forked from extern/nushell
139 lines
3.6 KiB
Rust
139 lines
3.6 KiB
Rust
use crate::prelude::*;
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use nu_engine::WholeStreamCommand;
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use nu_errors::ShellError;
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use nu_protocol::{Signature, SyntaxShape, Value};
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use nu_source::Tagged;
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#[derive(Deserialize)]
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struct NthArgs {
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row_number: Tagged<u64>,
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rest: Vec<Tagged<u64>>,
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skip: bool,
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}
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pub struct Nth;
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impl WholeStreamCommand for Nth {
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fn name(&self) -> &str {
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"nth"
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}
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fn signature(&self) -> Signature {
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Signature::build("nth")
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.required(
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"row number",
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SyntaxShape::Int,
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"the number of the row to return",
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)
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.rest(SyntaxShape::Any, "Optionally return more rows")
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.switch("skip", "Skip the rows instead of selecting them", Some('s'))
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}
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fn usage(&self) -> &str {
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"Return or skip only the selected rows."
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}
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fn run(&self, args: CommandArgs) -> Result<OutputStream, ShellError> {
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nth(args)
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}
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fn examples(&self) -> Vec<Example> {
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vec![
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Example {
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description: "Get the second row",
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example: "echo [first second third] | nth 1",
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result: Some(vec![Value::from("second")]),
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},
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Example {
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description: "Get the first and third rows",
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example: "echo [first second third] | nth 0 2",
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result: Some(vec![Value::from("first"), Value::from("third")]),
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},
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Example {
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description: "Skip the first and third rows",
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example: "echo [first second third] | nth --skip 0 2",
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result: Some(vec![Value::from("second")]),
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},
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]
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}
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}
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fn nth(args: CommandArgs) -> Result<OutputStream, ShellError> {
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let (
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NthArgs {
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row_number,
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rest: and_rows,
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skip,
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},
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input,
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) = args.process()?;
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let mut rows: Vec<_> = and_rows.into_iter().map(|x| x.item as usize).collect();
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rows.push(row_number.item as usize);
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rows.sort_unstable();
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Ok(NthIterator {
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input,
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rows,
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skip,
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current: 0,
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}
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.to_output_stream())
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}
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struct NthIterator {
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input: InputStream,
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rows: Vec<usize>,
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skip: bool,
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current: usize,
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}
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impl Iterator for NthIterator {
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type Item = Value;
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fn next(&mut self) -> Option<Self::Item> {
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loop {
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if !self.skip {
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if let Some(row) = self.rows.get(0) {
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if self.current == *row {
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self.rows.remove(0);
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self.current += 1;
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return self.input.next();
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} else {
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self.current += 1;
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let _ = self.input.next();
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continue;
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}
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} else {
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return None;
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}
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} else if let Some(row) = self.rows.get(0) {
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if self.current == *row {
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self.rows.remove(0);
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self.current += 1;
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let _ = self.input.next();
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continue;
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} else {
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self.current += 1;
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return self.input.next();
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}
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} else {
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return self.input.next();
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}
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}
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}
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}
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#[cfg(test)]
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mod tests {
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use super::Nth;
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use super::ShellError;
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#[test]
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fn examples_work_as_expected() -> Result<(), ShellError> {
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use crate::examples::test as test_examples;
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test_examples(Nth {})
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}
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}
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