// 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.

#[cfg(not(feature = "std"))]
use alloc::vec::Vec;
use bytes::{BufMut, BytesMut};
use core::borrow::Borrow;

use crate::traits::Encodable;

#[derive(Debug, Copy, Clone)]
struct ListInfo {
	position: usize,
	current: usize,
	max: Option<usize>,
}

impl ListInfo {
	fn new(position: usize, max: Option<usize>) -> ListInfo {
		ListInfo { position, current: 0, max }
	}
}

/// Appendable rlp encoder.
pub struct RlpStream {
	unfinished_lists: Vec<ListInfo>,
	start_pos: usize,
	buffer: BytesMut,
	finished_list: bool,
}

impl Default for RlpStream {
	fn default() -> Self {
		RlpStream::new()
	}
}

impl RlpStream {
	/// Initializes instance of empty `Stream`.
	pub fn new() -> Self {
		Self::new_with_buffer(BytesMut::with_capacity(1024))
	}

	/// Initializes the `Stream` as a list.
	pub fn new_list(len: usize) -> Self {
		Self::new_list_with_buffer(BytesMut::with_capacity(1024), len)
	}

	/// Initializes instance of empty `Stream`.
	pub fn new_with_buffer(buffer: BytesMut) -> Self {
		RlpStream { unfinished_lists: Vec::with_capacity(16), start_pos: buffer.len(), buffer, finished_list: false }
	}

	/// Initializes the `Stream` as a list.
	pub fn new_list_with_buffer(buffer: BytesMut, len: usize) -> Self {
		let mut stream = RlpStream::new_with_buffer(buffer);
		stream.begin_list(len);
		stream
	}

	fn total_written(&self) -> usize {
		self.buffer.len() - self.start_pos
	}

	/// Apends null to the end of stream, chainable.
	///
	/// ```
	/// use tetsy_rlp::RlpStream;
	/// let mut stream = RlpStream::new_list(2);
	/// stream.append_empty_data().append_empty_data();
	/// let out = stream.out();
	/// assert_eq!(out, vec![0xc2, 0x80, 0x80]);
	/// ```
	pub fn append_empty_data(&mut self) -> &mut Self {
		// self push raw item
		self.buffer.put_u8(0x80);

		// try to finish and prepend the length
		self.note_appended(1);

		// return chainable self
		self
	}

	/// Appends raw (pre-serialised) RLP data. Use with caution. Chainable.
	pub fn append_raw(&mut self, bytes: &[u8], item_count: usize) -> &mut Self {
		// push raw items
		self.buffer.extend_from_slice(bytes);

		// try to finish and prepend the length
		self.note_appended(item_count);

		// return chainable self
		self
	}

	/// Appends value to the end of stream, chainable.
	///
	/// ```
	/// use tetsy_rlp::RlpStream;
	/// let mut stream = RlpStream::new_list(2);
	/// stream.append(&"cat").append(&"dog");
	/// let out = stream.out();
	/// assert_eq!(out, vec![0xc8, 0x83, b'c', b'a', b't', 0x83, b'd', b'o', b'g']);
	/// ```
	pub fn append<E>(&mut self, value: &E) -> &mut Self
	where
		E: Encodable,
	{
		self.finished_list = false;
		value.rlp_append(self);
		if !self.finished_list {
			self.note_appended(1);
		}
		self
	}

	/// Appends iterator to the end of stream, chainable.
	///
	/// ```
	/// use tetsy_rlp::RlpStream;
	/// let mut stream = RlpStream::new_list(2);
	/// stream.append(&"cat").append_iter("dog".as_bytes().iter().cloned());
	/// let out = stream.out();
	/// assert_eq!(out, vec![0xc8, 0x83, b'c', b'a', b't', 0x83, b'd', b'o', b'g']);
	/// ```
	pub fn append_iter<I>(&mut self, value: I) -> &mut Self
	where
		I: IntoIterator<Item = u8>,
	{
		self.finished_list = false;
		self.encoder().encode_iter(value);
		if !self.finished_list {
			self.note_appended(1);
		}
		self
	}

	/// Appends list of values to the end of stream, chainable.
	pub fn append_list<E, K>(&mut self, values: &[K]) -> &mut Self
	where
		E: Encodable,
		K: Borrow<E>,
	{
		self.begin_list(values.len());
		for value in values {
			self.append(value.borrow());
		}
		self
	}

	/// Appends value to the end of stream, but do not count it as an appended item.
	/// It's useful for wrapper types
	pub fn append_internal<E>(&mut self, value: &E) -> &mut Self
	where
		E: Encodable,
	{
		value.rlp_append(self);
		self
	}

	/// Declare appending the list of given size, chainable.
	///
	/// ```
	/// use tetsy_rlp::RlpStream;
	/// let mut stream = RlpStream::new_list(2);
	/// stream.begin_list(2).append(&"cat").append(&"dog");
	/// stream.append(&"");
	/// let out = stream.out();
	/// assert_eq!(out, vec![0xca, 0xc8, 0x83, b'c', b'a', b't', 0x83, b'd', b'o', b'g', 0x80]);
	/// ```
	pub fn begin_list(&mut self, len: usize) -> &mut RlpStream {
		self.finished_list = false;
		match len {
			0 => {
				// we may finish, if the appended list len is equal 0
				self.buffer.put_u8(0xc0u8);
				self.note_appended(1);
				self.finished_list = true;
			}
			_ => {
				// payload is longer than 1 byte only for lists > 55 bytes
				// by pushing always this 1 byte we may avoid unnecessary shift of data
				self.buffer.put_u8(0);

				let position = self.total_written();
				self.unfinished_lists.push(ListInfo::new(position, Some(len)));
			}
		}

		// return chainable self
		self
	}

	/// Declare appending the list of unknown size, chainable.
	pub fn begin_unbounded_list(&mut self) -> &mut RlpStream {
		self.finished_list = false;
		// payload is longer than 1 byte only for lists > 55 bytes
		// by pushing always this 1 byte we may avoid unnecessary shift of data
		self.buffer.put_u8(0);
		let position = self.total_written();
		self.unfinished_lists.push(ListInfo::new(position, None));
		// return chainable self
		self
	}

	/// Appends raw (pre-serialised) RLP data. Checks for size overflow.
	pub fn append_raw_checked(&mut self, bytes: &[u8], item_count: usize, max_size: usize) -> bool {
		if self.estimate_size(bytes.len()) > max_size {
			return false;
		}
		self.append_raw(bytes, item_count);
		true
	}

	/// Calculate total RLP size for appended payload.
	pub fn estimate_size(&self, add: usize) -> usize {
		let total_size = self.total_written() + add;
		let mut base_size = total_size;
		for list in &self.unfinished_lists[..] {
			let len = total_size - list.position;
			if len > 55 {
				let leading_empty_bytes = (len as u64).leading_zeros() as usize / 8;
				let size_bytes = 8 - leading_empty_bytes;
				base_size += size_bytes;
			}
		}
		base_size
	}

	/// Returns current RLP size in bytes for the data pushed into the list.
	pub fn len(&self) -> usize {
		self.estimate_size(0)
	}

	pub fn is_empty(&self) -> bool {
		self.len() == 0
	}

	/// Clear the output stream so far.
	///
	/// ```
	/// use tetsy_rlp::RlpStream;
	/// let mut stream = RlpStream::new_list(3);
	/// stream.append(&"cat");
	/// stream.clear();
	/// stream.append(&"dog");
	/// let out = stream.out();
	/// assert_eq!(out, vec![0x83, b'd', b'o', b'g']);
	/// ```
	pub fn clear(&mut self) {
		// clear bytes
		self.buffer.truncate(self.start_pos);

		// clear lists
		self.unfinished_lists.clear();
	}

	/// Returns true if stream doesnt expect any more items.
	///
	/// ```
	/// use tetsy_rlp::RlpStream;
	/// let mut stream = RlpStream::new_list(2);
	/// stream.append(&"cat");
	/// assert_eq!(stream.is_finished(), false);
	/// stream.append(&"dog");
	/// assert_eq!(stream.is_finished(), true);
	/// let out = stream.out();
	/// assert_eq!(out, vec![0xc8, 0x83, b'c', b'a', b't', 0x83, b'd', b'o', b'g']);
	/// ```
	pub fn is_finished(&self) -> bool {
		self.unfinished_lists.is_empty()
	}

	/// Get raw encoded bytes
	pub fn as_raw(&self) -> &[u8] {
		//&self.encoder.bytes
		&self.buffer
	}

	/// Streams out encoded bytes.
	///
	/// panic! if stream is not finished.
	pub fn out(self) -> BytesMut {
		if self.is_finished() {
			self.buffer
		} else {
			panic!()
		}
	}

	/// Try to finish lists
	fn note_appended(&mut self, inserted_items: usize) {
		if self.unfinished_lists.is_empty() {
			return;
		}

		let back = self.unfinished_lists.len() - 1;
		let should_finish = match self.unfinished_lists.get_mut(back) {
			None => false,
			Some(ref mut x) => {
				x.current += inserted_items;
				match x.max {
					Some(ref max) if x.current > *max => panic!("You cannot append more items than you expect!"),
					Some(ref max) => x.current == *max,
					_ => false,
				}
			}
		};
		if should_finish {
			let x = self.unfinished_lists.pop().unwrap();
			let len = self.total_written() - x.position;
			self.encoder().insert_list_payload(len, x.position);
			self.note_appended(1);
		}
		self.finished_list = should_finish;
	}

	pub fn encoder(&mut self) -> BasicEncoder {
		BasicEncoder::new(self, self.start_pos)
	}

	/// Finalize current unbounded list. Panics if no unbounded list has been opened.
	pub fn finalize_unbounded_list(&mut self) {
		let list = self.unfinished_lists.pop().expect("No open list.");
		if list.max.is_some() {
			panic!("List type mismatch.");
		}
		let len = self.total_written() - list.position;
		self.encoder().insert_list_payload(len, list.position);
		self.note_appended(1);
		self.finished_list = true;
	}
}

pub struct BasicEncoder<'a> {
	buffer: &'a mut BytesMut,
	start_pos: usize,
}

impl<'a> BasicEncoder<'a> {
	fn new(stream: &'a mut RlpStream, start_pos: usize) -> Self {
		BasicEncoder { buffer: &mut stream.buffer, start_pos }
	}

	fn total_written(&self) -> usize {
		self.buffer.len() - self.start_pos
	}

	fn insert_size(&mut self, size: usize, position: usize) -> u8 {
		let size = size as u32;
		let leading_empty_bytes = size.leading_zeros() as usize / 8;
		let size_bytes = 4 - leading_empty_bytes as u8;
		let buffer: [u8; 4] = size.to_be_bytes();
		assert!(position <= self.total_written());

		self.buffer.extend_from_slice(&buffer[leading_empty_bytes..]);
		self.buffer[self.start_pos + position..].rotate_right(size_bytes as usize);
		size_bytes as u8
	}

	/// Inserts list prefix at given position
	fn insert_list_payload(&mut self, len: usize, pos: usize) {
		// 1 byte was already reserved for payload earlier
		match len {
			0..=55 => {
				self.buffer[self.start_pos + pos - 1] = 0xc0u8 + len as u8;
			}
			_ => {
				let inserted_bytes = self.insert_size(len, pos);
				self.buffer[self.start_pos + pos - 1] = 0xf7u8 + inserted_bytes;
			}
		};
	}

	pub fn encode_value(&mut self, value: &[u8]) {
		self.encode_iter(value.iter().cloned());
	}

	/// Pushes encoded value to the end of buffer
	pub fn encode_iter<I>(&mut self, value: I)
	where
		I: IntoIterator<Item = u8>,
	{
		let mut value = value.into_iter();
		let len = match value.size_hint() {
			(lower, Some(upper)) if lower == upper => lower,
			_ => {
				let value = value.collect::<Vec<_>>();
				return self.encode_iter(value);
			}
		};
		match len {
			// just 0
			0 => self.buffer.put_u8(0x80u8),
			len @ 1..=55 => {
				let first = value.next().expect("iterator length is higher than 1");
				if len == 1 && first < 0x80 {
					// byte is its own encoding if < 0x80
					self.buffer.put_u8(first);
				} else {
					// (prefix + length), followed by the string
					self.buffer.put_u8(0x80u8 + len as u8);
					self.buffer.put_u8(first);
					self.buffer.extend(value);
				}
			}
			// (prefix + length of length), followed by the length, followd by the string
			len => {
				self.buffer.put_u8(0);
				let position = self.total_written();
				let inserted_bytes = self.insert_size(len, position);
				self.buffer[self.start_pos + position - 1] = 0xb7 + inserted_bytes;
				self.buffer.extend(value);
			}
		}
	}
}