/**
 * @file
 * @brief extract strongly connected components of directed graphs
 */

/*************************************************************************
 * Copyright (c) 2011 AT&T Intellectual Property 
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors: Details at https://graphviz.org
 *************************************************************************/


/*
 * Written by Stephen North
 * Updated by Emden Gansner
 */

/*
 * This is a filter that reads a graph, searches for strongly
 * connected components, and writes each as a separate graph
 * along with a map of the components.
 */

#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <cgraph/cgraph.h>
#include <cgraph/ingraphs.h>
#include <cgraph/list.h>

#include <getopt.h>
#include "openFile.h"
#include <util/exit.h>
#include <util/unreachable.h>

#define INF UINT_MAX

typedef struct Agraphinfo_t {
    Agrec_t h;
    Agnode_t *rep;
} Agraphinfo_t;

typedef struct Agnodeinfo_t {
    Agrec_t h;
    unsigned int val;
    Agraph_t *scc;
} Agnodeinfo_t;

static Agnode_t *getrep(Agraph_t * g)
{
    return ((Agraphinfo_t *)g->base.data)->rep;
}
static void setrep(Agraph_t * g, Agnode_t * rep)
{
    ((Agraphinfo_t *)g->base.data)->rep = rep;
}
static Agraph_t *getscc(Agnode_t * n)
{
    return ((Agnodeinfo_t *)n->base.data)->scc;
}
static void setscc(Agnode_t * n, Agraph_t * scc)
{
    ((Agnodeinfo_t *)n->base.data)->scc = scc;
}
static unsigned getval(Agnode_t *n) {
    return ((Agnodeinfo_t *)n->base.data)->val;
}
static void setval(Agnode_t *n, unsigned v) {
    ((Agnodeinfo_t *)n->base.data)->val = v;
}

typedef struct {
    unsigned Comp;
    unsigned ID;
    int N_nodes_in_nontriv_SCC;
} sccstate;

static int wantDegenerateComp;
static int Silent;
static int StatsOnly;
static int Verbose;
static char *CmdName;
static char **Files;
static FILE *outfp;		/* output; stdout by default */

static void nodeInduce(Agraph_t * g, Agraph_t* map)
{
    Agnode_t *n;
    Agedge_t *e;
    Agraph_t* rootg = agroot (g);

    
    for (n = agfstnode(g); n; n = agnxtnode(g, n)) {
	for (e = agfstout(rootg, n); e; e = agnxtout(rootg, e)) {
	    if (agsubnode(g, aghead(e), 0))
		agsubedge(g, e, 1);
	    else {
		Agraph_t* tscc = getscc(agtail(e));
		Agraph_t* hscc = getscc(aghead(e));
		if (tscc && hscc)
		    agedge(map, getrep(tscc), getrep(hscc), NULL, 1);
	    }
	}
    }
}

DEFINE_LIST(node_stack, Agnode_t *)

static unsigned visit(Agnode_t *n, Agraph_t *map, node_stack_t *sp,
                      sccstate *st) {
    unsigned int m, min;
    Agnode_t *t;
    Agraph_t *subg;
    Agedge_t *e;

    min = ++st->ID;
    setval(n, min);
    node_stack_push_back(sp, n);

    for (e = agfstout(n->root, n); e; e = agnxtout(n->root, e)) {
	t = aghead(e);
	if (getval(t) == 0)
	    m = visit(t, map, sp, st);
	else
	    m = getval(t);
	if (m < min)
	    min = m;
    }

    if (getval(n) == min) {
	if (!wantDegenerateComp && *node_stack_back(sp) == n) {
	    setval(n, INF);
	    (void)node_stack_pop_back(sp);
	} else {
	    char name[32];
	    Agraph_t *G = agraphof(n);;
	    snprintf(name, sizeof(name), "cluster_%u", st->Comp++);
	    subg = agsubg(G, name, 1);
	    agbindrec(subg, "scc_graph", sizeof(Agraphinfo_t), true);
	    setrep(subg, agnode(map, name, 1));
	    do {
		t = node_stack_pop_back(sp);
		agsubnode(subg, t, 1);
		setval(t, INF);
		setscc(t, subg);
		st->N_nodes_in_nontriv_SCC++;
	    } while (t != n);
	    nodeInduce(subg, map);
	    if (!StatsOnly)
		agwrite(subg, outfp);
	}
    }
    return min;
}

static int label(Agnode_t * n, int nodecnt, int *edgecnt)
{
    Agedge_t *e;

    setval(n, 1);
    nodecnt++;
    for (e = agfstedge(n->root, n); e; e = agnxtedge(n->root, e, n)) {
	*edgecnt += 1;
	if (e->node == n)
	    e = agopp(e);
	if (!getval(e->node))
	    nodecnt = label(e->node, nodecnt, edgecnt);
    }
    return nodecnt;
}

static int
countComponents(Agraph_t * g, int *max_degree, float *nontree_frac)
{
    int nc = 0;
    int sum_edges = 0;
    int sum_nontree = 0;
    int deg;
    int n_edges;
    int n_nodes;
    Agnode_t *n;

    for (n = agfstnode(g); n; n = agnxtnode(g, n)) {
	if (!getval(n)) {
	    nc++;
	    n_edges = 0;
	    n_nodes = label(n, 0, &n_edges);
	    sum_edges += n_edges;
	    sum_nontree += n_edges - n_nodes + 1;
	}
    }
    if (max_degree) {
	int maxd = 0;
	for (n = agfstnode(g); n; n = agnxtnode(g, n)) {
	    deg = agdegree(g, n, 1, 1);
	    if (maxd < deg)
		maxd = deg;
	    setval(n, 0);
	}
	*max_degree = maxd;
    }
    if (nontree_frac) {
	if (sum_edges > 0)
	    *nontree_frac = (float) sum_nontree / (float) sum_edges;
	else
	    *nontree_frac = 0.0;
    }
    return nc;
}

static void process(Agraph_t * G)
{
    Agnode_t *n;
    Agraph_t *map;
    int nc = 0;
    float nontree_frac = 0;
    int Maxdegree = 0;
    node_stack_t stack = {0};
    sccstate state;

    aginit(G, AGRAPH, "scc_graph", sizeof(Agraphinfo_t), true);
    aginit(G, AGNODE, "scc_node", sizeof(Agnodeinfo_t), true);
    state.Comp = state.ID = 0;
    state.N_nodes_in_nontriv_SCC = 0;

    if (Verbose)
	nc = countComponents(G, &Maxdegree, &nontree_frac);

    map = agopen("scc_map", Agdirected, (Agdisc_t *) 0);
    for (n = agfstnode(G); n; n = agnxtnode(G, n))
	if (getval(n) == 0)
	    visit(n, map, &stack, &state);
    node_stack_free(&stack);
    if (!StatsOnly)
	agwrite(map, outfp);
    agclose(map);

    if (Verbose)
	fprintf(stderr, "%d %d %d %u %.4f %d %.4f\n",
		agnnodes(G), agnedges(G), nc, state.Comp,
		state.N_nodes_in_nontriv_SCC / (double) agnnodes(G),
		Maxdegree, nontree_frac);
    else if (!Silent)
	fprintf(stderr, "%d nodes, %d edges, %u strong components\n",
		agnnodes(G), agnedges(G), state.Comp);

}

static char *useString = "Usage: %s [-sdv?] <files>\n\
  -s           - only produce statistics\n\
  -S           - silent\n\
  -d           - allow degenerate components\n\
  -o<outfile>  - write to <outfile> (stdout)\n\
  -v           - verbose\n\
  -?           - print usage\n\
If no files are specified, stdin is used\n";

static void usage(int v)
{
    printf(useString, CmdName);
    graphviz_exit(v);
}

static void scanArgs(int argc, char **argv)
{
    int c;

    CmdName = argv[0];
    opterr = 0;
    while ((c = getopt(argc, argv, ":o:sdvS?")) != EOF) {
	switch (c) {
	case 's':
	    StatsOnly = 1;
	    break;
	case 'd':
	    wantDegenerateComp = 1;
	    break;
	case 'o':
	    if (outfp != NULL)
		fclose(outfp);
	    outfp = openFile(CmdName, optarg, "w");
	    break;
	case 'v':
	    Verbose = 1;
	    Silent = 0;
	    break;
	case 'S':
	    Verbose = 0;
	    Silent = 1;
	    break;
	case ':':
	    fprintf(stderr, "%s: option -%c missing argument - ignored\n", CmdName, optopt);
	    break;
	case '?':
	    if (optopt == '\0' || optopt == '?')
		usage(0);
	    else {
		fprintf(stderr, "%s: option -%c unrecognized\n",
			CmdName, optopt);
		usage(1);
	    }
	    break;
	default:
	    UNREACHABLE();
	}
    }
    argv += optind;
    argc -= optind;

    if (argc > 0)
	Files = argv;
    if (!outfp)
	outfp = stdout;		/* stdout the default */
}

int main(int argc, char **argv)
{
    Agraph_t *g;
    ingraph_state ig;

    scanArgs(argc, argv);
    newIngraph(&ig, Files);

    while ((g = nextGraph(&ig)) != 0) {
	if (agisdirected(g))
	    process(g);
	else
	    fprintf(stderr, "Graph %s in %s is undirected - ignored\n",
		    agnameof(g), fileName(&ig));
	agclose(g);
    }

    graphviz_exit(0);
}
