package main

// kernel_boot: which loader booted the machine, its entries, the kernels in /boot, the entry it booted and
// whether the fallback kernel is on the menu (novox/hq ADR 0508 §9, issue 1841). Reads only.

import (
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
	"syscall"
	"unicode/utf16"
)

const loaderSelected = "sys/firmware/efi/efivars/LoaderEntrySelected-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f"

// BootState is what kernel_boot answers.
type BootState struct {
	Loader          string   `json:"loader"`
	Entries         []string `json:"entries"`
	Kernels         []string `json:"kernels"`
	Booted          string   `json:"booted"`
	FallbackPresent bool     `json:"fallback_present"`
	BootFreeKiB     int64    `json:"boot_free_kib"`
}

var grubKernel = regexp.MustCompile(`(?m)^\s*linux\s+(?:/boot)?/(vmlinuz-\S+)`)
var grubTitle = regexp.MustCompile(`(?m)^\s*menuentry\s+'([^']*)'`)
var bootImage = regexp.MustCompile(`BOOT_IMAGE=(?:/boot)?/?(\S+)`)

// Boot reads the machine, the loader the way the boot-entries script does: the loader's EFI variable means
// systemd-boot, a grub.cfg without it GRUB.
func (m *Machine) Boot() (*BootState, error) {
	b := &BootState{Loader: "none", Entries: []string{}, Kernels: []string{}}
	files, _ := filepath.Glob(m.path("boot/vmlinuz-*"))
	for _, f := range files {
		b.Kernels = append(b.Kernels, filepath.Base(f))
	}
	sort.Strings(b.Kernels)
	hasKernel := func(name string) bool {
		for _, k := range b.Kernels {
			if k == name {
				return true
			}
		}
		return false
	}
	var s syscall.Statfs_t
	if err := syscall.Statfs(m.path("boot"), &s); err == nil {
		b.BootFreeKiB = int64(s.Bavail) * int64(s.Bsize) / 1024
	}
	if raw, err := os.ReadFile(m.path(loaderSelected)); err == nil {
		b.Loader = "systemd-boot"
		if len(raw) > 4 {
			var u []uint16
			for i := 4; i+1 < len(raw); i += 2 {
				u = append(u, uint16(raw[i])|uint16(raw[i+1])<<8)
			}
			b.Booted = strings.TrimRight(string(utf16.Decode(u)), "\x00")
		}
		files, _ := filepath.Glob(m.path("boot/loader/entries/*.conf"))
		for _, f := range files {
			b.Entries = append(b.Entries, filepath.Base(f))
		}
		sort.Strings(b.Entries)
		if raw, err := os.ReadFile(m.path("boot/loader/entries/mesh-linux-lts.conf")); err == nil {
			b.FallbackPresent = strings.Contains(string(raw), "/vmlinuz-linux-lts") && hasKernel("vmlinuz-linux-lts")
		}
		return b, nil
	}
	if raw, err := os.ReadFile(m.path("boot/grub/grub.cfg")); err == nil {
		b.Loader = "grub"
		for _, t := range grubTitle.FindAllStringSubmatch(string(raw), -1) {
			b.Entries = append(b.Entries, t[1])
		}
		for _, k := range grubKernel.FindAllStringSubmatch(string(raw), -1) {
			if k[1] == "vmlinuz-linux-lts" && hasKernel("vmlinuz-linux-lts") {
				b.FallbackPresent = true
			}
		}
		if cmd, err := m.read("proc/cmdline"); err == nil {
			if i := bootImage.FindStringSubmatch(cmd); i != nil {
				b.Booted = i[1]
			}
		}
	}
	return b, nil
}