A sample master-detail view with Ballast and Compose

diagram.md

Data flow diagram

graph TD
    AppVM
    ListVM
    EditorVM
    
    AppVM -->|AppContract.State| ListVM
    ListVM -->|AppContract.Inputs| AppVM
    ListVM -->|ListContract.State| ListScreen
    ListScreen -->|ListContract.Inputs| ListVM

    AppVM -->|AppContract.State| EditorVM
    EditorVM -->|AppContract.Inputs| AppVM
    EditorVM -->|EditorContract.State| EditorScreen
    EditorScreen -->|EditorContract.Inputs| EditorVM

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main.kt

// AppVM
// ---------------------------------------------------------------------------------------------------------------------

public object AppContract {
    public data class State(
        val selectedFile: String? = null
    )
    public sealed class Inputs {
        public data class SetSelectedFile(val selectedFile: String) : Inputs()
        public object CloseSelectedFile : Inputs()
    }
    public sealed class Events {
        
    }
}

public class AppInputHandler : InputHandler<AppContract.Inputs, AppContract.Events, AppContract.State> {
    override suspend fun InputHandlerScope<AppContract.Inputs, AppContract.Events, AppContract.State>.handleInput(
        input: AppContract.Inputs
    ): Unit = when(input) {
        is AppContract.Inputs.SetSelectedFile -> {
            updateState { it.copy(selectedFile = input.selectedFile) }
        }
        is AppContract.Inputs.CloseSelectedFile -> {
            updateState { it.copy(selectedFile = null) }
        }
    }
}

public fun getAppViewModel(coroutineScope: CoroutineScope): BallastViewModel<AppContract.Inputs, AppContract.Events, AppContract.State> { 
    TODO()
}

// ListVM
// ---------------------------------------------------------------------------------------------------------------------

public object ListContract {
    public data class State(
        val selectedFile: String? = null,
        val allFiles: List<String> = emptyList(),
    )
    public sealed class Inputs {
        public object Initialize: Inputs()
        public data class AppStateUpdated(val appState: AppContract.State) : Inputs()

        public data class FilesListUpdated(val files: List<String>) : Inputs()
        public data class OpenFile(val file: String) : Inputs()
        public data class CreateFile(val fileName: String) : Inputs()
        public data class DeleteFile(val file: String) : Inputs()
    }
    public sealed class Events { }
}

public class ListInputHandler(
    private val appViewModel: BallastViewModel<AppContract.Inputs, AppContract.Events, AppContract.State>
) : InputHandler<ListContract.Inputs, ListContract.Events, ListContract.State> {
    override suspend fun InputHandlerScope<ListContract.Inputs, ListContract.Events, ListContract.State>.handleInput(
        input: ListContract.Inputs
    ): Unit = when(input) {
        is ListContract.Inputs.Initialize -> {
            observeFlows(
                "AppStateUpdated",
                appViewModel.observeStates().map { ListContract.Inputs.AppStateUpdated(it) }m
            )
        }
        is ListContract.Inputs.AppStateUpdated -> {
            updateState { it.copy(selectedFile = input.appState.selectedFile) }
        }

        is ListContract.Inputs.FilesListUpdated -> {
            updateState { it.copy(allFiles = input.files) }
        }
        is ListContract.Inputs.OpenFile -> {
            sideJob("OpenFile") {
                appViewModel.send(AppContract.Inputs.SetSelectedFile(input.file))
            }
        }
        is ListContract.Inputs.CreateFile -> TODO()
        is ListContract.Inputs.DeleteFile -> TODO()
    }
}

public fun getListViewModel(coroutineScope: CoroutineScope, appViewModel: BallastViewModel<AppContract.Inputs, AppContract.Events, AppContract.State>): BallastViewModel<ListContract.Inputs, ListContract.Events, ListContract.State> {
    TODO()
}

// EditorVM
// ---------------------------------------------------------------------------------------------------------------------

public object EditorContract {
    public data class State(
        val selectedFile: String? = null
    )
    public sealed class Inputs {
        public object Initialize: Inputs()
        public data class AppStateUpdated(val appState: AppContract.State) : Inputs()
        public object CloseFile : Inputs()
    }
    public sealed class Events { }
}

public class EditorInputHandler(
    private val appViewModel: BallastViewModel<AppContract.Inputs, AppContract.Events, AppContract.State>
) : InputHandler<EditorContract.Inputs, EditorContract.Events, EditorContract.State> {
    override suspend fun InputHandlerScope<EditorContract.Inputs, EditorContract.Events, EditorContract.State>.handleInput(
        input: EditorContract.Inputs
    ): Unit = when(input) {
        is EditorContract.Inputs.Initialize -> {
            observeFlows("AppStateUpdated", appViewModel.observeStates().map { EditorContract.Inputs.AppStateUpdated(it) })
        }
        is EditorContract.Inputs.AppStateUpdated -> {
            updateState { it.copy(selectedFile = input.appState.selectedFile) }
        }
        is EditorContract.Inputs.CloseFile -> {
            sideJob("CloseFile") {
                appViewModel.send(AppContract.Inputs.CloseSelectedFile)
            }
        }
    }
}

public fun getEditorViewModel(coroutineScope: CoroutineScope): BallastViewModel<EditorContract.Inputs, EditorContract.Events, EditorContract.State> {
    TODO()
}

// Compose UI
// ---------------------------------------------------------------------------------------------------------------------

@Composable
public fun App() {
    val appCoroutineScope = rememberCoroutineScope()
    val appVm = remember(appCoroutineScope) { getAppViewModel(appCoroutineScope) }
    
    Row { 
        Column {
            ListView(appVm)
        }
        Column {
            EditorView(appVm)
        }
    }
}

@Composable
public fun ListView(appViewModel: BallastViewModel<AppContract.Inputs, AppContract.Events, AppContract.State>) {
    val listCoroutineScope = rememberCoroutineScope()
    val listVm = remember(listCoroutineScope, appViewModel) { getListViewModel(listCoroutineScope, appViewModel) }
    val listVmState by listVm.observeStates().collectAsState()
    // display files list
}

@Composable
public fun EditorView(appViewModel: BallastViewModel<AppContract.Inputs, AppContract.Events, AppContract.State>) {
    val editorCoroutineScope = rememberCoroutineScope()
    val editorVm = remember(editorCoroutineScope, appViewModel) { getEditorViewModel(editorCoroutineScope, appViewModel) }
    val editorVmState by editorVm.observeStates().collectAsState()
    // display selected file in the editor
}