RainbowLayout.kt

import androidx.compose.animation.RectPropKey
import androidx.compose.animation.core.FloatPropKey
import androidx.compose.animation.core.keyframes
import androidx.compose.animation.core.transitionDefinition
import androidx.compose.animation.core.tween
import androidx.compose.animation.transition
import androidx.compose.foundation.Canvas
import androidx.compose.foundation.Image
import androidx.compose.foundation.Text
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.material.Surface
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.ChatBubble
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clip
import androidx.compose.ui.draw.drawOpacity
import androidx.compose.ui.draw.drawShadow
import androidx.compose.ui.geometry.Offset
import androidx.compose.ui.geometry.Radius
import androidx.compose.ui.geometry.Rect
import androidx.compose.ui.geometry.Size
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.platform.DensityAmbient
import androidx.compose.ui.unit.Dp
import androidx.compose.ui.unit.dp
import androidx.ui.tooling.preview.Preview

private val circleSize = 60.dp
private val expandedSize = 300.dp

enum class IndicatorState { Collapsed, Expanded }

data class AnimationProperties(
    val size: RectPropKey,
    val colors: List<Color>,
    val colorSizes: List<RectPropKey>,
    val elevation: FloatPropKey,
    val contentAlpha: FloatPropKey
)

fun createProperties(colors: List<Color>): AnimationProperties {
    return AnimationProperties(
        size = RectPropKey("Container size"),
        elevation = FloatPropKey("Elevation"),
        colors = colors,
        colorSizes = colors.mapIndexed { index, _ ->
            RectPropKey("Animated color size $index")
        },
        contentAlpha = FloatPropKey("Content alpha")
    )
}

fun rect(w: Float, h: Float) = Rect(Offset(0), Size(w, h))

fun colorsTransition(
    properties: AnimationProperties,
    width: Float,
    height: Float,
) = transitionDefinition<IndicatorState> {

    val zero = rect(0f, 0f)
    val expanded = rect(width, height)

    state(IndicatorState.Collapsed) {
        this[properties.size] = zero
        this[properties.elevation] = 0f
        this[properties.contentAlpha] = 0f
        properties.colorSizes.forEach { this[it] = zero }
    }
    state(IndicatorState.Expanded) {
        this[properties.size] = expanded
        this[properties.elevation] = 32f
        this[properties.contentAlpha] = 1f
        properties.colorSizes.forEach { this[it] = expanded }
    }

    val n = properties.colors.size
    val breakpoints = (1..n+2).map { 150 * it }
    val offset = 100

    transition(fromState = IndicatorState.Collapsed, toState = IndicatorState.Expanded) {
        properties.elevation using keyframes { 0f at breakpoints[0] }
        properties.size using keyframes {
            rect(w = height, h = height) at breakpoints[0]
            durationMillis = breakpoints[1]
        }
        properties.colorSizes.forEachIndexed { index, sizeProperty ->
            sizeProperty using keyframes {
                val start = index + 2
                var remaining = start
                while(remaining > 0) {
                    val size = height / remaining
                    val time = breakpoints[start - remaining] - if(remaining != start) offset else 0
                    rect(size, size) at time
                    remaining -= 1
                }
                durationMillis = breakpoints[start]
            }
        }
        properties.contentAlpha using tween(
            delayMillis = breakpoints.last(),
            durationMillis = 300
        )
    }
}


@Composable
fun RainbowLayout(
    modifier: Modifier = Modifier,
    background: Color = Color.White,
    animatedColors: List<Color> = emptyList(),
    content: @Composable RowScope.()->Unit = { }
) {
    val circleSizePx = with(DensityAmbient.current) { circleSize.toPx() }
    val expandedSizePx = with(DensityAmbient.current) { expandedSize.toPx() }

    val properties = remember { createProperties(animatedColors) }
    val transition = transition(
        definition = remember { colorsTransition(properties, expandedSizePx, circleSizePx) },
        initState = IndicatorState.Collapsed,
        toState = IndicatorState.Expanded
    )

    val contentSize = transition[properties.size].size
    val contentSizeW = with(DensityAmbient.current) { contentSize.width.toDp() }
    val contentSizeH = with(DensityAmbient.current) { contentSize.height.toDp() }

    val shape = RoundedCornerShape(50)

    Box(modifier
        .width(contentSizeW.coerceAtLeast(circleSize))
        .height(contentSizeH.coerceAtLeast(circleSize))
        .drawShadow(elevation = Dp(transition[properties.elevation]), shape = shape)
    ) {
        Canvas(Modifier
            .align(Alignment.Center)
            .width(contentSizeW)
            .height(contentSizeH)
            .clip(shape)
            .background(background)
        ) {

            fun centerFor(rect: Size) = Offset(center.x - rect.width / 2, center.y - rect.height / 2)
            fun radiusFor(rect: Size) = Radius(rect.height / 2)

            animatedColors.forEachIndexed { i, color ->
                val size = transition[properties.colorSizes[i]].size
                drawRoundRect(
                    color = color,
                    topLeft = centerFor(size),
                    size = size,
                    radius = radiusFor(size)
                )
            }

        }

        val contentAlpha = transition[properties.contentAlpha]
        if(contentAlpha != 0f) {
            Row(
                modifier = Modifier.fillMaxSize().drawOpacity(contentAlpha),
                horizontalArrangement = Arrangement.Center,
                verticalAlignment = Alignment.CenterVertically,
            ) {
                content()
            }
        }

    }
}

@Preview
@Composable
private fun RainbowLayoutPreview() {
    Surface(Modifier.fillMaxSize(), color = Color.White) {
        Column(horizontalAlignment = Alignment.CenterHorizontally) {
            Spacer(Modifier.height(8.dp))
            RainbowLayout(animatedColors = listOf(
                Color(0xFF820263),
                Color(0xFFD90368),
                Color(0xFFEADEDA),
            )) {
                Image(asset = Icons.Filled.ChatBubble)
                Spacer(Modifier.width(16.dp))
                Text("Chat")
            }
            Spacer(Modifier.height(8.dp))
            RainbowLayout(
                background = Color(0xFF2C2846),
                animatedColors = listOf(
                    Color(0xFF3A726F),
                    Color(0xFF88B387),
                    Color.White
                )
            ) {
                Text("Test 1")
            }
            Spacer(Modifier.height(8.dp))
            RainbowLayout(animatedColors = listOf(
                Color(0xFF684551),
                Color(0xFFD5B0AC),
                Color(0xFFCEA0AE),
            )) {
                Text("Test 2")
            }
        }
    }
}