TypeScript/src/services/patternMatcher.ts

/* @internal */
namespace ts {
    // Note(cyrusn): this enum is ordered from strongest match type to weakest match type.
    export enum PatternMatchKind {
        exact,
        prefix,
        substring,
        camelCase
    }

    // Information about a match made by the pattern matcher between a candidate and the
    // search pattern.
    export interface PatternMatch {
        // What kind of match this was.  Exact matches are better than prefix matches which are
        // better than substring matches which are better than CamelCase matches.
        kind: PatternMatchKind;

        // If this was a camel case match, how strong the match is.  Higher number means
        // it was a better match.
        camelCaseWeight?: number;

        // If this was a match where all constituent parts of the candidate and search pattern
        // matched case sensitively or case insensitively.  Case sensitive matches of the kind
        // are better matches than insensitive matches.
        isCaseSensitive: boolean;

        // Whether or not this match occurred with the punctuation from the search pattern stripped
        // out or not.  Matches without the punctuation stripped are better than ones with punctuation
        // stripped.
        punctuationStripped: boolean;
    }

    // The pattern matcher maintains an internal cache of information as it is used.  Therefore,
    // you should not keep it around forever and should get and release the matcher appropriately
    // once you no longer need it.
    export interface PatternMatcher {
        // Used to match a candidate against the last segment of a possibly dotted pattern.  This
        // is useful as a quick check to prevent having to compute a container before calling
        // "getMatches".
        //
        // For example, if the search pattern is "ts.c.SK" and the candidate is "SyntaxKind", then
        // this will return a successful match, having only tested "SK" against "SyntaxKind".  At
        // that point a call can be made to 'getMatches("SyntaxKind", "ts.compiler")', with the
        // work to create 'ts.compiler' only being done once the first match succeeded.
        getMatchesForLastSegmentOfPattern(candidate: string): PatternMatch[];

        // Fully checks a candidate, with an dotted container, against the search pattern.
        // The candidate must match the last part of the search pattern, and the dotted container
        // must match the preceding segments of the pattern.
        getMatches(candidateContainers: string[], candidate: string): PatternMatch[];

        // Whether or not the pattern contained dots or not.  Clients can use this to determine
        // If they should call getMatches, or if getMatchesForLastSegmentOfPattern is sufficient.
        patternContainsDots: boolean;
    }

    // First we break up the pattern given by dots.  Each portion of the pattern between the
    // dots is a 'Segment'.  The 'Segment' contains information about the entire section of
    // text between the dots, as well as information about any individual 'Words' that we
    // can break the segment into.  A 'Word' is simply a contiguous sequence of characters
    // that can appear in a typescript identifier.  So "GetKeyword" would be one word, while
    // "Get Keyword" would be two words.  Once we have the individual 'words', we break those
    // into constituent 'character spans' of interest.  For example, while 'UIElement' is one
    // word, it make character spans corresponding to "U", "I" and "Element".  These spans
    // are then used when doing camel cased matches against candidate patterns.
    interface Segment {
        // Information about the entire piece of text between the dots.  For example, if the
        // text between the dots is 'GetKeyword', then TotalTextChunk.Text will be 'GetKeyword' and
        // TotalTextChunk.CharacterSpans will correspond to 'Get', 'Keyword'.
        totalTextChunk: TextChunk;

        // Information about the subwords compromising the total word.  For example, if the
        // text between the dots is 'GetFoo KeywordBar', then the subwords will be 'GetFoo'
        // and 'KeywordBar'.  Those individual words will have CharacterSpans of ('Get' and
        // 'Foo') and('Keyword' and 'Bar') respectively.
        subWordTextChunks: TextChunk[];
    }

    // Information about a chunk of text from the pattern.  The chunk is a piece of text, with
    // cached information about the character spans within in.  Character spans are used for
    // camel case matching.
    interface TextChunk {
        // The text of the chunk.  This should be a contiguous sequence of character that could
        // occur in a symbol name.
        text: string;

        // The text of a chunk in lower case.  Cached because it is needed often to check for
        // case insensitive matches.
        textLowerCase: string;

        // Whether or not this chunk is entirely lowercase. We have different rules when searching
        // for something entirely lowercase or not.
        isLowerCase: boolean;

        // The spans in this text chunk that we think are of interest and should be matched
        // independently.  For example, if the chunk is for "UIElement" the the spans of interest
        // correspond to "U", "I" and "Element".  If "UIElement" isn't found as an exact, prefix.
        // or substring match, then the character spans will be used to attempt a camel case match.
        characterSpans: TextSpan[];
    }

    function createPatternMatch(kind: PatternMatchKind, punctuationStripped: boolean, isCaseSensitive: boolean, camelCaseWeight?: number): PatternMatch {
        return {
            kind,
            punctuationStripped,
            isCaseSensitive,
            camelCaseWeight
        };
    }

    export function createPatternMatcher(pattern: string): PatternMatcher {
        // We'll often see the same candidate string many times when searching (For example, when
        // we see the name of a module that is used everywhere, or the name of an overload).  As
        // such, we cache the information we compute about the candidate for the life of this
        // pattern matcher so we don't have to compute it multiple times.
        const stringToWordSpans = createMap<TextSpan[]>();

        pattern = pattern.trim();

        const dotSeparatedSegments = pattern.split(".").map(p => createSegment(p.trim()));
        const invalidPattern = dotSeparatedSegments.length === 0 || forEach(dotSeparatedSegments, segmentIsInvalid);

        return {
            getMatches,
            getMatchesForLastSegmentOfPattern,
            patternContainsDots: dotSeparatedSegments.length > 1
        };

        // Quick checks so we can bail out when asked to match a candidate.
        function skipMatch(candidate: string) {
            return invalidPattern || !candidate;
        }

        function getMatchesForLastSegmentOfPattern(candidate: string): PatternMatch[] {
            if (skipMatch(candidate)) {
                return undefined;
            }

            return matchSegment(candidate, lastOrUndefined(dotSeparatedSegments));
        }

        function getMatches(candidateContainers: string[], candidate: string): PatternMatch[] {
            if (skipMatch(candidate)) {
                return undefined;
            }

            // First, check that the last part of the dot separated pattern matches the name of the
            // candidate.  If not, then there's no point in proceeding and doing the more
            // expensive work.
            const candidateMatch = matchSegment(candidate, lastOrUndefined(dotSeparatedSegments));
            if (!candidateMatch) {
                return undefined;
            }

            candidateContainers = candidateContainers || [];

            // -1 because the last part was checked against the name, and only the rest
            // of the parts are checked against the container.
            if (dotSeparatedSegments.length - 1 > candidateContainers.length) {
                // There weren't enough container parts to match against the pattern parts.
                // So this definitely doesn't match.
                return undefined;
            }

            // So far so good.  Now break up the container for the candidate and check if all
            // the dotted parts match up correctly.
            const totalMatch = candidateMatch;

            for (let i = dotSeparatedSegments.length - 2, j = candidateContainers.length - 1;
                 i >= 0;
                 i -= 1, j -= 1) {

                const segment = dotSeparatedSegments[i];
                const containerName = candidateContainers[j];

                const containerMatch = matchSegment(containerName, segment);
                if (!containerMatch) {
                    // This container didn't match the pattern piece.  So there's no match at all.
                    return undefined;
                }

                addRange(totalMatch, containerMatch);
            }

            // Success, this symbol's full name matched against the dotted name the user was asking
            // about.
            return totalMatch;
        }

        function getWordSpans(word: string): TextSpan[] {
            if (!(word in stringToWordSpans)) {
                stringToWordSpans[word] = breakIntoWordSpans(word);
            }

            return stringToWordSpans[word];
        }

        function matchTextChunk(candidate: string, chunk: TextChunk, punctuationStripped: boolean): PatternMatch {
            const index = indexOfIgnoringCase(candidate, chunk.textLowerCase);
            if (index === 0) {
                if (chunk.text.length === candidate.length) {
                    // a) Check if the part matches the candidate entirely, in an case insensitive or
                    //    sensitive manner.  If it does, return that there was an exact match.
                    return createPatternMatch(PatternMatchKind.exact, punctuationStripped, /*isCaseSensitive:*/ candidate === chunk.text);
                }
                else {
                    // b) Check if the part is a prefix of the candidate, in a case insensitive or sensitive
                    //    manner.  If it does, return that there was a prefix match.
                    return createPatternMatch(PatternMatchKind.prefix, punctuationStripped, /*isCaseSensitive:*/ startsWith(candidate, chunk.text));
                }
            }

            const isLowercase = chunk.isLowerCase;
            if (isLowercase) {
                if (index > 0) {
                    // c) If the part is entirely lowercase, then check if it is contained anywhere in the
                    //    candidate in a case insensitive manner.  If so, return that there was a substring
                    //    match.
                    //
                    //    Note: We only have a substring match if the lowercase part is prefix match of some
                    //    word part. That way we don't match something like 'Class' when the user types 'a'.
                    //    But we would match 'FooAttribute' (since 'Attribute' starts with 'a').
                    const wordSpans = getWordSpans(candidate);
                    for (const span of wordSpans) {
                        if (partStartsWith(candidate, span, chunk.text, /*ignoreCase:*/ true)) {
                            return createPatternMatch(PatternMatchKind.substring, punctuationStripped,
                                /*isCaseSensitive:*/ partStartsWith(candidate, span, chunk.text, /*ignoreCase:*/ false));
                        }
                    }
                }
            }
            else {
                // d) If the part was not entirely lowercase, then check if it is contained in the
                //    candidate in a case *sensitive* manner. If so, return that there was a substring
                //    match.
                if (candidate.indexOf(chunk.text) > 0) {
                    return createPatternMatch(PatternMatchKind.substring, punctuationStripped, /*isCaseSensitive:*/ true);
                }
            }

            if (!isLowercase) {
                // e) If the part was not entirely lowercase, then attempt a camel cased match as well.
                if (chunk.characterSpans.length > 0) {
                    const candidateParts = getWordSpans(candidate);
                    let camelCaseWeight = tryCamelCaseMatch(candidate, candidateParts, chunk, /*ignoreCase:*/ false);
                    if (camelCaseWeight !== undefined) {
                        return createPatternMatch(PatternMatchKind.camelCase, punctuationStripped, /*isCaseSensitive:*/ true, /*camelCaseWeight:*/ camelCaseWeight);
                    }

                    camelCaseWeight = tryCamelCaseMatch(candidate, candidateParts, chunk, /*ignoreCase:*/ true);
                    if (camelCaseWeight !== undefined) {
                        return createPatternMatch(PatternMatchKind.camelCase, punctuationStripped, /*isCaseSensitive:*/ false, /*camelCaseWeight:*/ camelCaseWeight);
                    }
                }
            }

            if (isLowercase) {
                // f) Is the pattern a substring of the candidate starting on one of the candidate's word boundaries?

                // We could check every character boundary start of the candidate for the pattern. However, that's
                // an m * n operation in the wost case. Instead, find the first instance of the pattern
                // substring, and see if it starts on a capital letter. It seems unlikely that the user will try to
                // filter the list based on a substring that starts on a capital letter and also with a lowercase one.
                // (Pattern: fogbar, Candidate: quuxfogbarFogBar).
                if (chunk.text.length < candidate.length) {
                    if (index > 0 && isUpperCaseLetter(candidate.charCodeAt(index))) {
                        return createPatternMatch(PatternMatchKind.substring, punctuationStripped, /*isCaseSensitive:*/ false);
                    }
                }
            }

            return undefined;
        }

        function containsSpaceOrAsterisk(text: string): boolean {
            for (let i = 0; i < text.length; i++) {
                const ch = text.charCodeAt(i);
                if (ch === CharacterCodes.space || ch === CharacterCodes.asterisk) {
                    return true;
                }
            }

            return false;
        }

        function matchSegment(candidate: string, segment: Segment): PatternMatch[] {
            // First check if the segment matches as is.  This is also useful if the segment contains
            // characters we would normally strip when splitting into parts that we also may want to
            // match in the candidate.  For example if the segment is "@int" and the candidate is
            // "@int", then that will show up as an exact match here.
            //
            // Note: if the segment contains a space or an asterisk then we must assume that it's a
            // multi-word segment.
            if (!containsSpaceOrAsterisk(segment.totalTextChunk.text)) {
                const match = matchTextChunk(candidate, segment.totalTextChunk, /*punctuationStripped:*/ false);
                if (match) {
                    return [match];
                }
            }

            // The logic for pattern matching is now as follows:
            //
            // 1) Break the segment passed in into words.  Breaking is rather simple and a
            //    good way to think about it that if gives you all the individual alphanumeric words
            //    of the pattern.
            //
            // 2) For each word try to match the word against the candidate value.
            //
            // 3) Matching is as follows:
            //
            //   a) Check if the word matches the candidate entirely, in an case insensitive or
            //    sensitive manner.  If it does, return that there was an exact match.
            //
            //   b) Check if the word is a prefix of the candidate, in a case insensitive or
            //      sensitive manner.  If it does, return that there was a prefix match.
            //
            //   c) If the word is entirely lowercase, then check if it is contained anywhere in the
            //      candidate in a case insensitive manner.  If so, return that there was a substring
            //      match.
            //
            //      Note: We only have a substring match if the lowercase part is prefix match of
            //      some word part. That way we don't match something like 'Class' when the user
            //      types 'a'. But we would match 'FooAttribute' (since 'Attribute' starts with
            //      'a').
            //
            //   d) If the word was not entirely lowercase, then check if it is contained in the
            //      candidate in a case *sensitive* manner. If so, return that there was a substring
            //      match.
            //
            //   e) If the word was not entirely lowercase, then attempt a camel cased match as
            //      well.
            //
            //   f) The word is all lower case. Is it a case insensitive substring of the candidate starting
            //      on a part boundary of the candidate?
            //
            // Only if all words have some sort of match is the pattern considered matched.

            const subWordTextChunks = segment.subWordTextChunks;
            let matches: PatternMatch[] = undefined;

            for (const subWordTextChunk of subWordTextChunks) {
                // Try to match the candidate with this word
                const result = matchTextChunk(candidate, subWordTextChunk, /*punctuationStripped:*/ true);
                if (!result) {
                    return undefined;
                }

                matches = matches || [];
                matches.push(result);
            }

            return matches;
        }

        function partStartsWith(candidate: string, candidateSpan: TextSpan, pattern: string, ignoreCase: boolean, patternSpan?: TextSpan): boolean {
            const patternPartStart = patternSpan ? patternSpan.start : 0;
            const patternPartLength = patternSpan ? patternSpan.length : pattern.length;

            if (patternPartLength > candidateSpan.length) {
                // Pattern part is longer than the candidate part. There can never be a match.
                return false;
            }

            if (ignoreCase) {
                for (let i = 0; i < patternPartLength; i++) {
                    const ch1 = pattern.charCodeAt(patternPartStart + i);
                    const ch2 = candidate.charCodeAt(candidateSpan.start + i);
                    if (toLowerCase(ch1) !== toLowerCase(ch2)) {
                        return false;
                    }
                }
            }
            else {
                for (let i = 0; i < patternPartLength; i++) {
                    const ch1 = pattern.charCodeAt(patternPartStart + i);
                    const ch2 = candidate.charCodeAt(candidateSpan.start + i);
                    if (ch1 !== ch2) {
                        return false;
                    }
                }
            }

            return true;
        }

        function tryCamelCaseMatch(candidate: string, candidateParts: TextSpan[], chunk: TextChunk, ignoreCase: boolean): number {
            const chunkCharacterSpans = chunk.characterSpans;

            // Note: we may have more pattern parts than candidate parts.  This is because multiple
            // pattern parts may match a candidate part.  For example "SiUI" against "SimpleUI".
            // We'll have 3 pattern parts Si/U/I against two candidate parts Simple/UI.  However, U
            // and I will both match in UI.

            let currentCandidate = 0;
            let currentChunkSpan = 0;
            let firstMatch: number = undefined;
            let contiguous: boolean = undefined;

            while (true) {
                // Let's consider our termination cases
                if (currentChunkSpan === chunkCharacterSpans.length) {
                    // We did match! We shall assign a weight to this
                    let weight = 0;

                    // Was this contiguous?
                    if (contiguous) {
                        weight += 1;
                    }

                    // Did we start at the beginning of the candidate?
                    if (firstMatch === 0) {
                        weight += 2;
                    }

                    return weight;
                }
                else if (currentCandidate === candidateParts.length) {
                    // No match, since we still have more of the pattern to hit
                    return undefined;
                }

                let candidatePart = candidateParts[currentCandidate];
                let gotOneMatchThisCandidate = false;

                // Consider the case of matching SiUI against SimpleUIElement. The candidate parts
                // will be Simple/UI/Element, and the pattern parts will be Si/U/I.  We'll match 'Si'
                // against 'Simple' first.  Then we'll match 'U' against 'UI'. However, we want to
                // still keep matching pattern parts against that candidate part.
                for (; currentChunkSpan < chunkCharacterSpans.length; currentChunkSpan++) {
                    const chunkCharacterSpan = chunkCharacterSpans[currentChunkSpan];

                    if (gotOneMatchThisCandidate) {
                        // We've already gotten one pattern part match in this candidate.  We will
                        // only continue trying to consumer pattern parts if the last part and this
                        // part are both upper case.
                        if (!isUpperCaseLetter(chunk.text.charCodeAt(chunkCharacterSpans[currentChunkSpan - 1].start)) ||
                            !isUpperCaseLetter(chunk.text.charCodeAt(chunkCharacterSpans[currentChunkSpan].start))) {
                            break;
                        }
                    }

                    if (!partStartsWith(candidate, candidatePart, chunk.text, ignoreCase, chunkCharacterSpan)) {
                        break;
                    }

                    gotOneMatchThisCandidate = true;

                    firstMatch = firstMatch === undefined ? currentCandidate : firstMatch;

                    // If we were contiguous, then keep that value.  If we weren't, then keep that
                    // value.  If we don't know, then set the value to 'true' as an initial match is
                    // obviously contiguous.
                    contiguous = contiguous === undefined ? true : contiguous;

                    candidatePart = createTextSpan(candidatePart.start + chunkCharacterSpan.length, candidatePart.length - chunkCharacterSpan.length);
                }

                // Check if we matched anything at all.  If we didn't, then we need to unset the
                // contiguous bit if we currently had it set.
                // If we haven't set the bit yet, then that means we haven't matched anything so
                // far, and we don't want to change that.
                if (!gotOneMatchThisCandidate && contiguous !== undefined) {
                    contiguous = false;
                }

                // Move onto the next candidate.
                currentCandidate++;
            }
        }
    }

    function createSegment(text: string): Segment {
        return {
            totalTextChunk: createTextChunk(text),
            subWordTextChunks: breakPatternIntoTextChunks(text)
        };
    }

    // A segment is considered invalid if we couldn't find any words in it.
    function segmentIsInvalid(segment: Segment) {
        return segment.subWordTextChunks.length === 0;
    }

    function isUpperCaseLetter(ch: number) {
        // Fast check for the ascii range.
        if (ch >= CharacterCodes.A && ch <= CharacterCodes.Z) {
            return true;
        }

        if (ch < CharacterCodes.maxAsciiCharacter || !isUnicodeIdentifierStart(ch, ScriptTarget.Latest)) {
            return false;
        }

        // TODO: find a way to determine this for any unicode characters in a
        // non-allocating manner.
        const str = String.fromCharCode(ch);
        return str === str.toUpperCase();
    }

    function isLowerCaseLetter(ch: number) {
        // Fast check for the ascii range.
        if (ch >= CharacterCodes.a && ch <= CharacterCodes.z) {
            return true;
        }

        if (ch < CharacterCodes.maxAsciiCharacter || !isUnicodeIdentifierStart(ch, ScriptTarget.Latest)) {
            return false;
        }


        // TODO: find a way to determine this for any unicode characters in a
        // non-allocating manner.
        const str = String.fromCharCode(ch);
        return str === str.toLowerCase();
    }

    // Assumes 'value' is already lowercase.
    function indexOfIgnoringCase(string: string, value: string): number {
        for (let i = 0, n = string.length - value.length; i <= n; i++) {
            if (startsWithIgnoringCase(string, value, i)) {
                return i;
            }
        }

        return -1;
    }

    // Assumes 'value' is already lowercase.
    function startsWithIgnoringCase(string: string, value: string, start: number): boolean {
        for (let i = 0, n = value.length; i < n; i++) {
            const ch1 = toLowerCase(string.charCodeAt(i + start));
            const ch2 = value.charCodeAt(i);

            if (ch1 !== ch2) {
                return false;
            }
        }

        return true;
    }

    function toLowerCase(ch: number): number {
        // Fast convert for the ascii range.
        if (ch >= CharacterCodes.A && ch <= CharacterCodes.Z) {
            return CharacterCodes.a + (ch - CharacterCodes.A);
        }

        if (ch < CharacterCodes.maxAsciiCharacter) {
            return ch;
        }

        // TODO: find a way to compute this for any unicode characters in a
        // non-allocating manner.
        return String.fromCharCode(ch).toLowerCase().charCodeAt(0);
    }

    function isDigit(ch: number) {
        // TODO(cyrusn): Find a way to support this for unicode digits.
        return ch >= CharacterCodes._0 && ch <= CharacterCodes._9;
    }

    function isWordChar(ch: number) {
        return isUpperCaseLetter(ch) || isLowerCaseLetter(ch) || isDigit(ch) || ch === CharacterCodes._ || ch === CharacterCodes.$;
    }

    function breakPatternIntoTextChunks(pattern: string): TextChunk[] {
        const result: TextChunk[] = [];
        let wordStart = 0;
        let wordLength = 0;

        for (let i = 0; i < pattern.length; i++) {
            const ch = pattern.charCodeAt(i);
            if (isWordChar(ch)) {
                if (wordLength === 0) {
                    wordStart = i;
                }
                wordLength++;
            }
            else {
                if (wordLength > 0) {
                    result.push(createTextChunk(pattern.substr(wordStart, wordLength)));
                    wordLength = 0;
                }
            }
        }

        if (wordLength > 0) {
            result.push(createTextChunk(pattern.substr(wordStart, wordLength)));
        }

        return result;
    }

    function createTextChunk(text: string): TextChunk {
        const textLowerCase = text.toLowerCase();
        return {
            text,
            textLowerCase,
            isLowerCase: text === textLowerCase,
            characterSpans: breakIntoCharacterSpans(text)
        };
    }

    /* @internal */ export function breakIntoCharacterSpans(identifier: string): TextSpan[] {
        return breakIntoSpans(identifier, /*word:*/ false);
    }

    /* @internal */ export function breakIntoWordSpans(identifier: string): TextSpan[] {
        return breakIntoSpans(identifier, /*word:*/ true);
    }

    function breakIntoSpans(identifier: string, word: boolean): TextSpan[] {
        const result: TextSpan[] = [];

        let wordStart = 0;
        for (let i = 1, n = identifier.length; i < n; i++) {
            const lastIsDigit = isDigit(identifier.charCodeAt(i - 1));
            const currentIsDigit = isDigit(identifier.charCodeAt(i));

            const hasTransitionFromLowerToUpper = transitionFromLowerToUpper(identifier, word, i);
            const hasTransitionFromUpperToLower = transitionFromUpperToLower(identifier, word, i, wordStart);

            if (charIsPunctuation(identifier.charCodeAt(i - 1)) ||
                charIsPunctuation(identifier.charCodeAt(i)) ||
                lastIsDigit !== currentIsDigit ||
                hasTransitionFromLowerToUpper ||
                hasTransitionFromUpperToLower) {

                if (!isAllPunctuation(identifier, wordStart, i)) {
                    result.push(createTextSpan(wordStart, i - wordStart));
                }

                wordStart = i;
            }
        }

        if (!isAllPunctuation(identifier, wordStart, identifier.length)) {
            result.push(createTextSpan(wordStart, identifier.length - wordStart));
        }

        return result;
    }

    function charIsPunctuation(ch: number) {
        switch (ch) {
            case CharacterCodes.exclamation:
            case CharacterCodes.doubleQuote:
            case CharacterCodes.hash:
            case CharacterCodes.percent:
            case CharacterCodes.ampersand:
            case CharacterCodes.singleQuote:
            case CharacterCodes.openParen:
            case CharacterCodes.closeParen:
            case CharacterCodes.asterisk:
            case CharacterCodes.comma:
            case CharacterCodes.minus:
            case CharacterCodes.dot:
            case CharacterCodes.slash:
            case CharacterCodes.colon:
            case CharacterCodes.semicolon:
            case CharacterCodes.question:
            case CharacterCodes.at:
            case CharacterCodes.openBracket:
            case CharacterCodes.backslash:
            case CharacterCodes.closeBracket:
            case CharacterCodes._:
            case CharacterCodes.openBrace:
            case CharacterCodes.closeBrace:
                return true;
        }

        return false;
    }

    function isAllPunctuation(identifier: string, start: number, end: number): boolean {
        for (let i = start; i < end; i++) {
            const ch = identifier.charCodeAt(i);

            // We don't consider _ or $ as punctuation as there may be things with that name.
            if (!charIsPunctuation(ch) || ch === CharacterCodes._ || ch === CharacterCodes.$) {
                return false;
            }
        }

        return true;
    }

    function transitionFromUpperToLower(identifier: string, word: boolean, index: number, wordStart: number): boolean {
        if (word) {
            // Cases this supports:
            // 1) IDisposable -> I, Disposable
            // 2) UIElement -> UI, Element
            // 3) HTMLDocument -> HTML, Document
            //
            // etc.
            if (index !== wordStart &&
                index + 1 < identifier.length) {
                const currentIsUpper = isUpperCaseLetter(identifier.charCodeAt(index));
                const nextIsLower = isLowerCaseLetter(identifier.charCodeAt(index + 1));

                if (currentIsUpper && nextIsLower) {
                    // We have a transition from an upper to a lower letter here.  But we only
                    // want to break if all the letters that preceded are uppercase.  i.e. if we
                    // have "Foo" we don't want to break that into "F, oo".  But if we have
                    // "IFoo" or "UIFoo", then we want to break that into "I, Foo" and "UI,
                    // Foo".  i.e. the last uppercase letter belongs to the lowercase letters
                    // that follows.  Note: this will make the following not split properly:
                    // "HELLOthere".  However, these sorts of names do not show up in .Net
                    // programs.
                    for (let i = wordStart; i < index; i++) {
                        if (!isUpperCaseLetter(identifier.charCodeAt(i))) {
                            return false;
                        }
                    }

                    return true;
                }
            }
        }

        return false;
    }

    function transitionFromLowerToUpper(identifier: string, word: boolean, index: number): boolean {
        const lastIsUpper = isUpperCaseLetter(identifier.charCodeAt(index - 1));
        const currentIsUpper = isUpperCaseLetter(identifier.charCodeAt(index));

        // See if the casing indicates we're starting a new word. Note: if we're breaking on
        // words, then just seeing an upper case character isn't enough.  Instead, it has to
        // be uppercase and the previous character can't be uppercase.
        //
        // For example, breaking "AddMetadata" on words would make: Add Metadata
        //
        // on characters would be: A dd M etadata
        //
        // Break "AM" on words would be: AM
        //
        // on characters would be: A M
        //
        // We break the search string on characters.  But we break the symbol name on words.
        const transition = word
            ? (currentIsUpper && !lastIsUpper)
            : currentIsUpper;
        return transition;
    }
}