feat: 투자 매매내역 수정 API (PUT /trades/{id})

- InvestController/Service/Mapper: updateTrade 추가
- 수정 결과를 시점별로 시뮬레이션해 보유수량이 음수가 되면 거부(매도 과다 방지)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/java/com/sb/web/account/controller/InvestController.java

@@ -23,6 +23,7 @@ import java.util.List;
  *   DELETE /api/account/invest/holdings/{id}       종목 삭제(매매이력 포함)
  *   GET    /api/account/invest/holdings/{id}/trades  매매이력
  *   POST   /api/account/invest/holdings/{id}/trades  매수/매도
+ *   PUT    /api/account/invest/trades/{id}         매매 수정
  *   DELETE /api/account/invest/trades/{id}         매매 삭제
  */
 @RestController
@@ -93,6 +94,14 @@ public class InvestController {
         return ResponseEntity.status(HttpStatus.CREATED).body(investService.addTrade(id, req, current.getId()));
     }
 
+    @PutMapping("/trades/{id}")
+    public TradeResponse updateTrade(
+            @PathVariable Long id,
+            @Valid @RequestBody TradeRequest req,
+            @RequestAttribute(AuthInterceptor.CURRENT_MEMBER) SessionUser current) {
+        return investService.updateTrade(id, req, current.getId());
+    }
+
     @DeleteMapping("/trades/{id}")
     public ResponseEntity<Void> deleteTrade(
             @PathVariable Long id,

src/main/java/com/sb/web/account/mapper/InvestMapper.java

@@ -38,6 +38,8 @@ public interface InvestMapper {
 
     int insertTrade(InvestTrade trade);
 
+    int updateTrade(InvestTrade trade);
+
     int deleteTrade(@Param("id") Long id, @Param("memberId") Long memberId);
 
     int deleteTradesByHolding(@Param("holdingId") Long holdingId, @Param("memberId") Long memberId);

src/main/java/com/sb/web/account/service/InvestService.java

@@ -138,6 +138,50 @@ public class InvestService {
         return TradeResponse.from(t);
     }
 
+    @Transactional
+    public TradeResponse updateTrade(Long id, TradeRequest req, Long memberId) {
+        InvestTrade existing = investMapper.findTradeByIdAndMember(id, memberId);
+        if (existing == null) {
+            throw new ApiException(HttpStatus.NOT_FOUND, "매매 내역을 찾을 수 없습니다.");
+        }
+        Long holdingId = existing.getHoldingId();
+        String type = "SELL".equals(req.getTradeType()) ? "SELL" : "BUY";
+        long fee = req.getFee() != null ? req.getFee() : 0L;
+
+        // 편집을 반영한 시점별 시뮬레이션 — 어느 시점에도 보유수량이 음수가 되면 거부
+        java.util.List<InvestTrade> sim = new java.util.ArrayList<>();
+        for (InvestTrade t : investMapper.findTradesByHolding(holdingId, memberId)) {
+            if (t.getId().equals(id)) {
+                sim.add(InvestTrade.builder().id(id).tradeType(type).tradeDate(req.getTradeDate())
+                        .quantity(req.getQuantity()).price(req.getPrice()).fee(fee).build());
+            } else {
+                sim.add(t);
+            }
+        }
+        sim.sort(java.util.Comparator.comparing(InvestTrade::getTradeDate)
+                .thenComparing(InvestTrade::getId));
+        BigDecimal running = BigDecimal.ZERO;
+        for (InvestTrade t : sim) {
+            if ("BUY".equals(t.getTradeType())) {
+                running = running.add(t.getQuantity());
+            } else {
+                running = running.subtract(t.getQuantity());
+                if (running.signum() < 0) {
+                    throw new ApiException(HttpStatus.BAD_REQUEST,
+                            "수정하면 보유수량이 음수가 됩니다. 매도 수량/순서를 확인하세요.");
+                }
+            }
+        }
+
+        existing.setTradeType(type);
+        existing.setTradeDate(req.getTradeDate());
+        existing.setQuantity(req.getQuantity());
+        existing.setPrice(req.getPrice());
+        existing.setFee(fee);
+        investMapper.updateTrade(existing);
+        return TradeResponse.from(existing);
+    }
+
     @Transactional
     public void deleteTrade(Long id, Long memberId) {
         if (investMapper.findTradeByIdAndMember(id, memberId) == null) {

src/main/resources/mapper/InvestMapper.xml

@@ -87,6 +87,13 @@
         VALUES (#{memberId}, #{holdingId}, #{tradeType}, #{tradeDate}, #{quantity}, #{price}, #{fee}, NOW())
     </insert>
 
+    <update id="updateTrade" parameterType="com.sb.web.account.domain.InvestTrade">
+        UPDATE invest_trade
+        SET trade_type = #{tradeType}, trade_date = #{tradeDate},
+            quantity = #{quantity}, price = #{price}, fee = #{fee}
+        WHERE id = #{id} AND member_id = #{memberId}
+    </update>
+
     <delete id="deleteTrade">
         DELETE FROM invest_trade WHERE id = #{id} AND member_id = #{memberId}
     </delete>