use crate::commands::WholeStreamCommand;
use crate::prelude::*;
use crate::utils::data_processing::{reducer_for, Reduce};
use nu_errors::ShellError;
use nu_protocol::{ReturnSuccess, ReturnValue, Signature, UntaggedValue, Value};
use num_traits::identities::Zero;

pub struct Sum;

impl WholeStreamCommand for Sum {
    fn name(&self) -> &str {
        "sum"
    }

    fn signature(&self) -> Signature {
        Signature::build("sum")
    }

    fn usage(&self) -> &str {
        "Sums the values."
    }

    fn run(
        &self,
        args: CommandArgs,
        registry: &CommandRegistry,
    ) -> Result<OutputStream, ShellError> {
        sum(RunnableContext {
            input: args.input,
            registry: registry.clone(),
            shell_manager: args.shell_manager,
            host: args.host,
            ctrl_c: args.ctrl_c,
            name: args.call_info.name_tag,
            raw_input: args.raw_input,
        })
    }

    fn examples(&self) -> Vec<Example> {
        vec![
            Example {
                description: "Sum a list of numbers",
                example: "echo [1 2 3] | sum",
                result: Some(vec![UntaggedValue::int(6).into()]),
            },
            Example {
                description: "Get the disk usage for the current directory",
                example: "ls --all --du | get size | sum",
                result: None,
            },
        ]
    }
}

fn sum(RunnableContext { mut input, .. }: RunnableContext) -> Result<OutputStream, ShellError> {
    let stream = async_stream! {
        let mut values = input.drain_vec().await;

        let action = reducer_for(Reduce::Sum);

        match action(Value::zero(), values) {
            Ok(total) => yield ReturnSuccess::value(total),
            Err(err) => yield Err(err),
        }
    };

    let stream: BoxStream<'static, ReturnValue> = stream.boxed();

    Ok(stream.to_output_stream())
}

#[cfg(test)]
mod tests {
    use super::Sum;

    #[test]
    fn examples_work_as_expected() {
        use crate::examples::test as test_examples;

        test_examples(Sum {})
    }
}