feat: webapp container tab state management

app/src/main/java/top/yeij/hearth/webapp/WebAppContainer.kt

@@ -0,0 +1,54 @@
+package top.yeij.hearth.webapp
+
+// 单个 WebView 标签：id 唯一标识，active 表示是否为当前激活标签
+// Single WebView tab: id is the unique key, active marks the currently-focused tab
+data class Tab(val id: String, val url: String, val active: Boolean = false)
+
+// 多标签状态管理（纯 Kotlin 数据层，不依赖 WebView，可 JVM 单测）
+// 真实 WebView 导航（goBack/goForward/reload）留待 Task 13 集成时接入
+// Multi-tab state management (pure Kotlin data layer, WebView-free, JVM-testable)
+// Real WebView navigation (goBack/goForward/reload) is wired up in Task 13
+class WebAppContainer {
+    private val tabs = mutableListOf<Tab>()
+
+    // 打开标签：已存在则激活它（不重复添加），否则新增并激活
+    // Open a tab: if it already exists just activate it, otherwise add and activate
+    fun open(id: String, url: String) {
+        val existing = tabs.find { it.id == id }
+        if (existing != null) {
+            setActive(id)
+            return
+        }
+        for (i in tabs.indices) tabs[i] = tabs[i].copy(active = false)
+        tabs.add(Tab(id, url, active = true))
+    }
+
+    // 关闭标签：若关闭后没有激活标签则激活第一个
+    // Close a tab: if none remain active, activate the first one
+    fun close(id: String) {
+        tabs.removeAll { it.id == id }
+        if (tabs.isNotEmpty() && tabs.none { it.active }) {
+            tabs[0] = tabs[0].copy(active = true)
+        }
+    }
+
+    // 切换激活标签
+    // Switch the active tab
+    fun switchTo(id: String) {
+        setActive(id)
+    }
+
+    // 返回标签列表副本（外部无法直接改动内部状态）
+    // Return a defensive copy of the tab list
+    fun tabs(): List<Tab> = tabs.toList()
+
+    private fun setActive(id: String) {
+        for (i in tabs.indices) tabs[i] = tabs[i].copy(active = tabs[i].id == id)
+    }
+
+    // 真实回退由 WebView 层实现，数据层仅占位返回 false
+    // Real back navigation lives in the WebView layer; data layer is a stub
+    fun goBack(): Boolean = false
+    fun goForward(): Boolean = false
+    fun reload() {}
+}

app/src/test/java/top/yeij/hearth/webapp/WebAppContainerTest.kt

@@ -0,0 +1,61 @@
+package top.yeij.hearth.webapp
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class WebAppContainerTest {
+    @Test
+    fun open_addsTab_andBecomesActive() {
+        val c = WebAppContainer()
+        c.open("a", "http://x/a")
+        c.open("b", "http://x/b")
+        assertEquals(2, c.tabs().size)
+        assertEquals("b", c.tabs().first { it.active }.id)
+    }
+
+    @Test
+    fun close_removesTab() {
+        val c = WebAppContainer()
+        c.open("a", "http://x/a"); c.open("b", "http://x/b")
+        c.close("a")
+        assertEquals(1, c.tabs().size)
+        assertEquals("b", c.tabs()[0].id)
+    }
+
+    @Test
+    fun goBack_noHistory_returnsFalse() {
+        val c = WebAppContainer()
+        c.open("a", "http://x/a")
+        assertTrue(!c.goBack()) // 无历史
+    }
+
+    @Test
+    fun open_existingTab_activatesWithoutDuplicating() {
+        val c = WebAppContainer()
+        c.open("a", "http://x/a")
+        c.open("b", "http://x/b")
+        c.open("a", "http://x/a")
+        assertEquals(2, c.tabs().size)
+        assertEquals("a", c.tabs().first { it.active }.id)
+    }
+
+    @Test
+    fun switchTo_activatesSpecifiedTab() {
+        val c = WebAppContainer()
+        c.open("a", "http://x/a")
+        c.open("b", "http://x/b")
+        c.switchTo("a")
+        assertEquals("a", c.tabs().first { it.active }.id)
+        assertEquals(1, c.tabs().count { it.active })
+    }
+
+    @Test
+    fun close_activeTab_activatesFirstRemaining() {
+        val c = WebAppContainer()
+        c.open("a", "http://x/a")
+        c.open("b", "http://x/b")
+        c.close("b")
+        assertEquals("a", c.tabs().first { it.active }.id)
+    }
+}