// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause

//go:build !plan9

// Package kube contains types and utilities for the Tailscale Kubernetes Operator.
package kube

import (
	"fmt"
	"iter"

	"tailscale.com/tailcfg"
)

const (
	Alpha1Version = "v1alpha1"

	DNSRecordsCMName = "dnsrecords"
	DNSRecordsCMKey  = "records.json"
)

type Records struct {
	// Version is the version of this Records configuration. Version is
	// written by the operator, i.e when it first populates the Records.
	// k8s-nameserver must verify that it knows how to parse a given
	// version.
	Version string `json:"version"`
	// IP4 contains a mapping of DNS names to IPv4 address(es).
	IP4 map[string][]string `json:"ip4"`
}

// TailscaledConfigFileName returns a tailscaled config file name in
// format expected by containerboot for the given CapVer.
func TailscaledConfigFileName(cap tailcfg.CapabilityVersion) string {
	if cap < 95 {
		return "tailscaled"
	}
	return fmt.Sprintf("cap-%v.hujson", cap)
}

// CapVerFromFileName parses the capability version from a tailscaled
// config file name previously generated by TailscaledConfigFileNameForCap.
func CapVerFromFileName(name string) (tailcfg.CapabilityVersion, error) {
	switch name {
	case "tailscaled", "tailscaled.hujson":
		// Unversioned names.
		return 0, nil
	default:
		var cap tailcfg.CapabilityVersion
		_, err := fmt.Sscanf(name, "cap-%d.hujson", &cap)
		return cap, err
	}
}

func SelectConfigFileName(files iter.Seq[string]) string {
	maxCapVer := tailcfg.CapabilityVersion(-1)
	var selectedName string
	for fileName := range files {
		capVer, err := CapVerFromFileName(fileName)
		if err != nil {
			continue
		}
		// 0 is "unversioned" (by capability - there is still a version inside
		// the config itself). Always prefer it to files that have a capability
		// version.
		if (capVer > maxCapVer && maxCapVer != 0) || capVer == 0 {
			maxCapVer = capVer
			selectedName = fileName
		}
	}

	return selectedName
}