Flow window function for log event flows -> lazy list UI

Window.kt

package com.android.atool.ui

import kotlinx.coroutines.channels.BufferOverflow.DROP_LATEST
import kotlinx.coroutines.flow.buffer
import kotlinx.coroutines.flow.channelFlow
import kotlinx.coroutines.flow.Flow

/**
 * Creates a [Flow] that emits sliding windows of the elements from the original [Flow].
 * Each emitted list represents a window of the specified [length]. The window starts with
 * the first emitted value, emitting a list of size 1, and grows until it reaches [length].
 *
 * The window slides by one element at a time. For example, if the original flow
 * emits `[1, 2, 3, 4, 5]` and `length` is 3, the resulting flow will emit:
 * `[1]`, `[1, 2]`, `[1, 2, 3]`, `[2, 3, 4]`, `[3, 4, 5]`.
 *
 * The latest result is buffered and replaced as needed to avoid overwhelming
 * downstream collectors when the source flow produces rapidly.
 *
 * @param length The size of each window. Must be greater than 0.
 * @return A [Flow] emitting lists of size [length], representing the sliding windows.
 * @throws IllegalArgumentException if [length] is not greater than 0.
 */
fun <T> Flow<T>.window(length: Int): Flow<List<T>> {
    require(length > 0) { "length must be greater than 0, but was $length" }

    return channelFlow {
        val buffer = ArrayDeque<T>(maxOf(length + 1, 16))

        this@window.collect { value ->
            buffer.addLast(value)
            if (buffer.size > length) {
                buffer.removeFirst()
            }
            send(buffer.toList())
        }
    }
        .buffer(capacity = 1, onBufferOverflow = DROP_LATEST)
}