demarches-normaliennes/app/graphql/connections/cursor_connection.rb

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module Connections
class CursorConnection < GraphQL::Pagination::Connection
def initialize(items, deprecated_order: nil, **kwargs)
super(items, **kwargs)
@deprecated_order = deprecated_order
end
def nodes
load_nodes
end
def has_previous_page
load_nodes
@has_previous_page
end
def has_next_page
load_nodes
@has_next_page
end
def cursor_for(item)
cursor_from_column(item, order_column)
end
private
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# [d1, d2, d3, d4, d5, d6]
#
# first: 2
# -> d1, d2
# first: 2, after: d2
# -> d3, d4
# first: 2, before: d3
# -> d1, d2
#
# last: 2
# -> d5, d6
# last: 2, before: d5
# -> d3, d4
# last: 2, after: d4
# -> d5, d6
#
# si after ou before present, last ou first donne juste limit
#
# order:
# order, ne sert rien si after ou before
#
# first: 2, order: desc => last: 2
# -> d5, d6
#
# last: 2, order: desc => first 2
# -> d1, d2
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def limit_and_inverted(first: nil, last: nil, after: nil, before: nil, order: nil)
limit = [first, last, max_page_size].compact.min + 1
inverted = last.present? || before.present?
if order == :desc && after.nil? && before.nil?
inverted = !inverted
end
[limit, inverted]
end
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def previous_page?(after, result_size, limit, inverted)
after.present? || (result_size == limit && inverted)
end
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def next_page?(before, result_size, limit, inverted)
before.present? || (result_size == limit && !inverted)
end
def load_nodes
@nodes ||= begin
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ensure_valid_params
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limit, inverted = limit_and_inverted(first:, last:, after:, before:, order: @deprecated_order)
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expected_size = limit - 1
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nodes = resolve_nodes(limit:, before:, after:, inverted:)
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result_size = nodes.size
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@has_previous_page = previous_page?(after, result_size, limit, inverted)
@has_next_page = next_page?(before, result_size, limit, inverted)
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trimmed_nodes = nodes.first(expected_size)
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trimmed_nodes.reverse! if inverted
trimmed_nodes
end
end
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def ensure_valid_params
if first.present? && last.present?
raise GraphQL::ExecutionError.new('Arguments "first" and "last" are exclusive', extensions: { code: :bad_request })
end
if before.present? && after.present?
raise GraphQL::ExecutionError.new('Arguments "before" and "after" are exclusive', extensions: { code: :bad_request })
end
if first.present? && first < 0
raise GraphQL::ExecutionError.new('Argument "first" must be a non-negative integer', extensions: { code: :bad_request })
end
if last.present? && last < 0
raise GraphQL::ExecutionError.new('Argument "last" must be a non-negative integer', extensions: { code: :bad_request })
end
end
def timestamp_and_id_from_cursor(cursor)
timestamp, id = decode(cursor).split(';')
[Time.zone.parse(timestamp), id.to_i]
end
def cursor_from_column(item, column)
encode([item.read_attribute(column).utc.strftime("%Y-%m-%dT%H:%M:%S.%NZ"), item.id].join(';'))
end
def order_column
:updated_at
end
def order_table
raise StandardError, 'Not implemented'
end
def resolve_nodes(before:, after:, limit:, inverted:)
order = inverted ? :desc : :asc
nodes = items.order(order_column => order, id: order)
nodes = nodes.limit(limit)
if before.present?
timestamp, id = timestamp_and_id_from_cursor(before)
nodes.where("(#{order_table}.#{order_column}, #{order_table}.id) < (?, ?)", timestamp, id)
elsif after.present?
timestamp, id = timestamp_and_id_from_cursor(after)
nodes.where("(#{order_table}.#{order_column}, #{order_table}.id) > (?, ?)", timestamp, id)
else
nodes
end
end
end
end