namespace ts {
    export interface DocumentHighlights {
        fileName: string;
        highlightSpans: HighlightSpan[];
    }

    /* @internal */
    export namespace DocumentHighlights {
        export function getDocumentHighlights(program: Program, cancellationToken: CancellationToken, sourceFile: SourceFile, position: number, sourceFilesToSearch: readonly SourceFile[]): DocumentHighlights[] | undefined {
            const node = getTouchingPropertyName(sourceFile, position);

            if (node.parent && (isJsxOpeningElement(node.parent) && node.parent.tagName === node || isJsxClosingElement(node.parent))) {
                // For a JSX element, just highlight the matching tag, not all references.
                const { openingElement, closingElement } = node.parent.parent;
                const highlightSpans = [openingElement, closingElement].map(({ tagName }) => getHighlightSpanForNode(tagName, sourceFile));
                return [{ fileName: sourceFile.fileName, highlightSpans }];
            }

            return getSemanticDocumentHighlights(position, node, program, cancellationToken, sourceFilesToSearch) || getSyntacticDocumentHighlights(node, sourceFile);
        }

        function getHighlightSpanForNode(node: Node, sourceFile: SourceFile): HighlightSpan {
            return {
                fileName: sourceFile.fileName,
                textSpan: createTextSpanFromNode(node, sourceFile),
                kind: HighlightSpanKind.none
            };
        }

        function getSemanticDocumentHighlights(position: number, node: Node, program: Program, cancellationToken: CancellationToken, sourceFilesToSearch: readonly SourceFile[]): DocumentHighlights[] | undefined {
            const sourceFilesSet = new Set(sourceFilesToSearch.map(f => f.fileName));
            const referenceEntries = FindAllReferences.getReferenceEntriesForNode(position, node, program, sourceFilesToSearch, cancellationToken, /*options*/ undefined, sourceFilesSet);
            if (!referenceEntries) return undefined;
            const map = arrayToMultiMap(referenceEntries.map(FindAllReferences.toHighlightSpan), e => e.fileName, e => e.span);
            return arrayFrom(map.entries(), ([fileName, highlightSpans]) => {
                if (!sourceFilesSet.has(fileName)) {
                    Debug.assert(program.redirectTargetsMap.has(fileName));
                    const redirectTarget = program.getSourceFile(fileName);
                    const redirect = find(sourceFilesToSearch, f => !!f.redirectInfo && f.redirectInfo.redirectTarget === redirectTarget)!;
                    fileName = redirect.fileName;
                    Debug.assert(sourceFilesSet.has(fileName));
                }
                return { fileName, highlightSpans };
            });
        }

        function getSyntacticDocumentHighlights(node: Node, sourceFile: SourceFile): DocumentHighlights[] | undefined {
            const highlightSpans = getHighlightSpans(node, sourceFile);
            return highlightSpans && [{ fileName: sourceFile.fileName, highlightSpans }];
        }

        function getHighlightSpans(node: Node, sourceFile: SourceFile): HighlightSpan[] | undefined {
            switch (node.kind) {
                case SyntaxKind.IfKeyword:
                case SyntaxKind.ElseKeyword:
                    return isIfStatement(node.parent) ? getIfElseOccurrences(node.parent, sourceFile) : undefined;
                case SyntaxKind.ReturnKeyword:
                    return useParent(node.parent, isReturnStatement, getReturnOccurrences);
                case SyntaxKind.ThrowKeyword:
                    return useParent(node.parent, isThrowStatement, getThrowOccurrences);
                case SyntaxKind.TryKeyword:
                case SyntaxKind.CatchKeyword:
                case SyntaxKind.FinallyKeyword:
                    const tryStatement = node.kind === SyntaxKind.CatchKeyword ? node.parent.parent : node.parent;
                    return useParent(tryStatement, isTryStatement, getTryCatchFinallyOccurrences);
                case SyntaxKind.SwitchKeyword:
                    return useParent(node.parent, isSwitchStatement, getSwitchCaseDefaultOccurrences);
                case SyntaxKind.CaseKeyword:
                case SyntaxKind.DefaultKeyword: {
                    if (isDefaultClause(node.parent) || isCaseClause(node.parent)) {
                        return useParent(node.parent.parent.parent, isSwitchStatement, getSwitchCaseDefaultOccurrences);
                    }
                    return undefined;
                }
                case SyntaxKind.BreakKeyword:
                case SyntaxKind.ContinueKeyword:
                    return useParent(node.parent, isBreakOrContinueStatement, getBreakOrContinueStatementOccurrences);
                case SyntaxKind.ForKeyword:
                case SyntaxKind.WhileKeyword:
                case SyntaxKind.DoKeyword:
                    return useParent(node.parent, (n): n is IterationStatement => isIterationStatement(n, /*lookInLabeledStatements*/ true), getLoopBreakContinueOccurrences);
                case SyntaxKind.ConstructorKeyword:
                    return getFromAllDeclarations(isConstructorDeclaration, [SyntaxKind.ConstructorKeyword]);
                case SyntaxKind.GetKeyword:
                case SyntaxKind.SetKeyword:
                    return getFromAllDeclarations(isAccessor, [SyntaxKind.GetKeyword, SyntaxKind.SetKeyword]);
                case SyntaxKind.AwaitKeyword:
                    return useParent(node.parent, isAwaitExpression, getAsyncAndAwaitOccurrences);
                case SyntaxKind.AsyncKeyword:
                    return highlightSpans(getAsyncAndAwaitOccurrences(node));
                case SyntaxKind.YieldKeyword:
                    return highlightSpans(getYieldOccurrences(node));
                default:
                    return isModifierKind(node.kind) && (isDeclaration(node.parent) || isVariableStatement(node.parent))
                        ? highlightSpans(getModifierOccurrences(node.kind, node.parent))
                        : undefined;
            }

            function getFromAllDeclarations<T extends Node>(nodeTest: (node: Node) => node is T, keywords: readonly SyntaxKind[]): HighlightSpan[] | undefined {
                return useParent(node.parent, nodeTest, decl => mapDefined(decl.symbol.declarations, d =>
                    nodeTest(d) ? find(d.getChildren(sourceFile), c => contains(keywords, c.kind)) : undefined));
            }

            function useParent<T extends Node>(node: Node, nodeTest: (node: Node) => node is T, getNodes: (node: T, sourceFile: SourceFile) => readonly Node[] | undefined): HighlightSpan[] | undefined {
                return nodeTest(node) ? highlightSpans(getNodes(node, sourceFile)) : undefined;
            }

            function highlightSpans(nodes: readonly Node[] | undefined): HighlightSpan[] | undefined {
                return nodes && nodes.map(node => getHighlightSpanForNode(node, sourceFile));
            }
        }

        /**
         * Aggregates all throw-statements within this node *without* crossing
         * into function boundaries and try-blocks with catch-clauses.
         */
        function aggregateOwnedThrowStatements(node: Node): readonly ThrowStatement[] | undefined {
            if (isThrowStatement(node)) {
                return [node];
            }
            else if (isTryStatement(node)) {
                // Exceptions thrown within a try block lacking a catch clause are "owned" in the current context.
                return concatenate(
                    node.catchClause ? aggregateOwnedThrowStatements(node.catchClause) : node.tryBlock && aggregateOwnedThrowStatements(node.tryBlock),
                    node.finallyBlock && aggregateOwnedThrowStatements(node.finallyBlock));
            }
            // Do not cross function boundaries.
            return isFunctionLike(node) ? undefined : flatMapChildren(node, aggregateOwnedThrowStatements);
        }

        /**
         * For lack of a better name, this function takes a throw statement and returns the
         * nearest ancestor that is a try-block (whose try statement has a catch clause),
         * function-block, or source file.
         */
        function getThrowStatementOwner(throwStatement: ThrowStatement): Node | undefined {
            let child: Node = throwStatement;

            while (child.parent) {
                const parent = child.parent;

                if (isFunctionBlock(parent) || parent.kind === SyntaxKind.SourceFile) {
                    return parent;
                }

                // A throw-statement is only owned by a try-statement if the try-statement has
                // a catch clause, and if the throw-statement occurs within the try block.
                if (isTryStatement(parent) && parent.tryBlock === child && parent.catchClause) {
                    return child;
                }

                child = parent;
            }

            return undefined;
        }

        function aggregateAllBreakAndContinueStatements(node: Node): readonly BreakOrContinueStatement[] | undefined {
            return isBreakOrContinueStatement(node) ? [node] : isFunctionLike(node) ? undefined : flatMapChildren(node, aggregateAllBreakAndContinueStatements);
        }

        function flatMapChildren<T>(node: Node, cb: (child: Node) => readonly T[] | T | undefined): readonly T[] {
            const result: T[] = [];
            node.forEachChild(child => {
                const value = cb(child);
                if (value !== undefined) {
                    result.push(...toArray(value));
                }
            });
            return result;
        }

        function ownsBreakOrContinueStatement(owner: Node, statement: BreakOrContinueStatement): boolean {
            const actualOwner = getBreakOrContinueOwner(statement);
            return !!actualOwner && actualOwner === owner;
        }

        function getBreakOrContinueOwner(statement: BreakOrContinueStatement): Node | undefined {
            return findAncestor(statement, node => {
                switch (node.kind) {
                    case SyntaxKind.SwitchStatement:
                        if (statement.kind === SyntaxKind.ContinueStatement) {
                            return false;
                        }
                        // falls through

                    case SyntaxKind.ForStatement:
                    case SyntaxKind.ForInStatement:
                    case SyntaxKind.ForOfStatement:
                    case SyntaxKind.WhileStatement:
                    case SyntaxKind.DoStatement:
                        return !statement.label || isLabeledBy(node, statement.label.escapedText);
                    default:
                        // Don't cross function boundaries.
                        // TODO: GH#20090
                        return isFunctionLike(node) && "quit";
                }
            });
        }

        function getModifierOccurrences(modifier: Modifier["kind"], declaration: Node): Node[] {
            return mapDefined(getNodesToSearchForModifier(declaration, modifierToFlag(modifier)), node => findModifier(node, modifier));
        }

        function getNodesToSearchForModifier(declaration: Node, modifierFlag: ModifierFlags): readonly Node[] | undefined {
            // Types of node whose children might have modifiers.
            const container = declaration.parent as ModuleBlock | SourceFile | Block | CaseClause | DefaultClause | ConstructorDeclaration | MethodDeclaration | FunctionDeclaration | ObjectTypeDeclaration | ObjectLiteralExpression;
            switch (container.kind) {
                case SyntaxKind.ModuleBlock:
                case SyntaxKind.SourceFile:
                case SyntaxKind.Block:
                case SyntaxKind.CaseClause:
                case SyntaxKind.DefaultClause:
                    // Container is either a class declaration or the declaration is a classDeclaration
                    if (modifierFlag & ModifierFlags.Abstract && isClassDeclaration(declaration)) {
                        return [...declaration.members, declaration];
                    }
                    else {
                        return container.statements;
                    }
                case SyntaxKind.Constructor:
                case SyntaxKind.MethodDeclaration:
                case SyntaxKind.FunctionDeclaration:
                    return [...container.parameters, ...(isClassLike(container.parent) ? container.parent.members : [])];
                case SyntaxKind.ClassDeclaration:
                case SyntaxKind.ClassExpression:
                case SyntaxKind.InterfaceDeclaration:
                case SyntaxKind.TypeLiteral:
                    const nodes = container.members;

                    // If we're an accessibility modifier, we're in an instance member and should search
                    // the constructor's parameter list for instance members as well.
                    if (modifierFlag & (ModifierFlags.AccessibilityModifier | ModifierFlags.Readonly)) {
                        const constructor = find(container.members, isConstructorDeclaration);
                        if (constructor) {
                            return [...nodes, ...constructor.parameters];
                        }
                    }
                    else if (modifierFlag & ModifierFlags.Abstract) {
                        return [...nodes, container];
                    }
                    return nodes;

                // Syntactically invalid positions that the parser might produce anyway
                case SyntaxKind.ObjectLiteralExpression:
                    return undefined;

                default:
                    Debug.assertNever(container, "Invalid container kind.");
            }
        }

        function pushKeywordIf(keywordList: Push<Node>, token: Node | undefined, ...expected: SyntaxKind[]): boolean {
            if (token && contains(expected, token.kind)) {
                keywordList.push(token);
                return true;
            }

            return false;
        }

        function getLoopBreakContinueOccurrences(loopNode: IterationStatement): Node[] {
            const keywords: Node[] = [];

            if (pushKeywordIf(keywords, loopNode.getFirstToken(), SyntaxKind.ForKeyword, SyntaxKind.WhileKeyword, SyntaxKind.DoKeyword)) {
                // If we succeeded and got a do-while loop, then start looking for a 'while' keyword.
                if (loopNode.kind === SyntaxKind.DoStatement) {
                    const loopTokens = loopNode.getChildren();

                    for (let i = loopTokens.length - 1; i >= 0; i--) {
                        if (pushKeywordIf(keywords, loopTokens[i], SyntaxKind.WhileKeyword)) {
                            break;
                        }
                    }
                }
            }

            forEach(aggregateAllBreakAndContinueStatements(loopNode.statement), statement => {
                if (ownsBreakOrContinueStatement(loopNode, statement)) {
                    pushKeywordIf(keywords, statement.getFirstToken(), SyntaxKind.BreakKeyword, SyntaxKind.ContinueKeyword);
                }
            });

            return keywords;
        }

        function getBreakOrContinueStatementOccurrences(breakOrContinueStatement: BreakOrContinueStatement): Node[] | undefined {
            const owner = getBreakOrContinueOwner(breakOrContinueStatement);

            if (owner) {
                switch (owner.kind) {
                    case SyntaxKind.ForStatement:
                    case SyntaxKind.ForInStatement:
                    case SyntaxKind.ForOfStatement:
                    case SyntaxKind.DoStatement:
                    case SyntaxKind.WhileStatement:
                        return getLoopBreakContinueOccurrences(<IterationStatement>owner);
                    case SyntaxKind.SwitchStatement:
                        return getSwitchCaseDefaultOccurrences(<SwitchStatement>owner);

                }
            }

            return undefined;
        }

        function getSwitchCaseDefaultOccurrences(switchStatement: SwitchStatement): Node[] {
            const keywords: Node[] = [];

            pushKeywordIf(keywords, switchStatement.getFirstToken(), SyntaxKind.SwitchKeyword);

            // Go through each clause in the switch statement, collecting the 'case'/'default' keywords.
            forEach(switchStatement.caseBlock.clauses, clause => {
                pushKeywordIf(keywords, clause.getFirstToken(), SyntaxKind.CaseKeyword, SyntaxKind.DefaultKeyword);

                forEach(aggregateAllBreakAndContinueStatements(clause), statement => {
                    if (ownsBreakOrContinueStatement(switchStatement, statement)) {
                        pushKeywordIf(keywords, statement.getFirstToken(), SyntaxKind.BreakKeyword);
                    }
                });
            });

            return keywords;
        }

        function getTryCatchFinallyOccurrences(tryStatement: TryStatement, sourceFile: SourceFile): Node[] {
            const keywords: Node[] = [];

            pushKeywordIf(keywords, tryStatement.getFirstToken(), SyntaxKind.TryKeyword);

            if (tryStatement.catchClause) {
                pushKeywordIf(keywords, tryStatement.catchClause.getFirstToken(), SyntaxKind.CatchKeyword);
            }

            if (tryStatement.finallyBlock) {
                const finallyKeyword = findChildOfKind(tryStatement, SyntaxKind.FinallyKeyword, sourceFile)!;
                pushKeywordIf(keywords, finallyKeyword, SyntaxKind.FinallyKeyword);
            }

            return keywords;
        }

        function getThrowOccurrences(throwStatement: ThrowStatement, sourceFile: SourceFile): Node[] | undefined {
            const owner = getThrowStatementOwner(throwStatement);

            if (!owner) {
                return undefined;
            }

            const keywords: Node[] = [];

            forEach(aggregateOwnedThrowStatements(owner), throwStatement => {
                keywords.push(findChildOfKind(throwStatement, SyntaxKind.ThrowKeyword, sourceFile)!);
            });

            // If the "owner" is a function, then we equate 'return' and 'throw' statements in their
            // ability to "jump out" of the function, and include occurrences for both.
            if (isFunctionBlock(owner)) {
                forEachReturnStatement(<Block>owner, returnStatement => {
                    keywords.push(findChildOfKind(returnStatement, SyntaxKind.ReturnKeyword, sourceFile)!);
                });
            }

            return keywords;
        }

        function getReturnOccurrences(returnStatement: ReturnStatement, sourceFile: SourceFile): Node[] | undefined {
            const func = <FunctionLikeDeclaration>getContainingFunction(returnStatement);
            if (!func) {
                return undefined;
            }

            const keywords: Node[] = [];
            forEachReturnStatement(cast(func.body, isBlock), returnStatement => {
                keywords.push(findChildOfKind(returnStatement, SyntaxKind.ReturnKeyword, sourceFile)!);
            });

            // Include 'throw' statements that do not occur within a try block.
            forEach(aggregateOwnedThrowStatements(func.body!), throwStatement => {
                keywords.push(findChildOfKind(throwStatement, SyntaxKind.ThrowKeyword, sourceFile)!);
            });

            return keywords;
        }

        function getAsyncAndAwaitOccurrences(node: Node): Node[] | undefined {
            const func = <FunctionLikeDeclaration>getContainingFunction(node);
            if (!func) {
                return undefined;
            }

            const keywords: Node[] = [];

            if (func.modifiers) {
                func.modifiers.forEach(modifier => {
                    pushKeywordIf(keywords, modifier, SyntaxKind.AsyncKeyword);
                });
            }

            forEachChild(func, child => {
                traverseWithoutCrossingFunction(child, node => {
                    if (isAwaitExpression(node)) {
                        pushKeywordIf(keywords, node.getFirstToken(), SyntaxKind.AwaitKeyword);
                    }
                });
            });


            return keywords;
        }

        function getYieldOccurrences(node: Node): Node[] | undefined {
            const func = getContainingFunction(node) as FunctionDeclaration;
            if (!func) {
                return undefined;
            }

            const keywords: Node[] = [];

            forEachChild(func, child => {
                traverseWithoutCrossingFunction(child, node => {
                    if (isYieldExpression(node)) {
                        pushKeywordIf(keywords, node.getFirstToken(), SyntaxKind.YieldKeyword);
                    }
                });
            });

            return keywords;
        }

        // Do not cross function/class/interface/module/type boundaries.
        function traverseWithoutCrossingFunction(node: Node, cb: (node: Node) => void) {
            cb(node);
            if (!isFunctionLike(node) && !isClassLike(node) && !isInterfaceDeclaration(node) && !isModuleDeclaration(node) && !isTypeAliasDeclaration(node) && !isTypeNode(node)) {
                forEachChild(node, child => traverseWithoutCrossingFunction(child, cb));
            }
        }

        function getIfElseOccurrences(ifStatement: IfStatement, sourceFile: SourceFile): HighlightSpan[] {
            const keywords = getIfElseKeywords(ifStatement, sourceFile);
            const result: HighlightSpan[] = [];

            // We'd like to highlight else/ifs together if they are only separated by whitespace
            // (i.e. the keywords are separated by no comments, no newlines).
            for (let i = 0; i < keywords.length; i++) {
                if (keywords[i].kind === SyntaxKind.ElseKeyword && i < keywords.length - 1) {
                    const elseKeyword = keywords[i];
                    const ifKeyword = keywords[i + 1]; // this *should* always be an 'if' keyword.

                    let shouldCombineElseAndIf = true;

                    // Avoid recalculating getStart() by iterating backwards.
                    for (let j = ifKeyword.getStart(sourceFile) - 1; j >= elseKeyword.end; j--) {
                        if (!isWhiteSpaceSingleLine(sourceFile.text.charCodeAt(j))) {
                            shouldCombineElseAndIf = false;
                            break;
                        }
                    }

                    if (shouldCombineElseAndIf) {
                        result.push({
                            fileName: sourceFile.fileName,
                            textSpan: createTextSpanFromBounds(elseKeyword.getStart(), ifKeyword.end),
                            kind: HighlightSpanKind.reference
                        });
                        i++; // skip the next keyword
                        continue;
                    }
                }

                // Ordinary case: just highlight the keyword.
                result.push(getHighlightSpanForNode(keywords[i], sourceFile));
            }

            return result;
        }

        function getIfElseKeywords(ifStatement: IfStatement, sourceFile: SourceFile): Node[] {
            const keywords: Node[] = [];

            // Traverse upwards through all parent if-statements linked by their else-branches.
            while (isIfStatement(ifStatement.parent) && ifStatement.parent.elseStatement === ifStatement) {
                ifStatement = ifStatement.parent;
            }

            // Now traverse back down through the else branches, aggregating if/else keywords of if-statements.
            while (true) {
                const children = ifStatement.getChildren(sourceFile);
                pushKeywordIf(keywords, children[0], SyntaxKind.IfKeyword);

                // Generally the 'else' keyword is second-to-last, so we traverse backwards.
                for (let i = children.length - 1; i >= 0; i--) {
                    if (pushKeywordIf(keywords, children[i], SyntaxKind.ElseKeyword)) {
                        break;
                    }
                }

                if (!ifStatement.elseStatement || !isIfStatement(ifStatement.elseStatement)) {
                    break;
                }

                ifStatement = ifStatement.elseStatement;
            }

            return keywords;
        }

        /**
         * Whether or not a 'node' is preceded by a label of the given string.
         * Note: 'node' cannot be a SourceFile.
         */
        function isLabeledBy(node: Node, labelName: __String): boolean {
            return !!findAncestor(node.parent, owner => !isLabeledStatement(owner) ? "quit" : owner.label.escapedText === labelName);
        }
    }
}
