package main

import (
	"embed"
	"encoding/json"
	"fmt"
	"net/http"
	"sort"
	"strconv"
	"strings"

	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmalert/notifier"
	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmalert/rule"
	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmalert/tpl"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/flagutil"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/httpserver"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/httputils"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/procutil"
)

var reloadAuthKey = flagutil.NewPassword("reloadAuthKey", "Auth key for /-/reload http endpoint. It must be passed via authKey query arg. It overrides -httpAuth.*")

var (
	apiLinks = [][2]string{
		// api links are relative since they can be used by external clients,
		// such as Grafana, and proxied via vmselect.
		{"api/v1/rules", "list all loaded groups and rules"},
		{"api/v1/alerts", "list all active alerts"},
		{fmt.Sprintf("api/v1/alert?%s=<int>&%s=<int>", paramGroupID, paramAlertID), "get alert status by group and alert ID"},
	}
	systemLinks = [][2]string{
		{"flags", "command-line flags"},
		{"metrics", "list of application metrics"},
		{"-/reload", "reload configuration"},
	}
	navItems = []tpl.NavItem{
		{Name: "vmalert", Url: "../vmalert"},
		{Name: "Groups", Url: "groups"},
		{Name: "Alerts", Url: "alerts"},
		{Name: "Notifiers", Url: "notifiers"},
		{Name: "Docs", Url: "https://docs.victoriametrics.com/vmalert/"},
	}
)

type requestHandler struct {
	m *manager
}

var (
	//go:embed static
	staticFiles   embed.FS
	staticHandler = http.FileServer(http.FS(staticFiles))
	staticServer  = http.StripPrefix("/vmalert", staticHandler)
)

func (rh *requestHandler) handler(w http.ResponseWriter, r *http.Request) bool {
	if strings.HasPrefix(r.URL.Path, "/vmalert/static") {
		staticServer.ServeHTTP(w, r)
		return true
	}

	switch r.URL.Path {
	case "/", "/vmalert", "/vmalert/":
		if r.Method != http.MethodGet {
			httpserver.Errorf(w, r, "path %q supports only GET method", r.URL.Path)
			return false
		}
		WriteWelcome(w, r)
		return true
	case "/vmalert/alerts":
		WriteListAlerts(w, r, rh.groupAlerts())
		return true
	case "/vmalert/alert":
		alert, err := rh.getAlert(r)
		if err != nil {
			httpserver.Errorf(w, r, "%s", err)
			return true
		}
		WriteAlert(w, r, alert)
		return true
	case "/vmalert/rule":
		rule, err := rh.getRule(r)
		if err != nil {
			httpserver.Errorf(w, r, "%s", err)
			return true
		}
		WriteRuleDetails(w, r, rule)
		return true
	case "/vmalert/groups":
		var data []apiGroup
		rf := extractRulesFilter(r)
		data = rh.groups(rf)
		WriteListGroups(w, r, data)
		return true
	case "/vmalert/notifiers":
		WriteListTargets(w, r, notifier.GetTargets())
		return true

	// special cases for Grafana requests,
	// served without `vmalert` prefix:
	case "/rules":
		// Grafana makes an extra request to `/rules`
		// handler in addition to `/api/v1/rules` calls in alerts UI,
		var data []apiGroup
		rf := extractRulesFilter(r)
		data = rh.groups(rf)
		WriteListGroups(w, r, data)
		return true

	case "/vmalert/api/v1/rules", "/api/v1/rules":
		// path used by Grafana for ng alerting
		var data []byte
		var err error

		rf := extractRulesFilter(r)
		data, err = rh.listGroups(rf)

		if err != nil {
			httpserver.Errorf(w, r, "%s", err)
			return true
		}
		w.Header().Set("Content-Type", "application/json")
		w.Write(data)
		return true

	case "/vmalert/api/v1/alerts", "/api/v1/alerts":
		// path used by Grafana for ng alerting
		data, err := rh.listAlerts()
		if err != nil {
			httpserver.Errorf(w, r, "%s", err)
			return true
		}
		w.Header().Set("Content-Type", "application/json")
		w.Write(data)
		return true
	case "/vmalert/api/v1/alert", "/api/v1/alert":
		alert, err := rh.getAlert(r)
		if err != nil {
			httpserver.Errorf(w, r, "%s", err)
			return true
		}
		data, err := json.Marshal(alert)
		if err != nil {
			httpserver.Errorf(w, r, "failed to marshal alert: %s", err)
			return true
		}
		w.Header().Set("Content-Type", "application/json")
		w.Write(data)
		return true
	case "/vmalert/api/v1/rule", "/api/v1/rule":
		rule, err := rh.getRule(r)
		if err != nil {
			httpserver.Errorf(w, r, "%s", err)
			return true
		}
		rwu := apiRuleWithUpdates{
			apiRule:      rule,
			StateUpdates: rule.Updates,
		}
		data, err := json.Marshal(rwu)
		if err != nil {
			httpserver.Errorf(w, r, "failed to marshal rule: %s", err)
			return true
		}
		w.Header().Set("Content-Type", "application/json")
		w.Write(data)
		return true
	case "/-/reload":
		if !httpserver.CheckAuthFlag(w, r, reloadAuthKey) {
			return true
		}
		logger.Infof("api config reload was called, sending sighup")
		procutil.SelfSIGHUP()
		w.WriteHeader(http.StatusOK)
		return true

	default:
		return false
	}
}

func (rh *requestHandler) getRule(r *http.Request) (apiRule, error) {
	groupID, err := strconv.ParseUint(r.FormValue(paramGroupID), 10, 64)
	if err != nil {
		return apiRule{}, fmt.Errorf("failed to read %q param: %w", paramGroupID, err)
	}
	ruleID, err := strconv.ParseUint(r.FormValue(paramRuleID), 10, 64)
	if err != nil {
		return apiRule{}, fmt.Errorf("failed to read %q param: %w", paramRuleID, err)
	}
	obj, err := rh.m.ruleAPI(groupID, ruleID)
	if err != nil {
		return apiRule{}, errResponse(err, http.StatusNotFound)
	}
	return obj, nil
}

func (rh *requestHandler) getAlert(r *http.Request) (*apiAlert, error) {
	groupID, err := strconv.ParseUint(r.FormValue(paramGroupID), 10, 64)
	if err != nil {
		return nil, fmt.Errorf("failed to read %q param: %w", paramGroupID, err)
	}
	alertID, err := strconv.ParseUint(r.FormValue(paramAlertID), 10, 64)
	if err != nil {
		return nil, fmt.Errorf("failed to read %q param: %w", paramAlertID, err)
	}
	a, err := rh.m.alertAPI(groupID, alertID)
	if err != nil {
		return nil, errResponse(err, http.StatusNotFound)
	}
	return a, nil
}

type listGroupsResponse struct {
	Status string `json:"status"`
	Data   struct {
		Groups []apiGroup `json:"groups"`
	} `json:"data"`
}

// see https://prometheus.io/docs/prometheus/latest/querying/api/#rules
type rulesFilter struct {
	files         []string
	groupNames    []string
	ruleNames     []string
	ruleType      string
	excludeAlerts bool
}

func extractRulesFilter(r *http.Request) rulesFilter {
	rf := rulesFilter{}

	var ruleType string
	ruleTypeParam := r.URL.Query().Get("type")
	// for some reason, `type` in filter doesn't match `type` in response,
	// so we use this matching here
	if ruleTypeParam == "alert" {
		ruleType = ruleTypeAlerting
	} else if ruleTypeParam == "record" {
		ruleType = ruleTypeRecording
	}
	rf.ruleType = ruleType

	rf.excludeAlerts = httputils.GetBool(r, "exclude_alerts")
	rf.ruleNames = append([]string{}, r.Form["rule_name[]"]...)
	rf.groupNames = append([]string{}, r.Form["rule_group[]"]...)
	rf.files = append([]string{}, r.Form["file[]"]...)
	return rf
}

func (rh *requestHandler) groups(rf rulesFilter) []apiGroup {
	rh.m.groupsMu.RLock()
	defer rh.m.groupsMu.RUnlock()

	isInList := func(list []string, needle string) bool {
		if len(list) < 1 {
			return true
		}
		for _, i := range list {
			if i == needle {
				return true
			}
		}
		return false
	}

	groups := make([]apiGroup, 0)
	for _, group := range rh.m.groups {
		if !isInList(rf.groupNames, group.Name) {
			continue
		}
		if !isInList(rf.files, group.File) {
			continue
		}

		g := groupToAPI(group)
		// the returned list should always be non-nil
		// https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4221
		filteredRules := make([]apiRule, 0)
		for _, r := range g.Rules {
			if rf.ruleType != "" && rf.ruleType != r.Type {
				continue
			}
			if !isInList(rf.ruleNames, r.Name) {
				continue
			}
			if rf.excludeAlerts {
				r.Alerts = nil
			}
			filteredRules = append(filteredRules, r)
		}
		g.Rules = filteredRules
		groups = append(groups, g)
	}
	// sort list of groups for deterministic output
	sort.Slice(groups, func(i, j int) bool {
		a, b := groups[i], groups[j]
		if a.Name != b.Name {
			return a.Name < b.Name
		}
		return a.File < b.File
	})
	return groups
}

func (rh *requestHandler) listGroups(rf rulesFilter) ([]byte, error) {
	lr := listGroupsResponse{Status: "success"}
	lr.Data.Groups = rh.groups(rf)
	b, err := json.Marshal(lr)
	if err != nil {
		return nil, &httpserver.ErrorWithStatusCode{
			Err:        fmt.Errorf(`error encoding list of active alerts: %w`, err),
			StatusCode: http.StatusInternalServerError,
		}
	}
	return b, nil
}

type listAlertsResponse struct {
	Status string `json:"status"`
	Data   struct {
		Alerts []*apiAlert `json:"alerts"`
	} `json:"data"`
}

func (rh *requestHandler) groupAlerts() []groupAlerts {
	rh.m.groupsMu.RLock()
	defer rh.m.groupsMu.RUnlock()

	var gAlerts []groupAlerts
	for _, g := range rh.m.groups {
		var alerts []*apiAlert
		for _, r := range g.Rules {
			a, ok := r.(*rule.AlertingRule)
			if !ok {
				continue
			}
			alerts = append(alerts, ruleToAPIAlert(a)...)
		}
		if len(alerts) > 0 {
			gAlerts = append(gAlerts, groupAlerts{
				Group:  groupToAPI(g),
				Alerts: alerts,
			})
		}
	}
	sort.Slice(gAlerts, func(i, j int) bool {
		return gAlerts[i].Group.Name < gAlerts[j].Group.Name
	})
	return gAlerts
}

func (rh *requestHandler) listAlerts() ([]byte, error) {
	rh.m.groupsMu.RLock()
	defer rh.m.groupsMu.RUnlock()

	lr := listAlertsResponse{Status: "success"}
	lr.Data.Alerts = make([]*apiAlert, 0)
	for _, g := range rh.m.groups {
		for _, r := range g.Rules {
			a, ok := r.(*rule.AlertingRule)
			if !ok {
				continue
			}
			lr.Data.Alerts = append(lr.Data.Alerts, ruleToAPIAlert(a)...)
		}
	}

	// sort list of alerts for deterministic output
	sort.Slice(lr.Data.Alerts, func(i, j int) bool {
		return lr.Data.Alerts[i].ID < lr.Data.Alerts[j].ID
	})

	b, err := json.Marshal(lr)
	if err != nil {
		return nil, &httpserver.ErrorWithStatusCode{
			Err:        fmt.Errorf(`error encoding list of active alerts: %w`, err),
			StatusCode: http.StatusInternalServerError,
		}
	}
	return b, nil
}

func errResponse(err error, sc int) *httpserver.ErrorWithStatusCode {
	return &httpserver.ErrorWithStatusCode{
		Err:        err,
		StatusCode: sc,
	}
}