//! Module for holding Monoid typeclass definitions and default implementations
//!
//! A `Monoid` is a Semigroup that has a defined empty/zero value. This allows us to
//! define a `combine_all` method to work on a list of said things:
#![cfg_attr(
    feature = "std",
    doc = r#"
Have you ever wanted to combine 2 Hashmaps such that for a given key, if it exists in both maps,
their values are summed in the new map?

# Examples

```
use std::collections::HashMap;
use frunk::{monoid, Monoid};

let vec_of_no_hashmaps: Vec<HashMap<i32, String>> = Vec::new();
assert_eq!(monoid::combine_all(&vec_of_no_hashmaps),
           <HashMap<i32, String> as Monoid>::empty());

let mut h1: HashMap<i32, String> = HashMap::new();
h1.insert(1, String::from("Hello"));  // h1 is HashMap( 1 -> "Hello")
let mut h2: HashMap<i32, String> = HashMap::new();
h2.insert(1, String::from(" World"));
h2.insert(2, String::from("Goodbye"));  // h2 is HashMap( 1 -> " World", 2 -> "Goodbye")
let mut h3: HashMap<i32, String> = HashMap::new();
h3.insert(3, String::from("Cruel World")); // h3 is HashMap( 3 -> "Cruel World")
let vec_of_hashes = vec![h1, h2, h3];

let mut h_expected: HashMap<i32, String> = HashMap::new();
h_expected.insert(1, String::from("Hello World"));
h_expected.insert(2, String::from("Goodbye"));
h_expected.insert(3, String::from("Cruel World"));
// h_expected is HashMap ( 1 -> "Hello World", 2 -> "Goodbye", 3 -> "Cruel World")
assert_eq!(monoid::combine_all(&vec_of_hashes), h_expected);
```"#
)]

use super::semigroup::{All, Any, Product, Semigroup};
#[cfg(feature = "std")]
use std::collections::*;
#[cfg(feature = "std")]
use std::hash::Hash;

/// A Monoid is a Semigroup that has an empty/ zero value
pub trait Monoid: Semigroup {
    /// For a given Monoid, returns its empty/zero value
    ///
    /// # Examples
    ///
    /// ```
    /// use frunk::Monoid;
    ///
    /// assert_eq!(<i16 as Monoid>::empty(), 0);
    /// ```
    fn empty() -> Self;
}

/// Return this combined with itself `n` times.
///
/// # Examples
///
/// ```
/// use frunk::monoid;
///
/// assert_eq!(monoid::combine_n(&Some(2), 4), Some(8));
/// ```
pub fn combine_n<T>(o: &T, times: u32) -> T
where
    T: Monoid + Semigroup + Clone,
{
    if times == 0 {
        <T as Monoid>::empty()
    } else {
        super::semigroup::combine_n(o, times)
    }
}

/// Given a sequence of `xs`, combine them and return the total
#[cfg_attr(
    feature = "std",
    doc = r#"
# Examples

```
use frunk::monoid::combine_all;

assert_eq!(combine_all(&vec![Some(1), Some(3)]), Some(4));

let empty_vec_opt_int: Vec<Option<i32>> = Vec::new();
assert_eq!(combine_all(&empty_vec_opt_int), None);

let vec_of_some_strings = vec![Some(String::from("Hello")), Some(String::from(" World"))];
assert_eq!(combine_all(&vec_of_some_strings), Some(String::from("Hello World")));
```"#
)]
pub fn combine_all<T>(xs: &[T]) -> T
where
    T: Monoid + Semigroup + Clone,
{
    xs.iter()
        .fold(<T as Monoid>::empty(), |acc, next| acc.combine(next))
}

impl<T> Monoid for Option<T>
where
    T: Semigroup + Clone,
{
    fn empty() -> Self {
        None
    }
}

#[cfg(feature = "std")]
impl Monoid for String {
    fn empty() -> Self {
        String::new()
    }
}

#[cfg(feature = "std")]
impl<T> Monoid for Vec<T>
where
    T: Clone,
{
    fn empty() -> Self {
        Vec::new()
    }
}

#[cfg(feature = "std")]
impl<T> Monoid for HashSet<T>
where
    T: Hash + Eq + Clone,
{
    fn empty() -> Self {
        HashSet::new()
    }
}

#[cfg(feature = "std")]
impl<K, V> Monoid for HashMap<K, V>
where
    K: Eq + Hash + Clone,
    V: Semigroup + Clone,
{
    fn empty() -> Self {
        HashMap::new()
    }
}

impl Monoid for All<bool> {
    fn empty() -> Self {
        All(true)
    }
}

impl Monoid for Any<bool> {
    fn empty() -> Self {
        Any(false)
    }
}

macro_rules! numeric_all_impls {
    ($($tr:ty)*) => {
      $(
        impl Monoid for All<$tr> {
            fn empty() -> Self { All(!0) }
        }
      )*
    }
}

numeric_all_impls! { usize u8 u16 u32 u64 isize i8 i16 i32 i64 }

macro_rules! numeric_any_impls {
    ($($tr:ty)*) => {
      $(
        impl Monoid for Any<$tr> {
            fn empty() -> Self { Any(0) }
        }
      )*
    }
}

numeric_any_impls! { usize u8 u16 u32 u64 isize i8 i16 i32 i64 }

macro_rules! numeric_monoid_imps {
  ($($zero: expr; $tr:ty),*) => {
    $(
      impl Monoid for $tr {
        fn empty() -> Self { $zero }
      }
    )*
  }
}

numeric_monoid_imps! {
    0; i8,
    0; i16,
    0; i32,
    0; i64,
    0; u8,
    0; u16,
    0; u32,
    0; u64,
    0; isize,
    0; usize,
    0f32; f32,
    0f64; f64
}

macro_rules! numeric_product_monoid_imps {
  ($($one: expr; $tr:ty),*) => {
    $(
      impl Monoid for Product<$tr> {
        fn empty() -> Self { Product($one) }
      }
    )*
  }
}

numeric_product_monoid_imps! {
    1; i8,
    1; i16,
    1; i32,
    1; i64,
    1; u8,
    1; u16,
    1; u32,
    1; u64,
    1; isize,
    1; usize,
    1f32; f32,
    1f64; f64
}

macro_rules! tuple_impls {
    () => {}; // no more

    (($idx:tt => $typ:ident), $( ($nidx:tt => $ntyp:ident), )*) => {
// Invoke recursive reversal of list that ends in the macro expansion implementation
// of the reversed list
//
        tuple_impls!([($idx, $typ);] $( ($nidx => $ntyp), )*);
        tuple_impls!($( ($nidx => $ntyp), )*); // invoke macro on tail
    };

// ([accumulatedList], listToReverse); recursively calls tuple_impls until the list to reverse
// + is empty (see next pattern)
//
    ([$(($accIdx: tt, $accTyp: ident);)+]  ($idx:tt => $typ:ident), $( ($nidx:tt => $ntyp:ident), )*) => {
      tuple_impls!([($idx, $typ); $(($accIdx, $accTyp); )*] $( ($nidx => $ntyp), ) *);
    };

// Finally expand into our implementation
    ([($idx:tt, $typ:ident); $( ($nidx:tt, $ntyp:ident); )*]) => {
        impl<$typ: Monoid, $( $ntyp: Monoid),*> Monoid for ($typ, $( $ntyp ),*) {
            fn empty() -> Self {
              (<$typ as Monoid>::empty(), $(<$ntyp as Monoid>::empty(), )*)
            }
        }
    }
}

tuple_impls! {
    (20 => U),
    (19 => T),
    (18 => S),
    (17 => R),
    (16 => Q),
    (15 => P),
    (14 => O),
    (13 => N),
    (12 => M),
    (11 => L),
    (10 => K),
    (9 => J),
    (8 => I),
    (7 => H),
    (6 => G),
    (5 => F),
    (4 => E),
    (3 => D),
    (2 => C),
    (1 => B),
    (0 => A),
}

#[cfg(test)]
mod tests {
    use super::super::semigroup::{All, Any, Product};
    use super::*;

    #[test]
    fn test_combine_n() {
        assert_eq!(combine_n(&1, 0), 0);
        assert_eq!(combine_n(&2, 1), 2);
        assert_eq!(combine_n(&Some(2), 0), None);
        assert_eq!(combine_n(&Some(2), 4), Some(8));
    }

    #[test]
    #[cfg(feature = "std")]
    fn test_combine_all_basic() {
        assert_eq!(combine_all(&[1, 2, 3]), 6);
        assert_eq!(combine_all(&[] as &[i32]), 0);
        assert_eq!(combine_all(&[] as &[Option<i32>]), None);

        let vec_of_some_strings = vec![Some("Hello".to_owned()), Some(" World".to_owned())];
        assert_eq!(
            combine_all(&vec_of_some_strings),
            Some("Hello World".to_owned())
        );
    }

    #[test]
    #[cfg(feature = "std")]
    fn test_combine_all_hashset() {
        let vec_of_no_hashes: Vec<HashSet<i32>> = Vec::new();
        assert_eq!(
            combine_all(&vec_of_no_hashes),
            <HashSet<i32> as Monoid>::empty()
        );

        let mut h1 = HashSet::new();
        h1.insert(1);
        let mut h2 = HashSet::new();
        h2.insert(2);
        let mut h3 = HashSet::new();
        h3.insert(3);
        let vec_of_hashes = vec![h1, h2, h3];
        let mut h_expected = HashSet::new();
        h_expected.insert(1);
        h_expected.insert(2);
        h_expected.insert(3);
        assert_eq!(combine_all(&vec_of_hashes), h_expected);
    }

    #[test]
    #[cfg(feature = "std")]
    fn test_combine_all_hashmap() {
        let vec_of_no_hashmaps: Vec<HashMap<i32, String>> = Vec::new();
        assert_eq!(
            combine_all(&vec_of_no_hashmaps),
            <HashMap<i32, String> as Monoid>::empty()
        );

        let mut h1: HashMap<i32, String> = HashMap::new();
        h1.insert(1, String::from("Hello")); // h1 is HashMap( 1 -> "Hello")
        let mut h2: HashMap<i32, String> = HashMap::new();
        h2.insert(1, String::from(" World"));
        h2.insert(2, String::from("Goodbye")); // h2 is HashMap( 1 -> " World", 2 -> "Goodbye")
        let mut h3: HashMap<i32, String> = HashMap::new();
        h3.insert(3, String::from("Cruel World")); // h3 is HashMap( 3 -> "Cruel World")
        let vec_of_hashes = vec![h1, h2, h3];

        let mut h_expected: HashMap<i32, String> = HashMap::new();
        h_expected.insert(1, String::from("Hello World"));
        h_expected.insert(2, String::from("Goodbye"));
        h_expected.insert(3, String::from("Cruel World")); // h_expected is HashMap ( 1 -> "Hello World", 2 -> "Goodbye", 3 -> "Cruel World")
        assert_eq!(combine_all(&vec_of_hashes), h_expected);
    }

    #[test]
    fn test_combine_all_all() {
        assert_eq!(combine_all(&[] as &[All<i32>]), All(!0));
        assert_eq!(combine_all(&[All(3), All(7)]), All(3));

        assert_eq!(combine_all(&[] as &[All<bool>]), All(true));
        assert_eq!(combine_all(&[All(false), All(false)]), All(false));
        assert_eq!(combine_all(&[All(true), All(true)]), All(true));
    }

    #[test]
    fn test_combine_all_any() {
        assert_eq!(combine_all(&[] as &[Any<i32>]), Any(0));
        assert_eq!(combine_all(&[Any(3), Any(8)]), Any(11));

        assert_eq!(combine_all(&[] as &[Any<bool>]), Any(false));
        assert_eq!(combine_all(&[Any(false), Any(false)]), Any(false));
        assert_eq!(combine_all(&[Any(true), Any(false)]), Any(true));
    }

    #[test]
    #[cfg(feature = "std")]
    fn test_combine_all_tuple() {
        let t1 = (1, 2.5f32, String::from("hi"), Some(3));
        let t2 = (1, 2.5f32, String::from(" world"), None);
        let t3 = (1, 2.5f32, String::from(", goodbye"), Some(10));
        let tuples = vec![t1, t2, t3];

        let expected = (3, 7.5f32, String::from("hi world, goodbye"), Some(13));
        assert_eq!(combine_all(&tuples), expected)
    }

    #[test]
    fn test_combine_all_product() {
        let v = [Product(2), Product(3), Product(4)];
        assert_eq!(combine_all(&v), Product(24))
    }
}