81 lines
1.7 KiB
Go
81 lines
1.7 KiB
Go
package kv
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import (
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"bytes"
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"sort"
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)
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// staticCursor implements the Cursor interface for a slice of
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// static key value pairs.
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type staticCursor struct {
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idx int
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pairs []Pair
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}
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// Pair is a struct for key value pairs.
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type Pair struct {
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Key []byte
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Value []byte
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}
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// NewStaticCursor returns an instance of a StaticCursor. It
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// destructively sorts the provided pairs to be in key ascending order.
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func NewStaticCursor(pairs []Pair) Cursor {
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sort.Slice(pairs, func(i, j int) bool {
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return bytes.Compare(pairs[i].Key, pairs[j].Key) < 0
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})
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return &staticCursor{
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pairs: pairs,
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}
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}
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// Seek searches the slice for the first key with the provided prefix.
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func (c *staticCursor) Seek(prefix []byte) ([]byte, []byte) {
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// TODO: do binary search for prefix since pairs are ordered.
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for i, pair := range c.pairs {
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if bytes.HasPrefix(pair.Key, prefix) {
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c.idx = i
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return pair.Key, pair.Value
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}
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}
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return nil, nil
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}
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func (c *staticCursor) getValueAtIndex(delta int) ([]byte, []byte) {
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idx := c.idx + delta
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if idx < 0 {
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return nil, nil
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}
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if idx >= len(c.pairs) {
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return nil, nil
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}
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c.idx = idx
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pair := c.pairs[c.idx]
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return pair.Key, pair.Value
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}
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// First retrieves the first element in the cursor.
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func (c *staticCursor) First() ([]byte, []byte) {
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return c.getValueAtIndex(-c.idx)
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}
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// Last retrieves the last element in the cursor.
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func (c *staticCursor) Last() ([]byte, []byte) {
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return c.getValueAtIndex(len(c.pairs) - 1 - c.idx)
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}
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// Next retrieves the next entry in the cursor.
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func (c *staticCursor) Next() ([]byte, []byte) {
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return c.getValueAtIndex(1)
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}
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// Prev retrieves the previous entry in the cursor.
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func (c *staticCursor) Prev() ([]byte, []byte) {
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return c.getValueAtIndex(-1)
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}
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