package com.suno.android.ui.screens.orpheus

import androidx.compose.foundation.layout.WindowInsets
import androidx.compose.foundation.layout.ime
import androidx.compose.foundation.lazy.LazyListState
import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.derivedStateOf
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableIntStateOf
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.runtime.snapshotFlow
import androidx.compose.ui.platform.LocalDensity
import com.suno.android.common_data.repos.orpheus.models.OrpheusMessage

@Composable
@Suppress("MagicNumber")
internal fun ChatAutoScrollEffect(
    listState: LazyListState,
    messages: List<OrpheusMessage>,
) {
    var userManuallyScrolledUp by remember { mutableStateOf(false) }
    val isScrollingUp = listState.isScrollingUp()
    val isAtBottom by remember(listState) {
        derivedStateOf {
            val lastVisibleItem = listState.layoutInfo.visibleItemsInfo.lastOrNull()
            lastVisibleItem?.index == listState.layoutInfo.totalItemsCount - 1
        }
    }

    // Track user scroll behavior
    LaunchedEffect(isScrollingUp, isAtBottom) {
        when {
            isScrollingUp -> userManuallyScrolledUp = true
            isAtBottom -> userManuallyScrolledUp = false
        }
    }

    // Auto-scroll when keyboard appears
    val density = LocalDensity.current
    val imeInsets = WindowInsets.ime
    LaunchedEffect(messages.size) {
        snapshotFlow { imeInsets.getBottom(density) }
            .collect { imeBottom ->
                if (imeBottom > 0 && messages.isNotEmpty()) {
                    userManuallyScrolledUp = false
                    listState.scrollToItem(messages.lastIndex)
                }
            }
    }

    // Auto-scroll when message content changes (streaming) or clips are added
    val lastMessage = messages.lastOrNull()
    LaunchedEffect(messages.size, lastMessage?.content, lastMessage?.generatedClips?.size) {
        if (!userManuallyScrolledUp && listState.canScrollForward && messages.isNotEmpty()) {
            listState.scrollToItem(messages.lastIndex, 1000)
        }
    }
}

@Composable
private fun LazyListState.isScrollingUp(): Boolean {
    var previousIndex by remember(this) { mutableIntStateOf(firstVisibleItemIndex) }
    var previousScrollOffset by remember(this) { mutableIntStateOf(firstVisibleItemScrollOffset) }
    return remember(this) {
        derivedStateOf {
            if (previousIndex != firstVisibleItemIndex) {
                previousIndex > firstVisibleItemIndex
            } else {
                previousScrollOffset > firstVisibleItemScrollOffset
            }.also {
                previousIndex = firstVisibleItemIndex
                previousScrollOffset = firstVisibleItemScrollOffset
            }
        }
    }.value
}