@aappddeevv/dynamics-client-ui/src/Dynamics/getXrmP.ts

## What is it? A library to help you create great dynamics applications.

/** Kept as a separate module to make bundling easier. */
import { XRM } from "./xrm"

/**
 * Get Xrm from a Promise. Uses polling to wait for
 * Xrm to become available. Default polling lasts 60 seconds
 * every 1/2 second. This only checks for Xrm on the parent window
* it does *not* walk the window hierarchy.
 */
export function getXrmP(maxIter: number=120, delta: number=500,
                        getXrm: () => XRM = () => (window.parent.Xrm as XRM)): Promise<XRM>
    {
        return wait(() => {
            const x = getXrm()
            return typeof x !== "undefined"
        },
                    maxIter, delta).then(() => getXrm())
    }

/** 
 * Get FormContext as a promise either from Xrm.Page or through the
 * FormContextHolder.
 */
export function getFormContextP(maxIter: number=120, delta: number=500): Promise<Xrm.FormContext> {
    const fchP  = wait(() =>{
        const tmp = (window.parent as any)
        return typeof tmp.FormContextP !== "undefined"
    }, maxIter, delta).then(() => (window.parent as any).FormContextP as Xrm.FormContext)

    const parentP = wait(() => {
        const x = (window.parent.Xrm as XRM)
        return x && (typeof x.Page !== "undefined")
    }, maxIter, delta).then(() => (window.parent.Xrm as XRM).Page)
    
    return Promise.race([parentP, fchP])
}

/** Wait for some condition to be true. Uses polling (setInterval) to iterate. */
export function wait(cond: (iteration: number) => boolean, maxIter: number,
                     delta: number): Promise<void>
    {
        if(maxIter <= 0 || delta <= 0) throw Error("maxIter and delta must be > 0")
        return new Promise<void>(function(resolve, reject) {
            let count=0
            const cancellable = setInterval(function() {
                if(count > maxIter) reject(null)
                count = count + 1
                const proceed = cond(count)
                if(proceed) {
                    clearInterval(cancellable)
                    resolve()
                }
            }, delta)
        })
    }