package main

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

	"github.com/VictoriaMetrics/VictoriaMetrics/lib/httpserver"
)

// APIAlert has info for an alert.
type APIAlert struct {
	ID          string            `json:"id"`
	Name        string            `json:"name"`
	Group       string            `json:"group"`
	Expression  string            `json:"expression"`
	State       string            `json:"state"`
	Value       string            `json:"value"`
	Labels      map[string]string `json:"labels"`
	Annotations map[string]string `json:"annotations"`
	ActiveAt    time.Time         `json:"activeAt"`
}

type requestHandler struct {
	groups []Group
}

var pathList = [][]string{
	{"/api/v1/alerts", "list all active alerts"},
	{"/api/v1/groupName/alertID/status", "get alert status by ID"},
	// /metrics is served by httpserver by default
	{"/metrics", "list of application metrics"},
}

func (rh *requestHandler) handler(w http.ResponseWriter, r *http.Request) bool {
	resph := responseHandler{w}
	switch r.URL.Path {
	case "/":
		for _, path := range pathList {
			p, doc := path[0], path[1]
			fmt.Fprintf(w, "<a href='%s'>%q</a> - %s<br/>", p, p, doc)
		}
		return true
	case "/api/v1/alerts":
		resph.handle(rh.list())
		return true
	default:
		// /api/v1/<groupName>/<alertID>/status
		if strings.HasSuffix(r.URL.Path, "/status") {
			resph.handle(rh.alert(r.URL.Path))
			return true
		}
		return false
	}
}

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

func (rh *requestHandler) list() ([]byte, error) {
	lr := listAlertsResponse{Status: "success"}
	for _, g := range rh.groups {
		for _, r := range g.Rules {
			lr.Data.Alerts = append(lr.Data.Alerts, r.AlertsAPI()...)
		}
	}

	// 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: %s`, err),
			StatusCode: http.StatusInternalServerError,
		}
	}
	return b, nil
}

func (rh *requestHandler) alert(path string) ([]byte, error) {
	parts := strings.SplitN(strings.TrimPrefix(path, "/api/v1/"), "/", 3)
	if len(parts) != 3 {
		return nil, &httpserver.ErrorWithStatusCode{
			Err:        fmt.Errorf(`path %q cointains /status suffix but doesn't match pattern "/group/alert/status"`, path),
			StatusCode: http.StatusBadRequest,
		}
	}
	group := strings.TrimRight(parts[0], "/")
	idStr := strings.TrimRight(parts[1], "/")
	id, err := strconv.ParseUint(idStr, 10, 0)
	if err != nil {
		return nil, &httpserver.ErrorWithStatusCode{
			Err:        fmt.Errorf(`cannot parse int from %q`, idStr),
			StatusCode: http.StatusBadRequest,
		}
	}
	for _, g := range rh.groups {
		if g.Name != group {
			continue
		}
		for _, rule := range g.Rules {
			if apiAlert := rule.AlertAPI(id); apiAlert != nil {
				return json.Marshal(apiAlert)
			}
		}
	}
	return nil, &httpserver.ErrorWithStatusCode{
		Err:        fmt.Errorf(`cannot find alert %s in %q`, idStr, group),
		StatusCode: http.StatusNotFound,
	}
}

// responseHandler wrapper on http.ResponseWriter with sugar
type responseHandler struct{ http.ResponseWriter }

func (w responseHandler) handle(b []byte, err error) {
	if err != nil {
		httpserver.Errorf(w, "%s", err)
		return
	}
	w.Header().Set("Content-Type", "application/json")
	w.Write(b)
}