param(
    [Parameter(Mandatory = $true, ValueFromPipeline = $true)]
    [string[]] $ShaFiles,
    [string] $RepoRoot = (Resolve-Path (Join-Path $PSScriptRoot "..")).Path,
    [switch] $WhatIf
)

Set-StrictMode -Version Latest
$ErrorActionPreference = "Stop"

function Resolve-HashTargetPath {
    param(
        [Parameter(Mandatory = $true)]
        [string] $ShaFileDirectory,
        [Parameter(Mandatory = $true)]
        [string] $PathText
    )

    $candidateRepoRoot = Join-Path $RepoRoot $PathText
    if (Test-Path -LiteralPath $candidateRepoRoot -PathType Leaf) {
        return (Resolve-Path -LiteralPath $candidateRepoRoot).Path
    }

    $candidateLocal = Join-Path $ShaFileDirectory $PathText
    if (Test-Path -LiteralPath $candidateLocal -PathType Leaf) {
        return (Resolve-Path -LiteralPath $candidateLocal).Path
    }

    throw "SHA256SUMS entry not found: '$PathText' (checked repo root and '$ShaFileDirectory')"
}

function Write-Utf8NoBomLf {
    param(
        [Parameter(Mandatory = $true)]
        [string] $Path,
        [Parameter(Mandatory = $true)]
        [string] $Content
    )

    $utf8NoBom = New-Object System.Text.UTF8Encoding($false)
    $bytes = $utf8NoBom.GetBytes($Content)
    [System.IO.File]::WriteAllBytes($Path, $bytes)
}

foreach ($shaFile in $ShaFiles) {
    $shaFilePath = (Resolve-Path -LiteralPath $shaFile).Path
    $shaFileDir = Split-Path -Parent $shaFilePath

    $inputLines = Get-Content -LiteralPath $shaFilePath
    $outputLines = New-Object System.Collections.Generic.List[string]

    foreach ($line in $inputLines) {
        $trimmed = $line.Trim()
        if ($trimmed.Length -eq 0 -or $trimmed.StartsWith("#")) {
            $outputLines.Add($line)
            continue
        }

        $pathText = $null
        $format = $null
        $separator = "  "

        if ($trimmed -match "^([0-9a-fA-F]{64})(\s+)(.+)$") {
            $format = "hash-first"
            $separator = $Matches[2]
            $pathText = $Matches[3].Trim()
        }
        elseif ($trimmed -match "^(.+?)(\s+)([0-9a-fA-F]{64})$") {
            $format = "path-first"
            $separator = $Matches[2]
            $pathText = $Matches[1].Trim()
        }
        else {
            throw "Unrecognized SHA256SUMS line format in '$shaFilePath': $line"
        }
        $targetPath = Resolve-HashTargetPath -ShaFileDirectory $shaFileDir -PathText $pathText
        $hash = (Get-FileHash -Algorithm SHA256 -LiteralPath $targetPath).Hash.ToLowerInvariant()

        if ($format -eq "hash-first") {
            $outputLines.Add("$hash$separator$pathText")
        }
        else {
            $outputLines.Add("$pathText$separator$hash")
        }
    }

    $content = ($outputLines -join "`n") + "`n"
    if ($WhatIf) {
        Write-Output "[whatif] Would update $shaFilePath"
        continue
    }

    Write-Utf8NoBomLf -Path $shaFilePath -Content $content
    Write-Output "Updated $shaFilePath"
}