@inherits DComponentBase

@* daisyUI Pagination: https://daisyui.com/components/pagination/ . A join of btn join-items; the page is 1-based
   (@bind-Current) and the current one is btn-active with aria-current="page". Beyond Siblings pages on each side of
   the current one, runs of pages collapse into a disabled ellipsis; the first and last pages always show. *@
<div @attributes="AdditionalAttributes" class="@Cx("join", Direction == DDirection.Vertical ? "join-vertical" : null, Class)">
	@if (ShowPreviousNext)
	{
		<button type="button" class="@ItemClass(false)" disabled="@(Current <= 1)" aria-label="@PreviousAriaLabel"
				@onclick="() => Go(Current - 1)">
			@PreviousText
		</button>
	}
	@foreach (var number in Pages())
	{
		if (number == 0)
		{
			<button type="button" class="@Cx(ItemClass(false), "btn-disabled")" disabled aria-hidden="true">@EllipsisText</button>
		}
		else
		{
			var target = number;
			<button type="button" class="@ItemClass(number == Current)" aria-current="@(number == Current ? "page" : null)"
					@onclick="() => Go(target)">
				@number
			</button>
		}
	}
	@if (ShowPreviousNext)
	{
		<button type="button" class="@ItemClass(false)" disabled="@(Current >= Count)" aria-label="@NextAriaLabel"
				@onclick="() => Go(Current + 1)">
			@NextText
		</button>
	}
</div>

@code {
	/// <summary>The number of pages.</summary>
	[Parameter] public int Count { get; set; }
	/// <summary>The current page, from 1 to Count.</summary>
	[Parameter] public int Current { get; set; } = 1;
	[Parameter] public EventCallback<int> CurrentChanged { get; set; }
	/// <summary>How many pages to show on each side of the current one before collapsing the rest into "…".</summary>
	[Parameter] public int Siblings { get; set; } = 1;
	[Parameter] public DSize Size { get; set; }
	[Parameter] public DDirection Direction { get; set; }
	[Parameter] public bool ShowPreviousNext { get; set; } = true;
	[Parameter] public string PreviousText { get; set; } = "«";
	[Parameter] public string NextText { get; set; } = "»";
	[Parameter] public string PreviousAriaLabel { get; set; } = "Previous page";
	[Parameter] public string NextAriaLabel { get; set; } = "Next page";
	[Parameter] public string EllipsisText { get; set; } = "…";

	string ItemClass(bool active) => Cx("join-item btn", SizeClass, active ? "btn-active" : null);

	string SizeClass => Size switch
	{
		DSize.Xs => "btn-xs",
		DSize.Sm => "btn-sm",
		DSize.Lg => "btn-lg",
		DSize.Xl => "btn-xl",
		_ => null
	};

	// The pages to show in order, with 0 standing for an ellipsis. A gap of a single page shows that page instead.
	IEnumerable<int> Pages()
	{
		if (Count <= 0)
			yield break;
		var current = Math.Clamp(Current, 1, Count);
		var siblings = Math.Clamp(Siblings, 0, Count);
		var from = Math.Max(1, current - siblings);
		var to = Math.Min(Count, current + siblings);
		if (from > 1)
		{
			yield return 1;
			if (from > 2)
				yield return from == 3 ? 2 : 0;
		}
		for (var page = from; page <= to; page++)
			yield return page;
		if (to < Count)
		{
			if (to < Count - 1)
				yield return to == Count - 2 ? Count - 1 : 0;
			yield return Count;
		}
	}

	async Task Go(int page)
	{
		page = Math.Clamp(page, 1, Math.Max(Count, 1));
		if (page == Current)
			return;
		Current = page;
		await CurrentChanged.InvokeAsync(page);
	}
}