<#
.SYNOPSIS

Generates normals report.

.DESCRIPTION

Processes all the .csv files in the nominated folder.  InputFolder is a required parameter.

.PARAMETER InputFolder

Location holding all the .csv files to process

.PARAMETER OutputFile

Filtered CSV file

.PARAMETER StartYear

First year to examine

.PARAMETER EndYear

Last year to examine

.PARAMETER help

Display help info

#>


param (
    [switch] $help,
    [string] $InputFolder,
    [string] $OutputFile = "",
    [int]    $StartYear = 1951,
    [int]    $EndYear = 1980
)

if ($help -or (-not $InputFolder))
{
    Get-Help $MyInvocation.MyCommand.Definition
    return
}

if (-not (Test-Path $InputFolder -PathType Container))

{
    $(throw "$InputFolder does not exist or is a file.")
}

if (-not $OutputFile)
{
    $s = Split-Path -Path $InputFolder -Leaf
    $OutputFile = [System.IO.Path]::ChangeExtension($s, ".normals.txt")
}

New-Item -Force -Type file $OutputFile | Out-Null

$csvfiles = $InputFolder + "\*.csv"

$dataRecords = @()

# scan each file
Get-ChildItem $csvfiles | Foreach-Object {
  # set initial state for each file
  $accumulator = @(0,0,0,0,0,0,0,0,0,0,0,0)
  $count = @(0,0,0,0,0,0,0,0,0,0,0,0)
  $mean = @(-99.9,-99.9,-99.9,-99.9,-99.9,-99.9,-99.9,-99.9,-99.9,-99.9,-99.9,-99.9)
  $parseState = 0

  # scan each line in the file
  Get-Content $_ | Foreach-Object {
      $parts      = $_.split(",")

      # Initial parse state -- Header up to Climate Identifier
      if ($parseState -eq 0) {
        if ($parts[0] -eq "`"Climate Identifier`"") {
            $ClimateIdentifier = $parts[1]
            $parseState = 1
        }
      } # $parseState -eq 0

      # Final parse state -- Body processing
      if ($parseState -eq 2) {

        $year =        $parts[1].Trim("`"")
        $month =       $parts[2].Trim("`"")
        $monthlyMean = $parts[5].Trim("`"")
        $meanFlag =    $parts[6].Trim("`"")

        # process only data in our year range, where data is not missing/incomplete/null
        if ( ($year -ge $StartYear) -and ($year -le $EndYear) -and
           ($meanFlag -cne "I") -and ($meanFlag -cne "M") -and $monthlyMean) {
          # increment counter and accumulate accumulator for the month
          $count[$month - 1] += 1
          $accumulator[$month - 1] += $monthlyMean
        }
      }

      # Intermediate parse state -- Skip rest of header and
      # step state on hitting the header line
      if ($parseState -eq 1) {
        if ($parts[0] -eq "`"Date/Time`"") {
            $parseState = 2
        }
      } # $parseState -eq 1

  } # all lines handled

  $line = "$ClimateIdentifier"
  $index = 0
  do {
    if ($count[$index] -gt 0) {
      $mean[$index] = $accumulator[$index]/$count[$index]
    }

    $line += ",{0,5:n1}, {1,2:n0}" -f $mean[$index], $count[$index]
    $index += 1
  } while ($index -lt 12)
  $dataRecords += $line
} # all files

# More efficient than $array = $array | Sort-Object
[Array]::Sort([array]$dataRecords)
$dataRecords | Foreach-Object { Add-Content $OutputFile $_ }