using System;
using System.Linq;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;

namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests
{
    [Trait("Category", "Unit")]
    public sealed class HistorianClusterEndpointPickerTests
    {
        private static HistorianConfiguration Config(params string[] nodes) => new()
        {
            ServerName = "ignored",
            ServerNames = nodes.ToList(),
            FailureCooldownSeconds = 60,
        };

        /// <summary>Verifies that a single-node configuration falls back to ServerName when ServerNames is empty.</summary>
        [Fact]
        public void Single_node_config_falls_back_to_ServerName_when_ServerNames_empty()
        {
            var cfg = new HistorianConfiguration { ServerName = "only-node", ServerNames = new() };
            var p = new HistorianClusterEndpointPicker(cfg);
            p.NodeCount.ShouldBe(1);
            p.GetHealthyNodes().ShouldBe(new[] { "only-node" });
        }

        /// <summary>Verifies that a failed node enters cooldown and is skipped from the healthy nodes list.</summary>
        [Fact]
        public void Failed_node_enters_cooldown_and_is_skipped()
        {
            var now = new DateTime(2026, 4, 18, 10, 0, 0, DateTimeKind.Utc);
            var p = new HistorianClusterEndpointPicker(Config("a", "b"), () => now);

            p.MarkFailed("a", "boom");
            p.GetHealthyNodes().ShouldBe(new[] { "b" });
        }

        /// <summary>Verifies that the cooldown period expires after the configured time window.</summary>
        [Fact]
        public void Cooldown_expires_after_configured_window()
        {
            var clock = new DateTime(2026, 4, 18, 10, 0, 0, DateTimeKind.Utc);
            var p = new HistorianClusterEndpointPicker(Config("a", "b"), () => clock);
            p.MarkFailed("a", "boom");
            p.GetHealthyNodes().ShouldBe(new[] { "b" });

            clock = clock.AddSeconds(61);
            p.GetHealthyNodes().ShouldBe(new[] { "a", "b" });
        }

        /// <summary>Verifies that marking a node healthy immediately clears its cooldown.</summary>
        [Fact]
        public void MarkHealthy_immediately_clears_cooldown()
        {
            var now = new DateTime(2026, 4, 18, 10, 0, 0, DateTimeKind.Utc);
            var p = new HistorianClusterEndpointPicker(Config("a"), () => now);
            p.MarkFailed("a", "boom");
            p.GetHealthyNodes().ShouldBeEmpty();
            p.MarkHealthy("a");
            p.GetHealthyNodes().ShouldBe(new[] { "a" });
        }

        /// <summary>Verifies that when all nodes are in cooldown, an empty healthy list is returned.</summary>
        [Fact]
        public void All_nodes_in_cooldown_returns_empty_healthy_list()
        {
            var now = new DateTime(2026, 4, 18, 10, 0, 0, DateTimeKind.Utc);
            var p = new HistorianClusterEndpointPicker(Config("a", "b"), () => now);
            p.MarkFailed("a", "x");
            p.MarkFailed("b", "y");
            p.GetHealthyNodes().ShouldBeEmpty();
            p.NodeCount.ShouldBe(2);
        }

        /// <summary>Verifies that a snapshot reports failure count and the last error message.</summary>
        [Fact]
        public void Snapshot_reports_failure_count_and_last_error()
        {
            var now = new DateTime(2026, 4, 18, 10, 0, 0, DateTimeKind.Utc);
            var p = new HistorianClusterEndpointPicker(Config("a"), () => now);
            p.MarkFailed("a", "first");
            p.MarkFailed("a", "second");

            var snap = p.SnapshotNodeStates().Single();
            snap.FailureCount.ShouldBe(2);
            snap.LastError.ShouldBe("second");
            snap.IsHealthy.ShouldBeFalse();
            snap.CooldownUntil.ShouldNotBeNull();
        }

        /// <summary>Verifies that duplicate hostnames are deduplicated case-insensitively.</summary>
        [Fact]
        public void Duplicate_hostnames_are_deduplicated_case_insensitively()
        {
            var p = new HistorianClusterEndpointPicker(Config("NodeA", "nodea", "NodeB"));
            p.NodeCount.ShouldBe(2);
        }
    }
}