package birdfmt

import (
	"fmt"
	"strings"
)

// BGP template names referenced by generated peers (BIRD 2).
const (
	BGPTemplateNameV4 = "bgp_template"
	BGPTemplateNameV6 = "bgp_template_v6"
)

// BGPTemplatesOptions holds ASN and export filters for template bgp bgp_template (+ v6 mirror).
// Templates use "local as <asn>;" only (no local IP); peers add neighbor / multihop / passive and optional "local … as …" override.
type BGPTemplatesOptions struct {
	LocalASN       uint32
	ExportFilterV4 string
	ExportFilterV6 string
}

// RenderBGPTemplates renders two template bgp blocks (IPv4 and IPv6 AFI).
func RenderBGPTemplates(opts BGPTemplatesOptions) (string, error) {
	if opts.LocalASN == 0 {
		return "", fmt.Errorf("birdfmt: template local ASN must be non-zero")
	}
	exp4 := "all"
	if strings.TrimSpace(opts.ExportFilterV4) != "" {
		exp4 = "filter " + strings.TrimSpace(opts.ExportFilterV4)
	}
	exp6 := "all"
	if strings.TrimSpace(opts.ExportFilterV6) != "" {
		exp6 = "filter " + strings.TrimSpace(opts.ExportFilterV6)
	}
	var b strings.Builder
	fmt.Fprintf(&b, "template bgp %s {\n", BGPTemplateNameV4)
	fmt.Fprintf(&b, "    local as %d;\n", opts.LocalASN)
	b.WriteString("    ipv4 {\n")
	b.WriteString("        import none;\n")
	b.WriteString("        export ")
	b.WriteString(exp4)
	b.WriteString(";\n")
	b.WriteString("    };\n")
	b.WriteString("    hold time 90;\n")
	b.WriteString("    keepalive time 30;\n")
	b.WriteString("}\n\n")
	fmt.Fprintf(&b, "template bgp %s {\n", BGPTemplateNameV6)
	fmt.Fprintf(&b, "    local as %d;\n", opts.LocalASN)
	b.WriteString("    ipv6 {\n")
	b.WriteString("        import none;\n")
	b.WriteString("        export ")
	b.WriteString(exp6)
	b.WriteString(";\n")
	b.WriteString("    };\n")
	b.WriteString("    hold time 90;\n")
	b.WriteString("    keepalive time 30;\n")
	b.WriteString("}\n")
	return b.String(), nil
}

// BGPPeerFromTemplateOptions describes protocol bgp NAME from TEMPLATE { … }.
type BGPPeerFromTemplateOptions struct {
	ProtocolName string
	TemplateName string
	NeighborIP   string
	NeighborASN  uint32
	// If set, emits "local … as …" before neighbor (overrides template local/ASN for this peer).
	OverrideLocalIP  string
	OverrideLocalASN uint32
}

// RenderProtocolBGPFromTemplate renders protocol bgp … from TEMPLATE { neighbor; multihop; passive; }.
func RenderProtocolBGPFromTemplate(opts BGPPeerFromTemplateOptions) (string, error) {
	if strings.TrimSpace(opts.ProtocolName) == "" {
		return "", fmt.Errorf("birdfmt: protocol name is required")
	}
	if strings.TrimSpace(opts.TemplateName) == "" {
		return "", fmt.Errorf("birdfmt: template name is required")
	}
	if strings.TrimSpace(opts.NeighborIP) == "" {
		return "", fmt.Errorf("birdfmt: neighbor is required")
	}
	if opts.NeighborASN == 0 {
		return "", fmt.Errorf("birdfmt: neighbor ASN must be non-zero")
	}
	if opts.OverrideLocalIP != "" && opts.OverrideLocalASN == 0 {
		return "", fmt.Errorf("birdfmt: override local ASN is required when override local IP is set")
	}

	var b strings.Builder
	b.WriteString("protocol bgp ")
	b.WriteString(strings.TrimSpace(opts.ProtocolName))
	b.WriteString(" from ")
	b.WriteString(strings.TrimSpace(opts.TemplateName))
	b.WriteString(" {\n")
	if ip := strings.TrimSpace(opts.OverrideLocalIP); ip != "" {
		b.WriteString("    local ")
		b.WriteString(ip)
		fmt.Fprintf(&b, " as %d;\n", opts.OverrideLocalASN)
	}
	b.WriteString("    neighbor ")
	b.WriteString(strings.TrimSpace(opts.NeighborIP))
	fmt.Fprintf(&b, " as %d;\n", opts.NeighborASN)
	b.WriteString("    multihop;\n")
	b.WriteString("    passive;\n")
	b.WriteString("}\n")
	return b.String(), nil
}

// BGPPeerIPv4Options describes a single BGP session (BIRD 2, IPv4 AF).
type BGPPeerIPv4Options struct {
	ProtocolName string // e.g. evobgp_peer_uplink
	LocalIP      string // e.g. 192.0.2.1
	LocalASN     uint32
	NeighborIP   string
	NeighborASN  uint32
	// ExportFilter is a filter name, or empty for "export all".
	ExportFilter string
	// ImportFilter is a filter name, or empty for "import all".
	ImportFilter string
}

// RenderProtocolBGPIPv4 renders a protocol bgp { … ipv4 { … } } block.
func RenderProtocolBGPIPv4(opts BGPPeerIPv4Options) (string, error) {
	if strings.TrimSpace(opts.ProtocolName) == "" {
		return "", fmt.Errorf("birdfmt: protocol name is required")
	}
	if strings.TrimSpace(opts.LocalIP) == "" || strings.TrimSpace(opts.NeighborIP) == "" {
		return "", fmt.Errorf("birdfmt: local and neighbor addresses are required")
	}
	if opts.LocalASN == 0 || opts.NeighborASN == 0 {
		return "", fmt.Errorf("birdfmt: AS numbers must be non-zero")
	}
	imp := "all"
	if strings.TrimSpace(opts.ImportFilter) != "" {
		imp = "filter " + strings.TrimSpace(opts.ImportFilter)
	}
	exp := "all"
	if strings.TrimSpace(opts.ExportFilter) != "" {
		exp = "filter " + strings.TrimSpace(opts.ExportFilter)
	}

	var b strings.Builder
	b.WriteString("protocol bgp ")
	b.WriteString(strings.TrimSpace(opts.ProtocolName))
	b.WriteString(" {\n")
	b.WriteString("    local ")
	b.WriteString(strings.TrimSpace(opts.LocalIP))
	fmt.Fprintf(&b, " as %d;\n", opts.LocalASN)
	b.WriteString("    neighbor ")
	b.WriteString(strings.TrimSpace(opts.NeighborIP))
	fmt.Fprintf(&b, " as %d;\n", opts.NeighborASN)
	b.WriteString("    ipv4 {\n")
	b.WriteString("        import ")
	b.WriteString(imp)
	b.WriteString(";\n")
	b.WriteString("        export ")
	b.WriteString(exp)
	b.WriteString(";\n")
	b.WriteString("    };\n")
	b.WriteString("}\n")
	return b.String(), nil
}

// BGPPeerIPv6Options describes a BGP session for the IPv6 AF.
type BGPPeerIPv6Options struct {
	ProtocolName string
	LocalIP      string
	LocalASN     uint32
	NeighborIP   string
	NeighborASN  uint32
	ExportFilter string
	ImportFilter string
}

// RenderProtocolBGPIPv6 renders a protocol bgp block with ipv6 { import/export }.
func RenderProtocolBGPIPv6(opts BGPPeerIPv6Options) (string, error) {
	if strings.TrimSpace(opts.ProtocolName) == "" {
		return "", fmt.Errorf("birdfmt: protocol name is required")
	}
	if strings.TrimSpace(opts.LocalIP) == "" || strings.TrimSpace(opts.NeighborIP) == "" {
		return "", fmt.Errorf("birdfmt: local and neighbor addresses are required")
	}
	if opts.LocalASN == 0 || opts.NeighborASN == 0 {
		return "", fmt.Errorf("birdfmt: AS numbers must be non-zero")
	}
	imp := "all"
	if strings.TrimSpace(opts.ImportFilter) != "" {
		imp = "filter " + strings.TrimSpace(opts.ImportFilter)
	}
	exp := "all"
	if strings.TrimSpace(opts.ExportFilter) != "" {
		exp = "filter " + strings.TrimSpace(opts.ExportFilter)
	}

	var b strings.Builder
	b.WriteString("protocol bgp ")
	b.WriteString(strings.TrimSpace(opts.ProtocolName))
	b.WriteString(" {\n")
	b.WriteString("    local ")
	b.WriteString(strings.TrimSpace(opts.LocalIP))
	fmt.Fprintf(&b, " as %d;\n", opts.LocalASN)
	b.WriteString("    neighbor ")
	b.WriteString(strings.TrimSpace(opts.NeighborIP))
	fmt.Fprintf(&b, " as %d;\n", opts.NeighborASN)
	b.WriteString("    ipv6 {\n")
	b.WriteString("        import ")
	b.WriteString(imp)
	b.WriteString(";\n")
	b.WriteString("        export ")
	b.WriteString(exp)
	b.WriteString(";\n")
	b.WriteString("    };\n")
	b.WriteString("}\n")
	return b.String(), nil
}