// Copyright (c) 2026 GeWuYou
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

namespace GFramework.Game.Internal;

/// <summary>
///     提供版本化数据迁移链的共享执行逻辑。
/// </summary>
/// <remarks>
///     该运行器只负责“按版本号推进”的公共约束，包括：
///     前向注册校验、缺失链路失败、声明目标版本与实际结果版本一致性，以及避免版本回退或死循环。
///     它不关心具体存储、日志、回写或异常吞吐策略；这些由调用方负责。
/// </remarks>
internal static class VersionedMigrationRunner
{
    /// <summary>
    ///     校验迁移注册是否表示一次有效的前向升级。
    /// </summary>
    /// <param name="subjectName">迁移所作用的主体名称，例如设置类型或存档类型。</param>
    /// <param name="migrationKind">用于异常消息的迁移类别名称。</param>
    /// <param name="fromVersion">源版本。</param>
    /// <param name="toVersion">目标版本。</param>
    /// <param name="paramName">异常中要使用的参数名。</param>
    /// <exception cref="ArgumentException">目标版本不大于源版本时抛出。</exception>
    internal static void ValidateForwardOnlyRegistration(
        string subjectName,
        string migrationKind,
        int fromVersion,
        int toVersion,
        string paramName)
    {
        if (toVersion <= fromVersion)
        {
            throw new ArgumentException(
                $"{migrationKind} for {subjectName} must advance the version number.",
                paramName);
        }
    }

    /// <summary>
    ///     按目标运行时版本执行连续迁移。
    /// </summary>
    /// <typeparam name="TData">迁移数据类型。</typeparam>
    /// <typeparam name="TMigration">迁移描述类型。</typeparam>
    /// <param name="data">原始加载的数据。</param>
    /// <param name="targetVersion">当前运行时支持的目标版本。</param>
    /// <param name="getVersion">从数据对象提取版本号的委托。</param>
    /// <param name="resolveMigration">根据当前版本查找下一步迁移器的委托。</param>
    /// <param name="getToVersion">从迁移器提取声明目标版本的委托。</param>
    /// <param name="applyMigration">执行单步迁移的委托。</param>
    /// <param name="subjectName">迁移主体名称，用于异常消息。</param>
    /// <param name="migrationKind">迁移类别名称，用于异常消息。</param>
    /// <returns>迁移到目标版本后的数据；如果已经是最新版本，则返回原对象。</returns>
    /// <exception cref="ArgumentNullException">
    ///     <paramref name="data" />、<paramref name="getVersion" />、<paramref name="resolveMigration" />、
    ///     <paramref name="getToVersion" /> 或 <paramref name="applyMigration" /> 为 <see langword="null" /> 时抛出。
    /// </exception>
    /// <exception cref="ArgumentException">
    ///     <paramref name="subjectName" /> 或 <paramref name="migrationKind" /> 为空白时抛出。
    /// </exception>
    /// <exception cref="InvalidOperationException">
    ///     数据版本高于当前运行时、迁移链缺失、迁移器返回 <see langword="null" />、
    ///     迁移结果版本与声明不一致、版本未前进或超出目标版本时抛出。
    /// </exception>
    internal static TData MigrateToTargetVersion<TData, TMigration>(
        TData data,
        int targetVersion,
        Func<TData, int> getVersion,
        Func<int, TMigration?> resolveMigration,
        Func<TMigration, int> getToVersion,
        Func<TMigration, TData, TData> applyMigration,
        string subjectName,
        string migrationKind)
        where TData : class
    {
        ArgumentNullException.ThrowIfNull(data);
        ArgumentNullException.ThrowIfNull(getVersion);
        ArgumentNullException.ThrowIfNull(resolveMigration);
        ArgumentNullException.ThrowIfNull(getToVersion);
        ArgumentNullException.ThrowIfNull(applyMigration);
        ArgumentException.ThrowIfNullOrWhiteSpace(subjectName);
        ArgumentException.ThrowIfNullOrWhiteSpace(migrationKind);

        var currentVersion = getVersion(data);
        if (currentVersion > targetVersion)
        {
            throw new InvalidOperationException(
                $"{subjectName} is version {currentVersion}, which is newer than the current runtime version {targetVersion}.");
        }

        if (currentVersion == targetVersion)
        {
            return data;
        }

        var current = data;

        while (currentVersion < targetVersion)
        {
            var migration = resolveMigration(currentVersion);
            if (migration is null)
            {
                throw new InvalidOperationException(
                    $"No {migrationKind} is registered for {subjectName} from version {currentVersion}.");
            }

            current = applyMigration(migration, current)
                ?? throw new InvalidOperationException(
                    $"{migrationKind} for {subjectName} from version {currentVersion} returned null.");

            var migratedVersion = getVersion(current);
            var declaredTargetVersion = getToVersion(migration);

            if (declaredTargetVersion != migratedVersion)
            {
                throw new InvalidOperationException(
                    $"{migrationKind} for {subjectName} declared target version {declaredTargetVersion} " +
                    $"but returned version {migratedVersion}.");
            }

            if (migratedVersion <= currentVersion)
            {
                throw new InvalidOperationException(
                    $"{migrationKind} for {subjectName} must advance beyond version {currentVersion}.");
            }

            if (migratedVersion > targetVersion)
            {
                throw new InvalidOperationException(
                    $"{migrationKind} for {subjectName} produced version {migratedVersion}, " +
                    $"which exceeds the current runtime version {targetVersion}.");
            }

            currentVersion = migratedVersion;
        }

        return current;
    }
}