package main

import (
	"bufio"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strings"
	"testing"

	"github.com/novox/mesh-controller/internal/link"
)

// The roles a copy of this test binary plays in TestAVerbRunsWhileItsBuildIsMovedOrDeleted.
const selfExecRole = "MESH_CONTROLLER_SELFEXEC_ROLE"

// TestSelfExecServer is a controller standing in, when run as one: it waits until its build has been
// moved, then runs a verb as the seat runs one, and prints what came of it as JSON.
func TestSelfExecServer(t *testing.T) {
	if os.Getenv(selfExecRole) != "server" {
		t.Skip("run by TestAVerbRunsWhileItsBuildIsMovedOrDeleted")
	}
	line, _ := bufio.NewReader(os.Stdin).ReadString('\n')
	if strings.TrimSpace(line) != "go" {
		t.Fatalf("told %q", line)
	}
	if err := os.Setenv(selfExecRole, "verb"); err != nil {
		t.Fatal(err)
	}
	answer, err := runVerb(t.Context(), []string{"-test.run", "^TestSelfExecVerb$", "-test.v"})
	said := map[string]any{"ok": answer.OK, "output": answer.Output}
	if err != nil {
		said["error"] = err.Error()
	}
	body, _ := json.Marshal(said)
	fmt.Println("ANSWER " + string(body))
}

// TestSelfExecVerb is the verb, when run as one.
func TestSelfExecVerb(t *testing.T) {
	if os.Getenv(selfExecRole) != "verb" {
		t.Skip("run by TestSelfExecServer")
	}
	fmt.Println("the verb ran")
}

// **A verb runs while the build it was started from is moved where its user may not go, or deleted**
// (novox/hq issue 289). The node-engine's witness moves a running controller's build into a directory
// only it may enter as it places the next, and deletes it once the next is proved; the controller
// still serving in between ran its verbs from the path and answered "permission denied".
//
// A copy of this test binary is the controller: started from one place, moved into a directory closed
// to everyone (or deleted), and only then asked to run a verb.
func TestAVerbRunsWhileItsBuildIsMovedOrDeleted(t *testing.T) {
	if runtime.GOOS != "linux" {
		t.Skip("the image is named through /proc on Linux only")
	}
	self, err := os.Executable()
	if err != nil {
		t.Fatal(err)
	}
	for _, how := range []string{"moved into a closed directory", "deleted"} {
		t.Run(how, func(t *testing.T) {
			root := t.TempDir()
			placed := filepath.Join(root, "mesh-controller", "mesh-controller")
			if err := os.MkdirAll(filepath.Dir(placed), 0o755); err != nil {
				t.Fatal(err)
			}
			copyFile(t, self, placed)

			server := exec.Command(placed, "-test.run", "^TestSelfExecServer$", "-test.v")
			server.Env = append(os.Environ(), selfExecRole+"=server")
			stdin, err := server.StdinPipe()
			if err != nil {
				t.Fatal(err)
			}
			stdout, err := server.StdoutPipe()
			if err != nil {
				t.Fatal(err)
			}
			server.Stderr = os.Stderr
			if err := server.Start(); err != nil {
				t.Fatal(err)
			}
			t.Cleanup(func() { _ = server.Process.Kill(); _ = server.Wait() })

			// What the witness does to a running build, once the process runs.
			switch how {
			case "deleted":
				if err := os.RemoveAll(filepath.Dir(placed)); err != nil {
					t.Fatal(err)
				}
			default:
				kept := filepath.Join(root, ".witness", "mesh-controller", "previous")
				if err := os.MkdirAll(filepath.Dir(kept), 0o700); err != nil {
					t.Fatal(err)
				}
				if err := os.Rename(filepath.Dir(placed), kept); err != nil {
					t.Fatal(err)
				}
				if err := os.Chmod(filepath.Join(root, ".witness"), 0); err != nil {
					t.Fatal(err)
				}
				t.Cleanup(func() { _ = os.Chmod(filepath.Join(root, ".witness"), 0o700) })
			}
			if _, err := io.WriteString(stdin, "go\n"); err != nil {
				t.Fatal(err)
			}
			out, _ := io.ReadAll(stdout)
			_ = server.Wait()
			var said struct {
				OK     bool   `json:"ok"`
				Output string `json:"output"`
				Error  string `json:"error"`
			}
			found := false
			for _, line := range strings.Split(string(out), "\n") {
				if rest, ok := strings.CutPrefix(line, "ANSWER "); ok {
					found = json.Unmarshal([]byte(rest), &said) == nil
				}
			}
			if !found {
				t.Fatalf("the controller standing in answered nothing:\n%s", out)
			}
			if said.Error != "" || !said.OK || !strings.Contains(said.Output, "the verb ran") {
				t.Fatalf("the verb did not run from the controller's own image after its build was %s: %+v", how, said)
			}
		})
	}
}

// A verb the controller cannot start from its own build is refused as a handover — marked so its
// caller asks again — never a permission error; and so is one arriving once the controller is stopping.
func TestAVerbThatCannotRunIsRefusedAsAHandover(t *testing.T) {
	closed := filepath.Join(t.TempDir(), "closed")
	if err := os.MkdirAll(closed, 0o700); err != nil {
		t.Fatal(err)
	}
	was := ownImage
	ownImage = func() string { return filepath.Join(closed, "gone", "mesh-controller") }
	t.Cleanup(func() { ownImage = was })
	_, err := runVerb(t.Context(), []string{"status"})
	if !errors.Is(err, link.ErrHandingOver) {
		t.Fatalf("a build that is not there was answered %v, not a handover", err)
	}

	ownImage = was
	handingOver.Store(true)
	t.Cleanup(func() { handingOver.Store(false) })
	if _, err := runVerb(t.Context(), []string{"-test.run", "^$"}); !errors.Is(err, link.ErrHandingOver) {
		t.Fatalf("a controller stopping ran a verb: %v", err)
	}
}

func copyFile(t *testing.T, from, to string) {
	t.Helper()
	in, err := os.Open(from)
	if err != nil {
		t.Fatal(err)
	}
	defer in.Close()
	out, err := os.OpenFile(to, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o755)
	if err != nil {
		t.Fatal(err)
	}
	if _, err := io.Copy(out, in); err != nil {
		t.Fatal(err)
	}
	if err := out.Close(); err != nil {
		t.Fatal(err)
	}
}