Preview diagram and PDF before sharing (iOS + Android)

iOS: route exports through QLPreviewController so users can inspect
before sharing. Android: add a zoomable full-screen diagram preview
with a share button; PDF still goes straight to the share sheet.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

android/app/src/main/java/app/voltplan/cable/pdf/SystemDiagram.kt

@@ -87,16 +87,20 @@ object SystemDiagram {
         onError: () -> Unit,
     ) {
         val bitmap = fetchOrFallback(context, state, unit)
+        share(context, bitmap, state.system?.name ?: "System")
+    }
+
+    suspend fun share(context: Context, bitmap: Bitmap, systemName: String) {
         val file = withContext(Dispatchers.IO) {
             val opaque = flattenOnWhite(bitmap)
-            val name = state.system?.name?.takeIf { it.isNotBlank() } ?: "System"
+            val name = systemName.takeIf { it.isNotBlank() } ?: "System"
             val dir = File(context.cacheDir, "exports").apply { mkdirs() }
             val out = File(dir, "${name.replace(Regex("[^A-Za-z0-9-_]"), "_")}-Diagram.png")
             out.outputStream().use { opaque.compress(Bitmap.CompressFormat.PNG, 100, it) }
             out
         }
         withContext(Dispatchers.Main) {
-            Analytics.log("Diagram Image Shared", mapOf("system" to (state.system?.name ?: "")))
+            Analytics.log("Diagram Image Shared", mapOf("system" to systemName))
             PdfShare.shareFile(context, file, "image/png")
         }
     }

android/app/src/main/java/app/voltplan/cable/ui/system/DiagramPreviewDialog.kt

@@ -0,0 +1,103 @@
+package app.voltplan.cable.ui.system
+
+import android.graphics.Bitmap
+import androidx.compose.foundation.Image
+import androidx.compose.foundation.gestures.rememberTransformableState
+import androidx.compose.foundation.gestures.transformable
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.outlined.ArrowBack
+import androidx.compose.material.icons.outlined.IosShare
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
+import androidx.compose.material3.TopAppBar
+import androidx.compose.runtime.Composable
+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.geometry.Offset
+import androidx.compose.ui.graphics.asImageBitmap
+import androidx.compose.ui.graphics.graphicsLayer
+import androidx.compose.ui.layout.ContentScale
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.window.Dialog
+import androidx.compose.ui.window.DialogProperties
+import app.voltplan.cable.R
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun DiagramPreviewDialog(
+    bitmap: Bitmap,
+    onShare: () -> Unit,
+    onDismiss: () -> Unit,
+) {
+    Dialog(
+        onDismissRequest = onDismiss,
+        properties = DialogProperties(usePlatformDefaultWidth = false),
+    ) {
+        Surface(
+            modifier = Modifier.fillMaxSize(),
+            color = MaterialTheme.colorScheme.background,
+        ) {
+            Scaffold(
+                topBar = {
+                    TopAppBar(
+                        title = { Text(stringResource(R.string.overview_share_diagram)) },
+                        navigationIcon = {
+                            IconButton(onClick = onDismiss) {
+                                Icon(Icons.AutoMirrored.Outlined.ArrowBack, contentDescription = stringResource(R.string.action_back))
+                            }
+                        },
+                        actions = {
+                            IconButton(onClick = onShare) {
+                                Icon(Icons.Outlined.IosShare, contentDescription = stringResource(R.string.overview_share_diagram))
+                            }
+                        },
+                    )
+                },
+            ) { padding ->
+                var scale by remember { mutableFloatStateOf(1f) }
+                var offset by remember { mutableStateOf(Offset.Zero) }
+                val transformState = rememberTransformableState { zoomChange, panChange, _ ->
+                    scale = (scale * zoomChange).coerceIn(1f, 8f)
+                    offset = if (scale == 1f) Offset.Zero else offset + panChange
+                }
+
+                Box(
+                    modifier = Modifier
+                        .fillMaxSize()
+                        .padding(padding)
+                        .transformable(transformState),
+                    contentAlignment = Alignment.Center,
+                ) {
+                    Image(
+                        bitmap = bitmap.asImageBitmap(),
+                        contentDescription = stringResource(R.string.overview_share_diagram),
+                        contentScale = ContentScale.Fit,
+                        modifier = Modifier
+                            .fillMaxSize()
+                            .padding(16.dp)
+                            .graphicsLayer(
+                                scaleX = scale,
+                                scaleY = scale,
+                                translationX = offset.x,
+                                translationY = offset.y,
+                            ),
+                    )
+                }
+            }
+        }
+    }
+}

android/app/src/main/java/app/voltplan/cable/ui/system/SystemDetailScreen.kt

@@ -54,6 +54,7 @@ import app.voltplan.cable.ui.theme.componentColor
 import app.voltplan.cable.data.ReviewPrompt
 import app.voltplan.cable.pdf.SystemDiagram
 import app.voltplan.cable.pdf.SystemOverviewPdf
+import android.graphics.Bitmap
 import android.widget.Toast
 import androidx.compose.material3.CircularProgressIndicator
 import androidx.compose.material3.DropdownMenu
@@ -106,6 +107,7 @@ fun SystemDetailScreen(
     var showSystemEditor by remember { mutableStateOf(false) }
     var showOverviewMenu by remember { mutableStateOf(false) }
     var exporting by remember { mutableStateOf(false) }
+    var diagramBitmapPreview by remember { mutableStateOf<Bitmap?>(null) }
     val system = state.system
 
     // Switch to the matching tab before opening an editor, so returning from the
@@ -167,13 +169,9 @@ fun SystemDetailScreen(
                                         showOverviewMenu = false
                                         scope.launch {
                                             exporting = true
-                                            var failed = false
-                                            SystemDiagram.exportAndShare(context, state, unitSystem) {
-                                                failed = true
-                                                Toast.makeText(context, R.string.overview_share_diagram_error, Toast.LENGTH_LONG).show()
-                                            }
+                                            val bitmap = SystemDiagram.fetchOrFallback(context, state, unitSystem)
                                             exporting = false
-                                            if (!failed) ReviewPrompt.registerSuccessfulExport(context)
+                                            diagramBitmapPreview = bitmap
                                         }
                                     },
                                 )
@@ -256,6 +254,20 @@ fun SystemDetailScreen(
         }
     }
 
+    diagramBitmapPreview?.let { bmp ->
+        DiagramPreviewDialog(
+            bitmap = bmp,
+            onShare = {
+                scope.launch {
+                    SystemDiagram.share(context, bmp, state.system?.name ?: "System")
+                    diagramBitmapPreview = null
+                    ReviewPrompt.registerSuccessfulExport(context)
+                }
+            },
+            onDismiss = { diagramBitmapPreview = null },
+        )
+    }
+
     if (showSystemEditor && system != null) {
         var location by remember { mutableStateOf(system.location) }
         AppearanceEditorSheet(