1// Package connections implement a generic GraphQL relay connection
2package connections
3
4import (
5 "encoding/base64"
6 "fmt"
7 "strconv"
8 "strings"
9
10 "github.com/git-bug/git-bug/api/graphql/models"
11)
12
13const cursorPrefix = "cursor:"
14
15// Edge define the contract for an edge in a relay connection
16type Edge interface {
17 GetCursor() string
18}
19
20// OffsetToCursor create the cursor string from an offset
21func OffsetToCursor(offset int) string {
22 str := fmt.Sprintf("%v%v", cursorPrefix, offset)
23 return base64.StdEncoding.EncodeToString([]byte(str))
24}
25
26// CursorToOffset re-derives the offset from the cursor string.
27func CursorToOffset(cursor string) (int, error) {
28 str := ""
29 b, err := base64.StdEncoding.DecodeString(cursor)
30 if err == nil {
31 str = string(b)
32 }
33 str = strings.Replace(str, cursorPrefix, "", -1)
34 offset, err := strconv.Atoi(str)
35 if err != nil {
36 return 0, fmt.Errorf("Invalid cursor")
37 }
38 return offset, nil
39}
40
41// EdgeMaker defines a function that takes a NodeType and an offset and
42// create an Edge.
43type EdgeMaker[NodeType any] func(value NodeType, offset int) Edge
44
45// ConMaker defines a function that creates a ConnectionType
46type ConMaker[NodeType any, EdgeType Edge, ConType any] func(
47 edges []*EdgeType,
48 nodes []NodeType,
49 info *models.PageInfo,
50 totalCount int) (*ConType, error)
51
52// Connection will paginate a source according to the input of a relay connection
53func Connection[NodeType any, EdgeType Edge, ConType any](
54 source []NodeType,
55 edgeMaker EdgeMaker[NodeType],
56 conMaker ConMaker[NodeType, EdgeType, ConType],
57 input models.ConnectionInput) (*ConType, error) {
58
59 var nodes []NodeType
60 var edges []*EdgeType
61 var cursors []string
62 var pageInfo = &models.PageInfo{}
63 var totalCount = len(source)
64
65 emptyCon, _ := conMaker(edges, nodes, pageInfo, 0)
66
67 offset := 0
68
69 if input.After != nil {
70 for i, value := range source {
71 edge := edgeMaker(value, i)
72 if edge.GetCursor() == *input.After {
73 // remove all previous element including the "after" one
74 source = source[i+1:]
75 offset = i + 1
76 pageInfo.HasPreviousPage = true
77 break
78 }
79 }
80 }
81
82 if input.Before != nil {
83 for i, value := range source {
84 edge := edgeMaker(value, i+offset)
85
86 if edge.GetCursor() == *input.Before {
87 // remove all after element including the "before" one
88 pageInfo.HasNextPage = true
89 break
90 }
91
92 e := edge.(EdgeType)
93 edges = append(edges, &e)
94 cursors = append(cursors, edge.GetCursor())
95 nodes = append(nodes, value)
96 }
97 } else {
98 edges = make([]*EdgeType, len(source))
99 cursors = make([]string, len(source))
100 nodes = source
101
102 for i, value := range source {
103 edge := edgeMaker(value, i+offset)
104 e := edge.(EdgeType)
105 edges[i] = &e
106 cursors[i] = edge.GetCursor()
107 }
108 }
109
110 if input.First != nil {
111 if *input.First < 0 {
112 return emptyCon, fmt.Errorf("first less than zero")
113 }
114
115 if len(edges) > *input.First {
116 // Slice result to be of length first by removing edges from the end
117 edges = edges[:*input.First]
118 cursors = cursors[:*input.First]
119 nodes = nodes[:*input.First]
120 pageInfo.HasNextPage = true
121 }
122 }
123
124 if input.Last != nil {
125 if *input.Last < 0 {
126 return emptyCon, fmt.Errorf("last less than zero")
127 }
128
129 if len(edges) > *input.Last {
130 // Slice result to be of length last by removing edges from the start
131 edges = edges[len(edges)-*input.Last:]
132 cursors = cursors[len(cursors)-*input.Last:]
133 nodes = nodes[len(nodes)-*input.Last:]
134 pageInfo.HasPreviousPage = true
135 }
136 }
137
138 // Fill up pageInfo cursors
139 if len(cursors) > 0 {
140 pageInfo.StartCursor = cursors[0]
141 pageInfo.EndCursor = cursors[len(cursors)-1]
142 }
143
144 return conMaker(edges, nodes, pageInfo, totalCount)
145}