use std::{fmt, iter::Peekable, str::Chars};

use super::{
	ParserError, Result,
	pos::{Pos, Span},
};

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum TokenKind {
	Eof,
	LineSeparator,

	MacroDefine,
	MacroEnd,
	Argument,

	PulseA,
	PulseB,
	Triangle,
	Noise,

	Volume,
	Pitch,
	DutyCycle,
	Mode,
	PauseLen,

	Identifier,
	Integer,
	Dash,
}
impl TokenKind {
	pub const fn name(self) -> &'static str {
		match self {
			Self::Eof => "end of file",
			Self::LineSeparator => "line seperator",

			Self::MacroDefine => "%define",
			Self::MacroEnd => "%end",
			Self::Argument => "$",

			Self::PulseA => "pulsea",
			Self::PulseB => "pulseb",
			Self::Triangle => "triangle",
			Self::Noise => "noise",

			Self::Volume => "volume",
			Self::Pitch => "pitch",
			Self::DutyCycle => "duty cycle",
			Self::Mode => "mode",
			Self::PauseLen => "pause len",

			Self::Identifier => "identifier",
			Self::Integer => "integer",
			Self::Dash => "dash",
		}
	}
}
impl fmt::Display for TokenKind {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		f.write_str(self.name())
	}
}
use TokenKind as K;

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct Token<'s> {
	pub span: Span,
	pub content: &'s str,
	pub kind: TokenKind,
}

pub struct Lexer<'s> {
	src: &'s str,
	chars: Peekable<Chars<'s>>,
	start_pos: Pos,
	pos: Pos,
}
impl<'s> Lexer<'s> {
	pub fn new(src: &'s str) -> Self {
		Self::new_at(src, 1)
	}

	pub fn new_at(src: &'s str, line: u32) -> Self {
		let pos = Pos {
			line,
			col: 1,
			idx: 0,
		};
		Self {
			src,
			chars: src.chars().peekable(),
			start_pos: pos,
			pos,
		}
	}

	fn invalid_char(&self, ch: char) -> ParserError {
		let span = Span::new(self.pos, self.pos.advance(ch));
		let msg = match ch as u32 {
			c @ 0x00..=0x7f => format!("invalid character (codepoint 0x{c:2x})"),
			c => format!("invalid character (codepoint U+{c:04x})"),
		};
		ParserError {
			span,
			msg,
			file: None,
		}
	}

	fn filter_char(&mut self, ch: Option<char>, advance: bool) -> Result<char> {
		match ch {
			Some(c) if c.is_control() && !matches!(c, '\n' | '\r' | '\t') => {
				Err(self.invalid_char(c))
			}
			Some(c) => {
				if advance {
					self.pos = self.pos.advance(c);
				}
				Ok(c)
			}
			None => Ok('\0'),
		}
	}

	fn peek(&mut self) -> Result<char> {
		let c = self.chars.peek().copied();
		self.filter_char(c, false)
	}

	fn next(&mut self) -> Result<char> {
		let c = self.chars.next();
		self.filter_char(c, true)
	}

	fn emit(&self, kind: TokenKind) -> Result<Token<'s>> {
		let span = Span::new(self.start_pos, self.pos);
		Ok(Token {
			span,
			content: span.of(self.src),
			kind,
		})
	}

	fn and_emit(&mut self, kind: TokenKind) -> Result<Token<'s>> {
		self.next()?;
		self.emit(kind)
	}

	fn unexpected(&mut self) -> Result<Token<'s>> {
		let c = self.peek()?;
		let span = Span::new(self.pos, self.pos.advance(c));
		let msg = match c {
			'\0' => "unexpected end of file".to_owned(),
			'\n' => "unexpected newline character".to_owned(),
			'\t' => "unexpected tab character".to_owned(),
			'\r' => "unexpected return character".to_owned(),
			c => format!("unexpected character {c}"),
		};
		Err(ParserError {
			span,
			msg,
			file: None,
		})
	}

	fn err<T>(&self, msg: &str) -> Result<T> {
		Err(ParserError {
			span: Span::new(self.start_pos, self.pos),
			msg: msg.to_owned(),
			file: None,
		})
	}

	fn next_ident(&mut self) -> Result<Token<'s>> {
		let first = self.next()?;
		loop {
			let c = self.peek()?;
			let cond = if ('a'..='g').contains(&first) {
				c.is_ascii_alphanumeric() || c == '#'
			} else {
				c.is_ascii_alphabetic()
			};
			if !cond {
				break;
			}
			self.next()?;
		}
		let kind = match Span::new(self.start_pos, self.pos).of(self.src) {
			"pulsea" | "a" => K::PulseA,
			"pulseb" | "b" => K::PulseB,
			"triangle" | "t" => K::Triangle,
			"noise" | "n" => K::Noise,
			"volume" | "v" => K::Volume,
			"pitch" | "p" => K::Pitch,
			"dutycycle" | "dc" | "w" => K::DutyCycle,
			"mode" | "m" => K::Mode,
			"puselen" | "P" => K::PauseLen,
			_ => K::Identifier,
		};
		self.emit(kind)
	}

	fn next_macro_ident(&mut self) -> Result<Token<'s>> {
		self.next()?;
		let ident = self.next_ident()?;
		let kind = match ident.content {
			"%macro" => K::MacroDefine,
			"%endmacro" => K::MacroEnd,
			_ => self.err("expected %macro or %endmacro")?,
		};
		self.start_pos = ident.span.start;
		self.emit(kind)
	}

	fn next_int(&mut self) -> Result<Token<'s>> {
		loop {
			let c = self.peek()?;
			if c.is_ascii_digit() {
				self.next()?;
			} else {
				return self.emit(K::Integer);
			}
		}
	}

	fn next_comment(&mut self) -> Result<Token<'s>> {
		while !matches!(self.peek()?, '\0' | '\n') {
			self.next()?;
		}
		self.next_token()
	}

	pub fn next_token(&mut self) -> Result<Token<'s>> {
		while matches!(self.peek()?, ' ' | '\t' | '\r') {
			self.next()?;
		}
		self.start_pos = self.pos;
		match self.peek()? {
			// misc
			'\0' => self.emit(K::Eof),
			'\n' => self.and_emit(K::LineSeparator),
			';' => self.next_comment(),
			// macros
			'%' => self.next_macro_ident(),
			'$' => self.and_emit(K::Argument),
			// pause
			'-' => self.and_emit(K::Dash),
			// integer
			c if c.is_ascii_digit() => self.next_int(),
			// ident
			c if c.is_ascii_alphabetic() => self.next_ident(),
			// rest
			_ => self.unexpected(),
		}
	}
}
impl<'s> Iterator for Lexer<'s> {
	type Item = Result<Token<'s>>;

	fn next(&mut self) -> Option<Self::Item> {
		Some(self.next_token())
	}
}