use rmcp::ErrorData;
use rmcp::model::Tool;
use serde_json::{Map, Value, json};
use crate::server::tool_trait::{McpTool, ToolContext, ToolOutput, require_resolved_path};
use crate::tool_defs::tool_def;
pub struct CtxDeltaTool;
impl McpTool for CtxDeltaTool {
fn name(&self) -> &'static str {
"ctx_delta"
}
fn tool_def(&self) -> Tool {
tool_def(
"ctx_delta",
"Incremental diff since last read — shows only changed lines after you edit.\n\
WORKFLOW: ctx_read(mode=full) -> edit -> ctx_delta (no re-read needed).\n\
Use INSTEAD of re-reading the whole file after modifications — saves 90%+ tokens\n\
on unchanged content. Path must have a prior ctx_read in this session\'s cache.\n\
For the full git diff against HEAD, use ctx_read(path, mode=diff) instead.",
json!({
"type": "object",
"properties": {
"path": { "type": "string", "description": "File path" }
},
"required": ["path"]
}),
)
}
fn handle(
&self,
args: &Map<String, Value>,
ctx: &ToolContext,
) -> Result<ToolOutput, ErrorData> {
let path = require_resolved_path(ctx, args, "path")?;
tokio::task::block_in_place(|| {
let cache_lock = ctx
.cache
.as_ref()
.ok_or_else(|| ErrorData::internal_error("cache not available", None))?;
let timeout_dur =
crate::core::io_health::adaptive_timeout(std::time::Duration::from_secs(10));
let Ok(mut cache) = tokio::runtime::Handle::current()
.block_on(tokio::time::timeout(timeout_dur, cache_lock.write()))
else {
crate::core::io_health::record_freeze();
return Err(ErrorData::internal_error(
"cache busy (ctx_delta) — retry in a moment",
None,
));
};
let output = crate::tools::ctx_delta::handle(&mut cache, &path);
let original = cache.get(&path).map_or(0, |e| e.original_tokens);
let tokens = crate::core::tokens::count_tokens(&output);
drop(cache);
if let Some(session_lock) = ctx.session.as_ref() {
let mut session = session_lock.blocking_write();
session.mark_modified(&path);
}
let saved = original.saturating_sub(tokens);
Ok(ToolOutput {
text: output,
original_tokens: original,
saved_tokens: saved,
mode: Some("delta".to_string()),
path: Some(path),
changed: false,
shell_outcome: None,
})
})
}
}