From 59bce04f2ec844ffcd89d14db6ed3e685288eaa1 Mon Sep 17 00:00:00 2001
From: Tom Tang <me@qwerzl.me>
Date: Thu, 17 Oct 2024 15:49:46 +0800
Subject: [PATCH] feat(google): allow configuring variable axes (#35)

---
 src/providers/google.ts       | 50 ++++++++++++++++++++++++++++++++---
 test/providers/google.test.ts | 29 ++++++++++++++++++++
 2 files changed, 76 insertions(+), 3 deletions(-)

diff --git a/src/providers/google.ts b/src/providers/google.ts
index 4b2737f..c4c1078 100644
--- a/src/providers/google.ts
+++ b/src/providers/google.ts
@@ -5,7 +5,20 @@ import { extractFontFaceData } from '../css/parse'
 import { $fetch } from '../fetch'
 import { defineFontProvider } from '../utils'
 
-export default defineFontProvider('google', async (_options, ctx) => {
+type VariableAxis = 'opsz' | 'slnt' | 'wdth' | (string & {})
+
+interface ProviderOption {
+  experimental?: {
+    /**
+     * Experimental: Setting variable axis configuration on a per-font basis.
+     */
+    variableAxis?: {
+      [key: string]: Partial<Record<VariableAxis, ([string, string] | string)[] >>
+    }
+  }
+}
+
+export default defineFontProvider<ProviderOption>('google', async (_options = {}, ctx) => {
   const googleFonts = await ctx.storage.getItem('google:meta.json', () => $fetch<{ familyMetadataList: FontIndexMeta[] }>('https://fonts.google.com/metadata/fonts', { responseType: 'json' }).then(r => r.familyMetadataList))
 
   const styleMap = {
@@ -34,7 +47,23 @@ export default defineFontProvider('google', async (_options, ctx) => {
     if (weights.length === 0 || styles.length === 0)
       return []
 
-    const resolvedVariants = weights.flatMap(w => [...styles].map(s => `${s},${w}`)).sort()
+    const resolvedAxes = []
+    let resolvedVariants: string[] = []
+
+    for (const axis of ['wght', 'ital', ...Object.keys(_options?.experimental?.variableAxis?.[family] ?? {})].sort(googleFlavoredSorting)) {
+      const axisValue = ({
+        wght: weights,
+        ital: styles,
+      })[axis] ?? _options!.experimental!.variableAxis![family]![axis]!.map(v => Array.isArray(v) ? `${v[0]}..${v[1]}` : v)
+
+      if (resolvedVariants.length === 0) {
+        resolvedVariants = axisValue
+      }
+      else {
+        resolvedVariants = resolvedVariants.flatMap(v => [...axisValue].map(o => [v, o].join(','))).sort()
+      }
+      resolvedAxes.push(axis)
+    }
 
     let css = ''
 
@@ -43,7 +72,7 @@ export default defineFontProvider('google', async (_options, ctx) => {
         baseURL: 'https://fonts.googleapis.com',
         headers: { 'user-agent': userAgents[extension as keyof typeof userAgents] },
         query: {
-          family: `${family}:` + `ital,wght@${resolvedVariants.join(';')}`,
+          family: `${family}:${resolvedAxes.join(',')}@${resolvedVariants.join(';')}`,
         },
       })
     }
@@ -64,6 +93,8 @@ export default defineFontProvider('google', async (_options, ctx) => {
   }
 })
 
+/** internal */
+
 interface FontIndexMeta {
   family: string
   subsets: string[]
@@ -80,3 +111,16 @@ interface FontIndexMeta {
     defaultValue: number
   }>
 }
+
+// Google wants lowercase letters to be in front of uppercase letters.
+function googleFlavoredSorting(a: string, b: string) {
+  const isALowercase = a.charAt(0) === a.charAt(0).toLowerCase()
+  const isBLowercase = b.charAt(0) === b.charAt(0).toLowerCase()
+
+  if (isALowercase !== isBLowercase) {
+    return Number(isBLowercase) - Number(isALowercase)
+  }
+  else {
+    return a.localeCompare(b)
+  }
+}
diff --git a/test/providers/google.test.ts b/test/providers/google.test.ts
index 9708e5b..e8cc77f 100644
--- a/test/providers/google.test.ts
+++ b/test/providers/google.test.ts
@@ -36,4 +36,33 @@ describe('google', () => {
     expect(resolvedStyles).toMatchObject(styles)
     expect(resolvedWeights).toMatchObject(weights)
   })
+
+  it('supports variable axes', async () => {
+    const unifont = await createUnifont([providers.google({
+      experimental: {
+        variableAxis: {
+          Recursive: {
+            slnt: [['-15', '0']],
+            CASL: [['0', '1']],
+            CRSV: ['1'],
+            MONO: [['0', '1']],
+          },
+        },
+      },
+    })])
+
+    const { fonts } = await unifont.resolveFont('Recursive')
+
+    const resolvedStyles = pickUniqueBy(fonts, fnt => fnt.style)
+    const resolvedWeights = pickUniqueBy(fonts, fnt => String(fnt.weight))
+
+    const styles = ['oblique 0deg 15deg', 'normal'] as ResolveFontOptions['styles']
+
+    // Variable wght and separate weights from 300 to 1000
+    const weights = ['300,1000', ...([...Array.from({ length: 7 }).keys()].map(i => String(i * 100 + 300)))]
+
+    expect(fonts).toHaveLength(11)
+    expect(resolvedStyles).toMatchObject(styles)
+    expect(resolvedWeights).toMatchObject(weights)
+  })
 })