Add domain validation in source settings

app/src/main/java/org/koitharu/kotatsu/utils/EditTextValidator.kt

@@ -0,0 +1,54 @@
+package org.koitharu.kotatsu.utils
+
+import android.content.Context
+import android.text.Editable
+import android.text.TextWatcher
+import android.widget.EditText
+import androidx.annotation.CallSuper
+import org.koitharu.kotatsu.utils.ext.getDisplayMessage
+import java.lang.ref.WeakReference
+
+abstract class EditTextValidator : TextWatcher {
+
+	private var editTextRef: WeakReference<EditText>? = null
+
+	protected val context: Context
+		get() = checkNotNull(editTextRef?.get()?.context) {
+			"EditTextValidator is not attached to EditText"
+		}
+
+	override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) = Unit
+
+	override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) = Unit
+
+	@CallSuper
+	override fun afterTextChanged(s: Editable?) {
+		val editText = editTextRef?.get() ?: return
+		val newText = s?.toString().orEmpty()
+		val result = runCatching {
+			validate(newText)
+		}.getOrElse { e ->
+			ValidationResult.Failed(e.getDisplayMessage(editText.resources))
+		}
+		editText.error = when (result) {
+			is ValidationResult.Failed -> result.message
+			ValidationResult.Success -> null
+		}
+	}
+
+	fun attachToEditText(editText: EditText) {
+		editTextRef = WeakReference(editText)
+		editText.removeTextChangedListener(this)
+		editText.addTextChangedListener(this)
+		afterTextChanged(editText.text)
+	}
+
+	abstract fun validate(text: String): ValidationResult
+
+	sealed class ValidationResult {
+
+		object Success : ValidationResult()
+
+		class Failed(val message: CharSequence) : ValidationResult()
+	}
+}