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