parsePattern.js

var parsePattern = function(pattern) {
    var placeholders = [];
    var substrings = [];

    var putSubstring = function(startPosition, endPosition, isPlaceholder) {
        var substring = pattern.substring(startPosition, endPosition);
        if (substring.length > 0) {
            substrings.push(substring);
            if (isPlaceholder) {
                placeholders.push(substrings.length - 1);
            }
        }
    };

    var currentPlaceholderState = false;
    var previousPlaceholderState = false;

    var startPosition = 0;
    var endPosition = 0;

    for (var i = 0; i < pattern.length; i++) {
        var letter = pattern[i];

        var isOpenBraceLetter = letter === '{';
        var isCloseBraceLetter = letter === '}';
        var isBraceLetter = isOpenBraceLetter || isCloseBraceLetter;
        var isEndLetter = i === pattern.length - 1;

        if (isBraceLetter) {
            currentPlaceholderState = isOpenBraceLetter;
            if (currentPlaceholderState != previousPlaceholderState) {
                putSubstring(startPosition, endPosition, previousPlaceholderState);
                previousPlaceholderState = currentPlaceholderState;
                startPosition = i + 1;
            }
        } else if(isEndLetter) {
            endPosition = pattern.length;
            putSubstring(startPosition, endPosition, previousPlaceholderState);
        } else {
            endPosition = i + 1;
        }
    }

    return {
        placeholders: placeholders,
        substrings: substrings
    };
};