package files

import (
	"errors"
	"io/fs"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"testing"

	"github.com/stretchr/testify/require"
)

type failingReader struct {
	sent bool
}

func (r *failingReader) Read(buffer []byte) (int, error) {
	if !r.sent {
		r.sent = true
		return copy(buffer, "partial"), nil
	}
	return 0, errors.New("copy failed")
}

type closeFailingFile struct {
	*os.File
}

func (f *closeFailingFile) Close() error {
	_ = f.File.Close()
	return errors.New("close failed")
}

func TestSaveStoresFileUnderProjectIdentityWithOpaqueKey(t *testing.T) {
	service := NewService(t.TempDir())
	projectIdentity := "019b0000-0000-7000-8000-000000000012"

	stored, err := service.Save(projectIdentity, "brief.md", strings.NewReader("hello"))

	require.NoError(t, err)
	require.Equal(t, "brief.md", stored.OriginalName)
	require.Contains(t, stored.RelativePath, "projects/"+projectIdentity+"/")
	require.NotContains(t, stored.RelativePath, "projects/12/")
	require.Regexp(t, `^[a-f0-9]{32}$`, stored.StorageKey)
	require.Equal(t, stored.StorageKey, filepath.Base(stored.RelativePath))
	require.FileExists(t, stored.AbsolutePath)
}

func TestSaveNeutralizesPathTraversal(t *testing.T) {
	service := NewService(t.TempDir())

	stored, err := service.Save("019b0000-0000-7000-8000-000000000012", "..\\..\\secret.txt", strings.NewReader("hello"))

	require.NoError(t, err)
	require.Equal(t, "secret.txt", stored.OriginalName)
	require.NotContains(t, stored.RelativePath, "secret.txt")
}

func TestSaveRemovesTemporaryAndPartialFilesWhenCopyFails(t *testing.T) {
	storageRoot := t.TempDir()
	service := NewService(storageRoot)

	_, err := service.Save("019b0000-0000-7000-8000-000000000012", "broken.bin", &failingReader{})

	require.ErrorContains(t, err, "copy failed")
	requireNoStoredFiles(t, storageRoot)
}

func TestSaveRemovesTemporaryFileWhenCloseFails(t *testing.T) {
	storageRoot := t.TempDir()
	service := NewService(storageRoot)
	service.createTemp = func(directory, pattern string) (stagedFile, error) {
		file, err := os.CreateTemp(directory, pattern)
		if err != nil {
			return nil, err
		}
		return &closeFailingFile{File: file}, nil
	}

	_, err := service.Save("019b0000-0000-7000-8000-000000000012", "broken.bin", strings.NewReader("content"))

	require.ErrorContains(t, err, "close failed")
	requireNoStoredFiles(t, storageRoot)
}

func TestSaveCollisionNeverOverwritesOrDeletesExistingFile(t *testing.T) {
	storageRoot := t.TempDir()
	service := NewService(storageRoot)
	service.newStorageKey = func() (string, error) { return "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", nil }
	projectIdentity := "019b0000-0000-7000-8000-000000000012"
	first, err := service.Save(projectIdentity, "first.bin", strings.NewReader("first owner"))
	require.NoError(t, err)

	_, err = service.Save(projectIdentity, "second.bin", strings.NewReader("second owner"))

	require.ErrorIs(t, err, ErrStorageKeyCollision)
	content, readErr := os.ReadFile(first.AbsolutePath)
	require.NoError(t, readErr)
	require.Equal(t, "first owner", string(content))
	requireOnlyStoredFile(t, storageRoot, first.AbsolutePath)
}

func TestConcurrentSaveWithSameKeyPublishesExactlyOneOwner(t *testing.T) {
	storageRoot := t.TempDir()
	service := NewService(storageRoot)
	service.newStorageKey = func() (string, error) { return "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb", nil }
	projectIdentity := "019b0000-0000-7000-8000-000000000012"
	start := make(chan struct{})
	type result struct {
		stored StoredFile
		err    error
	}
	results := make(chan result, 2)
	var ready sync.WaitGroup
	ready.Add(2)
	for _, body := range []string{"alpha", "beta"} {
		go func(content string) {
			ready.Done()
			<-start
			stored, err := service.Save(projectIdentity, content+".bin", strings.NewReader(content))
			results <- result{stored: stored, err: err}
		}(body)
	}
	ready.Wait()
	close(start)
	firstResult, secondResult := <-results, <-results

	errors := []error{firstResult.err, secondResult.err}
	require.Equal(t, 1, countNilErrors(errors))
	require.Equal(t, 1, countMatchingErrors(errors, ErrStorageKeyCollision))
	winner := firstResult.stored
	if firstResult.err != nil {
		winner = secondResult.stored
	}
	require.FileExists(t, winner.AbsolutePath)
	requireOnlyStoredFile(t, storageRoot, winner.AbsolutePath)
}

func requireNoStoredFiles(t *testing.T, storageRoot string) {
	t.Helper()
	require.NoError(t, filepath.WalkDir(storageRoot, func(path string, entry fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if path != storageRoot && !entry.IsDir() {
			t.Fatalf("unexpected stored file after failure: %s", path)
		}
		return nil
	}))
}

func requireOnlyStoredFile(t *testing.T, storageRoot, expectedPath string) {
	t.Helper()
	files := []string{}
	require.NoError(t, filepath.WalkDir(storageRoot, func(path string, entry fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if !entry.IsDir() {
			files = append(files, path)
		}
		return nil
	}))
	require.Equal(t, []string{expectedPath}, files)
}

func countNilErrors(values []error) int {
	count := 0
	for _, err := range values {
		if err == nil {
			count++
		}
	}
	return count
}

func countMatchingErrors(values []error, target error) int {
	count := 0
	for _, err := range values {
		if errors.Is(err, target) {
			count++
		}
	}
	return count
}