use std::fmt::{Debug, Display, Error as FmtError, Formatter};
use std::result;
use std::error;

use super::escaping::{escape, unescape};

pub const IRC_TRAILING: char = ':';
pub const IRC_TAG_START: char = '@';
pub const IRC_PREFIX_START: char = ':';
pub const IRC_TAG_VALUE_SEP: char = '=';
pub const IRC_TAG_VENDOR_SEP: char = '/';
pub const IRC_TAG_END_SEP: char = ';';
pub const IRC_PREFIX_USER_SEP: char = '!';
pub const IRC_PREFIX_HOST_SEP: char = '@';

pub type Result<T> = result::Result<T, ParseError>;

// CHECK FUNCTIONS
fn check_valid_key(ch: char) -> bool { ch.is_alphabetic() || ch.is_digit(10) || ch == '-' }

// CHAR HELPER FUNCTIONS
fn get_char_at(s: &str, ind: usize) -> char {
	s[ind..].chars().next().unwrap()
}

pub struct ParseError {
	message: &'static str,
	kind: ParseErrorKind,
}

impl ParseError {
	fn new_unexpected(msg: &'static str, ch: char) -> ParseError {
		ParseError {
			message: msg,
			kind: ParseErrorKind::Unexpected(ch)
		}
	}

	fn new_bad_syntax(msg: &'static str) -> ParseError {
		ParseError {
			message: msg,
			kind: ParseErrorKind::BadSyntax
		}
	}

	fn new_missing_command(msg: &'static str) -> ParseError {
		ParseError {
			message: msg,
			kind: ParseErrorKind::BadSyntax,
		}
	}
}

impl error::Error for ParseError {

}

impl Display for ParseError {
	fn fmt(&self, f: &mut Formatter) -> result::Result<(), FmtError> {
		f.write_str(self.message)?;
		f.write_str("; ")?;

		match &self.kind {
			ParseErrorKind::Unexpected(ch) => write!(f, "unexpected char '{}'", ch),
			ParseErrorKind::BadSyntax => f.write_str("bad syntax"),
			ParseErrorKind::MissingCommand => f.write_str("missing command"),
		}
	}
}

impl Debug for ParseError {
	fn fmt(&self, f: &mut Formatter) -> result::Result<(), FmtError> {
		<ParseError as Display>::fmt(self, f)
	}
}

pub enum ParseErrorKind {
	Unexpected(char),
	BadSyntax,
	MissingCommand,
}

/// A single IRC3 tag.
///
/// The [`vendor`] field of `Tag` is used to namespace tags.
/// This allows to differentiate between two equally named tags.
#[derive(PartialEq)]
pub struct Tag {
	key: String,
	vendor: Option<String>,
	value:  Option<String>,
}

impl Tag {
	pub fn new(key: &str, value: Option<&str>) -> Tag {
		Tag::new_with_vendor(key, value, None)
	}

	pub fn new_with_vendor(key: &str, value: Option<&str>, vendor: Option<&str>) -> Tag {
		Tag {
			key: String::from(key),
			vendor: match vendor {
				Some(s) => Some(String::from(s)),
				None => None,
			},
			value: match value {
				Some(s) => Some(String::from(s)),
				None => None,
			}
		}
	}

	pub fn key(&self) -> &str {
		&self.key
	}

	pub fn vendor(&self) -> Option<&str> {
		match &self.vendor {
			Some(s) => Some(s),
			None => None,
		}
	}

	pub fn value(&self) -> Option<&str> {
		match &self.value {
			Some(s) => Some(s),
			None => None,
		}
	}

	pub fn set_key(&mut self, key: &str) {
		self.key = String::from(key);
	}

	pub fn set_vendor(&mut self, vendor: &str) {
		self.vendor = Some(String::from(vendor));
	}

	pub fn set_value(&mut self, value: &str) {
		self.value = Some(String::from(value));
	}
}

impl Display for Tag {
	fn fmt(&self, f: &mut Formatter) -> result::Result<(), FmtError> {
		// turn the tag into the format used in the IRC 3.2 spec
		if let Some(ven) = &self.vendor {
			f.write_str(ven)?;
			f.write_str("/")?;
		}

		f.write_str(&self.key)?;

		if let Some(value) = &self.value {
			f.write_str("=")?;
			f.write_str(&escape(value))?;
		}

		Ok(())
	}
}

impl Debug for Tag {
	fn fmt(&self, f: &mut Formatter) -> result::Result<(), FmtError> {
		f.write_str(&self.key)?;
		if let Some(val) = &self.value { write!(f, "=\"{}\"", val)?; }
		if let Some(ven) = &self.vendor { write!(f, " ({})", ven)?; }

		Ok(())
	}
}

/// A prefix of an IRC message.
#[derive(PartialEq)]
pub struct Prefix {
	origin: String,
	user: Option<String>,
	host: Option<String>,
}

impl Prefix {
	pub fn new(origin: &str, user: Option<&str>, host: Option<&str>) -> Prefix {
		Prefix {
			origin: String::from(origin),
			user: match user {
				Some(s) => Some(String::from(s)),
				None => None,
			},
			host: match host {
				Some(s) => Some(String::from(s)),
				None => None,
			}
		}
	}

	pub fn parse(pre: &str) -> Prefix {
		Prefix {
			origin: match pre.find(IRC_PREFIX_USER_SEP) {
				Some(i) => String::from(&pre[..i]),
				None => match pre.find(IRC_PREFIX_HOST_SEP) {
					Some(i) => String::from(&pre[..i]),
					None => String::from(pre),
				}
			},
			user: match pre.find(IRC_PREFIX_USER_SEP) {
				Some(i) => match pre.find(IRC_PREFIX_HOST_SEP) {
					Some(j) => Some(String::from(&pre[(i+IRC_PREFIX_USER_SEP.len_utf8())..j])),
					None => Some(String::from(&pre[(i+IRC_PREFIX_USER_SEP.len_utf8())..])),
				},
				None => None,
			},
			host: match pre.find(IRC_PREFIX_HOST_SEP) {
				Some(i) => Some(String::from(&pre[(i+IRC_PREFIX_HOST_SEP.len_utf8())..])),
				None => None,
			}
		}
	}

	pub fn origin(&self) -> &str {
		&self.origin
	}

	pub fn user(&self) -> Option<&str> {
		match &self.user {
			Some(s) => Some(s),
			None => None,
		}
	}

	pub fn host(&self) -> Option<&str> {
		match &self.host {
			Some(s) => Some(s),
			None => None,
		}
	}

	pub fn set_origin(&mut self, s: &str) {
		self.origin = String::from(s);
	}

	pub fn set_user(&mut self, s: &str) {
		self.user = Some(String::from(s));
	}

	pub fn set_host(&mut self, s: &str) {
		self.host = Some(String::from(s));
	}
}

impl Display for Prefix {
	fn fmt(&self, f: &mut Formatter) -> result::Result<(), FmtError> {
		f.write_str(&self.origin)?;
		
		if let Some(user) = &self.user {
			f.write_str("!")?;
			f.write_str(user)?;
		}

		if let Some(host) = &self.host {
			f.write_str("@")?;
			f.write_str(host)?;
		}

		Ok(())
	}
}

impl Debug for Prefix {
	fn fmt(&self, f: &mut Formatter) -> result::Result<(), FmtError> {
		f.write_str("{")?;
		write!(f, "origin=\"{}\"", self.origin)?;
		if let Some(user) = &self.user {
			write!(f, ", user=\"{}\"", user)?;
		}
		if let Some(host) = &self.host {
			write!(f, ", host=\"{}\"", host)?;
		}
		f.write_str("}")
	}
}

/// An iterator over the tags of a raw IRC message.
pub struct TagsIter<'a> {
	cursor: usize,
	inner: &'a str,
}

impl<'a> TagsIter<'a> {
	pub fn new(tags: &'a str) -> TagsIter<'a> {
		TagsIter {
			cursor: 0,
			inner: tags,
		}
	}
}

impl<'a> Iterator for TagsIter<'a> {
	type Item = Result<Tag>;

	fn next(&mut self) -> Option<Self::Item> {
		if self.cursor >= self.inner.len() {
			return None
		}

		// start with a vendor
		let mut vendor: Option<String> = None;

		// reading metadata
		let mut has_value = false;

		// read key first
		let mut start = self.cursor;
		while self.cursor < self.inner.len() {
			let ch = get_char_at(self.inner, self.cursor);
			// check if this is a vendor string
			if ch == IRC_TAG_VENDOR_SEP {
				// set vendor string if it does not exist
				if vendor.is_none() {
					vendor = Some(String::from(&self.inner[start..self.cursor]));
					start = self.cursor + ch.len_utf8();
				} else {
					return Some(Err(ParseError::new_bad_syntax(
					"tags may only have one vendor")));
				}

				self.cursor += ch.len_utf8();
				continue;
			}

			// check if we need to break from reading the tag
			if ch == IRC_TAG_VALUE_SEP {
				has_value = true;
				break;
			}

			// check if the tag ends
			if ch == IRC_TAG_END_SEP {
				break;
			}

			// check if the character conforms to the standard
			if !check_valid_key(ch) {
				return Some(Err(ParseError::new_unexpected(
				"tags can only contain letters, digits or hyphens", ch)));
			}

			self.cursor += ch.len_utf8();
		}

		// write key range into a tag
		let tag = Tag{
			key: String::from(&self.inner[start..self.cursor]),
			vendor: vendor,
			value: if has_value {
				// skip over '='
				self.cursor += IRC_TAG_VALUE_SEP.len_utf8();

				// read value
				let start = self.cursor;
				while self.cursor < self.inner.len() {
					let ch = get_char_at(self.inner, self.cursor);

					if ch == IRC_TAG_END_SEP {
						break;
					}

					self.cursor += ch.len_utf8();
				}

				// clone tag
				Some(unescape(&self.inner[start..self.cursor]))
				// the escaping of values will occur during accesses to Tag
			} else {
				None
			},
		};

		// skip over semicolon
		self.cursor += IRC_TAG_END_SEP.len_utf8();

		Some(Ok(tag))
	}
}

/// Used to iterate over the contents of a raw IRC message's params
pub struct ParamsIter<'a> {
	cursor: usize,
	inner: &'a str,
}

impl<'a> ParamsIter<'a> {
	pub fn new(params: &'a str) -> ParamsIter<'a> {
		ParamsIter {
			cursor: 0,
			inner: params,
		}
	}
}

impl<'a> Iterator for ParamsIter<'a> {
	type Item = &'a str;

	fn next(&mut self) -> Option<Self::Item> {
		if self.cursor >= self.inner.len() {
			return None;
		}

		// reading metadata
		let mut trailing = false;

		let mut start = self.cursor;
		let mut offset: usize = 0;
		while self.cursor < self.inner.len() {
			let ch = get_char_at(self.inner, self.cursor);
			if ch.is_whitespace() && !trailing {
				offset += ch.len_utf8();
				// consume whitespace
				while self.cursor+offset < self.inner.len() {
					let ch = get_char_at(self.inner, self.cursor+offset);
					if !ch.is_whitespace() {
						break;
					}

					offset += ch.len_utf8();
				}

				break;
			}

			if start == self.cursor {
				// start of the parameter,
				if ch == IRC_TRAILING {
					trailing = true;
					start += ch.len_utf8();
				}
			}

			self.cursor += ch.len_utf8();
		}

		// return a result
		let slice = &self.inner[start..self.cursor];
		self.cursor += offset;
		Some(slice)
	}
}

/// A full IRC message that can be reprocessed back into its encoded form.
///
/// An IRC message can be parsed from a raw message, or it can built using
/// the [`new`] constructor and the builder functions [`with_tag`],
/// [`with_tag_vendor`], [`with_prefix`] and [`with_param`].
///
/// # Examples
/// ```rust
/// use irc3::Message;
///
/// fn main() {
/// 	const MSG: &'static str = ":dan!d@localhost PRIVMSG * :Hey guys, what's up?";
///
/// 	let built_message = Message::new("PRIVMSG")
/// 		.with_prefix("dan", Some("d"), Some("localhost"))
/// 		.with_param("*")
/// 		.with_param("Hey guys, what's up?");
/// 	
/// 	let parsed_message = Message::parse(MSG).unwrap();
///
/// 	assert!(built_message == parsed_message);
/// }
/// ```
#[derive(Debug, PartialEq)]
pub struct Message {
	tags: Vec<Tag>,
	prefix: Option<Prefix>,
	command: String,
	params: Vec<String>,
}

impl Message {
	pub fn new(command: &str) -> Message {
		Message {
			tags: Vec::new(),
			prefix: None,
			command: String::from(command),
			params: Vec::new(),
		}
	}

	pub fn parse<S: AsRef<str> + ?Sized>(s: &S) -> Result<Message> {
		let mut line = s.as_ref();

		if line.is_empty() {
			return Err(ParseError::new_missing_command("missing irc command!"))
		}

		Ok(Message {
			// check if the tags are present
			tags: if line.starts_with(IRC_TAG_START) {
				// tags are present, strip line of them!
				let mut split = line.splitn(2, char::is_whitespace);

				let tags = split.next().unwrap();
				line = match split.next() {
					Some(line) => line,
					None => return Err(ParseError::new_missing_command("missing irc command!")),
				};

				TagsIter::new(&tags[IRC_TAG_START.len_utf8()..]).filter_map(|r| match r {
					Ok(t) => Some(t),
					Err(_) => None,
				}).collect()
			} else {
				Vec::new()
			},
			// check if the prefix is present
			prefix: if line.starts_with(IRC_PREFIX_START) {
				// prefix is present!
				let mut split = line.splitn(2, char::is_whitespace);

				let prefix = split.next().unwrap();
				line = match split.next() {
					Some(line) => line,
					None => return Err(ParseError::new_missing_command("missing irc command!")),
				};

				Some(Prefix::parse(&prefix[IRC_PREFIX_START.len_utf8()..]))
			} else {
				None
			},
			// get the command (it must be present)
			command: {
				String::from(line.split(char::is_whitespace).next().unwrap())
			},
			params: {
				match line.splitn(2, char::is_whitespace).skip(1).next() {
					Some(line) => ParamsIter::new(line).map(|s| String::from(s)).collect(),
					None => Vec::new(),
				}
			}
		})
	}

	pub fn command(&self) -> &str {
		&self.command
	}

	pub fn has_prefix(&self) -> bool {
		self.prefix.is_some()
	}

	pub fn origin(&self) -> Option<&str> {
		match &self.prefix {
			Some(p) => Some(p.origin()),
			None => None,
		}
	}

	pub fn user(&self) -> Option<&str> {
		match &self.prefix {
			Some(p) => p.user(),
			None => None,
		}
	}

	pub fn host(&self) -> Option<&str> {
		match &self.prefix {
			Some(p) => p.host(),
			None => None,
		}
	}

	pub fn params(&self) -> std::slice::Iter<String> {
		self.params.iter()
	}

	pub fn param(&self, ind: usize) -> Option<&str> {
		match self.params.iter().skip(ind).next() {
			Some(s) => Some(s),
			None => None,
		}
	}

	pub fn tags(&self) -> std::slice::Iter<Tag> {
		self.tags.iter()
	}

	pub fn tag(&self, key: &str) -> Option<&Tag> {
		self.tags.iter().filter(|t| t.key() == key).next()
	}

	// Builder things
	pub fn with_prefix(mut self, origin: &str, user: Option<&str>, host: Option<&str>) -> Message {
		self.prefix = Some(Prefix::new(origin, user, host));
		self
	}

	pub fn with_tag(self, key: &str, value: Option<&str>) -> Message {
		self.with_tag_vendor(key, value, None)
	}

	pub fn with_tag_vendor(mut self, key: &str, value: Option<&str>, vendor: Option<&str>) -> Message {
		self.tags.push(Tag::new_with_vendor(key, value, vendor));
		self
	}

	pub fn with_param(mut self, param: &str) -> Message {
		self.params.push(String::from(param));
		self
	}
}

impl Display for Message {
	fn fmt(&self, f: &mut Formatter) -> result::Result<(), FmtError> {
		if self.tags.len() > 0 {
			f.write_str("@")?;
			for (i, t) in self.tags.iter().enumerate() {
				if i > 0 {
					f.write_str(";")?;
				}

				write!(f, "{}", t)?;
			}
			f.write_str(" ")?;
		}

		if let Some(prefix) = &self.prefix {
			write!(f, "{}", prefix)?;
			f.write_str(" ")?;
		}

		f.write_str(&self.command)?;

		if self.params.len() > 0 {
			f.write_str(" ")?;

			for (i, p) in self.params.iter().enumerate() {
				if i > 0 {
					f.write_str(" ")?;
				}

				// if this is the last parameter, do trailing
				if i >= self.params.len() - 1 {
					// try to write a trailing
					if p.split(char::is_whitespace).count() > 1 {
						f.write_str(":")?;
						f.write_str(p)?;
					} else {
						f.write_str(p)?;
					}
				} else {
					f.write_str(p)?;
				}
			}
		}

		Ok(())
	}
}