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#include "../native.h"
#include "../lists.h"
#include "../strings.h"
#include "../newstr.h"
#include "../variable.h"
/* Use quite klugy approach: when we add order dependency from 'a' to 'b',
just append 'b' to of value of variable 'a'.
*/
LIST *add_pair( PARSE *parse, FRAME *frame )
{
LIST* arg = lol_get( frame->args, 0 );
var_set(arg->string, list_copy(0, arg->next), VAR_APPEND);
return L0;
}
/** Given a list and a value, returns position of that value in
the list, or -1 if not found.
*/
int list_index(LIST* list, const char* value)
{
int result = 0;
for(; list; list = list->next, ++result) {
if (strcmp(list->string, value) == 0)
return result;
}
return -1;
}
enum colors { white, gray, black };
/* Main routite of topological sort. Calls itself recursively on all
adjacent vertices which were not yet visited. After that, 'current_vertex'
is added to '*result_ptr'.
*/
void do_ts(int** graph, int current_vertex, int* colors, int** result_ptr)
{
int i;
colors[current_vertex] = gray;
for(i = 0; graph[current_vertex][i] != -1; ++i) {
int adjacent_vertex = graph[current_vertex][i];
if (colors[adjacent_vertex] == white)
do_ts(graph, adjacent_vertex, colors, result_ptr);
else if (colors[adjacent_vertex] == gray)
; /* This is loop. Not sure what to do... */
}
colors[current_vertex] = black;
**result_ptr = current_vertex;
(*result_ptr)++;
}
void topological_sort(int** graph, int num_vertices, int* result)
{
int i;
int* colors = (int*)calloc(num_vertices, sizeof(int));
for (i = 0; i < num_vertices; ++i)
colors[i] = white;
for(i = 0; i < num_vertices; ++i)
if (colors[i] == white)
do_ts(graph, i, colors, &result);
free(colors);
}
LIST *order( PARSE *parse, FRAME *frame )
{
LIST* arg = lol_get( frame->args, 0 );
LIST* tmp;
LIST* result = 0;
int src, dst;
/* We need to create a graph of order dependencies between
the passed objects. We assume that there are no duplicates
passed to 'add_pair'.
*/
int length = list_length(arg);
int** graph = (int**)calloc(length, sizeof(int*));
int* order = (int*)malloc((length+1)*sizeof(int));
for(tmp = arg, src = 0; tmp; tmp = tmp->next, ++src) {
/* For all object this one depend upon, add elements
to 'graph' */
LIST* dependencies = var_get(tmp->string);
int index = 0;
graph[src] = (int*)calloc(list_length(dependencies)+1, sizeof(int));
for(; dependencies; dependencies = dependencies->next) {
int dst = list_index(arg, dependencies->string);
if (dst != -1)
graph[src][index++] = dst;
}
graph[src][index] = -1;
}
topological_sort(graph, length, order);
{
int index = length-1;
for(; index >= 0; --index) {
int i;
tmp = arg;
for (i = 0; i < order[index]; ++i, tmp = tmp->next);
result = list_new(result, tmp->string);
}
}
/* Clean up */
{
int i;
for(i = 0; i < length; ++i)
free(graph[i]);
free(graph);
free(order);
}
return result;
}
void init_order()
{
{
char* args[] = { "first", "second", 0 };
declare_native_rule("class@order", "add-pair", args, add_pair);
}
{
char* args[] = { "objects", "*", 0 };
declare_native_rule("class@order", "order", args, order);
}
}
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