/** \ingroup rpmts
 * \file lib/depends.c
 */

#include "system.h"

#include <rpm/rpmtag.h>
#include <rpm/rpmmacro.h>
#include <rpm/rpmlog.h>
#include <rpm/rpmds.h>

#include "lib/rpmte_internal.h"	/* XXX tsortInfo_s */
#include "lib/rpmts_internal.h"

#include "debug.h"

/*
 * Strongly Connected Components
 * set of packages (indirectly) requiering each other
 */
struct scc_s {
    int count; /* # of external requires this SCC has */
    /* int qcnt;  # of external requires pointing to this SCC */
    int size;  /* # of members */
    tsortInfo * members;
};

typedef struct scc_s * scc;

struct relation_s {
    tsortInfo   rel_suc;  // pkg requiring this package
    rpmsenseFlags rel_flags; // accumulated flags of the requirements
    struct relation_s * rel_next;
};

typedef struct relation_s * relation;

struct tsortInfo_s {
    rpmte te;
    int	     tsi_count;     // #pkgs this pkg requires
    int	     tsi_qcnt;      // #pkgs requiring this package
    int	     tsi_reqx;       // requires Idx/mark as (queued/loop)
    struct relation_s * tsi_relations;
    struct relation_s * tsi_forward_relations;
    tsortInfo tsi_suc;        // used for queuing (addQ)
    int      tsi_SccIdx;     // # of the SCC the node belongs to
                             // (1 for trivial SCCs)
    int      tsi_SccLowlink; // used for SCC detection
};

static void rpmTSIFree(tsortInfo tsi)
{
    relation rel;

    while (tsi->tsi_relations != NULL) {
	rel = tsi->tsi_relations;
	tsi->tsi_relations = tsi->tsi_relations->rel_next;
	free(rel);
    }
    while (tsi->tsi_forward_relations != NULL) {
	rel = tsi->tsi_forward_relations;
	tsi->tsi_forward_relations = \
	    tsi->tsi_forward_relations->rel_next;
	free(rel);
    }
}

static inline int addSingleRelation(rpmte p,
				    rpmte q,
				    rpmsenseFlags dsflags)
{
    struct tsortInfo_s *tsi_p, *tsi_q;
    relation rel;
    rpmElementType teType = rpmteType(p);
    rpmsenseFlags flags;

    /* Avoid deps outside this transaction and self dependencies */
    if (q == NULL || q == p)
	return 0;

    /* Erasures are reversed installs. */
    if (teType == TR_REMOVED) {
	rpmte r = p;
	p = q;
	q = r;
	flags = isErasePreReq(dsflags);
    } else {
	flags = isInstallPreReq(dsflags);
    }

    /* map legacy prereq to pre/preun as needed */
    if (isLegacyPreReq(dsflags)) {
	flags |= (teType == TR_ADDED) ?
	    RPMSENSE_SCRIPT_PRE : RPMSENSE_SCRIPT_PREUN;
    }

    tsi_p = rpmteTSI(p);
    tsi_q = rpmteTSI(q);

    /* if relation got already added just update the flags */
    if (tsi_q->tsi_relations && tsi_q->tsi_relations->rel_suc == tsi_p) {
	tsi_q->tsi_relations->rel_flags |= flags;
	tsi_p->tsi_forward_relations->rel_flags |= flags;
	return 0;
    }

    /* Record next "q <- p" relation (i.e. "p" requires "q"). */
    if (p != q) {
	/* bump p predecessor count */
	tsi_p->tsi_count++;
    }

    rel = xcalloc(1, sizeof(*rel));
    rel->rel_suc = tsi_p;
    rel->rel_flags = flags;

    rel->rel_next = tsi_q->tsi_relations;
    tsi_q->tsi_relations = rel;
    if (p != q) {
	/* bump q successor count */
	tsi_q->tsi_qcnt++;
    }

    rel = xcalloc(1, sizeof(*rel));
    rel->rel_suc = tsi_q;
    rel->rel_flags = flags;

    rel->rel_next = tsi_p->tsi_forward_relations;
    tsi_p->tsi_forward_relations = rel;

    return 0;
}

/**
 * Record next "q <- p" relation (i.e. "p" requires "q").
 * @param ts		transaction set
 * @param p		predecessor (i.e. package that "Requires: q")
 * @param requires	relation
 * @return		0 always
 */
static inline int addRelation(rpmts ts,
			      rpmal al,
			      rpmte p,
			      rpmds requires)
{
    rpmte q;
    rpmsenseFlags dsflags;

    dsflags = rpmdsFlags(requires);

    /* Avoid dependendencies which are not relevant for ordering */
    if (dsflags & (RPMSENSE_RPMLIB|RPMSENSE_CONFIG|RPMSENSE_PRETRANS|RPMSENSE_POSTTRANS))
	return 0;

    q = rpmalSatisfiesDepend(al, p, requires);

    /* Avoid deps outside this transaction and self dependencies */
    if (q == NULL || q == p)
	return 0;

    addSingleRelation(p, q, dsflags);

    return 0;
}

/**
 * Add element to list sorting by tsi_qcnt.
 * @param p		new element
 * @retval qp		address of first element
 * @retval rp		address of last element
 * @param prefcolor
 */
static void addQ(tsortInfo p, tsortInfo * qp, tsortInfo * rp,
		rpm_color_t prefcolor)
{
    tsortInfo q, qprev;
    rpm_color_t pcolor = rpmteColor(p->te);
    int tailcond;

    /* Mark the package as queued. */
    p->tsi_reqx = 1;

    if ((*rp) == NULL) {	/* 1st element */
	/* FIX: double indirection */
	(*rp) = (*qp) = p;
	return;
    }

    if (rpmteType(p->te) == TR_ADDED)
	tailcond = (pcolor && pcolor != prefcolor);
    else
	tailcond = (pcolor && pcolor == prefcolor);

    /* Find location in queue using metric tsi_qcnt and color. */
    for (qprev = NULL, q = (*qp);
	 q != NULL;
	 qprev = q, q = q->tsi_suc)
    {
	/* Place preferred color towards queue head on install, tail on erase */
	if (tailcond && (pcolor != rpmteColor(q->te)))
	    continue;

	if (q->tsi_qcnt <= p->tsi_qcnt)
	    break;
    }

    if (qprev == NULL) {	/* insert at beginning of list */
	p->tsi_suc = q;
	(*qp) = p;		/* new head */
    } else if (q == NULL) {	/* insert at end of list */
	qprev->tsi_suc = p;
	(*rp) = p;		/* new tail */
    } else {			/* insert between qprev and q */
	p->tsi_suc = q;
	qprev->tsi_suc = p;
    }
}

typedef struct sccData_s {
    int index;			/* DFS node number counter */
    tsortInfo *stack;		/* Stack of nodes */
    int stackcnt;		/* Stack top counter */
    scc SCCs;			/* Array of SCC's found */
    int sccCnt;			/* Number of SCC's found */
} * sccData;

static void tarjan(sccData sd, tsortInfo tsi)
{
    tsortInfo tsi_q;
    relation rel;

    /* use negative index numbers */
    sd->index--;
    /* Set the depth index for p */
    tsi->tsi_SccIdx = sd->index;
    tsi->tsi_SccLowlink = sd->index;

    sd->stack[sd->stackcnt++] = tsi;                   /* Push p on the stack */
    for (rel=tsi->tsi_relations; rel != NULL; rel=rel->rel_next) {
	/* Consider successors of p */
	tsi_q = rel->rel_suc;
	if (tsi_q->tsi_SccIdx > 0)
	    /* Ignore already found SCCs */
	    continue;
	if (tsi_q->tsi_SccIdx == 0){
	    /* Was successor q not yet visited? */
	    tarjan(sd, tsi_q);                       /* Recurse */
	    /* negative index numers: use max as it is closer to 0 */
	    tsi->tsi_SccLowlink = (
		tsi->tsi_SccLowlink > tsi_q->tsi_SccLowlink
		? tsi->tsi_SccLowlink : tsi_q->tsi_SccLowlink);
	} else {
	    tsi->tsi_SccLowlink = (
		tsi->tsi_SccLowlink > tsi_q->tsi_SccIdx
		? tsi->tsi_SccLowlink : tsi_q->tsi_SccIdx);
	}
    }

    if (tsi->tsi_SccLowlink == tsi->tsi_SccIdx) {
	/* v is the root of an SCC? */
	if (sd->stack[sd->stackcnt-1] == tsi) {
	    /* ignore trivial SCCs */
	    tsi_q = sd->stack[--sd->stackcnt];
	    tsi_q->tsi_SccIdx = 1;
	} else {
	    int stackIdx = sd->stackcnt;
	    do {
		tsi_q = sd->stack[--stackIdx];
		tsi_q->tsi_SccIdx = sd->sccCnt;
	    } while (tsi_q != tsi);

	    stackIdx = sd->stackcnt;
	    do {
		tsi_q = sd->stack[--stackIdx];
		/* Calculate count for the SCC */
		sd->SCCs[sd->sccCnt].count += tsi_q->tsi_count;
		/* Subtract internal relations */
		for (rel=tsi_q->tsi_relations; rel != NULL;
						    rel=rel->rel_next) {
		    if (rel->rel_suc != tsi_q &&
			    rel->rel_suc->tsi_SccIdx == sd->sccCnt)
			sd->SCCs[sd->sccCnt].count--;
		}
	    } while (tsi_q != tsi);
	    sd->SCCs[sd->sccCnt].size = sd->stackcnt - stackIdx;
	    /* copy members */
	    sd->SCCs[sd->sccCnt].members = xcalloc(sd->SCCs[sd->sccCnt].size,
					   sizeof(tsortInfo));
	    memcpy(sd->SCCs[sd->sccCnt].members, sd->stack + stackIdx,
		   sd->SCCs[sd->sccCnt].size * sizeof(tsortInfo));
	    sd->stackcnt = stackIdx;
	    sd->sccCnt++;
	}
    }
}

/* Search for SCCs and return an array last entry has a .size of 0 */
static scc detectSCCs(tsortInfo orderInfo, int nelem, int debugloops)
{
    /* Set up data structures needed for the tarjan algorithm */
    scc SCCs = xcalloc(nelem+3, sizeof(*SCCs));
    tsortInfo *stack = xcalloc(nelem, sizeof(*stack));
    struct sccData_s sd = { 0, stack, 0, SCCs, 2 };

    for (int i = 0; i < nelem; i++) {
	tsortInfo tsi = &orderInfo[i];
	/* Start a DFS at each node */
	if (tsi->tsi_SccIdx == 0)
	    tarjan(&sd, tsi);
    }

    free(stack);

    SCCs = xrealloc(SCCs, (sd.sccCnt+1)*sizeof(struct scc_s));

    /* Debug output */
    if (sd.sccCnt > 2) {
	int msglvl = debugloops ?  RPMLOG_WARNING : RPMLOG_DEBUG;
	rpmlog(msglvl, "%i Strongly Connected Components\n", sd.sccCnt-2);
	for (int i = 2; i < sd.sccCnt; i++) {
	    rpmlog(msglvl, "SCC #%i: %i members (%i external dependencies)\n",
			   i-1, SCCs[i].size, SCCs[i].count);

	    /* loop over members */
	    for (int j = 0; j < SCCs[i].size; j++) {
		tsortInfo member = SCCs[i].members[j];
		rpmlog(msglvl, "\t%s\n", rpmteNEVRA(member->te));
		/* show relations between members */
		relation rel = member->tsi_forward_relations;
		for (; rel != NULL; rel=rel->rel_next) {
		    if (rel->rel_suc->tsi_SccIdx!=i) continue;
		    rpmlog(msglvl, "\t\t%s %s\n",
			   rel->rel_flags ? "=>" : "->",
			   rpmteNEVRA(rel->rel_suc->te));
		}
	    }
	}
    }
    return SCCs;
}

static void collectTE(rpm_color_t prefcolor, tsortInfo q,
		      rpmte * newOrder, int * newOrderCount,
		      scc SCCs,
		      tsortInfo * queue_end,
		      tsortInfo * outer_queue,
		      tsortInfo * outer_queue_end)
{
    char deptypechar = (rpmteType(q->te) == TR_REMOVED ? '-' : '+');

    if (rpmIsDebug()) {
	int depth = 1;
	/* figure depth in tree for nice formatting */
	for (rpmte p = q->te; (p = rpmteParent(p)); depth++) {}
	rpmlog(RPMLOG_DEBUG, "%5d%5d%5d%5d %*s%c%s\n",
	       *newOrderCount, q->tsi_count, q->tsi_qcnt,
	       depth, (2 * depth), "",
	       deptypechar, rpmteNEVRA(q->te));
    }

    newOrder[*newOrderCount] = q->te;
    (*newOrderCount)++;

    /* T6. Erase relations. */
    for (relation rel = q->tsi_relations; rel != NULL; rel = rel->rel_next) {
	tsortInfo p = rel->rel_suc;
	/* ignore already collected packages */
	if (p->tsi_SccIdx == 0) continue;
	if (p == q) continue;

	if (p && (--p->tsi_count) == 0) {
	    (void) rpmteSetParent(p->te, q->te);

	    if (q->tsi_SccIdx > 1 && q->tsi_SccIdx != p->tsi_SccIdx) {
                /* Relation point outside of this SCC: add to outside queue */
		assert(outer_queue != NULL && outer_queue_end != NULL);
		addQ(p, outer_queue, outer_queue_end, prefcolor);
	    } else {
		addQ(p, &q->tsi_suc, queue_end, prefcolor);
	    }
	}
	if (p && p->tsi_SccIdx > 1 &&
	                 p->tsi_SccIdx != q->tsi_SccIdx) {
	    if (--SCCs[p->tsi_SccIdx].count == 0) {
		/* New SCC is ready, add this package as representative */
		(void) rpmteSetParent(p->te, q->te);

		if (outer_queue != NULL) {
		    addQ(p, outer_queue, outer_queue_end, prefcolor);
		} else {
		    addQ(p, &q->tsi_suc, queue_end, prefcolor);
		}
	    }
	}
    }
    q->tsi_SccIdx = 0;
}

static void dijkstra(const struct scc_s *SCC, int sccNr)
{
    int start, end;
    relation rel;

    /* can use a simple queue as edge weights are always 1 */
    tsortInfo * queue = xmalloc((SCC->size+1) * sizeof(*queue));

    /*
     * Find packages that are prerequired and use them as
     * starting points for the Dijkstra algorithm
     */
    start = end = 0;
    for (int i = 0; i < SCC->size; i++) {
	tsortInfo tsi = SCC->members[i];
	tsi->tsi_SccLowlink = INT_MAX;
	for (rel=tsi->tsi_forward_relations; rel != NULL; rel=rel->rel_next) {
	    if (rel->rel_flags && rel->rel_suc->tsi_SccIdx == sccNr) {
		if (rel->rel_suc != tsi) {
		    tsi->tsi_SccLowlink =  0;
		    queue[end++] = tsi;
		} else {
		    tsi->tsi_SccLowlink =  INT_MAX/2;
		}
		break;
	    }
	}
    }

    if (start == end) { /* no regular prereqs; add self prereqs to queue */
	for (int i = 0; i < SCC->size; i++) {
	    tsortInfo tsi = SCC->members[i];
	    if (tsi->tsi_SccLowlink != INT_MAX) {
		queue[end++] = tsi;
	    }
	}
    }

    /* Do Dijkstra */
    while (start != end) {
	tsortInfo tsi = queue[start++];
	for (rel=tsi->tsi_forward_relations; rel != NULL; rel=rel->rel_next) {
	    tsortInfo next_tsi = rel->rel_suc;
	    if (next_tsi->tsi_SccIdx != sccNr) continue;
	    if (next_tsi->tsi_SccLowlink > tsi->tsi_SccLowlink+1) {
		next_tsi->tsi_SccLowlink = tsi->tsi_SccLowlink + 1;
		queue[end++] = rel->rel_suc;
	    }
	}
    }
    free(queue);
}

static void collectSCC(rpm_color_t prefcolor, tsortInfo p_tsi,
		       rpmte * newOrder, int * newOrderCount,
		       scc SCCs, tsortInfo * queue_end)
{
    int sccNr = p_tsi->tsi_SccIdx;
    const struct scc_s * SCC = SCCs+sccNr;

    /* remove p from the outer queue */
    tsortInfo outer_queue_start = p_tsi->tsi_suc;
    p_tsi->tsi_suc = NULL;

    /*
     * Run a multi source Dijkstra's algorithm to find relations
     * that can be zapped with least danger to pre reqs.
     * As weight of the edges is always 1 it is not necessary to
     * sort the vertices by distance as the queue gets them
     * already in order
    */
    dijkstra(SCC, sccNr);

    while (1) {
	tsortInfo best = NULL;
	tsortInfo inner_queue_start, inner_queue_end;
	int best_score = 0;

	/* select best candidate to start with */
	for (int i = 0; i < SCC->size; i++) {
	    tsortInfo tsi = SCC->members[i];
	    if (tsi->tsi_SccIdx == 0) /* package already collected */
		continue;
	    if (tsi->tsi_SccLowlink >= best_score) {
		best = tsi;
		best_score = tsi->tsi_SccLowlink;
	    }
	}

	if (best == NULL) /* done */
	    break;

	/* collect best candidate and all packages that get freed */
	inner_queue_start = inner_queue_end = NULL;
	addQ(best, &inner_queue_start, &inner_queue_end, prefcolor);

	for (; inner_queue_start != NULL;
	     inner_queue_start = inner_queue_start->tsi_suc) {
	    /* Mark the package as unqueued. */
	    inner_queue_start->tsi_reqx = 0;
	    collectTE(prefcolor, inner_queue_start, newOrder, newOrderCount,
		      SCCs, &inner_queue_end, &outer_queue_start, queue_end);
	}
    }

    /* restore outer queue */
    p_tsi->tsi_suc = outer_queue_start;
}

int rpmtsOrder(rpmts ts)
{
    tsMembers tsmem = rpmtsMembers(ts);
    rpm_color_t prefcolor = rpmtsPrefColor(ts);
    rpmtsi pi; rpmte p;
    tsortInfo q, r;
    rpmte * newOrder;
    int newOrderCount = 0;
    int rc;
    rpmal erasedPackages;
    scc SCCs;
    int nelem = rpmtsNElements(ts);
    tsortInfo sortInfo = xcalloc(nelem, sizeof(struct tsortInfo_s));
    ARGV_t seenColls = NULL;

    (void) rpmswEnter(rpmtsOp(ts, RPMTS_OP_ORDER), 0);

    /* Create erased package index. */
    erasedPackages = rpmtsCreateAl(ts, TR_REMOVED);

    for (int i = 0; i < nelem; i++) {
	sortInfo[i].te = tsmem->order[i];
	rpmteSetTSI(tsmem->order[i], &sortInfo[i]);
    }

    /* Record relations. */
    rpmlog(RPMLOG_DEBUG, "========== recording tsort relations\n");
    pi = rpmtsiInit(ts);
    while ((p = rpmtsiNext(pi, 0)) != NULL) {
	rpmal al = (rpmteType(p) == TR_REMOVED) ? 
		   erasedPackages : tsmem->addedPackages;
	rpmds requires = rpmdsInit(rpmteDS(p, RPMTAG_REQUIRENAME));
	rpmds order = rpmdsInit(rpmteDS(p, RPMTAG_ORDERNAME));

	while (rpmdsNext(requires) >= 0) {
	    /* Record next "q <- p" relation (i.e. "p" requires "q"). */
	    (void) addRelation(ts, al, p, requires);
	}

	while (rpmdsNext(order) >= 0) {
	    /* Record next "q <- p" ordering request */
	    (void) addRelation(ts, al, p, order);
	}
    }

    seenColls = argvFree(seenColls);
    rpmtsiFree(pi);

    newOrder = xcalloc(tsmem->orderCount, sizeof(*newOrder));
    SCCs = detectSCCs(sortInfo, nelem, (rpmtsFlags(ts) & RPMTRANS_FLAG_DEPLOOPS));

    rpmlog(RPMLOG_DEBUG, "========== tsorting packages (order, #predecessors, #succesors, depth)\n");

    for (int i = 0; i < 2; i++) {
	/* Do two separate runs: installs first - then erases */
	int oType = !i ? TR_ADDED : TR_REMOVED;
	q = r = NULL;
	/* Scan for zeroes and add them to the queue */
	for (int e = 0; e < nelem; e++) {
	    tsortInfo p = &sortInfo[e];
	    if (rpmteType(p->te) != oType) continue;
	    if (p->tsi_count != 0)
		continue;
	    p->tsi_suc = NULL;
	    addQ(p, &q, &r, prefcolor);
	}

	/* Add one member of each leaf SCC */
	for (int i = 2; SCCs[i].members != NULL; i++) {
	    tsortInfo member = SCCs[i].members[0];
	    if (SCCs[i].count == 0 && rpmteType(member->te) == oType) {
		addQ(member, &q, &r, prefcolor);
	    }
	}

	while (q != NULL) {
	    /* Mark the package as unqueued. */
	    q->tsi_reqx = 0;
	    if (q->tsi_SccIdx > 1) {
		collectSCC(prefcolor, q, newOrder, &newOrderCount, SCCs, &r);
	    } else {
		collectTE(prefcolor, q, newOrder, &newOrderCount, SCCs, &r,
			  NULL, NULL);
	    }
	    q = q->tsi_suc;
	}
    }

    /* Clean up tsort data */
    for (int i = 0; i < nelem; i++) {
	rpmteSetTSI(tsmem->order[i], NULL);
	rpmTSIFree(&sortInfo[i]);
    }
    free(sortInfo);

    assert(newOrderCount == tsmem->orderCount);

    tsmem->order = _free(tsmem->order);
    tsmem->order = newOrder;
    tsmem->orderAlloced = tsmem->orderCount;
    rc = 0;

    for (int i = 2; SCCs[i].members != NULL; i++) {
	free(SCCs[i].members);
    }
    free(SCCs);
    rpmalFree(erasedPackages);

    (void) rpmswExit(rpmtsOp(ts, RPMTS_OP_ORDER), 0);

    return rc;
}
