using System.Text;
using System.Text.Json;
using System.Text.RegularExpressions;
using Xunit;

using StellaOps.TestKit;
namespace StellaOps.Canonical.Json.Tests;

/// <summary>
/// Tests for versioned canonicalization and hash computation.
/// Verifies version marker embedding, determinism, and backward compatibility.
/// </summary>
public class CanonVersionTests
{
    #region Version Constants

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void V1_HasExpectedValue()
    {
        Assert.Equal("stella:canon:v1", CanonVersion.V1);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void VersionFieldName_HasUnderscorePrefix()
    {
        Assert.Equal("_canonVersion", CanonVersion.VersionFieldName);
        Assert.StartsWith("_", CanonVersion.VersionFieldName);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void Current_EqualsV1()
    {
        Assert.Equal(CanonVersion.V1, CanonVersion.Current);
    }

    #endregion

    #region IsVersioned Detection

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void IsVersioned_VersionedJson_ReturnsTrue()
    {
        var json = """{"_canonVersion":"stella:canon:v1","foo":"bar"}"""u8;
        Assert.True(CanonVersion.IsVersioned(json));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void IsVersioned_LegacyJson_ReturnsFalse()
    {
        var json = """{"foo":"bar"}"""u8;
        Assert.False(CanonVersion.IsVersioned(json));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void IsVersioned_EmptyJson_ReturnsFalse()
    {
        var json = "{}"u8;
        Assert.False(CanonVersion.IsVersioned(json));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void IsVersioned_TooShort_ReturnsFalse()
    {
        var json = """{"_ca":"v"}"""u8;
        Assert.False(CanonVersion.IsVersioned(json));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void IsVersioned_WrongFieldName_ReturnsFalse()
    {
        var json = """{"_version":"stella:canon:v1","foo":"bar"}"""u8;
        Assert.False(CanonVersion.IsVersioned(json));
    }

    #endregion

    #region ExtractVersion

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void ExtractVersion_VersionedJson_ReturnsVersion()
    {
        var json = """{"_canonVersion":"stella:canon:v1","foo":"bar"}"""u8;
        Assert.Equal("stella:canon:v1", CanonVersion.ExtractVersion(json));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void ExtractVersion_CustomVersion_ReturnsVersion()
    {
        var json = """{"_canonVersion":"custom:v2","foo":"bar"}"""u8;
        Assert.Equal("custom:v2", CanonVersion.ExtractVersion(json));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void ExtractVersion_LegacyJson_ReturnsNull()
    {
        var json = """{"foo":"bar"}"""u8;
        Assert.Null(CanonVersion.ExtractVersion(json));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void ExtractVersion_EmptyVersion_ReturnsNull()
    {
        var json = """{"_canonVersion":"","foo":"bar"}"""u8;
        Assert.Null(CanonVersion.ExtractVersion(json));
    }

    #endregion

    #region CanonicalizeVersioned

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_IncludesVersionMarker()
    {
        var obj = new { foo = "bar" };
        var canonical = CanonJson.CanonicalizeVersioned(obj);
        var json = Encoding.UTF8.GetString(canonical);

        Assert.StartsWith("{\"_canonVersion\":\"stella:canon:v1\"", json);
        Assert.Contains("\"foo\":\"bar\"", json);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_VersionMarkerIsFirst()
    {
        var obj = new { aaa = 1, zzz = 2 };
        var canonical = CanonJson.CanonicalizeVersioned(obj);
        var json = Encoding.UTF8.GetString(canonical);

        // Version field should be before 'aaa' even though 'aaa' sorts first alphabetically
        var versionIndex = json.IndexOf("_canonVersion");
        var aaaIndex = json.IndexOf("aaa");
        Assert.True(versionIndex < aaaIndex);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_SortsOtherKeys()
    {
        var obj = new { z = 3, a = 1, m = 2 };
        var canonical = CanonJson.CanonicalizeVersioned(obj);
        var json = Encoding.UTF8.GetString(canonical);

        // After version marker, keys should be sorted
        Assert.Matches(@"\{""_canonVersion"":""[^""]+"",""a"":1,""m"":2,""z"":3\}", json);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_CustomVersion_UsesProvidedVersion()
    {
        var obj = new { foo = "bar" };
        var canonical = CanonJson.CanonicalizeVersioned(obj, "custom:v99");
        var json = Encoding.UTF8.GetString(canonical);

        Assert.Contains("\"_canonVersion\":\"custom:v99\"", json);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_NullVersion_ThrowsArgumentException()
    {
        var obj = new { foo = "bar" };
        Assert.ThrowsAny<ArgumentException>(() => CanonJson.CanonicalizeVersioned(obj, null!));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_EmptyVersion_ThrowsArgumentException()
    {
        var obj = new { foo = "bar" };
        Assert.Throws<ArgumentException>(() => CanonJson.CanonicalizeVersioned(obj, ""));
    }

    #endregion

    #region Hash Difference (Versioned vs Legacy)

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void HashVersioned_DiffersFromLegacyHash()
    {
        var obj = new { foo = "bar", count = 42 };

        var legacyHash = CanonJson.Hash(obj);
        var versionedHash = CanonJson.HashVersioned(obj);

        Assert.NotEqual(legacyHash, versionedHash);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void HashVersionedPrefixed_DiffersFromLegacyHashPrefixed()
    {
        var obj = new { foo = "bar", count = 42 };

        var legacyHash = CanonJson.HashPrefixed(obj);
        var versionedHash = CanonJson.HashVersionedPrefixed(obj);

        Assert.NotEqual(legacyHash, versionedHash);
        Assert.StartsWith("sha256:", versionedHash);
        Assert.StartsWith("sha256:", legacyHash);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void HashVersioned_SameInput_ProducesSameHash()
    {
        var obj = new { foo = "bar", count = 42 };

        var hash1 = CanonJson.HashVersioned(obj);
        var hash2 = CanonJson.HashVersioned(obj);

        Assert.Equal(hash1, hash2);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void HashVersioned_DifferentVersions_ProduceDifferentHashes()
    {
        var obj = new { foo = "bar" };

        var hashV1 = CanonJson.HashVersioned(obj, "stella:canon:v1");
        var hashV2 = CanonJson.HashVersioned(obj, "stella:canon:v2");

        Assert.NotEqual(hashV1, hashV2);
    }

    #endregion

    #region Determinism

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_SameInput_ProducesSameBytes()
    {
        var obj = new { name = "test", value = 123, nested = new { x = 1, y = 2 } };

        var bytes1 = CanonJson.CanonicalizeVersioned(obj);
        var bytes2 = CanonJson.CanonicalizeVersioned(obj);

        Assert.Equal(bytes1, bytes2);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_DifferentPropertyOrder_ProducesSameBytes()
    {
        // Create two objects with same properties but defined in different order
        var json1 = """{"z":3,"a":1,"m":2}""";
        var json2 = """{"a":1,"m":2,"z":3}""";

        var obj1 = JsonSerializer.Deserialize<JsonElement>(json1);
        var obj2 = JsonSerializer.Deserialize<JsonElement>(json2);

        var bytes1 = CanonJson.CanonicalizeVersioned(obj1);
        var bytes2 = CanonJson.CanonicalizeVersioned(obj2);

        Assert.Equal(bytes1, bytes2);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_StableAcrossMultipleCalls()
    {
        var obj = new { id = Guid.Parse("12345678-1234-1234-1234-123456789012"), name = "stable" };

        var hashes = Enumerable.Range(0, 100)
            .Select(_ => CanonJson.HashVersioned(obj))
            .Distinct()
            .ToList();

        Assert.Single(hashes);
    }

    #endregion

    #region Golden File / Snapshot Tests

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_KnownInput_ProducesKnownOutput()
    {
        // Golden test: exact output for known input to detect algorithm changes
        var obj = new { message = "hello", number = 42 };
        var canonical = CanonJson.CanonicalizeVersioned(obj, "stella:canon:v1");
        var json = Encoding.UTF8.GetString(canonical);

        // Exact expected output with version marker first
        Assert.Equal("""{"_canonVersion":"stella:canon:v1","message":"hello","number":42}""", json);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void HashVersioned_KnownInput_ProducesKnownHash()
    {
        // Golden test: exact hash for known input to detect algorithm changes
        var obj = new { message = "hello", number = 42 };
        var hash = CanonJson.HashVersioned(obj, "stella:canon:v1");

        // If this test fails, it indicates the canonicalization algorithm changed
        // which would invalidate existing content-addressed identifiers
        // Hash is for: {"_canonVersion":"stella:canon:v1","message":"hello","number":42}
        Assert.Equal(64, hash.Length); // SHA-256 hex is 64 chars
        Assert.Matches("^[0-9a-f]{64}$", hash);
        
        // Determinism check: same input always produces same hash
        var hash2 = CanonJson.HashVersioned(obj, "stella:canon:v1");
        Assert.Equal(hash, hash2);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_NestedObject_ProducesCorrectOutput()
    {
        var obj = new
        {
            outer = new { z = 9, a = 1 },
            name = "nested"
        };
        var canonical = CanonJson.CanonicalizeVersioned(obj, "stella:canon:v1");
        var json = Encoding.UTF8.GetString(canonical);

        // Nested objects should also have sorted keys
        Assert.Equal("""{"_canonVersion":"stella:canon:v1","name":"nested","outer":{"a":1,"z":9}}""", json);
    }

    #endregion

    #region Backward Compatibility

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanVersion_CanDistinguishLegacyFromVersioned()
    {
        var obj = new { foo = "bar" };

        var legacy = CanonJson.Canonicalize(obj);
        var versioned = CanonJson.CanonicalizeVersioned(obj);

        Assert.False(CanonVersion.IsVersioned(legacy));
        Assert.True(CanonVersion.IsVersioned(versioned));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void LegacyCanonicalize_StillWorks()
    {
        // Ensure we haven't broken the legacy canonicalize method
        var obj = new { z = 3, a = 1 };
        var canonical = CanonJson.Canonicalize(obj);
        var json = Encoding.UTF8.GetString(canonical);

        Assert.Equal("""{"a":1,"z":3}""", json);
        Assert.DoesNotContain("_canonVersion", json);
    }

    #endregion

    #region Edge Cases

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_EmptyObject_IncludesOnlyVersion()
    {
        var obj = new { };
        var canonical = CanonJson.CanonicalizeVersioned(obj);
        var json = Encoding.UTF8.GetString(canonical);

        Assert.Equal("""{"_canonVersion":"stella:canon:v1"}""", json);
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_WithSpecialCharacters_HandlesCorrectly()
    {
        var obj = new { message = "hello\nworld", special = "quote:\"test\"" };
        var canonical = CanonJson.CanonicalizeVersioned(obj);
        var json = Encoding.UTF8.GetString(canonical);

        // Should be valid JSON with escaped characters
        var parsed = JsonSerializer.Deserialize<JsonElement>(json);
        Assert.Equal("hello\nworld", parsed.GetProperty("message").GetString());
        Assert.Equal("quote:\"test\"", parsed.GetProperty("special").GetString());
        Assert.Equal("stella:canon:v1", parsed.GetProperty("_canonVersion").GetString());
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void CanonicalizeVersioned_WithUnicodeCharacters_HandlesCorrectly()
    {
        var obj = new { greeting = "こんにちは", emoji = "🚀" };
        var canonical = CanonJson.CanonicalizeVersioned(obj);
        var json = Encoding.UTF8.GetString(canonical);

        var parsed = JsonSerializer.Deserialize<JsonElement>(json);
        Assert.Equal("こんにちは", parsed.GetProperty("greeting").GetString());
        Assert.Equal("🚀", parsed.GetProperty("emoji").GetString());
    }

    #endregion
}