using w4c_workflows.Models.Nodes;

namespace w4c_workflows.Services.Nodes.Executors;

/// <summary>
/// Limit node. Keeps the first or last N items of the incoming batch and drops
/// the rest. Runs in all-items mode because "last N" needs the whole input.
/// </summary>
public sealed class LimitNodeExecutor : INodeExecutor
{
    public string Type => "core.limit";

    public Task<NodeExecutionOutcome> RunAsync(NodeExecutionContext context, CancellationToken ct)
    {
        var maxItems = NodeValueAccess.ReadInt(context.Parameters, "maxItems", 1);
        if (maxItems < 0)
            return Task.FromResult(NodeExecutionOutcome.Failed("maxItems must not be negative", "invalid_parameter"));

        var items = context.Input(0);
        var keep = NodeValueAccess.ReadString(context.Parameters, "keep") ?? "firstItems";

        IReadOnlyList<FlowItem> output = keep switch
        {
            "lastItems" => items.Skip(Math.Max(0, items.Count - maxItems)).ToList(),
            _ => items.Take(maxItems).ToList(),
        };

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