    to_raw_value(value).expect("a value serializes")
}

pub(crate) fn serve() -> ExitCode {
    let stdin = std::io::stdin();
    let mut stdout = std::io::stdout();
    for line in stdin.lock().lines() {
        let Ok(line) = line else {
            return ExitCode::from(2);
        };
        if line.trim().is_empty() {
            continue;
        }
        let Ok(request) = serde_json::from_str::<Value>(&line) else {
            // A frame that is not JSON has no id to answer against;
            // dropping it is the only honest option.
            continue;
        };
        let Some(response) = handle(&request) else {
            continue; // a notification: no reply
        };
        if writeln!(stdout, "{response}").is_err() || stdout.flush().is_err() {
            return ExitCode::from(2);
        }
    }
    ExitCode::SUCCESS
}

fn handle(request: &Value) -> Option<String> {
    let id = request.get("id").cloned();
    let method = request.get("method")?.as_str()?;
    // Notifications carry no id and get no reply.
    let id = id?;

    let result = match method {
        "initialize" => Ok(raw(&json!({
            "protocolVersion": PROTOCOL_VERSION,
            "capabilities": { "tools": {} },
            "serverInfo": { "name": "numbers-le", "version": env!("CARGO_PKG_VERSION") },
        }))),
        "tools/list" => Ok(raw(&json!({ "tools": tool_definitions() }))),
        "tools/call" => call_tool(request.get("params")),
        "ping" => Ok(raw(&json!({}))),
        other => Err((
            METHOD_NOT_FOUND,
            format!("this server does not implement {other}"),
        )),
    };

    let (ok, failed) = match result {
        Ok(result) => (Some(result), None),
        Err((code, message)) => (None, Some(Failure { code, message })),
    };
    let response = Response {
        jsonrpc: "2.0",
        id: &id,
        result: ok.as_deref(),
        error: failed,
    };
    Some(serde_json::to_string(&response).expect("a response serializes"))
}

fn tool_definitions() -> Value {
    json!([
        extract::definition(),
        {
            "name": "numbers_le_scan",
            "description": "Extract every string value from files or directories, with the \
                            file it came from and, where it can be located, its line and \
                            column. Reads the filesystem; never writes to it, and never judges \
                            a string.",
            "inputSchema": {
                "type": "object",
                "properties": {
                    "path": { "type": "string", "description": "a file or directory to read" },
                    "paths": {
                        "type": "array",
                        "items": { "type": "string" },
                        "description": "several files or directories, instead of `path`",
                    },
                    "format": {
                        "type": "string",
                        "description": "Force a format for every file instead of inferring one \
                                        per file name. An unrecognised name falls back to \
                                        quoted numbers.",
                    },
                    "dedupe": {
                        "type": "boolean",
                        "default": false,
                        "description": "Collapse repeated values to their first occurrence.",
                    },
                    "hidden": {
                        "type": "boolean",
                        "default": false,
                        "description": "Walk hidden files and directories too.",
                    },
                    "ignored": {
                        "type": "boolean",
                        "default": false,
                        "description": "Walk files excluded by .gitignore too.",
                    },
                },
            },
        },
    ])
}

/// Protocol failures (no tool named, an unknown tool) are JSON-RPC
/// errors; a tool that fails on its arguments returns a result carrying
/// `isError`, so a model reads the reason and reacts rather than
/// concluding the server is broken. Same rule as the npm server.
fn call_tool(params: Option<&Value>) -> Result<Box<RawValue>, (i64, String)> {
    let params = params.ok_or((INVALID_PARAMS, "no tool call was supplied".to_string()))?;
    let name = params
        .get("name")
        .and_then(Value::as_str)
        .ok_or((INVALID_PARAMS, "the tool call named no tool".to_string()))?;
    let arguments = params
        .get("arguments")
        .cloned()
        .unwrap_or_else(|| json!({}));

    match name {
        "extract_numbers" => Ok(match extract::run(&arguments) {
            Ok(result) => tool_result(&result),
            Err(message) => tool_failure(&message),
        }),
        "numbers_le_scan" => Ok(match scan_tool(&arguments) {
            Ok(result) => tool_result(&result),
            Err(message) => tool_failure(&message),
        }),
        other => Err((
            INVALID_PARAMS,
            format!("this server offers no tool named {other}"),
        )),
    }
}

fn scan_tool(arguments: &Value) -> Result<Envelope<Value>, String> {
    let inputs = requested_paths(arguments)?;
    let flag = |name: &str| {
        arguments
            .get(name)
            .and_then(Value::as_bool)
            .unwrap_or(false)
    };
    let walk_options = WalkOptions {
        hidden: flag("hidden"),
        respect_ignore: !flag("ignored"),
    };
    let options = ScanOptions {
        dedupe: flag("dedupe"),
        extract: Options,
        format: arguments
            .get("format")
            .and_then(Value::as_str)
            .map(|name| resolve_format(Some(name), None)),
    };

    let walked = walk::collect(&inputs, &walk_options)?;
    let scanned = walked
        .files
        .iter()
        .map(|target| scan::scan_file(target, options))
        .collect();
    // A binary file was never a text candidate, so it gets no report —
    // but the count is carried, because an agent reading `reports` as
    // the whole tree would otherwise be wrong about coverage.
    let (mut read, binary) = scan::partition(scanned);
    // Same rule as the CLI, and through the same helper: a path the walk
    // could not open is named rather than dropped or fatal.
    read.extend(
        walked
            .unreadable
            .iter()
            .map(|(path, reason)| scan::unreadable(path, reason)),
    );
    let reports: Vec<Value> = read
        .iter()
        .map(|report| serde_json::to_value(report).expect("a report serializes"))
        .collect();

    let numbers: u64 = reports
        .iter()
        .map(|report| report["summary"]["numbers"].as_u64().unwrap_or(0))
        .sum();
    let unlocated: u64 = reports
        .iter()
        .map(|report| report["summary"]["unlocated"].as_u64().unwrap_or(0))
        .sum();

    let mut diagnostics: Vec<Value> = reports
        .iter()
        .filter(|report| {
            report["diagnostics"]
                .as_array()
                .is_some_and(|list| list.iter().any(|d| d["severity"] == "error"))
        })
        .map(|report| {
            warning(
                "unreadable",
                &format!(
                    "{} could not be read, so this scan does not cover it",
                    report["file"].as_str().unwrap_or("a file")
                ),
            )
        })
        .collect();
    if unlocated > 0 {
        // A model treating these positions as a complete index needs to
        // know how much of it is not one.
        diagnostics.push(warning(
            "unlocated",
            &format!("{unlocated} values could not be located in their source"),
        ));
    }

    let count = reports.len();
    Ok(envelope(
        "numbers_le_scan",
        json!({ "reports": reports, "numbers": numbers, "binaryFiles": binary }),
        count,
        diagnostics,
        false,
    ))
}

fn requested_paths(arguments: &Value) -> Result<Vec<PathBuf>, String> {
    if let Some(path) = arguments.get("path").and_then(Value::as_str) {
        return Ok(vec![PathBuf::from(path)]);
    }
    if let Some(items) = arguments.get("paths").and_then(Value::as_array) {
        let paths: Vec<PathBuf> = items
            .iter()
            .filter_map(|item| item.as_str().map(PathBuf::from))
            .collect();
        if paths.is_empty() {
            return Err("the list of paths was empty".to_string());
        }
        return Ok(paths);
    }
    Err("no file or directory was supplied to read".to_string())
}

/// The one result shape every tool returns, matching the npm server's
/// envelope field for field: `{ ok, data, diagnostics, meta }`.
///
/// **`ok` reports whether the check ran, not whether the answer is
/// yes.** A file full of broken paths is the answer, not a failure to
/// produce one — conflating the two would have a model report a broken
/// tool when what it actually learned is that the paths are wrong.
///
/// Generic over its data so a tool whose data holds pre-rendered number
/// tokens keeps them: `Value` cannot carry a raw token, and putting one
/// in re-parses it.
#[derive(Serialize)]
pub(crate) struct Envelope<D: Serialize> {
    ok: bool,
    data: D,
    diagnostics: Vec<Value>,
    meta: Meta,
}

#[derive(Serialize)]
struct Meta {
    tool: &'static str,
    count: usize,
    truncated: bool,
}

pub(crate) fn envelope<D: Serialize>(
    tool: &'static str,
    data: D,
    count: usize,
    diagnostics: Vec<Value>,
    truncated: bool,
) -> Envelope<D> {
    let ok = !diagnostics
        .iter()
        .any(|diagnostic| diagnostic["severity"].as_str() == Some("error"));
    Envelope {
        ok,
        data,
        diagnostics,
        meta: Meta {
            tool,
            count,
            truncated,
        },
    }
}

/// An MCP tool result: the envelope as text (what a model reads) and
/// the same envelope structured. Identical to what the npm server
/// emits, so a caller diffing the two servers finds nothing.
///
/// Both halves are serialized from the envelope itself rather than from
/// a `Value` of it, so a number token survives into both.
#[derive(Serialize)]
struct ToolResult<'a, D: Serialize> {
    content: [Text; 1],
    #[serde(rename = "structuredContent")]
    structured_content: &'a Envelope<D>,
    #[serde(rename = "isError")]
    is_error: bool,
}

#[derive(Serialize)]
struct Text {
    #[serde(rename = "type")]
    kind: &'static str,
    text: String,
}

fn tool_result<D: Serialize>(envelope: &Envelope<D>) -> Box<RawValue> {
    let text = serde_json::to_string_pretty(envelope).expect("an envelope serializes");
    to_raw_value(&ToolResult {
        content: [Text { kind: "text", text }],
        structured_content: envelope,
        is_error: false,
    })
    .expect("a tool result serializes")
}

fn warning(code: &str, message: &str) -> Value {
    json!({ "severity": "warning", "code": code, "message": message })
}

/// The tool could not run on the arguments given. `isError` so a model
/// reads the message and corrects itself.
fn tool_failure(message: &str) -> Box<RawValue> {
    raw(&json!({
        "content": [{ "type": "text", "text": message }],
        "isError": true,
    }))
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::testing::TempTree;

    fn request(method: &str, params: &Value) -> Value {
        json!({ "jsonrpc": "2.0", "id": 1, "method": method, "params": params })
    }

    /// The reply, parsed. The server answers with text rather than a
    /// `Value` so a number token reaches stdout intact; a test that
    /// wants to index into it parses it back.
    fn reply(request: &Value) -> Value {
        serde_json::from_str(&handle(request).expect("a reply")).expect("a reply is JSON")
    }

    fn call(name: &str, arguments: &Value) -> Value {
        reply(&request(
            "tools/call",
            &json!({ "name": name, "arguments": arguments }),
        ))
    }

    #[test]
    fn initialize_answers_with_the_protocol_version() {
        let response = reply(&request("initialize", &json!({})));
        assert_eq!(response["result"]["protocolVersion"], PROTOCOL_VERSION);
        assert_eq!(response["result"]["serverInfo"]["name"], "numbers-le");
    }

    #[test]
    fn tools_list_offers_both_tools() {
        let response = reply(&request("tools/list", &json!({})));
        let tools = response["result"]["tools"].as_array().expect("tools");
        let names: Vec<&str> = tools.iter().filter_map(|t| t["name"].as_str()).collect();
        assert_eq!(names, ["extract_numbers", "numbers_le_scan"]);
    }

    #[test]
    fn a_notification_gets_no_reply() {
        let notification = json!({ "jsonrpc": "2.0", "method": "initialized" });
        assert!(handle(&notification).is_none());
    }

    #[test]
    fn an_unknown_method_is_a_protocol_error() {
        let response = reply(&request("does/not/exist", &json!({})));
        assert_eq!(response["error"]["code"], METHOD_NOT_FOUND);
    }

    #[test]
    fn an_unknown_tool_is_a_protocol_error() {
        let response = call("numbers_le_translate", &json!({}));
        assert_eq!(response["error"]["code"], INVALID_PARAMS);
    }

    /// A bad argument is the tool failing on what it was given, not the
    /// server breaking — so it comes back as a result carrying isError.
    #[test]
    fn a_missing_argument_is_a_tool_failure_not_a_protocol_error() {
        let response = call("numbers_le_scan", &json!({}));
        assert!(response.get("error").is_none(), "{response}");
        assert_eq!(response["result"]["isError"], true);
        assert!(
            response["result"]["content"][0]["text"]
                .as_str()
                .expect("a message")
                .contains("no file or directory")
        );
    }

    #[test]
    fn the_shared_tool_is_offered_and_answers() {
        let response = call(
            "extract_numbers",
            &json!({ "content": r#"{"a":8080}"#, "format": "json" }),
        );
        let envelope = &response["result"]["structuredContent"];
        assert_eq!(envelope["meta"]["tool"], "extract_numbers");
        assert_eq!(envelope["data"]["numbers"][0]["value"], 8080);
        assert_eq!(envelope["data"]["numbers"][0]["notation"], "decimal");
        assert_eq!(envelope["ok"], true);
        assert_eq!(response["result"]["isError"], false);
    }

    /// The shared tool reaches no filesystem — the property that lets an
    /// agent call it anywhere, and it must not regress.
    #[test]
    fn the_shared_tool_needs_no_filesystem() {
        let response = call(
            "extract_numbers",
            &json!({ "content": "const port = 8080;" }),
        );
        let envelope = &response["result"]["structuredContent"];
        assert_eq!(envelope["data"]["numbers"][0]["value"], 8080);
        assert!(envelope["data"].get("exists").is_none());
    }

    /// An unresolved format is a text scan, not a refusal.
    #[test]
    fn an_unknown_format_falls_back_rather_than_failing() {
        let response = call(
            "extract_numbers",
            &json!({ "content": "rate 0.0825", "format": "handwriting" }),
        );
        assert_eq!(response["result"]["isError"], false);
        let envelope = &response["result"]["structuredContent"];
        assert_eq!(envelope["data"]["fileType"], "unknown");
        assert_eq!(envelope["data"]["numbers"][0]["value"], 0.0825);
    }

    /// An empty answer is the scan running and finding nothing.
    #[test]
    fn a_document_with_no_numbers_is_an_ordinary_result() {
        let response = call("extract_numbers", &json!({ "content": "no digits here" }));
        let envelope = &response["result"]["structuredContent"];
        assert_eq!(response["result"]["isError"], false);
        assert_eq!(envelope["ok"], true);
        assert_eq!(envelope["meta"]["count"], 0);
    }

    #[test]
    fn the_scan_tool_reports_what_it_found() {
        let tree = TempTree::new("mcp-scan");
        tree.write("config.toml", "port = 8080\n");
        let response = call(
            "numbers_le_scan",
            &json!({ "path": tree.path().to_string_lossy() }),
        );
        let envelope = &response["result"]["structuredContent"];
        assert_eq!(response["result"]["isError"], false);
        assert_eq!(envelope["ok"], true);
        assert_eq!(envelope["data"]["numbers"], 1);
    }

    /// The scan tool carries positions — it read the file, so it knows.
    #[test]
    fn the_scan_tool_carries_positions() {
        let tree = TempTree::new("mcp-positions");
        tree.write("a.json", "{\"a\":8080}\n");
        let response = call(
            "numbers_le_scan",
            &json!({ "path": tree.path().to_string_lossy() }),
        );
        let found = &response["result"]["structuredContent"]["data"]["reports"][0]["numbers"][0];
        assert_eq!(found["value"], "8080");
        assert_eq!(found["line"], 1);
    }

    #[test]
    fn the_scan_tool_dedupes_on_request() {
        let tree = TempTree::new("mcp-dedupe");
        tree.write("a.json", "{\"a\":5,\"b\":5}\n");
        let path = tree.path().to_string_lossy().to_string();
        let kept = call("numbers_le_scan", &json!({ "path": path }));
        assert_eq!(kept["result"]["structuredContent"]["data"]["numbers"], 2);
        let deduped = call("numbers_le_scan", &json!({ "path": path, "dedupe": true }));
        assert_eq!(deduped["result"]["structuredContent"]["data"]["numbers"], 1);
    }

    /// Refusals speak the caller's vocabulary: an MCP caller has no
    /// command line, so no message may name a flag.
    #[test]
    fn no_message_mentions_a_command_line_flag() {
        let definitions = serde_json::to_string(&tool_definitions()).expect("serializes");
        assert!(!definitions.contains("--"), "{definitions}");

        let tree = TempTree::new("mcp-vocabulary");
        tree.write("a.json", "{\"a\":1}\n");
        for arguments in [
            json!({}),
            json!({ "paths": [] }),
            json!({ "path": "/no/such/place-xyz" }),
            json!({ "path": tree.path().to_string_lossy(), "magic": true }),
        ] {
            let rendered =
                serde_json::to_string(&call("numbers_le_scan", &arguments)).expect("serializes");
            assert!(!rendered.contains("--"), "{rendered}");
        }
    }

    /// Every tool returns the same envelope, so a caller writes one
    /// reader for all of them and for both servers.
    #[test]
    fn every_tool_returns_the_same_envelope_shape() {
        let tree = TempTree::new("mcp-envelope");
        tree.write("a.md", "x");
        let results = [
            call(
                "extract_numbers",
                &json!({ "content": "x", "format": "markdown" }),
            ),
            call(
                "numbers_le_scan",
                &json!({ "path": tree.path().to_string_lossy() }),
            ),
        ];
        for result in results {
            let envelope = &result["result"]["structuredContent"];
            assert!(envelope["ok"].is_boolean(), "{envelope}");
            assert!(!envelope["data"].is_null(), "{envelope}");
            assert!(envelope["diagnostics"].is_array(), "{envelope}");
            assert!(envelope["meta"]["tool"].is_string(), "{envelope}");
            assert!(envelope["meta"]["count"].is_number(), "{envelope}");
            assert!(envelope["meta"]["truncated"].is_boolean(), "{envelope}");
        }
    }
}