feat: add word suggestions and auto-correct (#58)

- Adds dictionary-based word suggestions while typing
- Auto-corrects misspelled words when pressing space
- Adds settings toggles for suggestions and auto-correct
- Disables suggestions and correct for password fields
- Uses wordfreq dictionary, only English in this commit

Author: koinsaari

app/src/main/assets/dictionaries/en_US.json

@@ -63,6 +63,8 @@ class SettingsActivity : SimpleActivity() {
         setupShowClipboardContent()
         setupSentencesCapitalization()
         setupShowNumbersRow()
+        setupShowSuggestions()
+        setupAutoCorrect()
         setupVoiceInputMethod()
 
         binding.apply {
@@ -283,4 +285,24 @@ class SettingsActivity : SimpleActivity() {
             }
         }
     }
+
+    private fun setupShowSuggestions() {
+        binding.apply {
+            settingsShowSuggestions.isChecked = config.showSuggestions
+            settingsShowSuggestionsHolder.setOnClickListener {
+                settingsShowSuggestions.toggle()
+                config.showSuggestions = settingsShowSuggestions.isChecked
+            }
+        }
+    }
+
+    private fun setupAutoCorrect() {
+        binding.apply {
+            settingsAutoCorrect.isChecked = config.autoCorrectOnSpace
+            settingsAutoCorrectHolder.setOnClickListener {
+                settingsAutoCorrect.toggle()
+                config.autoCorrectOnSpace = settingsAutoCorrect.isChecked
+            }
+        }
+    }
 }

app/src/main/kotlin/org/fossify/keyboard/activities/SettingsActivity.kt

@@ -91,4 +91,12 @@ class Config(context: Context) : BaseConfig(context) {
         recentEmojis.add(0, emoji)
         recentlyUsedEmojis = recentEmojis.take(RECENT_EMOJIS_LIMIT)
     }
+
+    var showSuggestions: Boolean
+        get() = prefs.getBoolean(SHOW_SUGGESTIONS, true)
+        set(showSuggestions) = prefs.edit().putBoolean(SHOW_SUGGESTIONS, showSuggestions).apply()
+
+    var autoCorrectOnSpace: Boolean
+        get() = prefs.getBoolean(AUTO_CORRECT_ON_SPACE, true)
+        set(autoCorrectOnSpace) = prefs.edit().putBoolean(AUTO_CORRECT_ON_SPACE, autoCorrectOnSpace).apply()
 }

app/src/main/kotlin/org/fossify/keyboard/helpers/Config.kt

@@ -24,6 +24,8 @@ const val SHOW_NUMBERS_ROW = "show_numbers_row"
 const val SELECTED_LANGUAGES = "selected_languages"
 const val VOICE_INPUT_METHOD = "voice_input_method"
 const val RECENTLY_USED_EMOJIS = "recently_used_emojis"
+const val SHOW_SUGGESTIONS = "show_suggestions"
+const val AUTO_CORRECT_ON_SPACE = "auto_correct_on_space"
 
 // differentiate current and pinned clips at the keyboards' Clipboard section
 const val ITEM_SECTION_LABEL = 0

app/src/main/kotlin/org/fossify/keyboard/helpers/Constants.kt

@@ -0,0 +1,151 @@
+package org.fossify.keyboard.helpers
+
+import android.content.Context
+import android.os.Handler
+import android.os.Looper
+import org.fossify.commons.helpers.ensureBackgroundThread
+import org.json.JSONArray
+import org.json.JSONException
+import java.io.IOException
+import java.util.Collections
+import kotlin.math.abs
+import kotlin.math.min
+
+private const val DEBOUNCE_DELAY_MS = 100L
+private const val MAX_SUGGESTIONS = 3
+private const val MAX_LENGTH_DIFF = 2
+private const val MAX_EDIT_DISTANCE = 2
+private const val MIN_WORD_LENGTH = 2
+private const val CACHE_SIZE = 20
+
+class SpellChecker(context: Context) {
+    @Volatile
+    private var dictionary: HashMap<String, Int>? = null
+    private val mainHandler = Handler(Looper.getMainLooper())
+    private var pendingRunnable: Runnable? = null
+    @Suppress("MagicNumber")
+    private val cache: MutableMap<String, List<String>> = Collections.synchronizedMap(
+        object : LinkedHashMap<String, List<String>>(CACHE_SIZE, 0.75f, true) {
+            override fun removeEldestEntry(eldest: MutableMap.MutableEntry<String, List<String>>) = size > CACHE_SIZE
+        }
+    )
+
+    var onSuggestionsReady: ((List<String>) -> Unit)? = null
+
+    init {
+        ensureBackgroundThread {
+            dictionary = loadDictionary(context)
+        }
+    }
+
+    fun checkWord(word: String) {
+        pendingRunnable?.let { mainHandler.removeCallbacks(it) }
+
+        pendingRunnable = Runnable {
+            ensureBackgroundThread {
+                val suggestions = findSuggestions(word)
+                mainHandler.post {
+                    onSuggestionsReady?.invoke(suggestions)
+                }
+            }
+        }
+
+        mainHandler.postDelayed(pendingRunnable!!, DEBOUNCE_DELAY_MS)
+    }
+
+    fun clear() {
+        pendingRunnable?.let { mainHandler.removeCallbacks(it) }
+        mainHandler.post {
+            onSuggestionsReady?.invoke(emptyList())
+        }
+    }
+
+    fun isValidWord(word: String): Boolean {
+        return dictionary?.containsKey(word.lowercase()) ?: true
+    }
+
+    fun destroy() {
+        pendingRunnable?.let { mainHandler.removeCallbacks(it) }
+        onSuggestionsReady = null
+    }
+
+    private fun loadDictionary(context: Context): HashMap<String, Int> {
+        val map = HashMap<String, Int>()
+        try {
+            val inputStream = context.assets.open("dictionaries/en_US.json")
+            val jsonString = inputStream.bufferedReader().use { it.readText() }
+            val jsonArray = JSONArray(jsonString)
+
+            for (i in 0 until jsonArray.length()) {
+                val entry = jsonArray.getJSONArray(i)
+                val word = entry.getString(0)
+                val rank = jsonArray.length() - i
+                map[word] = rank
+            }
+        } catch (_: IOException) {
+        } catch (_: JSONException) {
+        }
+        return map
+    }
+
+    private fun findSuggestions(input: String): List<String> {
+        val dict = dictionary ?: return emptyList()
+        if (input.length < MIN_WORD_LENGTH) return emptyList()
+
+        val inputLower = input.lowercase()
+
+        cache[inputLower]?.let { return it }
+
+        val prefixMatches = dict.keys
+            .filter { word -> word.startsWith(inputLower) && word != inputLower }
+            .sortedByDescending { dict[it] ?: 0 }
+            .take(MAX_SUGGESTIONS)
+
+        if (prefixMatches.isNotEmpty()) {
+            cache[inputLower] = prefixMatches
+            return prefixMatches
+        }
+
+        val firstChar = inputLower[0]
+        val inputLen = inputLower.length
+
+        val levenshteinMatches = dict.keys
+            .filter { word ->
+                word[0] == firstChar && abs(word.length - inputLen) <= MAX_LENGTH_DIFF
+            }
+            .map { word ->
+                word to levenshteinDistance(inputLower, word)
+            }
+            .filter { it.second <= MAX_EDIT_DISTANCE }
+            .sortedWith(compareBy({ it.second }, { -(dict[it.first] ?: 0) }))
+            .take(MAX_SUGGESTIONS)
+            .map { it.first }
+
+        cache[inputLower] = levenshteinMatches
+        return levenshteinMatches
+    }
+
+    private fun levenshteinDistance(a: String, b: String, maxDistance: Int = MAX_EDIT_DISTANCE): Int {
+        val m = a.length
+        val n = b.length
+        val dp = Array(m + 1) { IntArray(n + 1) }
+
+        for (i in 0..m) dp[i][0] = i
+        for (j in 0..n) dp[0][j] = j
+
+        for (i in 1..m) {
+            var rowMin = Int.MAX_VALUE
+            for (j in 1..n) {
+                val cost = if (a[i - 1] == b[j - 1]) 0 else 1
+                dp[i][j] = min(
+                    min(dp[i - 1][j] + 1, dp[i][j - 1] + 1),
+                    dp[i - 1][j - 1] + cost
+                )
+                rowMin = min(rowMin, dp[i][j])
+            }
+            if (rowMin > maxDistance) return maxDistance + 1
+        }
+
+        return dp[m][n]
+    }
+}