Dexcom API

An API that provides access to the developer.dexcom platform for acquiring
Continuous Glucose Monitoring (CGM) data. The primary responsibility of this API is to provide a mechanism for a client
to access Dexcom user data without having to use an HTTP interface. This API provides the following services:

* Access to all the developer.dexcom endpoints
* Automatic refreshing of Dexcom OAuth tokens

Since the Dexcom infrastructure does not support CORS, this package is suitable only for server-side systems. If you
try to use this module from within a web application, the user's web browser will generate a CORS violation exception.

Installation

npm install @umlss/dexcom-js --save

Basic Usage

Users of this package are responsible for acquiring Dexcom OAuth tokens
and packing those tokens within an object that is passed to most of this package's functions:

{
timestamp: epochMilliseconds,
dexcomOAuthToken: {
access_token: 'your access token',
expires_in: timeToLiveInSeconds,
token_type: 'Bearer',
refresh_token: 'your refresh token'
}
}

where

* timestamp is time, in epoch milliseconds (UTC), at which the Dexcom OAuth token was acquired
* dexcomOAuthToken is the Dexcom OAuth object issued by Dexcom

After the user has obtained the initial value of the Dexcom OAuth tokens, this package will be responsible for
refreshing the OAuth tokens when the API functions are invoked.

If the object returned by a function in this package contains a property named oauthTokens, then the function
automatically refreshed the OAuth tokens. In that case, the user is responsible for saving the value of oauthTokens
and using the new value of that object as an argument to subsequent function calls.

Configuration

Prior to using any of this package's functions (other than function setOptions()), the user must specify the
properties that provide access to the Dexcom platform:

const DexcomJS = require('@umlss/dexcom-js');

DexcomJS.setOptions({
clientId: 'your application client identifier',
clientSecret: 'your application client secret',
redirectUri: 'your application redirect uniform resource identifier',
apiUri: 'https://api.dexcom.com',
});

Determine if estimated glucose values exist for the previous 24 hours

The following example code illustrates how to use the getStatistics() function to determine if there are any
estimated glucose values over the previous 24-hour period of time:

const secondsPerDay = 86400;
const millisecondsPerSecond = 1000;

const oauthTokens = {
timestamp: epochMilliseconds,
dexcomOAuthToken: {
access_token: 'your access token',
expires_in: timeToLiveInSeconds,
token_type: 'Bearer',
refresh_token: 'your refresh token'
}
}

const endDate = new Date().getTime();
const startDate = endDate - (secondsPerDay * millisecondsPerSecond);

const results = await DexcomJS.getStatistics(oauthTokens, startDate, endDate);

if (('statistics' in results) && results.statistics.nValues) {
// Do whatever is appropriate...
}

if ('oauthTokens' in results) {
// Store the new OAuth tokens...
}

Get estimated glucose values for the previous 24 hours

The following example code illustrates how to use the getEstimatedGlucoseValues() function to obtain data samples
that were collected over the previous 24-hour period of time:

const secondsPerDay = 86400;
const millisecondsPerSecond = 1000;

const endDate = new Date().getTime();
const startDate = endDate - (secondsPerDay * millisecondsPerSecond);

const results = await DexcomJS.getEstimatedGlucoseValues(oauthTokens, startDate, endDate);

if (estimatedGlucoseValues in results) {
// Process the estimated glucose values
results.estimatedGlucoseValues.egvs.forEach(item => {
// See https://developer.dexcom.com/get-egvs
});
}

if (oauthTokens in results) {
// Store the new OAuth access and refresh tokens...
}

API

setOptions

setOptions(options)

Sets the options that will be used when refreshing an expired OAuth 2.0 access token.

Argument options is an object that contains the following properties:

| Property Name | Property Type | Description |
| --------------- | ------------- | ------------------------------------------------------------------------------------------------ |
| clientId | String | The client ID that was issued by Dexcom for your application. |
| clientSecret | String | The client secret that was issued by Dexcom for your application. |
| redirectUri | String | The redirect URI that Dexcom will use after the user completes the OAuth authentication process. |
| apiUri | String | The URI that will be used for accessing the Dexcom platform (typically https://api.dexcom.com) |

Note that the redirectUri property will not be accessed by Dexcom's systems as part of using this package. It is used
by the Dexcom API during the process of refreshing an expired access token.

getSandboxAuthenticationToken

getSandboxAuthenticationToken(user)

Obtains a Dexcom OAuth 2.0 access token for the Dexcom "sandbox" data.

Argument user is a String that may be any of the following values:

* SandboxUser1
* SandboxUser2
* SandboxUser3
* SandboxUser4
* SandboxUser5
* SandboxUser6

Note there was a breaking change on Dexcom's part on 4/27/2020. They used to support
bypassing most of the authorization system, and one would pass uauthcode in instead.
This is still supported by this module but is deprecated and may go away at some point.

The return value is a Promise that wraps an Object with the following properties:

{
"timestamp": epochMilliseconds,
"dexcomOAuthToken": {
"access_token": "your access token",
"expires_in": timeToLiveInSeconds,
"token_type": "Bearer",
"refresh_token": "your refresh token"
}
}

getEstimatedGlucoseValues

getEstimatedGlucoseValues(oauthTokens, startTime, endTime)

Obtains the estimated glucose values for the time range specified by arguments startDate and endDate.

Argument oauthTokens is an Object that contains the following properties:

{
"timestamp": epochMilliseconds,
"dexcomOAuthToken": {
"access_token": "your access token",
"expires_in": timeToLiveInSeconds,
"token_type": "Bearer",
"refresh_token": "your refresh token"
}
}

Arguments startDate and endDate are integer Numbers in the epoch milliseconds (UTC) format.

The return value is a Promise that wraps an Object with the following properties:

{
estimatedGlucoseValues: {