pkg/template/engine/values.go

// Licensed to Elasticsearch B.V. under one or more contributor
// license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright
// ownership. Elasticsearch B.V. licenses this file to you under
// the Apache License, Version 2.0 (the "License"); you may
// not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

package engine

import (
	"errors"
	"fmt"
	"io"
	"strings"

	"sigs.k8s.io/yaml"
)

// Inspired from Helm v3
// https://github.com/helm/helm/blob/master/pkg/chartutil/values.go

// ReadValues will parse YAML byte data into a Values.
func ReadValues(r io.Reader) (vals Values, err error) {
	// Drain reader
	data, err := io.ReadAll(r)
	if err != nil {
		return map[string]interface{}{}, err
	}

	// Try to unmarshal buffer as YAML
	err = yaml.Unmarshal(data, &vals)
	if len(vals) == 0 {
		vals = Values{}
	}

	// Return result
	return vals, err
}

// -----------------------------------------------------------------------------

// Values represents a collection of template values.
type Values map[string]interface{}

// YAML encodes the Values into a YAML string.
func (v Values) YAML() (string, error) {
	b, err := yaml.Marshal(v)
	return string(b), err
}

// Table gets a table (YAML subsection) from a Values object.
//
// The table is returned as a Values.
//
// Compound table names may be specified with dots:
//
//	foo.bar
//
// The above will be evaluated as "The table bar inside the table
// foo".
//
// An ErrNoTable is returned if the table does not exist.
func (v Values) Table(name string) (Values, error) {
	table := v
	var err error

	for _, n := range parsePath(name) {
		if table, err = tableLookup(table, n); err != nil {
			break
		}
	}
	return table, err
}

// AsMap is a utility function for converting Values to a map[string]interface{}.
//
// It protects against nil map panics.
func (v Values) AsMap() map[string]interface{} {
	if len(v) == 0 {
		return map[string]interface{}{}
	}
	return v
}

// Encode writes serialized Values information to the given io.Writer.
func (v Values) Encode(w io.Writer) error {
	out, err := yaml.Marshal(v)
	if err != nil {
		return fmt.Errorf("unable to encode values as yaml: %w", err)
	}
	_, err = w.Write(out)
	if err != nil {
		return fmt.Errorf("unable to write encoded values to writer: %w", err)
	}

	// No error
	return nil
}

// PathValue takes a path that traverses a YAML structure and returns the value at the end of that path.
// The path starts at the root of the YAML structure and is comprised of YAML keys separated by periods.
// Given the following YAML data the value at path "chapter.one.title" is "Loomings".
//
//	chapter:
//	  one:
//	    title: "Loomings"
func (v Values) PathValue(path string) (interface{}, error) {
	if path == "" {
		return nil, errors.New("YAML path cannot be empty")
	}
	return v.pathValue(parsePath(path))
}

func (v Values) pathValue(path []string) (interface{}, error) {
	if len(path) == 1 {
		// if exists must be root key not table
		if _, ok := v[path[0]]; ok && !istable(v[path[0]]) {
			return v[path[0]], nil
		}
		return nil, ErrNoValue{path[0]}
	}

	key, path := path[len(path)-1], path[:len(path)-1]
	// get our table for table path
	t, err := v.Table(joinPath(path...))
	if err != nil {
		return nil, ErrNoValue{key}
	}
	// check table for key and ensure value is not a table
	if k, ok := t[key]; ok && !istable(k) {
		return k, nil
	}
	return nil, ErrNoValue{key}
}

// -----------------------------------------------------------------------------

func tableLookup(v Values, simple string) (Values, error) {
	v2, ok := v[simple]
	if !ok {
		return v, ErrNoTable{simple}
	}
	if vv, ok := v2.(map[string]interface{}); ok {
		return vv, nil
	}

	// This catches a case where a value is of type Values, but doesn't (for some
	// reason) match the map[string]interface{}. This has been observed in the
	// wild, and might be a result of a nil map of type Values.
	if vv, ok := v2.(Values); ok {
		return vv, nil
	}

	return Values{}, ErrNoTable{simple}
}

// istable is a special-purpose function to see if the present thing matches the definition of a YAML table.
func istable(v interface{}) bool {
	_, ok := v.(map[string]interface{})
	return ok
}

// parsePath splits the given path using "."
func parsePath(key string) []string { return strings.Split(key, ".") }

// joinPath joins all path elements with "."
func joinPath(path ...string) string { return strings.Join(path, ".") }