ulapp/FieldLogger/ViewModels/JobsViewModel.cs

using System.Collections.ObjectModel;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using FieldLogger.Models;
using FieldLogger.Services;
using FieldLogger.Services.Data;

namespace FieldLogger.ViewModels;

public sealed partial class JobListItem : ObservableObject
{
    public required Job Job { get; init; }

    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(JobSummary))]
    [NotifyPropertyChangedFor(nameof(DeleteDescription))]
    [NotifyPropertyChangedFor(nameof(AccessibilityDescription))]
    private int _pointCount;

    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(ActiveStatusLabel))]
    [NotifyPropertyChangedFor(nameof(ActiveActionLabel))]
    [NotifyPropertyChangedFor(nameof(ActiveActionDescription))]
    [NotifyPropertyChangedFor(nameof(AccessibilityDescription))]
    private bool _isActive;

    public string Name => Job.Name;
    public string CreatedLabel => Job.CreatedUtc.ToLocalTime().ToString("g");
    public string ActiveStatusLabel => IsActive ? "ACTIVE JOB" : "NOT ACTIVE";
    public string ActiveActionLabel => IsActive ? "Active" : "Set active";
    public string JobSummary => $"Created {CreatedLabel} · {PointCount} {(PointCount == 1 ? "point" : "points")}";
    public string ActiveActionDescription => IsActive
        ? $"{Name} is already the active job"
        : $"Make {Name} the active capture job";
    public string DeleteDescription => $"Delete {Name} and its {PointCount} saved points";
    public string AccessibilityDescription => $"{Name}. {ActiveStatusLabel}. {JobSummary}.";
}

public sealed partial class JobsViewModel : ObservableObject
{
    private readonly AppDatabase _database;
    private readonly SettingsService _settings;
    private readonly SemaphoreSlim _refreshGate = new(1, 1);

    public ObservableCollection<JobListItem> Jobs { get; } = new();

    [ObservableProperty]
    private bool _isBusy;

    [ObservableProperty]
    private bool _isRefreshing;

    public JobsViewModel(AppDatabase database, SettingsService settings)
    {
        _database = database;
        _settings = settings;
    }

    public Task LoadAsync()
        => ReloadAsync(showRefreshIndicator: false, skipIfBusy: true);

    [RelayCommand]
    private Task RefreshAsync()
        => ReloadAsync(showRefreshIndicator: true, skipIfBusy: false);

    private async Task ReloadAsync(bool showRefreshIndicator, bool skipIfBusy)
    {
        var entered = skipIfBusy
            ? await _refreshGate.WaitAsync(0)
            : await WaitForRefreshGateAsync();
        if (!entered)
            return;

        try
        {
            IsBusy = true;
            if (showRefreshIndicator)
                IsRefreshing = true;

            var jobs = await _database.GetJobsAsync();
            var activeId = _settings.ActiveJobId;

            // Build a snapshot off-screen, then reconcile it with the existing observable
            // collection. Keeping the existing rows prevents CollectionView from repeatedly
            // discarding its measured cells and jumping back to the top.
            var items = new List<JobListItem>(jobs.Count);
            foreach (var job in jobs)
            {
                items.Add(new JobListItem
                {
                    Job = job,
                    PointCount = await _database.GetPointCountAsync(job.Id),
                    IsActive = job.Id == activeId,
                });
            }

            ApplySnapshot(items);
        }
        finally
        {
            if (showRefreshIndicator)
                IsRefreshing = false;
            IsBusy = false;
            _refreshGate.Release();
        }
    }

    private async Task<bool> WaitForRefreshGateAsync()
    {
        await _refreshGate.WaitAsync();
        return true;
    }

    private void ApplySnapshot(IReadOnlyList<JobListItem> incoming)
    {
        var incomingIds = incoming.Select(item => item.Job.Id).ToHashSet();

        for (var index = Jobs.Count - 1; index >= 0; index--)
        {
            if (!incomingIds.Contains(Jobs[index].Job.Id))
                Jobs.RemoveAt(index);
        }

        for (var targetIndex = 0; targetIndex < incoming.Count; targetIndex++)
        {
            var replacement = incoming[targetIndex];
            var existingIndex = -1;
            for (var index = targetIndex; index < Jobs.Count; index++)
            {
                if (Jobs[index].Job.Id == replacement.Job.Id)
                {
                    existingIndex = index;
                    break;
                }
            }

            if (existingIndex < 0)
            {
                Jobs.Insert(targetIndex, replacement);
                continue;
            }

            var existing = Jobs[existingIndex];
            existing.PointCount = replacement.PointCount;
            existing.IsActive = replacement.IsActive;

            if (existingIndex != targetIndex)
                Jobs.Move(existingIndex, targetIndex);
        }
    }

    [RelayCommand]
    private async Task NewJobAsync()
    {
        try
        {
            Console.WriteLine("NewJobAsync: Starting...");
            var name = await Shell.Current.DisplayPromptAsync("New Job", "Job name:",
                placeholder: $"Job {DateTime.Now:yyyy-MM-dd}");
            Console.WriteLine($"NewJobAsync: User entered: '{name}'");

            if (string.IsNullOrWhiteSpace(name))
            {
                Console.WriteLine("NewJobAsync: Name was empty, cancelling");
                return;
            }

            Console.WriteLine($"NewJobAsync: Creating job '{name.Trim()}'");
            var job = await _database.CreateJobAsync(name.Trim());
            Console.WriteLine($"NewJobAsync: Job created with ID {job.Id}");

            _settings.ActiveJobId = job.Id;
            Console.WriteLine($"NewJobAsync: Set active job to {job.Id}");

            await ReloadAsync(showRefreshIndicator: false, skipIfBusy: false);
            Console.WriteLine("NewJobAsync: Refresh complete");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"NewJobAsync: ERROR - {ex.Message}");
            Console.WriteLine($"NewJobAsync: Stack trace - {ex.StackTrace}");
        }
    }

    [RelayCommand]
    private async Task SetActiveAsync(JobListItem item)
    {
        _settings.ActiveJobId = item.Job.Id;
        foreach (var j in Jobs)
            j.IsActive = j.Job.Id == item.Job.Id;
        await Task.CompletedTask;
    }

    [RelayCommand]
    private Task OpenAsync(JobListItem item)
        => Shell.Current.GoToAsync($"jobdetail?jobId={item.Job.Id}");

    [RelayCommand]
    private async Task DeleteAsync(JobListItem item)
    {
        var confirmed = await Shell.Current.DisplayAlert("Delete Job",
            $"Delete \"{item.Job.Name}\" and its {item.PointCount} logged points?", "Delete", "Cancel");
        if (!confirmed)
            return;

        await _database.DeleteJobAsync(item.Job.Id);
        if (_settings.ActiveJobId == item.Job.Id)
            _settings.ActiveJobId = null;
        await ReloadAsync(showRefreshIndicator: false, skipIfBusy: false);
    }
}