#include <assert.h>

#if INTERFACE
/* Nodes for the paths through the DAG.
*/
struct PathNode {
  int rid;                 /* ID for this node */
  u8 fromIsParent;         /* True if pFrom is the parent of rid */
  u8 isPrim;               /* True if primary side of common ancestor */
  PathNode *pFrom;         /* Node we came from */
  union {
    PathNode *pPeer;       /* List of nodes of the same generation */
    PathNode *pTo;         /* Next on path from beginning to end */
  } u;
  PathNode *pAll;        /* List of all nodes */
};
#endif

/*
** Local variables for this module
*/
static struct {
  PathNode *pCurrent;   /* Current generation of nodes */
  PathNode *pAll;       /* All nodes */
  Bag seen;             /* Nodes seen before */
  int nStep;            /* Number of steps from first to last */
  PathNode *pStart;     /* Earliest node */
  PathNode *pPivot;     /* Common ancestor of pStart and pEnd */
  PathNode *pEnd;       /* Most recent */
} path;

/*
** Return the first (last) element of the computed path.
*/
PathNode *path_first(void){ return path.pStart; }

/*
** Create a new node
*/
static PathNode *path_new_node(int rid, PathNode *pFrom, int isParent){
  PathNode *p;

  p = fossil_malloc( sizeof(*p) );
  memset(p, 0, sizeof(*p));
  p->rid = rid;
  p->fromIsParent = isParent;
  p->pFrom = pFrom;
  p->u.pPeer = path.pCurrent;
  path.pCurrent = p;
  p->pAll = path.pAll;
  path.pAll = p;

  bag_insert(&path.seen, rid);
  return p;
}

/*
** Reset memory used by the shortest path algorithm.
*/
void path_reset(void){
  PathNode *p;
  while( path.pAll ){
    p = path.pAll;
    path.pAll = p->pAll;
    fossil_free(p);
  }
  bag_clear(&path.seen);
  path.pCurrent = 0;
  path.pAll = 0;
  path.pEnd = 0;
  path.nStep = 0;
}

/*
** Construct the path from path.pStart to path.pEnd in the u.pTo fields.
*/
void path_reverse_path(void){
  PathNode *p;
  for(p=path.pEnd; p && p->pFrom; p = p->pFrom){
    p->pFrom->u.pTo = p;
  }
  path.pEnd->u.pTo = 0;
  assert( p==path.pStart );
}

/*
** Compute the shortest path from iFrom to iTo
**
** If directOnly is true, then use only the "primary" links from parent to
** child.  In other words, ignore merges.
**
** Return a pointer to the beginning of the path (the iFrom node).  
** Elements of the path can be traversed by following the PathNode.u.pTo
** pointer chain.
**
** Return NULL if no path is found.
*/
PathNode *path_shortest(int iFrom, int iTo, int directOnly){
  Stmt s;
  PathNode *pPrev;
  PathNode *p;

  path_reset();

      while( db_step(&s)==SQLITE_ROW ){
        int cid = db_column_int(&s, 0);
        int isParent = db_column_int(&s, 1);
        if( bag_find(&path.seen, cid) ) continue;
        p = path_new_node(cid, pPrev, isParent);
        if( cid==iTo ){
          db_finalize(&s);
          path.pEnd = p;
          path_reverse_path();
          return path.pStart;
        }
      }
      db_reset(&s);
      pPrev = pPrev->u.pPeer;
    }
  }
  db_finalize(&s);
  path_reset();
  return 0;
}














/*
** Find the mid-point of the path.  If the path contains fewer than
** 2 steps, return 0.
*/
PathNode *path_midpoint(void){
  PathNode *p;
  int i;

  if( g.argc!=4 ) usage("VERSION1 VERSION2");
  iFrom = name_to_rid(g.argv[2]);
  iTo = name_to_rid(g.argv[3]);
  p = path_shortest(iFrom, iTo, directOnly);
  if( p==0 ){
    fossil_fatal("no path from %s to %s", g.argv[1], g.argv[2]);
  }

  for(n=1, p=path.pStart; p; p=p->u.pTo, n++){
    char *z;
    z = db_text(0,
      "SELECT substr(uuid,1,12) || ' ' || datetime(mtime)"
      "  FROM blob, event"
      " WHERE blob.rid=%d AND event.objid=%d AND event.type='ci'",
      p->rid, p->rid);
    printf("%4d: %s", n, z);
    fossil_free(z);
    if( p->u.pTo ){
      printf(" is a %s of\n", p->u.pTo->fromIsParent ? "parent" : "child");
    }else{
      printf("\n");
    }
  }
}

/*
** Find the closest common ancestor of two nodes.  "Closest" means the
** fewest number of arcs.
*/
int path_common_ancestor(int iMe, int iYou){
  Stmt s;
  PathNode *pPrev;
  PathNode *p;
  Bag me, you;

  if( iMe==iYou ) return iMe;
  if( iMe==0 || iYou==0 ) return 0;
  path_reset();
  path.pStart = path_new_node(iMe, 0, 0);
  path.pStart->isPrim = 1;
  path.pEnd = path_new_node(iYou, 0, 0);
  db_prepare(&s, "SELECT pid FROM plink WHERE cid=:cid");
  bag_init(&me);
  bag_insert(&me, iMe);
  bag_init(&you);
  bag_insert(&you, iYou);
  while( path.pCurrent ){
    pPrev = path.pCurrent;
    path.pCurrent = 0;
    while( pPrev ){
      db_bind_int(&s, ":cid", pPrev->rid);
      while( db_step(&s)==SQLITE_ROW ){
        int pid = db_column_int(&s, 0);
        if( bag_find(pPrev->isPrim ? &you : &me, pid) ){
          /* pid is the common ancestor */
          PathNode *pNext;
          for(p=path.pAll; p && p->rid!=pid; p=p->pAll){}
          assert( p!=0 );
          pNext = p;
          while( pNext ){
            pNext = p->pFrom;
            p->pFrom = pPrev;
            pPrev = p;
            p = pNext;
          }
          if( pPrev==path.pStart ) path.pStart = path.pEnd;
          path.pEnd = pPrev;
          path_reverse_path();
          db_finalize(&s);
          return pid;
        }else if( bag_find(&path.seen, pid) ){
          /* pid is just an alternative path on one of the legs */
          continue;
        }
        p = path_new_node(pid, pPrev, 0);
        p->isPrim = pPrev->isPrim;
        bag_insert(pPrev->isPrim ? &me : &you, pid);
      }
      db_reset(&s);
      pPrev = pPrev->u.pPeer;
    }
  }
  db_finalize(&s);
  path_reset();
  return 0;
}

/*
** COMMAND:  test-ancestor-path
**
** Usage: %fossil test-ancestor-path VERSION1 VERSION2
**
** Report the path from VERSION1 to VERSION2 through their most recent
** common ancestor.
*/
void ancestor_path_test_cmd(void){
  int iFrom;
  int iTo;
  int iPivot;
  PathNode *p;
  int n;

  db_find_and_open_repository(0,0);
  if( g.argc!=4 ) usage("VERSION1 VERSION2");
  iFrom = name_to_rid(g.argv[2]);
  iTo = name_to_rid(g.argv[3]);
  iPivot = path_common_ancestor(iFrom, iTo);
  for(n=1, p=path.pStart; p; p=p->u.pTo, n++){
    char *z;
    z = db_text(0,
      "SELECT substr(uuid,1,12) || ' ' || datetime(mtime)"
      "  FROM blob, event"
      " WHERE blob.rid=%d AND event.objid=%d AND event.type='ci'",
      p->rid, p->rid);
    printf("%4d: %s", n, z);
    fossil_free(z);
    if( p->rid==iFrom ) printf(" VERSION1");
    if( p->rid==iTo ) printf(" VERSION2");
    if( p->rid==iPivot ) printf(" PIVOT");
    printf("\n");
  }
}


/*
** A record of a file rename operation.
*/
typedef struct NameChange NameChange;
struct NameChange {
  int origName;        /* Original name of file */