refactor: Reorganize PrimerInputFieldContainer structure

Split container into focused files for better maintainability:
- Core struct and convenience initializer in main file
- View rendering logic in +Rendering extension
- Styling properties in +Styling extension
- Preview helpers in +PreviewHelpers extension

Updated preview format to use #Preview macro and changed access
control to internal to support multi-file organization.

Author: OnurVar

Sources/PrimerSDK/Classes/CheckoutComponents/Internal/Presentation/Components/Infrastructure/Containers/PrimerInputFieldContainer+PreviewHelpers.swift

@@ -0,0 +1,88 @@
+//
+//  PrimerInputFieldContainer+PreviewHelpers.swift
+//
+//  Copyright © 2025 Primer API Ltd. All rights reserved. 
+//  Licensed under the MIT License. See LICENSE file in the project root for full license information.
+
+import SwiftUI
+
+#if DEBUG
+@available(iOS 15.0, *)
+struct PreviewContainer: View {
+    let label: String?
+    let text: String
+    let errorMessage: String?
+
+    @State private var currentText: String
+    @State private var isValid = true
+    @State private var currentErrorMessage: String?
+    @State private var isFocused = false
+
+    init(label: String?, text: String, errorMessage: String?) {
+        self.label = label
+        self.text = text
+        self.errorMessage = errorMessage
+        self._currentText = State(initialValue: text)
+        self._currentErrorMessage = State(initialValue: errorMessage)
+    }
+
+    var body: some View {
+        PrimerInputFieldContainer(
+            label: label,
+            styling: nil,
+            text: $currentText,
+            isValid: $isValid,
+            errorMessage: $currentErrorMessage,
+            isFocused: $isFocused
+        ) {
+            TextField("Placeholder", text: $currentText, onEditingChanged: { focused in
+                isFocused = focused
+            })
+            .textFieldStyle(.plain)
+        }
+    }
+}
+
+@available(iOS 15.0, *)
+struct PreviewContainerWithRightComponent: View {
+    let label: String?
+    let text: String
+
+    @State private var currentText: String
+    @State private var isValid = true
+    @State private var errorMessage: String?
+    @State private var isFocused = false
+    @Environment(\.designTokens) private var tokens
+
+    init(label: String?, text: String) {
+        self.label = label
+        self.text = text
+        self._currentText = State(initialValue: text)
+    }
+
+    var body: some View {
+        PrimerInputFieldContainer(
+            label: label,
+            styling: nil,
+            text: $currentText,
+            isValid: $isValid,
+            errorMessage: $errorMessage,
+            isFocused: $isFocused,
+            textFieldBuilder: {
+                TextField("Placeholder", text: $currentText, onEditingChanged: { focused in
+                    isFocused = focused
+                })
+                .textFieldStyle(.plain)
+            },
+            rightComponent: {
+                let iconSize = PrimerSize.medium(tokens: tokens)
+                Image(systemName: "info.circle")
+                    .resizable()
+                    .aspectRatio(contentMode: .fit)
+                    .frame(width: iconSize, height: iconSize)
+                    .foregroundColor(PrimerCheckoutColors.textSecondary(tokens: tokens))
+            }
+        )
+    }
+}
+#endif

Sources/PrimerSDK/Classes/CheckoutComponents/Internal/Presentation/Components/Infrastructure/Containers/PrimerInputFieldContainer+Rendering.swift

@@ -0,0 +1,78 @@
+//
+//  PrimerInputFieldContainer+Rendering.swift
+//
+//  Copyright © 2025 Primer API Ltd. All rights reserved. 
+//  Licensed under the MIT License. See LICENSE file in the project root for full license information.
+
+import SwiftUI
+
+// MARK: - Label
+@available(iOS 15.0, *)
+extension PrimerInputFieldContainer {
+    func makeLabel(_ label: String) -> some View {
+        Text(label)
+            .font(labelFont)
+            .foregroundColor(labelForegroundColor)
+            .frame(height: PrimerComponentHeight.label)
+    }
+}
+
+// MARK: - TextField Container
+@available(iOS 15.0, *)
+extension PrimerInputFieldContainer {
+    func makeTextFieldContainer() -> some View {
+        HStack(spacing: PrimerSpacing.small(tokens: tokens), content: makeTextFieldContainerContent)
+            .padding(.leading, styling?.padding?.leading ?? PrimerSpacing.medium(tokens: tokens))
+            .padding(.trailing, styling?.padding?.trailing ?? PrimerSpacing.medium(tokens: tokens))
+            .frame(height: styling?.fieldHeight ?? PrimerSize.xxlarge(tokens: tokens))
+            .background(makeTextFieldContainerBackground())
+    }
+
+    func makeTextFieldContainerContent() -> some View {
+        Group {
+            textFieldBuilder()
+            Spacer()
+            rightComponent?()
+            if hasError { makeTextFieldContainerWarning() }
+        }
+    }
+
+    func makeTextFieldContainerBackground() -> some View {
+        RoundedRectangle(cornerRadius: PrimerRadius.small(tokens: tokens))
+            .strokeBorder(borderColor, lineWidth: textFieldContainerBackgroundLineWidth)
+            .background(makeTextFieldContainerBackgroundBackground())
+            .animation(AnimationConstants.focusAnimation, value: isFocused)
+    }
+
+    func makeTextFieldContainerBackgroundBackground() -> some View {
+        RoundedRectangle(cornerRadius: PrimerRadius.small(tokens: tokens))
+            .fill(styling?.backgroundColor ?? PrimerCheckoutColors.background(tokens: tokens))
+    }
+
+    func makeTextFieldContainerWarning() -> some View {
+        let iconSize = PrimerSize.medium(tokens: tokens)
+        return Image(systemName: "exclamationmark.triangle.fill")
+            .resizable()
+            .aspectRatio(contentMode: .fit)
+            .frame(width: iconSize, height: iconSize)
+            .foregroundColor(PrimerCheckoutColors.iconNegative(tokens: tokens))
+            .offset(x: hasError ? 0 : -10)
+            .opacity(hasError ? 1.0 : 0.0)
+            .animation(.spring(response: 0.3, dampingFraction: 0.7), value: hasError)
+    }
+}
+
+// MARK: - Error
+@available(iOS 15.0, *)
+extension PrimerInputFieldContainer {
+    func makeErrorMessage(_ errorMessage: String) -> some View {
+        Text(errorMessage)
+            .font(errorMessageFont)
+            .foregroundColor(errorMessageForegroundColor)
+            .frame(height: errorMessageHeight)
+            .offset(y: hasError ? 0 : -10)
+            .opacity(hasError ? 1.0 : 0.0)
+            .padding(.top, errorMessageTopPadding)
+            .animation(.spring(response: 0.3, dampingFraction: 0.7), value: hasError)
+    }
+}

Sources/PrimerSDK/Classes/CheckoutComponents/Internal/Presentation/Components/Infrastructure/Containers/PrimerInputFieldContainer+Styling.swift

@@ -0,0 +1,54 @@
+//
+//  PrimerInputFieldContainer+Styling.swift
+//
+//  Copyright © 2025 Primer API Ltd. All rights reserved. 
+//  Licensed under the MIT License. See LICENSE file in the project root for full license information.
+
+import SwiftUI
+
+// MARK: - Colors
+@available(iOS 15.0, *)
+extension PrimerInputFieldContainer {
+    var borderColor: Color {
+        if errorMessage?.isEmpty == false {
+            errorBorderColor
+        } else {
+            isFocused ? focusedBorderColor : defaultBorderColor
+        }
+    }
+
+    var labelForegroundColor: Color {
+        styling?.labelColor ?? PrimerCheckoutColors.textPrimary(tokens: tokens)
+    }
+
+    var errorMessageForegroundColor: Color {
+        PrimerCheckoutColors.textNegative(tokens: tokens)
+    }
+
+    var errorBorderColor: Color {
+        styling?.errorBorderColor ?? PrimerCheckoutColors.borderError(tokens: tokens)
+    }
+
+    var focusedBorderColor: Color {
+        styling?.focusedBorderColor ?? PrimerCheckoutColors.borderFocus(tokens: tokens)
+    }
+
+    var defaultBorderColor: Color {
+        styling?.borderColor ?? PrimerCheckoutColors.borderDefault(tokens: tokens)
+    }
+}
+
+// MARK: - Fonts
+@available(iOS 15.0, *)
+extension PrimerInputFieldContainer {
+    var errorMessageFont: Font { PrimerFont.bodySmall(tokens: tokens) }
+    var labelFont: Font { styling?.labelFont ?? PrimerFont.bodySmall(tokens: tokens) }
+}
+
+// MARK: - Spacing & Frame
+@available(iOS 15.0, *)
+extension PrimerInputFieldContainer {
+    var textFieldContainerBackgroundLineWidth: CGFloat { styling?.borderWidth ?? PrimerBorderWidth.standard }
+    var errorMessageHeight: CGFloat { hasError ? PrimerComponentHeight.errorMessage : 0 }
+    var errorMessageTopPadding: CGFloat { hasError ? PrimerSpacing.xsmall(tokens: tokens) : 0 }
+}