Update-Gits.ps1

<#
.SYNOPSIS
Scan all sub-folders looking for Git repos and fetch/pull each of them to
get latest code.

.PARAMETER Branch
Speciies the branch name, default is read from the .git\config file

.PARAMETER Merge
Merges main into the feature branch if the current branch is not main

.PARAMETER Project
Specifies the project (subfolder) to update. If not specified then it will
scan all subfolders and update every one that contains a .git folder. 

.PARAMETER Reset
Perform a hard reset to the tip of the specified Branch 
for each repo before fetch and pull. This is to discard all local changes.
#>

# CmdletBinding adds -Verbose functionality, SupportsShouldProcess adds -WhatIf
[CmdletBinding(SupportsShouldProcess = $true)]

param (
	[Parameter(Position = 0)] [string] $Project,
	[Parameter(Position = 1)] [string] $Branch,
	[switch] $Merge,
	[switch] $Reset
)

Begin
{
	$script:divider = New-Object String('-', 80)


	function Update
	{
		param (
			[Parameter(Mandatory = $true, Position = 0, ValueFromPipeline = $true)]
			[string] $Project
		)

		if ($Project -match '-skip')
		{
			Write-Host $divider
			Write-Host "... skipping $Project" -ForegroundColor DarkGray
			return
		}

		Push-Location $Project

		GetBranches

		$updated = (git log -1 --date=format:"%b %d, %Y" --format="%ad")
		Write-Verbose '$updated = (git log -1 --date=format:"%b %d, %Y" --format="%ad")'
		Write-Verbose "`$updated > $updated"

		if ($detached -and !$Branch -and !$Reset)
		{
			Write-Host $divider
			Write-Host "... detached HEAD at $active, last updated $updated" -ForegroundColor DarkGray
			return
		}

		$br = $Branch
		if (!$Branch)
		{
			if ($Reset -and $detached) { $br = $mainBr }
			else { $br = $active }
		}
		if ($br.StartsWith('origin/')) { $br = $br.Substring(7) }
		Write-Verbose "`$br > $br"

		Write-Host $divider
		$expected = $mainBr
		if ($expected.StartsWith('origin/')) { $expected = $mainBr.Substring(7) }
		if ($br -eq $expected)
		{
			Write-Host "... updating $Project from $br, last updated $updated" -ForegroundColor Blue
		}
		else
		{
			Write-Host "... updating $Project from " -ForegroundColor Blue -NoNewline
			Write-Host $br -ForegroundColor DarkYellow -NoNewline
			Write-Host ", last updated $updated" -ForegroundColor Blue
		}

		if ($Reset)
		{
			if ($detached)
			{
				Write-Verbose "git checkout $br"
				git checkout $br
			}

			# revert uncommitted changes that have been added to the index
			Write-Verbose "git reset --hard origin/$br"
			git reset --hard origin/$br
			# revert uncommitted, unindexed changes (f=force, d=recurse, x=uncontrolled)
			Write-Verbose 'git clean -dxf'
			git clean -dxf
		}

		($br -match '(?:origin/)?(.*)') | out-null ; $shortBr = $matches[1]
		($mainBr -match '(?:origin/)?(.*)') | out-null ; $shortMain = $matches[1]

		if ($Merge -and ($shortBr -ne $shortMain))
		{
			Write-Host "... merging $mainBr into $br" -ForegroundColor DarkCyan
			Write-Verbose "git fetch origin $shortMain"
			git fetch origin $shortMain
			Write-Verbose "git merge $mainBr"
			git merge $mainBr
		}

		Write-Verbose 'git fetch'
		git fetch #origin
		Write-Verbose 'git pull'
		git pull #origin $br

		if ($LASTEXITCODE -ne 0)
		{
			Write-Host
			Write-Host "*** failed git pull origin $br" -ForegroundColor Red
			Write-Host
		}
		else
		{
			$head = (git rev-parse --abbrev-ref HEAD)
			if ($head -ne 'main' -and $head -ne 'master')
			{
				$ahead = (git rev-list --count origin/$br..$head)
				$behind = (git rev-list --count $head..origin/$br)
				Write-Host "... branch is ahead $ahead commits and behind $behind commits" -ForegroundColor DarkGray
			}
		}

		Pop-Location
	}

	function GetBranches
	{
		$branches = (git branch)
		$script:active = $branches | ? { $_.startswith('*') } | % { $_.substring(2) }
		Write-Verbose '$active = git branch'
		Write-Verbose "`$active > $active"

		# get name of "main" branch from origin/HEAD
		$script:mainBr = (git branch -a | ? { $_ -match 'origin/HEAD -> (.*)' } | % { $Matches[1] })
		Write-Verbose '$mainBr = (git branch -a | ? { $_ -match ''origin/HEAD -> (.*)'' } | % { $Matches[1] })'
		Write-Verbose "`$mainBr > $mainBr"

		$script:detached = ($active -match '\(HEAD detached at ([a-f0-9]+)\)')
		if ($detached)
		{
			# $active will contain the commit hash
			$script:active = $matches[1]
			return
		}
	}
}
Process
{
	if ($Project)
	{
		$Host.PrivateData.VerboseForegroundColor = 'DarkGray'
		Update $Project
		$Host.PrivateData.VerboseForegroundColor = 'Yellow'
	}
	else
	{
		Get-ChildItem | `
			? { Test-Path (Join-Path $_.FullName '.git') } | `
			Select -ExpandProperty Name | `
			% { Update $_ }
	}
}