//! `Object` and tightly related types.

use core::{
    fmt,
    iter::{self, FromIterator},
    ops,
};

use crate::{
    alloc::{hash_map, HashMap, String},
    Value,
};

/// Object with zero or more named fields.
///
/// An object functions similarly to a `HashMap` with [`String`] keys and [`Value`]
/// values. It allows iteration over name-value pairs, random access by field name,
/// inserting / removing fields etc.
///
/// # Examples
///
/// ```
/// # use arithmetic_eval::{fns, Object, Value, ValueType};
/// let mut obj = Object::<u32>::default();
/// obj.insert("field", Value::Prim(0));
/// obj.insert("other_field", Value::Bool(false));
/// assert_eq!(obj.len(), 2);
/// assert_eq!(obj["field"].value_type(), ValueType::Prim);
/// assert!(obj.iter().all(|(_, val)| !val.is_void()));
///
/// // `Object` implements `FromIterator` / `Extend`.
/// let fields = vec![
///     ("third", Value::Prim(3)),
///     ("fourth", Value::native_fn(fns::Assert)),
/// ];
/// let mut other_obj: Object<u32> = fields.into_iter().collect();
/// other_obj.extend(obj);
/// assert_eq!(other_obj.len(), 4);
/// ```
#[derive(Debug, Clone, PartialEq)]
pub struct Object<T> {
    fields: HashMap<String, Value<T>>,
}

impl<T> From<Object<T>> for Value<T> {
    fn from(object: Object<T>) -> Self {
        Self::Object(object)
    }
}

impl<T> Default for Object<T> {
    fn default() -> Self {
        Self {
            fields: HashMap::new(),
        }
    }
}

impl<T: fmt::Display> fmt::Display for Object<T> {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter.write_str("#{ ")?;
        for (i, (name, value)) in self.iter().enumerate() {
            write!(formatter, "{name}: {value}")?;
            if i + 1 < self.len() {
                write!(formatter, ", ")?;
            } else {
                write!(formatter, " ")?;
            }
        }
        formatter.write_str("}")
    }
}

impl<T> Object<T> {
    /// Creates an object with a single field.
    pub fn just(field_name: impl Into<String>, value: Value<T>) -> Self {
        let fields = iter::once((field_name.into(), value)).collect();
        Self { fields }
    }

    /// Returns the number of fields in this object.
    pub fn len(&self) -> usize {
        self.fields.len()
    }

    /// Checks if this object is empty (has no fields).
    pub fn is_empty(&self) -> bool {
        self.fields.is_empty()
    }

    /// Iterates over name-value pairs for all fields defined in this object.
    pub fn iter(&self) -> impl Iterator<Item = (&str, &Value<T>)> + '_ {
        self.fields
            .iter()
            .map(|(name, value)| (name.as_str(), value))
    }

    /// Iterates over field names.
    pub fn field_names(&self) -> impl Iterator<Item = &str> + '_ {
        self.fields.keys().map(String::as_str)
    }

    /// Returns the value of a field with the specified name, or `None` if this object
    /// does not contain such a field.
    pub fn get(&self, field_name: &str) -> Option<&Value<T>> {
        self.fields.get(field_name)
    }

    /// Checks whether this object has a field with the specified name.
    pub fn contains_field(&self, field_name: &str) -> bool {
        self.fields.contains_key(field_name)
    }

    /// Inserts a field into this object.
    pub fn insert(&mut self, field_name: impl Into<String>, value: Value<T>) -> Option<Value<T>> {
        self.fields.insert(field_name.into(), value)
    }

    /// Removes and returns the specified field from this object.
    pub fn remove(&mut self, field_name: &str) -> Option<Value<T>> {
        self.fields.remove(field_name)
    }
}

impl<T> ops::Index<&str> for Object<T> {
    type Output = Value<T>;

    fn index(&self, index: &str) -> &Self::Output {
        &self.fields[index]
    }
}

impl<T> IntoIterator for Object<T> {
    type Item = (String, Value<T>);
    /// Iterator type should be considered an implementation detail.
    type IntoIter = hash_map::IntoIter<String, Value<T>>;

    fn into_iter(self) -> Self::IntoIter {
        self.fields.into_iter()
    }
}

impl<'r, T> IntoIterator for &'r Object<T> {
    type Item = (&'r str, &'r Value<T>);
    /// Iterator type should be considered an implementation detail.
    type IntoIter = Iter<'r, T>;

    fn into_iter(self) -> Self::IntoIter {
        self.fields
            .iter()
            .map(|(name, value)| (name.as_str(), value))
    }
}

pub type Iter<'r, T> = iter::Map<
    hash_map::Iter<'r, String, Value<T>>,
    fn((&'r String, &'r Value<T>)) -> (&'r str, &'r Value<T>),
>;

impl<T, S, V> FromIterator<(S, V)> for Object<T>
where
    S: Into<String>,
    V: Into<Value<T>>,
{
    fn from_iter<I: IntoIterator<Item = (S, V)>>(iter: I) -> Self {
        Self {
            fields: iter
                .into_iter()
                .map(|(name, value)| (name.into(), value.into()))
                .collect(),
        }
    }
}

impl<T, S, V> Extend<(S, V)> for Object<T>
where
    S: Into<String>,
    V: Into<Value<T>>,
{
    fn extend<I: IntoIterator<Item = (S, V)>>(&mut self, iter: I) {
        let new_fields = iter
            .into_iter()
            .map(|(name, value)| (name.into(), value.into()));
        self.fields.extend(new_fields);
    }
}

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

    #[test]
    fn object_to_string() {
        let mut obj = Object::<f32>::default();
        let obj_string = obj.to_string();
        assert_eq!(obj_string, "#{ }");

        obj.insert("x", Value::Prim(3.0));
        let obj_string = obj.to_string();
        assert_eq!(obj_string, "#{ x: 3 }");

        obj.insert("y", Value::Prim(4.0));
        let obj_string = obj.to_string();
        assert!(
            obj_string == "#{ x: 3, y: 4 }" || obj_string == "#{ y: 4, x: 3 }",
            "Unexpected obj_string: {obj_string}"
        );
    }
}