#include <c_KosarajuSharirSCC.h>
#include "c_DepthFirstOrder.h"

/* Private recursive DFS engine helper subroutine for the second pass grouping */
static void c_KosarajuSharirSCC_DFS(c_KosarajuSharirSCC_t* self, const c_Digraph_t* graph, c_size_t v) {
    self->marked[v] = C_TRUE;
    self->id[v] = self->count;

    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;
        c_err_t err = c_AdjList_Get(adj, i, &target_value);

        if (err == C_SUCCESS) {
            c_size_t w = (c_size_t)target_value;
            if (!self->marked[w]) {
                c_KosarajuSharirSCC_DFS(self, graph, w);
            }
        }
    }
}

c_err_t c_KosarajuSharirSCC_Init(c_KosarajuSharirSCC_t* self, c_Digraph_t* graph, c_Allocator_t* allocator) {
    if (!self || !graph || graph->V==0) return C_ERR_PARAM;

    self->allocator = allocator ? *allocator : c_DefaultAllocator;
    self->count = 0;
    self->V = graph->V;

    /* 1. Allocate primary tracking mapping buffers */
    self->marked = (c_bool_t*)c_Allocator_Calloc(&self->allocator, graph->V, sizeof(c_bool_t));
    self->id = (c_size_t*)c_Allocator_Calloc(&self->allocator, graph->V, sizeof(c_size_t));
    if (!self->marked || !self->id) {
        c_KosarajuSharirSCC_Destroy(self);
        return C_ERR_NOMEM;
    }

    /* 2. First Pass: Compute reverse post-order stream on the transposed/reversed graph */
    c_Digraph_t transposed;
    c_err_t err = c_Digraph_Reverse(graph, &transposed);
    if (err != C_SUCCESS) {
        c_KosarajuSharirSCC_Destroy(self);
        return err;
    }

    c_DepthFirstOrder_t dfs_order;
    err = c_DepthFirstOrder_Init(&dfs_order, &transposed, allocator);
    if (err != C_SUCCESS) {
        c_Digraph_Destroy(&transposed);
        c_KosarajuSharirSCC_Destroy(self);
        return err;
    }

    c_VertexIdList_t rev_post_order;
    c_VertexIdList_Init(&rev_post_order,0, allocator);
    err = c_DepthFirstOrder_GetReversePost(&dfs_order, &rev_post_order);

    /* Clean up the working transposed graph and its intermediate state variables */
    c_DepthFirstOrder_Destroy(&dfs_order);
    c_Digraph_Destroy(&transposed);

    if (err != C_SUCCESS) {
        c_VertexIdList_Destroy(&rev_post_order);
        c_KosarajuSharirSCC_Destroy(self);
        return err;
    }

    /* 3. Second Pass: Run standard DFS tracking on original graph using the reverse post-order sequence */
    c_size_t sequence_len = (c_size_t)c_VertexIdList_GetSize(&rev_post_order);
    for (c_size_t i = 0; i < sequence_len; ++i) {
        c_uint_t vertex_val = 0;
        err = c_VertexIdList_Get(&rev_post_order, i, &vertex_val);

        if (err == C_SUCCESS) {
            c_size_t v = (c_size_t)vertex_val;
            if (!self->marked[v]) {
                c_KosarajuSharirSCC_DFS(self, graph, v);
                self->count++; /* Advance component ID group grouping */
            }
        }
    }

    c_VertexIdList_Destroy(&rev_post_order);
    return C_SUCCESS;
}

void c_KosarajuSharirSCC_Destroy(c_KosarajuSharirSCC_t* self) {
    if (!self) return;
    if (self->marked) {
        c_Allocator_Free(&self->allocator, self->marked);
        self->marked = NULL;
    }
    if (self->id) {
        c_Allocator_Free(&self->allocator, self->id);
        self->id = NULL;
    }
    self->count = 0;
    self->V = 0;
}