require 'csv'

class PostImportSourceParser
  MAX_ROWS = 100
  MAX_BYTES = 1.megabyte
  MAX_CELL_BYTES = 20.kilobytes
  MAX_COLUMNS = 50

  def initialize source:, format:, has_header: false, json_path: nil
    @source = source.to_s
    @format = format.to_s
    @has_header = ActiveModel::Type::Boolean.new.cast(has_header)
    @json_path = json_path.to_s
  end

  def parse
    raise ArgumentError, '入力が大きすぎます．' if @source.bytesize > MAX_BYTES

    @format == 'json' ? parse_json : parse_delimited
  end

  private

  def parse_delimited
    separator = @format == 'csv' ? ',' : "\t"
    table = CSV.parse(@source, col_sep: separator).map { |row| row.map { _1.to_s.strip } }
    raise ArgumentError, '入力が空です．' if table.empty?

    headers = @has_header ? table.shift : nil
    ensure_limits!(table)
    width = table.map(&:length).max.to_i
    raise ArgumentError, "列数は #{ MAX_COLUMNS } 列までです．" if width > MAX_COLUMNS
    { columns: (0...width).map { |index| { key: index.to_s,
                                          label: "#{ column_name(index) }：#{ headers&.[](index).presence || '列' }" } },
      rows: table.each_with_index.map { |values, index| { source_row: index + (@has_header ? 2 : 1), values: } } }
  rescue CSV::MalformedCSVError => e
    raise ArgumentError, "CSV・TSV の形式が不正です: #{ e.message }"
  end

  def parse_json
    value = JSON.parse(@source, max_nesting: 20)
    @json_path.split('.').reject(&:blank?).each { |part| value = value.is_a?(Array) ? value[Integer(part)] : value.fetch(part) }
    raise ArgumentError, 'JSON の投稿候補は配列にしてください．' unless value.is_a?(Array)

    ensure_limits!(value)
    unless value.all?(Hash)
      invalid = value.each_with_index.filter_map { |item, index| index + 1 unless item.is_a?(Hash) }
      raise ArgumentError, "JSON の投稿候補は object の配列にしてください: 行 #{ invalid.join(', ') }"
    end
    keys = value.flat_map(&:keys).map(&:to_s).uniq
    raise ArgumentError, "列数は #{ MAX_COLUMNS } 列までです．" if keys.length > MAX_COLUMNS
    { columns: keys.each_with_index.map { |key, index| { key:, label: "#{ column_name(index) }：#{ key }" } },
      rows: value.each_with_index.map { |item, index| { source_row: index + 1,
                                                         values: keys.map { |key|
                                                           value = item.key?(key) ? item[key] : item[key.to_sym]
                                                           json_cell(value)
                                                         } } } }
  rescue JSON::ParserError, KeyError, ArgumentError => e
    raise ArgumentError, "JSON の形式が不正です: #{ e.message }"
  end

  def ensure_limits! rows
    raise ArgumentError, "取込件数は #{ MAX_ROWS } 件までです．" if rows.length > MAX_ROWS
    raise ArgumentError, 'セルが大きすぎます．' if rows.flatten.any? { _1.to_s.bytesize > MAX_CELL_BYTES }
  end

  def json_cell value
    case value
    when nil then ''
    when String, Numeric, TrueClass, FalseClass then value.to_s
    when Array, Hash then JSON.generate(value)
    else raise ArgumentError, 'JSON のセル値が不正です．'
    end
  end

  def column_name index
    name = +''
    loop do
      name.prepend((65 + (index % 26)).chr)
      index = (index / 26) - 1
      break if index < 0
    end
    name
  end
end