[CmdletBinding()]
param(
    [string]$DsViewPath = (Join-Path $env:ProgramFiles 'DSView'),
    [switch]$CheckOnly
)

$ErrorActionPreference = 'Stop'
Set-StrictMode -Version 2
# Resolve source paths relative to templates, never the caller working directory.
# Standalone DSView and SETGUI use the same adapters and parsing cores.
$templateRoot = [IO.Path]::GetFullPath((Join-Path $PSScriptRoot '../..'))
$targetRoot = [IO.Path]::GetFullPath($DsViewPath)
$decoderRoot = Join-Path $targetRoot 'decoders'

# Use .NET for compatibility with PowerShell lacking Get-FileHash.
# Release both stream and hashing provider even if reading fails.
function Get-ContentHash([string]$Path) {
    $algorithm = [Security.Cryptography.SHA256]::Create()
    $stream = [IO.File]::OpenRead($Path)
    try {
        return [BitConverter]::ToString($algorithm.ComputeHash($stream))
    } finally {
        $stream.Dispose()
        $algorithm.Dispose()
    }
}

# Check all existing ancestors: a junction under decoders/common could
# redirect a local-looking update outside the chosen installation.
function Assert-PlainPath([string]$Path) {
    $cursor = [IO.Path]::GetFullPath($Path)
    $first = $true
    while ($cursor) {
        if (Test-Path -LiteralPath $cursor) {
            $item = Get-Item -LiteralPath $cursor -Force
            if ($item.Attributes -band [IO.FileAttributes]::ReparsePoint) {
                throw "Symbolic links and junctions are not supported: $cursor"
            }
            if (-not $first -and -not $item.PSIsContainer) {
                throw "Expected a parent directory: $cursor"
            }
        }
        $parent = [IO.Path]::GetDirectoryName($cursor)
        if ($parent -eq $cursor) { break }
        $cursor = $parent
        $first = $false
    }
}

Assert-PlainPath $targetRoot
$exe = Join-Path $targetRoot 'DSView.exe'
if (-not (Test-Path -LiteralPath $exe -PathType Leaf)) {
    throw "DSView.exe not found in '$targetRoot'. Pass -DsViewPath with the installed DSView directory."
}
if (-not (Test-Path -LiteralPath (Join-Path $decoderRoot 'common') -PathType Container)) {
    throw "DSView decoders/common is missing. Select a complete DSView installation."
}

# An explicit allowlist excludes tests, bytecode and unrelated modules.
# The private common/setgui_decoders layout matches the embedded build.
$files = @()
foreach ($name in @('gate_driver_timing', 'transistor_pair', 'set_uart', 'set_can', 'pm35_uart')) {
    foreach ($leaf in @('__init__.py', 'pd.py')) {
        $files += [pscustomobject]@{
            Source = Join-Path $PSScriptRoot "decoders/$name/$leaf"
            Relative = "$name/$leaf"
        }
    }
}
foreach ($name in @('__init__', 'gate_timing', 'transistor_pair', 'set_uart', 'set_can', 'pm35_uart')) {
    $files += [pscustomobject]@{
        Source = Join-Path $templateRoot "python/logic_analyzer/decoders/$name.py"
        Relative = "common/setgui_decoders/$name.py"
    }
}
# Validate the entire payload and destination before changing any decoder.
foreach ($file in $files) {
    if (-not (Test-Path -LiteralPath $file.Source -PathType Leaf)) {
        throw "Missing templates source: $($file.Source). Initialize the templates submodule."
    }
    $destination = Join-Path $decoderRoot $file.Relative
    Assert-PlainPath $destination
    if (Test-Path -LiteralPath $destination -PathType Container) {
        throw "Expected a file, found a directory: $destination"
    }
    if ([IO.Path]::GetFullPath($file.Source) -eq [IO.Path]::GetFullPath($destination)) {
        throw 'The installation destination must differ from the templates source.'
    }
}
# Read-only validation does not create backups or check elevated write access.
# Real installation performs its own write-access check before copying.
if ($CheckOnly) {
    Write-Output "Validated $($files.Count) files for $targetRoot. No files changed."
    return
}
# A mapped/running Windows EXE cannot be opened for writing. Never terminate DSView.
try {
    $handle = [IO.File]::Open($exe, [IO.FileMode]::Open, [IO.FileAccess]::ReadWrite, [IO.FileShare]::Read)
    $handle.Dispose()
} catch {
    throw "Close DSView and check write permissions for '$targetRoot'. For Program Files, run PowerShell as administrator. $($_.Exception.Message)"
}

# Keep each previous version outside decoder discovery directories.
# Retain backups after success for manual recovery, not only after errors.
$backup = Join-Path $targetRoot ('set-decoder-backups/' + (Get-Date -Format 'yyyyMMdd-HHmmss') + '-' + [guid]::NewGuid().ToString('N'))
Assert-PlainPath $backup
# Back up all existing files before writing the first replacement.
foreach ($file in $files) {
    $destination = Join-Path $decoderRoot $file.Relative
    if (Test-Path -LiteralPath $destination -PathType Leaf) {
        $saved = Join-Path $backup $file.Relative
        [IO.Directory]::CreateDirectory([IO.Path]::GetDirectoryName($saved)) | Out-Null
        Copy-Item -LiteralPath $destination -Destination $saved
    }
}
# Track files before copying: a failed copy may leave a partial destination.
# Rollback must include that file as well as completed replacements.
$attempted = @()
try {
    foreach ($file in $files) {
        $destination = Join-Path $decoderRoot $file.Relative
        [IO.Directory]::CreateDirectory([IO.Path]::GetDirectoryName($destination)) | Out-Null
        $attempted += $file
        Copy-Item -LiteralPath $file.Source -Destination $destination -Force
        if ((Get-ContentHash $file.Source) -ne (Get-ContentHash $destination)) {
            throw "Copy verification failed: $destination"
        }
    }
} catch {
    $failure = $_
    # Restore overwritten files and remove only new files from our allowlist.
    # Never recursively delete decoder folders or remove unrelated analyzers.
    foreach ($file in $attempted) {
        $destination = Join-Path $decoderRoot $file.Relative
        $saved = Join-Path $backup $file.Relative
        try {
            if (Test-Path -LiteralPath $saved -PathType Leaf) {
                Copy-Item -LiteralPath $saved -Destination $destination -Force
            } elseif (Test-Path -LiteralPath $destination -PathType Leaf) {
                Remove-Item -LiteralPath $destination -Force
            }
        } catch {
            Write-Warning "Could not restore $destination. Retained backup: $backup"
        }
    }
    throw $failure
}
Write-Output "Installed: IGBT 1SP/1SD, SET UART, SET CAN, PM35 UART in $decoderRoot"
if (Test-Path -LiteralPath $backup) { Write-Output "Previous files retained in: $backup" }
Write-Output 'Restart DSView. Add UART/CAN first, then stack the corresponding SET decoder. No external Python is required.'