feat: Email & Password Validator and PasswordRule validations

auth/src/main/java/com/firebase/ui/auth/compose/configuration/AuthUIStringProvider.kt

@@ -23,19 +23,59 @@ import com.firebase.ui.auth.R
  * passwordsDoNotMatch(), etc., allowing for complete localization of the UI.
  */
 interface AuthUIStringProvider {
-    fun initializing(): String
-    fun signInWithGoogle(): String
-    fun invalidEmail(): String
-    fun passwordsDoNotMatch(): String
-}
+    /** Loading text displayed during initialization or processing states */
+    val initializing: String
+
+    /** Button text for Google sign-in option */
+    val signInWithGoogle: String
+
+    /** Error message when email address field is empty */
+    val missingEmailAddress: String
+
+    /** Error message when email address format is invalid */
+    val invalidEmailAddress: String
+
+    /** Generic error message for incorrect password during sign-in */
+    val invalidPassword: String
 
-class DefaultAuthUIStringProvider(private val context: Context) : AuthUIStringProvider {
-    override fun initializing(): String = ""
+    /** Error message when password confirmation doesn't match the original password */
+    val passwordsDoNotMatch: String
 
-    override fun signInWithGoogle(): String =
-        context.getString(R.string.fui_sign_in_with_google)
+    /** Error message when password doesn't meet minimum length requirement. Should support string formatting with minimum length parameter. */
+    val passwordTooShort: String
 
-    override fun invalidEmail(): String = ""
+    /** Error message when password is missing at least one uppercase letter (A-Z) */
+    val passwordMissingUppercase: String
+
+    /** Error message when password is missing at least one lowercase letter (a-z) */
+    val passwordMissingLowercase: String
+
+    /** Error message when password is missing at least one numeric digit (0-9) */
+    val passwordMissingDigit: String
+
+    /** Error message when password is missing at least one special character */
+    val passwordMissingSpecialCharacter: String
+}
 
-    override fun passwordsDoNotMatch(): String = ""
+internal class DefaultAuthUIStringProvider(private val context: Context) : AuthUIStringProvider {
+    override val initializing: String get() = ""
+    override val signInWithGoogle: String
+        get() = context.getString(R.string.fui_sign_in_with_google)
+    override val missingEmailAddress: String
+        get() = context.getString(R.string.fui_missing_email_address)
+    override val invalidEmailAddress: String
+        get() = context.getString(R.string.fui_invalid_email_address)
+    override val invalidPassword: String
+        get() = context.getString(R.string.fui_error_invalid_password)
+    override val passwordsDoNotMatch: String get() = ""
+    override val passwordTooShort: String
+        get() = context.getString(R.string.fui_error_password_too_short)
+    override val passwordMissingUppercase: String
+        get() = context.getString(R.string.fui_error_password_missing_uppercase)
+    override val passwordMissingLowercase: String
+        get() = context.getString(R.string.fui_error_password_missing_lowercase)
+    override val passwordMissingDigit: String
+        get() = context.getString(R.string.fui_error_password_missing_digit)
+    override val passwordMissingSpecialCharacter: String
+        get() = context.getString(R.string.fui_error_password_missing_special_character)
 }

auth/src/main/java/com/firebase/ui/auth/compose/configuration/PasswordRule.kt

@@ -22,31 +22,100 @@ abstract class PasswordRule {
     /**
      * Requires the password to have at least a certain number of characters.
      */
-    class MinimumLength(val value: Int) : PasswordRule()
+    class MinimumLength(val value: Int) : PasswordRule() {
+        override fun isValid(password: String): Boolean {
+            return password.length >= this@MinimumLength.value
+        }
+
+        override fun getErrorMessage(stringProvider: AuthUIStringProvider): String {
+            return stringProvider.passwordTooShort.format(value)
+        }
+    }
 
     /**
      * Requires the password to contain at least one uppercase letter (A-Z).
      */
-    object RequireUppercase : PasswordRule()
+    object RequireUppercase : PasswordRule() {
+        override fun isValid(password: String): Boolean {
+            return password.any { it.isUpperCase() }
+        }
+
+        override fun getErrorMessage(stringProvider: AuthUIStringProvider): String {
+            return stringProvider.passwordMissingUppercase
+        }
+    }
 
     /**
      * Requires the password to contain at least one lowercase letter (a-z).
      */
-    object RequireLowercase: PasswordRule()
+    object RequireLowercase : PasswordRule() {
+        override fun isValid(password: String): Boolean {
+            return password.any { it.isLowerCase() }
+        }
+
+        override fun getErrorMessage(stringProvider: AuthUIStringProvider): String {
+            return stringProvider.passwordMissingLowercase
+        }
+    }
 
     /**
      * Requires the password to contain at least one numeric digit (0-9).
      */
-    object RequireDigit: PasswordRule()
+    object RequireDigit : PasswordRule() {
+        override fun isValid(password: String): Boolean {
+            return password.any { it.isDigit() }
+        }
+
+        override fun getErrorMessage(stringProvider: AuthUIStringProvider): String {
+            return stringProvider.passwordMissingDigit
+        }
+    }
 
     /**
      * Requires the password to contain at least one special character (e.g., !@#$%^&*).
      */
-    object RequireSpecialCharacter: PasswordRule()
+    object RequireSpecialCharacter : PasswordRule() {
+        private val specialCharacters = "!@#$%^&*()_+-=[]{}|;:,.<>?".toSet()
+
+        override fun isValid(password: String): Boolean {
+            return password.any { it in specialCharacters }
+        }
+
+        override fun getErrorMessage(stringProvider: AuthUIStringProvider): String {
+            return stringProvider.passwordMissingSpecialCharacter
+        }
+    }
 
     /**
      * Defines a custom validation rule using a regular expression and provides a specific error
      * message on failure.
      */
-    class Custom(val regex: Regex, val errorMessage: String)
+    class Custom(
+        val regex: Regex,
+        val errorMessage: String
+    ) : PasswordRule() {
+        override fun isValid(password: String): Boolean {
+            return regex.matches(password)
+        }
+
+        override fun getErrorMessage(stringProvider: AuthUIStringProvider): String {
+            return errorMessage
+        }
+    }
+
+    /**
+     * Validates whether the given password meets this rule's requirements.
+     *
+     * @param password The password to validate
+     * @return true if the password meets this rule's requirements, false otherwise
+     */
+    internal abstract fun isValid(password: String): Boolean
+
+    /**
+     * Returns the appropriate error message for this rule when validation fails.
+     *
+     * @param stringProvider The string provider for localized error messages
+     * @return The localized error message for this rule
+     */
+    internal abstract fun getErrorMessage(stringProvider: AuthUIStringProvider): String
 }

auth/src/main/java/com/firebase/ui/auth/compose/configuration/validators/EmailValidator.kt

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2025 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the
+ * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.firebase.ui.auth.compose.configuration.validators
+
+import com.firebase.ui.auth.compose.configuration.AuthUIStringProvider
+
+internal class EmailValidator(override val stringProvider: AuthUIStringProvider) : FieldValidator {
+    private var _validationStatus = FieldValidationStatus(hasError = false, errorMessage = null)
+
+    override val hasError: Boolean
+        get() = _validationStatus.hasError
+
+    override val errorMessage: String
+        get() = _validationStatus.errorMessage ?: ""
+
+    override fun validate(value: String): Boolean {
+        if (value.isEmpty()) {
+            _validationStatus = FieldValidationStatus(
+                hasError = true,
+                errorMessage = stringProvider.missingEmailAddress
+            )
+            return false
+        }
+
+        if (!android.util.Patterns.EMAIL_ADDRESS.matcher(value).matches()) {
+            _validationStatus = FieldValidationStatus(
+                hasError = true,
+                errorMessage = stringProvider.invalidEmailAddress
+            )
+            return false
+        }
+
+        _validationStatus = FieldValidationStatus(hasError = false, errorMessage = null)
+        return true
+    }
+}

auth/src/main/java/com/firebase/ui/auth/compose/configuration/validators/FieldValidationStatus.kt

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2025 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the
+ * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.firebase.ui.auth.compose.configuration.validators
+
+/**
+ * Class for encapsulating [hasError] and [errorMessage] properties in
+ * internal FieldValidator subclasses.
+ */
+internal class FieldValidationStatus(
+    val hasError: Boolean,
+    val errorMessage: String? = null,
+)

auth/src/main/java/com/firebase/ui/auth/compose/configuration/validators/FieldValidator.kt

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2025 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the
+ * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.firebase.ui.auth.compose.configuration.validators
+
+import com.firebase.ui.auth.compose.configuration.AuthUIStringProvider
+
+/**
+ * An interface for validating input fields.
+ */
+interface FieldValidator {
+    val stringProvider: AuthUIStringProvider
+
+    /**
+     * Returns true if the last validation failed.
+     */
+    val hasError: Boolean
+
+    /**
+     * The error message for the current state.
+     */
+    val errorMessage: String
+
+    /**
+     * Runs validation on a value and returns true if valid.
+     */
+    fun validate(value: String): Boolean
+}

auth/src/main/java/com/firebase/ui/auth/compose/configuration/validators/PasswordValidator.kt

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2025 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the
+ * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.firebase.ui.auth.compose.configuration.validators
+
+import com.firebase.ui.auth.compose.configuration.AuthUIStringProvider
+import com.firebase.ui.auth.compose.configuration.PasswordRule
+
+internal class PasswordValidator(
+    override val stringProvider: AuthUIStringProvider,
+    private val rules: List<PasswordRule>
+) : FieldValidator {
+    private var _validationStatus = FieldValidationStatus(hasError = false, errorMessage = null)
+
+    override val hasError: Boolean
+        get() = _validationStatus.hasError
+
+    override val errorMessage: String
+        get() = _validationStatus.errorMessage ?: ""
+
+    override fun validate(value: String): Boolean {
+        if (value.isEmpty()) {
+            _validationStatus = FieldValidationStatus(
+                hasError = true,
+                errorMessage = stringProvider.invalidPassword
+            )
+            return false
+        }
+
+        for (rule in rules) {
+            if (!rule.isValid(value)) {
+                _validationStatus = FieldValidationStatus(
+                    hasError = true,
+                    errorMessage = rule.getErrorMessage(stringProvider)
+                )
+                return false
+            }
+        }
+
+        _validationStatus = FieldValidationStatus(hasError = false, errorMessage = null)
+        return true
+    }
+}

auth/src/main/res/values/strings.xml

@@ -93,6 +93,13 @@
     <string name="fui_error_unknown" translation_description="General error messages for an unknown failure.">An unknown error occurred.</string>
     <string name="fui_error_invalid_password" translation_description="Error message for when the user enters an invalid or wrong password.">Incorrect password.</string>
 
+    <!-- Password validation messages -->
+    <string name="fui_error_password_too_short" translation_description="Error message when password is too short">Password must be at least %1$d characters long</string>
+    <string name="fui_error_password_missing_uppercase" translation_description="Error message when password is missing uppercase letter">Password must contain at least one uppercase letter</string>
+    <string name="fui_error_password_missing_lowercase" translation_description="Error message when password is missing lowercase letter">Password must contain at least one lowercase letter</string>
+    <string name="fui_error_password_missing_digit" translation_description="Error message when password is missing digit">Password must contain at least one number</string>
+    <string name="fui_error_password_missing_special_character" translation_description="Error message when password is missing special character">Password must contain at least one special character</string>
+
     <!-- Accessibility -->
     <string name="fui_accessibility_logo" translation_description="Content description for app logo">App logo</string>