[CmdletBinding()]
param(
    [string]$BuildDirectory = (Join-Path $PSScriptRoot '..\build-msvc'),
    [double]$Tolerance = 0.01,
    [switch]$ShowAllDifferences
)

$cppRunner = Join-Path $BuildDirectory 'fluidsim_parity_trace.exe'
$csProject = Join-Path $PSScriptRoot 'CSharpParityTrace.csproj'
if (-not (Test-Path -LiteralPath $cppRunner)) { throw "C++ trace runner not found: $cppRunner" }

$cppText = & $cppRunner
if ($LASTEXITCODE -ne 0) { throw "C++ trace runner failed with exit code $LASTEXITCODE." }
$csText = & dotnet run --project $csProject --configuration Release --no-launch-profile --verbosity quiet
if ($LASTEXITCODE -ne 0) { throw "C# reference trace failed with exit code $LASTEXITCODE." }

$cppRows = @($cppText | Where-Object { $_ -match '^(step,|\d+,)' } | ConvertFrom-Csv)
$csRows = @($csText | Where-Object { $_ -match '^(step,|\d+,)' } | ConvertFrom-Csv)
if ($cppRows.Count -ne $csRows.Count) { throw "Checkpoint count differs: C++=$($cppRows.Count), C#=$($csRows.Count)." }

$columns = @('rpm', 'angle', 'cylinder1_pa', 'cylinder2_pa', 'intake_pa', 'exhaust_pa', 'speed_kmh',
    'valve1_in', 'valve2_in', 'intake_flow', 'exhaust_flow', 'pipe0_left_pa', 'pipe0_right_pa',
    'pipe1_left_pa', 'pipe1_right_pa', 'pipe2_left_pa', 'pipe2_right_pa',
    'pipe3_left_pa', 'pipe3_right_pa', 'pipe4_left_pa', 'pipe4_right_pa',
    'throttle_port_flow', 'runner1_port_flow', 'runner2_port_flow',
    'cyl1_intake_flow', 'cyl2_intake_flow', 'cyl1_exhaust_flow', 'cyl2_exhaust_flow',
    'pipe0_right_rho', 'pipe0_right_u', 'pipe1_left_rho', 'pipe1_left_u', 'pipe1_right_rho', 'pipe1_right_u',
    'pipe2_left_rho', 'pipe2_left_u', 'pipe2_right_rho', 'pipe2_right_u',
    'intake_rho', 'intake_temperature', 'pipe0_left_rho', 'pipe0_left_u')
$largestDifference = 0.0
$largestField = ''
$largestStep = 0
$differences = [System.Collections.Generic.List[object]]::new()
for ($rowIndex = 0; $rowIndex -lt $cppRows.Count; ++$rowIndex) {
    if ($cppRows[$rowIndex].step -ne $csRows[$rowIndex].step) { throw 'Checkpoint steps differ.' }
    foreach ($column in $columns) {
        $cppValue = [double]::Parse($cppRows[$rowIndex].$column, [Globalization.CultureInfo]::InvariantCulture)
        $csValue = [double]::Parse($csRows[$rowIndex].$column, [Globalization.CultureInfo]::InvariantCulture)
        $difference = [Math]::Abs($cppValue - $csValue)
        $scale = [Math]::Max(1.0, [Math]::Abs($csValue))
        $relativeDifference = $difference / $scale
        if ($relativeDifference -gt $largestDifference) {
            $largestDifference = $relativeDifference
            $largestField = $column
            $largestStep = [int]$cppRows[$rowIndex].step
        }
        if ($relativeDifference -gt 0.0) {
            $differences.Add([pscustomobject]@{
                Step = [int]$cppRows[$rowIndex].step
                Field = $column
                CSharp = $csValue
                Cpp = $cppValue
                RelativeDifference = $relativeDifference
            })
        }
        if ($ShowAllDifferences) {
            "step={0} {1}: C#={2:G9}, C++={3:G9}, rel={4:G6}" -f `
                $cppRows[$rowIndex].step, $column, $csValue, $cppValue, $relativeDifference
        }
    }
}

"Compared {0} checkpoints across {1} fields; tolerance {2:G6}." -f $cppRows.Count, $columns.Count, $Tolerance
"Largest relative difference: {0:G6} in {1} at step {2}." -f $largestDifference, $largestField, $largestStep
if ($largestDifference -gt $Tolerance) {
    'Largest remaining differences:'
    $differences | Sort-Object RelativeDifference -Descending | Select-Object -First 10 | ForEach-Object {
        "  step={0} {1}: C#={2:G9}, C++={3:G9}, rel={4:G6}" -f `
            $_.Step, $_.Field, $_.CSharp, $_.Cpp, $_.RelativeDifference
    }
}
if ($largestDifference -gt $Tolerance) { exit 1 }