feat(iptv): support multiple configurable Stalker portals with per-portal groups

app/src/main/kotlin/com/arflix/tv/data/repository/StalkerPortalSupport.kt

@@ -0,0 +1,74 @@
+package com.arflix.tv.data.repository
+
+import com.google.gson.Gson
+import com.google.gson.reflect.TypeToken
+
+/** Pseudo playlist id for the Stalker/Ministra portal source. */
+const val STALKER_PLAYLIST_ID = "stalker"
+
+/** Maximum number of Stalker portals a user can configure. */
+const val MAX_STALKER_PORTALS = 3
+
+/**
+ * Pure helpers for the Stalker multi-portal model. Kept dependency-free so they
+ * can be unit-tested without an Android context.
+ */
+internal object StalkerPortalSupport {
+
+    private val gson = Gson()
+
+    /**
+     * Channel ids use the `stalker:<portalId>:<origId>` shape. Returns the
+     * portal id segment, or null when the id is not a Stalker channel or the
+     * portal segment is missing.
+     */
+    fun portalIdFromChannelId(channelId: String): String? {
+        if (!channelId.startsWith("stalker:")) return null
+        val afterPrefix = channelId.removePrefix("stalker:")
+        val portalId = afterPrefix.substringBefore(':', missingDelimiterValue = "")
+        return portalId.takeIf { it.isNotBlank() }
+    }
+
+    fun normalizeStalkerPortalEntry(
+        portal: StalkerPortalEntry,
+        index: Int
+    ): StalkerPortalEntry? {
+        val portalUrl = runCatching { portal.portalUrl }.getOrNull().orEmpty().trim().trimEnd('/')
+        val macAddress = runCatching { portal.macAddress }.getOrNull().orEmpty().trim().uppercase()
+        if (portalUrl.isBlank() || macAddress.isBlank()) return null
+        return StalkerPortalEntry(
+            id = runCatching { portal.id }.getOrNull().orEmpty().trim().ifBlank { "stalker${index + 1}" },
+            name = runCatching { portal.name }.getOrNull().orEmpty().trim().ifBlank { "Portal ${index + 1}" },
+            portalUrl = portalUrl,
+            macAddress = macAddress,
+            enabled = runCatching { portal.enabled }.getOrDefault(true)
+        )
+    }
+
+    fun decodeStalkerPortals(raw: String, maxPortals: Int): List<StalkerPortalEntry> {
+        if (raw.isBlank()) return emptyList()
+        return runCatching {
+            val type = TypeToken.getParameterized(List::class.java, StalkerPortalEntry::class.java).type
+            gson.fromJson<List<StalkerPortalEntry>>(raw, type)
+                ?.mapIndexed { index, portal -> normalizeStalkerPortalEntry(portal, index) }
+                ?.filterNotNull()
+                ?.take(maxPortals)
+                ?: emptyList()
+        }.getOrDefault(emptyList())
+    }
+
+    /**
+     * Builds the migrated Portal 1 entry from legacy single-portal fields.
+     */
+    fun migratedPortalFromLegacy(portalUrl: String, macAddress: String): StalkerPortalEntry? {
+        val url = portalUrl.trim().trimEnd('/')
+        val mac = macAddress.trim().uppercase()
+        if (url.isBlank() || mac.isBlank()) return null
+        return StalkerPortalEntry(
+            id = "stalker1",
+            name = "Portal 1",
+            portalUrl = url,
+            macAddress = mac
+        )
+    }
+}