// Package probercore implements a prober's poll loop: register once with
// its site identity, then each cycle fetch the set of IPs currently under
// test and run inbound reachability checks (TCP connect on each configured
// port, ICMP echo) directly against each one — this is the real,
// unmediated network test; only the control channel goes through the
// Control API.
package probercore

import (
	"context"
	"fmt"
	"log/slog"
	"os"
	"time"

	"cloudipvalidator/internal/apiclient"
	"cloudipvalidator/internal/checkrunner"
	"cloudipvalidator/internal/config"
)

type Prober struct {
	cfg    *config.Prober
	client *apiclient.Client
	log    *slog.Logger
}

func New(cfg *config.Prober, log *slog.Logger) *Prober {
	timeout := time.Duration(cfg.Checks.TCPTimeoutSeconds) * time.Second
	if timeout <= 0 {
		timeout = 10 * time.Second
	}
	return &Prober{
		cfg:    cfg,
		client: apiclient.New(cfg.ControlAPIURL, timeout+5*time.Second),
		log:    log,
	}
}

func (p *Prober) Run(ctx context.Context) error {
	if err := p.register(ctx); err != nil {
		return fmt.Errorf("register: %w", err)
	}

	interval := time.Duration(p.cfg.PollIntervalSeconds) * time.Second
	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	for {
		p.pollOnce(ctx)
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-ticker.C:
		}
	}
}

type registerReq struct {
	SiteID   string `json:"site_id"`
	Hostname string `json:"hostname"`
}

func (p *Prober) register(ctx context.Context) error {
	hostname, _ := os.Hostname()
	_, err := p.client.Do(ctx, "POST", "/api/v1/probers/register", registerReq{SiteID: p.cfg.SiteID, Hostname: hostname}, nil)
	if err != nil {
		return err
	}
	p.log.Info("registered", "site_id", p.cfg.SiteID)
	return nil
}

type assignment struct {
	IPID      int64  `json:"ip_id"`
	IPAddress string `json:"ip_address"`
	Ports     []int  `json:"ports"`
	ICMP      bool   `json:"icmp"`
}

type resultDTO struct {
	IPID      int64  `json:"ip_id"`
	IPAddress string `json:"ip_address"`
	CheckType string `json:"check_type"`
	Success   bool   `json:"success"`
	LatencyMS int64  `json:"latency_ms"`
	Detail    string `json:"detail,omitempty"`
	CheckedAt string `json:"checked_at"`
	Complete  bool   `json:"complete"`
}

func (p *Prober) pollOnce(ctx context.Context) {
	if _, err := p.client.Do(ctx, "POST", "/api/v1/probers/"+p.cfg.SiteID+"/heartbeat", nil, nil); err != nil {
		p.log.Error("heartbeat", "err", err)
		return
	}

	var assignments []assignment
	ok, err := p.client.Do(ctx, "GET", "/api/v1/probers/"+p.cfg.SiteID+"/assignments", nil, &assignments)
	if err != nil {
		p.log.Error("get assignments", "err", err)
		return
	}
	if !ok || len(assignments) == 0 {
		return
	}

	for _, a := range assignments {
		p.probeOne(ctx, a)
	}
}

// extraChecksForPort returns checks to run in addition to the base
// TCPConnect for ports where a bare TCP handshake doesn't actually prove
// the expected service is behind it: a real TLS handshake on 443, a real
// SSH banner exchange on 22. nil for every other port.
func extraChecksForPort(host string, port int, timeout time.Duration) []func(ctx context.Context) checkrunner.Result {
	switch port {
	case 443:
		return []func(ctx context.Context) checkrunner.Result{
			checkrunner.TLSHandshake(host, port, timeout),
		}
	case 22:
		return []func(ctx context.Context) checkrunner.Result{
			checkrunner.SSHBanner(host, timeout),
		}
	default:
		return nil
	}
}

func (p *Prober) probeOne(ctx context.Context, a assignment) {
	tcpTimeout := time.Duration(p.cfg.Checks.TCPTimeoutSeconds) * time.Second
	icmpTimeout := time.Duration(p.cfg.Checks.ICMPTimeoutSeconds) * time.Second

	var results []resultDTO
	record := func(res checkrunner.Result) {
		results = append(results, resultDTO{
			IPID: a.IPID, IPAddress: a.IPAddress, CheckType: res.CheckType,
			Success: res.Success, LatencyMS: res.LatencyMS, Detail: res.Detail,
			CheckedAt: res.CheckedAt.Format(time.RFC3339Nano),
		})
	}

	for _, port := range a.Ports {
		record(checkrunner.TCPConnect(a.IPAddress, port, tcpTimeout)(ctx))
		for _, extra := range extraChecksForPort(a.IPAddress, port, tcpTimeout) {
			record(extra(ctx))
		}
	}
	if a.ICMP {
		record(checkrunner.ICMPEcho(a.IPAddress, p.cfg.Checks.ICMPCount, icmpTimeout)(ctx))
	}
	if len(results) > 0 {
		results[len(results)-1].Complete = true
	}

	body := struct {
		Results []resultDTO `json:"results"`
	}{results}
	if _, err := p.client.Do(ctx, "POST", "/api/v1/probers/"+p.cfg.SiteID+"/results", body, nil); err != nil {
		p.log.Error("post results", "ip", a.IPAddress, "err", err)
	}
}