Function Get-DefaultLog4NetPathForPackage {
<#

.SYNOPSIS
    Return a [string] path to the most environment-specific log4net.config file available in a base path or $null

.DESCRIPTION
    File path is determined by PackageName and SourcePath, which will usually be a TeamCity Agent parameter, but may
    be a local folder for testing or manual execution.
    Where EnvironmentName > EnvironmentType > base (Production) default:
    Given an EnvironmentName, or Designation, if a default log4net config file exists with that Designation as its suffix,
    returns path to that file.
    Given an EnvironmentType (other than Production), if a default log4net config file exists with that EnvironmentType as its
    suffix, returns path to that file.
    Given neither of the above, or if a matching file does not exist in the 'config-defaults' repo referenced by SourcePath
    for prior cases, return path to non-suffixed log4net.config for given PackageName, if it exists.
    Otherwise, returns $null.

.PARAMETER SourcePath
    [string] Path to the '/config-defaults/log4net' folder, probably partially derived from TeamCity Agent or Build parameters

.PARAMETER PackageName
    [string] The package name, as it exists in folder format on-disk, for the Chocolatey package needing a default log4net.config file

.PARAMETER EnvironmentType
    [string] Taken from machine.config AppSetting 'Environment.Type'. Example: "Staging" or "Production"

.PARAMETER EnvironmentName
    [string] The smallest form of the environment(pod,lane,box,designation) name;can be found in 'alk:pod', 'alk:lane', etc. Example: NI1, or 12.

.PARAMETER IsReliableService
    [switch] Boolean to determine if the package is a Reliable Service package. This changes the path where Log4Net defaults will look.

.OUTPUTS
    [string] Path to most environment-specific log4net default available for parameters given, or $null

.EXAMPLE
    Get-DefaultLog4NetPathForPackage -SourcePath "C:\AWSBuildAgentB1\work\blah\config-defaults\log4net" -PackageName "Alkami.MicroServices.Alerts.Service.Host" -EnvironmentName "SDKStg" -EnvironmentType "Staging"

Will return (if it exists): C:\AWSBuildAgentB1\work\blah\config-defaults\log4net\ProgramData\chocolatey\lib\Alkami.MicroServices.Alerts.Service.Host\tools\log4net.config.SDKStg
Else, will return (if it exists):
C:\AWSBuildAgentB1\work\blah\config-defaults\log4net\ProgramData\chocolatey\lib\Alkami.MicroServices.Alerts.Service.Host\tools\log4net.config.staging
Else, will return (if it exists):
C:\AWSBuildAgentB1\work\blah\config-defaults\log4net\ProgramData\chocolatey\lib\Alkami.MicroServices.Alerts.Service.Host\tools\log4net.config
Else, will return
$null

.EXAMPLE
    Get-DefaultLog4NetPathForPackage -SourcePath "C:\AWSBuildAgentB1\work\blah\config-defaults\log4net" -PackageName "Alkami.MicroServices.Alerts.Service.Host"

Will return (if it exists): C:\AWSBuildAgentB1\work\blah\config-defaults\log4net\ProgramData\chocolatey\lib\Alkami.MicroServices.Alerts.Service.Host\tools\log4net.config

.EXAMPLE
    Get-DefaultLog4NetPathForPackage -SourcePath "C:\AWSBuildAgentB1\work\blah\config-defaults\log4net" -PackageName "Alkami.MicroServices.Alerts.Service.Host" -EnvironmentName "SDKStg"

Will return (if it exists): C:\AWSBuildAgentB1\work\blah\config-defaults\log4net\ProgramData\chocolatey\lib\Alkami.MicroServices.Alerts.Service.Host\tools\log4net.config.SDKStg

.EXAMPLE
    Get-DefaultLog4NetPathForPackage -SourcePath "C:\AWSBuildAgentB1\work\blah\config-defaults\log4net" -PackageName "Alkami.MicroServices.Alerts.Service.Host" -EnvironmentType "Staging"

Will return (if it exists): C:\AWSBuildAgentB1\work\blah\config-defaults\log4net\ProgramData\chocolatey\lib\Alkami.MicroServices.Alerts.Service.Host\tools\log4net.config.staging
#>
[CmdletBinding()]
    param (
        [Parameter(Mandatory = $true)]
        [string]$SourcePath,
        [Parameter(Mandatory = $true)]
        [Alias('ElementName','ChocoPackageName')]
        [string]$PackageName,
        [Parameter()]
        [string]$EnvironmentType = "Production",
        [Parameter()]
        [Alias('Pod','Lane','Box','Designation')]
        [string]$EnvironmentName,
        [Parameter(Mandatory = $false)]
        [switch]$IsReliableService
    )
    $logLead = Get-LogLeadName
    Write-Host ("Find log4net default for: {0} : {1}" -f $EnvironmentType, $EnvironmentName)
    $baseFilter = "log4net.config"

    # {0} => Drive and path prefix, like %checkoutDir% or %systemDrive% sort of thing.
    # {1} => package name
    $agentPathTemplate = "{0}\ProgramData\chocolatey\lib\{1}\tools"
    if($IsReliableService) {
        # Reliable Services have a different folder structure.
        $agentPathTemplate = "{0}\ProgramData\chocolatey\lib\{1}\svc\Code"
    }
    # {0} => baseline filename - log4net.config
    # {1} => EnvironmentName or EnvironmentType filename suffix - "staging" or "production" or "NI1" or "12"
    $filenameTemplate = "{0}.{1}"

    # Determine if it's a load test environment, and override the environment type from what is in the environment.
    # In load test environments the environment type is generally Staging and we can't use it. If the ltm environment log4net cannot be found it will fall through to the production config.
    $isLoadTestEnvironment = (Test-IsLoadTestEnvironment -EnvironmentName $EnvironmentName)
    if($isLoadTestEnvironment) {
        $EnvironmentType = "ltm"
    }

    $filters = @{}
    $filters["base"] = $baseFilter
    $filters["podOrLane"] = $EnvironmentName
    $filters["environmentType"] = ($EnvironmentType.ToLower())

    $packageLog4NetFolderPath = ($agentPathTemplate -f $SourcePath, $PackageName)

    # Select the environment name level config if it exists.
    if ([string]::IsNullOrEmpty($filters["podOrLane"])) {
        Write-Host "$logLead : No environment name/designation specified"
    } else {
        $designationSpecificFilename = $filenameTemplate -f $filters["base"], $filters["podOrLane"]
        $designationSpecificPath = Join-Path -Path $packageLog4NetFolderPath -ChildPath $designationSpecificFilename
        if (($null -ne $designationSpecificPath) -and (Test-Path $designationSpecificPath)) {
            Write-Host ("$logLead : Found file for {0}. Selecting {1}" -f $filters["podOrLane"], $designationSpecificFilename)
            return $designationSpecificPath
        } else {
            Write-Host "$logLead : $designationSpecificPath not found"
        }
    }

    # Select the environment type level config if it exists.
    if ([string]::IsNullOrEmpty($filters["environmentType"]) -or $filters["environmentType"] -eq "Production") {
        Write-Host "$logLead : No environment type or Production specified"
    } else {
        $environmentSpecificFilename = $filenameTemplate -f $filters["base"], $filters["environmentType"]
        $environmentSpecificPath = Join-Path -Path $packageLog4NetFolderPath -ChildPath $environmentSpecificFilename
        if (($null -ne $environmentSpecificPath) -and (Test-Path $environmentSpecificPath)) {
            Write-Host ("$logLead : Found file for {0}. Selecting {1}" -f $filters["podOrLane"], $environmentSpecificFilename)
            return $environmentSpecificPath
        } else {
            Write-Host "$logLead : $environmentSpecificPath not found"
        }
    }

    # Otherwise default to the production log4net configs.
    $baseProdDefaultPath = Join-Path -Path $packageLog4NetFolderPath -ChildPath $filters["base"]
    if (Test-Path $baseProdDefaultPath) {
        Write-Host ("$logLead : Found Production log4net file. Selecting {0}" -f $filters["base"])
        return $baseProdDefaultPath
    } else {
        Write-Host "$logLead : $baseProdDefaultPath not found"
        return $null
    }
}