extern crate serde;
extern crate rustc_hex;

use std::fmt;

use serde::{de, Serializer, Deserializer};
use rustc_hex::{ToHex, FromHex};

/// Serializes a slice of bytes.
pub fn serialize<S>(bytes: &[u8], serializer: S) -> Result<S::Ok, S::Error> where
	S: Serializer,
{
	let hex = ToHex::to_hex(bytes);
	serializer.serialize_str(&format!("0x{}", hex))
}

/// Serialize a slice of bytes as uint.
///
/// The representation will have all leading zeros trimmed.
pub fn serialize_uint<S>(bytes: &[u8], serializer: S) -> Result<S::Ok, S::Error> where
	S: Serializer,
{
	let non_zero = bytes.iter().take_while(|b| **b == 0).count();
	let bytes = &bytes[non_zero..];
	if bytes.is_empty() {
		return serializer.serialize_str("0x0");
	}

	let hex = ToHex::to_hex(bytes);
	let has_leading_zero = !hex.is_empty() && &hex[0..1] == "0";
	serializer.serialize_str(
		&format!("0x{}", if has_leading_zero { &hex[1..] } else { &hex })
	)
}

/// Expected length of bytes vector.
#[derive(Debug, PartialEq, Eq)]
pub enum ExpectedLen {
	/// Any length in bytes.
	Any,
	/// Exact length in bytes.
	Exact(usize),
	/// A bytes length between (min; max].
	Between(usize, usize),
}

impl fmt::Display for ExpectedLen {
	fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
		match *self {
			ExpectedLen::Any => write!(fmt, "even length"),
			ExpectedLen::Exact(v) => write!(fmt, "length of {}", v * 2),
			ExpectedLen::Between(min, max) => write!(fmt, "length between ({}; {}]", min * 2, max * 2),
		}
	}
}

/// Deserialize into vector of bytes.
pub fn deserialize<'de, D>(deserializer: D) -> Result<Vec<u8>, D::Error> where
	D: Deserializer<'de>,
{
	deserialize_check_len(deserializer, ExpectedLen::Any)
}

/// Deserialize into vector of bytes with additional size check.
pub fn deserialize_check_len<'de, D>(deserializer: D, len: ExpectedLen) -> Result<Vec<u8>, D::Error> where
	D: Deserializer<'de>,
{
	struct Visitor {
		len: ExpectedLen,
	}

	impl<'a> de::Visitor<'a> for Visitor {
		type Value = Vec<u8>;

		fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
			write!(formatter, "a 0x-prefixed hex string with {}", self.len)
		}

		fn visit_str<E: de::Error>(self, v: &str) -> Result<Self::Value, E> {
			if v.len() < 2  || &v[0..2] != "0x" {
				return Err(E::custom("prefix is missing"))
			}

			let is_len_valid = match self.len {
				// just make sure that we have all nibbles
				ExpectedLen::Any => v.len() % 2 == 0,
				ExpectedLen::Exact(len) => v.len() == 2 * len + 2,
				ExpectedLen::Between(min, max) => v.len() <= 2 * max + 2 && v.len() > 2 * min + 2,
			};

			if !is_len_valid {
				return Err(E::invalid_length(v.len() - 2, &self))
			}

			let bytes = match self.len {
				ExpectedLen::Between(..) if v.len() % 2 != 0 => {
					FromHex::from_hex(&*format!("0{}", &v[2..]))
				},
				_ => FromHex::from_hex(&v[2..])
			};

			bytes.map_err(|e| E::custom(&format!("invalid hex value: {:?}", e)))
		}

		fn visit_string<E: de::Error>(self, v: String) -> Result<Self::Value, E> {
			self.visit_str(&v)
		}
	}
	// TODO [ToDr] Use raw bytes if we switch to RLP / binencoding
	// (visit_bytes, visit_bytes_buf)
	deserializer.deserialize_str(Visitor { len })
}