How to write common code for Jenkins Pipelines - jenkins

Question

I would like to know how one would write common code that is used by other var files. Any pointers to decent tutorials would be appreciated as I'm sure I will be writing many more modules. I have been trying to follow this: https://www.jenkins.io/doc/book/pipeline/shared-libraries/#writing-libraries but have very little knowledge of groovy.
From what I understand, files in var/ are loaded and are available within the pipeline syntax. Files located in src/ need to be imported by the files in var/ to be used. Is this correct?
I would like to produce the following:
A file that has common code such as AWS Account numbers, functions like ECR logins and a ECR string creator which requires the account number. I foresee many other common aws tasks living in here.
A file that has a list of commands to execute to do the work I want to do.
What I have currently (doesn't work):
// var/ECRPush.groovy
#Library('awsCommon')
import com.mycompany.awsCommon
def call(Map config=[:]) {
awsCommon.dockerLogin(config.account)
ecrAddress=awsCommon.ecrAddress(account:config.account, name:config.name) + ":" + config.tag
sh("docker tag ${config.sourceContainer} ${ecrAddress}")
sh("docker push ${ecrAddress}")
}
// src/com/mycompany/awsCommon/awsCommon.groovy
#!/usr/bin/env groovy
package com.mycomany.awsCommon
class awsCommon {
def Map accounts = [
"dev":"123",
"shared":"456"
]
// used as:
// account: account from accounts
// name: 'service'
def String ecrAddress(Map config=[:]) {
address = self.Accounts([config.account]) + ".dkr.ecr.eu-west-1.amazonaws.com/" + config.name
return address
}
def dockerLogin(String account) {
switch(account) {
case "shared":
echo 'login to Shared ECR'
withCredentials([aws(credentialsId: 'jenkins-aws-shared')]){
sh '$(aws ecr get-login --no-include-email --region eu-west-1)'
}
break
case "dev":
echo 'login to Dev ECR'
withCredentials([aws(credentialsId: 'jenkins-aws-dev')]){
sh '$(aws ecr get-login --no-include-email --region eu-west-1)'
}
break
}
}
}
// Example desired usage
#Library('jenkins-shared-lib-global') _
pipeline {
stage('ecr push') {
steps {
ECRPush(
account: 'dev',
name: 'ecs-testing',
sourceContainer: 'ecs-testing:dev',
tag: 'jenkins'
)
}
}
}