ai-app/app/androidApp/src/main/kotlin/com/example/aiapp/SessionImage.kt

package com.example.aiapp

import android.graphics.BitmapFactory
import androidx.compose.foundation.Image
import androidx.compose.foundation.background
import androidx.compose.foundation.clickable
import androidx.compose.foundation.gestures.detectTransformGestures
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.height
import androidx.compose.foundation.layout.size
import androidx.compose.material3.CircularProgressIndicator
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableFloatStateOf
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clip
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.graphics.FilterQuality
import androidx.compose.ui.graphics.ImageBitmap
import androidx.compose.ui.graphics.asImageBitmap
import androidx.compose.ui.graphics.graphicsLayer
import androidx.compose.ui.input.pointer.pointerInput
import androidx.compose.ui.layout.ContentScale
import androidx.compose.ui.platform.LocalDensity
import androidx.compose.ui.unit.Dp
import androidx.compose.ui.unit.dp
import androidx.compose.ui.unit.isSpecified
import androidx.compose.ui.window.Dialog
import androidx.compose.ui.window.DialogProperties
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.withContext

/**
 * One image from the session's files route: the bitmap once it arrives, and whether it never will.
 *
 * [failed] exists because the two empty states differ in kind -- still coming and never coming --
 * and a reader can act on the second; each caller supplies its own words for them.
 */
data class SessionBitmap(val bitmap: ImageBitmap?, val failed: Boolean)

/**
 * Fetches (authenticated, pinned) and decodes one transcript image, remembered per ref so scrolling
 * does not refetch.
 *
 * Shared by the transcript's images and the composer's pending attachments, because the fetch, the
 * decode and the two-state answer are one block of logic that had been written twice.
 */
@Composable
fun rememberSessionBitmap(settings: ServerSettings, sessionId: String, ref: String): SessionBitmap {
    var state by remember(ref) { mutableStateOf(SessionBitmap(null, failed = false)) }
    LaunchedEffect(ref) {
        state =
            try {
                val bytes =
                    withContext(Dispatchers.IO) { fetchSessionFile(settings, sessionId, ref) }
                val decoded = BitmapFactory.decodeByteArray(bytes, 0, bytes.size)?.asImageBitmap()
                SessionBitmap(decoded, failed = decoded == null)
            } catch (_: ApiException) {
                SessionBitmap(null, failed = true)
            }
    }
    return state
}

/**
 * An image in the transcript: a fixed-height thumbnail that opens full screen.
 *
 * The height is decided before the bytes arrive and never changes. An image row that grew when it
 * finished loading pushed everything below it, so a transcript being read scrolled itself while
 * somebody was looking at it -- and in a bottom-anchored list, images loading above the viewport
 * moved the text under the reader's eyes. Reserving the final height makes loading invisible, which
 * is what it should be.
 *
 * Four lines of body text, so a screenshot reads as an attachment beside the conversation rather
 * than as a page of its own. Full size is one tap away -- but the full-size view itself is not
 * here. [onOpen] hands the ref to the screen, which draws [SessionImageViewer] outside the list;
 * see that function for the reason.
 */
@Composable
fun SessionImage(
    settings: ServerSettings,
    sessionId: String,
    ref: String,
    onOpen: (String) -> Unit,
) {
    val (bitmap, failed) = rememberSessionBitmap(settings, sessionId, ref)
    val height = thumbnailHeight()
    val heightPx = with(LocalDensity.current) { height.roundToPx() }
    Box(Modifier.fillMaxWidth().height(height), contentAlignment = Alignment.CenterStart) {
        when (val image = bitmap) {
            // Two states, not one: an image still arriving and an image that will never arrive
            // look nothing alike to a reader who can do something about the second. So one gets a
            // spinner in the space the picture is about to fill, and the other gets words.
            null ->
                if (failed) {
                    Text(
                        "[image $ref unavailable]",
                        style = MaterialTheme.typography.bodySmall,
                        color = MaterialTheme.colorScheme.onSurfaceVariant,
                    )
                } else {
                    LoadingImage(height)
                }
            else ->
                Image(
                    bitmap = image,
                    contentDescription = "Attached image, tap to view full screen",
                    contentScale = ContentScale.Fit,
                    filterQuality = enlargingFilter(image.height, heightPx),
                    modifier = Modifier.fillMaxSize().clickable { onOpen(ref) },
                    alignment = Alignment.CenterStart,
                )
        }
    }
}

/**
 * The image somebody opened, drawn by the screen rather than by the row it was tapped in.
 *
 * The row is the wrong place to hold this, and it took a real fault to see why: an image from a
 * `Read` on its own is a row of one call, and the moment the next call arrives the two become a
 * group -- a different composable in a different part of the tree, so everything the old subtree
 * remembered goes, the dialog included. Somebody looking at a screenshot was thrown back to the
 * transcript because the session made another tool call. The same happens to a row regrouped by a
 * page of history landing.
 *
 * Held by the screen, none of that reaches it: what is open is a property of the screen, not of
 * whichever row happened to draw the thumbnail.
 *
 * The cost is one fetch, since the thumbnail's decoded bitmap belongs to a row this does not go
 * through. Paid deliberately rather than plumbed around: it is one request for a picture somebody
 * asked to see, and the loading and unavailable states below are the same two the thumbnail draws.
 */
@Composable
fun SessionImageViewer(
    settings: ServerSettings,
    sessionId: String,
    ref: String,
    onClose: () -> Unit,
) {
    val (bitmap, failed) = rememberSessionBitmap(settings, sessionId, ref)
    Dialog(
        onDismissRequest = onClose,
        properties = DialogProperties(usePlatformDefaultWidth = false),
    ) {
        Box(
            Modifier.fillMaxSize().background(Color.Black).clickable(onClick = onClose),
            contentAlignment = Alignment.Center,
        ) {
            when (val image = bitmap) {
                // Two states, not one, exactly as the thumbnail has them: still coming, and never
                // coming. Stated in white because this box paints its own black behind them and a
                // theme colour would be picked against a surface that is not there.
                null ->
                    if (failed) {
                        Text(
                            "Image $ref is unavailable",
                            color = Color.White,
                            style = MaterialTheme.typography.bodyMedium,
                        )
                    } else {
                        // The whole dialog is the area this picture is about to fill, so the
                        // spinner sits in the middle of it. White for the same reason the words
                        // beside it are: this box paints its own black, and a theme colour would
                        // be chosen against a surface that is not there.
                        CircularProgressIndicator(color = Color.White)
                    }
                else -> ZoomableImage(image)
            }
        }
    }
}

/**
 * The room a picture is about to take, with a spinner in the middle of it.
 *
 * A square of the row's own height rather than the full width of the transcript: the height is what
 * [SessionImage] reserves and the width is not known until the bytes arrive, so a full-width
 * placeholder would promise a picture wider than most of them turn out to be. Square is the closest
 * thing to "the size of it" that can be drawn before knowing.
 *
 * Tinted, so the reader can see that something is being kept for a picture. That is also what
 * distinguishes it from the failure beside it, which is words on the ordinary surface.
 */
@Composable
private fun LoadingImage(height: Dp) {
    Box(
        Modifier.size(height)
            .clip(MaterialTheme.shapes.small)
            .background(MaterialTheme.colorScheme.surfaceContainerHigh),
        contentAlignment = Alignment.Center,
    ) {
        CircularProgressIndicator(Modifier.size(LOADING_SPINNER), strokeWidth = 2.dp)
    }
}

/** Small enough to sit inside the thumbnail's square without filling it. */
private val LOADING_SPINNER = 24.dp

/**
 * Four lines of the body style the transcript is set in.
 *
 * Measured from the type rather than written as a dp, so it stays four lines when the text size
 * changes -- including when the reader has scaled fonts up, which is exactly when a hardcoded
 * height would be wrong.
 */
@Composable
private fun thumbnailHeight(): Dp {
    val line = MaterialTheme.typography.bodyLarge.lineHeight
    val density = LocalDensity.current
    return remember(line, density) {
        with(density) { if (line.isSpecified) (line * 4).toDp() else 96.dp }
    }
}

/**
 * Nearest neighbour when the image is being enlarged, smooth when it is being shrunk.
 *
 * A small image blown up with interpolation turns into a blur that hides what it is -- the same
 * image with hard pixel edges stays readable. Shrinking wants the opposite, so this is a decision
 * per image rather than a preference set once.
 */
private fun enlargingFilter(sourceHeight: Int, drawnHeight: Int): FilterQuality =
    if (sourceHeight < drawnHeight) FilterQuality.None else FilterQuality.High

/**
 * The image on its own, as large as it fits, with pinch to zoom.
 *
 * Inside a dialog rather than a screen -- see [SessionImageViewer] -- so the platform's back
 * gesture returns to the transcript instead of leaving the app. It opens fitted, the whole image
 * visible, which is the thing a reader wants first; zoom is theirs from there.
 */
@Composable
private fun ZoomableImage(image: ImageBitmap) {
    var scale by remember { mutableFloatStateOf(1f) }
    var offsetX by remember { mutableFloatStateOf(0f) }
    var offsetY by remember { mutableFloatStateOf(0f) }
    Image(
        bitmap = image,
        contentDescription = "Attached image",
        contentScale = ContentScale.Fit,
        // Zoomed in, the reader is looking at pixels on purpose.
        filterQuality = FilterQuality.None,
        modifier =
            Modifier.fillMaxSize()
                .pointerInput(Unit) {
                    detectTransformGestures { _, pan, zoom, _ ->
                        // Floor of 1 so the image cannot be pinched smaller than fitted, which is
                        // already the whole of it; a ceiling so it cannot be lost off-screen.
                        scale = (scale * zoom).coerceIn(1f, 8f)
                        if (scale > 1f) {
                            offsetX += pan.x
                            offsetY += pan.y
                        } else {
                            offsetX = 0f
                            offsetY = 0f
                        }
                    }
                }
                .graphicsLayer {
                    scaleX = scale
                    scaleY = scale
                    translationX = offsetX
                    translationY = offsetY
                },
    )
}