// Copyright 2015 Prometheus Team
// Licensed 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 dispatch

import (
	"encoding/json"
	"fmt"
	"maps"
	"strconv"
	"strings"
	"time"

	"github.com/prometheus/common/model"

	"github.com/prometheus/alertmanager/config"
	"github.com/prometheus/alertmanager/pkg/labels"
)

// DefaultRouteOpts are the defaulting routing options which apply
// to the root route of a routing tree.
var DefaultRouteOpts = RouteOpts{
	GroupWait:         30 * time.Second,
	GroupInterval:     5 * time.Minute,
	RepeatInterval:    4 * time.Hour,
	GroupBy:           map[model.LabelName]struct{}{},
	GroupByAll:        false,
	MuteTimeIntervals: []string{},
	Labels:            model.LabelSet{},
}

// A Route is a node that contains definitions of how to handle alerts.
type Route struct {
	parent *Route

	// The configuration parameters for matches of this route.
	RouteOpts RouteOpts

	// Matchers an alert has to fulfill to match
	// this route.
	Matchers labels.Matchers

	// If true, an alert matches further routes on the same level.
	Continue bool

	// Children routes of this route.
	Routes []*Route

	// Idx contains the index of this route in the config
	Idx int
}

// NewRoute returns a new route.
func NewRoute(cr *config.Route, parent *Route) *Route {
	counter := 0
	return newRoute(cr, parent, &counter)
}

func newRoute(cr *config.Route, parent *Route, counter *int) *Route {
	// Create default and overwrite with configured settings.
	opts := DefaultRouteOpts
	if parent != nil {
		opts = parent.RouteOpts
	}

	// Merge parent route labels and cr.Labels into opts.Labels. Always merge
	// into a fresh LabelSet so we never mutate the parent's map.
	if len(cr.Labels) != 0 {
		merged := model.LabelSet{}
		maps.Copy(merged, opts.Labels)
		maps.Copy(merged, cr.Labels)
		opts.Labels = merged
	}

	if cr.Receiver != "" {
		opts.Receiver = cr.Receiver
	}

	if cr.GroupBy != nil {
		opts.GroupBy = map[model.LabelName]struct{}{}
		for _, ln := range cr.GroupBy {
			opts.GroupBy[ln] = struct{}{}
		}
		opts.GroupByAll = false
	} else {
		if cr.GroupByAll {
			opts.GroupByAll = cr.GroupByAll
		}
	}

	if cr.GroupWait != nil {
		opts.GroupWait = time.Duration(*cr.GroupWait)
	}
	if cr.GroupInterval != nil {
		opts.GroupInterval = time.Duration(*cr.GroupInterval)
	}
	if cr.RepeatInterval != nil {
		opts.RepeatInterval = time.Duration(*cr.RepeatInterval)
	}

	matchers := cr.AllMatchers()

	opts.MuteTimeIntervals = cr.MuteTimeIntervals
	opts.ActiveTimeIntervals = cr.ActiveTimeIntervals

	route := &Route{
		parent:    parent,
		RouteOpts: opts,
		Matchers:  matchers,
		Continue:  cr.Continue,
	}

	// Create child routes first (they get lower indices)
	route.Routes = newRoutes(cr.Routes, route, counter)

	// Assign index to this route after all children have been indexed
	route.Idx = *counter
	*counter++

	return route
}

// newRoutes returns a slice of routes.
func newRoutes(croutes []*config.Route, parent *Route, counter *int) []*Route {
	res := []*Route{}
	for _, cr := range croutes {
		res = append(res, newRoute(cr, parent, counter))
	}
	return res
}

// Match does a depth-first left-to-right search through the route tree
// and returns the matching routing nodes.
func (r *Route) Match(lset model.LabelSet) []*Route {
	if !r.Matchers.Matches(lset) {
		return nil
	}

	var all []*Route

	for _, cr := range r.Routes {
		matches := cr.Match(lset)

		all = append(all, matches...)

		if matches != nil && !cr.Continue {
			break
		}
	}

	// If no child nodes were matches, the current node itself is a match.
	if len(all) == 0 {
		all = append(all, r)
	}

	return all
}

// Key returns a key for the route. It does not uniquely identify the route in general.
func (r *Route) Key() string {
	b := strings.Builder{}

	if r.parent != nil {
		b.WriteString(r.parent.Key())
		b.WriteRune('/')
	}
	b.WriteString(r.Matchers.String())
	return b.String()
}

// ID returns a unique identifier for the route.
func (r *Route) ID() string {
	b := strings.Builder{}

	if r.parent != nil {
		b.WriteString(r.parent.ID())
		b.WriteRune('/')
	}

	b.WriteString(r.Matchers.String())

	if r.parent != nil {
		for i := range r.parent.Routes {
			if r == r.parent.Routes[i] {
				b.WriteRune('/')
				b.WriteString(strconv.Itoa(i))
				break
			}
		}
	}

	return b.String()
}

// Walk traverses the route tree in depth-first order.
func (r *Route) Walk(visit func(*Route)) {
	visit(r)
	for i := range r.Routes {
		r.Routes[i].Walk(visit)
	}
}

// RouteOpts holds various routing options necessary for processing alerts
// that match a given route.
type RouteOpts struct {
	// The identifier of the associated notification configuration.
	Receiver string

	// What labels to group alerts by for notifications.
	GroupBy map[model.LabelName]struct{}

	// Use all alert labels to group.
	GroupByAll bool

	// How long to wait to group matching alerts before sending
	// a notification.
	GroupWait      time.Duration
	GroupInterval  time.Duration
	RepeatInterval time.Duration

	// A list of time intervals for which the route is muted.
	MuteTimeIntervals []string

	// A list of time intervals for which the route is active.
	ActiveTimeIntervals []string

	// Merged labels from this route and all of its parent routes.
	Labels model.LabelSet
}

func (ro *RouteOpts) String() string {
	var labels []model.LabelName
	for ln := range ro.GroupBy {
		labels = append(labels, ln)
	}
	return fmt.Sprintf("<RouteOpts send_to:%q group_by:%q group_by_all:%t timers:%q|%q>",
		ro.Receiver, labels, ro.GroupByAll, ro.GroupWait, ro.GroupInterval)
}

// MarshalJSON returns a JSON representation of the routing options.
func (ro *RouteOpts) MarshalJSON() ([]byte, error) {
	v := struct {
		Receiver       string           `json:"receiver"`
		GroupBy        model.LabelNames `json:"groupBy"`
		GroupByAll     bool             `json:"groupByAll"`
		GroupWait      time.Duration    `json:"groupWait"`
		GroupInterval  time.Duration    `json:"groupInterval"`
		RepeatInterval time.Duration    `json:"repeatInterval"`
	}{
		Receiver:       ro.Receiver,
		GroupByAll:     ro.GroupByAll,
		GroupWait:      ro.GroupWait,
		GroupInterval:  ro.GroupInterval,
		RepeatInterval: ro.RepeatInterval,
	}
	for ln := range ro.GroupBy {
		v.GroupBy = append(v.GroupBy, ln)
	}

	return json.Marshal(&v)
}