refactor(android): share the SAF scan percent and CUE helpers

The two SAF scans repeated the same progress arithmetic and CUE steps.
Only the runs that are identical are shared:

- safScanProgressPct(done, total) is the Int/Int to Double * 100.0
  expression all six percent sites used. The incremental scan keeps its
  zero-total guard (100.0), the full scan's call sites keep relying on a
  non-zero total as before.
- reportScanned() replaces the two identical scanned/error/percent
  updates in scanSafTree. The CUE-referenced audio skip keeps its own
  update, which never set errorCount.
- reportProcessed() moves above the changed-CUE loop, whose inline copy
  of its body it now replaces.
- resolveCueSheetAudio() covers the FILE line extraction plus sibling
  lookup that both changed-CUE loops and the unchanged-CUE loop ran.
- scanSafCueTracks() covers the audio name, timestamp, cover key and
  scanCueFromUri steps. The scans fall back to different timestamps
  when the audio's own cannot be read, so the fallback is a lambda and
  still runs only on that failure.

Cancellation checks, checkpoint writes, flushes, the copy/delete of the
temporary CUE file and every counter update stay in place and order;
progress values and the scan output are unchanged.

android/app/src/main/kotlin/com/zarz/spotiflac/MainActivitySafScan.kt

@@ -100,6 +100,10 @@ internal fun MainActivity.safScanStopRequested(cancelled: () -> Boolean = { fals
     return safScanCancel || cancelled()
 }
 
+/** The `progress_pct` value for [done] of [total] items; callers guard zero. */
+private fun safScanProgressPct(done: Int, total: Int): Double =
+    done.toDouble() / total.toDouble() * 100.0
+
 internal fun MainActivity.scanSafTree(
         treeUriStr: String,
         ndjsonOutputPath: String? = null,
@@ -231,7 +235,7 @@ internal fun MainActivity.scanSafTree(
             it.totalFiles = totalItems
             if (totalItems > 0 && earlyCheckpoint.isNotEmpty()) {
                 it.scannedFiles = earlyCheckpoint.size.coerceAtMost(totalItems)
-                it.progressPct = it.scannedFiles.toDouble() / totalItems.toDouble() * 100.0
+                it.progressPct = safScanProgressPct(it.scannedFiles, totalItems)
             }
         }
 
@@ -301,6 +305,15 @@ internal fun MainActivity.scanSafTree(
         var scanned = checkpoint.size.coerceAtMost(totalItems)
         var errors = traversalErrors
 
+        fun reportScanned() {
+            val pct = safScanProgressPct(scanned, totalItems)
+            updateSafScanProgress {
+                it.scannedFiles = scanned
+                it.errorCount = errors
+                it.progressPct = pct
+            }
+        }
+
         val cueReferencedAudioUris = mutableSetOf<String>()
 
         for (cue in cueFiles) {
@@ -327,13 +340,11 @@ internal fun MainActivity.scanSafTree(
                     continue
                 }
 
-                val audioFileName = extractCueAudioFileName(tempCuePath)
-
-                val audioDoc = resolveCueAudioSibling(
-                    parentDir = parentDir,
-                    cueName = cueName,
-                    audioFileName = audioFileName,
-                    childLookupCache = safChildLookupCache,
+                val audioDoc = resolveCueSheetAudio(
+                    tempCuePath,
+                    parentDir,
+                    cueName,
+                    safChildLookupCache,
                 )
 
                 if (audioDoc == null) {
@@ -349,26 +360,12 @@ internal fun MainActivity.scanSafTree(
                     continue
                 }
 
-                val audioName = try { audioDoc.name ?: "audio.flac" } catch (_: Exception) { "audio.flac" }
-                val audioLastModified = try { audioDoc.lastModified() } catch (_: Exception) { cueDoc.lastModified() }
-                val coverCacheKey = buildLibraryCoverCacheKey(
-                    audioDoc.uri.toString(),
-                    audioLastModified,
-                )
-
-                val cueLastModified = cue.lastModified
-
-                val cueResultsJson = scanCueFromUri(
-                    coreBackend,
+                val cueArray = scanSafCueTracks(
                     tempCuePath,
-                    audioDoc.uri,
-                    audioName,
-                    cueDoc.uri.toString(),
-                    cueLastModified,
-                    coverCacheKey,
-                )
-
-                val cueArray = JSONArray(cueResultsJson)
+                    audioDoc,
+                    cueUri,
+                    cue.lastModified,
+                ) { cueDoc.lastModified() }
                 for (j in 0 until cueArray.length()) {
                     putResult(cueArray.getJSONObject(j))
                 }
@@ -383,12 +380,7 @@ internal fun MainActivity.scanSafTree(
             }
 
             scanned++
-            val pct = scanned.toDouble() / totalItems.toDouble() * 100.0
-            updateSafScanProgress {
-                it.scannedFiles = scanned
-                it.errorCount = errors
-                it.progressPct = pct
-            }
+            reportScanned()
         }
 
         data class SafAudioScanOutcome(
@@ -417,7 +409,7 @@ internal fun MainActivity.scanSafTree(
             if (cueReferencedAudioUris.contains(stableUri)) {
                 recordCheckpoint(stableUri, lastModified)
                 scanned++
-                val pct = scanned.toDouble() / totalItems.toDouble() * 100.0
+                val pct = safScanProgressPct(scanned, totalItems)
                 updateSafScanProgress {
                     it.scannedFiles = scanned
                     it.progressPct = pct
@@ -485,12 +477,7 @@ internal fun MainActivity.scanSafTree(
             }
 
             scanned++
-            val pct = scanned.toDouble() / totalItems.toDouble() * 100.0
-            updateSafScanProgress {
-                it.scannedFiles = scanned
-                it.errorCount = errors
-                it.progressPct = pct
-            }
+            reportScanned()
         }
         if (!completed) {
             ndjsonWriter?.close()
@@ -717,6 +704,20 @@ internal fun MainActivity.scanSafTreeIncremental(
         var scanned = 0
         var errors = traversalErrors
 
+        fun reportProcessed() {
+            val processed = skippedCount + scanned
+            val pct = if (totalFiles > 0) {
+                safScanProgressPct(processed, totalFiles)
+            } else {
+                100.0
+            }
+            updateSafScanProgress {
+                it.scannedFiles = processed
+                it.errorCount = errors
+                it.progressPct = pct
+            }
+        }
+
         val cueReferencedAudioUris = mutableSetOf<String>()
 
         for ((cueDoc, parentDir, cueName, cueLastModified) in cueFilesToScan) {
@@ -744,13 +745,11 @@ internal fun MainActivity.scanSafTreeIncremental(
                     continue
                 }
 
-                val audioFileName = extractCueAudioFileName(tempCuePath)
-
-                val audioDoc = resolveCueAudioSibling(
-                    parentDir = parentDir,
-                    cueName = cueName,
-                    audioFileName = audioFileName,
-                    childLookupCache = safChildLookupCache,
+                val audioDoc = resolveCueSheetAudio(
+                    tempCuePath,
+                    parentDir,
+                    cueName,
+                    safChildLookupCache,
                 )
 
                 if (audioDoc == null) {
@@ -762,24 +761,12 @@ internal fun MainActivity.scanSafTreeIncremental(
 
                 cueReferencedAudioUris.add(audioDoc.uri.toString())
 
-                val audioName = try { audioDoc.name ?: "audio.flac" } catch (_: Exception) { "audio.flac" }
-                val audioLastModified = try { audioDoc.lastModified() } catch (_: Exception) { cueLastModified }
-                val coverCacheKey = buildLibraryCoverCacheKey(
-                    audioDoc.uri.toString(),
-                    audioLastModified,
-                )
-
-                val cueResultsJson = scanCueFromUri(
-                    coreBackend,
+                val cueArray = scanSafCueTracks(
                     tempCuePath,
-                    audioDoc.uri,
-                    audioName,
+                    audioDoc,
                     cueDoc.uri.toString(),
                     cueLastModified,
-                    coverCacheKey,
-                )
-
-                val cueArray = JSONArray(cueResultsJson)
+                ) { cueLastModified }
                 for (j in 0 until cueArray.length()) {
                     val trackObj = cueArray.getJSONObject(j)
                     putFile(trackObj)
@@ -797,17 +784,7 @@ internal fun MainActivity.scanSafTreeIncremental(
             }
 
             scanned++
-            val processed = skippedCount + scanned
-            val pct = if (totalFiles > 0) {
-                processed.toDouble() / totalFiles.toDouble() * 100.0
-            } else {
-                100.0
-            }
-            updateSafScanProgress {
-                it.scannedFiles = processed
-                it.errorCount = errors
-                it.progressPct = pct
-            }
+            reportProcessed()
         }
 
         for ((cueDoc, parentDir, cueName) in unchangedCueFiles) {
@@ -815,12 +792,11 @@ internal fun MainActivity.scanSafTreeIncremental(
             try {
                 tempCue = copyUriToTemp(coreBackend, cueDoc.uri, ".cue", cueName)
                 if (tempCue != null) {
-                    val audioFileName = extractCueAudioFileName(tempCue)
-                    val audioDoc = resolveCueAudioSibling(
-                        parentDir = parentDir,
-                        cueName = cueName,
-                        audioFileName = audioFileName,
-                        childLookupCache = safChildLookupCache,
+                    val audioDoc = resolveCueSheetAudio(
+                        tempCue,
+                        parentDir,
+                        cueName,
+                        safChildLookupCache,
                     )
                     if (audioDoc != null) {
                         cueReferencedAudioUris.add(audioDoc.uri.toString())
@@ -845,20 +821,6 @@ internal fun MainActivity.scanSafTreeIncremental(
             return result.toString()
         }
 
-        fun reportProcessed() {
-            val processed = skippedCount + scanned
-            val pct = if (totalFiles > 0) {
-                processed.toDouble() / totalFiles.toDouble() * 100.0
-            } else {
-                100.0
-            }
-            updateSafScanProgress {
-                it.scannedFiles = processed
-                it.errorCount = errors
-                it.progressPct = pct
-            }
-        }
-
         val pendingAudio = mutableListOf<ChangedAudio>()
         for (audio in audioFiles) {
             if (safScanStopRequested(cancelled)) return cancelledIncrementalResult()

android/app/src/main/kotlin/com/zarz/spotiflac/SafCueScan.kt

@@ -1,6 +1,7 @@
 package com.zarz.spotiflac
 
 import androidx.documentfile.provider.DocumentFile
+import org.json.JSONArray
 import java.io.File
 import java.util.Locale
 
@@ -101,3 +102,52 @@ internal fun MainActivity.resolveCueAudioSibling(
         }
         return null
     }
+
+/** Resolves the audio document named by a CUE sheet copied to [tempCuePath]. */
+internal fun MainActivity.resolveCueSheetAudio(
+    tempCuePath: String,
+    parentDir: DocumentFile,
+    cueName: String,
+    childLookupCache: MutableMap<String, Map<String, DocumentFile>>,
+): DocumentFile? {
+    val audioFileName = extractCueAudioFileName(tempCuePath)
+
+    return resolveCueAudioSibling(
+        parentDir = parentDir,
+        cueName = cueName,
+        audioFileName = audioFileName,
+        childLookupCache = childLookupCache,
+    )
+}
+
+/**
+ * Reads the virtual track rows of a CUE sheet against its resolved audio.
+ * [audioLastModifiedFallback] runs only when the audio's own timestamp
+ * cannot be read; the two scans fall back to different values.
+ */
+internal fun MainActivity.scanSafCueTracks(
+    tempCuePath: String,
+    audioDoc: DocumentFile,
+    cueUri: String,
+    cueLastModified: Long,
+    audioLastModifiedFallback: () -> Long,
+): JSONArray {
+    val audioName = try { audioDoc.name ?: "audio.flac" } catch (_: Exception) { "audio.flac" }
+    val audioLastModified = try { audioDoc.lastModified() } catch (_: Exception) { audioLastModifiedFallback() }
+    val coverCacheKey = buildLibraryCoverCacheKey(
+        audioDoc.uri.toString(),
+        audioLastModified,
+    )
+
+    val cueResultsJson = scanCueFromUri(
+        coreBackend,
+        tempCuePath,
+        audioDoc.uri,
+        audioName,
+        cueUri,
+        cueLastModified,
+        coverCacheKey,
+    )
+
+    return JSONArray(cueResultsJson)
+}