package layer

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"testing"

	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
	oidtest "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id/test"
	"github.com/stretchr/testify/require"
)

type readerInitiatorMock struct {
	parts map[oid.ID][]byte
}

func (r *readerInitiatorMock) initFrostFSObjectPayloadReader(_ context.Context, p getFrostFSParams) (io.Reader, error) {
	partPayload, ok := r.parts[p.oid]
	if !ok {
		return nil, errors.New("part not found")
	}

	if p.off+p.ln == 0 {
		return bytes.NewReader(partPayload), nil
	}

	if p.off > uint64(len(partPayload)-1) {
		return nil, fmt.Errorf("invalid offset: %d/%d", p.off, len(partPayload))
	}

	if p.off+p.ln > uint64(len(partPayload)) {
		return nil, fmt.Errorf("invalid range: %d-%d/%d", p.off, p.off+p.ln, len(partPayload))
	}

	return bytes.NewReader(partPayload[p.off : p.off+p.ln]), nil
}

func prepareDataReader() ([]byte, []partObj, *readerInitiatorMock) {
	mockInitReader := &readerInitiatorMock{
		parts: map[oid.ID][]byte{
			oidtest.ID(): []byte("first part 1"),
			oidtest.ID(): []byte("second part 2"),
			oidtest.ID(): []byte("third part 3"),
		},
	}

	var fullPayload []byte
	parts := make([]partObj, 0, len(mockInitReader.parts))
	for id, payload := range mockInitReader.parts {
		parts = append(parts, partObj{OID: id, Size: uint64(len(payload))})
		fullPayload = append(fullPayload, payload...)
	}

	return fullPayload, parts, mockInitReader
}

func TestMultiReader(t *testing.T) {
	ctx := context.Background()

	fullPayload, parts, mockInitReader := prepareDataReader()

	for _, tc := range []struct {
		name string
		off  uint64
		ln   uint64
		err  error
	}{
		{
			name: "simple read all",
		},
		{
			name: "simple read with length",
			ln:   uint64(len(fullPayload)),
		},
		{
			name: "middle of parts",
			off:  parts[0].Size + 2,
			ln:   4,
		},
		{
			name: "first and second",
			off:  parts[0].Size - 4,
			ln:   8,
		},
		{
			name: "first and third",
			off:  parts[0].Size - 4,
			ln:   parts[1].Size + 8,
		},
		{
			name: "offset out of range",
			off:  uint64(len(fullPayload) + 1),
			ln:   1,
			err:  errOffsetIsOutOfRange,
		},
		{
			name: "zero length",
			off:  parts[1].Size + 1,
			ln:   0,
			err:  errorZeroRangeLength,
		},
	} {
		t.Run(tc.name, func(t *testing.T) {
			multiReader, err := newMultiObjectReader(ctx, multiObjectReaderConfig{
				layer: mockInitReader,
				parts: parts,
				off:   tc.off,
				ln:    tc.ln,
			})
			require.ErrorIs(t, err, tc.err)

			if tc.err == nil {
				off := tc.off
				ln := tc.ln
				if off+ln == 0 {
					ln = uint64(len(fullPayload))
				}
				data, err := io.ReadAll(multiReader)
				require.NoError(t, err)
				require.Equal(t, fullPayload[off:off+ln], data)
			}
		})
	}
}