// Package firewall renders /etc/edgeguard/nftables.d/ruleset.nft from
// the relational state in PG (firewall_rules + ha_nodes).
//
// The base ruleset is hard-coded in the template (default-deny input,
// stateful baseline, SSH rate-limit, public :80 / :443, peer mTLS on
// :8443 from cluster IPs). Operator-defined rows in firewall_rules
// land at the bottom of input/forward/output.
//
// Reload uses `nft -f <path>` (atomic ruleset replace) — there is no
// systemctl reload for nftables.
package firewall

import (
	"bytes"
	"context"
	_ "embed"
	"fmt"
	"net"
	"os/exec"
	"path/filepath"
	"text/template"

	"github.com/jackc/pgx/v5/pgxpool"

	"git.netcell-it.de/projekte/edgeguard-native/internal/configgen"
)

//go:embed ruleset.nft.tpl
var rulesTpl string

var tpl = template.Must(template.New("ruleset").Parse(rulesTpl))

type Generator struct {
	Pool *pgxpool.Pool

	OutputPath string
	SkipReload bool
}

func New(pool *pgxpool.Pool) *Generator { return &Generator{Pool: pool} }

func (g *Generator) Name() string { return "nftables" }

func (g *Generator) Render(ctx context.Context) error {
	view, err := g.loadView(ctx)
	if err != nil {
		return fmt.Errorf("nftables: load state: %w", err)
	}
	var buf bytes.Buffer
	if err := tpl.Execute(&buf, view); err != nil {
		return fmt.Errorf("nftables: render template: %w", err)
	}
	out := g.OutputPath
	if out == "" {
		out = filepath.Join(configgen.EtcEdgeguard, "nftables.d", "ruleset.nft")
	}
	if err := configgen.AtomicWrite(out, buf.Bytes(), 0o644); err != nil {
		return fmt.Errorf("nftables: write: %w", err)
	}
	if g.SkipReload {
		return nil
	}
	if err := exec.Command("nft", "-f", out).Run(); err != nil {
		return fmt.Errorf("nftables: nft -f %s: %w", out, err)
	}
	return nil
}

type View struct {
	PeerIPv4 []string
	PeerIPv6 []string
	// Custom rules grouped by chain — the template iterates each
	// section independently so input/forward/output stay separate.
	CustomRulesInput   []Rule
	CustomRulesForward []Rule
	CustomRulesOutput  []Rule
}

type Rule struct {
	MatchExpr string
	Action    string
	Comment   string
}

func (g *Generator) loadView(ctx context.Context) (*View, error) {
	view := &View{}

	// Peer IPs from ha_nodes — splits IPv4 vs IPv6 so the template
	// can populate the right named set without runtime branching.
	peerRows, err := g.Pool.Query(ctx,
		`SELECT public_ip, internal_ip FROM ha_nodes`)
	if err != nil {
		return nil, fmt.Errorf("query ha_nodes: %w", err)
	}
	defer peerRows.Close()
	for peerRows.Next() {
		var pub, internal *string
		if err := peerRows.Scan(&pub, &internal); err != nil {
			return nil, err
		}
		for _, ip := range []*string{pub, internal} {
			if ip == nil {
				continue
			}
			parsed := net.ParseIP(*ip)
			if parsed == nil {
				continue
			}
			if parsed.To4() != nil {
				view.PeerIPv4 = append(view.PeerIPv4, parsed.String())
			} else {
				view.PeerIPv6 = append(view.PeerIPv6, parsed.String())
			}
		}
	}
	if err := peerRows.Err(); err != nil {
		return nil, err
	}

	// Custom firewall_rules — only active, ordered by priority.
	ruleRows, err := g.Pool.Query(ctx, `
SELECT chain, match_expr, action, COALESCE(comment, '')
FROM firewall_rules
WHERE active
ORDER BY chain ASC, priority DESC, id ASC`)
	if err != nil {
		return nil, fmt.Errorf("query firewall_rules: %w", err)
	}
	defer ruleRows.Close()
	for ruleRows.Next() {
		var chain, match, action, comment string
		if err := ruleRows.Scan(&chain, &match, &action, &comment); err != nil {
			return nil, err
		}
		r := Rule{MatchExpr: match, Action: action, Comment: comment}
		switch chain {
		case "input":
			view.CustomRulesInput = append(view.CustomRulesInput, r)
		case "forward":
			view.CustomRulesForward = append(view.CustomRulesForward, r)
		case "output":
			view.CustomRulesOutput = append(view.CustomRulesOutput, r)
		}
	}
	return view, ruleRows.Err()
}