fix: Bound live build output memory

app/src/main/java/com/itsaky/androidide/fragments/output/BuildOutputBuffer.kt

@@ -0,0 +1,160 @@
+/*
+ *  This file is part of AndroidIDE.
+ *
+ *  AndroidIDE is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  AndroidIDE is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *   along with AndroidIDE.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package com.itsaky.androidide.fragments.output
+
+import kotlinx.coroutines.channels.Channel
+
+/**
+ * Thread-safe pending build output with fixed memory and batch budgets.
+ *
+ * Inputs are indivisible unless one exceeds [maxPendingChars], in which case only its newest tail
+ * is retained. Older pending output is evicted first, while batches preserve the retained order.
+ */
+internal class BuildOutputBuffer(
+	private val maxPendingChars: Int = DEFAULT_MAX_PENDING_CHARS,
+	private val maxBatchChars: Int = DEFAULT_MAX_BATCH_CHARS,
+) {
+	data class Batch(
+		val text: String,
+		val sessionToken: Int,
+		val sourceChars: Int,
+		val omittedLines: Long,
+	)
+
+	private sealed interface Entry {
+		val sessionToken: Int
+
+		data class Text(
+			val value: String,
+			override val sessionToken: Int,
+		) : Entry
+
+		data class Omission(
+			var lineCount: Long,
+			var sourceChars: Int,
+			override val sessionToken: Int,
+		) : Entry
+	}
+
+	private val entries = ArrayDeque<Entry>()
+	private val available = Channel<Unit>(Channel.CONFLATED)
+	private val lock = Any()
+	private var retainedChars = 0
+
+	internal val pendingChars: Int
+		get() = synchronized(lock) { retainedChars }
+
+	init {
+		require(maxPendingChars > 0) { "maxPendingChars must be positive" }
+		require(maxBatchChars > 0) { "maxBatchChars must be positive" }
+	}
+
+	fun offer(
+		text: String,
+		sessionToken: Int,
+	) {
+		if (text.isEmpty()) return
+		val normalized = if (text.endsWith('\n')) text else "$text\n"
+		synchronized(lock) {
+			val existingOmission = entries.firstOrNull() as? Entry.Omission
+			if (existingOmission != null) entries.removeFirst()
+
+			var retained = normalized
+			var omittedLines = existingOmission?.lineCount ?: 0
+			var omittedChars = existingOmission?.sourceChars ?: 0
+			if (retained.length > maxPendingChars) {
+				val droppedPrefix = retained.dropLast(maxPendingChars)
+				omittedLines += lineCount(droppedPrefix)
+				omittedChars = saturatedAdd(omittedChars, droppedPrefix.length)
+				retained = retained.takeLast(maxPendingChars)
+			}
+			while (retainedChars > maxPendingChars - retained.length) {
+				val evicted = entries.removeFirst() as Entry.Text
+				retainedChars -= evicted.value.length
+				omittedLines += lineCount(evicted.value)
+				omittedChars = saturatedAdd(omittedChars, evicted.value.length)
+			}
+
+			if (omittedLines > 0) {
+				entries.addFirst(Entry.Omission(omittedLines, omittedChars, sessionToken))
+			}
+			entries.addLast(Entry.Text(retained, sessionToken))
+			retainedChars += retained.length
+			available.trySend(Unit)
+		}
+	}
+
+	suspend fun takeBatch(): Batch {
+		while (true) {
+			available.receive()
+			val batch = synchronized(lock) { takeAvailableBatch() }
+			if (batch != null) return batch
+		}
+	}
+
+	fun clear() {
+		synchronized(lock) {
+			entries.clear()
+			retainedChars = 0
+			while (available.tryReceive().isSuccess) {
+				// Discard stale wakeups from the cleared build session.
+			}
+		}
+	}
+
+	private fun takeAvailableBatch(): Batch? {
+		if (entries.isEmpty()) return null
+		val sessionToken = entries.first().sessionToken
+		val batch = StringBuilder(minOf(retainedChars, maxBatchChars))
+		var sourceChars = 0
+		var omittedLines = 0L
+		while (entries.isNotEmpty()) {
+			val entry = entries.first()
+			if (entry.sessionToken != sessionToken) break
+			if (entry is Entry.Text && batch.isNotEmpty() && batch.length + entry.value.length > maxBatchChars) break
+
+			entries.removeFirst()
+			when (entry) {
+				is Entry.Text -> {
+					batch.append(entry.value)
+					retainedChars -= entry.value.length
+					sourceChars = saturatedAdd(sourceChars, entry.value.length)
+				}
+				is Entry.Omission -> {
+					omittedLines += entry.lineCount
+					sourceChars = saturatedAdd(sourceChars, entry.sourceChars)
+				}
+			}
+		}
+		if (entries.isNotEmpty()) available.trySend(Unit)
+		return Batch(batch.toString(), sessionToken, sourceChars, omittedLines)
+	}
+
+	private fun lineCount(text: String): Long =
+		text.count { it == '\n' }.toLong() + if (text.endsWith('\n')) 0 else 1
+
+	private fun saturatedAdd(
+		left: Int,
+		right: Int,
+	): Int = (left.toLong() + right).coerceAtMost(Int.MAX_VALUE.toLong()).toInt()
+
+	companion object {
+		private const val DEFAULT_MAX_PENDING_CHARS = 256 * 1024
+		private const val DEFAULT_MAX_BATCH_CHARS = 32 * 1024
+	}
+}