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|
// Package zipkey implements ZipRun, a type that allows to attach a callback to
// a group of elements with a shared key taken from two streams.
package zipkey
import (
"bufio"
"io"
)
// Group groups items by key and will contain the complete records (e.g. line)
// for further processing.
type Group struct {
Key string
G0 []string
G1 []string
}
type (
keyFunc func(string) (string, error) // Given a line, extract the key.
groupFunc func(*Group) error
)
// ZipRun reads records (separated by sep) from two readers, extracts a key
// from each record with a keyFunc and collects records from the two streams
// into a Group. A callback groupFunc can be registered, which allows to
// customize the processing of the group. Current limitation: both streams need
// to use the same keyFunc.
type ZipRun struct {
r0, r1 *bufio.Reader
kf keyFunc
gf groupFunc
sep byte
}
// New create a new ready to run ZipRun value.
func New(r0, r1 io.Reader, kf keyFunc, gf groupFunc) *ZipRun {
return &ZipRun{
r0: bufio.NewReader(r0),
r1: bufio.NewReader(r1),
kf: kf,
gf: gf,
sep: '\n',
}
}
// Run starts reading from both readers. The process stops, if one reader is
// exhausted or reads from any reader fail.
func (c *ZipRun) Run() error {
var (
k0, k1, c0, c1 string // key: k0, k1; current line: c0, c1
done bool
err error
lineKey = func(r *bufio.Reader) (line, key string, err error) {
if line, err = r.ReadString(c.sep); err != nil {
return
}
key, err = c.kf(line)
return
}
)
for {
if done {
break
}
switch {
case k0 == "" || k0 < k1:
for k0 == "" || k0 < k1 {
c0, k0, err = lineKey(c.r0)
if err == io.EOF {
return nil
}
if err != nil {
return err
}
}
case k1 == "" || k0 > k1:
for k1 == "" || k0 > k1 {
c1, k1, err = lineKey(c.r1)
if err == io.EOF {
return nil
}
if err != nil {
return err
}
}
case k0 == k1:
g := &Group{
G0: []string{c0},
G1: []string{c1},
}
for {
c0, err = c.r0.ReadString(c.sep)
if err == io.EOF {
done = true
break
}
if err != nil {
return err
}
k, err := c.kf(c0)
if err != nil {
return err
}
if k == k0 {
g.G0 = append(g.G0, c0)
k0 = k
} else {
k0 = k
break
}
}
for {
c1, err = c.r1.ReadString(c.sep)
if err == io.EOF {
done = true
break
}
if err != nil {
return err
}
k, err := c.kf(c1)
if err != nil {
return err
}
if k == k1 {
g.G1 = append(g.G1, c1)
k1 = k
} else {
k1 = k
break
}
}
if c.gf != nil {
if err := c.gf(g); err != nil {
return err
}
}
}
}
return nil
}
|
