#include <platform.h>
#include <kernel/config.h>
#include <selist.h>
#include "pathfinder.h"

#include "region.h"
#include "terrain.h"

#include <limits.h>
#include <stdlib.h>
#include <assert.h>

#define MAXDEPTH 1024

bool allowed_walk(const region * src, const region * r)
{
    if (fval(r->terrain, WALK_INTO))
        return true;
    return false;
}

bool allowed_fly(const region * src, const region * r)
{
    if (fval(r->terrain, FLY_INTO))
        return true;
    return false;
}

typedef struct node {
    struct node *next;
    region *r;
    struct node *prev;
    int distance;
} node;

static node *node_garbage;

void pathfinder_cleanup(void)
{
    while (node_garbage) {
        node *n = node_garbage;
        node_garbage = n->next;
        free(n);
    }
}

static node *new_node(region * r, int distance, node * prev)
{
    node *n;
    if (node_garbage != NULL) {
        n = node_garbage;
        node_garbage = n->next;
    }
    else {
        n = malloc(sizeof(node));
        if (!n) abort();
    }
    n->next = NULL;
    n->prev = prev;
    n->r = r;
    n->distance = distance;
    return n;
}

static node *free_node(node * n)
{
    node *s = n->next;
    n->next = node_garbage;
    node_garbage = n;
    return s;
}

static void free_nodes(node * root)
{
    while (root != NULL) {
        region *r = root->r;
        freset(r, RF_MARK);
        root = free_node(root);
    }
}

struct selist *path_regions_in_range(struct region *handle_start, int maxdist,
    bool(*allowed) (const struct region *, const struct region *))
{
    selist * rlist = NULL;
    node *root = new_node(handle_start, 0, NULL);
    node **handle_end = &root->next;
    node *n = root;

    while (n != NULL) {
        region *r = n->r;
        int depth = n->distance + 1;
        int d;

        if (n->distance >= maxdist)
            break;
        for (d = 0; d != MAXDIRECTIONS; ++d) {
            region *rn = rconnect(r, d);
            if (rn == NULL)
                continue;
            if (fval(rn, RF_MARK))
                continue;               /* already been there */
            if (allowed && !allowed(r, rn))
                continue;               /* can't go there */

            /* add the region to the list of available ones. */
            selist_push(&rlist, rn);

            /* make sure we don't go here again, and put the region into the set for
               further BFS'ing */
            fset(rn, RF_MARK);
            *handle_end = new_node(rn, depth, n);
            handle_end = &(*handle_end)->next;
        }
        n = n->next;
    }
    free_nodes(root);

    return rlist;
}

static region **internal_path_find(region * handle_start, const region * target,
    int maxlen, bool(*allowed) (const region *, const region *))
{
    static region *path[MAXDEPTH + 2];    /* STATIC_RETURN: used for return, not across calls */
    direction_t d = MAXDIRECTIONS;
    node *root = new_node(handle_start, 0, NULL);
    node **handle_end = &root->next;
    node *n = root;
    assert(maxlen <= MAXDEPTH);
    fset(handle_start, RF_MARK);

    while (n != NULL) {
        region *r = n->r;
        int depth = n->distance + 1;
        if (n->distance >= maxlen)
            break;
        for (d = 0; d != MAXDIRECTIONS; ++d) {
            region *rn = rconnect(r, d);
            if (rn && !fval(rn, RF_MARK) && allowed(r, rn)) {
                if (rn == target) {
                    int i = depth;
                    path[i + 1] = NULL;
                    path[i] = rn;
                    while (n) {
                        path[--i] = n->r;
                        n = n->prev;
                    }
                    break;
                }
                else {
                    fset(rn, RF_MARK);
                    *handle_end = new_node(rn, depth, n);
                    handle_end = &(*handle_end)->next;
                }
            }
        }
        if (d != MAXDIRECTIONS) {
            break;
        }
        n = n->next;
    }
    free_nodes(root);
    if (d != MAXDIRECTIONS) {
        return path;
    }
    return NULL;
}

bool
path_exists(region * handle_start, const region * target, int maxlen,
bool(*allowed) (const region *, const region *))
{
    assert((!fval(handle_start, RF_MARK) && !fval(target, RF_MARK))
        || !"Some Algorithm did not clear its RF_MARKs!");
    if (handle_start == target)
        return true;
    if (internal_path_find(handle_start, target, maxlen, allowed) != NULL)
        return true;
    return false;
}

region **path_find(region * handle_start, const region * target, int maxlen,
    bool(*allowed) (const region *, const region *))
{
    assert((!fval(handle_start, RF_MARK) && !fval(target, RF_MARK))
        || !"Did you call path_init()?");
    return internal_path_find(handle_start, target, maxlen, allowed);
}