// selfupdate.go - upd updating itself.
//
// The mechanism is the one dx uses: --check-update looks, --update installs,
// and an ordinary run consults a note in the cache once a day and mentions a
// newer release on stderr - never asking in the foreground, never asking when
// nobody is watching. The work itself goes through upd's own machinery: the
// same forge layer, the same retries and CA fallback, the same checksum check
// and the same atomic install, so updating upd behaves like updating any other
// tool it installs.
//
// It assumes the layout build.sh produces: one release per version, whose tag
// is the bare number (2.0.6, a leading "v" is allowed), holding one asset
// "upd-<goos>-<goarch>" each - that is, exactly the files from ./bin.
package main

import (
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strconv"
	"strings"
	"time"
)

// ------------------------------------------------------------ Configuration

var selfUpdate = selfUpdater{
	repo:     "https://git.micw.org/mike/upd",
	name:     "upd",
	current:  version, // from main.go, set by -ldflags
	every:    24 * time.Hour,
	quietEnv: "UPD_NO_UPDATE_CHECK",
}

type selfUpdater struct {
	repo     string        // repo URL as in the browser: https://host/owner/repo
	name     string        // base name of the assets, "-<goos>-<goarch>" is added
	current  string        // the running version
	every    time.Duration // how often to look on its own; 0 turns that off
	quietEnv string        // this environment variable set: keep quiet as well
}

// updateRefreshFlag is the option upd calls itself with, in the background. It
// is deliberately absent from the help.
const updateRefreshFlag = "update-refresh"

// ------------------------------------------------------------ Looking by itself

// daily is the hook for the ordinary run. It costs nothing: in the foreground
// the network is never touched. What comes back is the line pointing at a new
// version - or "", when there is nothing to say. Should the note be older than
// `every`, daily starts a background run on the side, whose answer the next
// call will find waiting.
func (u selfUpdater) daily() string {
	if u.every <= 0 || os.Getenv(u.quietEnv) != "" || !isTerminal(os.Stderr) {
		return ""
	}
	st := u.loadState() // no file: the zero value, hence due at once

	if time.Since(st.Checked) >= u.every {
		// The timestamp moves on before the asking, not after: otherwise two
		// simultaneous runs start two queries, and a server that is not in the
		// mood would get a new one on every call. If the note does not stay
		// put, nothing is asked either - else an unwritable cache directory
		// would mean one process per call.
		st.Checked = time.Now()
		if u.saveState(st) == nil {
			u.spawnRefresh()
		}
	}

	if st.Latest == "" || compareVer(st.Latest, u.current) <= 0 {
		return ""
	}
	return fmt.Sprintf("Note: %s %s is available, run '%s --update'.", u.name, st.Latest, u.name)
}

// refresh is the background run: ask, write it down, stay quiet. The writing
// down is done by latest; if the query fails, the old state remains.
func (u selfUpdater) refresh() {
	_, _, _ = u.latest()
}

// spawnRefresh calls upd once more, only to ask, and does not wait. Without a
// Wait the child is adopted by init when this process ends - it thus outlives
// the call, and the call's output stays untouched by it.
func (u selfUpdater) spawnRefresh() {
	exe, err := os.Executable()
	if err != nil {
		return
	}
	cmd := exec.Command(exe, "--"+updateRefreshFlag)
	cmd.Stdin, cmd.Stdout, cmd.Stderr = nil, nil, nil // everything to /dev/null
	if cmd.Start() == nil {
		cmd.Process.Release()
	}
}

// --------------------------------------------------------------------- Note

// updateState is what is left between two calls: when the last question was
// asked and what came of it.
type updateState struct {
	Checked time.Time `json:"checked"`
	Latest  string    `json:"latest"`
}

// The note lives in the cache directory next to the ETag cache, not in the
// state directory: if it gets lost, the only cost is asking once too early.
// The name cannot collide with a cache file, those are hex digests.
func (u selfUpdater) statePath() string {
	return filepath.Join(cacheDir(), "selfupdate.json")
}

func (u selfUpdater) loadState() updateState {
	var st updateState
	readJSON(u.statePath(), &st) // a missing or broken file counts as none
	return st
}

func (u selfUpdater) saveState(st updateState) error {
	if err := os.MkdirAll(cacheDir(), 0o755); err != nil {
		return err
	}
	return writeJSON(u.statePath(), st)
}

// ------------------------------------------------------------------ The work

// check only looks and touches nothing.
func (u selfUpdater) check(w io.Writer) error {
	_, rel, err := u.latest()
	if err != nil {
		return err
	}
	if compareVer(rel.TagName, u.current) <= 0 {
		fmt.Fprintf(w, "%s %s is up to date\n", u.name, u.current)
		return nil
	}
	fmt.Fprintf(w, "%s %s is available, running %s\n", u.name, rel.TagName, u.current)
	if rel.HTMLURL != "" {
		fmt.Fprintf(w, "  %s\n", rel.HTMLURL)
	}
	fmt.Fprintf(w, "  run '%s --update' to install it\n", u.name)
	return nil
}

// install fetches the newest release and replaces the running file with it.
func (u selfUpdater) install(w io.Writer) error {
	c, rel, err := u.latest()
	if err != nil {
		return err
	}
	if compareVer(rel.TagName, u.current) <= 0 && !opt.force {
		fmt.Fprintf(w, "%s %s is up to date\n", u.name, u.current)
		return nil
	}

	want := fmt.Sprintf("%s-%s-%s", u.name, runtime.GOOS, runtime.GOARCH)
	var src *Asset
	for i := range rel.Assets {
		if rel.Assets[i].Name == want {
			src = &rel.Assets[i]
			break
		}
	}
	if src == nil {
		var have []string
		for _, a := range rel.Assets {
			have = append(have, a.Name)
		}
		return fmt.Errorf("release %s has no %q (only %s)", rel.TagName, want, strings.Join(have, ", "))
	}

	exe, err := os.Executable()
	if err != nil {
		return fmt.Errorf("cannot locate the running binary: %w", err)
	}
	// An installed upd may be a symlink into ./bin. What should be replaced is
	// the file behind it, not the link.
	if real, err := filepath.EvalSymlinks(exe); err == nil {
		exe = real
	}
	// Ask before the download, not after it: a missing write permission ought
	// to show up before a few megabytes have gone down the wire.
	if dir := filepath.Dir(exe); !writable(dir) {
		return fmt.Errorf("no write permission in %s (use sudo, or install upd elsewhere)", dir)
	}

	if opt.dryRun {
		fmt.Fprintf(w, "[dry-run] would install %s %s to %s\n", want, rel.TagName, exe)
		return nil
	}

	tmpdir, err := os.MkdirTemp("", "upd-self-")
	if err != nil {
		return err
	}
	defer os.RemoveAll(tmpdir)

	dl := filepath.Join(tmpdir, want)
	dlURL, dlHdr := c.assetURL(src)
	hdr := c.authHeaders()
	for k, v := range dlHdr {
		hdr[k] = v
	}
	fmt.Fprintf(w, "Downloading %s %s (%s) ...\n", want, rel.TagName, humanSize(src.Size))
	if err := downloadTo(dl, dlURL, hdr, src.Size); err != nil {
		return err
	}
	if st, err := os.Stat(dl); err == nil && src.Size > 0 && st.Size() < src.Size {
		return fmt.Errorf("incomplete download: %d of %d bytes", st.Size(), src.Size)
	}
	if err := verifyDownload(c, dl, src, rel.Assets, tmpdir); err != nil {
		return err
	}
	if err := os.Chmod(dl, 0o755); err != nil {
		return err
	}
	if err := u.probe(dl, rel.TagName); err != nil {
		return err
	}

	if err := installAtomic(dl, exe); err != nil {
		return err
	}
	stripQuarantine(exe)
	u.saveState(updateState{Checked: time.Now(), Latest: rel.TagName})

	fmt.Fprintf(w, "%s %s -> %s, at %s\n", u.name, u.current, rel.TagName, exe)
	return nil
}

// probe runs the freshly fetched binary once. That catches a file that is
// truncated, built for the wrong platform, or not executable in the first
// place, before it replaces the running one. The version flag is the built-in
// one, not spec.versionFlag(): what upd answers to is not the user's to
// configure here.
func (u selfUpdater) probe(path, tag string) error {
	got := installedVersion(path, &Spec{VersionFlag: "--version"})
	if got == "" {
		return fmt.Errorf("the downloaded binary does not run, %s left alone", u.name)
	}
	if got != normVer(tag) {
		return fmt.Errorf("the downloaded binary reports %s, expected %s", got, normVer(tag))
	}
	return nil
}

// latest asks the forge for the newest release, through the same code path an
// ordinary run uses, and notes down what came back.
func (u selfUpdater) latest() (*forgeCtx, *Release, error) {
	spec := &Spec{Repo: u.repo}
	c, err := newForgeCtx(spec)
	if err != nil {
		return nil, nil, err
	}
	rel, _, err := c.fetchRelease(spec)
	if err != nil {
		return nil, nil, err
	}
	if rel == nil { // --list on the command line: fetchRelease returns the list
		return nil, nil, fmt.Errorf("--list cannot be combined with --update")
	}

	// Every question that succeeds fills the note - no matter whether it came
	// from --update, from --check-update or from the background run.
	u.saveState(updateState{Checked: time.Now(), Latest: rel.TagName})
	return c, rel, nil
}

// ------------------------------------------------------------------ Numbers

// compareVer compares two versions component by component, numerically, so
// that 2.0.10 lands behind 2.0.9 and not in front of it. A leading "v" does not
// count, missing places count as 0 (2.1 == 2.1.0), and a suffix on the number
// makes the version older, not newer (2.0.6-rc1 < 2.0.6). The result is the one
// of strings.Compare: -1, 0, 1.
func compareVer(a, b string) int {
	as := strings.Split(normVer(a), ".")
	bs := strings.Split(normVer(b), ".")

	for i := 0; i < len(as) || i < len(bs); i++ {
		x, y := "0", "0"
		if i < len(as) {
			x = as[i]
		}
		if i < len(bs) {
			y = bs[i]
		}
		if c := compareVerPart(x, y); c != 0 {
			return c
		}
	}
	return 0
}

func compareVerPart(a, b string) int {
	na, ra := splitNum(a)
	nb, rb := splitNum(b)
	switch {
	case na != nb:
		if na < nb {
			return -1
		}
		return 1
	case ra == rb:
		return 0
	case ra == "": // 2.0.6 is finished, 2.0.6-rc1 is not yet
		return 1
	case rb == "":
		return -1
	}
	return strings.Compare(ra, rb)
}

// splitNum separates "10-rc1" into 10 and "-rc1".
func splitNum(s string) (int, string) {
	i := 0
	for i < len(s) && s[i] >= '0' && s[i] <= '9' {
		i++
	}
	n, _ := strconv.Atoi(s[:i])
	return n, s[i:]
}