probably BASIC move logic done

src/chess.c

@@ -71,8 +71,61 @@ bool get_move(move_t *move) {
     return is_move_in_bounds(*move);
 }
 
-bool perform_move(player_e player, move_t move) {
+bool compare_pos(pos_t a, pos_t b) {
+    return a.x == b.x && a.y == b.y;
+}
 
+/**
+ * check the wanted pos_t against all valid move options
+ * of the current piece
+ */
+bool is_move_legal(move_t move) {
+    valid_move_t valid_moves[PIECE_COUNT] = DEFAULT_VALID_MOVES;
+    for (int i = 0; i < PIECE_COUNT; i++) {
+        for (int j = 0; 
+            j < valid_moves[i].piece_move_count && 
+            move.piece == valid_moves[i].piece; 
+            j++
+        ) {
+            pos_t new_pos = {move.from.x+move.to.x, move.from.y+move.to.y};
+            if (compare_pos(new_pos, valid_moves[i].options[j]) == true) {
+                return true;
+            }
+        }
+    }
+
+    return false;
+}
+
+bool is_none(board_t board, pos_t pos) {
+    return board[pos.y][pos.x] == NONE;
+}
+
+// the move can be:
+// 1.  legal x illegal
+// 2.  the 'to' pos could be occupied x non-occupied
+// 2a. it could be capturable x non-capturable
+bool validate_move(board_t board, move_t move) {
+    bool none = is_none(board, move.to);
+    bool move_legal = is_move_legal(move);
+    if (none == true && move_legal == true) {         
+        // free ability to move
+        return true;
+    } else if (none == false && move_legal == true) {
+        // capturing
+        return true;
+    } else {
+        // otherwise, invalid move
+        return false;
+    }
+}
+
+/** TODO: capturing and promotions */
+bool perform_move(board_t *board, player_e player, move_t move) {
+    if (validate_move(*board, move) == true) {
+        *board[move.to.y][move.to.x] = move.piece; // move piece to wanted place
+        *board[move.from.y][move.from.x] = NONE; // erase the remnants
+    }
 }
 
 end_condition_e check_edge_cases(board_t board) {

src/chess.h

@@ -49,11 +49,6 @@ typedef struct {
     pos_t to;
 } move_t;
 
-typedef struct {
-    int dirx;
-    int diry; 
-} relative_move_t;
-
 // the default arrangment of pieces on the board
 #define BOARD_DEFAULT_CONFIG \
 (board_t){\
@@ -68,7 +63,7 @@ typedef struct {
 
 typedef struct {
     piece_e piece;
-    relative_move_t moves[MAX_PIECE_MOVE_COUNT];
+    pos_t options[MAX_PIECE_MOVE_COUNT];
     unsigned int piece_move_count;
 } valid_move_t;
 
@@ -90,27 +85,30 @@ typedef struct {
   * absolute x,y values -> e.g. the rook can move 
   * up, down, left, right * n -> and then bounds & edge cases are checked
   */
-#define DEFAULT_VALID_MOVES \
-(valid_move_t[PIECE_COUNT]){\
-    {NONE, (relative_move_t[0]){}, 0},\
-    {PAWN, (relative_move_t[4]){\
-        {0, -1}, {-1, -1}, {+1, -1}, {0, -2}\
+#define DEFAULT_VALID_MOVES (valid_move_t[PIECE_COUNT]){\
+    {NONE, {}, 0},\
+    {PAWN, {\
+        { 0, -1}, {-1, -1}, {+1, -1}, { 0, -2}\
     }, 4},\
-    {ROOK, (relative_move_t[4]){\
-        {0, -1}, {0, +1}, {-1, 0}, {+1, 0}\
+    {ROOK, {\
+        { 0, -1}, { 0, +1}, {-1,  0}, {+1,  0}\
     }, 4},\
-    {KNIGHT, (relative_move_t)[8], {\
+    {KNIGHT, {\
         {-1, -2}, {+1, -2}, {-2, -1}, {-2, +1},\
         {+2, -1}, {+2, +1}, {-1, -2}, {-1, +2}\
     }, 8},\
-    {BISHOP, (relative_move_t[4]){\
+    {BISHOP, {\
         {-1, -1}, {-1, +1}, {+1, -1}, {+1, +1}\
     }, 4},\
-    {QUEEN, (relative_move_t[8]){\
+    {QUEEN, {\
         {0,  -1}, {0,  +1}, {-1,  0}, {+1,  0},\
         {-1, -1}, {-1, +1}, {+1, -1}, {+1, +1}\
+    }, 8},\
+    {KING, {\
+        { 0, -1}, { 0, +1}, {-1,  0}, {+1,  0},\
+        {-1, -1}, {-1, +1}, {+1, -1}, {+1, +1}\
     }, 8}\
-}\
+}
 
 typedef enum {
     CHECKMATE,
@@ -128,7 +126,7 @@ void select_player(player_e *player, unsigned int round_count);
 bool get_move(move_t *move);
 
 // performs the move if is it possible
-bool perform_move(player_e player, move_t move);
+bool perform_move(board_t *board, player_e player, move_t move);
 
 // checks for captures, prommotions and mates
 end_condition_e check_edge_cases(board_t board);

src/main.c

@@ -37,7 +37,7 @@ int main() {
         
         get_move(&move);
 
-        perform_move(player, move);
+        perform_move(&board, player, move);
 
         end_condition = check_edge_cases(board);
         if (end_condition == CHECKMATE || end_condition == STALEMATE) {