From 9f4597b48c4f3877f63fb7daf068b0673c1e8f90 Mon Sep 17 00:00:00 2001
From: cketti <cketti@thunderbird.net>
Date: Tue, 9 May 2023 16:41:05 +0200
Subject: [PATCH] Add code to extract the base domain from a hostname

---
 .../autoconfig/BaseDomainExtractor.kt         | 10 +++++++
 .../autoconfig/OkHttpBaseDomainExtractor.kt   | 16 ++++++++++
 .../OkHttpBaseDomainExtractorTest.kt          | 29 +++++++++++++++++++
 3 files changed, 55 insertions(+)
 create mode 100644 feature/autodiscovery/autoconfig/src/main/kotlin/app/k9mail/autodiscovery/autoconfig/BaseDomainExtractor.kt
 create mode 100644 feature/autodiscovery/autoconfig/src/main/kotlin/app/k9mail/autodiscovery/autoconfig/OkHttpBaseDomainExtractor.kt
 create mode 100644 feature/autodiscovery/autoconfig/src/test/kotlin/app/k9mail/autodiscovery/autoconfig/OkHttpBaseDomainExtractorTest.kt

diff --git a/feature/autodiscovery/autoconfig/src/main/kotlin/app/k9mail/autodiscovery/autoconfig/BaseDomainExtractor.kt b/feature/autodiscovery/autoconfig/src/main/kotlin/app/k9mail/autodiscovery/autoconfig/BaseDomainExtractor.kt
new file mode 100644
index 000000000..b14e127dd
--- /dev/null
+++ b/feature/autodiscovery/autoconfig/src/main/kotlin/app/k9mail/autodiscovery/autoconfig/BaseDomainExtractor.kt
@@ -0,0 +1,10 @@
+package app.k9mail.autodiscovery.autoconfig
+
+/**
+ * Extract the base domain from a host name.
+ *
+ * An implementation needs to respect the [Public Suffix List](https://publicsuffix.org/).
+ */
+interface BaseDomainExtractor {
+    fun extractBaseDomain(domain: String): String
+}
diff --git a/feature/autodiscovery/autoconfig/src/main/kotlin/app/k9mail/autodiscovery/autoconfig/OkHttpBaseDomainExtractor.kt b/feature/autodiscovery/autoconfig/src/main/kotlin/app/k9mail/autodiscovery/autoconfig/OkHttpBaseDomainExtractor.kt
new file mode 100644
index 000000000..60f0f68a7
--- /dev/null
+++ b/feature/autodiscovery/autoconfig/src/main/kotlin/app/k9mail/autodiscovery/autoconfig/OkHttpBaseDomainExtractor.kt
@@ -0,0 +1,16 @@
+package app.k9mail.autodiscovery.autoconfig
+
+import okhttp3.HttpUrl
+
+class OkHttpBaseDomainExtractor : BaseDomainExtractor {
+    override fun extractBaseDomain(domain: String): String {
+        return domain.toHttpUrlOrNull().topPrivateDomain() ?: domain
+    }
+
+    private fun String.toHttpUrlOrNull(): HttpUrl {
+        return HttpUrl.Builder()
+            .scheme("https")
+            .host(this)
+            .build()
+    }
+}
diff --git a/feature/autodiscovery/autoconfig/src/test/kotlin/app/k9mail/autodiscovery/autoconfig/OkHttpBaseDomainExtractorTest.kt b/feature/autodiscovery/autoconfig/src/test/kotlin/app/k9mail/autodiscovery/autoconfig/OkHttpBaseDomainExtractorTest.kt
new file mode 100644
index 000000000..420b915f3
--- /dev/null
+++ b/feature/autodiscovery/autoconfig/src/test/kotlin/app/k9mail/autodiscovery/autoconfig/OkHttpBaseDomainExtractorTest.kt
@@ -0,0 +1,29 @@
+package app.k9mail.autodiscovery.autoconfig
+
+import assertk.assertThat
+import assertk.assertions.isEqualTo
+import org.junit.Test
+
+class OkHttpBaseDomainExtractorTest {
+    private val baseDomainExtractor = OkHttpBaseDomainExtractor()
+
+    @Test
+    fun `basic domain`() {
+        assertThat(baseDomainExtractor.extractBaseDomain("domain.example")).isEqualTo("domain.example")
+    }
+
+    @Test
+    fun `basic subdomain`() {
+        assertThat(baseDomainExtractor.extractBaseDomain("subdomain.domain.example")).isEqualTo("domain.example")
+    }
+
+    @Test
+    fun `domain with public suffix`() {
+        assertThat(baseDomainExtractor.extractBaseDomain("example.co.uk")).isEqualTo("example.co.uk")
+    }
+
+    @Test
+    fun `subdomain with public suffix`() {
+        assertThat(baseDomainExtractor.extractBaseDomain("subdomain.example.co.uk")).isEqualTo("example.co.uk")
+    }
+}