Add Regexp filter

Support the regexp filter as described in
http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl-regexp-filter.html.

Closes #27.

README.md

@@ -399,7 +399,7 @@ on the command line.
 - [x] `prefix`
 - [x] `query`
 - [x] `range`
-- [ ] `regexp`
+- [x] `regexp`
 - [ ] `script`
 - [x] `term`
 - [x] `terms`

search_filters_regexp.go

@@ -0,0 +1,90 @@
+// Copyright 2012-2015 Oliver Eilhard. All rights reserved.
+// Use of this source code is governed by a MIT-license.
+// See http://olivere.mit-license.org/license.txt for details.
+
+package elastic
+
+// RegexpFilter allows filtering for regular expressions.
+// See http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl-regexp-filter.html
+// and http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl-regexp-query.html#regexp-syntax
+// for details.
+type RegexpFilter struct {
+	Filter
+	name                  string
+	regexp                string
+	flags                 *string
+	maxDeterminizedStates *int
+	cache                 *bool
+	cacheKey              string
+	filterName            string
+}
+
+// NewRegexpFilter sets up a new RegexpFilter.
+func NewRegexpFilter(name, regexp string) RegexpFilter {
+	return RegexpFilter{name: name, regexp: regexp}
+}
+
+// Flags sets the regexp flags.
+// See http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl-regexp-query.html#_optional_operators
+// for details.
+func (f RegexpFilter) Flags(flags string) RegexpFilter {
+	f.flags = &flags
+	return f
+}
+
+func (f RegexpFilter) MaxDeterminizedStates(maxDeterminizedStates int) RegexpFilter {
+	f.maxDeterminizedStates = &maxDeterminizedStates
+	return f
+}
+
+func (f RegexpFilter) Cache(cache bool) RegexpFilter {
+	f.cache = &cache
+	return f
+}
+
+func (f RegexpFilter) CacheKey(cacheKey string) RegexpFilter {
+	f.cacheKey = cacheKey
+	return f
+}
+
+func (f RegexpFilter) FilterName(filterName string) RegexpFilter {
+	f.filterName = filterName
+	return f
+}
+
+func (f RegexpFilter) Source() interface{} {
+	// {
+	//   "regexp" : {
+	//     "..." : "..."
+	//   }
+	// }
+
+	source := make(map[string]interface{})
+
+	params := make(map[string]interface{})
+	source["regexp"] = params
+
+	if f.flags == nil {
+		params[f.name] = f.regexp
+	} else {
+		x := make(map[string]interface{})
+		x["value"] = f.regexp
+		x["flags"] = *f.flags
+		if f.maxDeterminizedStates != nil {
+			x["max_determinized_states"] = *f.maxDeterminizedStates
+		}
+		params[f.name] = x
+	}
+
+	if f.filterName != "" {
+		params["_name"] = f.filterName
+	}
+	if f.cache != nil {
+		params["_cache"] = *f.cache
+	}
+	if f.cacheKey != "" {
+		params["_cache_key"] = f.cacheKey
+	}
+
+	return source
+}

search_filters_regexp_test.go

@@ -0,0 +1,34 @@
+package elastic
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestRegexpFilter(t *testing.T) {
+	f := NewRegexpFilter("name.first", "s.*y")
+	data, err := json.Marshal(f.Source())
+	if err != nil {
+		t.Fatalf("marshaling to JSON failed: %v", err)
+	}
+	got := string(data)
+	expected := `{"regexp":{"name.first":"s.*y"}}`
+	if got != expected {
+		t.Errorf("expected\n%s\n,got:\n%s", expected, got)
+	}
+}
+
+func TestRegexpFilterWithFlags(t *testing.T) {
+	f := NewRegexpFilter("name.first", "s.*y")
+	f = f.Flags("INTERSECTION|COMPLEMENT|EMPTY")
+	f = f.FilterName("test").Cache(true).CacheKey("key")
+	data, err := json.Marshal(f.Source())
+	if err != nil {
+		t.Fatalf("marshaling to JSON failed: %v", err)
+	}
+	got := string(data)
+	expected := `{"regexp":{"_cache":true,"_cache_key":"key","_name":"test","name.first":{"flags":"INTERSECTION|COMPLEMENT|EMPTY","value":"s.*y"}}}`
+	if got != expected {
+		t.Errorf("expected\n%s\n,got:\n%s", expected, got)
+	}
+}