From 1a3107dba736f8eafb42856901640db553127a61 Mon Sep 17 00:00:00 2001
From: Samuel Newman <mozzius@protonmail.com>
Date: Wed, 11 Jun 2025 20:51:27 +0300
Subject: [PATCH] create `transparentifyColor` function

---
 src/alf/util/__tests__/colors.test.ts         | 48 +++++++++++++++++++
 src/alf/util/colorGeneration.ts               | 28 +++++++++++
 .../post-thread/PostThreadComposePrompt.tsx   |  6 +--
 3 files changed, 79 insertions(+), 3 deletions(-)
 create mode 100644 src/alf/util/__tests__/colors.test.ts

diff --git a/src/alf/util/__tests__/colors.test.ts b/src/alf/util/__tests__/colors.test.ts
new file mode 100644
index 0000000000..350b6ff4a4
--- /dev/null
+++ b/src/alf/util/__tests__/colors.test.ts
@@ -0,0 +1,48 @@
+import {jest} from '@jest/globals'
+
+import {logger} from '#/logger'
+import {transparentifyColor} from '../colorGeneration'
+
+jest.mock('#/logger', () => ({
+  logger: {warn: jest.fn()},
+}))
+
+describe('transparentifyColor', () => {
+  beforeEach(() => {
+    jest.clearAllMocks()
+  })
+
+  it('converts hsl() to hsla()', () => {
+    const result = transparentifyColor('hsl(120 100% 50%)', 0.5)
+    expect(result).toBe('hsla(120 100% 50%, 0.5)')
+  })
+
+  it('converts hsl() to hsla() - fully transparent', () => {
+    const result = transparentifyColor('hsl(120 100% 50%)', 0)
+    expect(result).toBe('hsla(120 100% 50%, 0)')
+  })
+
+  it('converts rgb() to rgba()', () => {
+    const result = transparentifyColor('rgb(255 0 0)', 0.75)
+    expect(result).toBe('rgba(255 0 0, 0.75)')
+  })
+
+  it('expands 3-digit hex and appends alpha channel', () => {
+    const result = transparentifyColor('#abc', 0.4)
+    expect(result).toBe('#aabbcc66')
+  })
+
+  it('appends alpha to 6-digit hex', () => {
+    const result = transparentifyColor('#aabbcc', 0.4)
+    expect(result).toBe('#aabbcc66')
+  })
+
+  it('returns the original string and warns for unsupported formats', () => {
+    const unsupported = 'blue'
+    const result = transparentifyColor(unsupported, 0.5)
+    expect(result).toBe(unsupported)
+    expect(logger.warn).toHaveBeenCalledWith(
+      `Could not make '${unsupported}' transparent`,
+    )
+  })
+})
diff --git a/src/alf/util/colorGeneration.ts b/src/alf/util/colorGeneration.ts
index 8d769b51b1..574ab0a496 100644
--- a/src/alf/util/colorGeneration.ts
+++ b/src/alf/util/colorGeneration.ts
@@ -1,3 +1,5 @@
+import {logger} from '#/logger'
+
 export const BLUE_HUE = 211
 export const RED_HUE = 346
 export const GREEN_HUE = 152
@@ -19,3 +21,29 @@ export function generateScale(start: number, end: number) {
 export const defaultScale = generateScale(6, 100)
 // dim shifted 6% lighter
 export const dimScale = generateScale(12, 100)
+
+export function transparentifyColor(color: string, alpha: number) {
+  if (color.startsWith('hsl(')) {
+    return 'hsla(' + color.slice('hsl('.length, -1) + `, ${alpha})`
+  } else if (color.startsWith('rgb(')) {
+    return 'rgba(' + color.slice('rgb('.length, -1) + `, ${alpha})`
+  } else if (color.startsWith('#')) {
+    if (color.length === 7) {
+      const alphaHex = Math.round(alpha * 255).toString(16)
+      // Per MDN: If there is only one number, it is duplicated: e means ee
+      // https://developer.mozilla.org/en-US/docs/Web/CSS/hex-color
+      return color.slice(0, 7) + alphaHex.padStart(2, alphaHex)
+    } else if (color.length === 4) {
+      // convert to 6-digit hex before adding alpha
+      const [r, g, b] = color.slice(1).split('')
+      const alphaHex = Math.round(alpha * 255).toString(16)
+      return `#${r.repeat(2)}${g.repeat(2)}${b.repeat(2)}${alphaHex.padStart(
+        2,
+        alphaHex,
+      )}`
+    }
+  } else {
+    logger.warn(`Could not make '${color}' transparent`)
+  }
+  return color
+}
diff --git a/src/view/com/post-thread/PostThreadComposePrompt.tsx b/src/view/com/post-thread/PostThreadComposePrompt.tsx
index 6b421e9de9..3de69337e1 100644
--- a/src/view/com/post-thread/PostThreadComposePrompt.tsx
+++ b/src/view/com/post-thread/PostThreadComposePrompt.tsx
@@ -10,6 +10,7 @@ import {useProfileQuery} from '#/state/queries/profile'
 import {useSession} from '#/state/session'
 import {UserAvatar} from '#/view/com/util/UserAvatar'
 import {atoms as a, ios, native, useBreakpoints, useTheme} from '#/alf'
+import {transparentifyColor} from '#/alf/util/colorGeneration'
 import {useInteractionState} from '#/components/hooks/useInteractionState'
 import {Text} from '#/components/Typography'
 
@@ -47,12 +48,11 @@ export function PostThreadComposePrompt({
       ]}>
       {!gtMobile && (
         <LinearGradient
+          key={t.name} // android does not update when you change the colors. sigh.
           start={[0.5, 0]}
           end={[0.5, 1]}
           colors={[
-            // "white transparent" - the CSS transparent keyword
-            // is black transparent
-            'rgba(255, 255, 255, 0)',
+            transparentifyColor(t.atoms.bg.backgroundColor, 0),
             t.atoms.bg.backgroundColor,
           ]}
           locations={[0.15, 0.4]}