nushell/src/eval.rs

use std::collections::HashMap;

use crate::{parser::Operator, Block, Call, Expr, Expression, ParserState, Span, Statement, VarId};

#[derive(Debug)]
pub enum ShellError {
    Mismatch(String, Span),
    Unsupported(Span),
    InternalError(String),
}

#[derive(Debug, Clone)]
pub enum Value {
    Int { val: i64, span: Span },
    Unknown,
}
impl Value {
    pub fn add(&self, rhs: &Value) -> Result<Value, ShellError> {
        match (self, rhs) {
            (Value::Int { val: lhs, .. }, Value::Int { val: rhs, .. }) => Ok(Value::Int {
                val: lhs + rhs,
                span: Span::unknown(),
            }),
            _ => Ok(Value::Unknown),
        }
    }
}

pub struct State<'a> {
    pub parser_state: &'a ParserState,
}

pub struct Stack {
    pub vars: HashMap<VarId, Value>,
}

impl Stack {
    pub fn get_var(&self, var_id: VarId) -> Result<Value, ShellError> {
        match self.vars.get(&var_id) {
            Some(v) => Ok(v.clone()),
            _ => Err(ShellError::InternalError("variable not found".into())),
        }
    }
}

pub fn eval_operator(
    state: &State,
    stack: &mut Stack,
    op: &Expression,
) -> Result<Operator, ShellError> {
    match op {
        Expression {
            expr: Expr::Operator(operator),
            ..
        } => Ok(operator.clone()),
        Expression { span, .. } => Err(ShellError::Mismatch("operator".to_string(), *span)),
    }
}

fn eval_call(state: &State, stack: &mut Stack, call: &Call) -> Result<Value, ShellError> {
    let decl = state.parser_state.get_decl(call.decl_id);

    if let Some(block_id) = decl.body {
        let block = state.parser_state.get_block(block_id);
        eval_block(state, stack, block)
    } else {
        Ok(Value::Unknown)
    }
}

pub fn eval_expression(
    state: &State,
    stack: &mut Stack,
    expr: &Expression,
) -> Result<Value, ShellError> {
    match &expr.expr {
        Expr::Int(i) => Ok(Value::Int {
            val: *i,
            span: expr.span,
        }),
        Expr::Var(var_id) => stack.get_var(*var_id),
        Expr::Call(call) => eval_call(state, stack, call),
        Expr::ExternalCall(_, _) => Err(ShellError::Unsupported(expr.span)),
        Expr::Operator(_) => Ok(Value::Unknown),
        Expr::BinaryOp(lhs, op, rhs) => {
            let lhs = eval_expression(state, stack, &lhs)?;
            let op = eval_operator(state, stack, &op)?;
            let rhs = eval_expression(state, stack, &rhs)?;

            match op {
                Operator::Plus => lhs.add(&rhs),
                _ => Ok(Value::Unknown),
            }
        }

        Expr::Subexpression(block_id) => {
            let block = state.parser_state.get_block(*block_id);

            eval_block(state, stack, block)
        }
        Expr::Block(_) => Err(ShellError::Unsupported(expr.span)),
        Expr::List(_) => Err(ShellError::Unsupported(expr.span)),
        Expr::Table(_, _) => Err(ShellError::Unsupported(expr.span)),
        Expr::Literal(_) => Err(ShellError::Unsupported(expr.span)),
        Expr::String(_) => Err(ShellError::Unsupported(expr.span)),
        Expr::Signature(_) => Err(ShellError::Unsupported(expr.span)),
        Expr::Garbage => Err(ShellError::Unsupported(expr.span)),
    }
}

pub fn eval_block(state: &State, stack: &mut Stack, block: &Block) -> Result<Value, ShellError> {
    let mut last = Ok(Value::Unknown);

    for stmt in &block.stmts {
        match stmt {
            Statement::Expression(expression) => {
                last = Ok(eval_expression(state, stack, expression)?);
            }
            _ => {}
        }
    }

    last
}