using System.ComponentModel;
using System.Text.Json;
using NucleicApp.Services;

namespace NucleicApp.ViewModels;

/// Presentation state for the first WinUI Home screen. It derives every value from
/// ``RendererStore`` projections; it never mutates host-owned state.
public sealed class HomeViewModel : ViewModelBase, IDisposable
{
    private readonly RendererStore store;
    private readonly Func<DateTimeOffset> now;

    public HomeViewModel(RendererStore store, Func<DateTimeOffset>? now = null)
    {
        this.store = store;
        this.now = now ?? (() => DateTimeOffset.Now);
        store.PropertyChanged += StoreChanged;
    }

    public string Greeting => now().Hour switch
    {
        >= 5 and < 12 => "Good morning",
        >= 12 and < 17 => "Good afternoon",
        >= 17 and < 22 => "Good evening",
        _ => "Hello",
    };

    public DashboardCounts Counts
    {
        get
        {
            if (store.Dashboard is not { } dashboard ||
                !dashboard.TryGetProperty("counts", out var counts)) return new();
            return new DashboardCounts(
                Int(counts, "projects"), Int(counts, "activeChats"),
                Int(counts, "chats"), Int(counts, "messages"), Long(counts, "tokens"));
        }
    }

    public string Subtitle => Counts.Chats == 0
        ? "Start a chat below to get going."
        : $"{Counts.ActiveChats} active of {Counts.Chats} chats · {Counts.Projects} "
            + (Counts.Projects == 1 ? "project" : "projects");

    public IReadOnlyList<SessionSummary> LiveSessions => store.Sessions
        .Where(session => !Bool(session.Raw, "archived"))
        .OrderByDescending(UpdatedAt)
        .ToArray();

    public IReadOnlyList<SessionSummary> NeedsAttention => LiveSessions
        .Where(session => session.PendingApprovalCount > 0 || session.Status == "awaitingApproval" ||
            (session.Status == "awaitingInput" && String(session.Raw, "disposition") == "awaitingInput"))
        .ToArray();

    public IReadOnlyList<SessionSummary> InProgress => LiveSessions
        .Where(session => session.Status is "provisioning" or "running")
        .ToArray();

    public int OpenTodoCount
    {
        get
        {
            if (store.Dashboard is not { } dashboard ||
                !dashboard.TryGetProperty("todos", out var todos) ||
                todos.ValueKind != JsonValueKind.Array) return 0;
            return todos.EnumerateArray().Count(todo => String(todo, "status") != "done");
        }
    }

    private void StoreChanged(object? sender, PropertyChangedEventArgs args)
    {
        if (args.PropertyName == nameof(RendererStore.Sessions))
        {
            Raise(nameof(LiveSessions));
            Raise(nameof(NeedsAttention));
            Raise(nameof(InProgress));
        }
        else if (args.PropertyName == nameof(RendererStore.Dashboard))
        {
            Raise(nameof(Counts));
            Raise(nameof(Subtitle));
            Raise(nameof(OpenTodoCount));
        }
    }

    private static bool Bool(JsonElement root, string name) =>
        root.TryGetProperty(name, out var value) && value.ValueKind == JsonValueKind.True;
    private static string? String(JsonElement root, string name) =>
        root.TryGetProperty(name, out var value) && value.ValueKind == JsonValueKind.String
            ? value.GetString() : null;
    private static int Int(JsonElement root, string name) =>
        root.TryGetProperty(name, out var value) && value.TryGetInt32(out var result) ? result : 0;
    private static long Long(JsonElement root, string name) =>
        root.TryGetProperty(name, out var value) && value.TryGetInt64(out var result) ? result : 0;
    private static double UpdatedAt(SessionSummary session) =>
        session.Raw.TryGetProperty("updatedAt", out var value) && value.TryGetDouble(out var result)
            ? result : 0;

    public void Dispose() => store.PropertyChanged -= StoreChanged;
}

public sealed record DashboardCounts(
    int Projects = 0, int ActiveChats = 0, int Chats = 0,
    int Messages = 0, long Tokens = 0);