ndyg.ca
crossing the streams
1use nu_engine::CallExt;
2use nu_protocol::engine::{Call, Command, EngineState, Stack};
3use nu_protocol::{Category, PipelineData, ShellError, Signature, SyntaxShape, Type};
4
5use crate::nu::util;
6use crate::store::Store;
7
8#[derive(Clone)]
9pub struct HeadCommand {
10 store: Store,
11 context_id: scru128::Scru128Id,
12}
13
14impl HeadCommand {
15 pub fn new(store: Store, context_id: scru128::Scru128Id) -> Self {
16 Self { store, context_id }
17 }
18}
19
20impl Command for HeadCommand {
21 fn name(&self) -> &str {
22 ".head"
23 }
24
25 fn signature(&self) -> Signature {
26 Signature::build(".head")
27 .input_output_types(vec![(Type::Nothing, Type::Any)])
28 .required("topic", SyntaxShape::String, "topic to get head frame from")
29 .named(
30 "context",
31 SyntaxShape::String,
32 "context ID (defaults to system context)",
33 None,
34 )
35 .category(Category::Experimental)
36 }
37
38 fn description(&self) -> &str {
39 "get the most recent frame for a topic"
40 }
41
42 fn run(
43 &self,
44 engine_state: &EngineState,
45 stack: &mut Stack,
46 call: &Call,
47 _input: PipelineData,
48 ) -> Result<PipelineData, ShellError> {
49 let topic: String = call.req(engine_state, stack, 0)?;
50 let context_str: Option<String> = call.get_flag(engine_state, stack, "context")?;
51 let context_id = if let Some(ctx) = context_str {
52 ctx.parse::<scru128::Scru128Id>()
53 .map_err(|e| ShellError::GenericError {
54 error: "Invalid context ID".into(),
55 msg: e.to_string(),
56 span: Some(call.head),
57 help: None,
58 inner: vec![],
59 })?
60 } else {
61 self.context_id
62 };
63 let span = call.head;
64
65 if let Some(frame) = self.store.head(&topic, context_id) {
66 Ok(PipelineData::Value(
67 util::frame_to_value(&frame, span),
68 None,
69 ))
70 } else {
71 Ok(PipelineData::Empty)
72 }
73 }
74}