package util

import (
	"os"
	"path/filepath"
	"testing"
)

func TestAtomicWriteFile(t *testing.T) {
	tests := []struct {
		name     string
		existing string
		data     []byte
		perm     os.FileMode
	}{
		{"a new file", "", []byte("hello"), 0644},
		{"replacing a shorter file", "old", []byte("a much longer set of contents"), 0644},
		{"replacing a longer file", "a much longer set of contents", []byte("new"), 0644},
		{"an empty payload", "something", []byte{}, 0644},
		{"a nil payload", "something", nil, 0644},
		{"a private mode", "", []byte("secret"), 0600},
		{"an executable mode", "", []byte("#!/bin/sh\n"), 0755},
		{"binary contents", "", []byte{0x00, 0xff, 0x10, 0x00}, 0644},
	}

	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			directory := t.TempDir()
			path := filepath.Join(directory, "target")

			if test.existing != "" {
				if err := os.WriteFile(path, []byte(test.existing), 0666); err != nil {
					t.Fatalf("could not write the file to be replaced: %v", err)
				}
			}

			if err := AtomicWriteFile(path, test.data, test.perm); err != nil {
				t.Fatalf("did not expect an error, got %v", err)
			}

			written, err := os.ReadFile(path)
			if err != nil {
				t.Fatalf("could not read the file back: %v", err)
			}
			if string(written) != string(test.data) {
				t.Errorf("expected contents %q got %q", string(test.data), string(written))
			}

			info, err := os.Stat(path)
			if err != nil {
				t.Fatalf("could not look at the file: %v", err)
			}
			if info.Mode().Perm() != test.perm {
				t.Errorf("expected mode %v got %v", test.perm, info.Mode().Perm())
			}

			entries, err := os.ReadDir(directory)
			if err != nil {
				t.Fatalf("could not list the directory: %v", err)
			}
			if len(entries) != 1 {
				names := make([]string, 0, len(entries))
				for _, entry := range entries {
					names = append(names, entry.Name())
				}
				t.Errorf("expected only the target file to be left, got %v", names)
			}
		})
	}
}

func TestAtomicWriteFileReportsAMissingDirectory(t *testing.T) {
	path := filepath.Join(t.TempDir(), "not-there", "target")

	if err := AtomicWriteFile(path, []byte("hello"), 0644); err == nil {
		t.Errorf("expected an error for a directory that does not exist")
	}
}

func TestAtomicWriteFileLeavesTheOldFileAloneOnFailure(t *testing.T) {
	directory := t.TempDir()
	path := filepath.Join(directory, "target")

	if err := os.WriteFile(path, []byte("original"), 0644); err != nil {
		t.Fatalf("could not write the file to be replaced: %v", err)
	}

	// A directory that cannot be written to means the temporary file cannot
	// be created, so the write has to fail before anything is replaced.
	if err := os.Chmod(directory, 0500); err != nil {
		t.Fatalf("could not change the directory mode: %v", err)
	}
	defer os.Chmod(directory, 0700)

	if os.Geteuid() == 0 {
		t.Skip("running as root, which ignores the directory mode")
	}

	if err := AtomicWriteFile(path, []byte("replacement"), 0644); err == nil {
		t.Fatalf("expected an error for a directory that cannot be written to")
	}

	existing, err := os.ReadFile(path)
	if err != nil {
		t.Fatalf("could not read the file back: %v", err)
	}
	if string(existing) != "original" {
		t.Errorf("expected the original contents to survive, got %q", string(existing))
	}
}