using System.Diagnostics;
using System.Text.Json.Nodes;

using decePubClient.E2E.Support;

using Microsoft.Playwright;

namespace decePubClient.E2E.Perf
{
	// The home feed with thousands of posts behind it: load0's home, filled by SocialPub's load runs
	// (tools/pasture/load.sh, the flood peer). Scrolls it until 100, 500, 1000 and 2000 posts are loaded (the feed renders
	// only the cards near the view, so it counts what it holds, data-feed-count) and measures, at each, how long the
	// pages took, the page's size (DOM nodes, JS and .NET heaps) and the long tasks; and the time to the first card. Writes perf.json next to the test output; nothing is asserted beyond reaching the cards, the numbers are
	// for comparing runs.
	[Trait("Category", "Perf")]
	public sealed class FeedPerfTests(Browser browser)
	{
		static readonly int[] Steps = [100, 500, 1000, 2000];

		[Fact]
		public async Task A_long_home_feed_scrolls_to_two_thousand_cards()
		{
			var persona = new Pasture.Persona("load0", "load0", "pastureroot", "Pasture-Pass-1!", null, null, null);
			await using var session = await SignIn.As(browser, persona, fresh: true);
			var page = session.Page;
			await page.EvaluateAsync("() => localStorage.removeItem('FeedFilter')");
			await page.AddInitScriptAsync(@"window.__longTasks = []; new PerformanceObserver(list => list.getEntries().forEach(e => window.__longTasks.push(e.duration))).observe({ type: 'longtask', buffered: true });");

			var clock = Stopwatch.StartNew();
			await page.GotoAsync($"{Pasture.Site}/");
			var cards = page.Locator("article[data-uri]");
			await cards.First.WaitForAsync(new() { Timeout = 60000 });
			var firstCard = clock.Elapsed.TotalMilliseconds;
			var loaded = page.Locator("[data-feed-count]");
			async Task<int> Loaded() => int.Parse(await loaded.GetAttributeAsync("data-feed-count") ?? "0");
			Assert.SkipWhen(await Loaded() < 20, "load0's home is short: run SocialPub's tools/pasture/load.sh first");

			var report = new JsonObject { ["firstCardMs"] = Math.Round(firstCard), ["steps"] = new JsonArray() };
			foreach (var target in Steps)
			{
				var step = Stopwatch.StartNew();
				var count = await Loaded();
				var stalled = Stopwatch.StartNew();
				while (count < target && stalled.Elapsed < TimeSpan.FromSeconds(20))
				{
					await page.EvaluateAsync("() => { const s = document.getElementById('feed-scroll'); s.scrollTop = s.scrollHeight; }");
					await page.WaitForTimeoutAsync(150);
					var now = await Loaded();
					if (now > count)
						stalled.Restart();
					count = now;
				}
				var metrics = await page.EvaluateAsync<JsonElementHolder>(@"() => {
					const heap = performance.memory ? performance.memory.usedJSHeapSize : null;
					const runtime = globalThis.getDotnetRuntime ? globalThis.getDotnetRuntime(0) : null;
					const wasm = runtime && runtime.Module && runtime.Module.HEAPU8 ? runtime.Module.HEAPU8.length : null;
					const tasks = window.__longTasks.splice(0);
					return { json: JSON.stringify({ dom: document.getElementsByTagName('*').length, jsHeap: heap, wasmHeap: wasm,
						longTasks: tasks.length, longTaskMs: Math.round(tasks.reduce((a, b) => a + b, 0)) }) };
				}");
				var row = JsonNode.Parse(metrics.Json)!.AsObject();
				row["target"] = target;
				row["posts"] = count;
				row["cards"] = await cards.CountAsync();
				row["seconds"] = Math.Round(step.Elapsed.TotalSeconds, 1);
				report["steps"]!.AsArray().Add(row);
				if (count < target)
					break;
			}

			var path = Path.Combine(AppContext.BaseDirectory, "perf.json");
			await File.WriteAllTextAsync(path, report.ToJsonString(new() { WriteIndented = true }));
			TestContext.Current.SendDiagnosticMessage(report.ToJsonString());
			Assert.True(report["steps"]!.AsArray().Count > 0);
			await session.AssertGuards();
		}

		public sealed class JsonElementHolder
		{
			public string Json { get; set; }
		}
	}
}