using System;
using System.Collections.Generic;
using System.Linq;

namespace ShrinkModFramework
{
    public interface IReadOnlyShrinkModRegistry<T>
    {
        string Name { get; }
        IReadOnlyCollection<ShrinkRegistryEntry<T>> Entries { get; }
        IReadOnlyCollection<ShrinkRegistryEntry<T>> BaseEntries { get; }
        bool Contains(string key);
        bool TryGet(string key, out T value);
        bool TryGetEntry(string key, out ShrinkRegistryEntry<T> entry);
        IReadOnlyList<ShrinkRegistryEntry<T>> GetOverrideCandidates(string key);
    }

    internal interface IShrinkOwnedRegistry
    {
        void RemoveOwnedEntries(string ownerModId);
    }

    internal sealed class ShrinkModRegistry<T> : IReadOnlyShrinkModRegistry<T>, IShrinkOwnedRegistry
    {
        private readonly Dictionary<string, ShrinkRegistryEntry<T>> _baseEntries =
            new(StringComparer.Ordinal);
        private readonly Dictionary<string, List<ShrinkRegistryEntry<T>>> _overrides =
            new(StringComparer.Ordinal);

        public string Name { get; }

        internal ShrinkModRegistry(string name)
        {
            if (string.IsNullOrWhiteSpace(name))
                throw new ArgumentException("注册表名称不能为空。", nameof(name));

            Name = name.Trim();
        }

        /// <summary>当前生效项；存在覆盖时返回最高优先级的覆盖项。</summary>
        public IReadOnlyCollection<ShrinkRegistryEntry<T>> Entries => _baseEntries.Keys
            .OrderBy(key => key, StringComparer.Ordinal)
            .Select(ResolveEntry)
            .ToArray();

        /// <summary>不应用覆盖的基础注册项快照。</summary>
        public IReadOnlyCollection<ShrinkRegistryEntry<T>> BaseEntries => _baseEntries.Values
            .OrderBy(entry => entry.Key, StringComparer.Ordinal)
            .ToArray();

        private void RegisterBase(string ownerModId, string key, T value)
        {
            ownerModId = NormalizeOwner(ownerModId);
            key = NormalizeKey(key);
            if (_baseEntries.ContainsKey(key))
                throw new InvalidOperationException($"注册表 '{Name}' 中已存在键 '{key}'。");

            _baseEntries.Add(key, new ShrinkRegistryEntry<T>(ownerModId, key, value));
        }

        /// <summary>
        /// 使用 owner 作为 namespace 注册内容，并返回最终键。localKey 只能是局部名称，不能包含冒号。
        /// </summary>
        public string RegisterNamespaced(string ownerModId, string localKey, T value)
        {
            ownerModId = NormalizeOwner(ownerModId);
            if (ownerModId.IndexOf(':') >= 0)
                throw new ArgumentException("归属模组 ID 不能包含 ':'。", nameof(ownerModId));
            if (string.IsNullOrWhiteSpace(localKey))
                throw new ArgumentException("局部注册键不能为空。", nameof(localKey));

            localKey = localKey.Trim();
            if (localKey.IndexOf(':') >= 0)
                throw new ArgumentException("局部注册键不能包含 ':'。", nameof(localKey));

            var key = ownerModId + ":" + localKey;
            RegisterBase(ownerModId, key, value);
            return key;
        }

        /// <summary>
        /// 为已有基础项注册显式覆盖。优先级越高越先命中；同一目标的相同优先级视为硬冲突。
        /// </summary>
        public void RegisterOverride(string ownerModId, string targetKey, int priority, T value)
        {
            ownerModId = NormalizeOwner(ownerModId);
            targetKey = NormalizeKey(targetKey);
            if (!_baseEntries.ContainsKey(targetKey))
                throw new InvalidOperationException(
                    $"注册表 '{Name}' 的覆盖目标 '{targetKey}' 不存在。");

            if (!_overrides.TryGetValue(targetKey, out var candidates))
            {
                candidates = new List<ShrinkRegistryEntry<T>>();
                _overrides.Add(targetKey, candidates);
            }

            if (candidates.Any(candidate => candidate.Priority == priority))
                throw new InvalidOperationException(
                    $"注册表 '{Name}' 的键 '{targetKey}' 在优先级 {priority} 存在覆盖冲突。");

            candidates.Add(ShrinkRegistryEntry<T>.CreateOverride(ownerModId, targetKey, priority, value));
        }

        public IReadOnlyList<ShrinkRegistryEntry<T>> GetOverrideCandidates(string key)
        {
            if (string.IsNullOrWhiteSpace(key) || !_overrides.TryGetValue(key.Trim(), out var candidates))
                return Array.Empty<ShrinkRegistryEntry<T>>();

            return candidates
                .OrderByDescending(candidate => candidate.Priority)
                .ThenBy(candidate => candidate.OwnerModId, StringComparer.Ordinal)
                .ToArray();
        }

        public bool Contains(string key) =>
            !string.IsNullOrWhiteSpace(key) && _baseEntries.ContainsKey(key.Trim());

        public bool TryGet(string key, out T value)
        {
            if (TryGetEntry(key, out var entry))
            {
                value = entry.Value;
                return true;
            }

            value = default;
            return false;
        }

        public bool TryGetEntry(string key, out ShrinkRegistryEntry<T> entry)
        {
            if (!string.IsNullOrWhiteSpace(key) && _baseEntries.ContainsKey(key.Trim()))
            {
                entry = ResolveEntry(key.Trim());
                return true;
            }

            entry = default;
            return false;
        }

        void IShrinkOwnedRegistry.RemoveOwnedEntries(string ownerModId)
        {
            if (string.IsNullOrWhiteSpace(ownerModId))
                return;

            ownerModId = ownerModId.Trim();
            var keys = _baseEntries
                .Where(pair => string.Equals(pair.Value.OwnerModId, ownerModId, StringComparison.Ordinal))
                .Select(pair => pair.Key)
                .ToArray();
            foreach (var key in keys)
                _baseEntries.Remove(key);

            var emptyOverrideTargets = new List<string>();
            foreach (var pair in _overrides)
            {
                pair.Value.RemoveAll(candidate =>
                    string.Equals(candidate.OwnerModId, ownerModId, StringComparison.Ordinal));
                if (pair.Value.Count == 0)
                    emptyOverrideTargets.Add(pair.Key);
            }

            foreach (var targetKey in emptyOverrideTargets)
                _overrides.Remove(targetKey);
        }

        private ShrinkRegistryEntry<T> ResolveEntry(string key)
        {
            if (_overrides.TryGetValue(key, out var candidates) && candidates.Count > 0)
            {
                return candidates
                    .OrderByDescending(candidate => candidate.Priority)
                    .ThenBy(candidate => candidate.OwnerModId, StringComparer.Ordinal)
                    .First();
            }

            return _baseEntries[key];
        }

        private static string NormalizeOwner(string ownerModId)
        {
            if (string.IsNullOrWhiteSpace(ownerModId))
                throw new ArgumentException("归属模组 ID 不能为空。", nameof(ownerModId));
            return ownerModId.Trim();
        }

        private static string NormalizeKey(string key)
        {
            if (string.IsNullOrWhiteSpace(key))
                throw new ArgumentException("注册键不能为空。", nameof(key));
            return key.Trim();
        }
    }

    public readonly struct ShrinkRegistryEntry<T>
    {
        public string OwnerModId { get; }
        public string Key { get; }
        public T Value { get; }
        public bool IsOverride { get; }
        public int Priority { get; }

        public ShrinkRegistryEntry(string ownerModId, string key, T value)
            : this(ownerModId, key, value, false, 0)
        {
        }

        private ShrinkRegistryEntry(string ownerModId, string key, T value, bool isOverride, int priority)
        {
            OwnerModId = ownerModId;
            Key = key;
            Value = value;
            IsOverride = isOverride;
            Priority = priority;
        }

        internal static ShrinkRegistryEntry<T> CreateOverride(
            string ownerModId, string key, int priority, T value) =>
            new(ownerModId, key, value, true, priority);
    }
}