package upgrade

import (
	"os"
	"path/filepath"
	"reflect"
	"sort"
	"testing"
	"time"
)

// deliver writes a version as a delivery would: a directory named for it with the binary inside.
// at fixes when it arrived, because "newest" is when it arrived and a test must not race the clock.
func deliver(t *testing.T, dir, version string, at time.Time) string {
	t.Helper()
	into := filepath.Join(dir, version)
	if err := os.MkdirAll(into, 0o755); err != nil {
		t.Fatal(err)
	}
	binary := filepath.Join(into, BinaryName)
	if err := os.WriteFile(binary, []byte("#!/bin/sh\nexit 0\n"), 0o755); err != nil {
		t.Fatal(err)
	}
	if err := os.Chtimes(binary, at, at); err != nil {
		t.Fatal(err)
	}
	if err := os.Chtimes(into, at, at); err != nil {
		t.Fatal(err)
	}
	return binary
}

// **Newest is when it arrived, not how its name sorts.**
//
// A version string is whatever the source was tagged or described as, and those do not sort: "1.10"
// orders before "1.9", and a commit hash orders before either. Ordering by name would start an older
// host and call that an upgrade.
func TestNewestIsWhenItArrivedAndNotHowItSorts(t *testing.T) {
	dir := t.TempDir()
	base := time.Now().Add(-time.Hour)
	deliver(t, dir, "1.10", base)                 // sorts LAST by name, arrived first
	deliver(t, dir, "1.9", base.Add(time.Minute)) // sorts first by name, arrived last

	got, err := Versions(dir)
	if err != nil {
		t.Fatal(err)
	}
	if len(got) != 2 || got[0].Version != "1.9" {
		t.Fatalf("newest is %+v, want the one that arrived last (1.9)", got)
	}
}

// A delivery that was interrupted leaves a directory with no executable in it. Running "the newest"
// would then mean running nothing, so it is not a version.
func TestADirectoryWithNoBinaryIsNotAVersion(t *testing.T) {
	dir := t.TempDir()
	if err := os.MkdirAll(filepath.Join(dir, "half-delivered"), 0o755); err != nil {
		t.Fatal(err)
	}
	deliver(t, dir, "good", time.Now().Add(-time.Hour))

	got, err := Versions(dir)
	if err != nil {
		t.Fatal(err)
	}
	if len(got) != 1 || got[0].Version != "good" {
		t.Fatalf("versions are %+v, want only the one with a binary", got)
	}
}

// Nothing delivered is not a fault. A machine whose host was placed by hand has no versions
// directory at all, and that must read as "no successor" rather than as an error that stops a
// reconcile.
func TestNoVersionsDirectoryIsNotAnError(t *testing.T) {
	got, err := Versions(filepath.Join(t.TempDir(), "absent"))
	if err != nil {
		t.Fatalf("an absent versions directory should not be an error: %v", err)
	}
	if len(got) != 0 {
		t.Fatalf("versions are %+v, want none", got)
	}
}

func TestTheNewestVersionIsTheSuccessorAndTheRunningOneIsNot(t *testing.T) {
	dir := t.TempDir()
	base := time.Now().Add(-time.Hour)
	deliver(t, dir, "one", base)
	deliver(t, dir, "two", base.Add(time.Minute))

	next, yes, err := Successor(dir, "one")
	if err != nil {
		t.Fatal(err)
	}
	if !yes || next.Version != "two" {
		t.Fatalf("successor is %+v (%v), want two", next, yes)
	}

	if _, yes, err := Successor(dir, "two"); err != nil || yes {
		t.Fatalf("the newest version is its own successor (%v, %v)", yes, err)
	}
}

// A host put there by hand, before any of this existed, is not among the delivered versions. What the
// mesh delivered is what it asked for, so that is a successor — otherwise the first delivery to such a
// machine would be ignored for ever, which is every machine in this mesh today.
func TestAHostThatWasNeverDeliveredHasASuccessor(t *testing.T) {
	dir := t.TempDir()
	deliver(t, dir, "delivered", time.Now().Add(-time.Hour))

	next, yes, err := Successor(dir, "copied-by-hand")
	if err != nil {
		t.Fatal(err)
	}
	if !yes || next.Version != "delivered" {
		t.Fatalf("successor is %+v (%v), want the delivered one", next, yes)
	}
}

// The running version and its predecessor are kept, and nothing else. The predecessor is exactly what
// a rollback starts; everything older has no reader.
func TestRetireKeepsTheRunningVersionAndItsPredecessor(t *testing.T) {
	dir := t.TempDir()
	base := time.Now().Add(-4 * time.Hour)
	for i, v := range []string{"one", "two", "three", "four"} {
		deliver(t, dir, v, base.Add(time.Duration(i)*time.Hour))
	}

	removed, err := Retire(dir, "four")
	if err != nil {
		t.Fatal(err)
	}
	sort.Strings(removed)
	if !reflect.DeepEqual(removed, []string{"one", "two"}) {
		t.Fatalf("retired %v, want one and two — three is the predecessor a rollback needs", removed)
	}
	for _, kept := range []string{"three", "four"} {
		if _, err := os.Stat(filepath.Join(dir, kept, BinaryName)); err != nil {
			t.Fatalf("%s was retired and a rollback now has nowhere to go: %v", kept, err)
		}
	}
}

// **Never the running version, whatever it is asked.** A host that deleted its own image would run
// until it stopped and then be unstartable, and the launcher's rollback reads a version rather than a
// process.
func TestRetireNeverRemovesTheRunningVersion(t *testing.T) {
	dir := t.TempDir()
	base := time.Now().Add(-2 * time.Hour)
	deliver(t, dir, "older", base)
	deliver(t, dir, "newer", base.Add(time.Hour))

	// Asked while running the OLDER one, which is what a machine looks like between a delivery and
	// the moment it stands aside.
	if _, err := Retire(dir, "older"); err != nil {
		t.Fatal(err)
	}
	if _, err := os.Stat(filepath.Join(dir, "older", BinaryName)); err != nil {
		t.Fatalf("the running version was retired: %v", err)
	}
}

// A machine running a hand-placed host keeps the newest delivered version, because that is what a
// rollback would reach for. Retiring it would leave the machine with no way back at all.
func TestRetireKeepsTheNewestWhenTheRunningVersionWasNeverDelivered(t *testing.T) {
	dir := t.TempDir()
	base := time.Now().Add(-3 * time.Hour)
	deliver(t, dir, "old", base)
	deliver(t, dir, "new", base.Add(time.Hour))

	removed, err := Retire(dir, "copied-by-hand")
	if err != nil {
		t.Fatal(err)
	}
	if !reflect.DeepEqual(removed, []string{"old"}) {
		t.Fatalf("retired %v, want only old — new is the rollback target", removed)
	}
	if _, err := os.Stat(filepath.Join(dir, "new", BinaryName)); err != nil {
		t.Fatalf("the only delivered version was retired: %v", err)
	}
}