output.ts

// Copyright 2016-2018, Pulumi Corporation.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import * as log from "./log";
import { Resource } from "./resource";
import * as runtime from "./runtime";
import * as utils from "./utils";

/**
 * Output helps encode the relationship between Resources in a Pulumi application. Specifically an
 * Output holds onto a piece of Data and the Resource it was generated from. An Output value can
 * then be provided when constructing new Resources, allowing that new Resource to know both the
 * value as well as the Resource the value came from.  This allows for a precise 'Resource
 * dependency graph' to be created, which properly tracks the relationship between resources.
 */
class OutputImpl<T> implements OutputInstance<T> {
    /**
     * @internal
     * A private field to help with RTTI that works in SxS scenarios.
     *
     * This is internal instead of being truly private, to support mixins and our serialization model.
     */
    // tslint:disable-next-line:variable-name
    public readonly __pulumiOutput: boolean = true;

    /**
     * @internal
     * Wheter or not this 'Output' wraps a secret value. Values which are marked as secret are stored in an
     * encrypted format when they are persisted as part of a state file. When`true` this "taints" any
     * additional resources created from it via an [all] or [apply], such that they are also treated as
     * secrets.
     */
    public readonly isSecret: Promise<boolean>;

    /**
     * @internal
     * Whether or not this 'Output' should actually perform .apply calls.  During a preview,
     * an Output value may not be known (because it would have to actually be computed by doing an
     * 'update').  In that case, we don't want to perform any .apply calls as the callbacks
     * may not expect an undefined value.  So, instead, we just transition to another Output
     * value that itself knows it should not perform .apply calls.
     */
    public readonly isKnown: Promise<boolean>;

    /**
     * @internal
     * Method that actually produces the concrete value of this output, as well as the total
     * deployment-time set of resources this output depends on.
     *
     * Only callable on the outside.
     */
    public readonly promise: () => Promise<T>;

    /**
     * @internal
     * The list of resource that this output value depends on.
     *
     * Only callable on the outside.
     */
    public readonly resources: () => Set<Resource>;

    public readonly apply: <U>(func: (t: T) => Input<U>) => Output<U>;
    public readonly get: () => T;

    /**
     * [toString] on an [Output<T>] is not supported.  This is because the value an [Output] points
     * to is asynchronously computed (and thus, this is akin to calling [toString] on a [Promise]).
     *
     * Calling this will simply return useful text about the issue, and will log a warning. In a
     * future version of `@pulumi/pulumi` this will be changed to throw an error when this occurs.
     *
     * To get the value of an Output<T> as an Output<string> consider either:
     * 1. `o.apply(v => ``prefix${v}suffix``)` or
     * 2. `pulumi.interpolate ``prefix${v}suffix`` `
     *
     * This will return an Output with the inner computed value and all resources still tracked. See
     * https://pulumi.io/help/outputs for more details
     */
    /** @internal */ public toString: () => string;

    /**
     * [toJSON] on an [Output<T>] is not supported.  This is because the value an [Output] points
     * to is asynchronously computed (and thus, this is akin to calling [toJSON] on a [Promise]).
     *
     * Calling this will simply return useful text about the issue, and will log a warning. In a
     * future version of `@pulumi/pulumi` this will be changed to throw an error when this occurs.
     *
     * To get the value of an Output as a JSON value or JSON string consider either:
     * 1. `o.apply(v => v.toJSON())` or
     * 2. `o.apply(v => JSON.stringify(v))`
     *
     * This will return an Output with the inner computed value and all resources still tracked.
     * See https://pulumi.io/help/outputs for more details
     */
    /** @internal */ public toJSON: () => any;

    // Statics

    /**
     * create takes any Input value and converts it into an Output, deeply unwrapping nested Input
     * values as necessary.
     */
    public static create<T>(val: Input<T>): Output<Unwrap<T>>;
    public static create<T>(val: Input<T> | undefined): Output<Unwrap<T | undefined>>;
    public static create<T>(val: Input<T | undefined>): Output<Unwrap<T | undefined>> {
        return output<T>(<any>val);
    }

    /**
     * Returns true if the given object is an instance of Output<T>.  This is designed to work even when
     * multiple copies of the Pulumi SDK have been loaded into the same process.
     */
    public static isInstance<T>(obj: any): obj is Output<T> {
        return utils.isInstance(obj, "__pulumiOutput");
    }

    /** @internal */
    public constructor(
            resources: Set<Resource> | Resource[] | Resource,
            promise: Promise<T>,
            isKnown: Promise<boolean>,
            isSecret: Promise<boolean>) {
        this.isKnown = isKnown;
        this.isSecret = isSecret;

        let resourcesArray: Resource[];

        // Always create a copy so that no one accidentally modifies our Resource list.
        if (Array.isArray(resources)) {
            resourcesArray = resources;
        } else if (resources instanceof Set) {
            resourcesArray = [...resources];
        } else {
            resourcesArray = [resources];
        }

        this.resources = () => new Set<Resource>(resourcesArray);
        this.promise = () => promise;

        const firstResource = resourcesArray[0];
        this.toString = () => {
            const message =
`Calling [toString] on an [Output<T>] is not supported.

To get the value of an Output<T> as an Output<string> consider either:
1: o.apply(v => \`prefix\${v}suffix\`)
2: pulumi.interpolate \`prefix\${v}suffix\`

See https://pulumi.io/help/outputs for more details.
This function may throw in a future version of @pulumi/pulumi.`;
            return message;
        };

        this.toJSON = () => {
            const message =
`Calling [toJSON] on an [Output<T>] is not supported.

To get the value of an Output as a JSON value or JSON string consider either:
    1: o.apply(v => v.toJSON())
    2: o.apply(v => JSON.stringify(v))

See https://pulumi.io/help/outputs for more details.
This function may throw in a future version of @pulumi/pulumi.`;
            return message;
        };

        this.apply = <U>(func: (t: T) => Input<U>) => {
            let innerDetailsResolve: (val: {isKnown: boolean, isSecret: boolean}) => void;
            const innerDetails = new Promise<any>(resolve => {
                innerDetailsResolve = resolve;
            });

            // The known state of the output we're returning depends on if we're known as well, and
            // if a potential lifted inner Output is known.  If we get an inner Output, and it is
            // not known itself, then the result we return should not be known.
            const resultIsKnown = Promise.all([isKnown, innerDetails]).then(([k1, k2]) => k1 && k2.isKnown);
            const resultIsSecret = Promise.all([isSecret, innerDetails]).then(([k1, k2]) => k1 || k2.isSecret);

            return new Output<U>(resources, promise.then(async v => {
                try {
                    if (runtime.isDryRun()) {
                        // During previews only perform the apply if the engine was able to
                        // give us an actual value for this Output.
                        const applyDuringPreview = await isKnown;

                        if (!applyDuringPreview) {
                            // We didn't actually run the function, our new Output is definitely
                            // **not** known.
                            innerDetailsResolve({
                                isKnown: false,
                                isSecret: await isSecret,
                            });
                            return <U><any>undefined;
                        }
                    }

                    const transformed = await func(v);
                    if (Output.isInstance(transformed)) {
                        // Note: if the func returned a Output, we unwrap that to get the inner value
                        // returned by that Output.  Note that we are *not* capturing the Resources of
                        // this inner Output.  That's intentional.  As the Output returned is only
                        // supposed to be related this *this* Output object, those resources should
                        // already be in our transitively reachable resource graph.

                        // The callback func has produced an inner Output that may be 'known' or 'unknown'.
                        // We have to properly forward that along to our outer output.  That way the Outer
                        // output doesn't consider itself 'known' then the inner Output did not.
                        innerDetailsResolve({
                            isKnown: await transformed.isKnown,
                            isSecret: await (transformed.isSecret || Promise.resolve(false)),
                        });
                        return await transformed.promise();
                    } else {
                        // We successfully ran the inner function.  Our new Output should be considered known.
                        innerDetailsResolve({
                            isKnown: true,
                            isSecret: false,
                        });
                        return transformed;
                    }
                }
                finally {
                    // Ensure we always resolve the inner isKnown value no matter what happens
                    // above. If anything failed along the way, consider this output to be
                    // not-known. Awaiting this Output's promise() will still throw, but await'ing
                    // the isKnown bit will just return 'false'.
                    innerDetailsResolve({
                        isKnown: false,
                        isSecret: false,
                    });
                }
            }), resultIsKnown, resultIsSecret);
        };

        this.get = () => {
            throw new Error(`Cannot call '.get' during update or preview.
To manipulate the value of this Output, use '.apply' instead.`);
        };

        return new Proxy(this, {
            get: (obj, prop: keyof T) => {
                // Recreate the prototype walk to ensure we find any actual members defined directly
                // on `Output<T>`.
                for (let o = obj; o; o = Object.getPrototypeOf(o)) {
                    if (o.hasOwnProperty(prop)) {
                        return (<any>o)[prop];
                    }
                }

                // Always explicitly fail on a member called 'then'.  It is used by other systems to
                // determine if this is a Promise, and we do not want to indicate that that's what
                // we are.
                if (prop === "then") {
                    return undefined;
                }

                // Do not lift members that start with __.  Technically, if all libraries were
                // using this version of pulumi/pulumi we would not need this.  However, this is
                // so that downstream consumers can use this version of pulumi/pulumi while also
                // passing these new Outputs to older versions of pulumi/pulumi.  The reason this
                // can be a problem is that older versions do an RTTI check that simply asks questions
                // like:
                //
                //      Is there a member on this object called '__pulumiResource'
                //
                // If we automatically lift such a member (even if it eventually points to 'undefined'),
                // then those RTTI checks will succeed.
                //
                // Note: this should be safe to not lift as, in general, properties with this prefix
                // are not at all common (and in general are used to represent private things anyway
                // that likely should not be exposed).
                //
                // Similarly, do not respond to the 'doNotCapture' member name.  It serves a similar
                // RTTI purpose.
                if (typeof prop === "string") {
                    if (prop.startsWith("__") || prop === "doNotCapture" || prop === "deploymentOnlyModule") {
                        return undefined;
                    }
                }

                // Fail out if we are being accessed using a symbol.  Many APIs will access with a
                // well known symbol (like 'Symbol.toPrimitive') to check for the presence of something.
                // They will only check for the existence of that member, and we don't want to make it
                // appear that have those.
                //
                // Another way of putting this is that we only forward 'string/number' members to our
                // underlying value.
                if (typeof prop === "symbol") {
                    return undefined;
                }

                // Else for *any other* property lookup, succeed the lookup and return a lifted
                // `apply` on the underlying `Output`.
                return obj.apply(ob => {
                    if (ob === undefined || ob === null) {
                        return undefined;
                    }

                    return ob[prop];
                });
            },
        });
    }
}

// Returns an promise denoting if the output is a secret or not. This is not the same as just calling `.isSecret`
// because in cases where the output does not have a `isSecret` property and it is a Proxy, we need to ignore
// the isSecret member that the proxy reports back.
/** @internal */
export function isSecretOutput<T>(o: Output<T>): Promise<boolean> {
    return Output.isInstance(o.isSecret) ? Promise.resolve(false) : o.isSecret;
}

/**
 * [output] takes any Input value and converts it into an Output, deeply unwrapping nested Input
 * values as necessary.
 *
 * The expected way to use this function is like so:
 *
 * ```ts
 *      var transformed = pulumi.output(someVal).apply(unwrapped => {
 *          // Do whatever you want now.  'unwrapped' will contain no outputs/promises inside
 *          // here, so you can easily do whatever sort of transformation is most convenient.
 *      });
 *
 *      // the result can be passed to another Resource.  The dependency information will be
 *      // properly maintained.
 *      var someResource = new SomeResource(name, { data: transformed ... });
 * ```
 */
export function output<T>(val: Input<T>): Output<Unwrap<T>>;
export function output<T>(val: Input<T> | undefined): Output<Unwrap<T | undefined>>;
export function output<T>(val: Input<T | undefined>): Output<Unwrap<T | undefined>> {
    if (val === null || typeof val !== "object") {
        // strings, numbers, booleans, functions, symbols, undefineds, nulls are all returned as
        // themselves.  They are always 'known' (i.e. we can safely 'apply' off of them even during
        // preview).
        return createSimpleOutput(val);
    }
    else if (Resource.isInstance(val)) {
        // Don't unwrap Resources, there are existing codepaths that return Resources through
        // Outputs and we want to preserve them as is when flattening.
        return createSimpleOutput(val);
    }
    else if (val instanceof Promise) {
        // For a promise, we can just treat the same as an output that points to that resource. So
        // we just create an Output around the Promise, and immediately apply the unwrap function on
        // it to transform the value it points at.
        return <any>new Output(new Set(), val, /*isKnown*/ Promise.resolve(true), /*isSecret*/ Promise.resolve(false)).apply(output);
    }
    else if (Output.isInstance(val)) {
        return <any>val.apply(output);
    }
    else if (val instanceof Array) {
        return <any>all(val.map(output));
    }
    else {
        const unwrappedObject: any = {};
        Object.keys(val).forEach(k => {
            unwrappedObject[k] = output((<any>val)[k]);
        });

        return <any>all(unwrappedObject);
    }
}

/**
 * [secret] behaves the same as [output] except the resturned output is marked as contating sensitive data.
 */
export function secret<T>(val: Input<T>): Output<Unwrap<T>>;
export function secret<T>(val: Input<T> | undefined): Output<Unwrap<T | undefined>>;
export function secret<T>(val: Input<T | undefined>): Output<Unwrap<T | undefined>> {
    const o = output(val);
    return new Output(o.resources(), o.promise(), o.isKnown, Promise.resolve(true));
}

function createSimpleOutput(val: any) {
    return new Output(
        new Set(),
        Promise.resolve(val),
        /*isKnown*/ Promise.resolve(true),
        /*isSecret */ Promise.resolve(false));
}

/**
 * Allows for multiple Output objects to be combined into a single Output object.  The single Output
 * will depend on the union of Resources that the individual dependencies depend on.
 *
 * This can be used in the following manner:
 *
 * ```ts
 * var d1: Output<string>;
 * var d2: Output<number>;
 *
 * var d3: Output<ResultType> = Output.all([d1, d2]).apply(([s, n]) => ...);
 * ```
 *
 * In this example, taking a dependency on d3 means a resource will depend on all the resources of
 * d1 and d2.
 */
// tslint:disable:max-line-length
export function all<T>(val: Record<string, Input<T>>): Output<Record<string, Unwrap<T>>>;
export function all<T1, T2, T3, T4, T5, T6, T7, T8>(values: [Input<T1> | undefined, Input<T2> | undefined, Input<T3> | undefined, Input<T4> | undefined, Input<T5> | undefined, Input<T6> | undefined, Input<T7> | undefined, Input<T8> | undefined]): Output<[Unwrap<T1>, Unwrap<T2>, Unwrap<T3>, Unwrap<T4>, Unwrap<T5>, Unwrap<T6>, Unwrap<T7>, Unwrap<T8>]>;
export function all<T1, T2, T3, T4, T5, T6, T7>(values: [Input<T1> | undefined, Input<T2> | undefined, Input<T3> | undefined, Input<T4> | undefined, Input<T5> | undefined, Input<T6> | undefined, Input<T7> | undefined]): Output<[Unwrap<T1>, Unwrap<T2>, Unwrap<T3>, Unwrap<T4>, Unwrap<T5>, Unwrap<T6>, Unwrap<T7>]>;
export function all<T1, T2, T3, T4, T5, T6>(values: [Input<T1> | undefined, Input<T2> | undefined, Input<T3> | undefined, Input<T4> | undefined, Input<T5> | undefined, Input<T6> | undefined]): Output<[Unwrap<T1>, Unwrap<T2>, Unwrap<T3>, Unwrap<T4>, Unwrap<T5>, Unwrap<T6>]>;
export function all<T1, T2, T3, T4, T5>(values: [Input<T1> | undefined, Input<T2> | undefined, Input<T3> | undefined, Input<T4> | undefined, Input<T5> | undefined]): Output<[Unwrap<T1>, Unwrap<T2>, Unwrap<T3>, Unwrap<T4>, Unwrap<T5>]>;
export function all<T1, T2, T3, T4>(values: [Input<T1> | undefined, Input<T2> | undefined, Input<T3> | undefined, Input<T4> | undefined]): Output<[Unwrap<T1>, Unwrap<T2>, Unwrap<T3>, Unwrap<T4>]>;
export function all<T1, T2, T3>(values: [Input<T1> | undefined, Input<T2> | undefined, Input<T3> | undefined]): Output<[Unwrap<T1>, Unwrap<T2>, Unwrap<T3>]>;
export function all<T1, T2>(values: [Input<T1> | undefined, Input<T2> | undefined]): Output<[Unwrap<T1>, Unwrap<T2>]>;
export function all<T>(ds: (Input<T> | undefined)[]): Output<Unwrap<T>[]>;
export function all<T>(val: Input<T>[] | Record<string, Input<T>>): Output<any> {
    if (val instanceof Array) {
        const allOutputs = val.map(v => output(v));

        const [resources, isKnown, isSecret] = getResourcesAndDetails(allOutputs);
        const promisedArray = Promise.all(allOutputs.map(o => o.promise()));

        return new Output<Unwrap<T>[]>(new Set<Resource>(resources), promisedArray, isKnown, isSecret);
    } else {
        const keysAndOutputs = Object.keys(val).map(key => ({ key, value: output(val[key]) }));
        const allOutputs = keysAndOutputs.map(kvp => kvp.value);

        const [resources, isKnown, isSecret] = getResourcesAndDetails(allOutputs);
        const promisedObject = getPromisedObject(keysAndOutputs);

        return new Output<Record<string, Unwrap<T>>>(new Set<Resource>(resources), promisedObject, isKnown, isSecret);
    }
}

async function getPromisedObject<T>(
        keysAndOutputs: { key: string, value: Output<Unwrap<T>> }[]): Promise<Record<string, Unwrap<T>>> {
    const result: Record<string, Unwrap<T>> = {};
    for (const kvp of keysAndOutputs) {
        result[kvp.key] = await kvp.value.promise();
    }

    return result;
}

function getResourcesAndDetails<T>(allOutputs: Output<Unwrap<T>>[]): [Resource[], Promise<boolean>, Promise<boolean>] {
    const allResources = allOutputs.reduce<Resource[]>((arr, o) => (arr.push(...o.resources()), arr), []);

    // A merged output is known if all of its inputs are known.
    const isKnown = Promise.all(allOutputs.map(o => o.isKnown)).then(ps => ps.every(b => b));

    // A merged output is secret if any of its inputs are secret.
    const isSecret = Promise.all(allOutputs.map(o => isSecretOutput(o))).then(ps => ps.find(b => b) !== undefined);

    return [allResources, isKnown, isSecret];
}

/**
 * [Input] is a property input for a resource.  It may be a promptly available T, a promise for one,
 * or the output from a existing Resource.
 */
// Note: we accept an OutputInstance (and not an Output) here to be *more* flexible in terms of
// what an Input is.  OutputInstance has *less* members than Output (because it doesn't lift anything).
export type Input<T> = T | Promise<T> | OutputInstance<T>;

/**
 * [Inputs] is a map of property name to property input, one for each resource property value.
 */
export type Inputs = Record<string, Input<any>>;

/**
 * The 'Unwrap' type allows us to express the operation of taking a type, with potentially deeply
 * nested Promises and Outputs and to then get that same type with all the Promises and Outputs
 * replaced with their wrapped type.  Note that this Unwrapping is 'deep'.  So if you had:
 *
 *      `type X = { A: Promise<{ B: Output<{ c: Input<boolean> }> }> }`
 *
 * Then `Unwrap<X>` would be equivalent to:
 *
 *      `...    = { A: { B: { C: boolean } } }`
 *
 * Unwrapping sees through Promises, Outputs, Arrays and Objects.
 *
 * Note: due to TypeScript limitations there are some things that cannot be expressed. Specifically,
 * if you had a `Promise<Output<T>>` then the Unwrap type would not be able to undo both of those
 * wraps. In practice that should be ok.  Values in an object graph should not wrap Outputs in
 * Promises.  Instead, any code that needs to work Outputs and also be async should either create
 * the Output with the Promise (which will collapse into just an Output).  Or, it should start with
 * an Output and call [apply] on it, passing in an async function.  This will also collapse and just
 * produce an Output.
 *
 * In other words, this should not be used as the shape of an object: `{ a: Promise<Output<...>> }`.
 * It should always either be `{ a: Promise<NonOutput> }` or just `{ a: Output<...> }`.
 */
export type Unwrap<T> =
    // 1. If we have a promise, just get the type it itself is wrapping and recursively unwrap that.
    // 2. Otherwise, if we have an output, do the same as a promise and just unwrap the inner type.
    // 3. Otherwise, we have a basic type.  Just unwrap that.
    T extends Promise<infer U1> ? UnwrapSimple<U1> :
    T extends OutputInstance<infer U2> ? UnwrapSimple<U2> :
    UnwrapSimple<T>;

type primitive = Function | string | number | boolean | undefined | null;

/**
 * Handles encountering basic types when unwrapping.
 */
export type UnwrapSimple<T> =
    // 1. Any of the primitive types just unwrap to themselves.
    // 2. An array of some types unwraps to an array of that type itself unwrapped. Note, due to a
    //    TS limitation we cannot express that as Array<Unwrap<U>> due to how it handles recursive
    //    types. We work around that by introducing an structurally equivalent interface that then
    //    helps make typescript defer type-evaluation instead of doing it eagerly.
    // 3. An object unwraps to an object with properties of the same name, but where the property
    //    types have been unwrapped.
    // 4. return 'never' at the end so that if we've missed something we'll discover it.
    T extends primitive ? T :
    T extends Resource ? T :
    T extends Array<infer U> ? UnwrappedArray<U> :
    T extends object ? UnwrappedObject<T> :
    never;

export interface UnwrappedArray<T> extends Array<Unwrap<T>> {}

export type UnwrappedObject<T> = {
    [P in keyof T]: Unwrap<T[P]>;
};

/**
 * Instance side of the [Output<T>] type.  Exposes the deployment-time and run-time mechanisms
 * for working with the underlying value of an [Output<T>].
 */
export interface OutputInstance<T> {
    /** @internal */ readonly isKnown: Promise<boolean>;
    /** @internal */ readonly isSecret: Promise<boolean>;
    /** @internal */ promise(): Promise<T>;
    /** @internal */ resources(): Set<Resource>;

    /**
     * Transforms the data of the output with the provided func.  The result remains a
     * Output so that dependent resources can be properly tracked.
     *
     * 'func' is not allowed to make resources.
     *
     * 'func' can return other Outputs.  This can be handy if you have a Output<SomeVal>
     * and you want to get a transitive dependency of it.  i.e.
     *
     * ```ts
     * var d1: Output<SomeVal>;
     * var d2 = d1.apply(v => v.x.y.OtherOutput); // getting an output off of 'v'.
     * ```
     *
     * In this example, taking a dependency on d2 means a resource will depend on all the resources
     * of d1.  It will *not* depend on the resources of v.x.y.OtherDep.
     *
     * Importantly, the Resources that d2 feels like it will depend on are the same resources as d1.
     * If you need have multiple Outputs and a single Output is needed that combines both
     * set of resources, then 'pulumi.all' should be used instead.
     *
     * This function will only be called execution of a 'pulumi up' request.  It will not run
     * during 'pulumi preview' (as the values of resources are of course not known then). It is not
     * available for functions that end up executing in the cloud during runtime.  To get the value
     * of the Output during cloud runtime execution, use `get()`.
     */
    apply<U>(func: (t: T) => Promise<U>): Output<U>;
    apply<U>(func: (t: T) => OutputInstance<U>): Output<U>;
    apply<U>(func: (t: T) => U): Output<U>;

    /**
     * Retrieves the underlying value of this dependency.
     *
     * This function is only callable in code that runs in the cloud post-deployment.  At this
     * point all Output values will be known and can be safely retrieved. During pulumi deployment
     * or preview execution this must not be called (and will throw).  This is because doing so
     * would allow Output values to flow into Resources while losing the data that would allow
     * the dependency graph to be changed.
     */
    get(): T;
}

/**
 * Static side of the [Output<T>] type.  Can be used to [create] Outputs as well as test
 * arbitrary values to see if they are [Output]s.
 */
export interface OutputConstructor {
    create<T>(val: Input<T>): Output<Unwrap<T>>;
    create<T>(val: Input<T> | undefined): Output<Unwrap<T | undefined>>;

    isInstance<T>(obj: any): obj is Output<T>;

    /** @internal */ new<T>(
            resources: Set<Resource> | Resource[] | Resource,
            promise: Promise<T>,
            isKnown: Promise<boolean>,
            isSecret: Promise<boolean>): Output<T>;
}

/**
 * [Output] helps encode the relationship between Resources in a Pulumi application. Specifically an
 * [Output] holds onto a piece of Data and the Resource it was generated from. An [Output] value can
 * then be provided when constructing new Resources, allowing that new Resource to know both the
 * value as well as the Resource the value came from.  This allows for a precise 'Resource
 * dependency graph' to be created, which properly tracks the relationship between resources.
 *
 * An [Output] is used in a Pulumi program differently depending on if the application is executing
 * at 'deployment time' (i.e. when actually running the 'pulumi' executable), or at 'run time' (i.e.
 * a piece of code running in some Cloud).
 *
 * At 'deployment time', the correct way to work with the underlying value is to call
 * [Output.apply(func)].  This allows the value to be accessed and manipulated, while still
 * resulting in an [Output] that is keeping track of [Resource]s appropriately.  At deployment time
 * the underlying value may or may not exist (for example, if a preview is being performed).  In
 * this case, the 'func' callback will not be executed, and calling [.apply] will immediately return
 * an [Output] that points to the [undefined] value.  During a normal [update] though, the 'func'
 * callbacks should always be executed.
 *
 * At 'run time', the correct way to work with the underlying value is to simply call [Output.get]
 * which will be promptly return the entire value.  This will be a simple JavaScript object that can
 * be manipulated as necessary.
 *
 * To ease with using [Output]s at 'deployment time', pulumi will 'lift' simple data properties of
 * an underlying value to the [Output] itself.  For example:
 *
 * ```ts
 *      const o: Output<{ name: string, age: number, orders: Order[] }> = ...;
 *      const name : Output<string> = o.name;
 *      const age  : Output<number> = o.age;
 *      const first: Output<Order>  = o.orders[0];
 * ```
 *
 * Instead of having to write:
 *
 * ```ts
 *      const o: Output<{ name: string, age: number, orders: Order[] }> = ...;
 *      const name : Output<string> = o.apply(v => v.name);
 *      const age  : Output<number> = o.apply(v => v.age);
 *      const first: Output<Order> = o.apply(v => v.orders[0]);
 * ```
 */
export type Output<T> = OutputInstance<T> & Lifted<T>;
// tslint:disable-next-line:variable-name
export const Output: OutputConstructor = <any>OutputImpl;

/**
 * The [Lifted] type allows us to express the operation of taking a type, with potentially deeply
 * nested objects and arrays and to then get a type with the same properties, except whose property
 * types are now [Output]s of the original property type.
 *
 * For example:
 *
 *
 *      `type X = { A: string, B: { c: boolean } }`
 *
 * Then `Lifted<X>` would be equivalent to:
 *
 *      `...    = { A: Output<string>, B: Output<{ C: Output<boolean> }> }`
 *
 * [Lifted] is somewhat the opposite of [Unwrap].  It's primary purpose is to allow an instance of
 * [Output<SomeType>] to provide simple access to the properties of [SomeType] directly on the instance
 * itself (instead of haveing to use [.apply]).
 *
 * This lifting only happens through simple pojo objects and arrays.  Functions, for example, are not
 * lifted.  So you cannot do:
 *
 * ```ts
 *      const o: Output<string> = ...;
 *      const c: Output<number> = o.charCodeAt(0);
 * ```
 *
 * Instead, you still need to write;
 *
 * ```ts
 *      const o: Output<string> = ...;
 *      const c: Output<number> = o.apply(v => v.charCodeAt(0));
 * ```
 */
export type Lifted<T> =
    // Output<T> is an intersection type with 'Lifted<T>'.  So, when we don't want to add any
    // members to Output<T>, we just return `{}` which will leave it untouched.
    T extends Resource ? {} :
    // Specially handle 'string' since TS doesn't map the 'String.Length' property to it.
    T extends string ? LiftedObject<String, NonFunctionPropertyNames<String>> :
    T extends Array<infer U> ? LiftedArray<U> :
    LiftedObject<T, NonFunctionPropertyNames<T>>;

// The set of property names in T that are *not* functions.
type NonFunctionPropertyNames<T> = { [K in keyof T]: T[K] extends Function ? never : K }[keyof T];

// Lift up all the non-function properties.  If it was optional before, keep it optional after.
// If it's require before, keep it required afterwards.
export type LiftedObject<T, K extends keyof T> = {
    [P in K]: Output<T[P]>
};

export type LiftedArray<T> = {
    /**
      * Gets the length of the array. This is a number one higher than the highest element defined
      * in an array.
      */
    readonly length: Output<number>;

    readonly [n: number]: Output<T>;
};

/**
 * [concat] takes a sequence of [Inputs], stringifies each, and concatenates all values into one
 * final string.  Individual inputs can be any sort of [Input] value.  i.e. they can be [Promise]s,
 * [Output]s, or just plain JavaScript values.  This can be used like so:
 *
 * ```ts
 *      // 'server' and 'loadBalancer' are both resources that expose [Output] properties.
 *      let val: Output<string> = pulumi.concat("http://", server.hostname, ":", loadBalancer.port);
 * ```
 *
 */
export function concat(...params: Input<any>[]): Output<string> {
    return output(params).apply(array => array.join(""));
}

/**
 * [interpolate] is similar to [concat] but is designed to be used as a tagged template expression.
 * i.e.:
 *
 * ```ts
 *      // 'server' and 'loadBalancer' are both resources that expose [Output] properties.
 *      let val: Output<string> = pulumi.interpolate `http://${server.hostname}:${loadBalancer.port}`
 * ```
 *
 * As with [concat] the 'placeholders' between `${}` can be any Inputs.  i.e. they can be
 * [Promise]s, [Output]s, or just plain JavaScript values.
 */
export function interpolate(literals: TemplateStringsArray, ...placeholders: Input<any>[]): Output<string> {
    return output(placeholders).apply(unwrapped => {
        let result = "";

        // interleave the literals with the placeholders
        for (let i = 0; i < unwrapped.length; i++) {
            result += literals[i];
            result += unwrapped[i];
        }

        // add the last literal
        result += literals[literals.length - 1];
        return result;
    });
}