path: root/calendar/layout.c

/* Event layout engine for Gnomecal
 *
 * Copyright (C) 1998 The Free Software Foundation
 *
 * Authors: Miguel de Icaza <miguel@nuclecu.unam.mx>
 *          Federico Mena <federico@nuclecu.unam.mx>
 */

#include <config.h>
#include <stdlib.h>
#include "layout.h"


/* This structure is used to pass around layout information among the internal layout functions */
struct layout_info {
    GList *events;          /* List of events from client */
    int num_events;         /* The number of events (length of the list) */
    LayoutQueryTimeFunc func;   /* Function to convert a list item to a start/end time pair */
    int num_rows;           /* Size of the time partition */
    time_t *partition;      /* The time partition containing start and end time values */
    int *array;         /* Working array of free and allocated time slots */
    int *allocations;       /* Returned array of slot allocations */
    int *slots;         /* Returned array of slots used */
    int num_slots;          /* Number of slots used */
};


/* This defines the maximum number of events to overlap per row.  More than that number of events
 * will not be displayed.  This is not ideal, so sue me.
 */
#define MAX_EVENTS_PER_ROW 32


/* Compares two time_t values, used for qsort() */
static int
compare_time_t (const void *a, const void *b)
{
    time_t ta, tb;

    ta = *((time_t *) a);
    tb = *((time_t *) b);

    if (ta < tb)
        return -1;
    else if (ta > tb)
        return 1;
    else
        return 0;
}

/* Builds a partition of the time range occupied by the events in the list.  It returns an array
 * with the times that define the partition and the number of items in the partition.
 */
static void
build_partition (struct layout_info *li)
{
    time_t *rows, *p, *q;
    GList *list;
    int i, unique_vals;

    /* This is the maximum number of rows we would need */

    li->num_rows = li->num_events * 2;

    /* Fill the rows with the times */

    rows = g_new (time_t, li->num_rows);

    for (list = li->events, p = rows; list; list = list->next) {
        (* li->func) (list, &p[0], &p[1]);
        p += 2;
    }

    /* Do a sort | uniq on the array */

    qsort (rows, li->num_rows, sizeof (time_t), compare_time_t);

    p = rows;
    q = rows + 1;
    unique_vals = 1;

    for (i = 1; i < li->num_rows; i++, q++)
        if (*q != *p) {
            unique_vals++;
            p++;
            *p = *q;
        }

    /* Return the number of unique values in the partition and the partition array itself */

    li->num_rows = unique_vals;
    li->partition = rows;
}

/* Returns the index of the element in the partition that corresponds to the specified time */
int
find_index (struct layout_info *li, time_t t)
{
    int i;

    for (i = 0; ; i++)
        if (li->partition[i] == t)
            return i;
}

#define xy(li, x, y) li->array[(y * MAX_EVENTS_PER_ROW) + (x)]

/* Checks that all the cells in the slot array at the specified slot column are free to use by an
 * event that has the specified range.
 */
static int
range_is_empty (struct layout_info *li, int slot, time_t start, time_t end)
{
    int i;

    for (i = find_index (li, start); li->partition[i] < end; i++)
        if (xy (li, slot, i) != -1)
            return FALSE;

    return TRUE;
}

/* Allocates a time in the slot array for the specified event's index */
static void
range_allocate (struct layout_info *li, int slot, time_t start, time_t end, int ev_num)
{
    int i;

    for (i = find_index (li, start); li->partition[i] < end; i++)
        xy (li, slot, i) = ev_num;
}

/* Performs the initial allocation of slots for events.  Each event gets one column; they will be
 * expanded in a later stage.  Returns the number of columns used.
 */
static void
initial_allocate (struct layout_info *li)
{
    GList *events;
    int i;
    int slot;
    int num_slots;
    time_t start, end;

    num_slots = 0;

    for (i = 0, events = li->events; events; events = events->next, i++) {
        (* li->func) (events, &start, &end);

        /* Start with no allocation, no columns */

        li->allocations[i] = -1;
        li->slots[i] = 0;

        /* Find a free column for the event */

        for (slot = 0; slot < MAX_EVENTS_PER_ROW; slot++)
            if (range_is_empty (li, slot, start, end)) {
                range_allocate (li, slot, start, end, i);

                li->allocations[i] = slot;
                li->slots[i] = 1;

                if ((slot + 1) > num_slots)
                    num_slots = slot + 1;

                break;
            }
    }

    li->num_slots = num_slots;
}

/* Returns the maximum number of columns that an event can expanded by in the slot array */
static int
columns_to_expand (struct layout_info *li, int ev_num, time_t start, time_t end)
{
    int cols;
    int slot;
    int i_start;
    int i;

    cols = 0;

    i_start = find_index (li, start);

    for (slot = li->allocations[ev_num] + 1; slot < li->num_slots; slot++) {
        for (i = i_start; li->partition[i] < end; i++)
            if (xy (li, slot, i) != -1)
                return cols;

        cols++;
    }

    return cols;
}

/* Expands an event by the specified number of columns */
static void
do_expansion (struct layout_info *li, int ev_num, time_t start, time_t end, int num_cols)
{
    int i, j;
    int slot;

    for (i = find_index (li, start); li->partition[i] < end; i++) {
        slot = li->allocations[ev_num] + 1;

        for (j = 0; j < num_cols; j++)
            xy (li, slot + j, i) = ev_num;
    }
}

/* Expands the events in the slot array to occupy as many columns as possible.  This is the second
 * pass of the layout algorithm.
 */
static void
expand_events (struct layout_info *li)
{
    GList *events;
    time_t start, end;
    int i;
    int cols;

    for (i = 0, events = li->events; events; events = events->next, i++) {
        (* li->func) (events, &start, &end);

        cols = columns_to_expand (li, i, start, end);

        if (cols == 0)
            continue; /* We can't expand this event */

        do_expansion (li, i, start, end, cols);

        li->slots[i] += cols;
    }
}

void
layout_events (GList *events, LayoutQueryTimeFunc func, int *num_slots, int **allocations, int **slots)
{
    struct layout_info li;
    int i;

    g_return_if_fail (num_slots != NULL);
    g_return_if_fail (allocations != NULL);
    g_return_if_fail (slots != NULL);

    if (!events) {
        *num_slots = 0;
        *allocations = NULL;
        *slots = NULL;

        return;
    }

    li.events = events;
    li.num_events = g_list_length (events);
    li.func = func;

    /* Build the partition of the time range, and then build the array of slots */

    build_partition (&li);

    li.array = g_new (int, li.num_rows * MAX_EVENTS_PER_ROW);
    for (i = 0; i < (li.num_rows * MAX_EVENTS_PER_ROW); i++)
        li.array[i] = -1; /* This is our 'empty' value */

    /* Build the arrays for allocations and columns used */

    li.allocations = g_new (int, li.num_events);
    li.slots = g_new (int, li.num_events);

    /* Perform initial allocation and then expand the events to as many slots as they can occupy */

    initial_allocate (&li);
    expand_events (&li);

    /* Clean up and return values */

    g_free (li.array);

    *num_slots = li.num_slots;
    *allocations = li.allocations;
    *slots = li.slots;
}