kdnotify/config/config.go

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

package config

import (
	"fmt"
	"text/template"

	"golang.org/x/exp/slices"
	"gopkg.in/yaml.v3"

	"git.st8l.com/luxolus/kdnotify/schema/notify"
	"git.st8l.com/luxolus/kdnotify/schema/notify/state"
	"git.st8l.com/luxolus/kdnotify/schema/notify/ty"
)

// Configuration for WatchHandlers, providing them an evaluation context
// and rules for handling notify events
type WatchConfig struct {
	// Arbitrary user input, accessible in WatchMatch.Exec templates
	Context any `yaml:"context"`
	// List of rules to use when handling notify events
	Rules []WatchRule `yaml:"rules"`
}

// Parse the given yaml, looking for the top level 'watch:' key, returning
// the unmarshaled WatchHandle configuration
func WatchConfigFromYAML(in []byte) (WatchConfig, error) {
	var visitor visitWatchConfig

	err := yaml.Unmarshal(in, &visitor)
	if err != nil {
		return WatchConfig{}, fmt.Errorf("while parsing 'watch': %w", err)
	}

	return visitor.Watch, nil
}

// A single rule to evaluate a notify event on.
//
// Each condition field (State, Type, Instance) is a logical OR
// while the fields together are a logical AND. Demonstrated:
//
//	if State.Contains($state) && Type.Contains($type) && Instance.Contains($instance) {
//	    os.Exec(Template)
//	}
//
// The one exception is if any check is empty, it is ignored
type WatchRule struct {
	// List of states that apply this rule, ignored if empty
	State state.State
	// List of types that apply this rule, ignored if empty
	Type ty.Type
	// List of instances that apply this rule, ignored if empty
	Instance []string
	// Template to evaluate and execute if the conditions match
	Exec *template.Template
}

// Check if the given message matches this WatchRule
func (w *WatchRule) Match(msg *notify.VrrpMessage) bool {
	if w.Type != ty.NULL && !w.Type.Has(msg.Type) {
		return false
	}
	if w.State != state.NULL && !w.State.Has(msg.State) {
		return false
	}
	if len(w.Instance) > 0 && !slices.Contains(w.Instance, msg.Instance) {
		return false
	}

	return true
}

func (w *WatchRule) UnmarshalYAML(value *yaml.Node) error {
	var visitor visitWatchRule

	switch value.Kind {
	case yaml.AliasNode:
		return w.UnmarshalYAML(value.Alias)
	default:
		err := value.Decode(&visitor)
		if err != nil {
			return err
		}
	}

	rule, err := visitor.IntoWatchRule()
	if err != nil {
		return fmt.Errorf("while parsing watch rule: %w", err)
	}
	*w = rule

	return nil
}

type visitWatchConfig struct {
	Watch WatchConfig `yaml:"watch"`
}

type visitWatchRule struct {
	State    sslice `yaml:"state,omitempty"`
	Type     sslice `yaml:"type,omitempty"`
	Instance sslice `yaml:"instance,omitempty"`
	Exec     string `yaml:"exec,omitempty"`
}

func (v visitWatchRule) IntoWatchRule() (WatchRule, error) {
	var rule WatchRule

	for _, val := range v.Type.Value {
		v := ty.ParseType(val)
		if v == ty.UNKNOWN {
			return rule, fmt.Errorf("unknown type: '%s'", val)
		}

		rule.Type |= v
	}

	for _, val := range v.State.Value {
		v := state.ParseState(val)
		if v == state.UNKNOWN {
			return rule, fmt.Errorf("unknown state: '%s'", val)
		}

		rule.State |= v
	}

	exec, err := template.New("WatchRule").Parse(v.Exec)
	if err != nil {
		return rule, fmt.Errorf("unable to parse exec template: %w", err)
	}
	rule.Exec = exec

	rule.Instance = v.Instance.Value

	return rule, nil
}

// Visitor for string or []string Yaml productions
type sslice struct {
	Value []string
}

func (v *sslice) UnmarshalYAML(value *yaml.Node) error {

	switch value.Kind {
	case yaml.AliasNode:
		return v.UnmarshalYAML(value.Alias)
	case yaml.SequenceNode:
		return value.Decode(&v.Value)
	case yaml.ScalarNode:
		var single string

		err := value.Decode(&single)
		if err != nil {
			return err
		}

		v.Value = append(v.Value, single)

		return nil
	default:
		error := fmt.Sprintf(
			"unable to parse string or string array at %d:%d from '%s'",
			value.Line, value.Column, value.Value,
		)

		return &yaml.TypeError{Errors: []string{error}}
	}
}