using System.Text.Json;

namespace Recordingtest.DiffReporter;

internal static class JsonDiffer
{
    public static IReadOnlyList<Hunk> Diff(JsonElement a, JsonElement b)
    {
        var aMap = new SortedDictionary<string, string>(StringComparer.Ordinal);
        var bMap = new SortedDictionary<string, string>(StringComparer.Ordinal);
        Flatten("$", a, aMap);
        Flatten("$", b, bMap);

        var hunks = new List<Hunk>();
        var allKeys = new SortedSet<string>(aMap.Keys, StringComparer.Ordinal);
        foreach (var k in bMap.Keys) allKeys.Add(k);

        int idx = 0;
        foreach (var key in allKeys)
        {
            var hasA = aMap.TryGetValue(key, out var av);
            var hasB = bMap.TryGetValue(key, out var bv);
            if (hasA && hasB)
            {
                if (!string.Equals(av, bv, StringComparison.Ordinal))
                    hunks.Add(new Hunk(idx, "changed", $"{key}={av}", $"{key}={bv}"));
            }
            else if (hasA)
            {
                hunks.Add(new Hunk(idx, "removed", $"{key}={av}", string.Empty));
            }
            else if (hasB)
            {
                hunks.Add(new Hunk(idx, "added", string.Empty, $"{key}={bv}"));
            }
            idx++;
        }
        return hunks;
    }

    private static void Flatten(string path, JsonElement el, IDictionary<string, string> map)
    {
        switch (el.ValueKind)
        {
            case JsonValueKind.Object:
                foreach (var p in el.EnumerateObject())
                    Flatten(path + "." + p.Name, p.Value, map);
                break;
            case JsonValueKind.Array:
                int i = 0;
                foreach (var item in el.EnumerateArray())
                {
                    Flatten(path + "[" + i + "]", item, map);
                    i++;
                }
                break;
            case JsonValueKind.String:
                map[path] = "\"" + el.GetString() + "\"";
                break;
            case JsonValueKind.Number:
                map[path] = el.GetRawText();
                break;
            case JsonValueKind.True:
                map[path] = "true";
                break;
            case JsonValueKind.False:
                map[path] = "false";
                break;
            case JsonValueKind.Null:
                map[path] = "null";
                break;
            default:
                map[path] = el.GetRawText();
                break;
        }
    }
}