package main

import "core:fmt"
import "core:c/libc"
import "core:math"

Lexer :: struct {
	data:                    ^[dynamic]u8,
	read_position:           u64,
	position:                TextPosition,
	char, next:              u8,
	last_token_kind:         TokenKind,
	should_return_semicolon: bool,
}

lexer_create :: proc(data: ^[dynamic]u8) -> ^Lexer {
	lexer := new(Lexer)
	lexer^ = {
		data = data,
		read_position = 0,
		position = TextPosition{line = 1, column = 1},
	}
	lexer_advance(lexer)
	lexer_advance(lexer)
	return lexer
}

@(private = "file")
lexer_advance :: proc(lexer: ^Lexer) {
	lexer.char = lexer.next
	if lexer.read_position < u64(len(lexer.data)) {
		lexer.next = lexer.data[lexer.read_position]
	} else {
		lexer.next = 0
	}
	lexer.read_position += 1
	if lexer.char == '\r' {
		lexer_advance(lexer)
	}
	if lexer.char == '\n' {
		lexer.position.line += 1
		lexer.position.column = 1
	} else {
		lexer.position.column += 1
	}
}

@(private = "file")
lexer_should_not_emit_semicolon :: proc(lexer: ^Lexer) -> bool {
	return(
		lexer.last_token_kind == .CloseBrace ||
		lexer.last_token_kind == .Semicolon ||
		lexer.last_token_kind == .EOF ||
		lexer.last_token_kind == .Invalid ||
		lexer.last_token_kind == .OpenParen ||
		lexer.last_token_kind == .OpenBrace ||
		lexer.last_token_kind == .OpenBracket ||
		lexer.last_token_kind == .CloseParen ||
		lexer.last_token_kind == .CloseBrace ||
		lexer.last_token_kind == .CloseBracket ||
		lexer.last_token_kind == .Add ||
		lexer.last_token_kind == .Subtract ||
		lexer.last_token_kind == .Multiply ||
		lexer.last_token_kind == .Divide ||
		lexer.last_token_kind == .Modulo ||
		lexer.last_token_kind == .Exponent ||
		lexer.last_token_kind == .Assign ||
		lexer.last_token_kind == .Not ||
		lexer.last_token_kind == .BitwiseAnd ||
		lexer.last_token_kind == .BitwiseOr ||
		lexer.last_token_kind == .BitwiseXOR ||
		lexer.last_token_kind == .BitwiseNot ||
		lexer.last_token_kind == .LessThan ||
		lexer.last_token_kind == .GreaterThan ||
		lexer.last_token_kind == .BitwiseLeftShift ||
		lexer.last_token_kind == .BitwiseRightShift ||
		lexer.last_token_kind == .Comma \
	)
}

@(private = "file")
lexer_skip_whitespace :: proc(lexer: ^Lexer) {
	// FIXME: Do the funny golang thing where newlines are semicolons based on some rules
	for lexer.char == ' ' || lexer.char == '\t' || lexer.char == '\r' || lexer.char == '\n' {
		if lexer.char == '\n' {
			if !lexer_should_not_emit_semicolon(lexer) {
				lexer.should_return_semicolon = true
				lexer_advance(lexer)
				return
			}
		}
		lexer_advance(lexer)
	}
}

lexer_next :: proc(lexer: ^Lexer) -> (ret: Token) {
	lexer_skip_whitespace(lexer)
	if lexer.char == '\\' {
		lexer_advance(lexer)
		for lexer.char != '\n' && lexer.char != 0 {
			lexer_advance(lexer)
		}
		return lexer_next(lexer)
	}

	if lexer.should_return_semicolon {
		lexer.should_return_semicolon = false
		return token_create(.Semicolon, TextRange{start = lexer.position, end = lexer.position})
	}

	defer lexer.last_token_kind = ret.kind

	crange := TextRange {
		start = lexer.position,
		end   = lexer.position,
	}

	ret = token_create(.Invalid, crange)
	should_advance := true

	switch lexer.char {
	case '+':
		ret = token_create(.Add, crange)
		if lexer.next == '+' {
			lexer_advance(lexer)
			crange.end = lexer.position
			ret = token_create(.Increment, crange)
		}
	case '-':
		ret = token_create(.Subtract, crange)
		if lexer.next == '-' {
			lexer_advance(lexer)
			crange.end = lexer.position
			ret = token_create(.Decrement, crange)
		} else if lexer.next == '>' {
			lexer_advance(lexer)
			crange.end = lexer.position
			ret = token_create(.Arrow, crange)
		}
	case '*':
		ret = token_create(.Multiply, crange)
	case '/':
		ret = token_create(.Divide, crange)
	case '%':
		ret = token_create(.Modulo, crange)
	case '`':
		ret = token_create(.Exponent, crange)
	case '=':
		ret = token_create(.Assign, crange)
		if lexer.next == '=' {
			lexer_advance(lexer)
			crange.end = lexer.position
			ret = token_create(.Equals, crange)
		}
	case '!':
		ret = token_create(.Not, crange)
		if lexer.next == '=' {
			lexer_advance(lexer)
			crange.end = lexer.position
			ret = token_create(.NotEquals, crange)
		}
	case '<':
		ret = token_create(.LessThan, crange)
		if lexer.next == '=' {
			lexer_advance(lexer)
			crange.end = lexer.position
			ret = token_create(.LessThanOrEqual, crange)
		} else if lexer.next == '<' {
			lexer_advance(lexer)
			crange.end = lexer.position
			ret = token_create(.BitwiseLeftShift, crange)
		}
	case '>':
		ret = token_create(.GreaterThan, crange)
		if lexer.next == '=' {
			lexer_advance(lexer)
			crange.end = lexer.position
			ret = token_create(.GreaterThanOrEqual, crange)
		} else if lexer.next == '>' {
			lexer_advance(lexer)
			crange.end = lexer.position
			ret = token_create(.BitwiseRightShift, crange)
		}
	case '&':
		ret = token_create(.BitwiseAnd, crange)
	case '|':
		ret = token_create(.BitwiseOr, crange)
	case '^':
		ret = token_create(.BitwiseXOR, crange)
	case '~':
		ret = token_create(.BitwiseNot, crange)
	case '(':
		ret = token_create(.OpenParen, crange)
	case ')':
		ret = token_create(.CloseParen, crange)
	case '[':
		ret = token_create(.OpenBracket, crange)
	case ']':
		ret = token_create(.CloseBracket, crange)
	case '{':
		ret = token_create(.OpenBrace, crange)
	case '}':
		ret = token_create(.CloseBrace, crange)

	case '?':
		ret = token_create(.Question, crange)
	case ':':
		ret = token_create(.Colon, crange)
	case '.':
		ret = token_create(.Dot, crange)
	case ',':
		ret = token_create(.Comma, crange)
	case ';':
		ret = token_create(.Semicolon, crange)

	case '"':
		ret = lexer_read_string(lexer, .String, '\"')
	case '\'':
		ret = lexer_read_string(lexer, .Character, '\'')
	case 'a' ..= 'z':
		fallthrough
	case 'A' ..= 'Z':
		fallthrough
	case '_':
		ret = lexer_read_identifier(lexer)
		should_advance = false
	case '0' ..= '9':
		ret = lexer_read_number(lexer)
		should_advance = false
	case 0:
		ret = token_create(.EOF, crange)
		should_advance = false
	}

	if should_advance {
		lexer_advance(lexer)
	}

	return
}

@(private = "file")
lexer_read_string :: proc(lexer: ^Lexer, kind: TokenKind, outer: u8) -> Token {
	crange := TextRange {
		start = lexer.position,
		end   = lexer.position,
	}

	lexer_advance(lexer)

	str: [dynamic]u8
	for lexer.char != outer {
		if lexer.char == '\\' {
			range := TextRange {
				start = lexer.position,
			}
			lexer_advance(lexer)
			switch lexer.char {
			case 'n':
				append(&str, '\n');break
			case 't':
				append(&str, '\t');break
			case 'b':
				append(&str, '\b');break
			case 'r':
				append(&str, '\r');break
			case '\\':
				append(&str, '\\');break
			case:
				range.end = lexer.position
				append(
					&g_message_list,
					message_create(
						.Warning,
						fmt.aprintf(
							"Invalid string/character escape: %c at %s",
							lexer.char,
							"TODO LOCATION",
						),
						range,
					),
				)
			}
			lexer_advance(lexer)
			continue
		}
		append(&str, lexer.char)

		lexer_advance(lexer)
	}
	crange.end = lexer.position

	return token_create_u8(kind, str, crange)
}

@(private = "file")
lexer_read_identifier :: proc(lexer: ^Lexer) -> Token {
	crange := TextRange {
		start = lexer.position,
	}

	str: [dynamic]u8
	for libc.isalnum(i32(lexer.char)) != 0 || lexer.char == '_' {
		append(&str, lexer.char)
		crange.end = lexer.position
		lexer_advance(lexer)
	}

	if compare_dyn_arr_string(
		   &str,
		   "fn",
	   ) {return token_create(.Function, crange)} else if compare_dyn_arr_string(&str, "struct") {return token_create(.Struct, crange)} else if compare_dyn_arr_string(&str, "enum") {return token_create(.Enum, crange)} else if compare_dyn_arr_string(&str, "union") {return token_create(.Union, crange)} else if compare_dyn_arr_string(&str, "type") {return token_create(.Type, crange)} else if compare_dyn_arr_string(&str, "use") {return token_create(.Use, crange)} else if compare_dyn_arr_string(&str, "pub") {return token_create(.Pub, crange)} else if compare_dyn_arr_string(&str, "let") {return token_create(.Let, crange)} else if compare_dyn_arr_string(&str, "mut") {return token_create(.Mut, crange)} else if compare_dyn_arr_string(&str, "as") {return token_create(.As, crange)} else if compare_dyn_arr_string(&str, "in") {return token_create(.In, crange)} else if compare_dyn_arr_string(&str, "if") {return token_create(.If, crange)} else if compare_dyn_arr_string(&str, "else") {return token_create(.Else, crange)} else if compare_dyn_arr_string(&str, "elif") {return token_create(.Elif, crange)} else if compare_dyn_arr_string(&str, "for") {return token_create(.For, crange)} else if compare_dyn_arr_string(&str, "break") {return token_create(.Break, crange)} else if compare_dyn_arr_string(&str, "continue") {return token_create(.Continue, crange)} else if compare_dyn_arr_string(&str, "switch") {return token_create(.Switch, crange)} else if compare_dyn_arr_string(&str, "case") {return token_create(.Case, crange)} else if compare_dyn_arr_string(&str, "ret") {return token_create(.Ret, crange)} else if compare_dyn_arr_string(&str, "static") {return token_create(.Static, crange)} else if compare_dyn_arr_string(&str, "defer") {return token_create(.Defer, crange)} else if compare_dyn_arr_string(&str, "let") {return token_create(.Let, crange)} else if compare_dyn_arr_string(&str, "and") {return token_create(.And, crange)} else if compare_dyn_arr_string(&str, "or") {return token_create(.Or, crange)}

	return token_create_u8(.Identifier, str, crange)
}

@(private = "file")
lexer_read_number :: proc(lexer: ^Lexer) -> Token {
	crange := TextRange {
		start = lexer.position,
		end   = lexer.position,
	}

	// FIXME: Implement binary
	ReadMode :: enum {
		Normal,
		Hex,
	}
	read_mode := ReadMode.Normal

	if lexer.char == '0' && lexer.next == 'x' {
		read_mode = .Hex
		lexer_advance(lexer)
		crange.end = lexer.position
		lexer_advance(lexer)
	}

	whole_part: u64 = 0
	if read_mode == .Normal {
		for libc.isdigit(i32(lexer.char)) != 0 && lexer.char > 0 {
			whole_part = whole_part * 10 + u64(lexer.char) - '0'
			crange.end = lexer.position
			lexer_advance(lexer)
		}
	} else if read_mode == .Hex {
		lowered := libc.tolower(i32(lexer.char))
		for libc.isxdigit(lowered) != 0 && lexer.char > 0 && lexer.char != '.' {
			digit := lowered - '0'
			if libc.isdigit(lowered) == 0 {
				digit = lowered - 'a' + 10
			}
			whole_part = (whole_part << 4) | u64(digit)
			crange.end = lexer.position
			lexer_advance(lexer)
		}
		whole_part = whole_part >> 4
	}

	if lexer.char == '.' {
		lexer_advance(lexer)

		// FIXME: Move this to another procedure because this is repeating lmfao
		fractional_part: u64 = 0
		if read_mode == .Normal {
			for libc.isdigit(i32(lexer.char)) != 0 && lexer.char > 0 {
				fractional_part = fractional_part * 10 + u64(lexer.char) - '0'
				crange.end = lexer.position
				lexer_advance(lexer)
			}
		} else if read_mode == .Hex {
			append(
				&g_message_list,
				message_create(
					.Error,
					"Hexadecimal floating point numbers are not supported yet",
					crange,
				),
			)
			lowered := libc.tolower(i32(lexer.char))
			for libc.isxdigit(lowered) != 0 && lexer.char > 0 {
				digit := lowered - '0'
				if libc.isdigit(lowered) == 0 {
					digit = lowered - 'a' + 10
				}
				fractional_part = fractional_part * 16 + u64(digit)
				crange.end = lexer.position
				lexer_advance(lexer)
			}
			fractional_part = fractional_part / 16
		}

		fractional_part_clone := fractional_part
		count := 0
		for fractional_part_clone != 0 {
			fractional_part_clone = fractional_part_clone / 10
			count = count + 1
		}

		floating: f64 = 0
		floating = f64(fractional_part) / math.pow_f64(10, f64(count)) + f64(whole_part)

		return token_create_f64(.Float, floating, crange)
	}

	return token_create_u64(.Integer, whole_part, crange)
}