fix(download): compare size estimates at each quality tier

lib/l10n/arb/app_en.arb

@@ -2129,7 +2129,7 @@
   },
   "downloadEstimatedSize": "≈ {size}",
   "@downloadEstimatedSize": {
-    "description": "Approximate audio file size, or total for all selected tracks; size includes units and may be a range",
+    "description": "Approximate audio file size, or total for all selected tracks; size includes units",
     "placeholders": {
       "size": {
         "type": "String"
@@ -2137,7 +2137,19 @@
     }
   },
   "downloadSizeUnavailable": "Size estimate unavailable",
-  "downloadSizeEstimateNote": "Estimated audio size before conversion, excluding artwork and tags. Actual size varies with quality and compression; data usage may be higher.",
+  "downloadEstimatedSizeAtQuality": "≈ {size} if {quality}",
+  "@downloadEstimatedSizeAtQuality": {
+    "description": "Conditional size estimate for a tier with an unknown actual quality; quality is the assumed bit depth and sample rate",
+    "placeholders": {
+      "size": {
+        "type": "String"
+      },
+      "quality": {
+        "type": "String"
+      }
+    }
+  },
+  "downloadSizeEstimateNote": "Estimates assume the quality shown. Lower quality can produce smaller files; compression also affects size. Excludes artwork and tags. Data usage may be higher.",
   "downloadConvertedSizeEstimate": "After conversion to {format}: {size}",
   "@downloadConvertedSizeEstimate": {
     "description": "Estimated size after the user's automatic conversion, excluding tags and artwork",

lib/l10n/arb/app_id.arb

@@ -6200,6 +6200,7 @@
   "libraryFilterMetadataMissingIsrc": "Missing ISRC",
   "downloadEstimatedSize": "≈ {size}",
   "downloadSizeUnavailable": "Estimasi ukuran belum tersedia",
-  "downloadSizeEstimateNote": "Perkiraan ukuran audio sebelum konversi, tanpa sampul dan tag. Ukuran sebenarnya bergantung pada kualitas dan kompresi; penggunaan data bisa lebih besar.",
+  "downloadEstimatedSizeAtQuality": "≈ {size} jika {quality}",
+  "downloadSizeEstimateNote": "Estimasi memakai kualitas yang tertera. Kualitas lebih rendah bisa menghasilkan file lebih kecil; kompresi juga memengaruhi ukuran. Tanpa sampul dan tag. Penggunaan data bisa lebih besar.",
   "downloadConvertedSizeEstimate": "Setelah konversi ke {format}: {size}"
 }

lib/utils/download_size_estimate.dart

@@ -1,13 +1,16 @@
-import 'dart:math' as math;
-
 import 'package:spotiflac_android/models/track.dart';
 import 'package:spotiflac_android/providers/extension_provider.dart';
 
 class DownloadSizeEstimate {
-  final int minBytes;
-  final int maxBytes;
+  final int bytes;
+  final int? assumedBitDepth;
+  final int? assumedSampleRate;
 
-  const DownloadSizeEstimate({required this.minBytes, required this.maxBytes});
+  const DownloadSizeEstimate({
+    required this.bytes,
+    this.assumedBitDepth,
+    this.assumedSampleRate,
+  });
 }
 
 /// Unknown durations must not make a batch estimate look like a complete total.
@@ -32,7 +35,7 @@ DownloadSizeEstimate? estimateDownloadSize({
   if (bitrate != null) {
     if (bitrate <= 0 || parameters.isMaximum) return null;
     final bytes = (seconds * bitrate * 1000 / 8).round();
-    return DownloadSizeEstimate(minBytes: bytes, maxBytes: bytes);
+    return DownloadSizeEstimate(bytes: bytes);
   }
 
   final depth = parameters.bitDepth;
@@ -44,15 +47,15 @@ DownloadSizeEstimate? estimateDownloadSize({
       parameters.channels <= 0) {
     return null;
   }
-  final minDepth = parameters.isMaximum ? math.min(depth, 16) : depth;
-  final minRate = parameters.isMaximum ? math.min(rate, 44100) : rate;
-  // A rough compressed-lossless range (50–80% of PCM), not a bound or a
-  // guarantee. Capped tiers can deliver CD quality instead of their maximum.
+  // Use one comparison estimate at the selected tier, assuming 65% of PCM.
+  // This is a heuristic, not a measurement of this recording's compression.
+  // For capped tiers the UI must show the assumed depth/rate: a provider can
+  // return lower quality, so the tier's maximum is not the track's actual size.
   // Artwork, tags, container overhead and later conversion are excluded.
   return DownloadSizeEstimate(
-    minBytes: (seconds * minDepth * minRate * parameters.channels / 8 * 0.5)
-        .round(),
-    maxBytes: (seconds * depth * rate * parameters.channels / 8 * 0.8).round(),
+    bytes: (seconds * depth * rate * parameters.channels / 8 * 0.65).round(),
+    assumedBitDepth: parameters.isMaximum ? depth : null,
+    assumedSampleRate: parameters.isMaximum ? rate : null,
   );
 }
 

lib/widgets/download_service_picker.dart

@@ -260,9 +260,15 @@ class _DownloadServicePickerState extends ConsumerState<DownloadServicePicker> {
 
   String _sizeLabel(BuildContext context, DownloadSizeEstimate? estimate) {
     if (estimate == null) return context.l10n.downloadSizeUnavailable;
-    final size = estimate.minBytes == estimate.maxBytes
-        ? formatBytes(estimate.maxBytes)
-        : '${formatBytes(estimate.minBytes)}–${formatBytes(estimate.maxBytes)}';
+    final size = formatBytes(estimate.bytes);
+    final depth = estimate.assumedBitDepth;
+    final rate = estimate.assumedSampleRate;
+    if (depth != null && rate != null) {
+      return context.l10n.downloadEstimatedSizeAtQuality(
+        size,
+        '$depth-bit/${formatSampleRateKHz(rate)}',
+      );
+    }
     return context.l10n.downloadEstimatedSize(size);
   }