param(
    [string]$OutputPath = ""
)

# Writes src\CultMath\Swizzles.g.cs: HLSL swizzles and mixed constructors for
# CultMath's vector types. The output is checked in; rerun after changing the
# family table below and commit both files together.

$ErrorActionPreference = "Stop"

if (-not $OutputPath) {
    $OutputPath = Join-Path $PSScriptRoot "..\src\CultMath\Swizzles.g.cs"
}

# Functions: emit math.<type>(...) constructor functions. double has none because
# a math.double3 method group would hide the double3 type name under
# `using static CultMath.math;` and HLSL shader code does not construct doubles.
$families = @(
    @{ Scalar = "float"; Sizes = @(2, 3, 4); Functions = $true },
    @{ Scalar = "int"; Sizes = @(2, 3, 4); Functions = $true },
    @{ Scalar = "bool"; Sizes = @(2, 3, 4); Functions = $true },
    @{ Scalar = "double"; Sizes = @(2, 3); Functions = $false }
)
$componentFields = @("x", "y", "z", "w")
$namings = @(@("x", "y", "z", "w"), @("r", "g", "b", "a"))

function Get-Compositions([int]$total) {
    # Ordered part sizes summing to $total, excluding the all-scalar form that the
    # hand-written base constructor already owns.
    $results = [System.Collections.Generic.List[object]]::new()
    function Expand([int]$remaining, [int[]]$prefix) {
        if ($remaining -eq 0) {
            if (@($prefix | Where-Object { $_ -ne 1 }).Count -gt 0) {
                $results.Add($prefix)
            }
            return
        }
        for ($part = 1; $part -le $remaining; $part++) {
            Expand ($remaining - $part) ($prefix + $part)
        }
    }
    Expand $total @()
    return , $results
}

$builder = [System.Text.StringBuilder]::new()
function Line([string]$text = "") { [void]$builder.Append($text).Append("`n") }

Line "// <auto-generated>"
Line "// Generated by tools/generate-swizzles.ps1. Do not edit by hand."
Line "// </auto-generated>"
Line ""
Line "namespace CultMath;"

$functionLines = [System.Collections.Generic.List[string]]::new()

foreach ($family in $families) {
    $scalar = $family.Scalar
    $maxSize = ($family.Sizes | Measure-Object -Maximum).Maximum
    foreach ($size in $family.Sizes) {
        $type = "$scalar$size"
        Line ""
        Line "public partial struct $type"
        Line "{"

        foreach ($composition in (Get-Compositions $size)) {
            $parameters = @()
            $arguments = @()
            $offset = 0
            foreach ($part in $composition) {
                $name = -join $componentFields[$offset..($offset + $part - 1)]
                if ($part -eq 1) {
                    $parameters += "$scalar $name"
                    $arguments += $name
                } else {
                    $parameters += "$scalar$part $name"
                    for ($i = 0; $i -lt $part; $i++) { $arguments += "$name.$($componentFields[$i])" }
                }
                $offset += $part
            }
            $parameterList = $parameters -join ", "
            Line "    public $type($parameterList) : this($($arguments -join ', ')) { }"
            if ($family.Functions) {
                $names = @($parameters | ForEach-Object { ($_ -split " ")[1] })
                $functionLines.Add("    public static $type $type($parameterList) => new($($names -join ', '));")
            }
        }

        # Single-component color aliases; x/y/z/w are the fields themselves.
        $letters = $namings[1]
        for ($i = 0; $i -lt $size; $i++) {
            Line "    public $scalar $($letters[$i]) { readonly get => $($componentFields[$i]); set => $($componentFields[$i]) = value; }"
        }

        foreach ($letters in $namings) {
            for ($length = 2; $length -le $maxSize; $length++) {
                $count = [math]::Pow($size, $length)
                for ($index = 0; $index -lt $count; $index++) {
                    [int[]]$digits = @()
                    [int]$remainder = $index
                    for ($d = 0; $d -lt $length; $d++) {
                        $digits = @([int]($remainder % $size)) + $digits
                        $remainder = [int][math]::Floor($remainder / $size)
                    }
                    $name = -join ($digits | ForEach-Object { $letters[$_] })
                    $getter = ($digits | ForEach-Object { $componentFields[$_] }) -join ", "
                    $resultType = "$scalar$length"
                    $unique = @($digits | Select-Object -Unique).Count -eq $length
                    if ($unique) {
                        $assignments = for ($d = 0; $d -lt $length; $d++) { "$($componentFields[$digits[$d]]) = value.$($componentFields[$d]);" }
                        Line "    public $resultType $name { readonly get => new($getter); set { $($assignments -join ' ') } }"
                    } else {
                        Line "    public readonly $resultType $name => new($getter);"
                    }
                }
            }
        }

        Line "}"
    }
}

Line ""
Line "public static partial class math"
Line "{"
foreach ($functionLine in $functionLines) { Line $functionLine }
Line "}"

$fullPath = [System.IO.Path]::GetFullPath($OutputPath)
$content = $builder.ToString() -replace "`n", "`r`n"
[System.IO.File]::WriteAllText($fullPath, $content, [System.Text.UTF8Encoding]::new($false))
Write-Host "Wrote $fullPath ($((Get-Item -LiteralPath $fullPath).Length) bytes)"