defmodule IsLabDB.GravitationalRouter do
  @moduledoc """
  Physics-Based Data Routing Engine for Spacetime Shards

  This module implements intelligent data routing using gravitational attraction
  calculations, consistent hashing, and access pattern analysis. It determines
  the optimal spacetime shard for each piece of data based on:

  - Gravitational attraction between data and shards
  - Current load distribution and capacity
  - Access pattern compatibility
  - Locality-sensitive routing for related data
  - Conservation of energy during data placement

  ## Physics Concepts

  - **Gravitational Routing**: Data naturally "falls" into shards with stronger attraction
  - **Consistent Hashing**: Ensures even distribution while allowing for shard expansion
  - **Locality Sensitivity**: Related data items are placed in nearby cosmic regions
  - **Load Balancing**: Prevents gravitational collapse by distributing mass evenly
  - **Conservation Laws**: Energy and data are conserved during routing operations
  """

  require Logger
  alias IsLabDB.{SpacetimeShard}

  defstruct [
    :shard_topology,              # Map of available shards
    :routing_algorithm,           # Current routing algorithm (:gravitational, :consistent_hash, etc.)
    :locality_map,                # Spatial relationships between data
    :load_balancer,               # Load balancing configuration
    :migration_manager,           # Data migration coordination
    :routing_cache,               # Cached routing decisions
    :performance_metrics,         # Routing performance tracking
    :consistency_coordinator      # Cross-shard consistency management
  ]

  ## PUBLIC API

  @doc """
  Initialize the gravitational routing system.

  ## Parameters
  - `shards` - List of spacetime shards to manage
  - `opts` - Router configuration options

  ## Options
  - `:routing_algorithm` - Primary routing algorithm (default: :gravitational)
  - `:cache_size` - Routing decision cache size (default: 1000)
  - `:rebalancing_threshold` - Load imbalance threshold (default: 0.3)
  - `:locality_range` - Locality sensitivity range (default: 100.0)

  ## Examples
      {:ok, router} = GravitationalRouter.initialize([hot_shard, warm_shard, cold_shard])
  """
  def initialize(shards, opts \\ []) do
    Logger.info("🌌 Initializing gravitational routing system with #{length(shards)} shards")

    # Create shard topology map
    shard_topology = Enum.reduce(shards, %{}, fn shard, acc ->
      Map.put(acc, shard.shard_id, shard)
    end)

    # Initialize routing components
    router = %__MODULE__{
      shard_topology: shard_topology,
      routing_algorithm: Keyword.get(opts, :routing_algorithm, :gravitational),
      locality_map: initialize_locality_map(),
      load_balancer: initialize_load_balancer(opts),
      migration_manager: initialize_migration_manager(),
      routing_cache: initialize_routing_cache(opts),
      performance_metrics: initialize_performance_metrics(),
      consistency_coordinator: initialize_consistency_coordinator()
    }

    # Start background processes
    start_background_processes(router)

    Logger.info("✨ Gravitational router initialized with #{router.routing_algorithm} algorithm")
    {:ok, router}
  end

  @doc """
  Determine the optimal shard for storing data using gravitational calculations.

  This is the main routing function that analyzes all available shards and
  selects the one with the strongest gravitational attraction for the data.

  ## Parameters
  - `router` - The gravitational router instance
  - `key` - Data key to route
  - `value` - Data value
  - `opts` - Routing options and metadata

  ## Options
  - `:access_pattern` - Expected access pattern (:hot, :warm, :cold)
  - `:priority` - Data priority level (:critical, :high, :normal, :low)
  - `:locality_group` - Locality group for related data placement
  - `:force_shard` - Force placement in specific shard (bypasses routing)

  ## Returns
  `{:ok, shard_id, routing_metadata}` or `{:error, reason}`

  ## Examples
      {:ok, :hot_data, metadata} = GravitationalRouter.route_data(router, "user:alice", user_data,
        access_pattern: :hot, priority: :critical)
  """
  def route_data(router, key, value, opts \\ []) do
    start_time = :os.system_time(:microsecond)

    # Check for forced shard placement
    case Keyword.get(opts, :force_shard) do
      nil ->
        # Perform gravitational routing
        perform_gravitational_routing(router, key, value, opts, start_time)

      forced_shard when is_atom(forced_shard) ->
        # Validate forced shard exists and accept it
        case Map.get(router.shard_topology, forced_shard) do
          nil ->
            {:error, {:invalid_shard, forced_shard}}
          _shard ->
            end_time = :os.system_time(:microsecond)
            metadata = %{
              routing_algorithm: :forced,
              operation_time: end_time - start_time,
              gravitational_score: 0.0,
              shard_id: forced_shard
            }
            {:ok, forced_shard, metadata}
        end
    end
  end

  @doc """
  Analyze current load distribution across all shards.

  Returns comprehensive analysis of load balancing, gravitational field
  distribution, and recommendations for optimization.

  ## Returns
  Map containing load analysis and rebalancing recommendations
  """
  def analyze_load_distribution(router) do
    shard_loads = Enum.map(router.shard_topology, fn {shard_id, shard} ->
      metrics = SpacetimeShard.get_shard_metrics(shard)
      {shard_id, metrics}
    end)

    total_items = Enum.reduce(shard_loads, 0, fn {_id, metrics}, acc ->
      acc + metrics.data_items
    end)

    # Calculate load imbalance
    load_imbalance = calculate_load_imbalance(shard_loads, total_items)

    # Detect gravitational hot spots
    gravitational_hotspots = detect_gravitational_hotspots(shard_loads)

    # Generate rebalancing recommendations
    recommendations = generate_rebalancing_recommendations(shard_loads, load_imbalance)

    %{
      total_data_items: total_items,
      shard_distribution: shard_loads,
      load_imbalance_factor: load_imbalance,
      gravitational_hotspots: gravitational_hotspots,
      rebalancing_needed: load_imbalance > router.load_balancer.imbalance_threshold,
      recommendations: recommendations,
      analysis_timestamp: :os.system_time(:millisecond)
    }
  end

  @doc """
  Execute load rebalancing across shards using gravitational migration.

  Automatically migrates data between shards to achieve better load
  distribution while respecting gravitational attraction principles.

  ## Parameters
  - `router` - The gravitational router
  - `analysis` - Load analysis from `analyze_load_distribution/1`
  - `opts` - Rebalancing options

  ## Options
  - `:migration_batch_size` - Number of items to migrate per batch (default: 100)
  - `:max_migration_time` - Maximum time for rebalancing operation (default: 30_000ms)
  - `:dry_run` - Only plan migrations without executing (default: false)

  ## Returns
  `{:ok, rebalancing_results}` or `{:error, reason}`
  """
  def execute_gravitational_rebalancing(router, analysis, opts \\ []) do
    Logger.info("🌌 Starting gravitational rebalancing operation")

    dry_run = Keyword.get(opts, :dry_run, false)
    batch_size = Keyword.get(opts, :migration_batch_size, 100)
    max_time = Keyword.get(opts, :max_migration_time, 30_000)

    start_time = :os.system_time(:millisecond)

    # Create migration plan based on analysis
    migration_plan = create_migration_plan(analysis, batch_size)

    if dry_run do
      Logger.info("📋 Dry run: Would migrate #{length(migration_plan.migrations)} data groups")
      {:ok, %{plan: migration_plan, executed: false}}
    else
      # Execute migration plan with time limit
      execute_migration_plan(router, migration_plan, start_time, max_time)
    end
  end

  @doc """
  Find all data items that should be co-located based on locality groups.

  Analyzes data relationships and identifies items that would benefit
  from gravitational clustering in the same or nearby shards.

  ## Parameters
  - `router` - The gravitational router
  - `locality_group` - Locality group identifier
  - `opts` - Search options

  ## Returns
  List of related data items and their optimal placement recommendations
  """
  def find_locality_clusters(router, locality_group, opts \\ []) do
    max_distance = Keyword.get(opts, :max_distance, router.load_balancer.locality_range)

    # Search for data in the specified locality group
    locality_items = search_locality_group(router, locality_group)

    # Calculate optimal clustering
    clusters = calculate_optimal_clustering(locality_items, max_distance)

    # Generate placement recommendations
    Enum.map(clusters, fn cluster ->
      optimal_shard = calculate_cluster_optimal_shard(router, cluster)
      %{
        cluster_id: cluster.id,
        items: cluster.items,
        current_distribution: cluster.current_distribution,
        recommended_shard: optimal_shard,
        clustering_score: cluster.cohesion_score
      }
    end)
  end

  @doc """
  Get comprehensive routing performance metrics.

  ## Returns
  Map containing routing performance statistics and efficiency metrics
  """
  def get_routing_metrics(router) do
    current_time = :os.system_time(:millisecond)

    base_metrics = %{
      total_routing_decisions: router.performance_metrics.total_decisions,
      cache_hit_rate: calculate_cache_hit_rate(router),
      average_routing_time: router.performance_metrics.avg_decision_time,
      algorithm_efficiency: calculate_algorithm_efficiency(router),
      load_balance_score: calculate_load_balance_score(router),
      gravitational_field_strength: calculate_total_gravitational_strength(router)
    }

    # Add per-shard routing statistics
    shard_stats = Enum.map(router.shard_topology, fn {shard_id, shard} ->
      try do
        shard_metrics = SpacetimeShard.get_shard_metrics(shard)
        routing_stats = get_shard_routing_stats(router, shard_id)
        {shard_id, Map.merge(shard_metrics, routing_stats)}
      rescue
        error ->
          Logger.warning("Failed to get metrics for shard #{shard_id}: #{inspect(error)}")
          # Return basic fallback metrics
          {shard_id, %{
            shard_id: shard_id,
            data_items: 0,
            memory_usage: 0,
            gravitational_field_strength: 0.0,
            entropy_level: 0.0
          }}
      end
    end) |> Enum.into(%{})

    Map.merge(base_metrics, %{
      shard_statistics: shard_stats,
      last_updated: current_time
    })
  end

  ## PRIVATE FUNCTIONS

  defp perform_gravitational_routing(router, key, value, opts, start_time) do
    # Check routing cache first
    cache_key = generate_cache_key(key, value, opts)

    # Check routing cache - currently always returns :miss (simplified implementation)
    case get_cached_routing_decision(router, cache_key) do
      :miss ->
        # Perform full gravitational calculation
        perform_full_gravitational_analysis(router, key, value, opts, start_time)

      # Note: In full implementation, would handle {:hit, cached_decision} case here
    end
  end

  defp perform_full_gravitational_analysis(router, key, value, opts, start_time) do
    access_metadata = %{
      access_pattern: Keyword.get(opts, :access_pattern, :balanced),
      priority: Keyword.get(opts, :priority, :normal),
      locality_group: Keyword.get(opts, :locality_group),
      access_frequency: Keyword.get(opts, :access_frequency, 1.0)
    }

    # Check for empty shard topology
    if map_size(router.shard_topology) == 0 do
      {:error, :no_shards_available}
    else
      # Calculate gravitational scores for all shards
      shard_scores = Enum.map(router.shard_topology, fn {shard_id, shard} ->
        score = SpacetimeShard.calculate_gravitational_score(shard, key, value, access_metadata)
        {shard_id, score, shard}
      end)

      # Apply consistent hashing for tie-breaking and stability
      shard_scores_with_hash = Enum.map(shard_scores, fn {shard_id, score, shard} ->
        hash_score = :erlang.phash2({key, shard_id}, 1000) / 1000.0
        adjusted_score = score * (1.0 + hash_score * 0.1)  # Small hash-based adjustment
        {shard_id, adjusted_score, shard}
      end)

      # Find the shard with highest gravitational attraction
      {best_shard_id, best_score, _best_shard} = Enum.max_by(shard_scores_with_hash, fn {_id, score, _shard} -> score end)

      end_time = :os.system_time(:microsecond)
      operation_time = end_time - start_time

      routing_metadata = %{
        routing_algorithm: router.routing_algorithm,
        operation_time: operation_time,
        gravitational_score: best_score,
        shard_id: best_shard_id,
        all_scores: Enum.map(shard_scores_with_hash, fn {id, score, _} ->
          %{shard_id: id, score: Float.round(score, 3)}
        end),
        cache_hit: false
      }

      # Cache this routing decision
      cache_routing_decision(router, generate_cache_key(key, value, opts), best_shard_id, routing_metadata)

      # Update routing performance metrics
      update_routing_metrics(router, :routing_decision, operation_time)

      Logger.debug("🎯 Routed #{key} to #{best_shard_id} (score: #{Float.round(best_score, 3)})")

      {:ok, best_shard_id, routing_metadata}
    end
  end

  defp initialize_locality_map() do
    %{
      groups: %{},
      spatial_index: %{},
      relationship_graph: %{}
    }
  end

  defp initialize_load_balancer(opts) do
    %{
      imbalance_threshold: Keyword.get(opts, :rebalancing_threshold, 0.3),
      locality_range: Keyword.get(opts, :locality_range, 100.0),
      migration_batch_size: Keyword.get(opts, :migration_batch_size, 100),
      rebalancing_interval: Keyword.get(opts, :rebalancing_interval, 300_000),
      last_rebalancing: :os.system_time(:millisecond)
    }
  end

  defp initialize_migration_manager() do
    %{
      active_migrations: %{},
      migration_history: [],
      migration_locks: %{}
    }
  end

  defp initialize_routing_cache(opts) do
    cache_size = Keyword.get(opts, :cache_size, 1000)

    %{
      decisions: %{},
      access_order: [],
      max_size: cache_size,
      hit_count: 0,
      miss_count: 0
    }
  end

  defp initialize_performance_metrics() do
    %{
      total_decisions: 0,
      total_decision_time: 0,
      avg_decision_time: 0.0,
      algorithm_switches: 0,
      cache_hits: 0,
      cache_misses: 0
    }
  end

  defp initialize_consistency_coordinator() do
    %{
      cross_shard_operations: %{},
      consistency_locks: %{},
      transaction_log: []
    }
  end

  defp start_background_processes(_router) do
    # Start background processes for maintenance
    # This would include periodic rebalancing, cache cleanup, etc.
    Logger.debug("🔄 Background routing processes initialized")
    :ok
  end

  defp calculate_load_imbalance(shard_loads, total_items) when total_items > 0 do
    # Calculate coefficient of variation for load distribution
    shard_count = length(shard_loads)
    expected_load = total_items / shard_count

    variance = Enum.reduce(shard_loads, 0.0, fn {_id, metrics}, acc ->
      deviation = metrics.data_items - expected_load
      acc + (deviation * deviation)
    end) / shard_count

    standard_deviation = :math.sqrt(variance)

    # Return coefficient of variation (0 = perfect balance, 1+ = very imbalanced)
    if expected_load > 0, do: standard_deviation / expected_load, else: 0.0
  end
  defp calculate_load_imbalance(_shard_loads, 0), do: 0.0

  defp detect_gravitational_hotspots(shard_loads) do
    # Find shards with unusually high gravitational field strength
    total_gravitational_strength = Enum.reduce(shard_loads, 0.0, fn {_id, metrics}, acc ->
      acc + metrics.gravitational_field_strength
    end)

    average_strength = total_gravitational_strength / length(shard_loads)

    Enum.filter(shard_loads, fn {_shard_id, metrics} ->
      metrics.gravitational_field_strength > average_strength * 1.5
    end)
    |> Enum.map(fn {shard_id, metrics} ->
      %{
        shard_id: shard_id,
        field_strength: metrics.gravitational_field_strength,
        severity: metrics.gravitational_field_strength / average_strength
      }
    end)
  end

  defp generate_rebalancing_recommendations(shard_loads, load_imbalance) do
    if load_imbalance > 0.3 do
      # Find overloaded and underloaded shards
      total_items = Enum.reduce(shard_loads, 0, fn {_id, metrics}, acc ->
        acc + metrics.data_items
      end)

      average_load = total_items / length(shard_loads)

      overloaded = Enum.filter(shard_loads, fn {_id, metrics} ->
        metrics.data_items > average_load * 1.2
      end)

      underloaded = Enum.filter(shard_loads, fn {_id, metrics} ->
        metrics.data_items < average_load * 0.8
      end)

      migration_recommendations = Enum.map(overloaded, fn {source_shard, metrics} ->
        excess_items = round(metrics.data_items - average_load)
        target_shard = find_best_migration_target(underloaded, excess_items)

        %{
          action: :migrate,
          from: source_shard,
          to: target_shard,
          estimated_items: excess_items,
          urgency: :medium
        }
      end)

      migration_recommendations
    else
      []
    end
  end

  defp find_best_migration_target(underloaded_shards, _excess_items) do
    # Find the shard with the most available capacity
    case underloaded_shards do
      [] -> nil
      [{shard_id, _metrics}] -> shard_id
      shards ->
        {best_shard_id, _} = Enum.min_by(shards, fn {_id, metrics} -> metrics.data_items end)
        best_shard_id
    end
  end

  defp create_migration_plan(analysis, batch_size) do
    migrations = Enum.map(analysis.recommendations, fn recommendation ->
      %{
        source_shard: recommendation.from,
        target_shard: recommendation.to,
        batch_size: batch_size,
        estimated_items: recommendation.estimated_items,
        urgency: recommendation.urgency
      }
    end)

    %{
      migrations: migrations,
      estimated_duration: length(migrations) * 5_000,  # 5 seconds per migration batch
      total_items: Enum.reduce(migrations, 0, fn m, acc -> acc + m.estimated_items end)
    }
  end

  defp execute_migration_plan(router, migration_plan, start_time, max_time) do
    Logger.info("🚀 Executing migration plan: #{length(migration_plan.migrations)} migrations")

    results = Enum.map(migration_plan.migrations, fn migration ->
      current_time = :os.system_time(:millisecond)
      elapsed_time = current_time - start_time

      if elapsed_time > max_time do
        Logger.warning("⏰ Migration timeout reached, stopping")
        {:error, :timeout}
      else
        execute_single_migration(router, migration)
      end
    end)

    successful_migrations = Enum.count(results, fn result ->
      case result do
        {:ok, _} -> true
        _ -> false
      end
    end)

    end_time = :os.system_time(:millisecond)
    total_time = end_time - start_time

    Logger.info("✅ Migration completed: #{successful_migrations}/#{length(migration_plan.migrations)} successful")

    {:ok, %{
      successful_migrations: successful_migrations,
      failed_migrations: length(results) - successful_migrations,
      total_duration_ms: total_time,
      migration_results: results
    }}
  end

  defp execute_single_migration(router, migration) do
    source_shard = Map.get(router.shard_topology, migration.source_shard)
    target_shard = Map.get(router.shard_topology, migration.target_shard)

    if source_shard && target_shard do
      SpacetimeShard.initiate_data_migration(source_shard, target_shard, %{
        batch_size: migration.batch_size,
        max_items: migration.estimated_items
      })
    else
      {:error, :invalid_shards}
    end
  end

  defp search_locality_group(_router, _locality_group) do
    # Placeholder for locality group search
    []
  end

  defp calculate_optimal_clustering(_locality_items, _max_distance) do
    # Placeholder for clustering calculation
    []
  end

  defp calculate_cluster_optimal_shard(_router, _cluster) do
    # Placeholder for cluster optimal shard calculation
    :hot_data
  end

  defp generate_cache_key(key, value, opts) do
    :crypto.hash(:md5, :erlang.term_to_binary({key, :erlang.phash2(value), opts}))
    |> Base.encode16(case: :lower)
  end

  defp get_cached_routing_decision(_router, _cache_key) do
    # Simplified cache implementation - always returns miss for now
    # In future versions, this could implement actual caching logic
    :miss
  end

  defp cache_routing_decision(_router, _cache_key, _shard_id, _metadata) do
    # Simplified cache implementation
    :ok
  end

  defp update_routing_metrics(_router, _operation_type, _operation_time) do
    # Update routing performance metrics
    :ok
  end

  defp calculate_cache_hit_rate(router) do
    total_requests = router.performance_metrics.cache_hits + router.performance_metrics.cache_misses
    if total_requests > 0 do
      router.performance_metrics.cache_hits / total_requests
    else
      0.0
    end
  end

  defp calculate_algorithm_efficiency(_router) do
    # Placeholder for algorithm efficiency calculation
    0.85
  end

  defp calculate_load_balance_score(_router) do
    # Placeholder for load balance score calculation
    0.92
  end

  defp calculate_total_gravitational_strength(router) do
    Enum.reduce(router.shard_topology, 0.0, fn {_id, shard}, acc ->
      try do
        metrics = SpacetimeShard.get_shard_metrics(shard)
        field_strength = metrics.gravitational_field_strength || 0.0
        acc + field_strength
      rescue
        _ -> acc  # Skip shards that can't provide metrics
      end
    end)
  end

  defp get_shard_routing_stats(_router, _shard_id) do
    # Placeholder for shard-specific routing statistics
    %{
      routing_decisions: 0,
      avg_routing_score: 0.0,
      migration_events: 0
    }
  end
end