feat: add header decoder

internal/utils/decoders/header_decoder.go

@@ -0,0 +1,122 @@
+package decoders
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+	"tinyauth/internal/config"
+
+	"github.com/traefik/paerser/parser"
+)
+
+// Based on: https://github.com/traefik/paerser/blob/master/parser/labels_decode.go (Apache 2.0 License)
+
+func DecodeHeaders(headers map[string]string) (config.App, error) {
+	var app config.App
+
+	err := decodeHeadersHelper(headers, &app, "tinyauth")
+
+	if err != nil {
+		return config.App{}, err
+	}
+
+	return app, nil
+}
+
+func decodeHeadersHelper(headers map[string]string, element any, rootName string, filters ...string) error {
+	node, err := decodeHeadersToNode(headers, rootName, filters...)
+
+	if err != nil {
+		return err
+	}
+
+	opts := parser.MetadataOpts{TagName: "header", AllowSliceAsStruct: true}
+	err = parser.AddMetadata(element, node, opts)
+
+	if err != nil {
+		return err
+	}
+
+	return parser.Fill(element, node, parser.FillerOpts{AllowSliceAsStruct: true})
+}
+
+func decodeHeadersToNode(headers map[string]string, rootName string, filters ...string) (*parser.Node, error) {
+	sortedKeys := sortKeys(headers, filters)
+
+	var node *parser.Node
+
+	for i, key := range sortedKeys {
+		split := strings.Split(strings.ToLower(key), "-")
+
+		if split[0] != rootName {
+			return nil, fmt.Errorf("invalid header root %s", split[0])
+		}
+
+		var parts []string
+		for _, v := range split {
+			if v == "" {
+				return nil, fmt.Errorf("invalid element: %s", key)
+			}
+
+			parts = append(parts, v)
+		}
+
+		if i == 0 {
+			node = &parser.Node{}
+		}
+
+		decodeHeaderToNode(node, parts, headers[key])
+	}
+
+	return node, nil
+}
+
+func decodeHeaderToNode(root *parser.Node, path []string, value string) {
+	if len(root.Name) == 0 {
+		root.Name = path[0]
+	}
+
+	if len(path) > 1 {
+		node := containsNode(root.Children, path[1])
+
+		if node != nil {
+			decodeHeaderToNode(node, path[1:], value)
+		} else {
+			child := &parser.Node{Name: path[1]}
+			decodeHeaderToNode(child, path[1:], value)
+			root.Children = append(root.Children, child)
+		}
+	} else {
+		root.Value = value
+	}
+}
+
+func containsNode(nodes []*parser.Node, name string) *parser.Node {
+	for _, node := range nodes {
+		if strings.EqualFold(node.Name, name) {
+			return node
+		}
+	}
+	return nil
+}
+
+func sortKeys(headers map[string]string, filters []string) []string {
+	var sortedKeys []string
+
+	for key := range headers {
+		if len(filters) == 0 {
+			sortedKeys = append(sortedKeys, key)
+			continue
+		}
+
+		for _, filter := range filters {
+			if len(key) >= len(filter) && strings.EqualFold(key[:len(filter)], filter) {
+				sortedKeys = append(sortedKeys, key)
+				continue
+			}
+		}
+	}
+
+	sort.Strings(sortedKeys)
+	return sortedKeys
+}