// Package gocacheplugin has no source of its own: this repo exists only to
// build the pinned upstream go-cache-plugin and ship it as a release. The tests
// therefore exercise the built binary rather than any local code.
package gocacheplugin

import (
	"debug/buildinfo"
	"debug/elf"
	"fmt"
	"io"
	"net/http"
	"net/http/httptest"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"sync/atomic"
	"testing"
)

const (
	upstreamPkg    = "github.com/tailscale/go-cache-plugin/cmd/go-cache-plugin"
	upstreamModule = "github.com/tailscale/go-cache-plugin"
)

var pluginBin string

func TestMain(m *testing.M) {
	dir, err := os.MkdirTemp("", "go-cache-plugin-test")
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
	pluginBin = filepath.Join(dir, "go-cache-plugin")
	build := exec.Command("go", "build", "-ldflags=-s -w", "-o", pluginBin, upstreamPkg)
	build.Env = append(os.Environ(), "CGO_ENABLED=0")
	if out, err := build.CombinedOutput(); err != nil {
		fmt.Fprintf(os.Stderr, "building %s: %v\n%s", upstreamPkg, err, out)
		_ = os.RemoveAll(dir)
		os.Exit(1)
	}
	code := m.Run()
	_ = os.RemoveAll(dir)
	os.Exit(code)
}

// A dynamically linked binary will not run on the estate's Alpine-based CI
// images, so CGO_ENABLED=0 must actually take effect.
func TestBinaryIsStatic(t *testing.T) {
	fi, err := os.Stat(pluginBin)
	if err != nil {
		t.Fatal(err)
	}
	if fi.Size() == 0 {
		t.Fatal("binary is empty")
	}
	f, err := elf.Open(pluginBin)
	if err != nil {
		t.Fatal(err)
	}
	defer func() { _ = f.Close() }()
	if s := f.Section(".interp"); s != nil {
		t.Error("binary has a .interp section, so it needs a dynamic loader")
	}
	libs, err := f.ImportedLibraries()
	if err != nil {
		t.Fatal(err)
	}
	if len(libs) != 0 {
		t.Errorf("binary links shared libraries: %v", libs)
	}
}

// The binary must come from the version go.mod pins, not from whatever the
// toolchain would resolve on its own.
func TestBuiltFromPinnedVersion(t *testing.T) {
	out, err := exec.Command("go", "list", "-m", "-f", "{{.Version}}", upstreamModule).Output()
	if err != nil {
		t.Fatal(err)
	}
	want := strings.TrimSpace(string(out))
	if want == "" {
		t.Fatalf("%s is not in the module graph", upstreamModule)
	}

	info, err := buildinfo.ReadFile(pluginBin)
	if err != nil {
		t.Fatal(err)
	}
	got := info.Main.Version
	for _, dep := range info.Deps {
		if dep.Path == upstreamModule {
			got = dep.Version
		}
	}
	if got != want {
		t.Errorf("binary built from %s %q, go.mod pins %q", upstreamModule, got, want)
	}
}

// Sanity check that the real entry point runs and parses flags: without a
// bucket the cache server must refuse to start.
func TestRequiresBucket(t *testing.T) {
	cmd := exec.Command(pluginBin, "--cache-dir="+t.TempDir())
	out, err := cmd.CombinedOutput()
	if err == nil {
		t.Fatalf("expected a non-zero exit, got success:\n%s", out)
	}
	if !strings.Contains(string(out), "--bucket") {
		t.Errorf("expected a usage error naming --bucket, got:\n%s", out)
	}
}

// End to end: drive a real `go build` through the binary as a GOCACHEPROG
// plugin, pointed at a stub S3 endpoint that misses every read. This is the
// only thing the repo ships, so it has to actually speak the protocol.
func TestServesGoCacheProg(t *testing.T) {
	var reqs atomic.Int64
	s3 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		reqs.Add(1)
		if r.Method == http.MethodPut || r.Method == http.MethodPost {
			_, _ = io.Copy(io.Discard, r.Body)
			w.WriteHeader(http.StatusOK)
			return
		}
		w.Header().Set("Content-Type", "application/xml")
		w.WriteHeader(http.StatusNotFound)
		_, _ = io.WriteString(w, `<?xml version="1.0" encoding="UTF-8"?><Error><Code>NoSuchKey</Code><Message>no such key</Message></Error>`)
	}))
	defer s3.Close()

	cacheDir := t.TempDir()
	src := t.TempDir()
	write(t, filepath.Join(src, "go.mod"), "module example.test\n\ngo 1.26.1\n")
	write(t, filepath.Join(src, "main.go"), "package main\n\nfunc main() { println(\"ok\") }\n")

	prog := strings.Join([]string{
		pluginBin,
		"--cache-dir=" + cacheDir,
		"--bucket=go-cache-test",
		"--region=us-east-1",
		"--s3-endpoint-url=" + s3.URL,
		"--s3-path-style",
	}, " ")

	build := exec.Command("go", "build", "-o", filepath.Join(src, "out"), ".")
	build.Dir = src
	build.Env = append(os.Environ(),
		"GOFLAGS=",
		"GOCACHEPROG="+prog,
		"AWS_ACCESS_KEY_ID=test",
		"AWS_SECRET_ACCESS_KEY=test",
	)
	if out, err := build.CombinedOutput(); err != nil {
		t.Fatalf("go build under GOCACHEPROG failed: %v\n%s", err, out)
	}
	if _, err := os.Stat(filepath.Join(src, "out")); err != nil {
		t.Fatalf("build produced no binary: %v", err)
	}
	if n := countFiles(t, cacheDir); n == 0 {
		t.Error("plugin staged nothing in the local cache directory")
	}
	if reqs.Load() == 0 {
		t.Error("plugin made no S3 requests")
	}
}

func write(t *testing.T, path, content string) {
	t.Helper()
	if err := os.WriteFile(path, []byte(content), 0o644); err != nil {
		t.Fatal(err)
	}
}

func countFiles(t *testing.T, dir string) int {
	t.Helper()
	var n int
	err := filepath.WalkDir(dir, func(_ string, d os.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if !d.IsDir() {
			n++
		}
		return nil
	})
	if err != nil {
		t.Fatal(err)
	}
	return n
}