use crate::{serde::Serializable, Reflect, ReflectMut, ReflectRef};
use std::any::Any;

/// A reflected Rust tuple struct.
///
/// Implementors of this trait allow their tuple fields to be addressed by
/// index.
///
/// This trait is automatically implemented for tuple struct types when using
/// `#[derive(Reflect)]`.
///
/// ```
/// use bevy_reflect::{Reflect, TupleStruct};
///
/// #[derive(Reflect)]
/// struct Foo(String);
///
/// # fn main() {
/// let foo = Foo("Hello, world!".to_string());
///
/// assert_eq!(foo.field_len(), 1);
///
/// let first = foo.field(0).unwrap();
/// assert_eq!(first.downcast_ref::<String>(), Some(&"Hello, world!".to_string()));
/// # }
/// ```
pub trait TupleStruct: Reflect {
    /// Returns a reference to the value of the field with index `index` as a
    /// `&dyn Reflect`.
    fn field(&self, index: usize) -> Option<&dyn Reflect>;

    /// Returns a mutable reference to the value of the field with index `index`
    /// as a `&mut dyn Reflect`.
    fn field_mut(&mut self, index: usize) -> Option<&mut dyn Reflect>;

    /// Returns the number of fields in the tuple struct.
    fn field_len(&self) -> usize;

    /// Returns an iterator over the values of the tuple struct's fields.
    fn iter_fields(&self) -> TupleStructFieldIter;

    /// Clones the struct into a [`DynamicTupleStruct`].
    fn clone_dynamic(&self) -> DynamicTupleStruct;
}

/// An iterator over the field values of a tuple struct.
pub struct TupleStructFieldIter<'a> {
    pub(crate) tuple_struct: &'a dyn TupleStruct,
    pub(crate) index: usize,
}

impl<'a> TupleStructFieldIter<'a> {
    pub fn new(value: &'a dyn TupleStruct) -> Self {
        TupleStructFieldIter {
            tuple_struct: value,
            index: 0,
        }
    }
}

impl<'a> Iterator for TupleStructFieldIter<'a> {
    type Item = &'a dyn Reflect;

    fn next(&mut self) -> Option<Self::Item> {
        let value = self.tuple_struct.field(self.index);
        self.index += 1;
        value
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let size = self.tuple_struct.field_len();
        (size, Some(size))
    }
}

impl<'a> ExactSizeIterator for TupleStructFieldIter<'a> {}

/// A convenience trait which combines fetching and downcasting of tuple
/// struct fields.
///
/// # Example
///
/// ```
/// use bevy_reflect::{GetTupleStructField, Reflect};
///
/// #[derive(Reflect)]
/// struct Foo(String);
///
/// # fn main() {
/// let mut foo = Foo("Hello, world!".to_string());
///
/// foo.get_field_mut::<String>(0).unwrap().truncate(5);
/// assert_eq!(foo.get_field::<String>(0), Some(&"Hello".to_string()));
/// # }
/// ```
pub trait GetTupleStructField {
    /// Returns a reference to the value of the field with index `index`,
    /// downcast to `T`.
    fn get_field<T: Reflect>(&self, index: usize) -> Option<&T>;

    /// Returns a mutable reference to the value of the field with index
    /// `index`, downcast to `T`.
    fn get_field_mut<T: Reflect>(&mut self, index: usize) -> Option<&mut T>;
}

impl<S: TupleStruct> GetTupleStructField for S {
    fn get_field<T: Reflect>(&self, index: usize) -> Option<&T> {
        self.field(index)
            .and_then(|value| value.downcast_ref::<T>())
    }

    fn get_field_mut<T: Reflect>(&mut self, index: usize) -> Option<&mut T> {
        self.field_mut(index)
            .and_then(|value| value.downcast_mut::<T>())
    }
}

impl GetTupleStructField for dyn TupleStruct {
    fn get_field<T: Reflect>(&self, index: usize) -> Option<&T> {
        self.field(index)
            .and_then(|value| value.downcast_ref::<T>())
    }

    fn get_field_mut<T: Reflect>(&mut self, index: usize) -> Option<&mut T> {
        self.field_mut(index)
            .and_then(|value| value.downcast_mut::<T>())
    }
}

/// A tuple struct which allows fields to be added at runtime.
#[derive(Default)]
pub struct DynamicTupleStruct {
    name: String,
    fields: Vec<Box<dyn Reflect>>,
}

impl DynamicTupleStruct {
    /// Returns the type name of the tuple struct.
    pub fn name(&self) -> &str {
        &self.name
    }

    /// Sets the type name of the tuple struct.
    pub fn set_name(&mut self, name: String) {
        self.name = name;
    }

    /// Appends an element with value `value` to the tuple struct.
    pub fn insert_boxed(&mut self, value: Box<dyn Reflect>) {
        self.fields.push(value);
    }

    /// Appends a typed element with value `value` to the tuple struct.
    pub fn insert<T: Reflect>(&mut self, value: T) {
        self.insert_boxed(Box::new(value));
    }
}

impl TupleStruct for DynamicTupleStruct {
    #[inline]
    fn field(&self, index: usize) -> Option<&dyn Reflect> {
        self.fields.get(index).map(|field| &**field)
    }

    #[inline]
    fn field_mut(&mut self, index: usize) -> Option<&mut dyn Reflect> {
        self.fields.get_mut(index).map(|field| &mut **field)
    }

    #[inline]
    fn field_len(&self) -> usize {
        self.fields.len()
    }

    #[inline]
    fn iter_fields(&self) -> TupleStructFieldIter {
        TupleStructFieldIter {
            tuple_struct: self,
            index: 0,
        }
    }

    fn clone_dynamic(&self) -> DynamicTupleStruct {
        DynamicTupleStruct {
            name: self.name.clone(),
            fields: self
                .fields
                .iter()
                .map(|value| value.clone_value())
                .collect(),
        }
    }
}

// SAFE: any and any_mut both return self
unsafe impl Reflect for DynamicTupleStruct {
    #[inline]
    fn type_name(&self) -> &str {
        self.name.as_str()
    }

    #[inline]
    fn any(&self) -> &dyn Any {
        self
    }

    #[inline]
    fn any_mut(&mut self) -> &mut dyn Any {
        self
    }

    #[inline]
    fn clone_value(&self) -> Box<dyn Reflect> {
        Box::new(self.clone_dynamic())
    }

    #[inline]
    fn reflect_ref(&self) -> ReflectRef {
        ReflectRef::TupleStruct(self)
    }

    #[inline]
    fn reflect_mut(&mut self) -> ReflectMut {
        ReflectMut::TupleStruct(self)
    }

    fn apply(&mut self, value: &dyn Reflect) {
        if let ReflectRef::TupleStruct(tuple_struct) = value.reflect_ref() {
            for (i, value) in tuple_struct.iter_fields().enumerate() {
                if let Some(v) = self.field_mut(i) {
                    v.apply(value)
                }
            }
        } else {
            panic!("Attempted to apply non-TupleStruct type to TupleStruct type.");
        }
    }

    fn set(&mut self, value: Box<dyn Reflect>) -> Result<(), Box<dyn Reflect>> {
        *self = value.take()?;
        Ok(())
    }

    fn reflect_hash(&self) -> Option<u64> {
        None
    }

    fn reflect_partial_eq(&self, value: &dyn Reflect) -> Option<bool> {
        tuple_struct_partial_eq(self, value)
    }

    fn serializable(&self) -> Option<Serializable> {
        None
    }
}

/// Compares a [`TupleStruct`] with a [`Reflect`] value.
///
/// Returns true if and only if all of the following are true:
/// - `b` is a tuple struct;
/// - `b` has the same number of fields as `a`;
/// - [`Reflect::reflect_partial_eq`] returns `Some(true)` for pairwise fields of `a` and `b`.
#[inline]
pub fn tuple_struct_partial_eq<S: TupleStruct>(a: &S, b: &dyn Reflect) -> Option<bool> {
    let tuple_struct = if let ReflectRef::TupleStruct(tuple_struct) = b.reflect_ref() {
        tuple_struct
    } else {
        return Some(false);
    };

    if a.field_len() != tuple_struct.field_len() {
        return Some(false);
    }

    for (i, value) in tuple_struct.iter_fields().enumerate() {
        if let Some(field_value) = a.field(i) {
            if let Some(false) | None = field_value.reflect_partial_eq(value) {
                return Some(false);
            }
        } else {
            return Some(false);
        }
    }

    Some(true)
}