Move pathfinders to dedicated files

cpp/src/pathfinder/bfs.cpp

@@ -0,0 +1,66 @@
+#include <queue>
+
+#include "bfs.hpp"
+
+#include "base.hpp"
+#include "map.hpp"
+#include "math.hpp"
+
+namespace pathfinder {
+  
+Path BFS::CalculatePath(WorldPos start_world, WorldPos end_world) {
+    if (m_Map == nullptr) return {};
+
+    const TilePos start = m_Map->WorldToTile(start_world);
+    const TilePos end   = m_Map->WorldToTile(end_world);
+
+    if (!m_Map->IsTilePosValid(start) || !m_Map->IsTilePosValid(end))
+        return {};
+    if (start == end) {
+        return {};
+    }
+    // clear previous run
+    m_CameFrom.clear();
+    m_Distance.clear();
+
+    std::queue<TilePos> frontier;
+    frontier.push(start);
+    m_CameFrom[start] = start;
+    m_Distance[start] = 0.0f;
+
+    // ---------------- build flow-field ----------------
+    bool early_exit = false;
+    while (!frontier.empty() && !early_exit) {
+        TilePos current = frontier.front();
+        frontier.pop();
+
+        for (TilePos next : m_Map->GetNeighbors(current)) {
+            if (m_CameFrom.find(next) == m_CameFrom.end()) {  // not visited
+                frontier.push(next);
+                m_Distance[next] = m_Distance[current] + 1.0f;
+                m_CameFrom[next] = current;
+
+                if (next == end) {          // early exit
+                    early_exit = true;
+                    break;
+                }
+            }
+        }
+    }
+
+    // --------------- reconstruct path -----------------
+    if (m_CameFrom.find(end) == m_CameFrom.end())
+        return {};                        // end not reached
+
+    Path path;
+    TilePos cur = end;
+    path.push_back(m_Map->TileToWorld(cur));
+    while (cur != start) {
+        cur = m_CameFrom[cur];
+        path.push_back(m_Map->TileToWorld(cur));
+    }
+    std::reverse(path.begin(), path.end());
+    return path;
+}
+
+} // pathfinder namespace