cersei-compression 0.1.9

//! Route a raw tool output through the right compression stage based on the
//! tool name and its input JSON.
//!
//! Every invocation emits a single `tracing::info!` event on the
//! `cersei_compression` target with before/after bytes, lines, savings
//! percent, strategy, and the matched rule / language. Subscribers can filter
//! with `RUST_LOG=cersei_compression=info`.

use crate::{ansi, code, level::CompressionLevel, toml_rules, truncate};
use serde_json::Value;

const MAX_LINES_SAFETY: usize = 600;

/// Infallible entry point. On any internal panic-free error we fall back to
/// the raw content unchanged so the agent loop never breaks.
pub fn compress_tool_output(
    tool_name: &str,
    tool_input: &Value,
    content: &str,
    level: CompressionLevel,
) -> String {
    if level.is_off() || content.is_empty() {
        return content.to_string();
    }

    let lowered = tool_name.to_ascii_lowercase();

    // strategy = short tag describing the branch we took
    // detail   = finer identifier (rule name, detected language, empty string, …)
    let (out, strategy, detail): (String, &'static str, String) = match lowered.as_str() {
        // ─── Shell-like tools → TOML rules DSL ───────────────────────────
        "bash" | "exec" | "execshell" | "shell" | "run" | "runshell" => {
            let command = tool_input
                .get("command")
                .and_then(Value::as_str)
                .unwrap_or("");
            let (out, rule) = compress_command(command, content, level);
            (out, "shell", rule)
        }

        // ─── File read → code filter ────────────────────────────────────
        "read" | "readfile" | "read_file" | "view" => {
            let path = tool_input
                .get("file_path")
                .or_else(|| tool_input.get("path"))
                .and_then(Value::as_str)
                .unwrap_or("");
            let lang = code::Language::from_path(path);
            let filtered = code::filter(content, lang, level);
            let capped = safety_cap(&filtered, level);
            (capped, "code", format!("{lang:?}"))
        }

        // ─── Structured retrieval tools pass straight through ────────────
        "grep" | "glob" | "list" | "ls" | "find" | "tree" => {
            (content.to_string(), "passthrough", String::new())
        }

        // ─── Web fetch → strip ANSI + generic TOML catch-all ─────────────
        "webfetch" | "web_fetch" | "fetch" | "http" => {
            let stripped = ansi::strip_ansi(content);
            let (out, rule) = compress_command("webfetch", &stripped, level);
            (out, "web", rule)
        }

        // ─── Anything else → minimal safety cap at Aggressive, else noop ─
        _ => {
            if matches!(level, CompressionLevel::Aggressive) {
                (safety_cap(content, level), "unknown-capped", String::new())
            } else {
                (content.to_string(), "unknown", String::new())
            }
        }
    };

    log_compression(tool_name, level, strategy, &detail, content, &out);
    out
}

/// Returns (filtered_output, matched_rule_name_or_empty).
fn compress_command(command: &str, content: &str, level: CompressionLevel) -> (String, String) {
    let stripped = ansi::strip_ansi(content);
    let (out, rule) = if let Some(filter) = toml_rules::find_matching(command.trim()) {
        (toml_rules::apply(filter, &stripped), filter.name.clone())
    } else {
        (stripped, String::new())
    };
    (safety_cap(&out, level), rule)
}

fn safety_cap(content: &str, level: CompressionLevel) -> String {
    let cap = match level {
        CompressionLevel::Off => return content.to_string(),
        CompressionLevel::Minimal => MAX_LINES_SAFETY,
        CompressionLevel::Aggressive => MAX_LINES_SAFETY / 2,
    };
    if content.lines().count() <= cap {
        content.to_string()
    } else {
        truncate::smart_truncate(content, cap)
    }
}

fn log_compression(
    tool: &str,
    level: CompressionLevel,
    strategy: &str,
    detail: &str,
    before: &str,
    after: &str,
) {
    let before_bytes = before.len();
    let after_bytes = after.len();
    let before_lines = before.lines().count();
    let after_lines = after.lines().count();
    let savings_pct = if before_bytes > 0 {
        100.0 * (before_bytes as f64 - after_bytes as f64) / before_bytes as f64
    } else {
        0.0
    };

    tracing::info!(
        target: "cersei_compression",
        tool,
        level = %level,
        strategy,
        detail,
        before_bytes,
        after_bytes,
        before_lines,
        after_lines,
        savings_pct = format!("{savings_pct:.1}"),
        "tool-output compressed"
    );
}

#[cfg(test)]
mod tests {
    use super::*;
    use serde_json::json;

    #[test]
    fn off_is_noop() {
        let raw = "\x1b[31mhello\x1b[0m";
        let out = compress_tool_output("Bash", &json!({}), raw, CompressionLevel::Off);
        assert_eq!(out, raw);
    }

    #[test]
    fn bash_strips_ansi_at_minimal() {
        let raw = "\x1b[31mfatal: not a git repo\x1b[0m";
        let out = compress_tool_output(
            "Bash",
            &json!({"command": "git status"}),
            raw,
            CompressionLevel::Minimal,
        );
        assert!(!out.contains("\x1b["));
        assert!(out.contains("fatal"));
    }

    #[test]
    fn read_preserves_json_when_data_file() {
        let raw = r#"{"a": 1, "packages": ["x/*"]}"#;
        let out = compress_tool_output(
            "Read",
            &json!({"file_path": "/x/package.json"}),
            raw,
            CompressionLevel::Aggressive,
        );
        assert!(out.contains("packages"));
        assert!(out.contains("x/*"));
    }

    #[test]
    fn read_strips_rust_comments_in_aggressive() {
        let raw = "\
// normal comment
/// doc comment
fn main() {
    let x = 1;
    println!(\"{}\", x);
}
";
        let out = compress_tool_output(
            "Read",
            &json!({"file_path": "src/main.rs"}),
            raw,
            CompressionLevel::Aggressive,
        );
        assert!(!out.contains("// normal comment"));
        assert!(out.contains("fn main"));
    }

    #[test]
    fn grep_passthrough() {
        let raw = "file.rs:1:hit\nfile.rs:2:hit2";
        let out = compress_tool_output(
            "Grep",
            &json!({"pattern": "hit"}),
            raw,
            CompressionLevel::Aggressive,
        );
        assert_eq!(out, raw);
    }
}