// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package gzip

import (
	"bufio"
	"bytes"
	"io"
	"reflect"
	"testing"
	"time"
)

// TestEmpty tests that an empty payload still forms a valid GZIP stream.
func TestEmpty(t *testing.T) {
	buf := new(bytes.Buffer)

	if err := NewWriter(buf).Close(); err != nil {
		t.Fatalf("Writer.Close: %v", err)
	}

	r, err := NewReader(buf)
	if err != nil {
		t.Fatalf("NewReader: %v", err)
	}
	if want := (Header{OS: 255}); !reflect.DeepEqual(r.Header, want) {
		t.Errorf("Header mismatch:\ngot  %#v\nwant %#v", r.Header, want)
	}
	b, err := io.ReadAll(r)
	if err != nil {
		t.Fatalf("ReadAll: %v", err)
	}
	if len(b) != 0 {
		t.Fatalf("got %d bytes, want 0", len(b))
	}
	if err := r.Close(); err != nil {
		t.Fatalf("Reader.Close: %v", err)
	}
}

// TestRoundTrip tests that gzipping and then gunzipping is the identity
// function.
func TestRoundTrip(t *testing.T) {
	buf := new(bytes.Buffer)

	w := NewWriter(buf)
	w.Comment = "comment"
	w.Extra = []byte("extra")
	w.ModTime = time.Unix(1e8, 0)
	w.Name = "name"
	if _, err := w.Write([]byte("payload")); err != nil {
		t.Fatalf("Write: %v", err)
	}
	if err := w.Close(); err != nil {
		t.Fatalf("Writer.Close: %v", err)
	}

	r, err := NewReader(buf)
	if err != nil {
		t.Fatalf("NewReader: %v", err)
	}
	b, err := io.ReadAll(r)
	if err != nil {
		t.Fatalf("ReadAll: %v", err)
	}
	if string(b) != "payload" {
		t.Fatalf("payload is %q, want %q", string(b), "payload")
	}
	if r.Comment != "comment" {
		t.Fatalf("comment is %q, want %q", r.Comment, "comment")
	}
	if string(r.Extra) != "extra" {
		t.Fatalf("extra is %q, want %q", r.Extra, "extra")
	}
	if r.ModTime.Unix() != 1e8 {
		t.Fatalf("mtime is %d, want %d", r.ModTime.Unix(), uint32(1e8))
	}
	if r.Name != "name" {
		t.Fatalf("name is %q, want %q", r.Name, "name")
	}
	if err := r.Close(); err != nil {
		t.Fatalf("Reader.Close: %v", err)
	}
}

// TestLatin1 tests the internal functions for converting to and from Latin-1.
func TestLatin1(t *testing.T) {
	latin1 := []byte{0xc4, 'u', 0xdf, 'e', 'r', 'u', 'n', 'g', 0}
	utf8 := "Äußerung"
	z := Reader{r: bufio.NewReader(bytes.NewReader(latin1))}
	s, err := z.readString()
	if err != nil {
		t.Fatalf("readString: %v", err)
	}
	if s != utf8 {
		t.Fatalf("read latin-1: got %q, want %q", s, utf8)
	}

	buf := bytes.NewBuffer(make([]byte, 0, len(latin1)))
	c := Writer{w: buf}
	if err = c.writeString(utf8); err != nil {
		t.Fatalf("writeString: %v", err)
	}
	s = buf.String()
	if s != string(latin1) {
		t.Fatalf("write utf-8: got %q, want %q", s, string(latin1))
	}
}

// TestLatin1RoundTrip tests that metadata that is representable in Latin-1
// survives a round trip.
func TestLatin1RoundTrip(t *testing.T) {
	testCases := []struct {
		name string
		ok   bool
	}{
		{"", true},
		{"ASCII is OK", true},
		{"unless it contains a NUL\x00", false},
		{"no matter where \x00 occurs", false},
		{"\x00\x00\x00", false},
		{"Látin-1 also passes (U+00E1)", true},
		{"but LĀtin Extended-A (U+0100) does not", false},
		{"neither does 日本語", false},
		{"invalid UTF-8 also \xffails", false},
		{"\x00 as does Látin-1 with NUL", false},
	}
	for _, tc := range testCases {
		buf := new(bytes.Buffer)

		w := NewWriter(buf)
		w.Name = tc.name
		err := w.Close()
		if (err == nil) != tc.ok {
			t.Errorf("Writer.Close: name = %q, err = %v", tc.name, err)
			continue
		}
		if !tc.ok {
			continue
		}

		r, err := NewReader(buf)
		if err != nil {
			t.Errorf("NewReader: %v", err)
			continue
		}
		_, err = io.ReadAll(r)
		if err != nil {
			t.Errorf("ReadAll: %v", err)
			continue
		}
		if r.Name != tc.name {
			t.Errorf("name is %q, want %q", r.Name, tc.name)
			continue
		}
		if err := r.Close(); err != nil {
			t.Errorf("Reader.Close: %v", err)
			continue
		}
	}
}

func TestWriterFlush(t *testing.T) {
	buf := new(bytes.Buffer)

	w := NewWriter(buf)
	w.Comment = "comment"
	w.Extra = []byte("extra")
	w.ModTime = time.Unix(1e8, 0)
	w.Name = "name"

	n0 := buf.Len()
	if n0 != 0 {
		t.Fatalf("buffer size = %d before writes; want 0", n0)
	}

	if err := w.Flush(); err != nil {
		t.Fatal(err)
	}

	n1 := buf.Len()
	if n1 == 0 {
		t.Fatal("no data after first flush")
	}

	w.Write([]byte("x"))

	n2 := buf.Len()
	if n1 != n2 {
		t.Fatalf("after writing a single byte, size changed from %d to %d; want no change", n1, n2)
	}

	if err := w.Flush(); err != nil {
		t.Fatal(err)
	}

	n3 := buf.Len()
	if n2 == n3 {
		t.Fatal("Flush didn't flush any data")
	}

	if err := w.Close(); err != nil {
		t.Fatal(err)
	}

}

// Multiple gzip files concatenated form a valid gzip file.
func TestConcat(t *testing.T) {
	var buf bytes.Buffer
	w := NewWriter(&buf)
	w.Write([]byte("hello "))
	w.Close()
	w = NewWriter(&buf)
	w.Write([]byte("world\n"))
	w.Close()

	r, err := NewReader(&buf)
	if err != nil {
		t.Fatal(err)
	}
	data, err := io.ReadAll(r)
	if string(data) != "hello world\n" || err != nil {
		t.Fatalf("ReadAll = %q, %v, want %q, nil", data, err, "hello world")
	}
}

func TestWriterReset(t *testing.T) {
	buf := new(bytes.Buffer)
	buf2 := new(bytes.Buffer)
	z := NewWriter(buf)
	msg := []byte("hello world")
	z.Write(msg)
	z.Close()
	z.Reset(buf2)
	z.Write(msg)
	z.Close()
	if buf.String() != buf2.String() {
		t.Errorf("buf2 %q != original buf of %q", buf2.String(), buf.String())
	}
}

type limitedWriter struct {
	N int
}

func (l *limitedWriter) Write(p []byte) (n int, err error) {
	if n := l.N; n < len(p) {
		l.N = 0
		return n, io.ErrShortWrite
	}
	l.N -= len(p)
	return len(p), nil
}

// Write should never return more bytes than the input slice.
func TestLimitedWrite(t *testing.T) {
	msg := []byte("a")

	for lim := 2; lim < 20; lim++ {
		z := NewWriter(&limitedWriter{lim})
		if n, _ := z.Write(msg); n > len(msg) {
			t.Errorf("Write() = %d, want %d or less", n, len(msg))
		}

		z.Reset(&limitedWriter{lim})
		z.Header = Header{
			Comment: "comment",
			Extra:   []byte("extra"),
			ModTime: time.Now(),
			Name:    "name",
			OS:      1,
		}
		if n, _ := z.Write(msg); n > len(msg) {
			t.Errorf("Write() = %d, want %d or less", n, len(msg))
		}
	}
}