1package connections
2
3import (
4 "fmt"
5
6 "github.com/MichaelMure/git-bug/api/graphql/models"
7)
8
9type Input struct {
10 After *string
11 Before *string
12 First *int
13 Last *int
14}
15
16// Result is the result of a GraphQL connection pagination
17type Result[NodeT any] struct {
18 // A list of edges.
19 Edges []*Edge[NodeT] `json:"edges"`
20 Nodes []NodeT `json:"nodes"`
21 // Information to aid in pagination.
22 PageInfo *models.PageInfo `json:"pageInfo"`
23 // Identifies the total count of items in the connection.
24 TotalCount int `json:"totalCount"`
25}
26
27// Edge hold a GraphQL connection edge
28type Edge[NodeT any] struct {
29 Cursor string `json:"cursor"`
30 Node NodeT `json:"node"`
31}
32
33func newEdge[NodeT any](node NodeT, offset int) *Edge[NodeT] {
34 return &Edge[NodeT]{Cursor: OffsetToCursor(offset), Node: node}
35}
36
37// Paginate will paginate a source according to the input of a relay connection
38func Paginate[NodeT any](source []NodeT, input Input) (*Result[NodeT], error) {
39 var nodes []NodeT
40 var edges []*Edge[NodeT]
41 var cursors []string
42 var pageInfo = &models.PageInfo{}
43 var totalCount = len(source)
44
45 offset := 0
46
47 if input.After != nil {
48 for i, value := range source {
49 edge := newEdge(value, offset)
50 if edge.Cursor == *input.After {
51 // remove all previous element including the "after" one
52 source = source[i+1:]
53 offset = i + 1
54 pageInfo.HasPreviousPage = true
55 break
56 }
57 }
58 }
59
60 if input.Before != nil {
61 for i, value := range source {
62 edge := newEdge(value, i+offset)
63 if edge.Cursor == *input.Before {
64 // remove all after element including the "before" one
65 pageInfo.HasNextPage = true
66 break
67 }
68 edges = append(edges, edge)
69 cursors = append(cursors, edge.Cursor)
70 nodes = append(nodes, value)
71 }
72 } else {
73 edges = make([]*Edge[NodeT], len(source))
74 cursors = make([]string, len(source))
75 nodes = source
76
77 for i, value := range source {
78 edge := newEdge(value, i+offset)
79 edges[i] = edge
80 cursors[i] = edge.Cursor
81 }
82 }
83
84 if input.First != nil {
85 if *input.First < 0 {
86 return nil, fmt.Errorf("first less than zero")
87 }
88
89 if len(edges) > *input.First {
90 // Slice result to be of length first by removing edges from the end
91 edges = edges[:*input.First]
92 cursors = cursors[:*input.First]
93 nodes = nodes[:*input.First]
94 pageInfo.HasNextPage = true
95 }
96 }
97
98 if input.Last != nil {
99 if *input.Last < 0 {
100 return nil, fmt.Errorf("last less than zero")
101 }
102
103 if len(edges) > *input.Last {
104 // Slice result to be of length last by removing edges from the start
105 edges = edges[len(edges)-*input.Last:]
106 cursors = cursors[len(cursors)-*input.Last:]
107 nodes = nodes[len(nodes)-*input.Last:]
108 pageInfo.HasPreviousPage = true
109 }
110 }
111
112 // Fill up pageInfo cursors
113 if len(cursors) > 0 {
114 pageInfo.StartCursor = cursors[0]
115 pageInfo.EndCursor = cursors[len(cursors)-1]
116 }
117
118 return &Result[NodeT]{
119 Edges: edges,
120 Nodes: nodes,
121 PageInfo: pageInfo,
122 TotalCount: totalCount,
123 }, nil
124}