added CharacterListViewModel and states with tests

Stream-iOS/Stream-iOS/Features/Characters/CharacterListState.swift

@@ -0,0 +1,12 @@
+//
+//  CharacterListState.swift
+//  Stream-iOS
+//
+//  Created by Ullash Podder on 20/07/2026.
+//
+enum CharacterListState: Equatable {
+    case idle
+    case loading
+    case loaded
+    case error(String)
+}

Stream-iOS/Stream-iOS/Features/Characters/CharacterListView.swift

@@ -0,0 +1,7 @@
+//
+//  CharacterListView.swift
+//  Stream-iOS
+//
+//  Created by Ullash Podder on 20/07/2026.
+//
+

Stream-iOS/Stream-iOS/Features/Characters/CharacterListViewModel.swift

@@ -0,0 +1,47 @@
+//
+//  CharacterListViewModel.swift
+//  Stream-iOS
+//
+//  Created by Ullash Podder on 20/07/2026.
+//
+
+import Foundation
+
+@MainActor
+@Observable
+final class CharacterListViewModel {
+    private(set) var characters: [CharacterDTO] = []
+    private(set) var state: CharacterListState = .idle
+
+    private let repository: CharacterRepository
+    private var currentPage = 0
+    private var totalPages = Int.max      // unknown until first response
+    private var isLoading = false          // the dedupe guard
+
+    init(repository: CharacterRepository) {
+        self.repository = repository
+    }
+
+    func loadNextPageIfNeeded() async {
+        // Guard 1: don't start a fetch while one is running
+        guard !isLoading else { return }
+        // Guard 2: don't fetch past the last page
+        guard currentPage < totalPages else { return }
+
+        isLoading = true
+        state = .loading
+        let nextPage = currentPage + 1
+
+        do {
+            let response = try await repository.fetchCharacters(page: nextPage)
+            characters.append(contentsOf: response.results)
+            currentPage = nextPage
+            totalPages = response.info.pages
+            state = .loaded
+        } catch {
+            state = .error("Could not load characters.")
+        }
+
+        isLoading = false
+    }
+}

Stream-iOS/Stream-iOS/Features/Characters/CharacterRowView.swift

@@ -0,0 +1,7 @@
+//
+//  CharacterRowView.swift
+//  Stream-iOS
+//
+//  Created by Ullash Podder on 20/07/2026.
+//
+

Stream-iOS/Stream-iOSTests/CharacterDecodingTests.swift

@@ -40,5 +40,63 @@ struct CharacterDecodingTests {
 
         #expect(dto.status == .unknown)
     }
+    func decodedFixturePage() throws -> PagedResponse<CharacterDTO> {
+        let data = try Fixture.load("character_page1")
+        let response = try JSONDecoder().decode(PagedResponse<CharacterDTO>.self, from: data)
+        return response
+    }
+//    when several calls to loadNextPageIfNeeded() overlap in time, exactly one fetch reaches the repository.
+    @MainActor @Test func loadsFirstPageAndPopulatesCharacters() async throws{
+//        arrange
+        let mockRepository = MockCharacterRepository()
+        mockRepository.result = .success( try decodedFixturePage())
+        let sut = CharacterListViewModel(repository: mockRepository)
+//        act
+        await sut.loadNextPageIfNeeded()
+//        assert
+        #expect(sut.state == .loaded)
+        #expect(sut.characters.count == 20)
+        #expect(mockRepository.requestedPages == [1])
+    }
+    @MainActor @Test func loadsSecondPageAndAppends() async throws{
+//        arrange
+        let mockRepository = MockCharacterRepository()
+        mockRepository.result = .success( try decodedFixturePage())
+        let sut = CharacterListViewModel(repository: mockRepository)
+//        act
+        await sut.loadNextPageIfNeeded()
+//        second call
+        await sut.loadNextPageIfNeeded()
+//        assert
+        #expect(sut.state == .loaded)
+        #expect(sut.characters.count == 40)
+        #expect(mockRepository.requestedPages == [1,2])
+    }
+    @MainActor @Test func concurrentLoadsRequestPageOnlyOnce() async throws{
+//        arrange
+        let mockRepository = MockCharacterRepository()
+        mockRepository.result = .success( try decodedFixturePage())
+        let sut = CharacterListViewModel(repository: mockRepository)
+//        act
+        await withTaskGroup (of:Void.self) { group in
+            for _ in 0..<3 {
+                group.addTask { await sut.loadNextPageIfNeeded() }
+            }
+        }
+//        assert
+        #expect(sut.state == .loaded)
+        #expect(sut.characters.count == 20)
+        #expect(mockRepository.requestedPages == [1])
+    }
+    @MainActor @Test func failedLoadSetsErrorStateAndKeepsCharactersEmpty() async throws {
+        let mockRepository = MockCharacterRepository()
+        mockRepository.result = .failure(APIError.httpStatus(500))
+        let sut = CharacterListViewModel(repository: mockRepository)
+
+        await sut.loadNextPageIfNeeded()
+
+        #expect(sut.characters.isEmpty)
+        // assert state is .error
+    }
 }
 

Stream-iOS/Stream-iOSTests/Mocks/MockCharacterRepository.swift

@@ -14,6 +14,7 @@ final class MockCharacterRepository: CharacterRepository, @unchecked Sendable {
 
     func fetchCharacters(page: Int) async throws -> PagedResponse<CharacterDTO> {
         requestedPages.append(page)
+        try await Task.sleep(for: .milliseconds(50))
         return try result.get()
     }
 }