1. 1
2. 2
3. 3
4. 4
5. 5
6. 6
7. 7
8. 8
9. 9
10. 10
11. 11
12. 12
13. 13
14. 14
15. 15
16. 16
17. 17
18. 18
19. 19
20. 20
21. 21
22. 22
23. 23
24. 24
25. 25
26. 26
27. 27
28. 28
29. 29
30. 30
31. 31
32. 32
33. 33
34. 34
35. 35
36. 36
37. 37
38. 38
39. 39
40. 40
41. 41
42. 42
43. 43
44. 44
45. 45
46. 46
47. 47
48. 48
49. 49
50. 50
51. 51
52. 52
53. 53
54. 54
55. 55
56. 56
57. 57
58. 58
59. 59
60. 60
61. 61
62. 62
63. 63
64. 64
65. 65
66. 66
67. 67
68. 68
69. 69
70. 70
71. 71
72. 72
73. 73
74. 74
75. 75
76. 76
77. 77
78. 78
79. 79
80. 80
81. 81
82. 82
83. 83
84. 84
85. 85
86. 86
87. 87
88. 88
89. 89
90. 90
91. 91
92. 92
93. 93
94. 94
95. 95
96. 96
97. 97
98. 98
99. 99
100. 100
101. 101
102. 102
103. 103
104. 104
105. 105
106. 106
107. 107
108. 108
109. 109
110. 110
111. 111
112. 112
113. 113
114. 114
115. 115
116. 116
117. 117
118. 118
119. 119
120. 120
121. 121
122. 122
123. 123
124. 124
125. 125
126. 126
127. 127
128. 128
129. 129
130. 130
131. 131
132. 132
133. 133
134. 134
135. 135
136. 136
137. 137
138. 138
139. 139
140. 140
141. 141
142. 142
143. 143
144. 144
145. 145
146. 146
147. 147
148. 148
149. 149
150. 150
151. 151
152. 152
153. 153
154. 154
155. 155
156. 156
157. 157
158. 158
159. 159
160. 160
161. 161
162. 162
163. 163
164. 164
165. 165
166. 166
167. 167
168. 168
169. 169
170. 170
171. 171
172. 172
173. 173
174. 174
175. 175
176. 176
177. 177
178. 178
179. 179
180. 180
181. 181
182. 182
183. 183
184. 184
185. 185

package buffer

import (
	"bytes"
	"encoding/gob"
	"io"
	"math"
)

type chain struct {
	Buf  BufferAt
	Next BufferAt
}

type nopBufferAt struct {
	Buffer
}

func (buf *nopBufferAt) ReadAt(p []byte, off int64) (int, error) {
	panic("ReadAt not implemented")
}

func (buf *nopBufferAt) WriteAt(p []byte, off int64) (int, error) {
	panic("WriteAt not implemented")
}

// toBufferAt converts a Buffer to a BufferAt with nop ReadAt and WriteAt funcs
func toBufferAt(buf Buffer) BufferAt {
	return &nopBufferAt{Buffer: buf}
}

// NewMultiAt returns a BufferAt which is the logical concatenation of the passed BufferAts.
// The data in the buffers is shifted such that there is no non-empty buffer following
// a non-full buffer, this process is also run after every Read.
// If no buffers are passed, the returned Buffer is nil.
func NewMultiAt(buffers ...BufferAt) BufferAt {
	if len(buffers) == 0 {
		return nil
	} else if len(buffers) == 1 {
		return buffers[0]
	}

	buf := &chain{
		Buf:  buffers[0],
		Next: NewMultiAt(buffers[1:]...),
	}

	buf.Defrag()

	return buf
}

// NewMulti returns a Buffer which is the logical concatenation of the passed buffers.
// The data in the buffers is shifted such that there is no non-empty buffer following
// a non-full buffer, this process is also run after every Read.
// If no buffers are passed, the returned Buffer is nil.
func NewMulti(buffers ...Buffer) Buffer {
	bufAt := make([]BufferAt, len(buffers))
	for i, buf := range buffers {
		bufAt[i] = toBufferAt(buf)
	}
	return NewMultiAt(bufAt...)
}

func (buf *chain) Reset() {
	buf.Next.Reset()
	buf.Buf.Reset()
}

func (buf *chain) Cap() (n int64) {
	Next := buf.Next.Cap()
	if buf.Buf.Cap() > math.MaxInt64-Next {
		return math.MaxInt64
	}
	return buf.Buf.Cap() + Next
}

func (buf *chain) Len() (n int64) {
	Next := buf.Next.Len()
	if buf.Buf.Len() > math.MaxInt64-Next {
		return math.MaxInt64
	}
	return buf.Buf.Len() + Next
}

func (buf *chain) Defrag() {
	for !Full(buf.Buf) && !Empty(buf.Next) {
		r := io.LimitReader(buf.Next, Gap(buf.Buf))
		if _, err := io.Copy(buf.Buf, r); err != nil && err != io.EOF {
			return
		}
	}
}

func (buf *chain) Read(p []byte) (n int, err error) {
	n, err = buf.Buf.Read(p)
	if len(p[n:]) > 0 && (err == nil || err == io.EOF) {
		m, err := buf.Next.Read(p[n:])
		n += m
		if err != nil {
			return n, err
		}
	}

	buf.Defrag()

	return n, err
}

func (buf *chain) ReadAt(p []byte, off int64) (n int, err error) {
	if buf.Buf.Len() < off {
		return buf.Next.ReadAt(p, off-buf.Buf.Len())
	}

	n, err = buf.Buf.ReadAt(p, off)
	if len(p[n:]) > 0 && (err == nil || err == io.EOF) {
		var m int
		m, err = buf.Next.ReadAt(p[n:], 0)
		n += m
	}
	return n, err
}

func (buf *chain) Write(p []byte) (n int, err error) {
	if n, err = buf.Buf.Write(p); err == io.ErrShortWrite {
		err = nil
	}
	p = p[n:]
	if len(p) > 0 && err == nil {
		m, err := buf.Next.Write(p)
		n += m
		if err != nil {
			return n, err
		}
	}
	return n, err
}

func (buf *chain) WriteAt(p []byte, off int64) (n int, err error) {
	switch {
	case buf.Buf.Cap() <= off: // past the end
		return buf.Next.WriteAt(p, off-buf.Buf.Cap())

	case buf.Buf.Cap() >= off+int64(len(p)): // fits in
		return buf.Buf.WriteAt(p, off)

	default: // partial fit
		n, err = buf.Buf.WriteAt(p, off)
		if len(p[n:]) > 0 && (err == nil || err == io.ErrShortWrite) {
			var m int
			m, err = buf.Next.WriteAt(p[n:], 0)
			n += m
		}
		return n, err
	}
}

func init() {
	gob.Register(&chain{})
	gob.Register(&nopBufferAt{})
}

func (buf *chain) MarshalBinary() ([]byte, error) {
	b := bytes.NewBuffer(nil)
	enc := gob.NewEncoder(b)
	if err := enc.Encode(&buf.Buf); err != nil {
		return nil, err
	}
	if err := enc.Encode(&buf.Next); err != nil {
		return nil, err
	}
	return b.Bytes(), nil
}

func (buf *chain) UnmarshalBinary(data []byte) error {
	b := bytes.NewBuffer(data)
	dec := gob.NewDecoder(b)
	if err := dec.Decode(&buf.Buf); err != nil {
		return err
	}
	if err := dec.Decode(&buf.Next); err != nil {
		return err
	}
	return nil
}