Lexer :: struct {
	input : string;
	cursor : int;
	start : int;
	current_line : int;
	current_column : int;

	result : *Compile_Result;

	path : string;
}

Token_Kind :: enum {
	TOKEN_FLOATLITERAL;
	TOKEN_INTLITERAL;

	TOKEN_LOGICALOR;
	TOKEN_LOGICALAND;
	TOKEN_ISEQUAL;
	TOKEN_ISNOTEQUAL;
	TOKEN_PLUSEQUALS;
	TOKEN_MINUSEQUALS;
	TOKEN_TIMESEQUALS;
	TOKEN_DIVEQUALS;
	TOKEN_MODEQUALS;
	TOKEN_LESSEQUALS;
	TOKEN_LESS;
	TOKEN_GREATEREQUALS;
	TOKEN_GREATER;
	TOKEN_COLON;
	TOKEN_DOUBLECOLON;
	TOKEN_ASSIGN;
	TOKEN_ARROW;
	TOKEN_AT;

	TOKEN_PLUS;
	TOKEN_STAR;
	TOKEN_SLASH;
	TOKEN_MOD;
	TOKEN_MINUS;

	TOKEN_LEFTBRACE;
	TOKEN_RIGHTBRACE;
	TOKEN_LEFTBRACKET;
	TOKEN_RIGHTBRACKET;
	TOKEN_LEFTPAREN;
	TOKEN_RIGHTPAREN;
	TOKEN_SEMICOLON;
	TOKEN_COMMA;
	TOKEN_DOT;
	TOKEN_DOTDOT;

	TOKEN_IDENTIFIER;

	// Keywords
	TOKEN_BOOL;
	
	TOKEN_CASE;
	TOKEN_CBUFFER;
	TOKEN_COLUMNMAJOR;
	TOKEN_CONST;
	TOKEN_CONSTANT_BUFFER;
	TOKEN_CONTINUE;

	TOKEN_DEFAULT;
	TOKEN_DIRECTIVE;
	TOKEN_DISCARD;
	TOKEN_DO;
	TOKEN_DOUBLE;

	TOKEN_ELSE;
	TOKEN_EXPORT;
	TOKEN_EXTERN;

	TOKEN_FALSE;
	TOKEN_FOR;

	TOKEN_HALF;
	TOKEN_HINT;

	TOKEN_IF;
	TOKEN_IN;
	TOKEN_INOUT;
	TOKEN_INSTANCE;

	TOKEN_MATRIX;
	TOKEN_META;

	TOKEN_OPTIONAL;
	TOKEN_OUT;

	TOKEN_PIXEL;
	TOKEN_PROPERTIES;

	TOKEN_RETURN;
	TOKEN_REGISTER;

	TOKEN_STRING;
	TOKEN_STRUCT;
	TOKEN_SWITCH;

	TOKEN_TRUE;

	TOKEN_UNORM;
	TOKEN_UNSIGNED;
	TOKEN_UINT;

	TOKEN_VECTOR;
	TOKEN_VERTEX;
	TOKEN_VOID;
	
	TOKEN_WHILE;
	
	TOKEN_EOF;
	TOKEN_ERROR;
}

Token :: struct {
	kind     : Token_Kind;
	union {
		ident_value   : string;
		integer_value : int;
		float_value   : float;
		string_value  : string;
	}

	source : *u8;

	// This could all be derived on demand
	line     : int;
	length   : int;
	column : int;
	index    : int;

	error    : string;

	builtin : bool; // @Incomplete: This is kind of a bad idea, but let's just do it for now...
}

Source_Range :: struct {
	begin : Token;
	end   : Token;
	main_token : Token;
}

is_at_end :: (using lexer : *Lexer) -> bool {
	return input.data[cursor] == #char "\0" || cursor == input.count;
}

peek_char :: (using lexer : *Lexer) -> u8 {
	return input.data[cursor];
}

peek_next_char :: (using lexer : *Lexer) -> u8 {
	if is_at_end(lexer) return #char "\0";
	return input.data[cursor + 1];
}

match_character :: (lexer : *Lexer, expected : u8) -> bool {
	if is_at_end(lexer) return false;
	if lexer.input.data[lexer.cursor] != expected return false;

	lexer.cursor += 1;
	return true;
}

identifier :: (lexer : *Lexer) -> *Token {
	while is_alpha(peek_char(lexer)) || is_digit(peek_char(lexer)) || peek_char(lexer) == #char "_" {
		advance(lexer);
	}

	return make_identifier(lexer, identifier_kind(lexer));
}

directive :: (lexer : *Lexer) -> *Token {
	advance(lexer);
	while is_alpha(peek_char(lexer)) || is_digit(peek_char(lexer)) || peek_char(lexer) == #char "_" {
		advance(lexer);
	}

	return make_directive(lexer);
}

number :: (lexer : *Lexer) -> *Token {
	while is_digit(peek_char(lexer)) advance(lexer);

	is_float := false;

	if peek_char(lexer) == #char "." && is_digit(peek_next_char(lexer)) {
		is_float = true;
		advance(lexer);
		f_suffix := false;
		while is_digit(peek_char(lexer)) {		
			advance(lexer);
		}
		if peek_char(lexer) == #char "f" {
			advance(lexer);
			record_error(lexer, "We don't use 'f' suffixes for floating point values.");
			return null;
		}
	}

	if is_float {
		return make_float(lexer);
	}
	return make_int(lexer);
}

identifier_kind :: (using lexer : *Lexer) -> Token_Kind {
	length := cursor - lexer.start;

	index := start;
	identifier : string;
	identifier.data = *input.data[start];
	identifier.count = length;

	if identifier == "bool"            return .TOKEN_BOOL;
	if identifier == "case"            return .TOKEN_CASE;
	if identifier == "columnmajor"     return .TOKEN_COLUMNMAJOR;
	if identifier == "const"           return .TOKEN_CONST;
	if identifier == "constant_buffer" return .TOKEN_CONSTANT_BUFFER;
	if identifier == "continue"        return .TOKEN_CONTINUE;
	if identifier == "default"         return .TOKEN_DEFAULT;
	if identifier == "directive"       return .TOKEN_DIRECTIVE;
	if identifier == "discard"         return .TOKEN_DIRECTIVE;
	if identifier == "discard"         return .TOKEN_DISCARD;
	if identifier == "do"              return .TOKEN_DO;
	if identifier == "double"          return .TOKEN_DOUBLE;
	if identifier == "else"            return .TOKEN_ELSE;
	if identifier == "export"          return .TOKEN_EXPORT;
	if identifier == "extern"          return .TOKEN_EXTERN;
	if identifier == "false"           return .TOKEN_FALSE;
	if identifier == "for"             return .TOKEN_FOR;
	if identifier == "half"            return .TOKEN_HALF;
	if identifier == "hint"            return .TOKEN_HINT;
	if identifier == "if"              return .TOKEN_IF;
	if identifier == "in"              return .TOKEN_IN;
	if identifier == "inout"           return .TOKEN_INOUT;
	if identifier == "instance"        return .TOKEN_INSTANCE;
	if identifier == "matrix"          return .TOKEN_MATRIX;
	if identifier == "meta"            return .TOKEN_META;
	if identifier == "optional"        return .TOKEN_OPTIONAL;
	if identifier == "out"             return .TOKEN_OUT;
	if identifier == "pixel"           return .TOKEN_PIXEL;
	if identifier == "properties"      return .TOKEN_PROPERTIES;
	if identifier == "return"          return .TOKEN_RETURN;
	if identifier == "register"        return .TOKEN_REGISTER;
	if identifier == "struct"          return .TOKEN_STRUCT;
	if identifier == "switch"          return .TOKEN_SWITCH;
	if identifier == "true"            return .TOKEN_TRUE;
	if identifier == "unorm"           return .TOKEN_UNORM;
	if identifier == "unsigned"        return .TOKEN_UNSIGNED;
	if identifier == "uint"            return .TOKEN_UINT;
	if identifier == "vector"          return .TOKEN_VECTOR;
	if identifier == "vertex"          return .TOKEN_VERTEX;
	if identifier == "void"            return .TOKEN_VOID;
	if identifier == "while"           return .TOKEN_WHILE;

	return .TOKEN_IDENTIFIER;
}

error_token :: (lexer : *Lexer, message : string) -> *Token {
	token : *Token = new_token(lexer, .TOKEN_ERROR);

	lexer.result.had_error = true;
	token.error = copy_string(message);

	return token;
}

// unable_to_open_file :: (state : *Parse_State, path : string, token : Token) {
// 	builder : String_Builder;
// 	init_string_builder(*builder,, temp);

// 	print_to_builder(*builder, "Unable to open file '%' for reading\n\n", path);

// 	location := generate_source_location_from_token(state, token);

// 	indent(*builder, 1);
// 	cyan(*builder);
// 	print_to_builder(*builder, "%\n", print_from_source_location(location));
// 	indent(*builder, 1);

// 	loc := location.begin;
// 	print_token_pointer(*builder,  loc);

// 	final_message := builder_to_string(*builder);
// 	record_error(state, token, final_message, false);
// }

record_error :: (lexer : *Lexer, message : string) {
	error : Compiler_Message;
	error.message_kind = .Error;
	error.message      = message;
	error.path         = lexer.path;

	token := error_token(lexer, message);
	source_location : Source_Range;
	source_location.main_token = token;

	token.length += token.column;
	token.source -= token.column;
	token.column = 0;

	source_location.begin = token;
	length := source_location.begin.column;

	source_location.end = token;

	array_add(*error.source_locations, source_location);

	lexer.result.had_error = true;
	array_add(*lexer.result.messages, error);
}

make_int :: (lexer : *Lexer) -> *Token {
	token : *Token = new_token(lexer, .TOKEN_INTLITERAL);

	str : string = .{ count = token.length,
					  data  = *lexer.input.data[lexer.start] };
	value, ok := string_to_int(str);

	if ok {
		token.integer_value = value;
	}
	return token;
}


make_float :: (lexer : *Lexer) -> *Token {
	token : *Token = new_token(lexer, .TOKEN_FLOATLITERAL);

	str : string = .{ count = token.length,
					  data  = *lexer.input.data[lexer.start] };
	value, ok := string_to_float(str);
	if ok {
		token.float_value = value;
	}
	
	return token;
}

new_token :: (lexer : *Lexer, kind : Token_Kind) -> *Token {
	length := lexer.cursor - lexer.start;
	token : Token;
	token.kind   = kind;
	token.line   = lexer.current_line;
	token.length = length;
	token.column = lexer.current_column;
	token.index  = lexer.cursor - token.length;
	
	if token.length > 0 {
		token.source   = *lexer.input[token.index];
	} else {
		token.source   = *lexer.input[token.index - 1];
	}
    lexer.current_column += length;

	array_add(*lexer.result.tokens, token);
	return *lexer.result.tokens[lexer.result.tokens.count - 1];
}

make_directive :: (lexer : *Lexer) -> *Token {
	lexer.start += 1;
	ident := make_identifier(lexer, .TOKEN_DIRECTIVE);
	if ident.ident_value == "load" {
		path_tok := scan_next_token(lexer);
		path := path_tok.string_value;
		result : Compile_Result;
		result.allocator   = lexer.result.allocator;
		result.environment = lexer.result.environment;

		result.file = make_file(*result, path);

		if result.file.source.count == 0 {
			// unable_to_open_file(lexer, path, path_tok);
			record_error(lexer, tprint("Unable to open file '%' for reading\n", path));
			return error_token(lexer, tprint("Unable to open file '%' for reading\n", path));
		}

		lex(*result);

		result.tokens.count -= 1; // @Note: remote TOKEN_EOF
		lexer.result.tokens.count -= 2;
		array_resize(*lexer.result.tokens, lexer.result.tokens.count + result.tokens.count);

		for tok : result.tokens {
			lexer.result.tokens[it_index] = tok;
		}
		return scan_next_token(lexer);;
	}
	return ident;
}

make_string :: (lexer : *Lexer) -> *Token {
	token : *Token = new_token(lexer, .TOKEN_STRING);

	name : string = .{ count = token.length - 2,
					   data  = *lexer.input.data[lexer.start + 1] };
	token.string_value = name;

	return token;
}

make_identifier :: (lexer : *Lexer, kind : Token_Kind) -> *Token {
	token : *Token = new_token(lexer, kind);

	name : string = .{ count = token.length,
					   data  = *lexer.input.data[lexer.start] };
	token.ident_value = name;

	return token;
}

make_token :: (lexer : *Lexer, token_kind : Token_Kind) -> *Token {
	return new_token(lexer, token_kind);
}

skip_whitespace :: (lexer : *Lexer) {
	while true {
		if is_at_end(lexer) return;
		c := peek_char(lexer);

		if c == {
			case #char " "; {
				lexer.current_column += 1;
				advance(lexer);
				continue;
			}
			case #char "\r"; #through;
			case #char "\t"; {
				advance(lexer);
				continue;
			}
			case #char "\n"; {
				advance(lexer);
				lexer.current_line += 1;
				lexer.current_column = 0;
				continue;
			}
			case #char "/"; {
				next := peek_next_char(lexer);
				if next == #char "/" {
					while peek_char(lexer) != #char "\n" && !is_at_end(lexer) {
						advance(lexer);
					}
					continue;
				} else {
					return;
				}
			}
		}
		return;
	}
}

advance :: (using lexer : *Lexer) -> u8 {
	c := input.data[cursor];
	cursor += 1;
	return c;
}

scan_next_token :: (lexer : *Lexer) -> *Token {
	skip_whitespace(lexer);
	lexer.start = lexer.cursor;

	if is_at_end(lexer) return make_token(lexer, .TOKEN_EOF);

	c := advance(lexer);

	if c == #char "#" return directive(lexer);
	if is_alpha(c) return identifier(lexer);
	if is_digit(c) return number(lexer);

	if c == {
		case #char "\""; {
			c = advance(lexer);
			// lexer.start = lexer.cursor;
			while c != #char "\"" {
				c = advance(lexer);
			}
			// lexer.cursor -= 1;
			tok := make_string(lexer);
			// advance(lexer);
			return tok;
		}
		case #char "+"; {
			if match_character(lexer, #char "=") return make_token(lexer, .TOKEN_PLUSEQUALS);
			return make_token(lexer, .TOKEN_PLUS);
		}
		case #char "-"; {
			if match_character(lexer, #char "=") return make_token(lexer, .TOKEN_MINUSEQUALS);
			if match_character(lexer, #char ">") return make_token(lexer, .TOKEN_ARROW);
			return make_token(lexer, .TOKEN_MINUS);
		}
		case #char "*"; {
			if match_character(lexer, #char "=") return make_token(lexer, .TOKEN_TIMESEQUALS);
			return make_token(lexer, .TOKEN_STAR);
		}
		case #char "/"; {
			if match_character(lexer, #char "=") return make_token(lexer, .TOKEN_DIVEQUALS);
			return make_token(lexer, .TOKEN_SLASH);
		}
		case #char "%"; {
			if match_character(lexer, #char "=") return make_token(lexer, .TOKEN_MODEQUALS);
			return make_token(lexer, .TOKEN_MOD);
		}
		case #char ":"; {
			if match_character(lexer, #char ":") return make_token(lexer, .TOKEN_DOUBLECOLON);
			return make_token(lexer, .TOKEN_COLON);
		}
		case #char "@"; {
			return make_token(lexer, .TOKEN_AT);
		}
		case #char "|"; {
			if match_character(lexer, #char "|") return make_token(lexer, .TOKEN_LOGICALOR);
		}
		case #char "&"; {
			if match_character(lexer, #char "&") return make_token(lexer, .TOKEN_LOGICALAND);
		}
		case #char "!"; {
			if match_character(lexer, #char "=") return make_token(lexer, .TOKEN_ISNOTEQUAL);
		}
		case #char "="; {
			if match_character(lexer, #char "=") return make_token(lexer, .TOKEN_ISEQUAL);
			return make_token(lexer, .TOKEN_ASSIGN);
		}
		case #char ">"; {
			if match_character(lexer, #char "=") return make_token(lexer, .TOKEN_GREATEREQUALS);
			return make_token(lexer, .TOKEN_GREATER);
		}
		case #char "<"; {
			if match_character(lexer, #char "=") return make_token(lexer, .TOKEN_LESSEQUALS);
			return make_token(lexer, .TOKEN_LESS);
		}
		case #char "{"; {
			return make_token(lexer, .TOKEN_LEFTBRACE);
		}
		case #char "}"; {
			return make_token(lexer, .TOKEN_RIGHTBRACE);
		}
		case #char "("; {
			return make_token(lexer, .TOKEN_LEFTPAREN);
		}
		case #char ")"; {
			return make_token(lexer, .TOKEN_RIGHTPAREN);
		}
		case #char "["; {
			return make_token(lexer, .TOKEN_LEFTBRACKET);
		}
		case #char "]"; {
			return make_token(lexer, .TOKEN_RIGHTBRACKET);
		}
		case #char ";"; return make_token(lexer, .TOKEN_SEMICOLON);
		case #char ","; return make_token(lexer, .TOKEN_COMMA);
		case #char "."; {
			if match_character(lexer, #char ".") return make_token(lexer, .TOKEN_DOTDOT);
			return make_token(lexer, .TOKEN_DOT);
		}
	}

	s : string = .{ count = 1, data = *c };
	record_error(lexer, tprint("Invalid token: %", s));
	return null;
	// return error_token(lexer, tprint("Invalid token: %", s));
}

lex :: (result : *Compile_Result) {
	if result.had_error {
		return;
	}

	lexer : Lexer;
	lexer.result = result;
	
	init_lexer_from_string(*lexer, result.file.source);
	lexer.path = result.file.path;
	token : *Token = scan_next_token(*lexer);
	while token && token.kind != .TOKEN_EOF {
		token = scan_next_token(*lexer);
	}
}

init_lexer_from_string :: (lexer : *Lexer, input : string) {
	ok := read_input_from_string(lexer, input);
	if !ok {
		record_error(lexer, "Unable to initialize from string\n");
		lexer.result.had_error = true;
	}
}

init_lexer_from_file :: (lexer : *Lexer, file_path : string) {
	ok := read_input_from_file(lexer, file_path);
	if !ok {
		record_error(lexer, tprint("Unable to read file: %\n", file_path));
		lexer.result.had_error = true;
	}
}

read_input_from_string :: (lexer : *Lexer, input : string) -> bool {
	lexer.input                   = input;
	lexer.cursor                  = 0;
	lexer.start                   = 0;
	lexer.current_line            = 1;
	lexer.current_column = 0;

	return true;
}

read_input_from_file :: (lexer : *Lexer, file_path : string) -> bool {
	assert(file_path != "");

	value, success := read_entire_file(file_path, true, true);
	if !success {
		free(value);
		return false;
	}

	lexer.path = copy_string(file_path);
	lexer.input                   = value;
	lexer.cursor                  = 0;
	lexer.start                   = 0;
	lexer.current_line            = 1;
	lexer.current_column = 0;

	return true;
}

// ===========================================================
// Pretty printing
pretty_print_token :: (token : *Token, builder : *String_Builder) {
	MAX :: 21;
	kind_name := enum_names(Token_Kind)[cast(int)token.kind];
	diff := MAX - kind_name.count;

	print_to_builder(builder, "{kind = %; ", token.kind);
	for i : 0..diff - 1 {
		append(builder, " ");
	}

	append_to_length :: (builder : *String_Builder, number : int) {
		if number < 10 {
			append(builder, "    ");
		} else if number < 100 {
			append(builder, "   ");
		} else if number < 1000 {
			append(builder, "  ");
		} else if number < 10000 {
			append(builder, " ");
		}
	}

	print_to_builder(builder, "; index = %", token.index);
	append_to_length(builder, token.index);

	print_to_builder(builder, "; length = %", token.length);
	append_to_length(builder, token.length);

	print_to_builder(builder, "line = %", token.line);
	append_to_length(builder, token.line);

	print_to_builder(builder, "; column = %", token.column);
	append_to_length(builder, token.column);
	
	append(builder, "; value ='");
	value_length : int;
	if token.kind == .TOKEN_IDENTIFIER {
		print_to_builder(builder, "%", token.ident_value);
	} else if token.kind == .TOKEN_INTLITERAL {
		print_to_builder(builder, "%", token.integer_value);
	} else if token.kind == .TOKEN_FLOATLITERAL {
		print_to_builder(builder, "%", token.float_value);
	} else if token.kind == .TOKEN_ERROR {
		print_to_builder(builder, "%", token.error);
	} else {
		source : string = .{ count = token.length,
							 data = token.source };
		print_to_builder(builder, "%", source);
	}
	append(builder, "'; }\n");
}

pretty_print_tokens :: (lexer : *Lexer, allocator : Allocator) -> string {
	builder : String_Builder;

	init_string_builder(*builder,, allocator);

	token : *Token = scan_next_token(lexer);
	while token && token.kind != .TOKEN_EOF {
		pretty_print_token(token, *builder);
		token = scan_next_token(lexer);
	}

	return builder_to_string(*builder,, allocator);
}

pretty_print_tokens :: (tokens : []Token, allocator : Allocator) -> string {
	builder : String_Builder;

	init_string_builder(*builder,, allocator);

	for token : tokens {
		pretty_print_token(*token, *builder);
	}
	return builder_to_string(*builder,, allocator);
}

output_as_code_string :: (lexer : *Lexer, allocator : *Allocator) -> string {
	builder : String_Builder;

	new_context := context;
	new_context.allocator = allocator;
	push_context new_context {
		init_string_builder(*builder); // @Incomplete: Consider passing builder as argument

		token : *Token = scan_next_token(lexer);
		while token && token.kind != .TOKEN_EOF {
			token = scan_next_token(lexer);
		}

		return builder_to_string(*builder);
	}	
}

print_token_pointer :: (builder : *String_Builder, token : Token) {
	for i : 0..token.column - 1 {
		append(builder, " ");
	}
	
	for i : 0..token.length - 1 {
		append(builder, "^");
	}
}

print_from_source_location :: (builder : *String_Builder, source_location : Source_Range, indentation : int = 0) {
	current := source_location.begin;
	begin := source_location.begin;
	end := source_location.end;
	begin_pos := 0;
	token_string : string;
	count := end.index - begin.index + end.length;

	if indentation > 0 {
		indent(builder, indentation);
		for 0..count - 1 {
			c := begin.source[it];
			if c == #char "\n" {
				append(builder, "\n");
				indent(builder, indentation);
			} else {
				s : string;
				s.count = 1;
				s.data = *c;
				print_to_builder(builder, "%", s);
			}

		}
	} else {
		token_string = .{ count = count, data = begin.source };
		indent(builder, indentation);
		print_to_builder(builder, "%", token_string);
	}
}

print_from_source_location :: (source_location : Source_Range, allocator := context.allocator, indentation : int = 0) -> string {
	builder : String_Builder;
	init_string_builder(*builder,, allocator);
	print_from_source_location(*builder, source_location);
	return builder_to_string(*builder,, allocator);
}


#import "Basic";
#import "File";