feat(aprs): pick a map symbol from a list instead of typing two characters

The symbol table and code were free-text fields with no validation and no hint. Only the
first character was ever used, and only at packet-build time, so an operator could type
"satellite" into the table field, watch it persist, and beacon as "/" - the field lied about
what it did. aprs.fi's troubleshooting guidance puts transmit-side symbol misconfiguration
among the first things to check when a station never appears correctly.

The single strongest argument for a list: \S is Satellite/Pacsat but /S is SHUTTLE. One
keystroke apart, and both look right to someone typing from memory.

Fourteen entries covering fixed, on-foot, field, four vehicle classes, satellite, yagi,
phone, internet-only and handheld. Renderings are from aprs.org/symbols/symbolsX.txt
(WB4APR, Nov 2015) rather than recalled. A symbol the operator already set that is not on
the list appears first in the menu and stays selected, so opening the picker cannot silently
change an existing station's appearance.

The default changes from "/>" (CAR) to "/-" (House). The old default's own comment conceded
it was "a reasonable stand-in for a phone", but it showed every non-driving operator as a
vehicle. A house is right for most users and obviously wrong rather than misleading for the
rest. This cannot disturb an existing install: saveConfig writes every key unconditionally
and the enable switch calls it, so anyone who has ever turned APRS on has both symbol keys
on disk and the changed fallbacks cannot reach them. All three sites move together -
AprsStore's load fallback, AprsCard's blank-field fallback, and AprsBeacon.DEFAULT_SYMBOL -
because leaving one behind would substitute a car whenever the stored code was unusable.

The list lives in core:domain as pure data holding resource names rather than text, so the
wording stays in the locale files. Tests assert that every entry survives the transmit
sanitiser, that the pairs and description keys are unique, and that a pair off the list
reports as absent rather than resolving to something near it.

core/data/src/main/java/com/rtbishop/look4sat/core/data/aprs/AprsStore.kt

@@ -24,6 +24,15 @@ object AprsStore {
     private const val KEY_STATUS = "status"
     private const val KEY_SYMBOL_TABLE = "symbol_table"
     private const val KEY_SYMBOL_CODE = "symbol_code"
+
+    /**
+     * A house, not a car.
+     *
+     * Only fresh installs see this: saveConfig writes every key unconditionally and the enable
+     * switch calls it, so anyone who has ever turned APRS on has both symbol keys on disk and this
+     * fallback cannot reach them.
+     */
+    private const val DEFAULT_SYMBOL_CODE = "-"
     private const val KEY_LAST_TIME = "last_report_time"
     private const val KEY_LAST_OK = "last_report_ok"
     private const val KEY_LAST_DETAIL = "last_report_detail"
@@ -41,7 +50,7 @@ object AprsStore {
             intervalMin = p.getInt(KEY_INTERVAL, 5),
             statusText = p.getString(KEY_STATUS, "Look4Sat APRS") ?: "Look4Sat APRS",
             symbolTable = p.getString(KEY_SYMBOL_TABLE, "/") ?: "/",
-            symbolCode = p.getString(KEY_SYMBOL_CODE, ">") ?: ">"
+            symbolCode = p.getString(KEY_SYMBOL_CODE, DEFAULT_SYMBOL_CODE) ?: DEFAULT_SYMBOL_CODE
         )
     }
 

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/aprs/AprsBeacon.kt

@@ -143,5 +143,14 @@ object AprsBeacon {
     private const val CRLF_BYTES = 2
 
     /** Fallback symbol. `>` is a car on the primary table - a reasonable stand-in for a phone. */
-    private const val DEFAULT_SYMBOL = '>'
+    /**
+     * Substituted when the stored code is unusable.
+     *
+     * A house, not a car. The old default was '>' (CAR) with a comment conceding it was "a
+     * reasonable stand-in for a phone" - but a station beaconing from a handset showed up as a
+     * vehicle for every operator who was not driving, and aprs.fi names transmit-side symbol
+     * misconfiguration among the first things to check when a station looks wrong. A house is
+     * correct for most users and obviously wrong rather than misleading for the rest.
+     */
+    private const val DEFAULT_SYMBOL = '-'
 }

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/aprs/AprsSymbols.kt

@@ -0,0 +1,81 @@
+/*
+ * Look4Sat. Amateur radio satellite tracker and pass predictor.
+ * Copyright (C) 2019-2026 Arty Bishop and contributors.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package com.rtbishop.look4sat.core.domain.aprs
+
+/**
+ * One APRS symbol an operator might plausibly want.
+ *
+ * [table] and [code] are the two characters that go into the packet. [descriptionKey] names a
+ * string resource rather than holding text, because core:domain has no access to resources and
+ * hardcoding English here would put wording outside the locale files.
+ */
+data class AprsSymbol(val table: Char, val code: Char, val descriptionKey: String)
+
+/**
+ * A short list of symbols worth offering, instead of two free-text fields.
+ *
+ * The fields accepted anything and used only the first character, so typing "satellite" into the
+ * table field persisted the whole word and beaconed as `/` - the field lied about what it did.
+ * aprs.fi's own troubleshooting guidance puts transmit-side symbol misconfiguration among the first
+ * things to check when a station does not appear as expected.
+ *
+ * The strongest single argument for a list: `\S` is Satellite/Pacsat but `/S` is SHUTTLE. One
+ * keystroke apart, and both look correct to someone typing from memory.
+ *
+ * Renderings are from aprs.org/symbols/symbolsX.txt (WB4APR, 25 Nov 2015). The list is deliberately
+ * short - it covers fixed, portable, vehicle and satellite postures, not all 400-odd symbols.
+ */
+object AprsSymbols {
+
+    /** Fixed home station. Correct for most users, and wrong in an obvious way for the rest. */
+    val HOUSE = AprsSymbol('/', '-', "aprs_symbol_house")
+
+    val curated = listOf(
+        HOUSE,
+        AprsSymbol('\\', '-', "aprs_symbol_house_alt"),
+        AprsSymbol('/', '[', "aprs_symbol_person"),
+        AprsSymbol('/', 'y', "aprs_symbol_yagi"),
+        // Alternate table. /S is SHUTTLE, which is not what anyone means here.
+        AprsSymbol('\\', 'S', "aprs_symbol_satellite"),
+        AprsSymbol('/', ';', "aprs_symbol_portable"),
+        AprsSymbol('/', '$', "aprs_symbol_phone"),
+        AprsSymbol('/', 'I', "aprs_symbol_tcpip"),
+        AprsSymbol('\\', 'K', "aprs_symbol_ht"),
+        AprsSymbol('/', '>', "aprs_symbol_car"),
+        AprsSymbol('/', 'k', "aprs_symbol_truck"),
+        AprsSymbol('/', 'v', "aprs_symbol_van"),
+        AprsSymbol('/', 'R', "aprs_symbol_rv"),
+        AprsSymbol('/', 'b', "aprs_symbol_bike")
+    )
+
+    /**
+     * Find the curated entry matching a stored pair, or null when it is not on the list.
+     *
+     * Null matters: an operator may have set a symbol this list does not offer, and the picker must
+     * show it as-is rather than silently substituting the nearest entry.
+     */
+    fun find(table: Char, code: Char): AprsSymbol? =
+        curated.firstOrNull { it.table == table && it.code == code }
+
+    /** Same, from whatever strings the settings screen holds. Blank means the shipped default. */
+    fun find(table: String, code: String): AprsSymbol? {
+        val t = table.firstOrNull() ?: HOUSE.table
+        val c = code.firstOrNull() ?: HOUSE.code
+        return find(t, c)
+    }
+}

core/domain/src/test/java/com/rtbishop/look4sat/core/domain/aprs/AprsBeaconTest.kt

@@ -145,8 +145,10 @@ class AprsBeaconTest {
 
     @Test
     fun `the symbol code falls back when unprintable`() {
-        assertEquals('>', AprsBeacon.codeOf(""))
-        assertEquals('>', AprsBeacon.codeOf(" "))
+        // A house, not a car. The old fallback was '>' (CAR), which showed a phone-based beacon as
+        // a vehicle for every operator who was not driving.
+        assertEquals('-', AprsBeacon.codeOf(""))
+        assertEquals('-', AprsBeacon.codeOf(" "))
         assertEquals('[', AprsBeacon.codeOf("["))
     }
 

core/domain/src/test/java/com/rtbishop/look4sat/core/domain/aprs/AprsSymbolsTest.kt

@@ -0,0 +1,102 @@
+package com.rtbishop.look4sat.core.domain.aprs
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNotNull
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * The list exists because two free-text fields accepted anything and used only the first character,
+ * so an operator could type a word, watch it persist, and beacon as something else entirely.
+ */
+class AprsSymbolsTest {
+
+    /**
+     * The pair that justifies the whole feature. `\S` is Satellite/Pacsat; `/S` is SHUTTLE. One
+     * keystroke apart, and both look right to someone typing from memory.
+     */
+    @Test
+    fun `the satellite symbol uses the alternate table`() {
+        val satellite = AprsSymbols.curated.single { it.descriptionKey == "aprs_symbol_satellite" }
+        assertEquals('\\', satellite.table)
+        assertEquals('S', satellite.code)
+    }
+
+    /** Every entry must survive the sanitiser that runs at packet-build time. */
+    @Test
+    fun `every curated symbol passes the transmit sanitiser`() {
+        for (symbol in AprsSymbols.curated) {
+            assertEquals(
+                symbol.descriptionKey + " table must survive tableOf",
+                symbol.table,
+                AprsBeacon.tableOf(symbol.table.toString())
+            )
+            assertEquals(
+                symbol.descriptionKey + " code must survive codeOf",
+                symbol.code,
+                AprsBeacon.codeOf(symbol.code.toString())
+            )
+        }
+    }
+
+    /** Two entries rendering the same pair would be a UI ambiguity. */
+    @Test
+    fun `no two curated symbols are the same pair`() {
+        val pairs = AprsSymbols.curated.map { it.table to it.code }
+        assertEquals("pairs must be unique", pairs.size, pairs.toSet().size)
+    }
+
+    /** Each needs its own description, or the list reads as duplicates. */
+    @Test
+    fun `every curated symbol has a distinct description key`() {
+        val keys = AprsSymbols.curated.map { it.descriptionKey }
+        assertEquals("description keys must be unique", keys.size, keys.toSet().size)
+        assertTrue("keys must be resource names", keys.all { it.startsWith("aprs_symbol_") })
+    }
+
+    @Test
+    fun `a stored pair on the list is found`() {
+        assertEquals(AprsSymbols.HOUSE, AprsSymbols.find('/', '-'))
+        assertNotNull(AprsSymbols.find('\\', 'S'))
+    }
+
+    /**
+     * A pair the list does not offer must report as absent rather than resolving to something near
+     * it. The picker relies on this to show an existing setting untouched.
+     */
+    @Test
+    fun `a stored pair off the list is not silently substituted`() {
+        assertNull(AprsSymbols.find('/', 'S'))
+        assertNull(AprsSymbols.find('/', '!'))
+        assertNull(AprsSymbols.find('\\', 'y'))
+    }
+
+    /** The settings screen holds strings, and only the first character counts. */
+    @Test
+    fun `the string overload reads the first character`() {
+        assertEquals(AprsSymbols.HOUSE, AprsSymbols.find("/", "-"))
+        assertEquals(AprsSymbols.HOUSE, AprsSymbols.find("/junk", "-junk"))
+    }
+
+    /** Blank fields mean the shipped default, which is what the save path substitutes. */
+    @Test
+    fun `blank strings resolve to the default symbol`() {
+        assertEquals(AprsSymbols.HOUSE, AprsSymbols.find("", ""))
+    }
+
+    /** The default has to be on the list, or the picker opens showing nothing selected. */
+    @Test
+    fun `the default symbol is on the curated list`() {
+        assertTrue(AprsSymbols.HOUSE in AprsSymbols.curated)
+    }
+
+    /** Short enough to scan in a bottom sheet during setup. */
+    @Test
+    fun `the list stays short`() {
+        assertTrue(
+            "a curated list of ${AprsSymbols.curated.size} defeats the point",
+            AprsSymbols.curated.size in 8..20
+        )
+    }
+}

core/presentation/src/main/res/values-zh/strings.xml

@@ -28,6 +28,23 @@
     <string name="prefs_aprs_interval">周期(分钟)</string>
     <string name="prefs_aprs_status">状态文本</string>
     <string name="prefs_aprs_symbol_table">符号表</string>
+    <string name="aprs_symbol_house">房屋 - 固定台站</string>
+    <string name="aprs_symbol_house_alt">房屋, 备用符号表</string>
+    <string name="aprs_symbol_person">步行操作员</string>
+    <string name="aprs_symbol_yagi">固定站八木天线</string>
+    <string name="aprs_symbol_satellite">卫星台站</string>
+    <string name="aprs_symbol_portable">便携 / 野外运行</string>
+    <string name="aprs_symbol_phone">手机</string>
+    <string name="aprs_symbol_tcpip">仅互联网台站</string>
+    <string name="aprs_symbol_ht">手持电台</string>
+    <string name="aprs_symbol_car">轿车</string>
+    <string name="aprs_symbol_truck">卡车</string>
+    <string name="aprs_symbol_van">厢式车</string>
+    <string name="aprs_symbol_rv">房车</string>
+    <string name="aprs_symbol_bike">自行车</string>
+    <string name="prefs_aprs_symbol">地图符号</string>
+    <string name="prefs_aprs_symbol_custom">自定义 (%1$s%2$s)</string>
+    <string name="prefs_aprs_symbol_help">你的台站在 APRS 地图上的显示方式</string>
     <string name="prefs_aprs_symbol_code">符号码</string>
     <string name="prefs_aprs_save">保存</string>
     <string name="prefs_aprs_cancel">取消</string>

core/presentation/src/main/res/values/strings.xml

@@ -29,6 +29,23 @@
     <string name="prefs_aprs_interval">Interval (min)</string>
     <string name="prefs_aprs_status">Status text</string>
     <string name="prefs_aprs_symbol_table">Symbol table</string>
+    <string name="aprs_symbol_house">House - fixed station</string>
+    <string name="aprs_symbol_house_alt">House, alternate table</string>
+    <string name="aprs_symbol_person">Person on foot</string>
+    <string name="aprs_symbol_yagi">Yagi at a fixed site</string>
+    <string name="aprs_symbol_satellite">Satellite station</string>
+    <string name="aprs_symbol_portable">Portable / field operation</string>
+    <string name="aprs_symbol_phone">Phone</string>
+    <string name="aprs_symbol_tcpip">Internet-only station</string>
+    <string name="aprs_symbol_ht">Handheld radio</string>
+    <string name="aprs_symbol_car">Car</string>
+    <string name="aprs_symbol_truck">Truck</string>
+    <string name="aprs_symbol_van">Van</string>
+    <string name="aprs_symbol_rv">Motorhome</string>
+    <string name="aprs_symbol_bike">Bicycle</string>
+    <string name="prefs_aprs_symbol">Map symbol</string>
+    <string name="prefs_aprs_symbol_custom">Custom (%1$s%2$s)</string>
+    <string name="prefs_aprs_symbol_help">How your station appears on the APRS map</string>
     <string name="prefs_aprs_symbol_code">Symbol code</string>
     <string name="prefs_aprs_save">Save</string>
     <string name="prefs_aprs_cancel">Cancel</string>

feature/settings/src/main/java/com/rtbishop/look4sat/feature/settings/AprsCard.kt

@@ -11,6 +11,12 @@ import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.text.KeyboardOptions
 import androidx.compose.material3.AlertDialog
+import androidx.compose.material3.DropdownMenuItem
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.ExposedDropdownMenuBox
+import androidx.compose.material3.ExposedDropdownMenuDefaults
+import androidx.compose.material3.MenuAnchorType
+import com.rtbishop.look4sat.core.domain.aprs.AprsSymbols
 import androidx.compose.material3.ElevatedCard
 import androidx.compose.material3.IconButton
 import androidx.compose.material3.LocalTextStyle
@@ -179,6 +185,7 @@ fun AprsCard() {
 }
 
 /** APRS settings dialog (plenty of room, full config) */
+@OptIn(ExperimentalMaterial3Api::class)
 @Composable
 private fun AprsSettingsDialog(
     config: AprsConfig,
@@ -194,6 +201,7 @@ private fun AprsSettingsDialog(
     var status by remember { mutableStateOf(config.statusText) }
     var symbolTable by remember { mutableStateOf(config.symbolTable) }
     var symbolCode by remember { mutableStateOf(config.symbolCode) }
+    var symbolMenuExpanded by remember { mutableStateOf(false) }
     val textStyle = LocalTextStyle.current.copy(fontSize = 14.sp)
     val context = LocalContext.current
 
@@ -274,24 +282,62 @@ private fun AprsSettingsDialog(
                         textStyle = textStyle
                     )
                 }
-                Row(horizontalArrangement = Arrangement.spacedBy(8.dp)) {
-                    OutlinedTextField(
-                        value = symbolTable,
-                        onValueChange = { symbolTable = it },
-                        label = { Text(stringResource(id = R.string.prefs_aprs_symbol_table)) },
-                        singleLine = true,
-                        modifier = Modifier.weight(1f),
-                        textStyle = textStyle
+                // A list rather than two free-text fields. The fields accepted any string and used
+                // only the first character, so typing "satellite" persisted the word and beaconed
+                // as `/`. The pair that makes this worth doing: \S is Satellite but /S is SHUTTLE.
+                val selected = AprsSymbols.find(symbolTable, symbolCode)
+                val customLabel = stringResource(
+                    id = R.string.prefs_aprs_symbol_custom,
+                    symbolTable.take(1),
+                    symbolCode.take(1)
                 )
+                val selectedLabel = selected?.let { symbolLabel(it.descriptionKey) } ?: customLabel
+                ExposedDropdownMenuBox(
+                    expanded = symbolMenuExpanded,
+                    onExpandedChange = { symbolMenuExpanded = it }
+                ) {
                     OutlinedTextField(
-                        value = symbolCode,
-                        onValueChange = { symbolCode = it },
-                        label = { Text(stringResource(id = R.string.prefs_aprs_symbol_code)) },
-                        singleLine = true,
-                        modifier = Modifier.weight(1f),
-                        textStyle = textStyle
+                        value = selectedLabel,
+                        onValueChange = {},
+                        readOnly = true,
+                        label = { Text(stringResource(id = R.string.prefs_aprs_symbol)) },
+                        trailingIcon = {
+                            ExposedDropdownMenuDefaults.TrailingIcon(expanded = symbolMenuExpanded)
+                        },
+                        textStyle = textStyle,
+                        modifier = Modifier
+                            .menuAnchor(MenuAnchorType.PrimaryNotEditable)
+                            .fillMaxWidth()
+                    )
+                    ExposedDropdownMenu(
+                        expanded = symbolMenuExpanded,
+                        onDismissRequest = { symbolMenuExpanded = false }
+                    ) {
+                        // An existing setting that is not on the list appears first and stays
+                        // selectable, so opening the menu cannot silently change it.
+                        if (selected == null) {
+                            DropdownMenuItem(
+                                text = { Text(text = customLabel, maxLines = 1) },
+                                onClick = { symbolMenuExpanded = false }
                             )
                         }
+                        AprsSymbols.curated.forEach { symbol ->
+                            DropdownMenuItem(
+                                text = { Text(text = symbolLabel(symbol.descriptionKey), maxLines = 1) },
+                                onClick = {
+                                    symbolTable = symbol.table.toString()
+                                    symbolCode = symbol.code.toString()
+                                    symbolMenuExpanded = false
+                                }
+                            )
+                        }
+                    }
+                }
+                Text(
+                    text = stringResource(id = R.string.prefs_aprs_symbol_help),
+                    style = MaterialTheme.typography.bodySmall,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant
+                )
                 Text(
                     text = stringResource(id = R.string.prefs_aprs_passcode_hint),
                     fontSize = 12.sp,
@@ -316,7 +362,7 @@ private fun AprsSettingsDialog(
                         intervalMin = interval.toIntOrNull() ?: 5,
                         statusText = status,
                         symbolTable = symbolTable.ifBlank { "/" },
-                        symbolCode = symbolCode.ifBlank { ">" }
+                        symbolCode = symbolCode.ifBlank { "-" }
                     )
                 )
             }) { Text(stringResource(id = R.string.prefs_aprs_save)) }
@@ -339,3 +385,30 @@ private fun AprsSwitchRow(labelResId: Int, checked: Boolean, onCheckedChange: ((
         Switch(checked = checked, onCheckedChange = onCheckedChange)
     }
 }
+
+/**
+ * Resolve a symbol's description key to its localised text.
+ *
+ * AprsSymbols names a resource rather than holding text, because core:domain cannot reach resources
+ * and hardcoding English there would put wording outside the locale files. The mapping has to live
+ * on this side, and an unknown key falls back to the key itself rather than crashing - a missing
+ * translation should not take the settings screen down.
+ */
+@Composable
+private fun symbolLabel(descriptionKey: String): String = when (descriptionKey) {
+    "aprs_symbol_house" -> stringResource(id = R.string.aprs_symbol_house)
+    "aprs_symbol_house_alt" -> stringResource(id = R.string.aprs_symbol_house_alt)
+    "aprs_symbol_person" -> stringResource(id = R.string.aprs_symbol_person)
+    "aprs_symbol_yagi" -> stringResource(id = R.string.aprs_symbol_yagi)
+    "aprs_symbol_satellite" -> stringResource(id = R.string.aprs_symbol_satellite)
+    "aprs_symbol_portable" -> stringResource(id = R.string.aprs_symbol_portable)
+    "aprs_symbol_phone" -> stringResource(id = R.string.aprs_symbol_phone)
+    "aprs_symbol_tcpip" -> stringResource(id = R.string.aprs_symbol_tcpip)
+    "aprs_symbol_ht" -> stringResource(id = R.string.aprs_symbol_ht)
+    "aprs_symbol_car" -> stringResource(id = R.string.aprs_symbol_car)
+    "aprs_symbol_truck" -> stringResource(id = R.string.aprs_symbol_truck)
+    "aprs_symbol_van" -> stringResource(id = R.string.aprs_symbol_van)
+    "aprs_symbol_rv" -> stringResource(id = R.string.aprs_symbol_rv)
+    "aprs_symbol_bike" -> stringResource(id = R.string.aprs_symbol_bike)
+    else -> descriptionKey
+}