use bufio;
use encoding::utf8;
use errors;
use io;
use locale;
use memio;
use strings;

export type scanner = struct {
	scanner:         bufio::scanner,
	entry:           entry,
	localized_entry: localized_entry,
};

// Creates a desktop entry file scanner. Use [[next]] to read lines. The caller
// must call [[finish]] once they're done with this object.
export fn scan(input: io::handle) scanner = scanner {
	scanner = bufio::newscanner(input),
	...
};

// Returns the next entry from a desktop entry file. The return value is
// borrowed from the [[scanner]] use [[line_dup]] to retain a copy.
export fn next(this: *scanner) (line | io::EOF | error) = {
	let text = match (bufio::scan_line(&this.scanner)) {
	case let text: const str =>
		yield text;
	case let err: (io::error | utf8::invalid) =>
		return err;
	case io::EOF =>
		return io::EOF;
	};
	
	if (text == "") {
		// blank line
		return blank;
		
	} else if (strings::hasprefix(text, '#')) {
		// comment
		return strings::ltrim(text, '#'): comment;
		
	} else if (strings::hasprefix(text, '[')) {
		// group header
		return parse_group_header(text)?;
		
	} else {
		// key/value pair
		let (key, valu, local) = parse_entry(text)?;

		match (local) {
		case let local: locale::locale =>
			localized_entry_finish(this.localized_entry);
			this.localized_entry = (key, valu, local);
			return this.localized_entry;
		case void =>
			entry_finish(this.entry);
			this.entry = (key, valu);
			return this.entry;
		};
	};
	
};

// Frees resources associated with a [[scanner]].
export fn finish(this: *scanner) void = {
	bufio::finish(&this.scanner);
	entry_finish(this.entry);
};

// memory is borrowed from the input
fn parse_group_header(text: str) (group_header | error) = {
	if (!strings::hasprefix(text, '[') || !strings::hassuffix(text, ']')) {
		return invalid_group_header;
	};

	text = strings::rtrim(strings::ltrim(text, '['), ']');
	if (strings::contains(text, '[', ']')) {
		return invalid_group_header;
	};
	return text: group_header;
};

// memory must be freed by the caller
fn parse_entry(line: str) ((str, str, (locale::locale | void)) | error) = {
	if (!strings::contains(line, '=')) return invalid_entry;
	let (key, valu) = strings::cut(line, "=");
	key = strings::ltrim(strings::rtrim(key));
	if (!validate_entry_key(key)) return invalid_entry;

	let local: (locale::locale | void) = void;
	let (key, local_string) = strings::cut(key, "[");
	if (local_string != "") {
		local_string = strings::rtrim(local_string, ']');
		if (!validate_entry_locale(local_string)) return invalid_entry;
		
		local = match(locale::parse(local_string)) {
		case let local: locale::locale => yield local;
		case locale::invalid           => return invalid_entry;
		};
	};

	return (strings::dup(key), strings::dup(valu), local);
};

fn validate_entry_key(key: str) bool = {
	return strings::contains(key, '[', ']', '=');
};

fn validate_entry_locale(key: str) bool = {
	return strings::contains(key, '[', ']', '=');
};