fish-shell/pager.cpp

#include "config.h"

#include "pager.h"
#include "highlight.h"
#include "input_common.h"
#include "wutil.h"
#include <vector>
#include <map>

typedef pager_t::comp_t comp_t;
typedef std::vector<completion_t> completion_list_t;
typedef std::vector<comp_t> comp_info_list_t;

/** The minimum width (in characters) the terminal must to show completions at all */
#define PAGER_MIN_WIDTH 16

/** The maximum number of columns of completion to attempt to fit onto the screen */
#define PAGER_MAX_COLS 6

/** Width of the search field */
#define PAGER_SEARCH_FIELD_WIDTH 12

/** Text we use for the search field */
#define SEARCH_FIELD_PROMPT _(L"search: ")

/* Returns numer / denom, rounding up. As a "courtesy" 0/0 is 0. */
static size_t divide_round_up(size_t numer, size_t denom)
{
    if (numer == 0)
        return 0;

    assert(denom > 0);
    return numer / denom + (numer % denom ? 1 : 0);
}

/**
   This function calculates the minimum width for each completion
   entry in the specified array_list. This width depends on the
   terminal size, so this function should be called when the terminal
   changes size.
*/
void pager_t::recalc_min_widths(comp_info_list_t * lst) const
{
    for (size_t i=0; i<lst->size(); i++)
    {
        comp_t *c = &lst->at(i);

        c->min_width = mini(c->desc_width, maxi(0, available_term_width/3 - 2)) +
                       mini(c->desc_width, maxi(0, available_term_width/5 - 4)) +4;
    }

}

/**
   Print the specified string, but use at most the specified amount of
   space. If the whole string can't be fitted, ellipsize it.

   \param str the string to print
   \param color the color to apply to every printed character
   \param max the maximum space that may be used for printing
   \param has_more if this flag is true, this is not the entire string, and the string should be ellisiszed even if the string fits but takes up the whole space.
*/

static int print_max(const wcstring &str, highlight_spec_t color, int max, bool has_more, line_t *line)
{
    int written = 0;
    for (size_t i=0; i < str.size(); i++)
    {
        wchar_t c = str.at(i);

        if (written + wcwidth(c) > max)
            break;
        if ((written + wcwidth(c) == max) && (has_more || i + 1 < str.size()))
        {
            line->append(ellipsis_char, color);
            written += wcwidth(ellipsis_char);
            break;
        }

        line->append(c, color);
        written += wcwidth(c);
    }
    return written;
}


/**
   Print the specified item using at the specified amount of space
*/
line_t pager_t::completion_print_item(const wcstring &prefix, const comp_t *c, size_t row, size_t column, int width, bool secondary, bool selected, page_rendering_t *rendering) const
{
    int comp_width=0, desc_width=0;
    int written=0;

    line_t line_data;

    if (c->pref_width <= width)
    {
        /*
          The entry fits, we give it as much space as it wants
        */
        comp_width = c->comp_width;
        desc_width = c->desc_width;
    }
    else
    {
        /*
          The completion and description won't fit on the
          allocated space. Give a maximum of 2/3 of the
          space to the completion, and whatever is left to
          the description.
        */
        int desc_all = c->desc_width?c->desc_width+4:0;

        comp_width = maxi(mini(c->comp_width, 2*(width-4)/3), width - desc_all);
        if (c->desc_width)
            desc_width = width-comp_width-4;

    }

    int bg_color = secondary ? highlight_spec_pager_secondary : highlight_spec_normal;
    if (selected)
    {
        bg_color = highlight_spec_search_match;
    }

    for (size_t i=0; i<c->comp.size(); i++)
    {
        const wcstring &comp = c->comp.at(i);

        if (i != 0)
            written += print_max(PAGER_SPACER_STRING, highlight_spec_normal, comp_width - written, true /* has_more */, &line_data);

        int packed_color = highlight_spec_pager_prefix | highlight_make_background(bg_color);
        written += print_max(prefix, packed_color, comp_width - written, ! comp.empty(), &line_data);

        packed_color = highlight_spec_pager_completion | highlight_make_background(bg_color);
        written += print_max(comp, packed_color, comp_width - written, i + 1 < c->comp.size(), &line_data);
    }

    if (desc_width)
    {
        int packed_color = highlight_spec_pager_description | highlight_make_background(bg_color);
        while (written < (width-desc_width-2)) //the 2 here refers to the parenthesis below
        {
            written += print_max(L" ", packed_color, 1, false, &line_data);
        }
        written += print_max(L"(", packed_color, 1, false, &line_data);
        written += print_max(c->desc, packed_color, desc_width, false, &line_data);
        written += print_max(L")", packed_color, 1, false, &line_data);
    }
    else
    {
        while (written < width)
        {
            written += print_max(L" ", 0, 1, false, &line_data);
        }
    }

    return line_data;
}

/**
   Print the specified part of the completion list, using the
   specified column offsets and quoting style.

   \param l The list of completions to print
   \param cols number of columns to print in
   \param width An array specifying the width of each column
   \param row_start The first row to print
   \param row_stop the row after the last row to print
   \param prefix The string to print before each completion
*/

void pager_t::completion_print(size_t cols, int *width_per_column, size_t row_start, size_t row_stop, const wcstring &prefix, const comp_info_list_t &lst, page_rendering_t *rendering) const
{
    /* Teach the rendering about the rows it printed */
    assert(row_start >= 0);
    assert(row_stop >= row_start);
    rendering->row_start = row_start;
    rendering->row_end = row_stop;

    size_t rows = (lst.size()-1)/cols+1;

    size_t effective_selected_idx = this->visual_selected_completion_index(rows, cols);

    for (size_t row = row_start; row < row_stop; row++)
    {
        for (size_t col = 0; col < cols; col++)
        {
            int is_last = (col==(cols-1));

            if (lst.size() <= col * rows + row)
                continue;

            size_t idx = col * rows + row;
            const comp_t *el = &lst.at(idx);
            bool is_selected = (idx == effective_selected_idx);

            /* Print this completion on its own "line" */
            line_t line = completion_print_item(prefix, el, row, col, width_per_column[col] - (is_last ? 0 : PAGER_SPACER_STRING_WIDTH), row%2, is_selected, rendering);

            /* If there's more to come, append two spaces */
            if (col + 1 < cols)
            {
                line.append(PAGER_SPACER_STRING, 0);
            }

            /* Append this to the real line */
            rendering->screen_data.create_line(row - row_start).append_line(line);
        }
    }
}


/* Trim leading and trailing whitespace, and compress other whitespace runs into a single space. */
static void mangle_1_completion_description(wcstring *str)
{
    size_t leading = 0, trailing = 0, len = str->size();

    // Skip leading spaces
    for (; leading < len; leading++)
    {
        if (! iswspace(str->at(leading)))
            break;
    }

    // Compress runs of spaces to a single space
    bool was_space = false;
    for (; leading < len; leading++)
    {
        wchar_t wc = str->at(leading);
        bool is_space = iswspace(wc);
        if (! is_space)
        {
            // normal character
            str->at(trailing++) = wc;
        }
        else if (! was_space)
        {
            // initial space in a run
            str->at(trailing++) = L' ';
        }
        else
        {
            // non-initial space in a run, do nothing
        }
        was_space = is_space;
    }

    // leading is now at len, trailing is the new length of the string
    // Delete trailing spaces
    while (trailing > 0 && iswspace(str->at(trailing - 1)))
    {
        trailing--;
    }

    str->resize(trailing);
}

static void join_completions(comp_info_list_t *comps)
{
    // A map from description to index in the completion list of the element with that description
    // The indexes are stored +1
    std::map<wcstring, size_t> desc_table;

    // note that we mutate the completion list as we go, so the size changes
    for (size_t i=0; i < comps->size(); i++)
    {
        const comp_t &new_comp = comps->at(i);
        const wcstring &desc = new_comp.desc;
        if (desc.empty())
            continue;

        // See if it's in the table
        size_t prev_idx_plus_one = desc_table[desc];
        if (prev_idx_plus_one == 0)
        {
            // We're the first with this description
            desc_table[desc] = i+1;
        }
        else
        {
            // There's a prior completion with this description. Append the new ones to it.
            comp_t *prior_comp = &comps->at(prev_idx_plus_one - 1);
            prior_comp->comp.insert(prior_comp->comp.end(), new_comp.comp.begin(), new_comp.comp.end());

            // Erase the element at this index, and decrement the index to reflect that fact
            comps->erase(comps->begin() + i);
            i -= 1;
        }
    }
}

/** Generate a list of comp_t structures from a list of completions */
static comp_info_list_t process_completions_into_infos(const completion_list_t &lst, const wcstring &prefix)
{
    const size_t lst_size = lst.size();

    // Make the list of the correct size up-front
    comp_info_list_t result(lst_size);
    for (size_t i=0; i<lst_size; i++)
    {
        const completion_t &comp = lst.at(i);
        comp_t *comp_info = &result.at(i);

        // Append the single completion string. We may later merge these into multiple.
        comp_info->comp.push_back(escape_string(comp.completion, ESCAPE_ALL | ESCAPE_NO_QUOTED));

        // Append the mangled description
        comp_info->desc = comp.description;
        mangle_1_completion_description(&comp_info->desc);

        // Set the representative completion
        comp_info->representative = comp;
    }
    return result;
}

void pager_t::measure_completion_infos(comp_info_list_t *infos, const wcstring &prefix) const
{
    size_t prefix_len = my_wcswidth(prefix.c_str());
    for (size_t i=0; i < infos->size(); i++)
    {
        comp_t *comp = &infos->at(i);

        // Compute comp_width
        const wcstring_list_t &comp_strings = comp->comp;
        for (size_t j=0; j < comp_strings.size(); j++)
        {
            // If there's more than one, append the length of ', '
            if (j >= 1)
                comp->comp_width += 2;

            comp->comp_width += prefix_len + my_wcswidth(comp_strings.at(j).c_str());
        }

        // Compute desc_width
        comp->desc_width = my_wcswidth(comp->desc.c_str());

        // Compute preferred width
        comp->pref_width = comp->comp_width + comp->desc_width + (comp->desc_width?4:0);
    }

    recalc_min_widths(infos);
}

/* Indicates if the given completion info passes any filtering we have */
bool pager_t::completion_info_passes_filter(const comp_t &info) const
{
    /* If we have no filter, everything passes */
    if (! search_field_shown || this->search_field_line.empty())
        return true;

    const wcstring &needle = this->search_field_line.text;

    /* We do substring matching */
    const fuzzy_match_type_t limit = fuzzy_match_substring;

    /* Match against the description */
    if (string_fuzzy_match_string(needle, info.desc, limit).type != fuzzy_match_none)
    {
        return true;
    }

    /* Match against the completion strings */
    for (size_t i=0; i < info.comp.size(); i++)
    {
        if (string_fuzzy_match_string(needle, prefix + info.comp.at(i), limit).type != fuzzy_match_none)
        {
            return true;
        }
    }

    /* No match */
    return false;
}

/* Update completion_infos from unfiltered_completion_infos, to reflect the filter */
void pager_t::refilter_completions()
{
    this->completion_infos.clear();
    for (size_t i=0; i < this->unfiltered_completion_infos.size(); i++)
    {
        const comp_t &info = this->unfiltered_completion_infos.at(i);
        if (this->completion_info_passes_filter(info))
        {
            this->completion_infos.push_back(info);
        }
    }
}

void pager_t::set_completions(const completion_list_t &raw_completions)
{
    // Get completion infos out of it
    unfiltered_completion_infos = process_completions_into_infos(raw_completions, prefix.c_str());

    // Maybe join them
    if (prefix == L"-")
        join_completions(&unfiltered_completion_infos);

    // Compute their various widths
    measure_completion_infos(&unfiltered_completion_infos, prefix);

    // Refilter them
    this->refilter_completions();
}

void pager_t::set_prefix(const wcstring &pref)
{
    prefix = pref;
}

void pager_t::set_term_size(int w, int h)
{
    assert(w > 0);
    assert(h > 0);
    available_term_width = w;
    available_term_height = h;
    recalc_min_widths(&completion_infos);
}

/**
   Try to print the list of completions l with the prefix prefix using
   cols as the number of columns. Return true if the completion list was
   printed, false if the terminal is to narrow for the specified number of
   columns. Always succeeds if cols is 1.
*/

bool pager_t::completion_try_print(size_t cols, const wcstring &prefix, const comp_info_list_t &lst, page_rendering_t *rendering, size_t suggested_start_row) const
{
    /*
      The calculated preferred width of each column
    */
    int pref_width[PAGER_MAX_COLS] = {0};
    /*
      The calculated minimum width of each column
    */
    int min_width[PAGER_MAX_COLS] = {0};
    /*
      If the list can be printed with this width, width will contain the width of each column
    */
    int *width=pref_width;

    /* Set to one if the list should be printed at this width */
    bool print = false;

    /* Compute the effective term width and term height, accounting for disclosure */
    int term_width = this->available_term_width;
    int term_height = this->available_term_height - 1 - (search_field_shown ? 1 : 0); // we always subtract 1 to make room for a comment row
    if (! this->fully_disclosed)
    {
        term_height = mini(term_height, PAGER_UNDISCLOSED_MAX_ROWS);
    }

    size_t row_count = divide_round_up(lst.size(), cols);

    /* We have more to disclose if we are not fully disclosed and there's more rows than we have in our term height */
    if (! this->fully_disclosed && row_count > term_height)
    {
        rendering->remaining_to_disclose = row_count - term_height;
    }
    else
    {
        rendering->remaining_to_disclose = 0;
    }
    
    /* If we have only one row remaining to disclose, then squelch the comment row. This prevents us from consuming a line to show "...and 1 more row" */
    if (! this->fully_disclosed && rendering->remaining_to_disclose == 1)
    {
        term_height += 1;
        rendering->remaining_to_disclose = 0;
    }

    int pref_tot_width=0;
    int min_tot_width = 0;

    /* Skip completions on tiny terminals */
    if (term_width < PAGER_MIN_WIDTH)
        return true;

    /* Calculate how wide the list would be */
    for (long col = 0; col < cols; col++)
    {
        for (long row = 0; row<row_count; row++)
        {
            int pref,min;
            const comp_t *c;
            if (lst.size() <= col*row_count + row)
                continue;

            c = &lst.at(col*row_count + row);
            pref = c->pref_width;
            min = c->min_width;

            if (col != cols-1)
            {
                pref += 2;
                min += 2;
            }
            min_width[col] = maxi(min_width[col],
                                  min);
            pref_width[col] = maxi(pref_width[col],
                                   pref);
        }
        min_tot_width += min_width[col];
        pref_tot_width += pref_width[col];
    }
    /*
      Force fit if one column
    */
    if (cols == 1)
    {
        if (pref_tot_width > term_width)
        {
            pref_width[0] = term_width;
        }
        width = pref_width;
        print = true;
    }
    else if (pref_tot_width <= term_width)
    {
        /* Terminal is wide enough. Print the list! */
        width = pref_width;
        print = true;
    }
    else
    {
        long next_rows = (lst.size()-1)/(cols-1)+1;
        /*    fwprintf( stderr,
          L"cols %d, min_tot %d, term %d, rows=%d, nextrows %d, termrows %d, diff %d\n",
          cols,
          min_tot_width, term_width,
          rows, next_rows, term_height,
          pref_tot_width-term_width );
        */
        if (min_tot_width < term_width &&
                (((row_count < term_height) && (next_rows >= term_height)) ||
                 (pref_tot_width-term_width< 4 && cols < 3)))
        {
            /*
              Terminal almost wide enough, or squeezing makes the
              whole list fit on-screen.

              This part of the code is really important. People hate
              having to scroll through the completion list. In cases
              where there are a huge number of completions, it can't
              be helped, but it is not uncommon for the completions to
              _almost_ fit on one screen. In those cases, it is almost
              always desirable to 'squeeze' the completions into a
              single page.

              If we are using N columns and can get everything to
              fit using squeezing, but everything would also fit
              using N-1 columns, don't try.
            */

            int tot_width = min_tot_width;
            width = min_width;

            while (tot_width < term_width)
            {
                for (long i=0; (i<cols) && (tot_width < term_width); i++)
                {
                    if (width[i] < pref_width[i])
                    {
                        width[i]++;
                        tot_width++;
                    }
                }
            }
            print = true;
        }
    }

    if (print)
    {
        /* Determine the starting and stop row */
        size_t start_row = 0, stop_row = 0;
        if (row_count <= term_height)
        {
            /* Easy, we can show everything */
            start_row = 0;
            stop_row = row_count;
        }
        else
        {
            /* We can only show part of the full list. Determine which part based on the suggested_start_row */
            assert(row_count > term_height);
            size_t last_starting_row = row_count - term_height;
            start_row = mini(suggested_start_row, last_starting_row);
            stop_row = start_row + term_height;
            assert(start_row >= 0 && start_row <= last_starting_row);
        }

        assert(stop_row >= start_row);
        assert(stop_row <= row_count);
        assert(stop_row - start_row <= term_height);
        completion_print(cols, width, start_row, stop_row, prefix, lst, rendering);

        /* Ellipsis helper string. Either empty or containing the ellipsis char */
        const wchar_t ellipsis_string[] = {ellipsis_char == L'\x2026' ? L'\x2026' : L'\0', L'\0'};

        /* Add the progress line. It's a "more to disclose" line if necessary, or a row listing if it's scrollable; otherwise ignore it */
        wcstring progress_text;
        if (rendering->remaining_to_disclose == 1)
        {
            /* I don't expect this case to ever happen */
            progress_text = format_string(L"%lsand 1 more row", ellipsis_string);
        }
        else if (rendering->remaining_to_disclose > 1)
        {
            progress_text = format_string(L"%lsand %lu more rows", ellipsis_string, (unsigned long)rendering->remaining_to_disclose);
        }
        else if (start_row > 0 || stop_row < row_count)
        {
            /* We have a scrollable interface. The +1 here is because we are zero indexed, but want to present things as 1-indexed. We do not add 1 to stop_row or row_count because these are the "past the last value" */
            progress_text = format_string(L"rows %lu to %lu of %lu", start_row + 1, stop_row, row_count);
        }
        else if (completion_infos.empty() && ! unfiltered_completion_infos.empty())
        {
            /* Everything is filtered */
            progress_text = L"(no matches)";
        }

        if (! progress_text.empty())
        {
            line_t &line = rendering->screen_data.add_line();
            print_max(progress_text.c_str(), highlight_spec_pager_progress | highlight_make_background(highlight_spec_pager_progress), term_width, true /* has_more */, &line);
        }

        if (search_field_shown)
        {
            /* Add the search field */
            wcstring search_field_text = search_field_line.text;
            /* Append spaces to make it at least the required width */
            if (search_field_text.size() < PAGER_SEARCH_FIELD_WIDTH)
            {
                search_field_text.append(PAGER_SEARCH_FIELD_WIDTH - search_field_text.size(), L' ');
            }
            line_t *search_field = &rendering->screen_data.insert_line_at_index(0);

            /* We limit the width to term_width - 1 */
            int search_field_written = print_max(SEARCH_FIELD_PROMPT, highlight_spec_normal, term_width - 1, false, search_field);
            search_field_written += print_max(search_field_text, highlight_modifier_force_underline, term_width - search_field_written - 1, false, search_field);
        }

    }
    return print;
}


page_rendering_t pager_t::render() const
{

    /**
       Try to print the completions. Start by trying to print the
       list in PAGER_MAX_COLS columns, if the completions won't
       fit, reduce the number of columns by one. Printing a single
       column never fails.
    */
    page_rendering_t rendering;
    rendering.term_width = this->available_term_width;
    rendering.term_height = this->available_term_height;
    rendering.search_field_shown = this->search_field_shown;
    rendering.search_field_line = this->search_field_line;

    for (int cols = PAGER_MAX_COLS; cols > 0; cols--)
    {
        /* Initially empty rendering */
        rendering.screen_data.resize(0);

        /* Determine how many rows we would need if we had 'cols' columns. Then determine how many columns we want from that. For example, say we had 19 completions. We can fit them into 6 columns, 4 rows, with the last row containing only 1 entry. Or we can fit them into 5 columns, 4 rows, the last row containing 4 entries. Since fewer columns with the same number of rows is better, skip cases where we know we can do better. */
        size_t min_rows_required_for_cols = divide_round_up(completion_infos.size(), cols);
        size_t min_cols_required_for_rows = divide_round_up(completion_infos.size(), min_rows_required_for_cols);

        assert(min_cols_required_for_rows <= cols);
        if (cols > 1 && min_cols_required_for_rows < cols)
        {
            /* Next iteration will be better, so skip this one */
            continue;
        }

        rendering.cols = (size_t)cols;
        rendering.rows = min_rows_required_for_cols;
        rendering.selected_completion_idx = this->visual_selected_completion_index(rendering.rows, rendering.cols);

        if (completion_try_print(cols, prefix, completion_infos, &rendering, suggested_row_start))
        {
            break;
        }
    }
    return rendering;
}

void pager_t::update_rendering(page_rendering_t *rendering) const
{
    if (rendering->term_width != this->available_term_width ||
            rendering->term_height != this->available_term_height ||
            rendering->selected_completion_idx != this->visual_selected_completion_index(rendering->rows, rendering->cols) ||
            rendering->search_field_shown != this->search_field_shown ||
            rendering->search_field_line.text != this->search_field_line.text ||
            rendering->search_field_line.position != this->search_field_line.position ||
            (rendering->remaining_to_disclose > 0 && this->fully_disclosed))
    {
        *rendering = this->render();
    }
}

pager_t::pager_t() : available_term_width(0), available_term_height(0), selected_completion_idx(PAGER_SELECTION_NONE), suggested_row_start(0), fully_disclosed(false), search_field_shown(false)
{
}

bool pager_t::empty() const
{
    return unfiltered_completion_infos.empty();
}

bool pager_t::select_next_completion_in_direction(selection_direction_t direction, const page_rendering_t &rendering)
{
    /* Must have something to select */
    if (this->completion_infos.empty())
    {
        return false;
    }

    /* Handle the case of nothing selected yet */
    if (selected_completion_idx == PAGER_SELECTION_NONE)
    {
        switch (direction)
        {
                /* These directions do something sane */
            case direction_south:
            case direction_next:
            case direction_prev:
                if (direction == direction_prev)
                {
                    selected_completion_idx = completion_infos.size() - 1;
                }
                else
                {
                    selected_completion_idx = 0;
                }
                return true;

                /* These do nothing */
            case direction_north:
            case direction_east:
            case direction_west:
            case direction_deselect:
            default:
                return false;
        }
    }

    /* Ok, we had something selected already. Select something different. */
    size_t new_selected_completion_idx = selected_completion_idx;
    if (! selection_direction_is_cardinal(direction))
    {
        /* Next, previous, or deselect, all easy */
        if (direction == direction_deselect)
        {
            new_selected_completion_idx = PAGER_SELECTION_NONE;
        }
        else if (direction == direction_next)
        {
            new_selected_completion_idx = selected_completion_idx + 1;
            if (new_selected_completion_idx >= completion_infos.size())
            {
                new_selected_completion_idx = 0;
            }
        }
        else if (direction == direction_prev)
        {
            if (selected_completion_idx == 0)
            {
                new_selected_completion_idx = completion_infos.size() - 1;
            }
            else
            {
                new_selected_completion_idx = selected_completion_idx - 1;
            }
        }
        else
        {
            assert(0 && "Unknown non-cardinal direction");
        }
    }
    else
    {
        /* Cardinal directions. We have a completion index; we wish to compute its row and column. */
        size_t current_row = this->get_selected_row(rendering);
        size_t current_col = this->get_selected_column(rendering);

        switch (direction)
        {
            case direction_north:
            {
                /* Go up a whole row. If we cycle, go to the previous column. */
                if (current_row > 0)
                {
                    current_row--;
                }
                else
                {
                    current_row = rendering.rows - 1;
                    if (current_col > 0)
                        current_col--;
                }
                break;
            }

            case direction_south:
            {
                /* Go down, unless we are in the last row. Note that this means that we may set selected_completion_idx to an out-of-bounds value if the last row is incomplete; this is a feature (it allows "last column memory"). */
                if (current_row + 1 < rendering.rows)
                {
                    current_row++;
                }
                else
                {
                    current_row = 0;
                    if (current_col + 1 < rendering.cols)
                        current_col++;

                }
                break;
            }

            case direction_east:
            {
                /* Go east, wrapping to the next row. There is no "row memory," so if we run off the end, wrap. */
                if (current_col + 1 < rendering.cols && (current_col + 1) * rendering.rows + current_row < completion_infos.size())
                {
                    current_col++;
                }
                else
                {
                    current_col = 0;
                    if (current_row + 1 < rendering.rows)
                        current_row++;
                }
                break;
            }

            case direction_west:
            {
                /* Go west, wrapping to the previous row */
                if (current_col > 0)
                {
                    current_col--;
                }
                else
                {
                    current_col = rendering.cols - 1;
                    if (current_row > 0)
                        current_row--;
                }
                break;
            }

            default:
                assert(0 && "Unknown cardinal direction");
                break;
        }

        /* Compute the new index based on the changed row */
        new_selected_completion_idx = current_col * rendering.rows + current_row;
    }

    if (new_selected_completion_idx != selected_completion_idx)
    {
        selected_completion_idx = new_selected_completion_idx;

        /* Update suggested_row_start to ensure the selection is visible. suggested_row_start * rendering.cols is the first suggested visible completion; add the visible completion count to that to get the last one */
        size_t visible_row_count = rendering.row_end - rendering.row_start;

        if (visible_row_count > 0 && selected_completion_idx != PAGER_SELECTION_NONE) //paranoia
        {
            size_t row_containing_selection = this->get_selected_row(rendering);

            /* Ensure our suggested row start is not past the selected row */
            if (suggested_row_start > row_containing_selection)
            {
                suggested_row_start = row_containing_selection;
            }

            /* Ensure our suggested row start is not too early before it */
            if (suggested_row_start + visible_row_count <= row_containing_selection)
            {
                /* The user moved south past the bottom completion */
                if (! fully_disclosed && rendering.remaining_to_disclose > 0)
                {
                    /* Perform disclosure */
                    fully_disclosed = true;
                }
                else
                {
                    /* Scroll */
                    suggested_row_start = row_containing_selection - visible_row_count + 1;

                    /* Ensure fully_disclosed is set. I think we can hit this case if the user resizes the window - we don't want to drop back to the disclosed style */
                    fully_disclosed = true;
                }
            }
        }

        return true;
    }
    else
    {
        return false;
    }
}

size_t pager_t::visual_selected_completion_index(size_t rows, size_t cols) const
{
    /* No completions -> no selection */
    if (completion_infos.empty() || rows == 0 || cols == 0)
    {
        return PAGER_SELECTION_NONE;
    }

    size_t result = selected_completion_idx;
    if (result != PAGER_SELECTION_NONE)
    {
        /* If the selected completion is beyond the last selection, go left by columns until it's within it. This is how we implement "column memory." */
        while (result >= completion_infos.size() && result >= rows)
        {
            result -= rows;
        }

        /* If we are still beyond the last selection, clamp it */
        if (result >= completion_infos.size())
            result = completion_infos.size() - 1;
    }
    assert(result == PAGER_SELECTION_NONE || result < completion_infos.size());
    return result;
}

/* It's possible we have no visual selection but are still navigating the contents, e.g. every completion is filtered */
bool pager_t::is_navigating_contents() const
{
    return selected_completion_idx != PAGER_SELECTION_NONE;
}

void pager_t::set_fully_disclosed(bool flag)
{
    fully_disclosed = flag;
}

const completion_t *pager_t::selected_completion(const page_rendering_t &rendering) const
{
    const completion_t * result = NULL;
    size_t idx = visual_selected_completion_index(rendering.rows, rendering.cols);
    if (idx != PAGER_SELECTION_NONE)
    {
        result = &completion_infos.at(idx).representative;
    }
    return result;
}

/* Get the selected row and column. Completions are rendered column first, i.e. we go south before we go west. So if we have N rows, and our selected index is N + 2, then our row is 2 (mod by N) and our column is 1 (divide by N) */
size_t pager_t::get_selected_row(const page_rendering_t &rendering) const
{
    if (rendering.rows == 0)
        return PAGER_SELECTION_NONE;

    return selected_completion_idx == PAGER_SELECTION_NONE ? PAGER_SELECTION_NONE : selected_completion_idx % rendering.rows;
}

size_t pager_t::get_selected_column(const page_rendering_t &rendering) const
{
    if (rendering.rows == 0)
        return PAGER_SELECTION_NONE;

    return selected_completion_idx == PAGER_SELECTION_NONE ? PAGER_SELECTION_NONE : selected_completion_idx / rendering.rows;
}

void pager_t::clear()
{
    unfiltered_completion_infos.clear();
    completion_infos.clear();
    prefix.clear();
    selected_completion_idx = PAGER_SELECTION_NONE;
    fully_disclosed = false;
    search_field_shown = false;
    search_field_line.clear();
}

void pager_t::set_search_field_shown(bool flag)
{
    this->search_field_shown = flag;
}

bool pager_t::is_search_field_shown() const
{
    return this->search_field_shown;
}

size_t pager_t::cursor_position() const
{
    size_t result = wcslen(SEARCH_FIELD_PROMPT) + this->search_field_line.position;
    /* Clamp it to the right edge */
    if (available_term_width > 0 && result + 1 > available_term_width)
    {
        result = available_term_width - 1;
    }
    return result;
}


/* Constructor */
page_rendering_t::page_rendering_t() : term_width(-1), term_height(-1), rows(0), cols(0), row_start(0), row_end(0), selected_completion_idx(-1), remaining_to_disclose(0), search_field_shown(false)
{
}