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// This module defines traits to specifiy a key as defined in DDS specification.
// See e.g. Figure 2.3 in "2.2.1.2.2 Overall Conceptual Model"
use std::collections::hash_map::DefaultHasher;
use std::hash::{Hash, Hasher};
use byteorder::{LittleEndian};
use rand::Rng;
use serde::{Serialize, Deserialize, de::DeserializeOwned};

use crate::serialization::cdr_serializer::to_bytes;

/// A sample data type may be `Keyed` : It allows a Key to be extracted from the sample.
/// In its simplest form, the key may be just a part of the sample data, but it can be anything
/// computable from a sample by an application-defined function.
///
/// The key is used to distinguish between different Instances of the data in a DDS Topic.
///
/// A `Keyed` type has an associated type `K`, which is the actual key type. `K` must
/// implement [`Key`]. Otherwise, `K` can be chosen to suit the application. It is advisable that `K`
/// is something that can be cloned with reasonable effort.
///
/// [`Key`]: trait.Key.html

pub trait Keyed {
  //type K: Key;  // This does not work yet is stable Rust, 2020-08-11
  // Instead, where D:Keyed we do anything with D::K, we must specify bound:
  // where <D as Keyed>::K : Key,
  type K;

  fn get_key(&self) -> Self::K;
  fn get_hash(&self) -> u64
  where
    Self::K: Key,
  {
    let mut hasher = DefaultHasher::new();
    self.get_key().hash(&mut hasher);
    hasher.finish()
  }
}

/// Key trait for Keyed Topics
///
/// It is a combination of traits from the standard library
/// * [PartialEq](https://doc.rust-lang.org/std/cmp/trait.PartialEq.html)
/// * [Eq](https://doc.rust-lang.org/std/cmp/trait.Eq.html)
/// * [PartialOrd](https://doc.rust-lang.org/std/cmp/trait.PartialOrd.html)
/// * [Ord](https://doc.rust-lang.org/std/cmp/trait.Ord.html)
/// * [Hash](https://doc.rust-lang.org/std/hash/trait.Hash.html)
/// * [Clone](https://doc.rust-lang.org/std/clone/trait.Clone.html)
///
/// and Serde traits
/// * [Serialize](https://docs.serde.rs/serde/trait.Serialize.html) and
/// * [DeserializeOwned](https://docs.serde.rs/serde/de/trait.DeserializeOwned.html) .

pub trait Key:
  Eq + PartialEq + PartialOrd + Ord + Hash + Clone + Serialize + DeserializeOwned
{
  // no methods required
  fn into_hash_key(&self) -> u128 {
    let cdr_bytes = match to_bytes::<Self, LittleEndian>(&self) {
      Ok(b) => b,
      _ => Vec::new(),
    };

    let digest = if cdr_bytes.len() > 16 {
      md5::compute(&cdr_bytes).to_vec()
    } else {
      cdr_bytes
    };

    let mut digarr: [u8; 16] = [0; 16];
    for i in 0..digest.len() {
      digarr[i] = digest[i];
    }

    u128::from_le_bytes(digarr)
  }
}

impl Key for () {
  fn into_hash_key(&self) -> u128 {
    0
  }
}

/// Key for a reference type `&D` is the same as for the value type `D`.
/// This is required internally for the implementation of NoKey topics.
impl<D: Keyed> Keyed for &D {
  type K = D::K;
  fn get_key(&self) -> Self::K {
    (*self).get_key()
  }
}

// TODO: might want to implement this for each primitive?
impl Key for bool {}
impl Key for char {}
impl Key for i8 {}
impl Key for i16 {}
impl Key for i32 {}
impl Key for i64 {}
impl Key for i128 {}
impl Key for isize {}
impl Key for u8 {}
impl Key for u16 {}
impl Key for u32 {}
impl Key for u64 {}
impl Key for u128 {}
impl Key for usize {}

impl Key for String {}

#[derive(Debug, Eq, PartialEq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
/// Key type to identicy data instances in builtin topics
pub struct BuiltInTopicKey {
  /// IDL PSM (2.3.3, pg 138) uses array of 3x long to implement this
  value: [i32; 3],
}

impl BuiltInTopicKey {
  pub fn get_random_key() -> BuiltInTopicKey {
    let mut rng = rand::thread_rng();
    BuiltInTopicKey {
      value: [rng.gen(), rng.gen(), rng.gen()],
    }
  }

  pub fn default() -> BuiltInTopicKey {
    BuiltInTopicKey { value: [0, 0, 0] }
  }
}