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

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

impl Command for Enter {
    fn name(&self) -> &str {
        "enter"
    }

    fn signature(&self) -> Signature {
        Signature::build("enter")
            .required(
                "path",
                SyntaxShape::Filepath,
                "the path to enter as a new shell",
            )
            .category(Category::Shells)
    }

    fn usage(&self) -> &str {
        "Enters a new shell at the given path."
    }

    fn run(
        &self,
        engine_state: &EngineState,
        stack: &mut Stack,
        call: &Call,
        _input: PipelineData,
    ) -> Result<PipelineData, ShellError> {
        let new_path: Value = call.req(engine_state, stack, 0)?;

        let cwd = current_dir(engine_state, stack)?;

        if let Ok(s) = new_path.as_string() {
            let path = nu_path::expand_path_with(s, &cwd);
            if !path.exists() {
                return Err(ShellError::DirectoryNotFound(new_path.span()?));
            }
        }

        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 mut 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 + 1 > shells.len() {
            shells.push(new_path.clone());
            current_shell = shells.len();
        } else {
            shells.insert(current_shell + 1, new_path.clone());
            current_shell += 1;
        }

        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))
    }
}