use std::any::Any;

use crate::{serde::Serializable, FromReflect, Reflect, ReflectMut, ReflectRef};

/// A reflected Rust tuple.
///
/// This trait is automatically implemented for arbitrary tuples of up to 12
/// elements, provided that each element implements [`Reflect`].
///
/// # Example
///
/// ```
/// use bevy_reflect::Tuple;
///
/// # fn main() {
/// let foo = ("blue".to_string(), 42_i32);
/// assert_eq!(foo.field_len(), 2);
///
/// let first = foo.field(0).unwrap();
/// assert_eq!(first.downcast_ref::<String>(), Some(&"blue".to_string()));
/// # }
/// ```
pub trait Tuple: 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.
    fn field_len(&self) -> usize;

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

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

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

impl<'a> TupleFieldIter<'a> {
    pub fn new(value: &'a dyn Tuple) -> Self {
        TupleFieldIter {
            tuple: value,
            index: 0,
        }
    }
}

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

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

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

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

/// A convenience trait which combines fetching and downcasting of tuple
/// fields.
///
/// # Example
///
/// ```
/// use bevy_reflect::GetTupleField;
///
/// # fn main() {
/// let foo = ("blue".to_string(), 42_i32);
///
/// assert_eq!(foo.get_field::<String>(0), Some(&"blue".to_string()));
/// assert_eq!(foo.get_field::<i32>(1), Some(&42));
/// # }
/// ```
pub trait GetTupleField {
    /// 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: Tuple> GetTupleField 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 GetTupleField for dyn Tuple {
    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 which allows fields to be added at runtime.
#[derive(Default)]
pub struct DynamicTuple {
    name: String,
    fields: Vec<Box<dyn Reflect>>,
}

impl DynamicTuple {
    /// Returns the type name of the tuple.
    ///
    /// The tuple's name is automatically generated from its element types.
    pub fn name(&self) -> &str {
        &self.name
    }

    /// Manually sets the type name of the tuple.
    ///
    /// Note that the tuple name will be overwritten when elements are added.
    pub fn set_name(&mut self, name: String) {
        self.name = name;
    }

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

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

    fn generate_name(&mut self) {
        let name = &mut self.name;
        name.clear();
        name.push('(');
        for (i, field) in self.fields.iter().enumerate() {
            if i > 0 {
                name.push_str(", ");
            }
            name.push_str(field.type_name());
        }
        name.push(')');
    }
}

impl Tuple for DynamicTuple {
    #[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) -> TupleFieldIter {
        TupleFieldIter {
            tuple: self,
            index: 0,
        }
    }

    #[inline]
    fn clone_dynamic(&self) -> DynamicTuple {
        DynamicTuple {
            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 DynamicTuple {
    #[inline]
    fn type_name(&self) -> &str {
        self.name()
    }

    #[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::Tuple(self)
    }

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

    fn apply(&mut self, value: &dyn Reflect) {
        tuple_apply(self, value);
    }

    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_partial_eq(self, value)
    }

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

/// Applies the elements of `b` to the corresponding elements of `a`.
///
/// # Panics
///
/// This function panics if `b` is not a tuple.
#[inline]
pub fn tuple_apply<T: Tuple>(a: &mut T, b: &dyn Reflect) {
    if let ReflectRef::Tuple(tuple) = b.reflect_ref() {
        for (i, value) in tuple.iter_fields().enumerate() {
            if let Some(v) = a.field_mut(i) {
                v.apply(value);
            }
        }
    } else {
        panic!("Attempted to apply non-Tuple type to Tuple type.");
    }
}

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

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

    for (a_field, b_field) in a.iter_fields().zip(b.iter_fields()) {
        match a_field.reflect_partial_eq(b_field) {
            Some(false) | None => return Some(false),
            Some(true) => {}
        }
    }

    Some(true)
}

macro_rules! impl_reflect_tuple {
    {$($index:tt : $name:tt),*} => {
        impl<$($name: Reflect),*> Tuple for ($($name,)*) {
            #[inline]
            fn field(&self, index: usize) -> Option<&dyn Reflect> {
                match index {
                    $($index => Some(&self.$index as &dyn Reflect),)*
                    _ => None,
                }
            }

            #[inline]
            fn field_mut(&mut self, index: usize) -> Option<&mut dyn Reflect> {
                match index {
                    $($index => Some(&mut self.$index as &mut dyn Reflect),)*
                    _ => None,
                }
            }

            #[inline]
            fn field_len(&self) -> usize {
                let indices: &[usize] = &[$($index as usize),*];
                indices.len()
            }

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

            #[inline]
            fn clone_dynamic(&self) -> DynamicTuple {
                let mut dyn_tuple = DynamicTuple {
                    name: String::default(),
                    fields: self
                        .iter_fields()
                        .map(|value| value.clone_value())
                        .collect(),
                };
                dyn_tuple.generate_name();
                dyn_tuple
            }
        }

        // SAFE: any and any_mut both return self
        unsafe impl<$($name: Reflect),*> Reflect for ($($name,)*) {
            fn type_name(&self) -> &str {
                std::any::type_name::<Self>()
            }

            fn any(&self) -> &dyn Any {
                self
            }

            fn any_mut(&mut self) -> &mut dyn Any {
                self
            }

            fn apply(&mut self, value: &dyn Reflect) {
                crate::tuple_apply(self, value);
            }

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

            fn reflect_ref(&self) -> ReflectRef {
                ReflectRef::Tuple(self)
            }

            fn reflect_mut(&mut self) -> ReflectMut {
                ReflectMut::Tuple(self)
            }

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

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

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

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

        impl<$($name: FromReflect),*> FromReflect for ($($name,)*)
        {
            fn from_reflect(reflect: &dyn Reflect) -> Option<Self> {
                if let ReflectRef::Tuple(_ref_tuple) = reflect.reflect_ref() {
                    Some(
                        (
                            $(
                                <$name as FromReflect>::from_reflect(_ref_tuple.field($index)?)?,
                            )*
                        )
                    )
                } else {
                    None
                }
            }
        }
    }
}

impl_reflect_tuple! {}
impl_reflect_tuple! {0: A}
impl_reflect_tuple! {0: A, 1: B}
impl_reflect_tuple! {0: A, 1: B, 2: C}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F, 6: G}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F, 6: G, 7: H}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F, 6: G, 7: H, 8: I}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F, 6: G, 7: H, 8: I, 9: J}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F, 6: G, 7: H, 8: I, 9: J, 10: K}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F, 6: G, 7: H, 8: I, 9: J, 10: K, 11: L}