use ascii;
use strconv;
use strings;

// TODO icon_theme references an "integer" data type. support that here.

// Parses a string value. It may contain all ASCII characters except for control
// characters. The memory must be freed by the caller.
// Specification: §4
export fn parse_string(in: str) (str | error) = {
	for (let char .. strings::toutf8(in)) {
		if (!ascii::valid(char: rune)) return invalid_ascii;
	};
	return parse_localestring(in);
};

// Parses a localestring value. It is user displayable, and is encoded in UTF-8.
// The memory must be freed by the caller.
// Specification: §4
export fn parse_localestring(in: str) (str | error) = {
	let escaper = escape_string(in);
	let string = match(string_escaper_next(&escaper)?) {
	case let string: str => yield string;
	case done            => return "";
	};
	if (len(escaper) > 0) {
		free(string);
		return expected_single;
	};
	return string;
};

// Parses an iconstring value. It is the name of an icon; it may be an absolute
// path, or a symbolic name for an icon located using the algorithm described in
// the Icon Theme Specification. Such values are not user-displayable, and are
// encoded in UTF-8. The memory must be freed by the caller.
// Specification: §4
export fn parse_iconstring(in: str) (str | error) = parse_localestring(in);

// Parses a boolean value. It must either be the string "true" or "false".
// Specification: §4
export fn parse_boolean(in: str) (bool | error) = {
	if (strings::contains(in, ";")) return expected_single;
	if (in == "true" ) return true;
	if (in == "false") return false;
	return invalid_boolean;
};

// Parses a numeric value. It must be a valid floating point number as
// recognized by the %f specifier for scanf in the C locale.
// Specification: §4
export fn parse_numeric(in: str) (f64 | error) = match (strconv::stof64(in)) {
case let float: f64 => yield float;
case =>
	if (strings::contains(in, ";")) return expected_single;
	yield invalid_numeric;
};

// Parses multiple string values. See [[parse_string]] for more information. The
// memory must be freed by the caller.
// Specification: §4
export fn parse_strings(in: str) ([]str | error) = {
	for (let char .. strings::toutf8(in)) {
		if (!ascii::valid(char: rune)) return invalid_ascii;
	};
	return parse_localestrings(in);
};

// Parses multiple localestring values. See [[parse_localestring]] for more
// information. The memory must be freed by the caller.
// Specification: §4
export fn parse_localestrings(in: str) ([]str | error) = {
	let escaper = escape_string(in);
	let result: []str = alloc([], 0);
	for (let in => string_escaper_next(&escaper)) {
		match (in) {
		case let string: str =>
			append(result, string);
		case let err: error =>
			strings::freeall(result);
			return err;
		};
	};
	return result;
};

// Parses multiple iconstring values. See [[parse_iconstring]] for more
// information. The memory must be freed by the caller.
// Specification: §4
export fn parse_iconstrings(in: str) ([]str | error) = parse_localestrings(in);

// Parses multiple boolean values. See [[parse_boolean]] for more information.
// The memory must be freed by the caller.
// Specification: §4
export fn parse_booleans(in: str) ([]bool | error) = {
	let splitte = split(in);
	let result: []bool = alloc([], 0);
	for (let in => splitter_next(&splitte)) {
		match (parse_boolean(in)) {
		case let boolean: bool =>
			append(result, boolean);
		case let err: error =>
			free(result);
			return err;
		};
	};
	return result;
};

// Parses multiple numeric values. See [[parse_numeric]] for more information.
// The memory must be freed by the caller.
// Specification: §4
export fn parse_numerics(in: str) ([]f64 | error) = {
	let splitte = split(in);
	let result: []f64 = alloc([], 0);
	for (let in => splitter_next(&splitte)) {
		match (parse_numeric(in)) {
		case let number: f64 =>
			append(result, number);
		case let err: error =>
			free(result);
			return err;
		};
	};
	return result;
};

type string_escaper = []u8;

fn escape_string(in: str) string_escaper = strings::toutf8(in): string_escaper;

fn string_escaper_next(this: *string_escaper) (str | done | error) = {
	if (len(*this) < 1) return done;
	let result: []u8 = alloc([], 0);
	let end = 0z;
	let saw_escape = false;
	for (let byte .. *this) {
		end += 1;
		if (saw_escape) {
			switch (byte) {
			case ';'  => append(result, ';');
			case 's'  => append(result, ' ');
			case 'n'  => append(result, '\n');
			case 't'  => append(result, '\t');
			case 'r'  => append(result, '\r');
			case '\\' => append(result, '\\');
			case =>
				free(result);
				return invalid_escape;
			};
			saw_escape = false;
		} else {
			switch (byte) {
			case ';'  => break;
			case '\\' => saw_escape = true;
			case      => append(result, byte);
			};
		};
	};
	*this = (*this)[end..];
	return strings::fromutf8_unsafe(result);
};

type splitter = []u8;

fn split(in: str) splitter = strings::toutf8(in): splitter;

fn splitter_next(this: *splitter) (str | done) = {
	if (len(*this) < 1) return done;
	let end   = 0z;
	let knife = 0z;
	for (let byte .. *this) {
		knife += 1;
		if (byte == ';') {
			break;
		} else {
			end += 1;
		};
	};
	let result = this[..end];
	*this = (*this)[knife..];
	return strings::fromutf8_unsafe(result);
};