package fileutil

import (
	"context"
	"errors"
	"os"
	"path/filepath"
	"strings"
	"testing"
)

func TestWriteFileAtomicCreatesParentDirectory(t *testing.T) {
	path := filepath.Join(t.TempDir(), "nested", "artifact.txt")

	if err := WriteFileAtomic(path, []byte("artifact")); err != nil {
		t.Fatalf("WriteFileAtomic() error = %v", err)
	}

	data, err := os.ReadFile(path)
	if err != nil {
		t.Fatalf("ReadFile() error = %v", err)
	}
	if string(data) != "artifact" {
		t.Fatalf("data = %q, want artifact", data)
	}
	info, err := os.Stat(path)
	if err != nil || info.Mode().Perm() != 0o600 {
		t.Fatalf("output mode/error = %o/%v", info.Mode().Perm(), err)
	}
}

func TestWriteFileAtomicOverwritesTarget(t *testing.T) {
	path := filepath.Join(t.TempDir(), "artifact.txt")
	if err := WriteFileAtomic(path, []byte("old")); err != nil {
		t.Fatalf("WriteFileAtomic() initial error = %v", err)
	}

	if err := WriteFileAtomic(path, []byte("new")); err != nil {
		t.Fatalf("WriteFileAtomic() overwrite error = %v", err)
	}

	data, err := os.ReadFile(path)
	if err != nil {
		t.Fatalf("ReadFile() error = %v", err)
	}
	if string(data) != "new" {
		t.Fatalf("data = %q, want new", data)
	}
}

func TestWriteFileAtomicSupportsLongestFileName(t *testing.T) {
	directory := t.TempDir()
	name := strings.Repeat("a", maxFileNameBytes-len(".md")) + ".md"
	path := filepath.Join(directory, name)
	if err := os.WriteFile(path, []byte("old"), 0o600); err != nil {
		t.Fatal(err)
	}

	if err := WriteFileAtomic(path, []byte("new")); err != nil {
		t.Fatalf("WriteFileAtomic() error = %v", err)
	}
	data, err := os.ReadFile(path)
	if err != nil || string(data) != "new" {
		t.Fatalf("output/error = %q/%v", data, err)
	}
	info, err := os.Stat(path)
	if err != nil || info.Mode().Perm() != 0o600 {
		t.Fatalf("output mode/error = %o/%v", info.Mode().Perm(), err)
	}
	matches, err := filepath.Glob(filepath.Join(directory, ".weatherreporter-*.tmp"))
	if err != nil || len(matches) != 0 {
		t.Fatalf("temporary files/error = %v/%v", matches, err)
	}
}

func TestWriteFileAtomicRejectsUnsafeFinalDestinations(t *testing.T) {
	dir := t.TempDir()
	backing := filepath.Join(dir, "backing.md")
	if err := os.WriteFile(backing, []byte("old"), 0o600); err != nil {
		t.Fatal(err)
	}
	for _, tt := range []struct {
		name  string
		setup func(t *testing.T, path string)
	}{
		{
			name: "directory",
			setup: func(t *testing.T, path string) {
				t.Helper()
				if err := os.Mkdir(path, 0o755); err != nil {
					t.Fatal(err)
				}
			},
		},
		{
			name: "symbolic link",
			setup: func(t *testing.T, path string) {
				t.Helper()
				if err := os.Symlink(backing, path); err != nil {
					t.Fatal(err)
				}
			},
		},
	} {
		t.Run(tt.name, func(t *testing.T) {
			target := filepath.Join(dir, tt.name)
			tt.setup(t, target)
			before, err := os.Lstat(target)
			if err != nil {
				t.Fatal(err)
			}

			if err := WriteFileAtomic(target, []byte("new")); err == nil {
				t.Fatal("WriteFileAtomic() error = nil")
			}
			after, err := os.Lstat(target)
			if err != nil || after.Mode() != before.Mode() {
				t.Fatalf("target mode/error = %v/%v, want %v", after.Mode(), err, before.Mode())
			}
			matches, err := filepath.Glob(filepath.Join(dir, ".weatherreporter-*.tmp"))
			if err != nil || len(matches) != 0 {
				t.Fatalf("temporary files/error = %v/%v", matches, err)
			}
		})
	}
	data, err := os.ReadFile(backing)
	if err != nil || string(data) != "old" {
		t.Fatalf("symbolic link target/error = %q/%v", data, err)
	}
}

func TestWriteFileAtomicContextPreservesDestinationWhenCanceledAtPublication(t *testing.T) {
	path := filepath.Join(t.TempDir(), "artifact.txt")
	if err := os.WriteFile(path, []byte("old"), 0o600); err != nil {
		t.Fatal(err)
	}
	ctx, cancel := context.WithCancel(context.Background())
	cancel()

	err := WriteFileAtomicContext(ctx, path, []byte("new"))
	if !errors.Is(err, context.Canceled) {
		t.Fatalf("WriteFileAtomicContext() error = %v, want context cancellation", err)
	}
	data, readErr := os.ReadFile(path)
	if readErr != nil || string(data) != "old" {
		t.Fatalf("output/error = %q/%v", data, readErr)
	}
	matches, globErr := filepath.Glob(filepath.Join(filepath.Dir(path), ".weatherreporter-*.tmp"))
	if globErr != nil || len(matches) != 0 {
		t.Fatalf("temporary files/error = %v/%v", matches, globErr)
	}
}