subset-fonts.ps1

#!/bin/env pwsh

Set-StrictMode -Version 3.0
$ErrorActionPreference = "Stop"

# Features included by default by pyftsubset are:
# ['BUZZ', 'Buzz', 'HARF', 'Harf', 'abvf', 'abvm',
#  'abvs', 'akhn', 'blwf', 'blwm', 'blws', 'calt',
#  'ccmp', 'cfar', 'chws', 'cjct', 'clig', 'cswh',
#  'curs', 'dist', 'dnom', 'fin2', 'fin3', 'fina',
#  'frac', 'half', 'haln', 'halt', 'init', 'isol',
#  'jalt', 'kern', 'liga', 'ljmo', 'locl', 'ltra',
#  'ltrm', 'mark', 'med2', 'medi', 'mkmk', 'mset',
#  'nukt', 'numr', 'pref', 'pres', 'pstf', 'psts',
#  'rand', 'rclt', 'rkrf', 'rlig', 'rphf', 'rtla',
#  'rtlm', 'rvrn', 'stch', 'tjmo', 'valt', 'vatu',
#  'vchw', 'vert', 'vhal', 'vjmo', 'vkrn', 'vpal',
#  'vrt2']

$fonts = [ordered]@{
    "charis" = @{
        "Dir" = "Charis_SIL"
        "Family" = "Charis SIL"
        "Subsets" = [ordered]@{
            # This operates as a fallback for missing characters in SS4.
            # e.g. COMBINING VERTICAL LINE ABOVE
            # both the base character and the combining one are required
            "LatinFallback" = @{
                "Blocks" = @("BasicLatin", "CombiningDiacriticalMarks")
            }
            # Mediaeval & Egyptological
            "Historical" = @{
                "Blocks" = @("LatinExtendedD")
            }
        }
    }
    "sourceserif4" = @{
        "Family" = "Source Serif 4"
        "Dir" = "SourceSerif4"
        "Subsets" = [ordered]@{
            "Latin" = @{
                "Features" = "ordn,smcp,c2sc,subs,sups,case,kern,onum,tnum"
                # diacritical marks must be included here or they won't combine
                "Blocks" = @("BasicLatin", "GeneralPunctuation", "Latin1Supplement", "CombiningDiacriticalMarks")
            }
            # Don't need smcp/c2sc for these
            "LatinExt" = @{
                "Blocks" = @("LatinExtendedA", "SpacingModifierLetters", "IpaExtensions")
            }
            # Chinese (Pinyin & Jyutping) transliteration
            "ChineseTranslit" = @{
                "Blocks" = @( "LatinExtendedB", "SuperscriptsandSubscripts")
            }
            # Vietnamese and Indic transliteration
            "VietIndic" = @{
                "Blocks" = @("LatinExtendedAdditional")
            }
            "Cyrillic" = @{
                "Blocks" = @("Cyrillic")
            }
            "Greek" = @{
                "Blocks" = @("GreekandCoptic")
            }
        }
    }
}

foreach ($font in $fonts.GetEnumerator()) {
    $fontName = $font.Key
    $dir = $font.Value.Dir
    $fontFamily = $font.Value.Family
    $subsets = $font.Value.Subsets

    pushd "input-fonts/$dir"
    mkdir -p "../../fonts/$fontName"

    $css = "../../fonts/$fontName.css"
    echo "" > $css # blank it

    function whitelistFromBlock([string]$block) {
        $range = [System.Text.Unicode.UnicodeRanges]::$block
        if ($range -eq $null) {
            throw "no such block $block"
        }

        return "U+$($range.FirstCodePoint.ToString("x4"))-$(($range.FirstCodePoint + $range.Length - 1).ToString("x4"))"
    }

    foreach ($subset in $subsets.GetEnumerator()) {
        $name = $subset.Key
        echo "$name - $($subset.Value.Blocks)"
        $whitelist = ($subset.Value.Blocks | %{ whitelistFromBlock($_) }) -join ','
        if ($subset.Value.ContainsKey('Additional')) {
            $whitelist += ",$($subset.Value.Additional)"
        }

        $features = @()
        if ($subset.Value.ContainsKey('Features')) {
            $features = @("--layout-features+=$($subset.Value.Features)")
            echo $features
        }

        foreach ($file in Get-ChildItem -Filter '*.woff2' -File) {
            $targetFile = Join-Path "../../fonts/$fontName" ($file.Name -replace "-", "-$name-")
            pyftsubset $file --unicodes=$whitelist --flavor=woff2 --harfbuzz-repacker --output-file=$targetFile `
                @features `
                --drop-tables+=Silt # --drop-tables+=name --drop-tables+=post

            echo "/* $name ($($subset.Value.Blocks -join ', ')) */" >> $css
            echo "@font-face {" >> $css
            echo "    font-family: '$fontFamily';" >> $css
            echo "    src: local('$fontFamily'), url('/fonts/$fontName/$(Split-Path -Leaf $targetFile)') format('woff2');" >> $css
            if ($subset.Value.ContainsKey("Display")) {
                echo "    font-display: $($subset.Value.Display);" >> $css
            } else {
                echo "    font-display: swap;" >> $css
            }
            if ($file.Name -like "*Italic*") {
                echo "    font-style: italic;" >> $css
            }
            if ($file.Name -like "*Bold*") {
                echo "    font-weight: bold;" >> $css
            }
            echo "    unicode-range: $whitelist;" >> $css
            echo "}" >> $css
        }
    }

    popd
}