advanced-calculator/src/AdvancedCalculator/ViewModels/MainViewModel.cs

using System.Collections.ObjectModel;
using System.Threading.Tasks;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using AdvancedCalculator.Models;
using AdvancedCalculator.Services;
using CSMic;
using System;
using System.Reflection;

namespace AdvancedCalculator.ViewModels;

public partial class MainViewModel : ViewModelBase
{
    private readonly ICalculatorService _calculatorService;
    public event EventHandler<string>? CopyRequested;

    public MainViewModel()
        : this(new CalculatorService())
    {
    }

    public MainViewModel(ICalculatorService calculatorService)
    {
        _calculatorService = calculatorService;
        History = new ObservableCollection<HistoryItem>();
        Variables = new ObservableCollection<VariableItem>();
    }

    [ObservableProperty]
    private string _inputText = string.Empty;

    [ObservableProperty]
    private bool _isFunctionsPanelOpen;

    [ObservableProperty]
    private int _selectedHistoryIndex = -1;

    // Caret position in the input TextBox
    [ObservableProperty]
    private int _caretIndex;

    public ObservableCollection<HistoryItem> History { get; }
    public ObservableCollection<VariableItem> Variables { get; }

    // App version string, sourced from AssemblyInformationalVersion
    public string AppVersion { get; } =
        typeof(MainViewModel).Assembly
            .GetCustomAttribute<AssemblyInformationalVersionAttribute>()?
            .InformationalVersion ?? "0.0.0";

    [RelayCommand]
    private void ToggleFunctions()
    {
        IsFunctionsPanelOpen = !IsFunctionsPanelOpen;
    }

    // Insert helpers for touch: appends tokens to the input box
    [RelayCommand]
    private void InsertVariable(VariableItem variableItem)
    {
        if (variableItem == null) return;
        if (string.IsNullOrWhiteSpace(variableItem.VariableName))
            return;
        InsertToken(variableItem.VariableName);
    }

    [RelayCommand]
    private void InsertFunction(FunctionDefinitionItem functionDefintionItem)
    {
        if (functionDefintionItem == null) return;
        if (string.IsNullOrWhiteSpace(functionDefintionItem.FunctionName))
            return;
        InsertToken(functionDefintionItem.FunctionName + "()");
        // Place caret inside the parentheses
        if (!string.IsNullOrEmpty(InputText))
        {
            CaretIndex = Math.Max(0, InputText.Length - 1);
        }
        // Close the functions flyout after insertion for smoother UX
        IsFunctionsPanelOpen = false;
    }

    private void InsertToken(string token)
    {
        if (string.IsNullOrEmpty(InputText))
        {
            InputText = token;
            return;
        }

        if (!char.IsWhiteSpace(InputText[^1]))
            InputText += " ";

        InputText += token;
    }

    [RelayCommand(AllowConcurrentExecutions = false)]
    private async Task Submit()
    {
        var text = InputText?.Trim();
        if (string.IsNullOrEmpty(text))
            return;

        var result = await _calculatorService.InterpretAsync(text);

        History.Add(new HistoryItem { Input = text, Output = result.Output });

        Variables.Clear();
        foreach (var v in result.Variables)
        {
            Variables.Add(v);
        }

        InputText = string.Empty;
        SelectedHistoryIndex = History.Count - 1;
    }

    // Copy helpers (MVVM-pure): build text in VM, View handles clipboard via CopyRequested
    [RelayCommand]
    private void CopyHistoryInput(HistoryItem? item)
    {
        if (item is null || string.IsNullOrWhiteSpace(item.Input)) return;
        CopyRequested?.Invoke(this, item.Input);
    }

    [RelayCommand]
    private void CopyHistoryOutput(HistoryItem? item)
    {
        if (item is null || string.IsNullOrWhiteSpace(item.Output)) return;
        CopyRequested?.Invoke(this, item.Output);
    }

    [RelayCommand]
    private void CopyHistoryBoth(HistoryItem? item)
    {
        if (item is null) return;
        var input = item.Input?.Trim();
        var output = item.Output?.Trim();
        if (string.IsNullOrEmpty(input) && string.IsNullOrEmpty(output)) return;
        if (string.IsNullOrEmpty(input)) { CopyRequested?.Invoke(this, output!); return; }
        if (string.IsNullOrEmpty(output)) { CopyRequested?.Invoke(this, input!); return; }

        CopyRequested?.Invoke(this, $"{input} = {output}");
    }
}