NPM module for common functions in backend

useful in a setup with
- serverless stack
- AWS

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All functions can be imported from their respective modules (results in lowest packages size), e.g.:
``javascript
import { sleep } from 'blob-common/core/sleep';
import { btoa } from 'blob-common/core/base64';
`

All functions can be imported directly from the core, e.g.:
`javascript
import { sleep, btoa } from 'blob-common';
`

NB: the sanitize function is not included in the core, due to the relatively large size of imported package.

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| Module |Function | Description
|---------------|------------------------|-------------------
| /base64 | otob(object) | takes an object and coverts to base64 string
| /base64 | btoa(base64String) | inverse: takes a base64 string and returns an object
| /date | now() | returns a string of the current date in format yyyy-mm-dd
| /date | diffDate(dateStr, days) | takes a dateStr in standard format and difference, returns a dateStr in the standard format
| /date | expireDate(dateStr) | takes a dateStr in standard format and returns a date 30 days later in the standard format
| /handler | handler(lamdba) | wrapper function for event handler (to log errors)
| /handler | getUserFromEvent(event)| returns the userId (from AWS cognito user pool) of authenticated User
| /handler | apiCall(promise) | async wrapper for promise, returns the a tuple [err, result]
| /ids | newPhotoId() | returns a newly generated photoId (starts with P)
| /ids | newGroupId() | returns a newly generated groupId (starts with G)
| /ids | newAlbumId() | returns a newly generated albumId (starts with A)
| /RND | RND | returns a random number between 1 and 15, usable as an index key in dynamoDb to spread database load on very large queries
| /sleep | sleep(ms) | await sleep(1000) sleeps for 1 second. Used in tests to wait for dynamoDB to have processed updates
| /sanitize | sanitize(dirty) | sanitizes a string from any sequences that may cause security issues (e.g. when using name string in an email message)

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| Module |Function | Description
|---------------|---------------------------------------|-------------------
| /db | dynamoDb.get(params) | returns a promise for DynamoDb function using the params. Uses AWS-SDK, refer to official docs for more info. Also has functions .put, .update, .delete, query, transact (for TransactWrite)
| /db | dbUpdate(PK, SK, key, newVal) | returns a promise for a single update on the database, setting key to new value provided in newVal
| /db | dbUpdateMulti(PK, SK, newKV) | returns a promise for a single update on the database at multiple keys. newKV is an object containing keys to be updated with new values
| /dbClean | cleanRecord(object) | removes keys RK, datePK, dateSK, cognitoId from the object - useful for storing data as derived items in other items (e.g. owner as part of photo object)
| /dbCreate | dbItem(object) | returns an object with extended keys for database: createdAt, RK, datePK, dateSK
| /dbCreate | dbCreateItem(object) | returns a promise to create an expanded item in database from object (object must have PK and SK keys)


Some caveats on the specific dynamoDB functions:
- eu-central-1 is the standard region chosen
- to work, there should be a process.env.photoTable variable for all functions (except dynamoDb)
- database must have PK (string) as primary key, and SK (string) as sortkey




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| Module |Function | Description
|---------------|---------------------------------------|-------------------
| /s3 | s3.getMetadata(params) | returns a promise for an s3 function using the params.
| /s3 | s3.delete(params) | deletes stuff.
| /s3 | s3.get(params) | gets an object.
| /s3 | s3.list(params) | lists a bucket probably.
| /s3 | s3.getSignedUrl(params) | gets a signed url for ADDING a file to s3 (for uploads).
| /s3 | s3.getSignedUrlGet(params) | gets a signed url for READING a file from s3.
| /ses | ses.send(params) | sends an email from ses using params - returns promise
| /ses | ses.sendEmail(params) | sends an email from ses using {toEmail, fromEmail, subject, data, textData} - returns promise

NB:
- toEmail can be either a string or an array of strings (multiple recipients)

Caveats:
- s3 function uses s3 bucket specified in process.env.photoBucket or process.env.devBucket




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| Module |Function | Description
|---------------|---------------------------------------|-------------------
| /email | emailBody(rows) | returns email body with rows
| /email | row(cells) | generic row containing array of cells
| /email | headerRow(logoSrc, frontendUrl)| header row with logo, links to frontend
| /email | footerRow |
| /email | photoRow(photoSrc, linkUrl) | row containing (header) photo
| /email | textCell(subtype) | cell containing greeting, paragraph or buttonEscape (small text with link)
| /email | dividerCell(dividerSrc) |
| /email | buttonCell(text, link) |
| /email | codeCell(code) | big text block centered with code
| /email | signatureCell(src) | left aligned signature under email
| /email | greeting(text) |
| /email | paragraph(text) |
| /email | buttonEscape(url) |
| /email | makeEmailSrc(url, width, height)| returns publicly accessible url for image in S3 bucket

Caveats:
- makeEmailSrc uses s3 bucketname from process.env.bucket or process.env.devBucket




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| Module |Function | Description
|--------------------|-------------------------------|-------------------
| /cognito | cognito.disableUser(userId) | disables a user in the cognito user pool
| /cognito | cognito.deleteUser(userId) | deletes a user in the cognito user pool

Caveats:
- uses cognito userpool id from process.env.userPoolId or process.env.devUserPoolId`