defmodule Xbase.MemoHandler do
  @moduledoc """
  Handles coordinated operations between DBF and DBT files for memo field support.
  
  Provides high-level API for seamless memo content handling in record operations,
  automatic file discovery, and transaction safety across both file types.
  """

  alias Xbase.Parser
  alias Xbase.DbtParser
  alias Xbase.DbtWriter
  alias Xbase.Types.DbtFile

  defstruct [:dbf, :dbt, :dbf_path, :dbt_path, :memo_mode]

  @type t :: %__MODULE__{
    dbf: map(),
    dbt: DbtFile.t() | nil,
    dbf_path: String.t(),
    dbt_path: String.t() | nil,
    memo_mode: :auto | :required | :disabled
  }

  @doc """
  Opens a DBF file with automatic memo file discovery and coordination.
  
  ## Parameters
  - `dbf_path` - Path to the DBF file
  - `modes` - File access modes (default: [:read])
  - `opts` - Options for memo handling
    - `:memo` - Memo mode (:auto, :required, :disabled)
    - `:dbt_path` - Explicit DBT file path (overrides auto-discovery)
  
  ## Returns
  - `{:ok, MemoHandler.t()}` - Successfully opened coordinated files
  - `{:error, reason}` - Error opening files
  
  ## Examples
      # Automatic memo file discovery
      {:ok, handler} = MemoHandler.open_dbf_with_memo("data.dbf")
      
      # Read-write mode with required memo support
      {:ok, handler} = MemoHandler.open_dbf_with_memo("data.dbf", [:read, :write], memo: :required)
      
      # Explicit DBT file path
      {:ok, handler} = MemoHandler.open_dbf_with_memo("data.dbf", [], dbt_path: "memos.dbt")
  """
  def open_dbf_with_memo(dbf_path, modes \\ [:read], opts \\ []) do
    memo_mode = Keyword.get(opts, :memo, :auto)
    explicit_dbt_path = Keyword.get(opts, :dbt_path)
    
    # Open DBF file first
    case Parser.open_dbf(dbf_path, modes) do
      {:ok, dbf} ->
        # Check if DBF supports memo fields
        if has_memo_support?(dbf) do
          dbt_path = explicit_dbt_path || discover_dbt_path(dbf_path)
          open_memo_file(dbf, dbf_path, dbt_path, modes, memo_mode)
        else
          case memo_mode do
            :required ->
              Parser.close_dbf(dbf)
              {:error, :dbf_no_memo_support}
            _ ->
              # DBF without memo support, return handler without DBT
              {:ok, %__MODULE__{
                dbf: dbf,
                dbt: nil,
                dbf_path: dbf_path,
                dbt_path: nil,
                memo_mode: :disabled
              }}
          end
        end
      {:error, reason} ->
        {:error, reason}
    end
  end

  @doc """
  Creates a new DBF file with memo support and coordinated DBT file.
  
  ## Parameters
  - `dbf_path` - Path for the new DBF file
  - `fields` - Field definitions for the DBF file
  - `opts` - Options for file creation
    - `:version` - DBF version (automatically set to memo-capable if memo fields present)
    - `:dbt_path` - Explicit DBT file path (defaults to replacing .dbf with .dbt)
    - `:block_size` - DBT block size (default: 512)
  
  ## Returns
  - `{:ok, MemoHandler.t()}` - Successfully created coordinated files
  - `{:error, reason}` - Error creating files
  """
  def create_dbf_with_memo(dbf_path, fields, opts \\ []) do
    has_memo_fields = Enum.any?(fields, fn field -> field.type == "M" end)
    
    if has_memo_fields do
      # Force memo-capable version
      version = Keyword.get(opts, :version, 0x8B)  # dBase IV with memo
      dbt_path = Keyword.get(opts, :dbt_path, replace_extension(dbf_path, ".dbt"))
      block_size = Keyword.get(opts, :block_size, 512)
      
      # Create DBF file first
      case Parser.create_dbf(dbf_path, fields, Keyword.put(opts, :version, version)) do
        {:ok, dbf} ->
          # Create coordinated DBT file
          case DbtWriter.create_dbt(dbt_path, version: :dbase_iii, block_size: block_size) do
            {:ok, dbt} ->
              {:ok, %__MODULE__{
                dbf: dbf,
                dbt: dbt,
                dbf_path: dbf_path,
                dbt_path: dbt_path,
                memo_mode: :auto
              }}
            {:error, reason} ->
              Parser.close_dbf(dbf)
              File.rm(dbf_path)  # Clean up DBF file
              {:error, {:dbt_creation_failed, reason}}
          end
        {:error, reason} ->
          {:error, reason}
      end
    else
      # No memo fields, create regular DBF file
      case Parser.create_dbf(dbf_path, fields, opts) do
        {:ok, dbf} ->
          {:ok, %__MODULE__{
            dbf: dbf,
            dbt: nil,
            dbf_path: dbf_path,
            dbt_path: nil,
            memo_mode: :disabled
          }}
        {:error, reason} ->
          {:error, reason}
      end
    end
  end

  @doc """
  Appends a record with automatic memo content handling.
  
  ## Parameters
  - `handler` - MemoHandler structure
  - `record_data` - Map of field names to values, where memo fields contain content strings
  
  ## Returns
  - `{:ok, updated_handler}` - Successfully appended record with memo content
  - `{:error, reason}` - Error appending record
  
  ## Example
      record_data = %{
        "NAME" => "John Doe",
        "NOTES" => "This memo content will be automatically stored in the DBT file"
      }
      {:ok, updated_handler} = MemoHandler.append_record_with_memo(handler, record_data)
  """
  def append_record_with_memo(%__MODULE__{memo_mode: :disabled} = handler, record_data) do
    # No memo support, use regular record append
    case Parser.append_record(handler.dbf, record_data) do
      {:ok, updated_dbf} ->
        {:ok, %{handler | dbf: updated_dbf}}
      {:error, reason} ->
        {:error, reason}
    end
  end

  def append_record_with_memo(%__MODULE__{} = handler, record_data) do
    # Process memo fields and convert content to references
    case process_memo_fields(handler, record_data) do
      {:ok, {processed_data, updated_handler}} ->
        # Append record with memo references
        case Parser.append_record(updated_handler.dbf, processed_data) do
          {:ok, updated_dbf} ->
            {:ok, %{updated_handler | dbf: updated_dbf}}
          {:error, reason} ->
            {:error, reason}
        end
      {:error, reason} ->
        {:error, reason}
    end
  end

  @doc """
  Updates a record with automatic memo content handling.
  
  ## Parameters
  - `handler` - MemoHandler structure
  - `record_index` - Zero-based record index to update
  - `record_data` - Map of field names to values for update
  
  ## Returns
  - `{:ok, updated_handler}` - Successfully updated record with memo content
  - `{:error, reason}` - Error updating record
  """
  def update_record_with_memo(%__MODULE__{memo_mode: :disabled} = handler, record_index, record_data) do
    # No memo support, use regular record update
    case Parser.update_record(handler.dbf, record_index, record_data) do
      {:ok, updated_dbf} ->
        {:ok, %{handler | dbf: updated_dbf}}
      {:error, reason} ->
        {:error, reason}
    end
  end

  def update_record_with_memo(%__MODULE__{} = handler, record_index, record_data) do
    # For updates, we need to handle memo field updates carefully
    # Read existing record to preserve non-updated memo references
    case Parser.read_record(handler.dbf, record_index) do
      {:ok, existing_record} ->
        # Extract data from Record struct
        existing_data = existing_record.data
        
        # Merge update data with existing record
        _merged_data = Map.merge(existing_data, record_data)
        
        # Process memo fields in the merged data
        case process_memo_fields_for_update(handler, existing_data, record_data) do
          {:ok, {processed_data, updated_handler}} ->
            # Update record with processed memo references
            case Parser.update_record(updated_handler.dbf, record_index, processed_data) do
              {:ok, updated_dbf} ->
                {:ok, %{updated_handler | dbf: updated_dbf}}
              {:error, reason} ->
                {:error, reason}
            end
          {:error, reason} ->
            {:error, reason}
        end
      {:error, reason} ->
        {:error, reason}
    end
  end

  @doc """
  Reads a record with automatic memo content resolution.
  
  ## Parameters
  - `handler` - MemoHandler structure
  - `record_index` - Zero-based record index to read
  
  ## Returns
  - `{:ok, record_data}` - Record data with memo content resolved
  - `{:error, reason}` - Error reading record
  """
  def read_record_with_memo(%__MODULE__{} = handler, record_index) do
    case Parser.read_record(handler.dbf, record_index) do
      {:ok, record_struct} ->
        # Extract data from Record struct and resolve memo content
        resolve_memo_content(handler, record_struct.data)
      {:error, reason} ->
        {:error, reason}
    end
  end

  @doc """
  Closes both DBF and DBT files properly.
  
  ## Parameters
  - `handler` - MemoHandler structure
  
  ## Returns
  - `:ok` - Files closed successfully
  """
  def close_memo_files(%__MODULE__{} = handler) do
    # Close DBF file
    Parser.close_dbf(handler.dbf)
    
    # Close DBT file if present
    if handler.dbt do
      DbtWriter.close_dbt(handler.dbt)
    end
    
    :ok
  end

  @doc """
  Executes a function with transaction safety across both DBF and DBT files.
  
  ## Parameters
  - `handler` - MemoHandler structure
  - `transaction_fn` - Function to execute with the handler
  
  ## Returns
  - `{:ok, {result, updated_handler}}` - Transaction successful
  - `{:error, reason}` - Transaction failed, changes rolled back
  """
  def memo_transaction(%__MODULE__{} = handler, transaction_fn) do
    # Create backups of both files
    dbf_backup = handler.dbf_path <> ".bak"
    dbt_backup = if handler.dbt_path, do: handler.dbt_path <> ".bak", else: nil
    
    try do
      # Backup DBF file
      File.cp!(handler.dbf_path, dbf_backup)
      
      # Backup DBT file if it exists
      if dbt_backup && File.exists?(handler.dbt_path) do
        File.cp!(handler.dbt_path, dbt_backup)
      end
      
      # Execute transaction
      case transaction_fn.(handler) do
        {:ok, result, updated_handler} ->
          # Transaction succeeded, clean up backups
          File.rm(dbf_backup)
          if dbt_backup, do: File.rm(dbt_backup)
          {:ok, {result, updated_handler}}
        {:error, reason} ->
          # Transaction failed, restore from backups
          restore_from_backup(handler, dbf_backup, dbt_backup)
          {:error, reason}
      end
    rescue
      e ->
        # Exception occurred, restore from backups
        restore_from_backup(handler, dbf_backup, dbt_backup)
        {:error, {:exception, e}}
    end
  end

  # Private helper functions

  defp has_memo_support?(%{header: header}) do
    # Check if DBF version supports memo fields
    header.version in [0x83, 0x8B, 0xF5]
  end

  defp discover_dbt_path(dbf_path) do
    replace_extension(dbf_path, ".dbt")
  end

  defp replace_extension(path, new_ext) do
    Path.rootname(path) <> new_ext
  end

  defp open_memo_file(dbf, dbf_path, dbt_path, modes, memo_mode) do
    write_mode = :write in modes
    
    case File.exists?(dbt_path) do
      true ->
        # DBT file exists, open it
        open_function = if write_mode, do: &DbtWriter.open_dbt_for_writing/1, else: &DbtParser.open_dbt/1
        case open_function.(dbt_path) do
          {:ok, dbt} ->
            {:ok, %__MODULE__{
              dbf: dbf,
              dbt: dbt,
              dbf_path: dbf_path,
              dbt_path: dbt_path,
              memo_mode: memo_mode
            }}
          {:error, reason} ->
            Parser.close_dbf(dbf)
            {:error, {:dbt_open_failed, reason}}
        end
      false ->
        case memo_mode do
          :required ->
            Parser.close_dbf(dbf)
            {:error, :dbt_file_required}
          :auto when write_mode ->
            # Create new DBT file for writing
            case DbtWriter.create_dbt(dbt_path) do
              {:ok, dbt} ->
                {:ok, %__MODULE__{
                  dbf: dbf,
                  dbt: dbt,
                  dbf_path: dbf_path,
                  dbt_path: dbt_path,
                  memo_mode: memo_mode
                }}
              {:error, reason} ->
                Parser.close_dbf(dbf)
                {:error, {:dbt_creation_failed, reason}}
            end
          _ ->
            # Auto mode without write access, or disabled - no DBT file
            {:ok, %__MODULE__{
              dbf: dbf,
              dbt: nil,
              dbf_path: dbf_path,
              dbt_path: nil,
              memo_mode: memo_mode
            }}
        end
    end
  end

  defp process_memo_fields(%__MODULE__{dbt: nil}, record_data) do
    # No DBT file available, ensure no memo content is provided
    memo_fields = get_memo_fields_with_content(record_data)
    if Enum.empty?(memo_fields) do
      {:ok, {record_data, nil}}  # No handler update needed
    else
      {:error, {:memo_content_without_dbt, memo_fields}}
    end
  end

  defp process_memo_fields(%__MODULE__{} = handler, record_data) do
    # Process each memo field that contains string content
    memo_fields = get_memo_fields(handler.dbf)
    process_memo_fields_recursive(handler, record_data, memo_fields, %{})
  end

  defp process_memo_fields_recursive(handler, record_data, [], processed_data) do
    # All fields processed
    final_data = Map.merge(record_data, processed_data)
    {:ok, {final_data, handler}}
  end

  defp process_memo_fields_recursive(handler, record_data, [field_name | rest], processed_data) do
    case Map.get(record_data, field_name) do
      content when is_binary(content) ->
        # Write memo content and get block reference
        case DbtWriter.write_memo(handler.dbt, content) do
          {:ok, {block_number, updated_dbt}} ->
            updated_handler = %{handler | dbt: updated_dbt}
            updated_processed = Map.put(processed_data, field_name, {:memo_ref, block_number})
            process_memo_fields_recursive(updated_handler, record_data, rest, updated_processed)
          {:error, reason} ->
            {:error, {:memo_write_failed, field_name, reason}}
        end
      {:memo_ref, _block_number} = memo_ref ->
        # Already a memo reference, keep as-is
        updated_processed = Map.put(processed_data, field_name, memo_ref)
        process_memo_fields_recursive(handler, record_data, rest, updated_processed)
      nil ->
        # No value for this memo field, continue
        process_memo_fields_recursive(handler, record_data, rest, processed_data)
      other ->
        # Invalid value for memo field
        {:error, {:invalid_memo_value, field_name, other}}
    end
  end

  defp process_memo_fields_for_update(handler, existing_record, update_data) do
    # Only process memo fields that are being updated
    memo_fields = get_memo_fields(handler.dbf)
    updated_memo_fields = Enum.filter(memo_fields, fn field -> Map.has_key?(update_data, field) end)
    
    process_memo_update_fields_recursive(handler, existing_record, update_data, updated_memo_fields, %{})
  end

  defp process_memo_update_fields_recursive(handler, _existing_record, update_data, [], processed_data) do
    # All updated memo fields processed
    final_data = Map.merge(update_data, processed_data)
    {:ok, {final_data, handler}}
  end

  defp process_memo_update_fields_recursive(handler, existing_record, update_data, [field_name | rest], processed_data) do
    case Map.get(update_data, field_name) do
      content when is_binary(content) ->
        # Check if we can reuse existing block
        existing_ref = Map.get(existing_record, field_name)
        case reuse_or_create_memo_block(handler, existing_ref, content) do
          {:ok, {memo_ref, updated_handler}} ->
            updated_processed = Map.put(processed_data, field_name, memo_ref)
            process_memo_update_fields_recursive(updated_handler, existing_record, update_data, rest, updated_processed)
          {:error, reason} ->
            {:error, {:memo_update_failed, field_name, reason}}
        end
      {:memo_ref, _block_number} = memo_ref ->
        # New memo reference provided
        updated_processed = Map.put(processed_data, field_name, memo_ref)
        process_memo_update_fields_recursive(handler, existing_record, update_data, rest, updated_processed)
      other ->
        {:error, {:invalid_memo_update_value, field_name, other}}
    end
  end

  defp reuse_or_create_memo_block(handler, {:memo_ref, block_number}, content) do
    # Try to update existing block
    case DbtWriter.update_memo(handler.dbt, block_number, content) do
      {:ok, updated_dbt} ->
        {:ok, {{:memo_ref, block_number}, %{handler | dbt: updated_dbt}}}
      {:error, _reason} ->
        # Update failed, create new block
        create_new_memo_block(handler, content)
    end
  end

  defp reuse_or_create_memo_block(handler, _other, content) do
    # No existing reference, create new block
    create_new_memo_block(handler, content)
  end

  defp create_new_memo_block(handler, content) do
    case DbtWriter.write_memo(handler.dbt, content) do
      {:ok, {block_number, updated_dbt}} ->
        {:ok, {{:memo_ref, block_number}, %{handler | dbt: updated_dbt}}}
      {:error, reason} ->
        {:error, reason}
    end
  end

  defp resolve_memo_content(%__MODULE__{dbt: nil}, record_data) do
    # No DBT file, return record as-is
    {:ok, record_data}
  end

  defp resolve_memo_content(%__MODULE__{} = handler, record_data) do
    memo_fields = get_memo_fields(handler.dbf)
    resolve_memo_content_recursive(handler, record_data, memo_fields, %{})
  end

  defp resolve_memo_content_recursive(_handler, record_data, [], resolved_data) do
    # All memo fields resolved
    final_data = Map.merge(record_data, resolved_data)
    {:ok, final_data}
  end

  defp resolve_memo_content_recursive(handler, record_data, [field_name | rest], resolved_data) do
    case Map.get(record_data, field_name) do
      {:memo_ref, block_number} when block_number > 0 ->
        # Resolve memo reference to content
        case DbtParser.read_memo(handler.dbt, block_number) do
          {:ok, content} ->
            updated_resolved = Map.put(resolved_data, field_name, content)
            resolve_memo_content_recursive(handler, record_data, rest, updated_resolved)
          {:error, reason} ->
            {:error, {:memo_read_failed, field_name, block_number, reason}}
        end
      {:memo_ref, 0} ->
        # Empty memo reference
        updated_resolved = Map.put(resolved_data, field_name, "")
        resolve_memo_content_recursive(handler, record_data, rest, updated_resolved)
      _other ->
        # Not a memo reference or already resolved
        resolve_memo_content_recursive(handler, record_data, rest, resolved_data)
    end
  end

  defp get_memo_fields(%{fields: fields}) do
    fields
    |> Enum.filter(fn field -> field.type == "M" end)
    |> Enum.map(fn field -> field.name end)
  end

  defp get_memo_fields_with_content(record_data) do
    record_data
    |> Enum.filter(fn {_key, value} -> is_binary(value) end)
    |> Enum.map(fn {key, _value} -> key end)
  end

  defp restore_from_backup(handler, dbf_backup, dbt_backup) do
    # Restore DBF file
    if File.exists?(dbf_backup) do
      File.cp!(dbf_backup, handler.dbf_path)
      File.rm(dbf_backup)
    end
    
    # Restore DBT file
    if dbt_backup && File.exists?(dbt_backup) do
      File.cp!(dbt_backup, handler.dbt_path)
      File.rm(dbt_backup)
    end
  end
end