using System;
using BrewMonster;
using UnityEngine;
using UnityEngine.AddressableAssets;
using UnityEngine.ResourceManagement.ResourceLocations;

namespace BrewMonster.Scripts
{
    /// <summary>
    /// Runtime rewrite of bundle/catalog URLs via <see cref="Addressables.InternalIdTransformFunc"/>
    /// (e.g. swap CDN host or path prefix). Must run before the first successful remote load — ideally before
    /// <see cref="Addressables.InitializeAsync"/> if all remote ids should be rewritten.
    /// </summary>
    public static class AddressablesRuntimeUrlRewriter
    {
        static Func<IResourceLocation, string> s_previousTransform;
        static string s_fromPrefix;
        static string s_toPrefix;

        /// <summary>
        /// When true, the installed rewriter calls the previous <see cref="Addressables.InternalIdTransformFunc"/> first.
        /// </summary>
        public static bool ChainPreviousTransform { get; set; } = true;

        /// <summary>
        /// Replaces the start of each location’s <see cref="IResourceLocation.InternalId"/> when it begins with
        /// <paramref name="fromPrefix"/> (e.g. build-time profile URL) by <paramref name="toPrefix"/> (runtime CDN).
        /// </summary>
        public static void InstallPrefixRewrite(string fromPrefix, string toPrefix)
        {
            if (string.IsNullOrEmpty(fromPrefix))
            {
                BMLogger.LogError("AddressablesRuntimeUrlRewriter: fromPrefix is null or empty.");
                return;
            }

            s_fromPrefix = fromPrefix;
            s_toPrefix = toPrefix ?? string.Empty;

            if (ChainPreviousTransform)
                s_previousTransform = Addressables.InternalIdTransformFunc;

            Addressables.InternalIdTransformFunc = Transform;
            BMLogger.Log($"AddressablesRuntimeUrlRewriter: Installed prefix rewrite (from length={fromPrefix.Length}, to length={s_toPrefix.Length}).");
        }

        /// <summary>
        /// Removes this package’s rewrite and restores the delegate that was present at install time (if any).
        /// </summary>
        public static void ClearInstalledRewrite()
        {
            if (Addressables.InternalIdTransformFunc == Transform)
            {
                Addressables.InternalIdTransformFunc = s_previousTransform;
                s_previousTransform = null;
                s_fromPrefix = null;
                s_toPrefix = null;
                BMLogger.Log("AddressablesRuntimeUrlRewriter: Cleared installed rewrite.");
            }
        }

        static string Transform(IResourceLocation location)
        {
            string id = location != null ? location.InternalId : null;
            if (string.IsNullOrEmpty(id))
                return id;

            if (ChainPreviousTransform && s_previousTransform != null)
                id = s_previousTransform(location);

            if (!string.IsNullOrEmpty(s_fromPrefix) &&
                id.StartsWith(s_fromPrefix, StringComparison.OrdinalIgnoreCase))
            {
                return s_toPrefix + id.Substring(s_fromPrefix.Length);
            }

            return id;
        }
    }
}