Add Cache

app/core/src/main/java/com/fsck/k9/cache/Cache.kt

@@ -0,0 +1,12 @@
+package com.fsck.k9.cache
+
+interface Cache<KEY : Any, VALUE : Any> {
+
+    operator fun get(key: KEY): VALUE?
+
+    operator fun set(key: KEY, value: VALUE)
+
+    fun hasKey(key: KEY): Boolean
+
+    fun clear()
+}

app/core/src/main/java/com/fsck/k9/cache/ExpiringCache.kt

@@ -0,0 +1,45 @@
+package com.fsck.k9.cache
+
+import com.fsck.k9.Clock
+
+internal class ExpiringCache<KEY : Any, VALUE : Any>(
+    private val clock: Clock,
+    private val delegateCache: Cache<KEY, VALUE> = InMemoryCache(),
+    private var lastClearTime: Long = clock.time,
+    private val cacheTimeValidity: Long = CACHE_TIME_VALIDITY_IN_MILLIS
+) : Cache<KEY, VALUE> {
+
+    override fun get(key: KEY): VALUE? {
+        recycle()
+        return delegateCache[key]
+    }
+
+    override fun set(key: KEY, value: VALUE) {
+        recycle()
+        delegateCache[key] = value
+    }
+
+    override fun hasKey(key: KEY): Boolean {
+        recycle()
+        return delegateCache.hasKey(key)
+    }
+
+    override fun clear() {
+        lastClearTime = clock.time
+        delegateCache.clear()
+    }
+
+    private fun recycle() {
+        if (isExpired()) {
+            clear()
+        }
+    }
+
+    private fun isExpired(): Boolean {
+        return (clock.time - lastClearTime) >= cacheTimeValidity
+    }
+
+    private companion object {
+        const val CACHE_TIME_VALIDITY_IN_MILLIS = 30_000L
+    }
+}

app/core/src/main/java/com/fsck/k9/cache/InMemoryCache.kt

@@ -0,0 +1,21 @@
+package com.fsck.k9.cache
+
+internal class InMemoryCache<KEY : Any, VALUE : Any>(
+    private val cache: MutableMap<KEY, VALUE> = mutableMapOf()
+) : Cache<KEY, VALUE> {
+    override fun get(key: KEY): VALUE? {
+        return cache[key]
+    }
+
+    override fun set(key: KEY, value: VALUE) {
+        cache[key] = value
+    }
+
+    override fun hasKey(key: KEY): Boolean {
+        return cache.containsKey(key)
+    }
+
+    override fun clear() {
+        cache.clear()
+    }
+}

app/core/src/main/java/com/fsck/k9/cache/SynchronizedCache.kt

@@ -0,0 +1,30 @@
+package com.fsck.k9.cache
+
+internal class SynchronizedCache<KEY : Any, VALUE : Any>(
+    private val delegateCache: Cache<KEY, VALUE>
+) : Cache<KEY, VALUE> {
+
+    override fun get(key: KEY): VALUE? {
+        synchronized(delegateCache) {
+            return delegateCache[key]
+        }
+    }
+
+    override fun set(key: KEY, value: VALUE) {
+        synchronized(delegateCache) {
+            delegateCache[key] = value
+        }
+    }
+
+    override fun hasKey(key: KEY): Boolean {
+        synchronized(delegateCache) {
+            return delegateCache.hasKey(key)
+        }
+    }
+
+    override fun clear() {
+        synchronized(delegateCache) {
+            delegateCache.clear()
+        }
+    }
+}

app/core/src/test/java/com/fsck/k9/cache/CacheTest.kt

@@ -0,0 +1,77 @@
+package com.fsck.k9.cache
+
+import com.fsck.k9.TestClock
+import com.google.common.truth.Truth.assertThat
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.Parameterized
+
+data class CacheTestData<KEY : Any, VALUE : Any>(
+    val name: String,
+    val createCache: () -> Cache<KEY, VALUE>
+) {
+    override fun toString(): String = name
+}
+
+@RunWith(Parameterized::class)
+class CacheTest(data: CacheTestData<Any, Any>) {
+
+    private val testSubject = data.createCache()
+
+    companion object {
+        @JvmStatic
+        @Parameterized.Parameters(name = "{0}")
+        fun data(): Collection<CacheTestData<Any, Any>> {
+            return listOf(
+                CacheTestData("InMemoryCache") { InMemoryCache() },
+                CacheTestData("ExpiringCache") { ExpiringCache(TestClock(), InMemoryCache()) },
+                CacheTestData("SynchronizedCache") { SynchronizedCache(InMemoryCache()) }
+            )
+        }
+
+        const val KEY = "key"
+        const val VALUE = "value"
+    }
+
+    @Test
+    fun `get should return null with empty cache`() {
+        assertThat(testSubject[KEY]).isNull()
+    }
+
+    @Test
+    fun `set should add entry with empty cache`() {
+        testSubject[KEY] = VALUE
+
+        assertThat(testSubject[KEY]).isEqualTo(VALUE)
+    }
+
+    @Test
+    fun `set should overwrite entry when already present`() {
+        testSubject[KEY] = VALUE
+
+        testSubject[KEY] = "$VALUE changed"
+
+        assertThat(testSubject[KEY]).isEqualTo("$VALUE changed")
+    }
+
+    @Test
+    fun `hasKey should answer no with empty cache`() {
+        assertThat(testSubject.hasKey(KEY)).isFalse()
+    }
+
+    @Test
+    fun `hasKey should answer yes when cache has entry`() {
+        testSubject[KEY] = VALUE
+
+        assertThat(testSubject.hasKey(KEY)).isTrue()
+    }
+
+    @Test
+    fun `clear should empty cache`() {
+        testSubject[KEY] = VALUE
+
+        testSubject.clear()
+
+        assertThat(testSubject[KEY]).isNull()
+    }
+}

app/core/src/test/java/com/fsck/k9/cache/ExpiringCacheTest.kt

@@ -0,0 +1,68 @@
+package com.fsck.k9.cache
+
+import com.fsck.k9.TestClock
+import com.google.common.truth.Truth.assertThat
+import kotlin.test.Test
+
+class ExpiringCacheTest {
+
+    private val clock = TestClock()
+
+    private val testSubject: Cache<String, String> = ExpiringCache(clock, InMemoryCache())
+
+    @Test
+    fun `get should return null when entry present and cache expired`() {
+        testSubject[KEY] = VALUE
+        advanceClockBy(CACHE_TIME_VALIDITY_IN_MILLIS)
+
+        val result = testSubject[KEY]
+
+        assertThat(result).isNull()
+    }
+
+    @Test
+    fun `set should clear cache and add new entry when cache expired`() {
+        testSubject[KEY] = VALUE
+        advanceClockBy(CACHE_TIME_VALIDITY_IN_MILLIS)
+
+        testSubject[KEY + 1] = "$VALUE changed"
+
+        assertThat(testSubject[KEY]).isNull()
+        assertThat(testSubject[KEY + 1]).isEqualTo("$VALUE changed")
+    }
+
+    @Test
+    fun `hasKey should answer no when cache has entry and validity expired`() {
+        testSubject[KEY] = VALUE
+        advanceClockBy(CACHE_TIME_VALIDITY_IN_MILLIS)
+
+        assertThat(testSubject.hasKey(KEY)).isFalse()
+    }
+
+    @Test
+    fun `should keep cache when time progresses within expiration`() {
+        testSubject[KEY] = VALUE
+        advanceClockBy(CACHE_TIME_VALIDITY_IN_MILLIS - 1)
+
+        assertThat(testSubject[KEY]).isEqualTo(VALUE)
+    }
+
+    @Test
+    fun `should empty cache after time progresses to expiration`() {
+        testSubject[KEY] = VALUE
+
+        advanceClockBy(CACHE_TIME_VALIDITY_IN_MILLIS)
+
+        assertThat(testSubject[KEY]).isNull()
+    }
+
+    private fun advanceClockBy(timeInMillis: Long) {
+        clock.time = clock.time + timeInMillis
+    }
+
+    private companion object {
+        const val KEY = "key"
+        const val VALUE = "value"
+        const val CACHE_TIME_VALIDITY_IN_MILLIS = 30_000L
+    }
+}