namespace ts {
    export function preProcessFile(sourceText: string, readImportFiles = true, detectJavaScriptImports = false): PreProcessedFileInfo {
        const pragmaContext: PragmaContext = {
            languageVersion: ScriptTarget.ES5, // controls whether the token scanner considers unicode identifiers or not - shouldn't matter, since we're only using it for trivia
            pragmas: undefined,
            checkJsDirective: undefined,
            referencedFiles: [],
            typeReferenceDirectives: [],
            libReferenceDirectives: [],
            amdDependencies: [],
            hasNoDefaultLib: undefined,
            moduleName: undefined
        };
        const importedFiles: FileReference[] = [];
        let ambientExternalModules: { ref: FileReference, depth: number }[] | undefined;
        let lastToken: SyntaxKind;
        let currentToken: SyntaxKind;
        let braceNesting = 0;
        // assume that text represent an external module if it contains at least one top level import/export
        // ambient modules that are found inside external modules are interpreted as module augmentations
        let externalModule = false;

        function nextToken() {
            lastToken = currentToken;
            currentToken = scanner.scan();
            if (currentToken === SyntaxKind.OpenBraceToken) {
                braceNesting++;
            }
            else if (currentToken === SyntaxKind.CloseBraceToken) {
                braceNesting--;
            }
            return currentToken;
        }

        function getFileReference() {
            const fileName = scanner.getTokenValue();
            const pos = scanner.getTokenPos();
            return { fileName, pos, end: pos + fileName.length };
        }

        function recordAmbientExternalModule(): void {
            if (!ambientExternalModules) {
                ambientExternalModules = [];
            }
            ambientExternalModules.push({ ref: getFileReference(), depth: braceNesting });
        }

        function recordModuleName() {
            importedFiles.push(getFileReference());

            markAsExternalModuleIfTopLevel();
        }

        function markAsExternalModuleIfTopLevel() {
            if (braceNesting === 0) {
                externalModule = true;
            }
        }

        /**
         * Returns true if at least one token was consumed from the stream
         */
        function tryConsumeDeclare(): boolean {
            let token = scanner.getToken();
            if (token === SyntaxKind.DeclareKeyword) {
                // declare module "mod"
                token = nextToken();
                if (token === SyntaxKind.ModuleKeyword) {
                    token = nextToken();
                    if (token === SyntaxKind.StringLiteral) {
                        recordAmbientExternalModule();
                    }
                }
                return true;
            }

            return false;
        }

        /**
         * Returns true if at least one token was consumed from the stream
         */
        function tryConsumeImport(): boolean {
            if (lastToken === SyntaxKind.DotToken) {
                return false;
            }
            let token = scanner.getToken();
            if (token === SyntaxKind.ImportKeyword) {
                token = nextToken();
                if (token === SyntaxKind.OpenParenToken) {
                    token = nextToken();
                    if (token === SyntaxKind.StringLiteral || token === SyntaxKind.NoSubstitutionTemplateLiteral) {
                        // import("mod");
                        recordModuleName();
                        return true;
                    }
                }
                else if (token === SyntaxKind.StringLiteral) {
                    // import "mod";
                    recordModuleName();
                    return true;
                }
                else {
                    if (token === SyntaxKind.TypeKeyword) {
                        const skipTypeKeyword = scanner.lookAhead(() => {
                            const token = scanner.scan();
                            return token !== SyntaxKind.FromKeyword && (
                                token === SyntaxKind.AsteriskToken ||
                                token === SyntaxKind.OpenBraceToken ||
                                token === SyntaxKind.Identifier ||
                                isKeyword(token)
                            );
                        });
                        if (skipTypeKeyword) {
                            token = nextToken();
                        }
                    }

                    if (token === SyntaxKind.Identifier || isKeyword(token)) {
                        token = nextToken();
                        if (token === SyntaxKind.FromKeyword) {
                            token = nextToken();
                            if (token === SyntaxKind.StringLiteral) {
                                // import d from "mod";
                                recordModuleName();
                                return true;
                            }
                        }
                        else if (token === SyntaxKind.EqualsToken) {
                            if (tryConsumeRequireCall(/*skipCurrentToken*/ true)) {
                                return true;
                            }
                        }
                        else if (token === SyntaxKind.CommaToken) {
                            // consume comma and keep going
                            token = nextToken();
                        }
                        else {
                            // unknown syntax
                            return true;
                        }
                    }

                    if (token === SyntaxKind.OpenBraceToken) {
                        token = nextToken();
                        // consume "{ a as B, c, d as D}" clauses
                        // make sure that it stops on EOF
                        while (token !== SyntaxKind.CloseBraceToken && token !== SyntaxKind.EndOfFileToken) {
                            token = nextToken();
                        }

                        if (token === SyntaxKind.CloseBraceToken) {
                            token = nextToken();
                            if (token === SyntaxKind.FromKeyword) {
                                token = nextToken();
                                if (token === SyntaxKind.StringLiteral) {
                                    // import {a as A} from "mod";
                                    // import d, {a, b as B} from "mod"
                                    recordModuleName();
                                }
                            }
                        }
                    }
                    else if (token === SyntaxKind.AsteriskToken) {
                        token = nextToken();
                        if (token === SyntaxKind.AsKeyword) {
                            token = nextToken();
                            if (token === SyntaxKind.Identifier || isKeyword(token)) {
                                token = nextToken();
                                if (token === SyntaxKind.FromKeyword) {
                                    token = nextToken();
                                    if (token === SyntaxKind.StringLiteral) {
                                        // import * as NS from "mod"
                                        // import d, * as NS from "mod"
                                        recordModuleName();
                                    }
                                }
                            }
                        }
                    }
                }

                return true;
            }

            return false;
        }

        function tryConsumeExport(): boolean {
            let token = scanner.getToken();
            if (token === SyntaxKind.ExportKeyword) {
                markAsExternalModuleIfTopLevel();
                token = nextToken();
                if (token === SyntaxKind.TypeKeyword) {
                    const skipTypeKeyword = scanner.lookAhead(() => {
                        const token = scanner.scan();
                        return token === SyntaxKind.AsteriskToken ||
                            token === SyntaxKind.OpenBraceToken;
                    });
                    if (skipTypeKeyword) {
                        token = nextToken();
                    }
                }
                if (token === SyntaxKind.OpenBraceToken) {
                    token = nextToken();
                    // consume "{ a as B, c, d as D}" clauses
                    // make sure it stops on EOF
                    while (token !== SyntaxKind.CloseBraceToken && token !== SyntaxKind.EndOfFileToken) {
                        token = nextToken();
                    }

                    if (token === SyntaxKind.CloseBraceToken) {
                        token = nextToken();
                        if (token === SyntaxKind.FromKeyword) {
                            token = nextToken();
                            if (token === SyntaxKind.StringLiteral) {
                                // export {a as A} from "mod";
                                // export {a, b as B} from "mod"
                                recordModuleName();
                            }
                        }
                    }
                }
                else if (token === SyntaxKind.AsteriskToken) {
                    token = nextToken();
                    if (token === SyntaxKind.FromKeyword) {
                        token = nextToken();
                        if (token === SyntaxKind.StringLiteral) {
                            // export * from "mod"
                            recordModuleName();
                        }
                    }
                }
                else if (token === SyntaxKind.ImportKeyword) {
                    token = nextToken();
                    if (token === SyntaxKind.TypeKeyword) {
                        const skipTypeKeyword = scanner.lookAhead(() => {
                            const token = scanner.scan();
                            return token === SyntaxKind.Identifier ||
                                isKeyword(token);
                        });
                        if (skipTypeKeyword) {
                            token = nextToken();
                        }
                    }
                    if (token === SyntaxKind.Identifier || isKeyword(token)) {
                        token = nextToken();
                        if (token === SyntaxKind.EqualsToken) {
                            if (tryConsumeRequireCall(/*skipCurrentToken*/ true)) {
                                return true;
                            }
                        }
                    }
                }

                return true;
            }

            return false;
        }

        function tryConsumeRequireCall(skipCurrentToken: boolean, allowTemplateLiterals = false): boolean {
            let token = skipCurrentToken ? nextToken() : scanner.getToken();
            if (token === SyntaxKind.RequireKeyword) {
                token = nextToken();
                if (token === SyntaxKind.OpenParenToken) {
                    token = nextToken();
                    if (token === SyntaxKind.StringLiteral ||
                        allowTemplateLiterals && token === SyntaxKind.NoSubstitutionTemplateLiteral) {
                        //  require("mod");
                        recordModuleName();
                    }
                }
                return true;
            }
            return false;
        }

        function tryConsumeDefine(): boolean {
            let token = scanner.getToken();
            if (token === SyntaxKind.Identifier && scanner.getTokenValue() === "define") {
                token = nextToken();
                if (token !== SyntaxKind.OpenParenToken) {
                    return true;
                }

                token = nextToken();
                if (token === SyntaxKind.StringLiteral || token === SyntaxKind.NoSubstitutionTemplateLiteral) {
                    // looks like define ("modname", ... - skip string literal and comma
                    token = nextToken();
                    if (token === SyntaxKind.CommaToken) {
                        token = nextToken();
                    }
                    else {
                        // unexpected token
                        return true;
                    }
                }

                // should be start of dependency list
                if (token !== SyntaxKind.OpenBracketToken) {
                    return true;
                }

                // skip open bracket
                token = nextToken();
                // scan until ']' or EOF
                while (token !== SyntaxKind.CloseBracketToken && token !== SyntaxKind.EndOfFileToken) {
                    // record string literals as module names
                    if (token === SyntaxKind.StringLiteral || token === SyntaxKind.NoSubstitutionTemplateLiteral) {
                        recordModuleName();
                    }

                    token = nextToken();
                }
                return true;

            }
            return false;
        }

        function processImports(): void {
            scanner.setText(sourceText);
            nextToken();
            // Look for:
            //    import "mod";
            //    import d from "mod"
            //    import {a as A } from "mod";
            //    import * as NS from "mod"
            //    import d, {a, b as B} from "mod"
            //    import i = require("mod");
            //    import("mod");

            //    export * from "mod"
            //    export {a as b} from "mod"
            //    export import i = require("mod")
            //    (for JavaScript files) require("mod")

            // Do not look for:
            //    AnySymbol.import("mod")
            //    AnySymbol.nested.import("mod")

            while (true) {
                if (scanner.getToken() === SyntaxKind.EndOfFileToken) {
                    break;
                }

                if (scanner.getToken() === SyntaxKind.TemplateHead) {
                    const stack = [scanner.getToken()];
                    loop: while (length(stack)) {
                        const token = scanner.scan();
                        switch (token) {
                            case SyntaxKind.EndOfFileToken:
                                break loop;
                            case SyntaxKind.ImportKeyword:
                                tryConsumeImport();
                                break;
                            case SyntaxKind.TemplateHead:
                                stack.push(token);
                                break;
                            case SyntaxKind.OpenBraceToken:
                                if (length(stack)) {
                                    stack.push(token);
                                }
                                break;
                            case SyntaxKind.CloseBraceToken:
                                if (length(stack)) {
                                    if (lastOrUndefined(stack) === SyntaxKind.TemplateHead) {
                                        if (scanner.reScanTemplateToken(/* isTaggedTemplate */ false) === SyntaxKind.TemplateTail) {
                                            stack.pop();
                                        }
                                    }
                                    else {
                                        stack.pop();
                                    }
                                }
                                break;
                        }
                    }
                    nextToken();
                }

                // check if at least one of alternative have moved scanner forward
                if (tryConsumeDeclare() ||
                    tryConsumeImport() ||
                    tryConsumeExport() ||
                    (detectJavaScriptImports && (
                        tryConsumeRequireCall(/*skipCurrentToken*/ false, /*allowTemplateLiterals*/ true) ||
                        tryConsumeDefine()
                    ))) {
                    continue;
                }
                else {
                    nextToken();
                }
            }

            scanner.setText(undefined);
        }

        if (readImportFiles) {
            processImports();
        }
        processCommentPragmas(pragmaContext, sourceText);
        processPragmasIntoFields(pragmaContext, noop);
        if (externalModule) {
            // for external modules module all nested ambient modules are augmentations
            if (ambientExternalModules) {
                // move all detected ambient modules to imported files since they need to be resolved
                for (const decl of ambientExternalModules) {
                    importedFiles.push(decl.ref);
                }
            }
            return { referencedFiles: pragmaContext.referencedFiles, typeReferenceDirectives: pragmaContext.typeReferenceDirectives, libReferenceDirectives: pragmaContext.libReferenceDirectives, importedFiles, isLibFile: !!pragmaContext.hasNoDefaultLib, ambientExternalModules: undefined };
        }
        else {
            // for global scripts ambient modules still can have augmentations - look for ambient modules with depth > 0
            let ambientModuleNames: string[] | undefined;
            if (ambientExternalModules) {
                for (const decl of ambientExternalModules) {
                    if (decl.depth === 0) {
                        if (!ambientModuleNames) {
                            ambientModuleNames = [];
                        }
                        ambientModuleNames.push(decl.ref.fileName);
                    }
                    else {
                        importedFiles.push(decl.ref);
                    }
                }
            }
            return { referencedFiles: pragmaContext.referencedFiles, typeReferenceDirectives: pragmaContext.typeReferenceDirectives, libReferenceDirectives: pragmaContext.libReferenceDirectives, importedFiles, isLibFile: !!pragmaContext.hasNoDefaultLib, ambientExternalModules: ambientModuleNames };
        }
    }
}