package server

import (
	"net/http"
	"sync"
	"time"

	"housecarl/internal/version"
)

// fallbackInForce is what status and /healthz say while the boot fallback
// (render.Fallback) is in force.
const fallbackInForce = "the boot fallback is in force, not Housecarl's ruleset: the saved ruleset failed to load at boot (journalctl -u housecarl-ruleset), and housecarld couldn't apply it since; it lets nothing new in from external zones (with none, nothing but loopback)"

// health is GET /healthz, for monitoring (Checkmk, a load balancer). It
// needs no authentication, so it says only what a monitor needs, and reads
// the ruleset at most every few seconds however often it is asked.
type health struct {
	OK       bool   `json:"ok"`
	Version  string `json:"version"`
	Firewall string `json:"firewall"` // applied, unconfigured, fallback, missing
	// Mode is enforcing, or shadow: the ruleset blocks nothing.
	Mode string `json:"mode"`
	// Probation: changes waiting to be confirmed, rolled back otherwise.
	Probation int `json:"probation"`
	// Warnings are the codes of the machine's problems (nftables_service).
	Warnings []string `json:"warnings"`
}

const healthTTL = 5 * time.Second

type healthCache struct {
	mu  sync.Mutex
	at  time.Time
	out health
}

func (s *Server) healthz(w http.ResponseWriter, r *http.Request) {
	c := &s.health
	c.mu.Lock()
	if time.Since(c.at) >= healthTTL {
		c.out, c.at = s.checkHealth(r), time.Now()
	}
	out := c.out
	c.mu.Unlock()
	code := http.StatusOK
	if !out.OK {
		code = http.StatusServiceUnavailable
	}
	writeJSON(w, code, out)
}

func (s *Server) checkHealth(r *http.Request) health {
	out := health{Version: version.String(), Warnings: []string{}, Mode: s.mode()}
	t, err := s.fw.Table(r.Context())
	switch {
	case err != nil && s.eng.State().Empty():
		out.Firewall, out.OK = "unconfigured", true
	case err != nil:
		out.Firewall = "missing"
	case t.Fallback:
		out.Firewall = "fallback"
	default:
		out.Firewall, out.OK = "applied", true
	}
	pr := s.probationStatus()
	out.Probation = len(pr.Pending) + pr.Takeovers
	// The other tables matter in shadow mode (shadow_unprotected).
	var ruleset []byte
	if s.cfg.Shadow {
		ruleset, _ = s.fw.ListRuleset(r.Context())
	}
	for _, p := range s.hostProblems(r.Context(), ruleset) {
		out.Warnings = append(out.Warnings, p.Code)
	}
	return out
}