using Shouldly;
using Xunit;

namespace ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests;

/// <summary>
///     Unit tests for the OperationLimits chunking surface (PR #275 / opcuaclient-3). Focused
///     on the static <see cref="OpcUaClientDriver.ChunkBy{T}"/> helper + the
///     <see cref="OpcUaClientDriver.OperationLimitsCache"/> sentinel semantics. Live
///     end-to-end tests against an in-process server land in the integration suite.
/// </summary>
[Trait("Category", "Unit")]
public sealed class OpcUaClientOperationLimitsTests
{
    [Fact]
    public void ChunkBy_with_cap_5_splits_12_items_into_3_slices_of_5_5_2()
    {
        // The PR-3 acceptance scenario: server advertises MaxNodesPerRead=5, client batches a
        // 12-tag read; driver must issue exactly 3 wire calls of sizes 5/5/2 in order.
        var input = Enumerable.Range(0, 12).ToArray();

        var slices = OpcUaClientDriver.ChunkBy<int>(input, cap: 5).ToArray();

        slices.Length.ShouldBe(3);
        slices[0].Count.ShouldBe(5);
        slices[1].Count.ShouldBe(5);
        slices[2].Count.ShouldBe(2);
        // Order + offsets must reflect the original sequence — chunking must not reorder
        // tags, otherwise the indexMap ↔ result-index alignment breaks.
        slices[0].ShouldBe(new[] { 0, 1, 2, 3, 4 });
        slices[1].ShouldBe(new[] { 5, 6, 7, 8, 9 });
        slices[2].ShouldBe(new[] { 10, 11 });
    }

    [Fact]
    public void ChunkBy_with_null_cap_yields_single_slice_no_chunking()
    {
        // cap=null is the "fetch hasn't completed" / "server reports 0 = no limit" sentinel.
        // Both must collapse to a single SDK call so the wire path doesn't change when the
        // server doesn't impose a cap.
        var input = Enumerable.Range(0, 12).ToArray();

        var slices = OpcUaClientDriver.ChunkBy<int>(input, cap: null).ToArray();

        slices.Length.ShouldBe(1, "null cap means no chunking — single SDK call");
        slices[0].Count.ShouldBe(12);
    }

    [Fact]
    public void ChunkBy_with_zero_cap_yields_single_slice_no_chunking()
    {
        // OPC UA Part 5: 0 is the wire-level "no limit" sentinel. NormalizeLimit folds it
        // into null upstream of ChunkBy, but the chunker itself must also treat 0 as
        // no-chunking — defence in depth in case a caller bypasses NormalizeLimit.
        var input = Enumerable.Range(0, 7).ToArray();

        var slices = OpcUaClientDriver.ChunkBy<int>(input, cap: 0).ToArray();

        slices.Length.ShouldBe(1);
        slices[0].Count.ShouldBe(7);
    }

    [Fact]
    public void ChunkBy_with_cap_larger_than_input_yields_single_slice()
    {
        var input = new[] { 1, 2, 3 };

        var slices = OpcUaClientDriver.ChunkBy<int>(input, cap: 100).ToArray();

        slices.Length.ShouldBe(1);
        slices[0].Count.ShouldBe(3);
    }

    [Fact]
    public void ChunkBy_with_empty_input_yields_no_slices()
    {
        // Empty batch must short-circuit before the wire call — saves a round-trip and
        // matches the !toSend.Count == 0 guard in the driver.
        var input = Array.Empty<int>();

        var slices = OpcUaClientDriver.ChunkBy<int>(input, cap: 5).ToArray();

        slices.Length.ShouldBe(0);
    }

    [Fact]
    public void ChunkBy_with_cap_equal_to_input_size_yields_single_slice()
    {
        // Edge case: exactly N items at cap N. Must NOT produce an extra empty slice.
        var input = Enumerable.Range(0, 5).ToArray();

        var slices = OpcUaClientDriver.ChunkBy<int>(input, cap: 5).ToArray();

        slices.Length.ShouldBe(1);
        slices[0].Count.ShouldBe(5);
    }

    [Fact]
    public void ChunkBy_with_cap_1_splits_each_item_into_its_own_slice()
    {
        // Pathological cap — degrades to N wire calls. Verifies the chunker handles the
        // boundary cleanly without off-by-one.
        var input = new[] { 10, 20, 30 };

        var slices = OpcUaClientDriver.ChunkBy<int>(input, cap: 1).ToArray();

        slices.Length.ShouldBe(3);
        slices[0].ShouldBe(new[] { 10 });
        slices[1].ShouldBe(new[] { 20 });
        slices[2].ShouldBe(new[] { 30 });
    }

    [Fact]
    public void OperationLimitsCache_records_all_four_caps_as_nullable_uint()
    {
        // The cache surfaces the four limits the driver chunks against. Storing as uint?
        // lets the chunker distinguish "not yet fetched" / "no limit" (null) from "limit=N".
        var cache = new OpcUaClientDriver.OperationLimitsCache(
            MaxNodesPerRead: 100u,
            MaxNodesPerWrite: 50u,
            MaxNodesPerBrowse: null,
            MaxNodesPerHistoryReadData: 10u);

        cache.MaxNodesPerRead.ShouldBe(100u);
        cache.MaxNodesPerWrite.ShouldBe(50u);
        cache.MaxNodesPerBrowse.ShouldBeNull();
        cache.MaxNodesPerHistoryReadData.ShouldBe(10u);
    }

    [Fact]
    public void Driver_starts_with_no_cached_OperationLimits()
    {
        // Pre-init / pre-first-batch state: cache is null so callers fall through to
        // single-call behaviour. Lazy fetch happens on the first ReadAsync/WriteAsync.
        using var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions(), "opcua-cache-init");

        drv.OperationLimitsForTest.ShouldBeNull();
    }
}