package birdfmt

import (
	"fmt"
	"strings"
)

// Directory and fragment file names for EvoBGP-generated includes (relative to bird.conf).
const (
	DirBirdD = "bird.d"

	FragmentPrefixesV4  = "evobgp_prefixes_v4.conf"
	FragmentPrefixesV6  = "evobgp_prefixes_v6.conf"
	FragmentFiltersV4   = "evobgp_filters_v4.conf"
	FragmentFiltersV6   = "evobgp_filters_v6.conf"
	FragmentBGPTemplate = "evobgp_bgp_template.conf"
	FragmentPeers       = "evobgp_peers.conf"
)

// FragmentIncludePath returns a POSIX include path such as bird.d/evobgp_prefixes_v4.conf.
func FragmentIncludePath(fragmentBaseName string) string {
	if fragmentBaseName == "" {
		return DirBirdD + "/"
	}
	return DirBirdD + "/" + fragmentBaseName
}

// StandardIncludeFragments is the recommended order: filters before BGP templates and peers.
func StandardIncludeFragments() []string {
	return []string{
		FragmentIncludePath(FragmentFiltersV4),
		FragmentIncludePath(FragmentFiltersV6),
		FragmentIncludePath(FragmentBGPTemplate),
		FragmentIncludePath(FragmentPrefixesV4),
		FragmentIncludePath(FragmentPrefixesV6),
		FragmentIncludePath(FragmentPeers),
	}
}

// MainBirdConfOptions describes the top-level bird.conf skeleton EvoBGP expects beside bird.d/.
type MainBirdConfOptions struct {
	// RouterID is the BIRD router id (IPv4 dotted quad recommended).
	RouterID string
	// Includes are paths as in include "…" (e.g. bird.d/evobgp_prefixes_v4.conf).
	Includes []string
	// Preamble is optional comment lines (each line prefixed with #), no trailing newline required.
	Preamble string
}

// RenderMainBirdConf returns a BIRD 2 main config: device, direct, include lines.
// RouterID must be non-empty.
func RenderMainBirdConf(opts MainBirdConfOptions) (string, error) {
	if strings.TrimSpace(opts.RouterID) == "" {
		return "", fmt.Errorf("birdfmt: router id is required")
	}
	var b strings.Builder
	pre := strings.TrimSpace(opts.Preamble)
	if pre != "" {
		for _, line := range strings.Split(pre, "\n") {
			line = strings.TrimRight(line, "\r")
			if line == "" {
				b.WriteByte('\n')
				continue
			}
			if !strings.HasPrefix(line, "#") {
				b.WriteString("# ")
			}
			b.WriteString(line)
			b.WriteByte('\n')
		}
		b.WriteByte('\n')
	}
	b.WriteString("router id ")
	b.WriteString(strings.TrimSpace(opts.RouterID))
	b.WriteString(";\n\n")
	for _, inc := range opts.Includes {
		inc = strings.TrimSpace(inc)
		if inc == "" {
			continue
		}
		b.WriteString("include \"")
		b.WriteString(inc)
		b.WriteString("\";\n")
	}
	if len(opts.Includes) > 0 {
		b.WriteByte('\n')
	}
	b.WriteString(`protocol device {
}

protocol direct {
    ipv4;
    ipv6;
}
`)
	return b.String(), nil
}