dust/src/abstract_tree/index.rs

use serde::{Deserialize, Serialize};
use tree_sitter::Node;

use crate::{AbstractTree, Error, IndexExpression, List, Map, Result, Type, Value};

/// Abstract representation of an index expression.
///
/// An index is a means of accessing values stored in list, maps and strings.
#[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq, PartialOrd, Ord)]
pub struct Index {
    pub collection: IndexExpression,
    pub index: IndexExpression,
    pub index_end: Option<IndexExpression>,
}

impl AbstractTree for Index {
    fn from_syntax_node(source: &str, node: Node, context: &Map) -> Result<Self> {
        Error::expect_syntax_node(source, "index", node)?;

        let collection_node = node.child(0).unwrap();
        let collection = IndexExpression::from_syntax_node(source, collection_node, context)?;

        let index_node = node.child(2).unwrap();
        let index = IndexExpression::from_syntax_node(source, index_node, context)?;

        let index_end_node = node.child(4);
        let index_end = if let Some(index_end_node) = index_end_node {
            Some(IndexExpression::from_syntax_node(
                source,
                index_end_node,
                context,
            )?)
        } else {
            None
        };

        Ok(Index {
            collection,
            index,
            index_end,
        })
    }

    fn run(&self, source: &str, context: &Map) -> Result<Value> {
        let collection = self.collection.run(source, context)?;

        match collection {
            Value::List(list) => {
                let index = self.index.run(source, context)?.as_integer()? as usize;

                let item = if let Some(index_end) = &self.index_end {
                    let index_end = index_end.run(source, context)?.as_integer()? as usize;
                    let sublist = list.items()[index..=index_end].to_vec();

                    Value::List(List::with_items(sublist))
                } else {
                    list.items().get(index).cloned().unwrap_or_default()
                };

                Ok(item)
            }
            Value::Map(map) => {
                let value = if let IndexExpression::Identifier(identifier) = &self.index {
                    let key = identifier.inner();

                    map.variables()?
                        .get(key)
                        .map(|(value, _)| value.clone())
                        .unwrap_or_default()
                } else {
                    let value = self.index.run(source, context)?;
                    let key = value.as_string()?;

                    map.variables()?
                        .get(key)
                        .map(|(value, _)| value.clone())
                        .unwrap_or_default()
                };

                Ok(value)
            }
            Value::String(string) => {
                let index = self.index.run(source, context)?.as_integer()? as usize;
                let item = string.chars().nth(index).unwrap_or_default();

                Ok(Value::String(item.to_string()))
            }
            _ => Err(Error::ExpectedCollection { actual: collection }),
        }
    }

    fn expected_type(&self, context: &Map) -> Result<Type> {
        match self.collection.expected_type(context)? {
            Type::List(item_type) => Ok(*item_type.clone()),
            Type::Map => Ok(Type::Any),
            Type::None => Ok(Type::None),
            r#type => Ok(r#type),
        }
    }
}