using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace JobTrackerApi.Models;

public sealed record DashboardWidget(string Id, bool Visible, string Size,
    [property: JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)] int? X = null,
    [property: JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)] int? Y = null,
    [property: JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)] int? W = null,
    [property: JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)] int? H = null);
public sealed record DashboardLayout(int Version, long Revision, IReadOnlyList<DashboardWidget> Widgets)
{
    public const int MaxBytes = 16 * 1024;
    // Responses cross a JavaScript client; the incremented revision must remain an exact integer there.
    private const long MaxRevision = 9_007_199_254_740_991L;
    private static readonly HashSet<string> KnownIds = new(StringComparer.Ordinal)
        { "cards", "attention", "funnel", "activity", "stageAge", "sources", "salary", "companies", "skills" };

    public static DashboardLayout? Parse(JsonElement root, bool reading = false, long revision = 0)
    {
        if (root.ValueKind != JsonValueKind.Object || !root.TryGetProperty("version", out var version) || version.ValueKind != JsonValueKind.Number || !version.TryGetInt32(out var v) || v is not (1 or 2)
            || !root.TryGetProperty("widgets", out var widgets) || widgets.ValueKind != JsonValueKind.Array || widgets.GetArrayLength() > 32) return null;
        if (!reading && (!root.TryGetProperty("revision", out var rev) || rev.ValueKind != JsonValueKind.Number || !rev.TryGetInt64(out revision) || revision < 0 || revision >= MaxRevision)) return null;
        var result = new List<DashboardWidget>();
        var seen = new HashSet<string>(StringComparer.Ordinal);
        foreach (var widget in widgets.EnumerateArray())
        {
            if (widget.ValueKind != JsonValueKind.Object || !widget.TryGetProperty("id", out var idValue) || idValue.ValueKind != JsonValueKind.String
                || !KnownIds.Contains(idValue.GetString()!) || !seen.Add(idValue.GetString()!)
                || !widget.TryGetProperty("visible", out var visible) || (visible.ValueKind != JsonValueKind.True && visible.ValueKind != JsonValueKind.False))
            {
                if (reading) continue;
                return null;
            }
            var id = idValue.GetString()!;
            var size = widget.TryGetProperty("size", out var sizeValue) && sizeValue.ValueKind == JsonValueKind.String ? sizeValue.GetString() : null;
            if (size is not ("standard" or "full") || (id == "cards" && size != "full"))
            {
                if (!reading) return null;
                size = id == "cards" ? "full" : "standard";
            }
            if (v == 1) result.Add(new DashboardWidget(id, visible.GetBoolean(), size));
            else
            {
                static bool Integer(JsonElement item, string key, out int number)
                {
                    number = 0;
                    return item.TryGetProperty(key, out var field) && field.ValueKind == JsonValueKind.Number && field.TryGetInt32(out number);
                }
                if (!Integer(widget, "x", out var x) || !Integer(widget, "y", out var y) || !Integer(widget, "w", out var w) || !Integer(widget, "h", out var h)
                    || x is < 0 or > 12 || y is < 0 or > 256 || w is < 4 or > 12 || h is < 4 or > 24 || x + w > 12 || y + h > 256
                    || (id == "cards" && w != 12) || (!reading && size != (w == 12 ? "full" : "standard")))
                {
                    if (reading) continue;
                    return null;
                }
                result.Add(new DashboardWidget(id, visible.GetBoolean(), w == 12 ? "full" : "standard", x, y, w, h));
            }
        }
        if (!reading && v == 2)
        {
            var visibleWidgets = result.Where(widget => widget.Visible).ToArray();
            for (var first = 0; first < visibleWidgets.Length; first++)
                for (var second = first + 1; second < visibleWidgets.Length; second++)
                {
                    var a = visibleWidgets[first]; var b = visibleWidgets[second];
                    if (a.X < b.X + b.W && a.X + a.W > b.X && a.Y < b.Y + b.H && a.Y + a.H > b.Y) return null;
                }
        }
        return new DashboardLayout(v, revision, result);
    }

    public static DashboardLayout Read(string? json, long revision)
    {
        if (json is not null && Encoding.UTF8.GetByteCount(json) <= MaxBytes)
        {
            try
            {
                using var document = JsonDocument.Parse(json);
                if (document.RootElement.ValueKind == JsonValueKind.Object
                    && document.RootElement.TryGetProperty("version", out var version) && version.ValueKind == JsonValueKind.Number
                    && version.TryGetInt32(out var futureVersion) && futureVersion > 2)
                    return new(futureVersion, revision, []);
                return Parse(document.RootElement, reading: true, revision) ?? new(1, revision, []);
            }
            catch (JsonException) { }
        }
        return new(1, revision, []);
    }
}