using Microsoft.AspNetCore.Http;
using System;
using System.Collections.Generic;
using System.Linq;

namespace StellaOps.Registry.TokenService;

public static class RegistryScopeParser
{
    public static IReadOnlyList<RegistryAccessRequest> Parse(IQueryCollection query)
    {
        ArgumentNullException.ThrowIfNull(query);

        var scopes = new List<string>();

        if (query.TryGetValue("scope", out var scopeValues))
        {
            foreach (var scope in scopeValues)
            {
                if (string.IsNullOrWhiteSpace(scope))
                {
                    continue;
                }

                // Support space-delimited scopes per OAuth2 spec
                foreach (var component in scope.Split(' ', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries))
                {
                    scopes.Add(component);
                }
            }
        }

        var requests = new List<RegistryAccessRequest>(scopes.Count);
        foreach (var scope in scopes)
        {
            var request = ParseScope(scope);
            requests.Add(request);
        }

        return requests;
    }

    private static RegistryAccessRequest ParseScope(string scope)
    {
        var segments = scope.Split(':', StringSplitOptions.TrimEntries);
        if (segments.Length < 1)
        {
            throw new InvalidScopeException(scope, "scope missing resource type");
        }

        var type = segments[0];
        if (!string.Equals(type, "repository", StringComparison.OrdinalIgnoreCase))
        {
            throw new InvalidScopeException(scope, $"unsupported resource type '{type}'");
        }

        if (segments.Length < 2 || string.IsNullOrWhiteSpace(segments[1]))
        {
            throw new InvalidScopeException(scope, "repository scope missing name");
        }

        var name = segments[1];
        var actions = segments.Length >= 3 && !string.IsNullOrWhiteSpace(segments[2])
            ? segments[2].Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
            : Array.Empty<string>();

        if (actions.Length == 0)
        {
            actions = new[] { "pull" };
        }

        var normalized = actions
            .Select(action => action.ToLowerInvariant())
            .Distinct(StringComparer.OrdinalIgnoreCase)
            .ToArray();

        return new RegistryAccessRequest(type.ToLowerInvariant(), name, normalized);
    }
}

public sealed class InvalidScopeException : Exception
{
    public InvalidScopeException(string scope, string reason)
        : base($"Invalid scope '{scope}': {reason}")
    {
        Scope = scope;
        Reason = reason;
    }

    public string Scope { get; }

    public string Reason { get; }
}