package birdfmt

import (
	"fmt"
	"net/netip"
	"strings"
)

// Parent protocol names for discovery listeners (not spawned session names).
const (
	DiscoveryProtocolV4 = "evobgp_discover_v4"
	DiscoveryProtocolV6 = "evobgp_discover_v6"
)

// DynamicBGPDiscoveryOptions configures quarantine dynamic BGP listeners.
type DynamicBGPDiscoveryOptions struct {
	RangesV4          []string // CIDR prefixes
	RangesV6          []string
	RequireExternal   bool // neighbor range … external (default true)
	DynamicNameDigits int  // default 4
}

// RenderDynamicBGPDiscovery renders passive dynamic BGP quarantine listeners.
// Spawned sessions use DynamicPeerProtocolPrefix ("evobgp_dyn_").
// Channel policy is always import none / export none (no announcements until approve).
func RenderDynamicBGPDiscovery(opts DynamicBGPDiscoveryOptions) (string, error) {
	digits := opts.DynamicNameDigits
	if digits <= 0 {
		digits = 4
	}
	var parts []string
	if len(opts.RangesV4) > 0 {
		s, err := renderDynamicDiscoveryAF(DiscoveryProtocolV4, BGPTemplateNameV4, "ipv4", opts.RangesV4, opts.RequireExternal, digits)
		if err != nil {
			return "", err
		}
		parts = append(parts, s)
	}
	if len(opts.RangesV6) > 0 {
		s, err := renderDynamicDiscoveryAF(DiscoveryProtocolV6, BGPTemplateNameV6, "ipv6", opts.RangesV6, opts.RequireExternal, digits)
		if err != nil {
			return "", err
		}
		parts = append(parts, s)
	}
	if len(parts) == 0 {
		return "", nil
	}
	return strings.Join(parts, "\n"), nil
}

func renderDynamicDiscoveryAF(protoName, templateName, af string, ranges []string, external bool, digits int) (string, error) {
	var cleaned []string
	for _, r := range ranges {
		r = strings.TrimSpace(r)
		if r == "" {
			continue
		}
		pfx, err := netip.ParsePrefix(r)
		if err != nil {
			return "", fmt.Errorf("birdfmt: invalid discovery range %q: %w", r, err)
		}
		if af == "ipv4" && !pfx.Addr().Is4() {
			return "", fmt.Errorf("birdfmt: discovery range %q is not IPv4", r)
		}
		if af == "ipv6" && !pfx.Addr().Is6() {
			return "", fmt.Errorf("birdfmt: discovery range %q is not IPv6", r)
		}
		cleaned = append(cleaned, pfx.Masked().String())
	}
	if len(cleaned) == 0 {
		return "", nil
	}

	var b strings.Builder
	fmt.Fprintf(&b, "protocol bgp %s from %s {\n", protoName, templateName)
	for _, cidr := range cleaned {
		b.WriteString("    neighbor range ")
		b.WriteString(cidr)
		if external {
			b.WriteString(" external")
		}
		b.WriteString(";\n")
	}
	fmt.Fprintf(&b, "    dynamic name \"%s\";\n", DynamicPeerProtocolPrefix)
	fmt.Fprintf(&b, "    dynamic name digits %d;\n", digits)
	b.WriteString("    multihop;\n")
	b.WriteString("    passive;\n")
	fmt.Fprintf(&b, "    %s {\n", af)
	b.WriteString("        import none;\n")
	b.WriteString("        export none;\n")
	b.WriteString("    };\n")
	b.WriteString("}\n")
	return b.String(), nil
}

// ParseDiscoveryRanges splits a settings string (comma / newline / space separated) into CIDRs.
func ParseDiscoveryRanges(raw string) []string {
	raw = strings.TrimSpace(raw)
	if raw == "" {
		return nil
	}
	raw = strings.ReplaceAll(raw, ",", " ")
	raw = strings.ReplaceAll(raw, "\n", " ")
	raw = strings.ReplaceAll(raw, ";", " ")
	fields := strings.Fields(raw)
	out := make([]string, 0, len(fields))
	seen := map[string]struct{}{}
	for _, f := range fields {
		f = strings.TrimSpace(f)
		if f == "" {
			continue
		}
		if _, ok := seen[f]; ok {
			continue
		}
		seen[f] = struct{}{}
		out = append(out, f)
	}
	return out
}