'use strict';

var GROUP_LEFT_TO_RIGHT,
    GROUP_RIGHT_TO_LEFT,
    EXPRESSION_LEFT_TO_RIGHT,
    EXPRESSION_RIGHT_TO_LEFT;

/*
 * Character ranges of left-to-right characters.
 */

GROUP_LEFT_TO_RIGHT = 'A-Za-z\u00C0-\u00D6\u00D8-\u00F6' +
    '\u00F8-\u02B8\u0300-\u0590\u0800-\u1FFF\u200E\u2C00-\uFB1C' +
    '\uFE00-\uFE6F\uFEFD-\uFFFF';

/*
 * Character ranges of right-to-left characters.
 */

GROUP_RIGHT_TO_LEFT = '\u0591-\u07FF\uFB1D-\uFDFD\uFE70-\uFEFC';

/*
 * Expression to match a left-to-right string.
 *
 * Matches the start of a string, followed by zero or
 * more non-right-to-left characters, followed by a
 * left-to-right character.
 */

EXPRESSION_LEFT_TO_RIGHT = new RegExp(
    '^[^' + GROUP_RIGHT_TO_LEFT + ']*[' + GROUP_LEFT_TO_RIGHT + ']'
);

/*
 * Expression to match a right-to-left string.
 *
 * Matches the start of a string, followed by zero or
 * more non-left-to-right characters, followed by a
 * right-to-left character.
 */

EXPRESSION_RIGHT_TO_LEFT = new RegExp(
    '^[^' + GROUP_LEFT_TO_RIGHT + ']*[' + GROUP_RIGHT_TO_LEFT + ']'
);

/**
 * Detect the direction of text.
 *
 * @param {string} value - value to stringify and check.
 * @return {string} - One of `"rtl"`, `"ltr"`, or
 *   `"neutral"`.
 */
function direction(value) {
    value = value.toString();

    if (EXPRESSION_RIGHT_TO_LEFT.test(value)) {
        return 'rtl';
    }

    if (EXPRESSION_LEFT_TO_RIGHT.test(value)) {
        return 'ltr';
    }

    return 'neutral';
}

/*
 * Expose `direction`.
 */

module.exports = direction;