package content

import (
	"bytes"
	"context"
	"io"
	"strings"
	"testing"

	"github.com/containerd/containerd/errdefs"
	"github.com/gotestyourself/gotestyourself/assert"
	is "github.com/gotestyourself/gotestyourself/assert/cmp"
	"github.com/opencontainers/go-digest"
)

type copySource struct {
	reader io.Reader
	size   int64
	digest digest.Digest
}

func TestCopy(t *testing.T) {
	defaultSource := newCopySource("this is the source to copy")

	var testcases = []struct {
		name     string
		source   copySource
		writer   fakeWriter
		expected string
	}{
		{
			name:     "copy no offset",
			source:   defaultSource,
			writer:   fakeWriter{},
			expected: "this is the source to copy",
		},
		{
			name:     "copy with offset from seeker",
			source:   defaultSource,
			writer:   fakeWriter{status: Status{Offset: 8}},
			expected: "the source to copy",
		},
		{
			name:     "copy with offset from unseekable source",
			source:   copySource{reader: bytes.NewBufferString("foobar"), size: 6},
			writer:   fakeWriter{status: Status{Offset: 3}},
			expected: "bar",
		},
		{
			name:   "commit already exists",
			source: defaultSource,
			writer: fakeWriter{commitFunc: func() error {
				return errdefs.ErrAlreadyExists
			}},
		},
	}

	for _, testcase := range testcases {
		t.Run(testcase.name, func(t *testing.T) {
			err := Copy(context.Background(),
				&testcase.writer,
				testcase.source.reader,
				testcase.source.size,
				testcase.source.digest)

			assert.NilError(t, err)
			assert.Check(t, is.Equal(testcase.source.digest, testcase.writer.commitedDigest))
			assert.Check(t, is.Equal(testcase.expected, testcase.writer.String()))
		})
	}
}

func newCopySource(raw string) copySource {
	return copySource{
		reader: strings.NewReader(raw),
		size:   int64(len(raw)),
		digest: digest.FromBytes([]byte(raw)),
	}
}

type fakeWriter struct {
	bytes.Buffer
	commitedDigest digest.Digest
	status         Status
	commitFunc     func() error
}

func (f *fakeWriter) Close() error {
	f.Buffer.Reset()
	return nil
}

func (f *fakeWriter) Commit(ctx context.Context, size int64, expected digest.Digest, opts ...Opt) error {
	f.commitedDigest = expected
	if f.commitFunc == nil {
		return nil
	}
	return f.commitFunc()
}

func (f *fakeWriter) Digest() digest.Digest {
	return f.commitedDigest
}

func (f *fakeWriter) Status() (Status, error) {
	return f.status, nil
}

func (f *fakeWriter) Truncate(size int64) error {
	f.Buffer.Truncate(int(size))
	return nil
}