ScadaBridge/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Shared/LineDiffView.razor

@using System.Text.Json

@*
   LineDiffView (Component #24, Task M8 E2).

   Renders a single Code field's "lineDiff" payload — the line-level diff that the
   importer attaches to a Modified ImportPreviewItem's FieldDiffJson for code fields —
   as a compact, GitHub-style +/- list. Pure presentation: it takes an already-parsed
   JsonElement (the value of the "lineDiff" key) and walks its "hunks" array.

   hunk op ∈ "context" | "add" | "remove" (lowercase):
     context → muted line, both old/new line numbers
     add     → green-ish line, new line number only (no oldLineNo)
     remove  → red-ish line, old line number only (no newLineNo)

   When the payload's "truncated" flag is true a trailing marker summarises the
   addedCount / removedCount the diff could not show in full.

   No third-party diff/charting library — Bootstrap utility classes + a small
   monospace block only.
*@

@if (_hunks.Count == 0 && !_truncated)
{
    <div class="text-muted small fst-italic" data-testid="line-diff-empty">No line-level changes.</div>
}
else
{
    <div class="border rounded bg-body-tertiary font-monospace small overflow-auto"
         style="max-height: 22rem;" data-testid="line-diff">
        @foreach (var hunk in _hunks)
        {
            var (rowCls, gutter, sign) = hunk.Op switch
            {
                "add" => ("bg-success-subtle text-success-emphasis", FormatGutter(null, hunk.NewLineNo), "+"),
                "remove" => ("bg-danger-subtle text-danger-emphasis", FormatGutter(hunk.OldLineNo, null), "-"),
                _ => ("text-body-secondary", FormatGutter(hunk.OldLineNo, hunk.NewLineNo), " "),
            };
            <div class="d-flex @rowCls" data-testid="@($"line-diff-{hunk.Op}")">
                <span class="px-2 text-body-tertiary text-nowrap user-select-none"
                      style="min-width: 6.5rem;">@gutter</span>
                <span class="px-1 text-nowrap user-select-none">@sign</span>
                <span class="px-2 text-break flex-grow-1" style="white-space: pre-wrap;">@hunk.Text</span>
            </div>
        }
    </div>

    @if (_truncated)
    {
        <div class="text-muted small fst-italic mt-1" data-testid="line-diff-truncated">
            … diff truncated (+@_addedCount / -@_removedCount more)
        </div>
    }
}

@code {
    /// <summary>
    /// The parsed value of a Modified item's <c>FieldDiffJson</c> code field's
    /// <c>lineDiff</c> key. When null the component renders nothing meaningful —
    /// callers should only render it for code fields that actually carry a
    /// <c>lineDiff</c> object.
    /// </summary>
    [Parameter]
    public JsonElement? LineDiff { get; set; }

    private readonly List<Hunk> _hunks = new();
    private bool _truncated;
    private int _addedCount;
    private int _removedCount;

    private sealed record Hunk(string Op, string Text, int? OldLineNo, int? NewLineNo);

    protected override void OnParametersSet()
    {
        _hunks.Clear();
        _truncated = false;
        _addedCount = 0;
        _removedCount = 0;

        if (LineDiff is not { ValueKind: JsonValueKind.Object } payload)
        {
            return;
        }

        if (payload.TryGetProperty("truncated", out var truncatedEl)
            && truncatedEl.ValueKind is JsonValueKind.True or JsonValueKind.False)
        {
            _truncated = truncatedEl.GetBoolean();
        }
        if (payload.TryGetProperty("addedCount", out var addedEl)
            && addedEl.ValueKind == JsonValueKind.Number)
        {
            _addedCount = addedEl.GetInt32();
        }
        if (payload.TryGetProperty("removedCount", out var removedEl)
            && removedEl.ValueKind == JsonValueKind.Number)
        {
            _removedCount = removedEl.GetInt32();
        }

        if (payload.TryGetProperty("hunks", out var hunksEl)
            && hunksEl.ValueKind == JsonValueKind.Array)
        {
            foreach (var h in hunksEl.EnumerateArray())
            {
                if (h.ValueKind != JsonValueKind.Object)
                {
                    continue;
                }
                var op = h.TryGetProperty("op", out var opEl) && opEl.ValueKind == JsonValueKind.String
                    ? opEl.GetString() ?? "context"
                    : "context";
                var text = h.TryGetProperty("text", out var textEl) && textEl.ValueKind == JsonValueKind.String
                    ? textEl.GetString() ?? string.Empty
                    : string.Empty;
                int? oldLineNo = h.TryGetProperty("oldLineNo", out var oldEl) && oldEl.ValueKind == JsonValueKind.Number
                    ? oldEl.GetInt32()
                    : null;
                int? newLineNo = h.TryGetProperty("newLineNo", out var newEl) && newEl.ValueKind == JsonValueKind.Number
                    ? newEl.GetInt32()
                    : null;
                _hunks.Add(new Hunk(op, text, oldLineNo, newLineNo));
            }
        }
    }

    private static string FormatGutter(int? oldLineNo, int? newLineNo)
    {
        var left = oldLineNo?.ToString() ?? string.Empty;
        var right = newLineNo?.ToString() ?? string.Empty;
        return $"{left,3} {right,3}";
    }
}