using System.Text.Json.Nodes;
using w4c_workflows.Models.Nodes;

namespace w4c_workflows.Services.Nodes.Executors;

/// <summary>
/// Merge node. Combines two input ports into one:
///   - <c>append</c> — input 0 items then input 1 items;
///   - <c>chooseBranch</c> — the items of the first non-empty input;
///   - <c>combineByPosition</c> — pair items by index and shallow-merge their
///     fields (input 1 overrides input 0); items past the shorter input pass
///     through unchanged.
/// Runs in all-items mode because it has more than one input port.
/// </summary>
public sealed class MergeNodeExecutor : INodeExecutor
{
    public string Type => "core.merge";

    public Task<NodeExecutionOutcome> RunAsync(NodeExecutionContext context, CancellationToken ct)
    {
        var first = context.Input(0);
        var second = context.Input(1);
        var mode = context.Parameters["mode"] is JsonValue value && value.TryGetValue<string>(out var text)
            ? text
            : "append";

        var items = mode switch
        {
            "chooseBranch" => first.Count > 0 ? first.ToList() : second.ToList(),
            "combineByPosition" => CombineByPosition(first, second),
            _ => first.Concat(second).ToList(),
        };

        return Task.FromResult(NodeExecutionOutcome.Single(items));
    }

    private static List<FlowItem> CombineByPosition(
        IReadOnlyList<FlowItem> first, IReadOnlyList<FlowItem> second)
    {
        var merged = new List<FlowItem>(Math.Max(first.Count, second.Count));
        for (var i = 0; i < first.Count || i < second.Count; i++)
        {
            var left = i < first.Count ? first[i] : null;
            var right = i < second.Count ? second[i] : null;

            if (left == null)
            {
                merged.Add(right!);
                continue;
            }
            if (right == null)
            {
                merged.Add(left);
                continue;
            }

            var json = (JsonObject)left.Json.DeepClone();
            foreach (var (name, node) in right.Json)
                json[name] = node?.DeepClone();

            merged.Add(new FlowItem
            {
                Json = json,
                Binary = left.Binary ?? right.Binary,
                Origin = left.Origin ?? right.Origin,
            });
        }

        return merged;
    }
}