First working interface

lib/export/csv_exporter_base.dart

@@ -14,15 +14,15 @@ class ExportResult {
   final int bytesWritten;
 }
 
-/// Builds CSV row strings. Shared by both platform implementations so the
-/// row layout is defined exactly once.
-class CsvRowBuilder {
-  CsvRowBuilder(this.layout);
+/// Builds rows for the data CSV. Needs a layout to know which channels are
+/// enabled and what their column names should be.
+class CsvDataRowBuilder {
+  CsvDataRowBuilder(this.layout);
   final LayoutController layout;
 
-  /// Header row for data CSV. Disabled channels are omitted; pause and the
-  /// 8 status fields always appear.
-  String dataHeader() {
+  /// Header row. Disabled channels are omitted; pause and the 8 status
+  /// fields always appear.
+  String header() {
     final cols = <String>['timestamp_us'];
     for (var ch = 1; ch <= 16; ch++) {
       if (layout.configFor(ch).enabled) {
@@ -37,7 +37,7 @@ class CsvRowBuilder {
   }
 
   /// Row for one packet. Missing values are blank cells.
-  String dataRow(packet) {
+  String row(packet) {
     final cells = <String>[];
     cells.add(packet.hasTimestampUs() ? packet.timestampUs.toString() : '');
     for (var ch = 1; ch <= 16; ch++) {
@@ -51,16 +51,6 @@ class CsvRowBuilder {
     return cells.join(',');
   }
 
-  String logHeader() => 'timestamp_us,severity,error_number,description';
-
-  String logRow(entry) {
-    final ts = entry.hasTimestampUs() ? entry.timestampUs.toString() : '';
-    final sev = entry.hasSeverity() ? entry.severity.name : '';
-    final err = entry.hasErrorNumber() ? entry.errorNumber.toString() : '';
-    final desc = entry.hasDescription() ? _escape(entry.description) : '';
-    return '$ts,$sev,$err,$desc';
-  }
-
   static String _channelCell(packet, int ch) {
     switch (ch) {
       case 1:  return packet.hasCh1()  ? packet.ch1.toString()  : '';
@@ -99,6 +89,22 @@ class CsvRowBuilder {
 
   /// Strip characters that would break CSV column names.
   static String _safe(String s) => s.replaceAll(RegExp(r'[,\s]+'), '_');
+}
+
+/// Builds rows for the log CSV. Takes no layout — log output is
+/// fully determined by the `LogPacket` itself.
+class CsvLogRowBuilder {
+  const CsvLogRowBuilder();
+
+  String header() => 'timestamp_us,severity,error_number,description';
+
+  String row(entry) {
+    final ts = entry.hasTimestampUs() ? entry.timestampUs.toString() : '';
+    final sev = entry.hasSeverity() ? entry.severity.name : '';
+    final err = entry.hasErrorNumber() ? entry.errorNumber.toString() : '';
+    final desc = entry.hasDescription() ? _escape(entry.description) : '';
+    return '$ts,$sev,$err,$desc';
+  }
 
   /// Escape a free-form field for CSV. Wraps in quotes if needed.
   static String _escape(String s) {

lib/export/csv_exporter_io.dart

@@ -20,16 +20,16 @@ class CsvExporterImpl implements CsvExporter {
     required LayoutController layout,
     ProgressCallback? onProgress,
   }) async {
-    final builder = CsvRowBuilder(layout);
+    final builder = CsvDataRowBuilder(layout);
     final dir = await getApplicationDocumentsDirectory();
     final ts = DateTime.now().toIso8601String().replaceAll(':', '-');
     final file = File('${dir.path}/telemetry_data_$ts.csv');
     final sink = file.openWrite();
-    sink.writeln(builder.dataHeader());
+    sink.writeln(builder.header());
     final total = buffer.length;
     var written = 0;
     for (var i = 0; i < total; i++) {
-      sink.writeln(builder.dataRow(buffer[i]));
+      sink.writeln(builder.row(buffer[i]));
       written++;
       if (written % _chunkRows == 0) {
         onProgress?.call(written / total);
@@ -51,17 +51,16 @@ class CsvExporterImpl implements CsvExporter {
     required LogBuffer buffer,
     ProgressCallback? onProgress,
   }) async {
-    // Logs don't need a layout to format (no column projection).
     final dir = await getApplicationDocumentsDirectory();
     final ts = DateTime.now().toIso8601String().replaceAll(':', '-');
     final file = File('${dir.path}/telemetry_log_$ts.csv');
     final sink = file.openWrite();
-    final builder = CsvRowBuilder(_NoLayoutPlaceholder());
-    sink.writeln(builder.logHeader());
+    const builder = CsvLogRowBuilder();
+    sink.writeln(builder.header());
     final total = buffer.length;
     var written = 0;
     for (final entry in buffer.iterate()) {
-      sink.writeln(builder.logRow(entry));
+      sink.writeln(builder.row(entry));
       written++;
       if (written % _chunkRows == 0) {
         onProgress?.call(written / total);
@@ -77,10 +76,3 @@ class CsvExporterImpl implements CsvExporter {
     );
   }
 }
-
-/// CsvRowBuilder.logRow doesn't actually need a layout. We pass a placeholder
-/// so we don't have to plumb a real one through for log-only exports.
-class _NoLayoutPlaceholder implements LayoutController {
-  @override
-  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
-}

lib/export/csv_exporter_web.dart

@@ -22,14 +22,14 @@ class CsvExporterImpl implements CsvExporter {
     required LayoutController layout,
     ProgressCallback? onProgress,
   }) async {
-    final builder = CsvRowBuilder(layout);
+    final builder = CsvDataRowBuilder(layout);
     final chunks = <String>[];
-    chunks.add('${builder.dataHeader()}\n');
+    chunks.add('${builder.header()}\n');
     final total = buffer.length;
     final sb = StringBuffer();
     var written = 0;
     for (var i = 0; i < total; i++) {
-      sb.writeln(builder.dataRow(buffer[i]));
+      sb.writeln(builder.row(buffer[i]));
       written++;
       if (written % _chunkRows == 0) {
         chunks.add(sb.toString());
@@ -53,14 +53,14 @@ class CsvExporterImpl implements CsvExporter {
     required LogBuffer buffer,
     ProgressCallback? onProgress,
   }) async {
-    final builder = CsvRowBuilder(_NoLayoutPlaceholder());
+    const builder = CsvLogRowBuilder();
     final chunks = <String>[];
-    chunks.add('${builder.logHeader()}\n');
+    chunks.add('${builder.header()}\n');
     final total = buffer.length;
     final sb = StringBuffer();
     var written = 0;
     for (final entry in buffer.iterate()) {
-      sb.writeln(builder.logRow(entry));
+      sb.writeln(builder.row(entry));
       written++;
       if (written % _chunkRows == 0) {
         chunks.add(sb.toString());
@@ -104,8 +104,3 @@ class CsvExporterImpl implements CsvExporter {
     html.Url.revokeObjectUrl(url);
   }
 }
-
-class _NoLayoutPlaceholder implements LayoutController {
-  @override
-  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
-}