From 0ea8da6d9456538a4738d6409550f3657f83db04 Mon Sep 17 00:00:00 2001
From: guzzilar <iam.nuttanon@gmail.com>
Date: Wed, 29 May 2019 13:49:32 +0700
Subject: [PATCH 1/9] Implementing Backend classes to handle each individual
 payment method's information.

---
 composer.json                                 |   9 ++
 .../class-omise-backend-installment.php       | 123 ++++++++++++++
 includes/backends/class-omise-backend.php     |  25 +++
 includes/class-omise-capabilities.php         |   7 +
 omise-woocommerce.php                         |   2 +
 phpunit.xml                                   |  18 +++
 tests/unit/class-omise-unit-test.php          |  16 ++
 .../class-omise-backend-installment-test.php  | 151 ++++++++++++++++++
 8 files changed, 351 insertions(+)
 create mode 100644 composer.json
 create mode 100644 includes/backends/class-omise-backend-installment.php
 create mode 100644 includes/backends/class-omise-backend.php
 create mode 100644 phpunit.xml
 create mode 100644 tests/unit/class-omise-unit-test.php
 create mode 100644 tests/unit/includes/backends/class-omise-backend-installment-test.php

diff --git a/composer.json b/composer.json
new file mode 100644
index 00000000..704bb843
--- /dev/null
+++ b/composer.json
@@ -0,0 +1,9 @@
+{
+    "name": "omise/omise-woocommerce",
+    "description": "An official payment extension which provides support for Omise payment gateway for store builders working on the WooCommerce platform.",
+    "homepage": "https://www.omise.co/",
+    "license": "MIT",
+    "require-dev": {
+        "phpunit/phpunit": "^8.1"
+    }
+}
diff --git a/includes/backends/class-omise-backend-installment.php b/includes/backends/class-omise-backend-installment.php
new file mode 100644
index 00000000..672a20a0
--- /dev/null
+++ b/includes/backends/class-omise-backend-installment.php
@@ -0,0 +1,123 @@
+<?php
+/**
+ * Note: all of calculations in this class are based only on Thailand VAT and fee
+ *       as currently Installment feature supported only for merchants
+ *       that have registered with Omise Thailand account.
+ *
+ * @since 3.4
+ *
+ * @method public initiate
+ * @method public get_available_providers
+ * @method public filter_available_terms
+ * @method public calculate_monthly_payment_amount
+ */
+class Omise_Backend_Installment extends Omise_Backend {
+	/**
+	 * @var array  of known installment providers.
+	 */
+	protected static $providers = array();
+
+	public function initiate() {
+		self::$providers = array(
+			'installment_first_choice' => array(
+				'bank_code'          => 'first_choice',
+				'title'              => __( 'Krungsri First Choice', 'omise' ),
+				'interest_rate'      => 0.013,
+				'min_allowed_amount' => 300.00,
+			),
+
+			'installment_bay' => array(
+				'bank_code'          => 'bay',
+				'title'              => __( 'Krungsri', 'omise' ),
+				'interest_rate'      => 0.008,
+				'min_allowed_amount' => 300.00,
+			),
+
+			'installment_ktc' => array(
+				'bank_code'          => 'ktc',
+				'title'              => __( 'Krungthai Card (KTC)', 'omise' ),
+				'interest_rate'      => 0.008,
+				'min_allowed_amount' => 300.00,
+			),
+
+			'installment_bbl' => array(
+				'bank_code'          => 'bbl',
+				'title'              => __( 'Bangkok Bank', 'omise' ),
+				'interest_rate'      => 0.008,
+				'min_allowed_amount' => 500.00,
+			),
+
+			'installment_kbank' => array(
+				'bank_code'          => 'kbank',
+				'title'              => __( 'Kasikorn Bank', 'omise' ),
+				'interest_rate'      => 0.0065,
+				'min_allowed_amount' => 500.00,
+			),
+		);
+	}
+
+	/**
+	 * @param  string $currency
+	 * @param  float  $purchase_amount
+	 *
+	 * @return array  of an available installment providers
+	 */
+	public function get_available_providers( $currency, $purchase_amount ) {
+		// Note: as installment payment at the moment only supports for THB currency, so the 
+		//       $purchase_amount is multiplied with 100 to convert the amount into subunit (satang).
+		$providers = $this->capabilities()->getInstallmentBackends( $currency, ( $purchase_amount * 100 ) );
+
+		foreach ( $providers as &$provider ) {
+			$provider->provider_code             = str_replace( 'installment_', '', $provider->_id );
+			$provider->provider_name             = isset( self::$providers[ $provider->_id ] ) ? self::$providers[ $provider->_id ]['title'] : strtoupper( $provider->code );
+			$provider->allowed_installment_terms = $this->filter_available_terms( $provider->allowed_installment_terms, self::$providers[ $provider->_id ], $purchase_amount );
+		}
+
+		return $providers;
+	}
+
+	/**
+	 * @param  array $available_terms
+	 * @param  array $provider_detail
+	 * @param  float $purchase_amount
+	 *
+	 * @return array  of an filtered available terms
+	 */
+	public function filter_available_terms( $available_terms, $provider_detail, $purchase_amount ) {
+		$filtered_available_terms = array();
+
+		sort( $available_terms );
+
+		for ( $i = 0; $i < count( $available_terms ); $i++ ) {
+			$term           = $available_terms[ $i ];
+			$monthly_amount = $this->calculate_monthly_payment_amount(
+				$purchase_amount,
+				$term,
+				$this->capabilities()->is_zero_interest() ? 0 : $provider_detail['interest_rate']
+			);
+
+			if ( $monthly_amount < $provider_detail['min_allowed_amount'] ) {
+				break;
+			}
+
+			$filtered_available_terms[ $i ] = array(
+				'term'           => $term,
+				'monthly_amount' => $monthly_amount
+			);
+		}
+
+		return $filtered_available_terms;
+	}
+
+	/**
+	 * @param  float $purchase_amount
+	 * @param  int   $term             installment term.
+	 * @param  float $interest_rate    its value can be '0' if merchant absorbs an interest.
+	 *
+	 * @return float  of a installment monthly payment (round up to 2 decimals).
+	 */
+	public function calculate_monthly_payment_amount( $purchase_amount, $term, $interest_rate ) {
+		$interest = $purchase_amount * $term * $interest_rate;
+		return round( ( $purchase_amount + $interest ) / $term, 2 );
+	}
+}
diff --git a/includes/backends/class-omise-backend.php b/includes/backends/class-omise-backend.php
new file mode 100644
index 00000000..fabf9356
--- /dev/null
+++ b/includes/backends/class-omise-backend.php
@@ -0,0 +1,25 @@
+<?php
+/**
+ * @since 3.4
+ */
+class Omise_Backend {
+	public function __construct() {
+		$this->initiate();
+	}
+
+	/**
+	 * Class initiation.
+	 *
+	 * @return void
+	 */
+	public function initiate() {
+		return;
+	}
+
+	/**
+	 * @return Omise_Capabilities  Instant.
+	 */
+	public function capabilities() {
+		return Omise_Capabilities::retrieve();
+	}
+}
diff --git a/includes/class-omise-capabilities.php b/includes/class-omise-capabilities.php
index 218f50cb..41e9eaee 100644
--- a/includes/class-omise-capabilities.php
+++ b/includes/class-omise-capabilities.php
@@ -45,4 +45,11 @@ public function getInstallmentBackends( $currency = '', $amount = null ) {
 
 		return $this->capabilities->getBackends( $params );
 	}
+
+	/**
+	 * @return bool  True if merchant absorbs an interest or else, false.
+	 */
+	public function is_zero_interest() {
+		return $this->capabilities['zero_interest_installments'];
+	}
 }
diff --git a/omise-woocommerce.php b/omise-woocommerce.php
index 49dcf163..146a3b3e 100644
--- a/omise-woocommerce.php
+++ b/omise-woocommerce.php
@@ -117,6 +117,8 @@ private function define_constants() {
 	private function include_classes() {
 		defined( 'OMISE_WOOCOMMERCE_PLUGIN_PATH' ) || define( 'OMISE_WOOCOMMERCE_PLUGIN_PATH', __DIR__ );
 
+		require_once OMISE_WOOCOMMERCE_PLUGIN_PATH . '/includes/backends/class-omise-backend.php';
+		require_once OMISE_WOOCOMMERCE_PLUGIN_PATH . '/includes/backends/class-omise-backend-installment.php';
 		require_once OMISE_WOOCOMMERCE_PLUGIN_PATH . '/includes/classes/class-omise-charge.php';
 		require_once OMISE_WOOCOMMERCE_PLUGIN_PATH . '/includes/classes/class-omise-card-image.php';
 		require_once OMISE_WOOCOMMERCE_PLUGIN_PATH . '/includes/events/class-omise-event-charge-capture.php';
diff --git a/phpunit.xml b/phpunit.xml
new file mode 100644
index 00000000..3e35e659
--- /dev/null
+++ b/phpunit.xml
@@ -0,0 +1,18 @@
+<phpunit
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/8.1/phpunit.xsd"
+	backupGlobals="true"
+	backupStaticAttributes="false"
+	colors="true"
+	stopOnError="false"
+	stopOnFailure="false"
+	stopOnIncomplete="false"
+	stopOnSkipped="false"
+	stopOnRisky="false"
+	verbose="true">
+	<testsuites>
+		<testsuite name="Omise WooCommerce Test Suite">
+			<directory suffix="-test.php">tests/unit</directory>
+		</testsuite>
+	</testsuites>
+</phpunit>
diff --git a/tests/unit/class-omise-unit-test.php b/tests/unit/class-omise-unit-test.php
new file mode 100644
index 00000000..85a59684
--- /dev/null
+++ b/tests/unit/class-omise-unit-test.php
@@ -0,0 +1,16 @@
+<?php
+
+class Omise_Unit_Test {
+	public static function include_class( $path ): void {
+		require_once __DIR__ . '/../../includes/' . $path;
+	}
+}
+
+/**
+ * Mock WordPress __() function.
+ *
+ * @see wp-includes/l10n.php
+ */
+function __( $text, $domain = 'default' ) {
+	return $text;
+}
diff --git a/tests/unit/includes/backends/class-omise-backend-installment-test.php b/tests/unit/includes/backends/class-omise-backend-installment-test.php
new file mode 100644
index 00000000..e7176d76
--- /dev/null
+++ b/tests/unit/includes/backends/class-omise-backend-installment-test.php
@@ -0,0 +1,151 @@
+<?php
+use PHPUnit\Framework\TestCase;
+require_once __DIR__ . '/../../class-omise-unit-test.php';
+
+class Omise_Backend_Installment_Test extends TestCase {
+	public static function setUpBeforeClass(): void {
+		Omise_Unit_Test::include_class( 'backends/class-omise-backend.php' );
+		Omise_Unit_Test::include_class( 'backends/class-omise-backend-installment.php' );
+	}
+
+	/**
+	 * @test
+	 */
+	public function filtering_bbl_installment_term() {
+		$installment_backend = new Omise_Backend_Installment();
+		$purchase_amount     = 3000.00;
+		$available_terms     = array( 3, 4, 6, 8, 10 );
+		$provider_detail     = array(
+			'bank_code'          => 'bbl',
+			'title'              => __( 'Bangkok Bank', 'omise' ),
+			'interest_rate'      => 0.008,
+			'min_allowed_amount' => 500.00,
+		);
+
+		$result = $installment_backend->filter_available_terms( $available_terms, $provider_detail, $purchase_amount );
+
+		$this->assertEquals( 3, count( $result ) );
+		$this->assertEquals( array(
+			array( 'term' => 3, 'monthly_amount' => 1024.00 ),
+			array( 'term' => 4, 'monthly_amount' => 774.00 ),
+			array( 'term' => 6, 'monthly_amount' => 524.00 ),
+		), $result );
+	}
+
+	/**
+	 * @test
+	 */
+	public function making_sure_that_we_can_filter_terms_properly_even_available_terms_is_not_in_a_proper_order() {
+		$installment_backend = new Omise_Backend_Installment();
+		$purchase_amount     = 3000.00;
+		$available_terms     = array( 3, 10, 4, 8, 6 );
+		$provider_detail     = array(
+			'bank_code'          => 'bbl',
+			'title'              => __( 'Bangkok Bank', 'omise' ),
+			'interest_rate'      => 0.008,
+			'min_allowed_amount' => 500.00,
+		);
+
+		$result = $installment_backend->filter_available_terms( $available_terms, $provider_detail, $purchase_amount );
+
+		$this->assertEquals( 3, count( $result ) );
+		$this->assertEquals( array(
+			array( 'term' => 3, 'monthly_amount' => 1024.00 ),
+			array( 'term' => 4, 'monthly_amount' => 774.00 ),
+			array( 'term' => 6, 'monthly_amount' => 524.00 ),
+		), $result );
+	}
+
+	/**
+	 * @test
+	 */
+	public function correctly_calculating_monthly_payment_amount_as_buyer_absorbs_case_1() {
+		$installment_backend = new Omise_Backend_Installment();
+		$purchase_amount     = 10000.00;
+		$term                = 10;
+		$interest_rate       = 0.008;
+
+		$result = $installment_backend->calculate_monthly_payment_amount( $purchase_amount, $term, $interest_rate );
+
+		$this->assertEquals( 1080.00, $result );
+	}
+
+	/**
+	 * @test
+	 */
+	public function correctly_calculating_monthly_payment_amount_as_buyer_absorbs_case_2() {
+		$installment_backend = new Omise_Backend_Installment();
+		$purchase_amount     = 17900.00;
+		$term                = 6;
+		$interest_rate       = 0.0069;
+
+		$result = $installment_backend->calculate_monthly_payment_amount( $purchase_amount, $term, $interest_rate );
+
+		$this->assertEquals( 3106.84, $result );
+	}
+
+	/**
+	 * @test
+	 */
+	public function correctly_calculating_monthly_payment_amount_as_buyer_absorbs_case_3() {
+		$installment_backend = new Omise_Backend_Installment();
+		$purchase_amount     = 5000.00;
+		$term                = 10;
+		$interest_rate       = 0.008;
+
+		$result = $installment_backend->calculate_monthly_payment_amount( $purchase_amount, $term, $interest_rate );
+
+		$this->assertEquals( 540.00, $result );
+	}
+
+	/**
+	 * @test
+	 */
+	public function correctly_calculating_monthly_payment_amount_as_merchant_absorbs_case_1() {
+		$installment_backend = new Omise_Backend_Installment();
+		$purchase_amount     = 10000.00;
+		$term                = 10;
+		$interest_rate       = 0;
+
+		$result = $installment_backend->calculate_monthly_payment_amount( $purchase_amount, $term, $interest_rate );
+
+		$this->assertEquals( 1000.00, $result );
+	}
+
+	/**
+	 * @test
+	 */
+	public function correctly_calculating_monthly_payment_amount_as_merchant_absorbs_case_2() {
+		$installment_backend = new Omise_Backend_Installment();
+		$purchase_amount     = 5000.00;
+		$term                = 6;
+		$interest_rate       = 0;
+
+		$result = $installment_backend->calculate_monthly_payment_amount( $purchase_amount, $term, $interest_rate );
+
+		$this->assertEquals( 833.33, $result );
+	}
+}
+
+/**
+ * Mock Omise_Capabilities class.
+ * NOTE: This might not be an ideal way to mock a class,
+ *       feel free to enhance the test or the core code.
+ *
+ * @see includes/class-omise-capabilities
+ */
+class Omise_Capabilities {
+	/**
+	 * @var self
+	 */
+	protected static $the_instance = null;
+
+	public static function retrieve() {
+		self::$the_instance = new self();
+		return self::$the_instance;
+	}
+
+	public function is_zero_interest() {
+		return false;
+	}
+}

From 6df8c7b33563da784e7fca0cc5d0e523828274c7 Mon Sep 17 00:00:00 2001
From: guzzilar <iam.nuttanon@gmail.com>
Date: Wed, 29 May 2019 15:21:24 +0700
Subject: [PATCH 2/9] Implementing Backend class to Omise_Payment_Installment.

---
 .../class-omise-payment-installment.php       | 25 ++++++-------------
 includes/gateway/class-omise-payment.php      |  7 ++++++
 templates/payment/form-installment.php        |  4 +--
 3 files changed, 16 insertions(+), 20 deletions(-)

diff --git a/includes/gateway/class-omise-payment-installment.php b/includes/gateway/class-omise-payment-installment.php
index 90ae2a3a..287669ab 100644
--- a/includes/gateway/class-omise-payment-installment.php
+++ b/includes/gateway/class-omise-payment-installment.php
@@ -33,6 +33,8 @@ public function __construct() {
 			$this->title       = $this->get_option( 'title' );
 			$this->description = $this->get_option( 'description' );
 
+			$this->backend     = new Omise_Backend_Installment;
+
 			add_action( 'woocommerce_update_options_payment_gateways_' . $this->id, array( $this, 'process_admin_options' ) );
 			add_action( 'woocommerce_api_' . $this->id . '_callback', array( $this, 'callback' ) );
 		}
@@ -69,27 +71,14 @@ public function init_form_fields() {
 		 * @inheritdoc
 		 */
 		public function payment_fields() {
-			$provider_names = array(
-				'installment_bay'          => __( 'Krungsri', 'omise' ),
-				'installment_first_choice' => __( 'Krungsri First Choice', 'omise' ),
-				'installment_kbank'        => __( 'Kasikorn Bank', 'omise' ),
-				'installment_bbl'          => __( 'Bangkok Bank', 'omise' ),
-				'installment_ktc'          => __( 'Krungthai Card (KTC)', 'omise' ),
-			);
-
-			$currency             = get_woocommerce_currency();
-			$cart_total           = WC()->cart->total;
-			$capabilities         = Omise_Capabilities::retrieve();
-			$installment_backends = $capabilities->getInstallmentBackends( $currency, $this->format_amount_subunit( $cart_total, $currency ) );
-
-			foreach ( $installment_backends as &$backend ) {
-				$backend->provider_code = str_replace( 'installment_', '', $backend->_id );
-				$backend->provider_name = isset( $provider_names[ $backend->_id ] ) ? $provider_names[ $backend->_id ] : strtoupper( $backend->provider_code );
-			}
+			$currency   = get_woocommerce_currency();
+			$cart_total = WC()->cart->total;
 
 			Omise_Util::render_view(
 				'templates/payment/form-installment.php',
-				array( 'installment_backends' => $installment_backends )
+				array(
+					'installment_backends' => $this->backend->get_available_providers( $currency, $cart_total )
+				)
 			);
 		}
 
diff --git a/includes/gateway/class-omise-payment.php b/includes/gateway/class-omise-payment.php
index a2c823c4..97817d38 100644
--- a/includes/gateway/class-omise-payment.php
+++ b/includes/gateway/class-omise-payment.php
@@ -27,6 +27,13 @@ abstract class Omise_Payment extends WC_Payment_Gateway {
 	 */
 	public $id = 'omise';
 
+	/**
+	 * @since 3.4
+	 *
+	 * @var   \Omise_Backend
+	 */
+	protected $backend;
+
 	/**
 	 * @see omise/includes/class-omise-setting.php
 	 *
diff --git a/templates/payment/form-installment.php b/templates/payment/form-installment.php
index 56f8fef6..66f5d779 100644
--- a/templates/payment/form-installment.php
+++ b/templates/payment/form-installment.php
@@ -10,8 +10,8 @@
 							<span class="title"><?php echo $backend->provider_name; ?></span><br/>
 							<select id="<?php echo $backend->_id; ?>_installment_terms" name="<?php echo $backend->_id; ?>_installment_terms" class="installment-term-select-box">
 								<option>Select term</option>
-								<?php foreach ( $backend->allowed_installment_terms as $term ) : ?>
-									<option value="<?php echo $term; ?>"><?php echo $term; ?> <?php echo __('months'); ?></option>
+								<?php foreach ( $backend->allowed_installment_terms as $installment_term ) : ?>
+									<option value="<?php echo $installment_term['term']; ?>"><?php echo $installment_term['term']; ?> <?php echo __('months'); ?></option>
 								<?php endforeach; ?>
 							</select>
 						</div>

From b227959066fc81fb830a28bbb6aa8727b6ff71f0 Mon Sep 17 00:00:00 2001
From: guzzilar <iam.nuttanon@gmail.com>
Date: Wed, 29 May 2019 16:33:29 +0700
Subject: [PATCH 3/9] Displaing installment interest fee at the checkout page
 (for Installment payment method).

---
 assets/css/omise-css.css                      | 23 +++++++++++++++++--
 .../class-omise-backend-installment.php       |  1 +
 .../class-omise-payment-installment.php       |  3 ++-
 templates/payment/form-installment.php        | 10 +++++++-
 4 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/assets/css/omise-css.css b/assets/css/omise-css.css
index bf89f39c..9f494ee2 100644
--- a/assets/css/omise-css.css
+++ b/assets/css/omise-css.css
@@ -37,6 +37,16 @@ fieldset.card-exists {
 	font-size: 80%;
 }
 
+#payment .payment_methods li .payment_box fieldset#omise-form-installment .omise-buttom-note {
+	margin-top: 4em;
+}
+
+#payment .payment_methods li .payment_box fieldset#omise-form-installment .omise-installment-interest-rate {
+	color: #aaa;
+	font-size: 80%;
+	line-height: 1;
+}
+
 
 /**
  * 2). Components
@@ -51,7 +61,16 @@ fieldset.card-exists {
 }
 
 /**
- * 2.2). Form, bank list components
+ * 2.2). Components
+ */
+.omise-buttom-note {
+	margin-top: 2em;
+	color: #aaa;
+	font-size: 80%;
+}
+
+/**
+ * 2.3). Form, bank list components
  */
 ul.omise-banks-list {
 	margin: 0;
@@ -149,7 +168,7 @@ ul.omise-banks-list {
 }
 
 /**
- * 2.3). Bank logos
+ * 2.4). Bank logos
  */
 /** BAY **/
 .bank-logo.bay {
diff --git a/includes/backends/class-omise-backend-installment.php b/includes/backends/class-omise-backend-installment.php
index 672a20a0..d68a0d80 100644
--- a/includes/backends/class-omise-backend-installment.php
+++ b/includes/backends/class-omise-backend-installment.php
@@ -71,6 +71,7 @@ public function get_available_providers( $currency, $purchase_amount ) {
 			$provider->provider_code             = str_replace( 'installment_', '', $provider->_id );
 			$provider->provider_name             = isset( self::$providers[ $provider->_id ] ) ? self::$providers[ $provider->_id ]['title'] : strtoupper( $provider->code );
 			$provider->allowed_installment_terms = $this->filter_available_terms( $provider->allowed_installment_terms, self::$providers[ $provider->_id ], $purchase_amount );
+			$provider->interest                  = $this->capabilities()->is_zero_interest() ? 0 : ( self::$providers[ $provider->_id ]['interest_rate'] * 100 );
 		}
 
 		return $providers;
diff --git a/includes/gateway/class-omise-payment-installment.php b/includes/gateway/class-omise-payment-installment.php
index 287669ab..7e9ae95d 100644
--- a/includes/gateway/class-omise-payment-installment.php
+++ b/includes/gateway/class-omise-payment-installment.php
@@ -77,7 +77,8 @@ public function payment_fields() {
 			Omise_Util::render_view(
 				'templates/payment/form-installment.php',
 				array(
-					'installment_backends' => $this->backend->get_available_providers( $currency, $cart_total )
+					'installment_backends' => $this->backend->get_available_providers( $currency, $cart_total ),
+					'is_zero_interest'     => $this->backend->capabilities()->is_zero_interest()
 				)
 			);
 		}
diff --git a/templates/payment/form-installment.php b/templates/payment/form-installment.php
index 66f5d779..1a3b6eac 100644
--- a/templates/payment/form-installment.php
+++ b/templates/payment/form-installment.php
@@ -11,14 +11,22 @@
 							<select id="<?php echo $backend->_id; ?>_installment_terms" name="<?php echo $backend->_id; ?>_installment_terms" class="installment-term-select-box">
 								<option>Select term</option>
 								<?php foreach ( $backend->allowed_installment_terms as $installment_term ) : ?>
-									<option value="<?php echo $installment_term['term']; ?>"><?php echo $installment_term['term']; ?> <?php echo __('months'); ?></option>
+									<option value="<?php echo $installment_term['term']; ?>"><?php echo $installment_term['term']; ?> <?php echo __('months'); ?> ( <?php echo wc_price( $installment_term['monthly_amount'] ); ?> / <?php echo __('months'); ?> )</option>
 								<?php endforeach; ?>
 							</select>
+							<?php if ( ! $viewData['is_zero_interest'] ): ?>
+								<br/><span class="omise-installment-interest-rate">( <?php echo __( 'interest', 'omise' ); ?> <?php echo $backend->interest; ?>% )</span>
+							<?php endif; ?>
 						</div>
 					</label>
 				</li>
 			<?php endforeach; ?>
 		</ul>
+		<div class="omise-buttom-note">
+			<p>
+				<?php echo $viewData['is_zero_interest'] ? 'All installment payments are interest free' : __( 'Monthly payment rates shown may be inaccurate as interest rates are subject to change by its bank issuer.', 'omise' ); ?>
+			</p>
+		</div>
 	</fieldset>
 <?php else: ?>
 	<p>

From 312029c4fbf3ec59dc623381047174739474657e Mon Sep 17 00:00:00 2001
From: guzzilar <iam.nuttanon@gmail.com>
Date: Wed, 5 Jun 2019 18:39:09 +0800
Subject: [PATCH 4/9] Applying & addressing all issues from the feedbacks at
 the code review, PR #115.

---
 .../class-omise-backend-installment.php       | 12 +++++------
 templates/payment/form-installment.php        | 20 +++++++++++++++++--
 .../class-omise-backend-installment-test.php  | 12 +++++------
 3 files changed, 30 insertions(+), 14 deletions(-)

diff --git a/includes/backends/class-omise-backend-installment.php b/includes/backends/class-omise-backend-installment.php
index d68a0d80..16c32783 100644
--- a/includes/backends/class-omise-backend-installment.php
+++ b/includes/backends/class-omise-backend-installment.php
@@ -8,7 +8,7 @@
  *
  * @method public initiate
  * @method public get_available_providers
- * @method public filter_available_terms
+ * @method public get_valid_terms
  * @method public calculate_monthly_payment_amount
  */
 class Omise_Backend_Installment extends Omise_Backend {
@@ -70,7 +70,7 @@ public function get_available_providers( $currency, $purchase_amount ) {
 		foreach ( $providers as &$provider ) {
 			$provider->provider_code             = str_replace( 'installment_', '', $provider->_id );
 			$provider->provider_name             = isset( self::$providers[ $provider->_id ] ) ? self::$providers[ $provider->_id ]['title'] : strtoupper( $provider->code );
-			$provider->allowed_installment_terms = $this->filter_available_terms( $provider->allowed_installment_terms, self::$providers[ $provider->_id ], $purchase_amount );
+			$provider->allowed_installment_terms = $this->get_valid_terms( $provider->allowed_installment_terms, self::$providers[ $provider->_id ], $purchase_amount );
 			$provider->interest                  = $this->capabilities()->is_zero_interest() ? 0 : ( self::$providers[ $provider->_id ]['interest_rate'] * 100 );
 		}
 
@@ -84,13 +84,13 @@ public function get_available_providers( $currency, $purchase_amount ) {
 	 *
 	 * @return array  of an filtered available terms
 	 */
-	public function filter_available_terms( $available_terms, $provider_detail, $purchase_amount ) {
+	public function get_valid_terms( $available_terms, $provider_detail, $purchase_amount ) {
 		$filtered_available_terms = array();
 
 		sort( $available_terms );
 
-		for ( $i = 0; $i < count( $available_terms ); $i++ ) {
-			$term           = $available_terms[ $i ];
+		foreach ( $available_terms as $key => $available_term ) {
+			$term           = $available_terms[ $key ];
 			$monthly_amount = $this->calculate_monthly_payment_amount(
 				$purchase_amount,
 				$term,
@@ -101,7 +101,7 @@ public function filter_available_terms( $available_terms, $provider_detail, $pur
 				break;
 			}
 
-			$filtered_available_terms[ $i ] = array(
+			$filtered_available_terms[ $key ] = array(
 				'term'           => $term,
 				'monthly_amount' => $monthly_amount
 			);
diff --git a/templates/payment/form-installment.php b/templates/payment/form-installment.php
index 1a3b6eac..76da4705 100644
--- a/templates/payment/form-installment.php
+++ b/templates/payment/form-installment.php
@@ -11,11 +11,27 @@
 							<select id="<?php echo $backend->_id; ?>_installment_terms" name="<?php echo $backend->_id; ?>_installment_terms" class="installment-term-select-box">
 								<option>Select term</option>
 								<?php foreach ( $backend->allowed_installment_terms as $installment_term ) : ?>
-									<option value="<?php echo $installment_term['term']; ?>"><?php echo $installment_term['term']; ?> <?php echo __('months'); ?> ( <?php echo wc_price( $installment_term['monthly_amount'] ); ?> / <?php echo __('months'); ?> )</option>
+									<option value="<?php echo $installment_term['term']; ?>">
+										<?php
+										echo sprintf(
+											__( '%d months', 'omise', 'omise_installment_term_option' ),
+											$installment_term['term']
+										);
+										?>
+
+										<?php
+										echo sprintf(
+											__( '( %s / months )', 'omise', 'omise_installment_payment_per_month' ),
+											wc_price( $installment_term['monthly_amount'] )
+										);
+										?>
+									</option>
 								<?php endforeach; ?>
 							</select>
 							<?php if ( ! $viewData['is_zero_interest'] ): ?>
-								<br/><span class="omise-installment-interest-rate">( <?php echo __( 'interest', 'omise' ); ?> <?php echo $backend->interest; ?>% )</span>
+								<br/><span class="omise-installment-interest-rate">
+									<?php echo sprintf( __( '( interest %g%% )', 'omise' ), $backend->interest ); ?>
+								</span>
 							<?php endif; ?>
 						</div>
 					</label>
diff --git a/tests/unit/includes/backends/class-omise-backend-installment-test.php b/tests/unit/includes/backends/class-omise-backend-installment-test.php
index e7176d76..f92719de 100644
--- a/tests/unit/includes/backends/class-omise-backend-installment-test.php
+++ b/tests/unit/includes/backends/class-omise-backend-installment-test.php
@@ -11,10 +11,10 @@ public static function setUpBeforeClass(): void {
 	/**
 	 * @test
 	 */
-	public function filtering_bbl_installment_term() {
+	public function get_only_valid_terms_from_given_bbl_allowed_installment_terms() {
 		$installment_backend = new Omise_Backend_Installment();
 		$purchase_amount     = 3000.00;
-		$available_terms     = array( 3, 4, 6, 8, 10 );
+		$allowed_terms     = array( 3, 4, 6, 8, 10 );
 		$provider_detail     = array(
 			'bank_code'          => 'bbl',
 			'title'              => __( 'Bangkok Bank', 'omise' ),
@@ -22,7 +22,7 @@ public function filtering_bbl_installment_term() {
 			'min_allowed_amount' => 500.00,
 		);
 
-		$result = $installment_backend->filter_available_terms( $available_terms, $provider_detail, $purchase_amount );
+		$result = $installment_backend->get_valid_terms( $allowed_terms, $provider_detail, $purchase_amount );
 
 		$this->assertEquals( 3, count( $result ) );
 		$this->assertEquals( array(
@@ -35,7 +35,7 @@ public function filtering_bbl_installment_term() {
 	/**
 	 * @test
 	 */
-	public function making_sure_that_we_can_filter_terms_properly_even_available_terms_is_not_in_a_proper_order() {
+	public function get_only_valid_terms_from_given_bbl_unsorted_allowed_installment_terms() {
 		$installment_backend = new Omise_Backend_Installment();
 		$purchase_amount     = 3000.00;
 		$available_terms     = array( 3, 10, 4, 8, 6 );
@@ -46,7 +46,7 @@ public function making_sure_that_we_can_filter_terms_properly_even_available_ter
 			'min_allowed_amount' => 500.00,
 		);
 
-		$result = $installment_backend->filter_available_terms( $available_terms, $provider_detail, $purchase_amount );
+		$result = $installment_backend->get_valid_terms( $available_terms, $provider_detail, $purchase_amount );
 
 		$this->assertEquals( 3, count( $result ) );
 		$this->assertEquals( array(
@@ -141,7 +141,7 @@ class Omise_Capabilities {
 	protected static $the_instance = null;
 
 	public static function retrieve() {
-		self::$the_instance = new self();
+		self::$the_instance = self::$the_instance ?: new self();
 		return self::$the_instance;
 	}
 

From 810520a7bc33adbaf2b17fbc98c065da75fc9fdd Mon Sep 17 00:00:00 2001
From: guzzilar <iam.nuttanon@gmail.com>
Date: Thu, 6 Jun 2019 14:16:51 +0800
Subject: [PATCH 5/9] Omise_Backend_Installment::get_valid_terms(), leaning the
 method (more efficient).

---
 includes/backends/class-omise-backend-installment.php | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/includes/backends/class-omise-backend-installment.php b/includes/backends/class-omise-backend-installment.php
index 16c32783..936bf2e5 100644
--- a/includes/backends/class-omise-backend-installment.php
+++ b/includes/backends/class-omise-backend-installment.php
@@ -85,12 +85,11 @@ public function get_available_providers( $currency, $purchase_amount ) {
 	 * @return array  of an filtered available terms
 	 */
 	public function get_valid_terms( $available_terms, $provider_detail, $purchase_amount ) {
-		$filtered_available_terms = array();
+		$valid_terms = array();
 
 		sort( $available_terms );
 
-		foreach ( $available_terms as $key => $available_term ) {
-			$term           = $available_terms[ $key ];
+		foreach ( $available_terms as $term ) {
 			$monthly_amount = $this->calculate_monthly_payment_amount(
 				$purchase_amount,
 				$term,
@@ -101,13 +100,13 @@ public function get_valid_terms( $available_terms, $provider_detail, $purchase_a
 				break;
 			}
 
-			$filtered_available_terms[ $key ] = array(
+			$valid_terms[] = array(
 				'term'           => $term,
 				'monthly_amount' => $monthly_amount
 			);
 		}
 
-		return $filtered_available_terms;
+		return $valid_terms;
 	}
 
 	/**

From 24cb3855ad524b74ab63bfe6563e10ba98ee42ad Mon Sep 17 00:00:00 2001
From: guzzilar <iam.nuttanon@gmail.com>
Date: Thu, 6 Jun 2019 17:57:19 +0800
Subject: [PATCH 6/9] Applying & addressing all issues from the second
 feedbacks at the code review, PR #115.

---
 .../class-omise-backend-installment.php       | 54 ++++++++++---------
 includes/class-omise-capabilities.php         |  2 +-
 templates/payment/form-installment.php        | 10 ++--
 .../class-omise-backend-installment-test.php  | 40 ++++++--------
 4 files changed, 51 insertions(+), 55 deletions(-)

diff --git a/includes/backends/class-omise-backend-installment.php b/includes/backends/class-omise-backend-installment.php
index 936bf2e5..40ca95f8 100644
--- a/includes/backends/class-omise-backend-installment.php
+++ b/includes/backends/class-omise-backend-installment.php
@@ -1,6 +1,6 @@
 <?php
 /**
- * Note: all of calculations in this class are based only on Thailand VAT and fee
+ * Note: all calculations in this class are based only on Thailand VAT and fee
  *       as currently Installment feature supported only for merchants
  *       that have registered with Omise Thailand account.
  *
@@ -8,7 +8,7 @@
  *
  * @method public initiate
  * @method public get_available_providers
- * @method public get_valid_terms
+ * @method public get_available_plans
  * @method public calculate_monthly_payment_amount
  */
 class Omise_Backend_Installment extends Omise_Backend {
@@ -68,56 +68,60 @@ public function get_available_providers( $currency, $purchase_amount ) {
 		$providers = $this->capabilities()->getInstallmentBackends( $currency, ( $purchase_amount * 100 ) );
 
 		foreach ( $providers as &$provider ) {
-			$provider->provider_code             = str_replace( 'installment_', '', $provider->_id );
-			$provider->provider_name             = isset( self::$providers[ $provider->_id ] ) ? self::$providers[ $provider->_id ]['title'] : strtoupper( $provider->code );
-			$provider->allowed_installment_terms = $this->get_valid_terms( $provider->allowed_installment_terms, self::$providers[ $provider->_id ], $purchase_amount );
-			$provider->interest                  = $this->capabilities()->is_zero_interest() ? 0 : ( self::$providers[ $provider->_id ]['interest_rate'] * 100 );
+			$provider_detail = self::$providers[ $provider->_id ];
+
+			$provider->provider_code      = str_replace( 'installment_', '', $provider->_id );
+			$provider->provider_name      = isset( $provider_detail ) ? $provider_detail['title'] : strtoupper( $provider->code );
+			$provider->interest_rate      = $this->capabilities()->is_zero_interest() ? 0 : ( $provider_detail['interest_rate'] * 100 );
+			$provider->available_plans    = $this->get_available_plans(
+				$purchase_amount,
+				$provider->allowed_installment_terms,
+				$provider->interest_rate,
+				$provider_detail['min_allowed_amount']
+			);
 		}
 
 		return $providers;
 	}
 
 	/**
-	 * @param  array $available_terms
-	 * @param  array $provider_detail
 	 * @param  float $purchase_amount
+	 * @param  array $allowed_installment_terms
+	 * @param  float $interest_rate
+	 * @param  float $min_allowed_amount
 	 *
 	 * @return array  of an filtered available terms
 	 */
-	public function get_valid_terms( $available_terms, $provider_detail, $purchase_amount ) {
-		$valid_terms = array();
+	public function get_available_plans( $purchase_amount, $allowed_installment_terms, $interest_rate, $min_allowed_amount ) {
+		$plans = array();
 
-		sort( $available_terms );
+		sort( $allowed_installment_terms );
 
-		foreach ( $available_terms as $term ) {
-			$monthly_amount = $this->calculate_monthly_payment_amount(
-				$purchase_amount,
-				$term,
-				$this->capabilities()->is_zero_interest() ? 0 : $provider_detail['interest_rate']
-			);
+		foreach ( $allowed_installment_terms as $term_length ) {
+			$monthly_amount = $this->calculate_monthly_payment_amount( $purchase_amount, $term_length, $interest_rate );
 
-			if ( $monthly_amount < $provider_detail['min_allowed_amount'] ) {
+			if ( $monthly_amount < $min_allowed_amount ) {
 				break;
 			}
 
-			$valid_terms[] = array(
-				'term'           => $term,
+			$plans[] = array(
+				'term_length'    => $term_length,
 				'monthly_amount' => $monthly_amount
 			);
 		}
 
-		return $valid_terms;
+		return $plans;
 	}
 
 	/**
 	 * @param  float $purchase_amount
-	 * @param  int   $term             installment term.
+	 * @param  int   $term_length      A length of a given installment term.
 	 * @param  float $interest_rate    its value can be '0' if merchant absorbs an interest.
 	 *
 	 * @return float  of a installment monthly payment (round up to 2 decimals).
 	 */
-	public function calculate_monthly_payment_amount( $purchase_amount, $term, $interest_rate ) {
-		$interest = $purchase_amount * $term * $interest_rate;
-		return round( ( $purchase_amount + $interest ) / $term, 2 );
+	public function calculate_monthly_payment_amount( $purchase_amount, $term_length, $interest_rate ) {
+		$interest = $purchase_amount * $term_length * $interest_rate;
+		return round( ( $purchase_amount + $interest ) / $term_length, 2 );
 	}
 }
diff --git a/includes/class-omise-capabilities.php b/includes/class-omise-capabilities.php
index 41e9eaee..2dd0937d 100644
--- a/includes/class-omise-capabilities.php
+++ b/includes/class-omise-capabilities.php
@@ -47,7 +47,7 @@ public function getInstallmentBackends( $currency = '', $amount = null ) {
 	}
 
 	/**
-	 * @return bool  True if merchant absorbs an interest or else, false.
+	 * @return bool  True if merchant absorbs the interest or else, false.
 	 */
 	public function is_zero_interest() {
 		return $this->capabilities['zero_interest_installments'];
diff --git a/templates/payment/form-installment.php b/templates/payment/form-installment.php
index 76da4705..1a10a990 100644
--- a/templates/payment/form-installment.php
+++ b/templates/payment/form-installment.php
@@ -10,19 +10,19 @@
 							<span class="title"><?php echo $backend->provider_name; ?></span><br/>
 							<select id="<?php echo $backend->_id; ?>_installment_terms" name="<?php echo $backend->_id; ?>_installment_terms" class="installment-term-select-box">
 								<option>Select term</option>
-								<?php foreach ( $backend->allowed_installment_terms as $installment_term ) : ?>
-									<option value="<?php echo $installment_term['term']; ?>">
+								<?php foreach ( $backend->available_plans as $installment_plan ) : ?>
+									<option value="<?php echo $installment_plan['term_length']; ?>">
 										<?php
 										echo sprintf(
 											__( '%d months', 'omise', 'omise_installment_term_option' ),
-											$installment_term['term']
+											$installment_plan['term_length']
 										);
 										?>
 
 										<?php
 										echo sprintf(
 											__( '( %s / months )', 'omise', 'omise_installment_payment_per_month' ),
-											wc_price( $installment_term['monthly_amount'] )
+											wc_price( $installment_plan['monthly_amount'] )
 										);
 										?>
 									</option>
@@ -30,7 +30,7 @@
 							</select>
 							<?php if ( ! $viewData['is_zero_interest'] ): ?>
 								<br/><span class="omise-installment-interest-rate">
-									<?php echo sprintf( __( '( interest %g%% )', 'omise' ), $backend->interest ); ?>
+									<?php echo sprintf( __( '( interest %g%% )', 'omise' ), $backend->interest_rate ); ?>
 								</span>
 							<?php endif; ?>
 						</div>
diff --git a/tests/unit/includes/backends/class-omise-backend-installment-test.php b/tests/unit/includes/backends/class-omise-backend-installment-test.php
index f92719de..02b901a1 100644
--- a/tests/unit/includes/backends/class-omise-backend-installment-test.php
+++ b/tests/unit/includes/backends/class-omise-backend-installment-test.php
@@ -11,48 +11,40 @@ public static function setUpBeforeClass(): void {
 	/**
 	 * @test
 	 */
-	public function get_only_valid_terms_from_given_bbl_allowed_installment_terms() {
+	public function get_only_valid_plans_from_given_bbl_allowed_installment_terms() {
 		$installment_backend = new Omise_Backend_Installment();
 		$purchase_amount     = 3000.00;
-		$allowed_terms     = array( 3, 4, 6, 8, 10 );
-		$provider_detail     = array(
-			'bank_code'          => 'bbl',
-			'title'              => __( 'Bangkok Bank', 'omise' ),
-			'interest_rate'      => 0.008,
-			'min_allowed_amount' => 500.00,
-		);
+		$allowed_terms       = array( 3, 4, 6, 8, 10 );
+		$interest_rate       = 0.008;
+		$min_allowed_amount  = 500.00;
 
-		$result = $installment_backend->get_valid_terms( $allowed_terms, $provider_detail, $purchase_amount );
+		$result = $installment_backend->get_available_plans( $purchase_amount, $allowed_terms, $interest_rate, $min_allowed_amount );
 
 		$this->assertEquals( 3, count( $result ) );
 		$this->assertEquals( array(
-			array( 'term' => 3, 'monthly_amount' => 1024.00 ),
-			array( 'term' => 4, 'monthly_amount' => 774.00 ),
-			array( 'term' => 6, 'monthly_amount' => 524.00 ),
+			array( 'term_length' => 3, 'monthly_amount' => 1024.00 ),
+			array( 'term_length' => 4, 'monthly_amount' => 774.00 ),
+			array( 'term_length' => 6, 'monthly_amount' => 524.00 ),
 		), $result );
 	}
 
 	/**
 	 * @test
 	 */
-	public function get_only_valid_terms_from_given_bbl_unsorted_allowed_installment_terms() {
+	public function get_only_valid_plans_from_given_bbl_unsorted_allowed_installment_terms() {
 		$installment_backend = new Omise_Backend_Installment();
 		$purchase_amount     = 3000.00;
-		$available_terms     = array( 3, 10, 4, 8, 6 );
-		$provider_detail     = array(
-			'bank_code'          => 'bbl',
-			'title'              => __( 'Bangkok Bank', 'omise' ),
-			'interest_rate'      => 0.008,
-			'min_allowed_amount' => 500.00,
-		);
+		$allowed_terms       = array( 3, 10, 4, 8, 6 );
+		$interest_rate       = 0.008;
+		$min_allowed_amount  = 500.00;
 
-		$result = $installment_backend->get_valid_terms( $available_terms, $provider_detail, $purchase_amount );
+		$result = $installment_backend->get_available_plans( $purchase_amount, $allowed_terms, $interest_rate, $min_allowed_amount );
 
 		$this->assertEquals( 3, count( $result ) );
 		$this->assertEquals( array(
-			array( 'term' => 3, 'monthly_amount' => 1024.00 ),
-			array( 'term' => 4, 'monthly_amount' => 774.00 ),
-			array( 'term' => 6, 'monthly_amount' => 524.00 ),
+			array( 'term_length' => 3, 'monthly_amount' => 1024.00 ),
+			array( 'term_length' => 4, 'monthly_amount' => 774.00 ),
+			array( 'term_length' => 6, 'monthly_amount' => 524.00 ),
 		), $result );
 	}
 

From 44da8e89d23362832ff0bc992a1ed37cc717a1a4 Mon Sep 17 00:00:00 2001
From: guzzilar <iam.nuttanon@gmail.com>
Date: Thu, 6 Jun 2019 18:01:24 +0800
Subject: [PATCH 7/9] Code styling.

---
 includes/backends/class-omise-backend-installment.php | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/includes/backends/class-omise-backend-installment.php b/includes/backends/class-omise-backend-installment.php
index 40ca95f8..2502a8a5 100644
--- a/includes/backends/class-omise-backend-installment.php
+++ b/includes/backends/class-omise-backend-installment.php
@@ -70,10 +70,10 @@ public function get_available_providers( $currency, $purchase_amount ) {
 		foreach ( $providers as &$provider ) {
 			$provider_detail = self::$providers[ $provider->_id ];
 
-			$provider->provider_code      = str_replace( 'installment_', '', $provider->_id );
-			$provider->provider_name      = isset( $provider_detail ) ? $provider_detail['title'] : strtoupper( $provider->code );
-			$provider->interest_rate      = $this->capabilities()->is_zero_interest() ? 0 : ( $provider_detail['interest_rate'] * 100 );
-			$provider->available_plans    = $this->get_available_plans(
+			$provider->provider_code   = str_replace( 'installment_', '', $provider->_id );
+			$provider->provider_name   = isset( $provider_detail ) ? $provider_detail['title'] : strtoupper( $provider->code );
+			$provider->interest_rate   = $this->capabilities()->is_zero_interest() ? 0 : ( $provider_detail['interest_rate'] * 100 );
+			$provider->available_plans = $this->get_available_plans(
 				$purchase_amount,
 				$provider->allowed_installment_terms,
 				$provider->interest_rate,

From 59d81e0c86beee7ebefe9c6740bc675001e17907 Mon Sep 17 00:00:00 2001
From: guzzilar <iam.nuttanon@gmail.com>
Date: Thu, 6 Jun 2019 19:31:25 +0800
Subject: [PATCH 8/9] Omise_Backend_Installment, improving its readability on
 an interest rate.

---
 .../backends/class-omise-backend-installment.php | 16 ++++++++--------
 .../class-omise-backend-installment-test.php     | 10 +++++-----
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/includes/backends/class-omise-backend-installment.php b/includes/backends/class-omise-backend-installment.php
index 2502a8a5..8d582366 100644
--- a/includes/backends/class-omise-backend-installment.php
+++ b/includes/backends/class-omise-backend-installment.php
@@ -22,35 +22,35 @@ public function initiate() {
 			'installment_first_choice' => array(
 				'bank_code'          => 'first_choice',
 				'title'              => __( 'Krungsri First Choice', 'omise' ),
-				'interest_rate'      => 0.013,
+				'interest_rate'      => 1.3,
 				'min_allowed_amount' => 300.00,
 			),
 
 			'installment_bay' => array(
 				'bank_code'          => 'bay',
 				'title'              => __( 'Krungsri', 'omise' ),
-				'interest_rate'      => 0.008,
+				'interest_rate'      => 0.8,
 				'min_allowed_amount' => 300.00,
 			),
 
 			'installment_ktc' => array(
 				'bank_code'          => 'ktc',
 				'title'              => __( 'Krungthai Card (KTC)', 'omise' ),
-				'interest_rate'      => 0.008,
+				'interest_rate'      => 0.8,
 				'min_allowed_amount' => 300.00,
 			),
 
 			'installment_bbl' => array(
 				'bank_code'          => 'bbl',
 				'title'              => __( 'Bangkok Bank', 'omise' ),
-				'interest_rate'      => 0.008,
+				'interest_rate'      => 0.8,
 				'min_allowed_amount' => 500.00,
 			),
 
 			'installment_kbank' => array(
 				'bank_code'          => 'kbank',
 				'title'              => __( 'Kasikorn Bank', 'omise' ),
-				'interest_rate'      => 0.0065,
+				'interest_rate'      => 0.65,
 				'min_allowed_amount' => 500.00,
 			),
 		);
@@ -72,7 +72,7 @@ public function get_available_providers( $currency, $purchase_amount ) {
 
 			$provider->provider_code   = str_replace( 'installment_', '', $provider->_id );
 			$provider->provider_name   = isset( $provider_detail ) ? $provider_detail['title'] : strtoupper( $provider->code );
-			$provider->interest_rate   = $this->capabilities()->is_zero_interest() ? 0 : ( $provider_detail['interest_rate'] * 100 );
+			$provider->interest_rate   = $this->capabilities()->is_zero_interest() ? 0 : ( $provider_detail['interest_rate'] );
 			$provider->available_plans = $this->get_available_plans(
 				$purchase_amount,
 				$provider->allowed_installment_terms,
@@ -116,12 +116,12 @@ public function get_available_plans( $purchase_amount, $allowed_installment_term
 	/**
 	 * @param  float $purchase_amount
 	 * @param  int   $term_length      A length of a given installment term.
-	 * @param  float $interest_rate    its value can be '0' if merchant absorbs an interest.
+	 * @param  float $interest_rate    Its value can be '0' if merchant absorbs an interest.
 	 *
 	 * @return float  of a installment monthly payment (round up to 2 decimals).
 	 */
 	public function calculate_monthly_payment_amount( $purchase_amount, $term_length, $interest_rate ) {
-		$interest = $purchase_amount * $term_length * $interest_rate;
+		$interest = $purchase_amount * $interest_rate * $term_length / 100;
 		return round( ( $purchase_amount + $interest ) / $term_length, 2 );
 	}
 }
diff --git a/tests/unit/includes/backends/class-omise-backend-installment-test.php b/tests/unit/includes/backends/class-omise-backend-installment-test.php
index 02b901a1..aeebd82f 100644
--- a/tests/unit/includes/backends/class-omise-backend-installment-test.php
+++ b/tests/unit/includes/backends/class-omise-backend-installment-test.php
@@ -15,7 +15,7 @@ public function get_only_valid_plans_from_given_bbl_allowed_installment_terms()
 		$installment_backend = new Omise_Backend_Installment();
 		$purchase_amount     = 3000.00;
 		$allowed_terms       = array( 3, 4, 6, 8, 10 );
-		$interest_rate       = 0.008;
+		$interest_rate       = 0.8;
 		$min_allowed_amount  = 500.00;
 
 		$result = $installment_backend->get_available_plans( $purchase_amount, $allowed_terms, $interest_rate, $min_allowed_amount );
@@ -35,7 +35,7 @@ public function get_only_valid_plans_from_given_bbl_unsorted_allowed_installment
 		$installment_backend = new Omise_Backend_Installment();
 		$purchase_amount     = 3000.00;
 		$allowed_terms       = array( 3, 10, 4, 8, 6 );
-		$interest_rate       = 0.008;
+		$interest_rate       = 0.8;
 		$min_allowed_amount  = 500.00;
 
 		$result = $installment_backend->get_available_plans( $purchase_amount, $allowed_terms, $interest_rate, $min_allowed_amount );
@@ -55,7 +55,7 @@ public function correctly_calculating_monthly_payment_amount_as_buyer_absorbs_ca
 		$installment_backend = new Omise_Backend_Installment();
 		$purchase_amount     = 10000.00;
 		$term                = 10;
-		$interest_rate       = 0.008;
+		$interest_rate       = 0.8;
 
 		$result = $installment_backend->calculate_monthly_payment_amount( $purchase_amount, $term, $interest_rate );
 
@@ -69,7 +69,7 @@ public function correctly_calculating_monthly_payment_amount_as_buyer_absorbs_ca
 		$installment_backend = new Omise_Backend_Installment();
 		$purchase_amount     = 17900.00;
 		$term                = 6;
-		$interest_rate       = 0.0069;
+		$interest_rate       = 0.69;
 
 		$result = $installment_backend->calculate_monthly_payment_amount( $purchase_amount, $term, $interest_rate );
 
@@ -83,7 +83,7 @@ public function correctly_calculating_monthly_payment_amount_as_buyer_absorbs_ca
 		$installment_backend = new Omise_Backend_Installment();
 		$purchase_amount     = 5000.00;
 		$term                = 10;
-		$interest_rate       = 0.008;
+		$interest_rate       = 0.8;
 
 		$result = $installment_backend->calculate_monthly_payment_amount( $purchase_amount, $term, $interest_rate );
 

From 0dfec4053e98caa82b6b5947fc20b7c5e06346ed Mon Sep 17 00:00:00 2001
From: guzzilar <iam.nuttanon@gmail.com>
Date: Fri, 7 Jun 2019 12:36:56 +0800
Subject: [PATCH 9/9] templates/payment/form-installment.php, complete a
 missing translation.

---
 templates/payment/form-installment.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/templates/payment/form-installment.php b/templates/payment/form-installment.php
index 1a10a990..df0046ca 100644
--- a/templates/payment/form-installment.php
+++ b/templates/payment/form-installment.php
@@ -40,7 +40,7 @@
 		</ul>
 		<div class="omise-buttom-note">
 			<p>
-				<?php echo $viewData['is_zero_interest'] ? 'All installment payments are interest free' : __( 'Monthly payment rates shown may be inaccurate as interest rates are subject to change by its bank issuer.', 'omise' ); ?>
+				<?php echo $viewData['is_zero_interest'] ? __( 'All installment payments are interest free', 'omise' ) : __( 'Monthly payment rates shown may be inaccurate as interest rates are subject to change by its bank issuer.', 'omise' ); ?>
 			</p>
 		</div>
 	</fieldset>