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

package com.example.aiapp

import androidx.compose.foundation.background
import androidx.compose.foundation.clickable
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.Spacer
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.layout.width
import androidx.compose.foundation.shape.CornerSize
import androidx.compose.material3.CardDefaults
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
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.text.style.TextOverflow
import androidx.compose.ui.unit.dp

/**
 * A message another agent sent this session, closed until somebody asks.
 *
 * Closed by default, like a tool call and for the same reason: these are long, there can be several
 * in a row, and what a reader scanning the transcript needs from one is that it happened and who
 * sent it. The first line comes with the heading because a name alone does not say which message
 * this was.
 *
 * Drawn as its own kind rather than as the reader's own bubble. They did not say this, and a
 * transcript that puts it in their voice is making a claim about who asked for the work that
 * follows -- which is exactly the question a peer message is usually the answer to.
 *
 * Opened, the card is drawn in *pieces* -- this heading and one [PeerBlockRow] per markdown block,
 * each its own item of the transcript list. See [TranscriptUnit.PeerHead] for the measurements that
 * bought; what matters here is that the pieces have to add up to the card that was there before, so
 * the fill, the corner radius and the padding all live in [peerSurface] rather than being written
 * out at each piece.
 */
@Composable
fun PeerHeadRow(
    item: TranscriptItem.PeerNote,
    open: Boolean,
    onToggle: () -> Unit,
    modifier: Modifier = Modifier,
) {
    Column(
        modifier.cardPiece(
            top = true,
            bottom = !open,
            fill = CardDefaults.cardColors().containerColor,
            onPress = onToggle,
        )
    ) {
        Row(verticalAlignment = Alignment.CenterVertically) {
            Text("Message from ${item.from}", style = MaterialTheme.typography.titleSmall)
            if (!open) {
                Spacer(Modifier.width(8.dp))
                Text(
                    item.text.lineSequence().firstOrNull { it.isNotBlank() }.orEmpty(),
                    style = MaterialTheme.typography.bodySmall,
                    color = MaterialTheme.colorScheme.onSurfaceVariant,
                    maxLines = 1,
                    // The head, not the tail: a message is identified by how it opens.
                    overflow = TextOverflow.Ellipsis,
                )
            }
        }
    }
}

/**
 * One block of an opened peer message, on the same card the heading started.
 *
 * Clickable like the heading, so the card still shuts wherever it is pressed -- it was one control
 * before it was several items, and which piece the finger lands on is not something the reader
 * chose.
 */
@Composable
fun PeerBlockRow(unit: TranscriptUnit.PeerBlock, replies: ParsedReplies, onToggle: () -> Unit) {
    Column(
        Modifier.cardPiece(
            top = false,
            bottom = unit.last,
            fill = CardDefaults.cardColors().containerColor,
            onPress = onToggle,
        )
    ) {
        // The gap the card's own column used to provide between its heading and its prose, and
        // between one block and the next -- inside the piece, so the card's fill runs through it.
        MarkdownPiece(unit.text, unit.piece, replies, Modifier.padding(top = unit.spacing))
    }
}

/**
 * One piece of a card drawn in slices: the fill, the corners it owns, and the room inside it.
 *
 * A filled Material card is elevation zero ([CardDefaults] takes it from `FilledCardTokens`, which
 * is `Level0`), so there is no shadow that a seam would show through -- which is the whole reason a
 * card can be cut up at all. Each piece paints the caller's container colour the way a
 * [androidx.compose .material3.Card] would and rounds only the corners at the ends of the message,
 * so the pieces abut into one continuous card. Shared by the two rows that are cut this way -- an
 * opened peer message and a long user message -- because two copies of the corner logic is how one
 * of them grows a seam.
 *
 * The padding is the other half of it: 12dp all round was the card's own, so the top piece keeps
 * the top of it, the bottom piece the bottom, and the middle pieces neither.
 */
@Composable
fun Modifier.cardPiece(
    top: Boolean,
    bottom: Boolean,
    fill: Color,
    onPress: (() -> Unit)? = null,
): Modifier {
    val square = CornerSize(0.dp)
    val shape =
        MaterialTheme.shapes.medium.copy(
            topStart = if (top) MaterialTheme.shapes.medium.topStart else square,
            topEnd = if (top) MaterialTheme.shapes.medium.topEnd else square,
            bottomStart = if (bottom) MaterialTheme.shapes.medium.bottomStart else square,
            bottomEnd = if (bottom) MaterialTheme.shapes.medium.bottomEnd else square,
        )
    return fillMaxWidth()
        .clip(shape)
        .background(fill)
        .then(if (onPress == null) Modifier else Modifier.clickable(onClick = onPress))
        .padding(
            start = CARD_PADDING,
            end = CARD_PADDING,
            top = if (top) CARD_PADDING else 0.dp,
            bottom = if (bottom) CARD_PADDING else 0.dp,
        )
}

/** The room inside a sliced card, which was `Card { Column(padding(12.dp)) }`. */
private val CARD_PADDING = 12.dp