using System.Collections.Generic;
using System.Linq;
using Microsoft.Extensions.Configuration;

namespace Jellyfin.Server.Extensions;

/// <summary>
/// Extensions for building the application configuration.
/// </summary>
public static class ConfigurationBuilderExtensions
{
    /// <summary>
    /// The environment variable prefix that maps onto this fork's own <c>Jellyfin:*</c> configuration
    /// keys, for example <c>Jellyfin__TranscodeStore__RedisConnectionString</c>.
    /// </summary>
    public const string JellyfinSectionEnvironmentPrefix = "Jellyfin__";

    /// <summary>
    /// The configuration section root this fork keeps its own settings under.
    /// </summary>
    public const string JellyfinSectionRoot = "Jellyfin";

    /// <summary>
    /// Adds environment variables named <c>Jellyfin__Section__Key</c> as the configuration keys
    /// <c>Jellyfin:Section:Key</c>.
    /// </summary>
    /// <remarks>
    /// The base configuration only reads <c>JELLYFIN_</c> prefixed environment variables, so the
    /// unprefixed form every manifest, chart and document uses would otherwise be dropped and the
    /// feature it configures would stay off with no error.
    /// </remarks>
    /// <param name="builder">The configuration builder.</param>
    /// <returns>The updated configuration builder.</returns>
    public static IConfigurationBuilder AddJellyfinSectionEnvironmentVariables(this IConfigurationBuilder builder)
    {
        // Read through the framework provider so "__" to ":" normalisation and case handling match the
        // prefixed form exactly; the prefix it strips is then put back as the section root.
        var scoped = new ConfigurationBuilder()
            .AddEnvironmentVariables(JellyfinSectionEnvironmentPrefix)
            .Build();

        var entries = scoped.AsEnumerable()
            .Where(entry => entry.Value is not null)
            .Select(entry => new KeyValuePair<string, string?>(
                ConfigurationPath.Combine(JellyfinSectionRoot, entry.Key),
                entry.Value))
            .ToList();

        return builder.AddInMemoryCollection(entries);
    }
}