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use nu_engine::current_dir;
use nu_protocol::ast::Call;
use nu_protocol::engine::{Command, EngineState, Stack};
use nu_protocol::{Category, Example, PipelineData, ShellError, Signature, Value};

/// Source a file for environment variables.
#[derive(Clone)]
pub struct PrevShell;

impl Command for PrevShell {
    fn name(&self) -> &str {
        "p"
    }

    fn signature(&self) -> Signature {
        Signature::build("p").category(Category::Shells)
    }

    fn usage(&self) -> &str {
        "Switch to the previous shell."
    }

    fn run(
        &self,
        engine_state: &EngineState,
        stack: &mut Stack,
        call: &Call,
        _input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        let cwd = current_dir(engine_state, stack)?;
        let cwd = Value::String {
            val: cwd.to_string_lossy().to_string(),
            span: call.head,
        };

        let shells = stack.get_env_var(engine_state, "NUSHELL_SHELLS");
        let shells = if let Some(v) = shells {
            v.as_list()
                .map(|x| x.to_vec())
                .unwrap_or_else(|_| vec![cwd])
        } else {
            vec![cwd]
        };

        let current_shell = stack.get_env_var(engine_state, "NUSHELL_CURRENT_SHELL");
        let mut current_shell = if let Some(v) = current_shell {
            v.as_integer().unwrap_or_default() as usize
        } else {
            0
        };

        if current_shell == 0 {
            current_shell = shells.len() - 1;
        } else {
            current_shell -= 1;
        }

        let new_path = shells[current_shell].clone();

        stack.add_env_var(
            "NUSHELL_SHELLS".into(),
            Value::List {
                vals: shells,
                span: call.head,
            },
        );
        stack.add_env_var(
            "NUSHELL_CURRENT_SHELL".into(),
            Value::Int {
                val: current_shell as i64,
                span: call.head,
            },
        );

        stack.add_env_var("PWD".into(), new_path);

        Ok(PipelineData::new(call.head))
    }

    fn examples(&self) -> Vec<Example> {
        vec![
            Example {
                description: "Make two directories and enter new shells for them, use `p` to jump to the previous shell",
                example: r#"mkdir foo bar; enter foo; enter ../bar; p"#,
                result: None,
            },
            Example {
                description: "Run `p` several times and note the changes of current directory",
                example: r#"p"#,
                result: None,
            },
        ]
    }
}