using StellaOps.Cli.Services.Models;

namespace StellaOps.Cli.Services;

internal static class OciImageReferenceParser
{
    public static OciImageReference Parse(string reference)
    {
        if (string.IsNullOrWhiteSpace(reference))
        {
            throw new ArgumentException("Image reference is required.", nameof(reference));
        }

        reference = reference.Trim();
        if (reference.StartsWith("http://", StringComparison.OrdinalIgnoreCase) ||
            reference.StartsWith("https://", StringComparison.OrdinalIgnoreCase) ||
            reference.StartsWith("docker://", StringComparison.OrdinalIgnoreCase))
        {
            return ParseUri(reference);
        }

        var registry = string.Empty;
        var remainder = reference;
        var parts = reference.Split('/', StringSplitOptions.RemoveEmptyEntries);

        if (parts.Length > 1 && LooksLikeRegistry(parts[0]))
        {
            registry = parts[0];
            remainder = string.Join('/', parts.Skip(1));
        }
        else
        {
            registry = "docker.io";
        }

        var repository = remainder;
        string? tag = null;
        string? digest = null;

        var atIndex = remainder.LastIndexOf('@');
        if (atIndex >= 0)
        {
            repository = remainder[..atIndex];
            digest = remainder[(atIndex + 1)..];
        }
        else
        {
            var lastColon = remainder.LastIndexOf(':');
            var lastSlash = remainder.LastIndexOf('/');
            if (lastColon > lastSlash)
            {
                repository = remainder[..lastColon];
                tag = remainder[(lastColon + 1)..];
            }
        }

        if (string.IsNullOrWhiteSpace(repository))
        {
            throw new ArgumentException("Image repository is required.", nameof(reference));
        }

        if (string.Equals(registry, "docker.io", StringComparison.OrdinalIgnoreCase) &&
            !repository.Contains('/', StringComparison.Ordinal))
        {
            repository = $"library/{repository}";
        }

        if (string.IsNullOrWhiteSpace(tag) && string.IsNullOrWhiteSpace(digest))
        {
            tag = "latest";
        }

        return new OciImageReference
        {
            Registry = registry,
            Repository = repository,
            Tag = tag,
            Digest = digest,
            Original = reference
        };
    }

    private static OciImageReference ParseUri(string reference)
    {
        if (!Uri.TryCreate(reference, UriKind.Absolute, out var uri))
        {
            throw new ArgumentException("Invalid image reference URI.", nameof(reference));
        }

        var registry = uri.Authority;
        var remainder = uri.AbsolutePath.Trim('/');

        string? tag = null;
        string? digest = null;

        var atIndex = remainder.LastIndexOf('@');
        if (atIndex >= 0)
        {
            digest = remainder[(atIndex + 1)..];
            remainder = remainder[..atIndex];
        }
        else
        {
            var lastColon = remainder.LastIndexOf(':');
            if (lastColon > remainder.LastIndexOf('/'))
            {
                tag = remainder[(lastColon + 1)..];
                remainder = remainder[..lastColon];
            }
        }

        if (string.Equals(registry, "docker.io", StringComparison.OrdinalIgnoreCase) &&
            !remainder.Contains('/', StringComparison.Ordinal))
        {
            remainder = $"library/{remainder}";
        }

        if (string.IsNullOrWhiteSpace(tag) && string.IsNullOrWhiteSpace(digest))
        {
            tag = "latest";
        }

        return new OciImageReference
        {
            Registry = registry,
            Repository = remainder,
            Tag = tag,
            Digest = digest,
            Original = reference
        };
    }

    private static bool LooksLikeRegistry(string value)
    {
        if (string.Equals(value, "localhost", StringComparison.OrdinalIgnoreCase))
        {
            return true;
        }

        return value.Contains('.', StringComparison.Ordinal) || value.Contains(':', StringComparison.Ordinal);
    }
}