From ec818aef816a56029f55c90ee2045975f3372092 Mon Sep 17 00:00:00 2001
From: John Adler <adlerjohn@users.noreply.github.com>
Date: Tue, 14 Jun 2022 13:25:44 -0400
Subject: [PATCH] Export `SetCell` and `GetCell`. (#92)

* Export SetCells.

* Make SetCell panic on trying to set non-nil cell. Add internal setCell that doesn't have this check.
---
 datasquare.go                 | 21 +++++++++++++++++----
 extendeddatacrossword.go      |  2 +-
 extendeddatacrossword_test.go |  8 ++++----
 3 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/datasquare.go b/datasquare.go
index 5c0a3cf..9af39e1 100644
--- a/datasquare.go
+++ b/datasquare.go
@@ -2,6 +2,7 @@ package rsmt2d
 
 import (
 	"errors"
+	"fmt"
 	"math"
 )
 
@@ -117,7 +118,7 @@ func (ds *dataSquare) rowSlice(x uint, y uint, length uint) [][]byte {
 }
 
 // row returns a row slice.
-// Do not modify this slice directly, instead use setCell.
+// Do not modify this slice directly, instead use SetCell.
 func (ds *dataSquare) row(x uint) [][]byte {
 	return ds.rowSlice(x, 0, ds.width)
 }
@@ -144,7 +145,7 @@ func (ds *dataSquare) colSlice(x uint, y uint, length uint) [][]byte {
 }
 
 // col returns a column slice.
-// Do not modify this slice directly, instead use setCell.
+// Do not modify this slice directly, instead use SetCell.
 func (ds *dataSquare) col(y uint) [][]byte {
 	return ds.colSlice(0, y, ds.width)
 }
@@ -231,8 +232,8 @@ func (ds *dataSquare) getColRoot(y uint) []byte {
 	return tree.Root()
 }
 
-// getCell returns a copy of single chunk at a specific cell.
-func (ds *dataSquare) getCell(x uint, y uint) []byte {
+// GetCell returns a copy of a specific cell.
+func (ds *dataSquare) GetCell(x uint, y uint) []byte {
 	if ds.squareRow[x][y] == nil {
 		return nil
 	}
@@ -241,6 +242,18 @@ func (ds *dataSquare) getCell(x uint, y uint) []byte {
 	return cell
 }
 
+// SetCell sets a specific cell. Cell to set must be `nil`.
+// Panics if attempting to set a cell that is not `nil`.
+func (ds *dataSquare) SetCell(x uint, y uint, newChunk []byte) {
+	if ds.squareRow[x][y] != nil {
+		panic(fmt.Sprintf("cannot set cell (%d, %d) as it already has a value %x", x, y, ds.squareRow[x][y]))
+	}
+	ds.squareRow[x][y] = newChunk
+	ds.squareCol[y][x] = newChunk
+	ds.resetRoots()
+}
+
+// setCell sets a specific cell.
 func (ds *dataSquare) setCell(x uint, y uint, newChunk []byte) {
 	ds.squareRow[x][y] = newChunk
 	ds.squareCol[y][x] = newChunk
diff --git a/extendeddatacrossword.go b/extendeddatacrossword.go
index e9c9558..e450b35 100644
--- a/extendeddatacrossword.go
+++ b/extendeddatacrossword.go
@@ -364,7 +364,7 @@ func (eds *ExtendedDataSquare) rowRangeNoMissingData(r, start, end uint) bool {
 
 func (eds *ExtendedDataSquare) colRangeNoMissingData(c, start, end uint) bool {
 	for r := start; r <= end && r < eds.width; r++ {
-		if eds.squareRow[r][c]  == nil {
+		if eds.squareRow[r][c] == nil {
 			return false
 		}
 	}
diff --git a/extendeddatacrossword_test.go b/extendeddatacrossword_test.go
index ed23729..f109fd1 100644
--- a/extendeddatacrossword_test.go
+++ b/extendeddatacrossword_test.go
@@ -54,10 +54,10 @@ func TestRepairExtendedDataSquare(t *testing.T) {
 		if err != nil {
 			t.Errorf("unexpected err while repairing data square: %v, codec: :%s", err, codecName)
 		} else {
-			assert.Equal(t, original.getCell(0, 0), ones)
-			assert.Equal(t, original.getCell(0, 1), twos)
-			assert.Equal(t, original.getCell(1, 0), threes)
-			assert.Equal(t, original.getCell(1, 1), fours)
+			assert.Equal(t, original.GetCell(0, 0), ones)
+			assert.Equal(t, original.GetCell(0, 1), twos)
+			assert.Equal(t, original.GetCell(1, 0), threes)
+			assert.Equal(t, original.GetCell(1, 1), fours)
 		}
 
 		flattened = original.flattened()