#include <c_DirectedCycle.h>


/* Private recursive engine helper */
static void c_DirectedCycle_DFS(c_DirectedCycle_t* self, const c_Digraph_t* graph, c_size_t v) {
    self->on_stack[v] = C_TRUE;
    self->marked[v] = C_TRUE;

    c_AdjList_t* adj = &graph->adj_list[v];
    c_size_t size = (c_size_t)c_AdjList_GetSize(adj);

    for (c_size_t i = 0; i < size; ++i) {
        c_uint_t target_value = 0;
        /* Safely query edge list element matching custom pointer specifications */
        c_err_t err = c_AdjList_Get(adj, i, &target_value);

        if (err == C_SUCCESS) {
            c_size_t w = (c_size_t)target_value;

            /* Short-circuit if a cycle has already been detected */
            if (c_DirectedCycle_HasCycle(self)) return;

            if (!self->marked[w]) {
                self->edge_to[w] = v;
                c_DirectedCycle_DFS(self, graph, w);
            }
            /* Cycle detected! Trace back path sequence */
            else if (self->on_stack[w]) {
                /* Collect cycle steps onto a temporary reverse stack trace */
                c_size_t* reverse_stack = (c_size_t*)c_Allocator_Calloc(&self->allocator, graph->V, sizeof(c_size_t));
                if (!reverse_stack) return;

                c_size_t stack_size = 0;
                for (c_size_t x = v; x != w; x = self->edge_to[x]) {
                    reverse_stack[stack_size++] = x;
                }
                reverse_stack[stack_size++] = w;
                reverse_stack[stack_size++] = v;

                /* Push structured forward order into the self->cycle storage container using VertexIdList interface */
                while (stack_size > 0) {
                    c_VertexIdList_Append(&self->cycle, (c_uint_t)reverse_stack[--stack_size]);
                }

                c_Allocator_Free(&self->allocator, reverse_stack);
                return;
            }
        }
    }

    self->on_stack[v] = C_FALSE;
}

c_err_t c_DirectedCycle_Init(c_DirectedCycle_t* self, const c_Digraph_t* graph, c_Allocator_t* allocator) {
    if (!self || !graph) return C_ERR_PARAM;

    self->allocator = allocator ? *allocator : c_DefaultAllocator;
    self->marked = (c_bool_t*)c_Allocator_Calloc(&self->allocator, graph->V, sizeof(c_bool_t));
    self->edge_to = (c_size_t*)c_Allocator_Calloc(&self->allocator, graph->V, sizeof(c_size_t));
    self->on_stack = (c_bool_t*)c_Allocator_Calloc(&self->allocator, graph->V, sizeof(c_bool_t));

    /* Using c_VertexIdList_Init mapper directly onto your internal cycle storage */
    c_VertexIdList_Init(&self->cycle,0, allocator);

    if (!self->marked || !self->edge_to || !self->on_stack) {
        c_DirectedCycle_Destroy(self);
        return C_ERR_NOMEM;
    }

    /* Iterate through all vertices to handle disconnected graph structures */
    for (c_size_t v = 0; v < graph->V; ++v) {
        if (!self->marked[v] && !c_DirectedCycle_HasCycle(self)) {
            c_DirectedCycle_DFS(self, graph, v);
        }
    }

    return C_SUCCESS;
}

void c_DirectedCycle_Destroy(c_DirectedCycle_t* self) {
    if (!self) return;
    if (self->marked) c_Allocator_Free(&self->allocator, self->marked);
    if (self->edge_to) c_Allocator_Free(&self->allocator, self->edge_to);
    if (self->on_stack) c_Allocator_Free(&self->allocator, self->on_stack);

    c_VertexIdList_Destroy(&self->cycle);

    self->marked = NULL;
    self->edge_to = NULL;
    self->on_stack = NULL;
}

c_err_t c_DirectedCycle_GetCycle(c_DirectedCycle_t* self, c_VertexIdList_t* out_cycle) {
    if (!self || !out_cycle) return C_ERR_PARAM;
    if (!c_DirectedCycle_HasCycle(self)) return C_ERR_FAIL;

    c_size_t size = (c_size_t)c_VertexIdList_GetSize(&self->cycle);
    for (c_size_t i = 0; i < size; ++i) {
        c_uint_t val = 0;
        /* Using the safe pointer signature format */
        c_err_t err = c_VertexIdList_Get((c_VertexIdList_t*)&self->cycle, i, &val);
        if (err == C_SUCCESS) {
            c_err_t app_err = c_VertexIdList_Append(out_cycle, val);
            if (app_err != C_SUCCESS) return app_err;
        }
    }
    return C_SUCCESS;
}