module main

import term

enum TokenType as u8 {
	kw_let
	kw_const
	type
	kw_if
	kw_else
	kw_for
	kw_break
	kw_fn
	kw_return
	kw_print
	kw_struct
	integer
	real
	boolean
	identifier
	plus
	minus
	star
	slash
	equals
	less
	greater
	eq_eq
	greater_eq
	less_eq
	not_eq
	plus_eq
	minus_eq
	star_eq
	slash_eq
	increment
	decrement
	lparen
	rparen
	lsqparen
	rsqparen
	lbracket
	rbracket
	dot
	comma
	semicolon
	colon
	eof
	unknown
}

struct Token {
	type TokenType
	text string
}

fn str_from_toktype(type TokenType) string {
	return type.str()
}

fn toktype_from_delimiter(delimiter string) TokenType {
	return match delimiter {
		'(' {.lparen}
		')' {.rparen}
		'[' {.lsqparen}
		']' {.rsqparen}
		'{' {.lbracket}
		'}' {.rbracket}
		'+' {.plus}
		'-' {.minus}
		'*' {.star}
		'/' {.slash}
		'=' {.equals}
		'<' {.less}
		'>' {.greater}
		'.' {.dot}
		',' {.comma}
		';' {.semicolon}
		':' {.colon}
		'==' {.eq_eq}
    '>=' {.greater_eq}
    '<=' {.less_eq}
    '!=' {.not_eq}
		'+=' {.plus_eq}
		'-=' {.minus_eq}
		'*=' {.star_eq}
		'/=' {.slash_eq}
		'++' {.increment}
		'--' {.decrement}
		else {.unknown}
	}
}

fn toktype_from_kw(kw string) TokenType {
	return match kw {
		'let' {.kw_let}
		'const' {.kw_const}
		'void', 'real', 'bool', 'int' {.type}
		'if' {.kw_if}
		'else' {.kw_else}
		'for' {.kw_for}
		'break' {.kw_break}
		'fn' {.kw_fn}
		'return' {.kw_return}
		'true', 'false' {.boolean}
		'print' {.kw_print}
		'struct' {.kw_struct}
		else {.unknown}
	}
}

fn is_delimiter(c u8, is_inside_number bool) bool {
	return " +-*/.,;:%<>()[]{}=\n".contains(c.ascii_str()) && (c.ascii_str() != '.' || !is_inside_number)
}

fn is_real(str string) bool {
	left, right := str.split_once(".") or {return false}
	return !right.contains(".") && left.is_int() && right.is_int()
}

fn is_keyword(str string) bool {
	return [
		"void", "int", "real", "bool", "if", "else", "for", "break", "fn", "return", "let", "const", "true", "false", "print", "struct"
	].contains(str)
}

fn print_tok(tok Token) {
	println("${tok.text.replace("\n", "\\n"):8} (${str_from_toktype(tok.type)})")
}

fn print_toks(toks []Token) {
	for tok in toks {
		print_tok(tok)
	}
}

fn lex(input string) ?[]Token {
	mut left := 0
	mut right := 0
	mut line := 1
	mut tokens := []Token{}
	mut is_inside_number := false

	for (right < input.len && left <= right) {
		if input[right] == `\n` {
			line++
		}
		if !is_delimiter(input[right], is_inside_number) {
			is_inside_number = input[left].str().is_int()
			right++
		}
		if right >= input.len {
			break
		}
		if is_delimiter(input[right], is_inside_number) && left == right {
			if !input[right].is_space() {
				mut tok_str := input[right].ascii_str()
					if right + 1 < input.len {
						combined := input.substr(right, right + 2)
						if combined in ['==', '>=', '<=', '!=', '+=', '-=', '*=', '/=', '++', '--'] {
							tok_str = combined
								right++
						}
					}
				tokens << Token{toktype_from_delimiter(tok_str), tok_str}
			}
			right++
			left = right
		}
		else if (is_delimiter(input[right], is_inside_number) && left != right) || (right == input.len && left != right) {
			subs := input.substr(left, right)
			if is_keyword(subs) {
				tokens << Token{toktype_from_kw(subs), subs}
			} else if subs.is_int() {
				tokens << Token{TokenType.integer, subs}
			} else if is_real(subs) {
				tokens << Token{TokenType.real, subs}
			} else if subs.is_identifier() {
				tokens << Token{TokenType.identifier, subs}
			} else if !subs.is_identifier() && !is_delimiter(input[right-1], is_inside_number)  {
				eprintln(term.red("ERROR: found invalid token " + subs + " at line " + line.str()))
				return none
			}
			left = right
		}
	}
	tokens << Token{TokenType.eof, "EOF"}
	return tokens
}