Merge pull request #402 from ijt/add-last-command

Add `last` filter

src/commands/last.rs

@@ -0,0 +1,59 @@
+use crate::commands::WholeStreamCommand;
+use crate::errors::ShellError;
+use crate::parser::CommandRegistry;
+use crate::prelude::*;
+
+pub struct Last;
+
+impl WholeStreamCommand for Last {
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        last(args, registry)
+    }
+
+    fn name(&self) -> &str {
+        "last"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("last").required("amount", SyntaxType::Literal)
+    }
+}
+
+fn last(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {
+    let args = args.evaluate_once(registry)?;
+
+    let amount = args.expect_nth(0)?.as_i64();
+
+    let amount = match amount {
+        Ok(o) => o,
+        Err(_) => {
+            return Err(ShellError::labeled_error(
+                "Value is not a number",
+                "expected integer",
+                args.expect_nth(0)?.span(),
+            ))
+        }
+    };
+
+    if amount <= 0 {
+        return Err(ShellError::labeled_error(
+            "Value is too low",
+            "expected a positive integer",
+            args.expect_nth(0)?.span(),
+        ))
+    }
+
+    let stream = async_stream_block! {
+        let v: Vec<_> = args.input.into_vec().await;
+        let k = v.len() - (amount as usize);
+        for x in v[k..].iter() {
+            let y: Tagged<Value> = x.clone();
+            yield ReturnSuccess::value(y)
+        }
+    };
+    Ok(stream.to_output_stream())
+}