// Copyright 2020 Parity Technologies
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Generetes trie root.
//!
//! This module should be used to generate trie root hash.

#![cfg_attr(not(feature = "std"), no_std)]

#[cfg(not(feature = "std"))]
extern crate alloc;

#[cfg(feature = "std")]
mod rstd {
	pub use std::collections::BTreeMap;
}

#[cfg(not(feature = "std"))]
mod rstd {
	pub use alloc::collections::BTreeMap;
	pub use alloc::vec::Vec;
}

use core::cmp;
use core::iter::once;
use rstd::*;

use tetsy_hash_db::Hasher;
use tetsy_rlp::RlpStream;

fn shared_prefix_len<T: Eq>(first: &[T], second: &[T]) -> usize {
	first.iter().zip(second.iter()).position(|(f, s)| f != s).unwrap_or_else(|| cmp::min(first.len(), second.len()))
}

/// Generates a trie root hash for a vector of values
///
/// ```
/// use hex_literal::hex;
/// use vapory_types::H256;
/// use tetsy_triehash::ordered_trie_root;
/// use keccak_hasher::KeccakHasher;
///
/// let v = &["doe", "reindeer"];
/// let root = H256::from(hex!("e766d5d51b89dc39d981b41bda63248d7abce4f0225eefd023792a540bcffee3"));
/// assert_eq!(ordered_trie_root::<KeccakHasher, _>(v), root.as_ref());
/// ```
pub fn ordered_trie_root<H, I>(input: I) -> H::Out
where
	I: IntoIterator,
	I::Item: AsRef<[u8]>,
	H: Hasher,
	<H as tetsy_hash_db::Hasher>::Out: cmp::Ord,
{
	trie_root::<H, _, _, _>(input.into_iter().enumerate().map(|(i, v)| (tetsy_rlp::encode(&i), v)))
}

/// Generates a trie root hash for a vector of key-value tuples
///
/// ```
/// use hex_literal::hex;
/// use tetsy_triehash::trie_root;
/// use vapory_types::H256;
/// use keccak_hasher::KeccakHasher;
///
/// let v = vec![
/// 	("doe", "reindeer"),
/// 	("dog", "puppy"),
/// 	("dogglesworth", "cat"),
/// ];
///
/// let root = H256::from(hex!("8aad789dff2f538bca5d8ea56e8abe10f4c7ba3a5dea95fea4cd6e7c3a1168d3"));
/// assert_eq!(trie_root::<KeccakHasher, _, _, _>(v), root.as_ref());
/// ```
pub fn trie_root<H, I, A, B>(input: I) -> H::Out
where
	I: IntoIterator<Item = (A, B)>,
	A: AsRef<[u8]> + Ord,
	B: AsRef<[u8]>,
	H: Hasher,
	<H as tetsy_hash_db::Hasher>::Out: cmp::Ord,
{
	// first put elements into btree to sort them and to remove duplicates
	let input = input.into_iter().collect::<BTreeMap<_, _>>();

	let mut nibbles = Vec::with_capacity(input.keys().map(|k| k.as_ref().len()).sum::<usize>() * 2);
	let mut lens = Vec::with_capacity(input.len() + 1);
	lens.push(0);
	for k in input.keys() {
		for &b in k.as_ref() {
			nibbles.push(b >> 4);
			nibbles.push(b & 0x0F);
		}
		lens.push(nibbles.len());
	}

	// then move them to a vector
	let input = input.into_iter().zip(lens.windows(2)).map(|((_, v), w)| (&nibbles[w[0]..w[1]], v)).collect::<Vec<_>>();

	let mut stream = RlpStream::new();
	hash256rlp::<H, _, _>(&input, 0, &mut stream);
	H::hash(&stream.out())
}

/// Generates a key-hashed (secure) trie root hash for a vector of key-value tuples.
///
/// ```
/// use hex_literal::hex;
/// use vapory_types::H256;
/// use tetsy_triehash::sec_trie_root;
/// use keccak_hasher::KeccakHasher;
///
/// let v = vec![
/// 	("doe", "reindeer"),
/// 	("dog", "puppy"),
/// 	("dogglesworth", "cat"),
/// ];
///
/// let root = H256::from(hex!("d4cd937e4a4368d7931a9cf51686b7e10abb3dce38a39000fd7902a092b64585"));
/// assert_eq!(sec_trie_root::<KeccakHasher, _, _, _>(v), root.as_ref());
/// ```
pub fn sec_trie_root<H, I, A, B>(input: I) -> H::Out
where
	I: IntoIterator<Item = (A, B)>,
	A: AsRef<[u8]>,
	B: AsRef<[u8]>,
	H: Hasher,
	<H as tetsy_hash_db::Hasher>::Out: cmp::Ord,
{
	trie_root::<H, _, _, _>(input.into_iter().map(|(k, v)| (H::hash(k.as_ref()), v)))
}

/// Hex-prefix Notation. First nibble has flags: oddness = 2^0 & termination = 2^1.
///
/// The "termination marker" and "leaf-node" specifier are completely equivalent.
///
/// Input values are in range `[0, 0xf]`.
///
/// ```markdown
///  [0,0,1,2,3,4,5]   0x10012345 // 7 > 4
///  [0,1,2,3,4,5]     0x00012345 // 6 > 4
///  [1,2,3,4,5]       0x112345   // 5 > 3
///  [0,0,1,2,3,4]     0x00001234 // 6 > 3
///  [0,1,2,3,4]       0x101234   // 5 > 3
///  [1,2,3,4]         0x001234   // 4 > 3
///  [0,0,1,2,3,4,5,T] 0x30012345 // 7 > 4
///  [0,0,1,2,3,4,T]   0x20001234 // 6 > 4
///  [0,1,2,3,4,5,T]   0x20012345 // 6 > 4
///  [1,2,3,4,5,T]     0x312345   // 5 > 3
///  [1,2,3,4,T]       0x201234   // 4 > 3
/// ```
fn hex_prefix_encode<'a>(nibbles: &'a [u8], leaf: bool) -> impl Iterator<Item = u8> + 'a {
	let inlen = nibbles.len();
	let oddness_factor = inlen % 2;

	let first_byte = {
		let mut bits = ((inlen as u8 & 1) + (2 * leaf as u8)) << 4;
		if oddness_factor == 1 {
			bits += nibbles[0];
		}
		bits
	};
	once(first_byte).chain(nibbles[oddness_factor..].chunks(2).map(|ch| ch[0] << 4 | ch[1]))
}

fn hash256rlp<H, A, B>(input: &[(A, B)], pre_len: usize, stream: &mut RlpStream)
where
	A: AsRef<[u8]>,
	B: AsRef<[u8]>,
	H: Hasher,
{
	let inlen = input.len();

	// in case of empty slice, just append empty data
	if inlen == 0 {
		stream.append_empty_data();
		return;
	}

	// take slices
	let key: &[u8] = &input[0].0.as_ref();
	let value: &[u8] = &input[0].1.as_ref();

	// if the slice contains just one item, append the suffix of the key
	// and then append value
	if inlen == 1 {
		stream.begin_list(2);
		stream.append_iter(hex_prefix_encode(&key[pre_len..], true));
		stream.append(&value);
		return;
	}

	// get length of the longest shared prefix in slice keys
	let shared_prefix = input
		.iter()
		// skip first tuple
		.skip(1)
		// get minimum number of shared nibbles between first and each successive
		.fold(key.len(), |acc, &(ref k, _)| cmp::min(shared_prefix_len(key, k.as_ref()), acc));

	// if shared prefix is higher than current prefix append its
	// new part of the key to the stream
	// then recursively append suffixes of all items who had this key
	if shared_prefix > pre_len {
		stream.begin_list(2);
		stream.append_iter(hex_prefix_encode(&key[pre_len..shared_prefix], false));
		hash256aux::<H, _, _>(input, shared_prefix, stream);
		return;
	}

	// an item for every possible nibble/suffix
	// + 1 for data
	stream.begin_list(17);

	// if first key len is equal to prefix_len, move to next element
	let mut begin = if pre_len == key.len() { 1 } else { 0 };

	// iterate over all possible nibbles
	for i in 0..16 {
		// count how many successive elements have same next nibble
		let len = input.iter().skip(begin).take_while(|pair| pair.0.as_ref()[pre_len] == i).count();

		// if at least 1 successive element has the same nibble
		// append their suffixes
		match len {
			0 => {
				stream.append_empty_data();
			}
			_ => hash256aux::<H, _, _>(&input[begin..(begin + len)], pre_len + 1, stream),
		}
		begin += len;
	}

	// if fist key len is equal prefix, append its value
	if pre_len == key.len() {
		stream.append(&value);
	} else {
		stream.append_empty_data();
	}
}

fn hash256aux<H, A, B>(input: &[(A, B)], pre_len: usize, stream: &mut RlpStream)
where
	A: AsRef<[u8]>,
	B: AsRef<[u8]>,
	H: Hasher,
{
	let mut s = RlpStream::new();
	hash256rlp::<H, _, _>(input, pre_len, &mut s);
	let out = s.out();
	match out.len() {
		0..=31 => stream.append_raw(&out, 1),
		_ => stream.append(&H::hash(&out).as_ref()),
	};
}

#[cfg(test)]
mod tests {
	use super::{hex_prefix_encode, shared_prefix_len, trie_root};
	use vapory_types::H256;
	use hex_literal::hex;
	use keccak_hasher::KeccakHasher;

	#[test]
	fn test_hex_prefix_encode() {
		let v = vec![0, 0, 1, 2, 3, 4, 5];
		let e = vec![0x10, 0x01, 0x23, 0x45];
		let h = hex_prefix_encode(&v, false).collect::<Vec<_>>();
		assert_eq!(h, e);

		let v = vec![0, 1, 2, 3, 4, 5];
		let e = vec![0x00, 0x01, 0x23, 0x45];
		let h = hex_prefix_encode(&v, false).collect::<Vec<_>>();
		assert_eq!(h, e);

		let v = vec![0, 1, 2, 3, 4, 5];
		let e = vec![0x20, 0x01, 0x23, 0x45];
		let h = hex_prefix_encode(&v, true).collect::<Vec<_>>();
		assert_eq!(h, e);

		let v = vec![1, 2, 3, 4, 5];
		let e = vec![0x31, 0x23, 0x45];
		let h = hex_prefix_encode(&v, true).collect::<Vec<_>>();
		assert_eq!(h, e);

		let v = vec![1, 2, 3, 4];
		let e = vec![0x00, 0x12, 0x34];
		let h = hex_prefix_encode(&v, false).collect::<Vec<_>>();
		assert_eq!(h, e);

		let v = vec![4, 1];
		let e = vec![0x20, 0x41];
		let h = hex_prefix_encode(&v, true).collect::<Vec<_>>();
		assert_eq!(h, e);
	}

	#[test]
	fn simple_test() {
		assert_eq!(
			trie_root::<KeccakHasher, _, _, _>(vec![(
				b"A",
				b"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" as &[u8]
			)]),
			H256::from(hex!("d23786fb4a010da3ce639d66d5e904a11dbc02746d1ce25029e53290cabf28ab")).as_ref(),
		);
	}

	#[test]
	fn test_tetsy_triehash_out_of_order() {
		assert_eq!(
			trie_root::<KeccakHasher, _, _, _>(vec![
				(vec![0x01u8, 0x23], vec![0x01u8, 0x23]),
				(vec![0x81u8, 0x23], vec![0x81u8, 0x23]),
				(vec![0xf1u8, 0x23], vec![0xf1u8, 0x23]),
			]),
			trie_root::<KeccakHasher, _, _, _>(vec![
				(vec![0x01u8, 0x23], vec![0x01u8, 0x23]),
				(vec![0xf1u8, 0x23], vec![0xf1u8, 0x23]), // last two tuples are swapped
				(vec![0x81u8, 0x23], vec![0x81u8, 0x23]),
			]),
		);
	}

	#[test]
	fn test_shared_prefix() {
		let a = vec![1, 2, 3, 4, 5, 6];
		let b = vec![4, 2, 3, 4, 5, 6];
		assert_eq!(shared_prefix_len(&a, &b), 0);
	}

	#[test]
	fn test_shared_prefix2() {
		let a = vec![1, 2, 3, 3, 5];
		let b = vec![1, 2, 3];
		assert_eq!(shared_prefix_len(&a, &b), 3);
	}

	#[test]
	fn test_shared_prefix3() {
		let a = vec![1, 2, 3, 4, 5, 6];
		let b = vec![1, 2, 3, 4, 5, 6];
		assert_eq!(shared_prefix_len(&a, &b), 6);
	}
}