using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using Xunit;

namespace Basis.Contrib.Crypto
{
	public class Ed25519Tests
	{
		record Example(string Pubkey, string Privkey, string Message, string Signature);

		private static List<Example> RfcTestVectors()
		{
			return new List<Example>()
			{
				// Examples from https://datatracker.ietf.org/doc/html/rfc8032#section-7.1
				new(
					Pubkey: "d75a980182b10ab7d54bfed3c964073a"
						+ "0ee172f3daa62325af021a68f707511a",
					Privkey: "9d61b19deffd5a60ba844af492ec2cc4"
						+ "4449c5697b326919703bac031cae7f60",
					Message: "",
					Signature: "e5564300c360ac729086e2cc806e828a"
						+ "84877f1eb8e5d974d873e06522490155"
						+ "5fb8821590a33bacc61e39701cf9b46b"
						+ "d25bf5f0595bbe24655141438e7a100b"
				),
				new(
					Pubkey: "3d4017c3e843895a92b70aa74d1b7ebc"
						+ "9c982ccf2ec4968cc0cd55f12af4660c",
					Privkey: "4ccd089b28ff96da9db6c346ec114e0f"
						+ "5b8a319f35aba624da8cf6ed4fb8a6fb",
					Message: "72",
					Signature: "92a009a9f0d4cab8720e820b5f642540"
						+ "a2b27b5416503f8fb3762223ebdb69da"
						+ "085ac1e43e15996e458f3613d0f11d8c"
						+ "387b2eaeb4302aeeb00d291612bb0c00"
				),
				new(
					Pubkey: "fc51cd8e6218a1a38da47ed00230f058"
						+ "0816ed13ba3303ac5deb911548908025",
					Privkey: "c5aa8df43f9f837bedb7442f31dcb7b1"
						+ "66d38535076f094b85ce3a2e0b4458f7",
					Message: "af82",
					Signature: "6291d657deec24024827e69c3abe01a3"
						+ "0ce548a284743a445e3680d7db5ac3ac"
						+ "18ff9b538d16f290ae67f760984dc659"
						+ "4a7c15e9716ed28dc027beceea1ec40a"
				),
				new(
					Pubkey: "278117fc144c72340f67d0f2316e8386"
						+ "ceffbf2b2428c9c51fef7c597f1d426e",
					Privkey: "f5e5767cf153319517630f226876b86c"
						+ "8160cc583bc013744c6bf255f5cc0ee5",
					Message: "08b8b2b733424243760fe426a4b54908"
						+ "632110a66c2f6591eabd3345e3e4eb98"
						+ "fa6e264bf09efe12ee50f8f54e9f77b1"
						+ "e355f6c50544e23fb1433ddf73be84d8"
						+ "79de7c0046dc4996d9e773f4bc9efe57"
						+ "38829adb26c81b37c93a1b270b20329d"
						+ "658675fc6ea534e0810a4432826bf58c"
						+ "941efb65d57a338bbd2e26640f89ffbc"
						+ "1a858efcb8550ee3a5e1998bd177e93a"
						+ "7363c344fe6b199ee5d02e82d522c4fe"
						+ "ba15452f80288a821a579116ec6dad2b"
						+ "3b310da903401aa62100ab5d1a36553e"
						+ "06203b33890cc9b832f79ef80560ccb9"
						+ "a39ce767967ed628c6ad573cb116dbef"
						+ "efd75499da96bd68a8a97b928a8bbc10"
						+ "3b6621fcde2beca1231d206be6cd9ec7"
						+ "aff6f6c94fcd7204ed3455c68c83f4a4"
						+ "1da4af2b74ef5c53f1d8ac70bdcb7ed1"
						+ "85ce81bd84359d44254d95629e9855a9"
						+ "4a7c1958d1f8ada5d0532ed8a5aa3fb2"
						+ "d17ba70eb6248e594e1a2297acbbb39d"
						+ "502f1a8c6eb6f1ce22b3de1a1f40cc24"
						+ "554119a831a9aad6079cad88425de6bd"
						+ "e1a9187ebb6092cf67bf2b13fd65f270"
						+ "88d78b7e883c8759d2c4f5c65adb7553"
						+ "878ad575f9fad878e80a0c9ba63bcbcc"
						+ "2732e69485bbc9c90bfbd62481d9089b"
						+ "eccf80cfe2df16a2cf65bd92dd597b07"
						+ "07e0917af48bbb75fed413d238f5555a"
						+ "7a569d80c3414a8d0859dc65a46128ba"
						+ "b27af87a71314f318c782b23ebfe808b"
						+ "82b0ce26401d2e22f04d83d1255dc51a"
						+ "ddd3b75a2b1ae0784504df543af8969b"
						+ "e3ea7082ff7fc9888c144da2af58429e"
						+ "c96031dbcad3dad9af0dcbaaaf268cb8"
						+ "fcffead94f3c7ca495e056a9b47acdb7"
						+ "51fb73e666c6c655ade8297297d07ad1"
						+ "ba5e43f1bca32301651339e22904cc8c"
						+ "42f58c30c04aafdb038dda0847dd988d"
						+ "cda6f3bfd15c4b4c4525004aa06eeff8"
						+ "ca61783aacec57fb3d1f92b0fe2fd1a8"
						+ "5f6724517b65e614ad6808d6f6ee34df"
						+ "f7310fdc82aebfd904b01e1dc54b2927"
						+ "094b2db68d6f903b68401adebf5a7e08"
						+ "d78ff4ef5d63653a65040cf9bfd4aca7"
						+ "984a74d37145986780fc0b16ac451649"
						+ "de6188a7dbdf191f64b5fc5e2ab47b57"
						+ "f7f7276cd419c17a3ca8e1b939ae49e4"
						+ "88acba6b965610b5480109c8b17b80e1"
						+ "b7b750dfc7598d5d5011fd2dcc5600a3"
						+ "2ef5b52a1ecc820e308aa342721aac09"
						+ "43bf6686b64b2579376504ccc493d97e"
						+ "6aed3fb0f9cd71a43dd497f01f17c0e2"
						+ "cb3797aa2a2f256656168e6c496afc5f"
						+ "b93246f6b1116398a346f1a641f3b041"
						+ "e989f7914f90cc2c7fff357876e506b5"
						+ "0d334ba77c225bc307ba537152f3f161"
						+ "0e4eafe595f6d9d90d11faa933a15ef1"
						+ "369546868a7f3a45a96768d40fd9d034"
						+ "12c091c6315cf4fde7cb68606937380d"
						+ "b2eaaa707b4c4185c32eddcdd306705e"
						+ "4dc1ffc872eeee475a64dfac86aba41c"
						+ "0618983f8741c5ef68d3a101e8a3b8ca"
						+ "c60c905c15fc910840b94c00a0b9d0",
					Signature: "0aab4c900501b3e24d7cdf4663326a3a"
						+ "87df5e4843b2cbdb67cbf6e460fec350"
						+ "aa5371b1508f9f4528ecea23c436d94b"
						+ "5e8fcd4f681e30a6ac00a9704a188a03"
				),
				new(
					Pubkey: "ec172b93ad5e563bf4932c70e1245034"
						+ "c35467ef2efd4d64ebf819683467e2bf",
					Privkey: "833fe62409237b9d62ec77587520911e"
						+ "9a759cec1d19755b7da901b96dca3d42",
					Message: "ddaf35a193617abacc417349ae204131"
						+ "12e6fa4e89a97ea20a9eeee64b55d39a"
						+ "2192992a274fc1a836ba3c23a3feebbd"
						+ "454d4423643ce80e2a9ac94fa54ca49f",
					Signature: "dc2a4459e7369633a52b1bf277839a00"
						+ "201009a3efbf3ecb69bea2186c26b589"
						+ "09351fc9ac90b3ecfdfbc7c66431e030"
						+ "3dca179c138ac17ad9bef1177331a704"
				),
			};
		}

		[Fact]
		public void RfcTestVectorsShouldVerify()
		{
			var testVectors = RfcTestVectors();
			int i = 0;
			foreach (var e in testVectors)
			{
				Console.WriteLine($"testing example {i}");
				var pubkey = new PubKey(Convert.FromHexString(e.Pubkey));
				var payload = new Payload(Convert.FromHexString(e.Message));
				var signature = new Signature(Convert.FromHexString(e.Signature));
				Debug.Assert(Ed25519.Verify(pubkey, signature, payload));

				i += 1;
			}
		}

		[Fact]
		public void RfcTestVectorsShouldSign()
		{
			var testVectors = RfcTestVectors();
			int i = 0;
			foreach (var e in testVectors)
			{
				Console.WriteLine($"testing example {i}");
				var expectedPubkey = new PubKey(Convert.FromHexString(e.Pubkey));
				var privkey = new PrivKey(Convert.FromHexString(e.Privkey));
				var payload = new Payload(Convert.FromHexString(e.Message));
				var expectedSignature = new Signature(
					Convert.FromHexString(e.Signature)
				);

				PubKey convertedPubkey =
					Ed25519.ConvertPrivkeyToPubkey(privkey)
					?? throw new Exception("should not have been null");
				Debug.Assert(
					convertedPubkey == expectedPubkey,
					"pubkey derived from privkey did not match what was expected"
				);

				Debug.Assert(
					Ed25519.Sign(privkey, payload, out Signature? sig),
					"signing should always succeed with a valid pubkey"
				);
				Debug.Assert(
					sig is not null,
					"sig should not be null when signing succeeds"
				);
				Debug.Assert(
					sig == expectedSignature,
					"signature should match expected signature"
				);

				i += 1;
			}
		}

		[Fact]
		public void SlightlyModifiedFromTestVectorsShouldFailVerification()
		{
			var testVectors = RfcTestVectors();
			int i = 0;
			foreach (var e in testVectors)
			{
				Console.WriteLine($"testing example {i}");
				var pubkey = new PubKey(Convert.FromHexString(e.Pubkey));
				var payload = new Payload(Convert.FromHexString(e.Message));
				var signature = new Signature(Convert.FromHexString(e.Signature));

				// Try using valid but mismatched pubkey
				var badPubkey = new PubKey(
					Convert.FromHexString(
						"411D2E24033EA71821F8D5C65F45CFB3FA5E06E30F860B3D8E6DA309D668BBD1"
					)
				);
				Debug.Assert(
					!Ed25519.Verify(badPubkey, signature, payload),
					"Corrupting pubkey should have failed to verify"
				);

				// Try mutating signature
				var badSignature = new Signature(signature.V.ToArray()); // copy
				badSignature.V[0] = (byte)(signature.V[0] ^ byte.MaxValue);
				Debug.Assert(
					!Ed25519.Verify(pubkey, badSignature, payload),
					"Corrupting signature should have failed to verify"
				);

				// Try mutating payload
				Payload badPayload;
				if (payload.V.Length == 0)
				{
					badPayload = new Payload(new byte[] { 0x69 });
				}
				else
				{
					var tmp = pubkey.V.ToArray(); // copy
					tmp[0] = (byte)(pubkey.V[0] ^ byte.MaxValue);
					badPayload = new Payload(tmp);
				}
				Debug.Assert(
					!Ed25519.Verify(pubkey, signature, badPayload),
					"Corrupting payload should have failed to verify"
				);

				i += 1;
			}
		}

		[Fact]
		public void EmptyOrNullShouldFailVerification()
		{
			var example = RfcTestVectors()[2]; // Pick one that does not have anything empty
			var pubkey = new PubKey(Convert.FromHexString(example.Pubkey));
			var payload = new Payload(Convert.FromHexString(example.Message));
			var signature = new Signature(Convert.FromHexString(example.Signature));

			Debug.Assert(
				!Ed25519.Verify(new PubKey(Array.Empty<byte>()), signature, payload),
				"empty pubkey should fail"
			);

			Debug.Assert(
				!Ed25519.Verify(pubkey, new Signature(Array.Empty<byte>()), payload),
				"empty sig should fail"
			);

			Debug.Assert(
				!Ed25519.Verify(pubkey, signature, new Payload(Array.Empty<byte>())),
				"empty payload should fail"
			);
		}

		[Fact]
		public void EmptyPrivkeyShouldFailSigning()
		{
			Debug.Assert(
				!Ed25519.Sign(
					new PrivKey(Array.Empty<byte>()),
					new Payload(Array.Empty<byte>()),
					out Signature? sig
				),
				"empty privkey should fail signing and return false"
			);
			Debug.Assert(
				sig is null,
				"empty privkey should fail signing and return null for sig"
			);
		}
	}
}
