fix: keep dark-mode message text readable on light sender backgrounds

feature/mail/message/reader/impl/src/androidHostTest/kotlin/net/thunderbird/feature/mail/message/reader/impl/css/DefaultGlobalCssStyleProviderTest.kt

@@ -2,23 +2,50 @@ package net.thunderbird.feature.mail.message.reader.impl.css
 
 import assertk.assertThat
 import assertk.assertions.contains
+import assertk.assertions.doesNotContain
 import kotlin.test.Test
 import net.thunderbird.core.common.mail.html.HtmlSettings
 import net.thunderbird.feature.mail.message.reader.api.css.CssClassNameProvider
 import net.thunderbird.feature.mail.message.reader.api.css.CssVariableNameProvider
 
 class DefaultGlobalCssStyleProviderTest {
 
+    @Test
+    fun `style should advertise light only color scheme when dark mode is enabled`() {
+        // Arrange
+        val testSubject = createTestSubject()
+
+        // Act
+        val style = testSubject.create(createHtmlSettings(useDarkMode = true)).style
+
+        // Assert
+        assertThat(style).contains(":root { color-scheme: only light; }")
+    }
+
+    @Test
+    fun `style should not override color scheme when dark mode is disabled`() {
+        // Arrange
+        val testSubject = createTestSubject()
+
+        // Act
+        val style = testSubject.create(createHtmlSettings(useDarkMode = false)).style
+
+        // Assert
+        assertThat(style).doesNotContain("color-scheme")
+    }
+
     @Test
     fun `style should set main content box sizing to border box`() {
         // Arrange
         val testSubject = createTestSubject()
 
         // Act
-        val style = testSubject.create(createHtmlSettings()).style
+        val styles = createStylesForBothThemeConfigurations(testSubject)
 
         // Assert
-        assertThat(style).contains("box-sizing: border-box")
+        styles.forEach { style ->
+            assertThat(style).contains("box-sizing: border-box")
+        }
     }
 
     @Test
@@ -27,12 +54,16 @@ class DefaultGlobalCssStyleProviderTest {
         val testSubject = createTestSubject()
 
         // Act
-        val style = testSubject.create(createHtmlSettings()).style
-        val mainContentRule = style.mainContentRule()
+        val styles = createStylesForBothThemeConfigurations(testSubject)
 
         // Assert
-        assertThat(mainContentRule).contains("width: 100%")
-        assertThat(mainContentRule).contains("padding: 0 8px")
+        styles.forEach { style ->
+            val mainContentRule = style.mainContentRule()
+
+            assertThat(mainContentRule).contains("width: 100%")
+            assertThat(mainContentRule).contains("overflow-wrap: break-word")
+            assertThat(mainContentRule).contains("padding: 0 8px")
+        }
     }
 
     @Test
@@ -41,10 +72,45 @@ class DefaultGlobalCssStyleProviderTest {
         val testSubject = createTestSubject()
 
         // Act
-        val style = testSubject.create(createHtmlSettings()).style
+        val styles = createStylesForBothThemeConfigurations(testSubject)
+
+        // Assert
+        styles.forEach { style ->
+            assertThat(style).contains("white-space: pre-wrap")
+        }
+    }
+
+    @Test
+    fun `style should preserve selectable content`() {
+        // Arrange
+        val testSubject = createTestSubject()
+
+        // Act
+        val styles = createStylesForBothThemeConfigurations(testSubject)
+
+        // Assert
+        styles.forEach { style ->
+            assertThat(style).contains("\n    user-select: auto;\n")
+            assertThat(style).contains("-webkit-user-select: auto")
+        }
+    }
+
+    @Test
+    fun `style should preserve blockquote styling`() {
+        // Arrange
+        val testSubject = createTestSubject()
+
+        // Act
+        val styles = createStylesForBothThemeConfigurations(testSubject)
 
         // Assert
-        assertThat(style).contains("white-space: pre-wrap")
+        styles.forEach { style ->
+            assertThat(style).contains("margin: auto 0 auto 0.8ex !important")
+            assertThat(style).contains("padding-left: 1ex !important")
+            assertThat(style).contains("border-left-width: 1px !important")
+            assertThat(style).contains("border-left-style: solid !important")
+            assertThat(style).contains("border-left-color: var(--blockquote-default-border-left-color, #ccc)")
+        }
     }
 
     private fun createTestSubject(): DefaultGlobalCssStyleProvider.Factory {
@@ -54,9 +120,18 @@ class DefaultGlobalCssStyleProviderTest {
         )
     }
 
-    private fun createHtmlSettings(): HtmlSettings {
+    private fun createStylesForBothThemeConfigurations(
+        testSubject: DefaultGlobalCssStyleProvider.Factory,
+    ): List<String> {
+        return listOf(
+            testSubject.create(createHtmlSettings(useDarkMode = false)).style,
+            testSubject.create(createHtmlSettings(useDarkMode = true)).style,
+        )
+    }
+
+    private fun createHtmlSettings(useDarkMode: Boolean): HtmlSettings {
         return HtmlSettings(
-            useDarkMode = false,
+            useDarkMode = useDarkMode,
             useFixedWidthFont = false,
         )
     }

feature/mail/message/reader/impl/src/commonMain/kotlin/net/thunderbird/feature/mail/message/reader/impl/css/DefaultGlobalCssStyleProvider.kt

@@ -10,10 +10,12 @@ import org.intellij.lang.annotations.Language
 internal class DefaultGlobalCssStyleProvider private constructor(
     cssClassNameProvider: CssClassNameProvider,
     cssVariableNameProvider: CssVariableNameProvider,
+    useDarkMode: Boolean,
 ) : GlobalCssStyleProvider {
     @Language("HTML")
     override val style: String = """
         |<style>
+        |${if (useDarkMode) "  :root { color-scheme: only light; }" else ""}
         |  body { font-size: 0.9rem; }
         |  .clear:after {
         |    content: "";
@@ -51,6 +53,7 @@ internal class DefaultGlobalCssStyleProvider private constructor(
         override fun create(htmlSettings: HtmlSettings): CssStyleProvider = DefaultGlobalCssStyleProvider(
             cssClassNameProvider = cssClassNameProvider,
             cssVariableNameProvider = cssVariableNameProvider,
+            useDarkMode = htmlSettings.useDarkMode,
         )
     }
 }