From bd862b51161fab8a62bcae49eb7452a82dd2b70a Mon Sep 17 00:00:00 2001
From: Martin Czygan <martin.czygan@gmail.com>
Date: Tue, 1 Jun 2021 12:53:37 +0200
Subject: add match set

---
 skate/matchset.go      | 73 +++++++++++++++++++++++++++++++++++++++++++++
 skate/matchset_test.go | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 154 insertions(+)
 create mode 100644 skate/matchset.go
 create mode 100644 skate/matchset_test.go

(limited to 'skate')

diff --git a/skate/matchset.go b/skate/matchset.go
new file mode 100644
index 0000000..c8882e2
--- /dev/null
+++ b/skate/matchset.go
@@ -0,0 +1,73 @@
+package skate
+
+import (
+	"bytes"
+	"index/suffixarray"
+	"io"
+	"sync"
+)
+
+const matchSetSep = "\u001F"
+
+// MatchSet allows to match a string against multiple strings at once.  Rough
+// performance number: looking up ~80K different strings in 1M strings takes
+// about <2s.
+//
+// The original use case was to match ~80K+ journal name abbreviations against
+// 100M+ container name strings in references.
+type MatchSet struct {
+	index *suffixarray.Index
+	b     []byte
+	sep   string
+}
+
+var (
+	bufPool = sync.Pool{
+		New: func() interface{} {
+			var buf bytes.Buffer
+			return buf
+		},
+	}
+)
+
+// NewMatchSet creates a new MatchSet given a number of strings patterns. If
+// any of the given strings contains the ASCII unit separator (1F), you may get
+// unexpected results.
+func NewMatchSet(ss []string) *MatchSet {
+	buf := bufPool.Get().(bytes.Buffer)
+	buf.Reset()
+	defer bufPool.Put(buf)
+	for _, s := range ss {
+		_, _ = io.WriteString(&buf, matchSetSep)
+		_, _ = io.WriteString(&buf, s)
+	}
+	return &MatchSet{
+		b:     buf.Bytes(),
+		index: suffixarray.New(buf.Bytes()),
+		sep:   matchSetSep,
+	}
+}
+
+// Lookup will match a given string as against all strings in the match set. If
+// n < 0, all results are returned, otherwise at most n results are returned.
+func (ms *MatchSet) Lookup(s string, n int) (result []string) {
+	buf := bufPool.Get().(bytes.Buffer)
+	buf.Reset()
+	defer bufPool.Put(buf)
+	_, _ = io.WriteString(&buf, matchSetSep)
+	_, _ = io.WriteString(&buf, s)
+	indices := ms.index.Lookup(buf.Bytes(), n)
+	for _, i := range indices {
+		var (
+			offset = i + len(matchSetSep) + 1
+			k      = bytes.Index(ms.b[offset:], []byte(matchSetSep))
+		)
+		if k == -1 {
+			k = len(ms.b)
+		} else {
+			k = k + offset
+		}
+		result = append(result, string(ms.b[i+1:k]))
+	}
+	return
+}
diff --git a/skate/matchset_test.go b/skate/matchset_test.go
new file mode 100644
index 0000000..0436faf
--- /dev/null
+++ b/skate/matchset_test.go
@@ -0,0 +1,81 @@
+package skate
+
+import (
+	"reflect"
+	"sort"
+	"testing"
+)
+
+func TestMatchSetLookup(t *testing.T) {
+	var cases = []struct {
+		s      string
+		ps     []string
+		n      int
+		result []string
+	}{
+		{
+			s:      "",
+			ps:     []string{},
+			n:      -1,
+			result: nil,
+		},
+		{
+			s:      "hello",
+			ps:     []string{"lo"},
+			n:      -1,
+			result: nil,
+		},
+		{
+			s:      "hello",
+			ps:     []string{"zz"},
+			n:      -1,
+			result: nil,
+		},
+		{
+			s:      "hello",
+			ps:     []string{"h", "he", "hel"},
+			n:      -1,
+			result: nil,
+		},
+		{
+			s:      "hello",
+			ps:     []string{"hello"},
+			n:      -1,
+			result: []string{"hello"},
+		},
+		{
+			s:      "hello world",
+			ps:     []string{"hello", "world"},
+			n:      -1,
+			result: nil,
+		},
+		{
+			s:      "he",
+			ps:     []string{"hello", "world", "hel"},
+			n:      -1,
+			result: []string{"hello", "hel"},
+		},
+		{
+			s: "american italian proceedings",
+			ps: []string{
+				"italian",
+				"american",
+				"american italian",
+				"american italian proceedings",
+				"proceedings",
+			},
+			n:      -1,
+			result: []string{"american italian proceedings"},
+		},
+	}
+	for _, c := range cases {
+		ms := NewMatchSet(c.ps)
+		result := ms.Lookup(c.s, c.n)
+		sort.Strings(result)
+		sort.Strings(c.result)
+		if !reflect.DeepEqual(result, c.result) {
+			t.Errorf("got %v, want %v -> s=%s ps=%s",
+				result, c.result, c.s, c.ps)
+		}
+	}
+}
-- 
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