Read lines as sequence from the given stream or reader.

LineSequence.kt

/**
 * Read the [InputStream] and yield a [CharSequence] every time a new line is found.
 *
 * @receiver The [InputStream] to parse.
 * @return a sequence of each line in the stream. (without new lines)
 */
fun InputStream.lineSequence(): Sequence<CharSequence> = lineSequence { read() }
fun Reader.lineSequence(): Sequence<CharSequence> = lineSequence { read() }

/**
 * Returns a sequence of lines parsed from the [characterProvider].
 *
 * @param characterProvider A function that provides characters in the stream as integers.
 * @return A sequence of String without new line.
 */
private fun lineSequence(characterProvider: () -> Int) = sequence {
    val buffer = StringBuilder()
    var peek: Int? = null

    fun peek(): Int {
        if (peek != null) return peek!!
        peek = characterProvider()
        return peek!!
    }

    fun consume() {
        peek = null
    }

    fun next() = peek().also { consume() }

    while (true) {
        val current = next()
        if (current == -1) break
        when (val char = current.toChar()) {
            '\n' -> {
                yield(buffer.toString())
                buffer.clear()
            }

            '\r' -> {
                if (peek().toChar() == '\n') consume()
                yield(buffer.toString())
                buffer.clear()
            }

            else -> buffer.append(char)
        }
    }

    yield(buffer.toString())
    buffer.clear()
}