port liquid filters from gojekyll

go.mod

@@ -6,12 +6,12 @@ require (
 	github.com/fsnotify/fsnotify v1.7.0
 	github.com/niklasfasching/go-org v1.7.0
 	github.com/osteele/liquid v1.3.2
+	github.com/yuin/goldmark v1.7.0
 	gopkg.in/yaml.v3 v3.0.1
 )
 
 require (
 	github.com/osteele/tuesday v1.0.3 // indirect
-	github.com/yuin/goldmark v1.7.0 // indirect
 	golang.org/x/net v0.0.0-20201224014010-6772e930b67b // indirect
 	golang.org/x/sys v0.4.0 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect

templates/filters.go

@@ -0,0 +1,123 @@
+package templates
+
+import (
+	"fmt"
+	"reflect"
+
+	"github.com/osteele/liquid/evaluator"
+	"github.com/osteele/liquid/expressions"
+)
+
+// copied from  https://github.com/osteele/gojekyll/blob/main/filters/filters.go
+
+func filter(values []map[string]interface{}, key string) []interface{} {
+	var result []interface{}
+	for _, value := range values {
+		if _, ok := value[key]; ok {
+			result = append(result, value)
+		}
+	}
+	return result
+}
+
+func groupByExpFilter(array []map[string]interface{}, name string, expr expressions.Closure) ([]map[string]interface{}, error) {
+	rt := reflect.ValueOf(array)
+	if !(rt.Kind() != reflect.Array || rt.Kind() == reflect.Slice) {
+		return nil, nil
+	}
+	groups := map[interface{}][]interface{}{}
+	for i := 0; i < rt.Len(); i++ {
+		item := rt.Index(i).Interface()
+		key, err := expr.Bind(name, item).Evaluate()
+		if err != nil {
+			return nil, err
+		}
+		if group, found := groups[key]; found {
+			groups[key] = append(group, item)
+		} else {
+			groups[key] = []interface{}{item}
+		}
+	}
+	var result []map[string]interface{}
+	for k, v := range groups {
+		result = append(result, map[string]interface{}{"name": k, "items": v})
+	}
+	return result, nil
+}
+
+func groupByFilter(array []map[string]interface{}, property string) []map[string]interface{} {
+	rt := reflect.ValueOf(array)
+	if !(rt.Kind() != reflect.Array || rt.Kind() == reflect.Slice) {
+		return nil
+	}
+	groups := map[interface{}][]interface{}{}
+	for i := 0; i < rt.Len(); i++ {
+		irt := rt.Index(i)
+		if irt.Kind() == reflect.Map && irt.Type().Key().Kind() == reflect.String {
+			krt := irt.MapIndex(reflect.ValueOf(property))
+			if krt.IsValid() && krt.CanInterface() {
+				key := krt.Interface()
+				if group, found := groups[key]; found {
+					groups[key] = append(group, irt.Interface())
+				} else {
+					groups[key] = []interface{}{irt.Interface()}
+				}
+			}
+		}
+	}
+	var result []map[string]interface{}
+	for k, v := range groups {
+		result = append(result, map[string]interface{}{"name": k, "items": v})
+	}
+	return result
+}
+
+func sortFilter(array []interface{}, key interface{}, nilFirst func(bool) bool) []interface{} {
+	nf := nilFirst(true)
+	result := make([]interface{}, len(array))
+	copy(result, array)
+	if key == nil {
+		evaluator.Sort(result)
+	} else {
+		// TODO error if key is not a string
+		evaluator.SortByProperty(result, key.(string), nf)
+	}
+	return result
+}
+
+func whereExpFilter(array []interface{}, name string, expr expressions.Closure) ([]interface{}, error) {
+	rt := reflect.ValueOf(array)
+	if rt.Kind() != reflect.Array && rt.Kind() != reflect.Slice {
+		return nil, nil
+	}
+	var result []interface{}
+	for i := 0; i < rt.Len(); i++ {
+		item := rt.Index(i).Interface()
+		value, err := expr.Bind(name, item).Evaluate()
+		if err != nil {
+			return nil, err
+		}
+		if value != nil && value != false {
+			result = append(result, item)
+		}
+	}
+	return result, nil
+}
+
+func whereFilter(array []map[string]interface{}, key string, value interface{}) []interface{} {
+	rt := reflect.ValueOf(array)
+	if rt.Kind() != reflect.Array && rt.Kind() != reflect.Slice {
+		return nil
+	}
+	var result []interface{}
+	for i := 0; i < rt.Len(); i++ {
+		item := rt.Index(i)
+		if item.Kind() == reflect.Map && item.Type().Key().Kind() == reflect.String {
+			attr := item.MapIndex(reflect.ValueOf(key))
+			if attr.IsValid() && fmt.Sprint(attr) == value {
+				result = append(result, item.Interface())
+			}
+		}
+	}
+	return result
+}

templates/templates.go

@@ -1,4 +1,3 @@
-// TODO consider making this another package
 package templates
 
 import (
@@ -27,7 +26,25 @@ type Template struct {
 }
 
 func NewEngine() *Engine {
-	return liquid.NewEngine()
+	// a lot of the filters and tags available at jekyll aren't default liquid
+	// manually adding them here as in https://github.com/osteele/gojekyll/blob/main/filters/filters.go
+
+	e := liquid.NewEngine()
+
+	e.RegisterFilter("filter", filter)
+	e.RegisterFilter("group_by", groupByFilter)
+	e.RegisterFilter("group_by_exp", groupByExpFilter)
+	e.RegisterFilter("sort", sortFilter)
+	e.RegisterFilter("where", whereFilter)
+	e.RegisterFilter("where_exp", whereExpFilter)
+
+	e.RegisterFilter("absolute_url", func(s string) string {
+		// FIXME implement after adding a config struct, using the url
+		// return utils.URLJoin(c.AbsoluteURL, c.BaseURL, s)
+		return s
+	})
+
+	return e
 }
 
 func Parse(engine *Engine, path string) (*Template, error) {