/*
 * Copyright 2009, Ingo Weinhold, ingo_weinhold@gmx.de.
 * Distributed under the terms of the MIT License.
 */

#include "chart/DefaultChartAxisLegendSource.h"

#include <math.h>
#include <stdio.h>

#include "chart/ChartDataRange.h"
#include "chart/StringChartLegend.h"


int32
DefaultChartAxisLegendSource::GetAxisLegends(const ChartDataRange& range,
        ChartLegend** legends, double* values, int32 maxLegends)
{
// TODO: Also support scientific notation! Otherwise the numbers can get really
// long.
        double start = range.min;
        double end = range.max;
        double rangeSpan = end - start;

        if (rangeSpan >= maxLegends / 2) {
                // We only need to consider the integer part.

                // find an interval so that we get maxLegends / 2 to maxLegends legends
                double baseInterval = 1;
                double relativeFactor = 1;
                while (rangeSpan / baseInterval / relativeFactor >= maxLegends) {
                        if (relativeFactor == 1) {
                                relativeFactor = 2;
                        } else if (relativeFactor == 2) {
                                relativeFactor = 5;
                        } else if (relativeFactor == 5) {
                                baseInterval *= 10;
                                relativeFactor = 1;
                        }
                }

                // generate the legends
                int32 count = 0;
                double interval = baseInterval * relativeFactor;
                double value = ceil(start / interval) * interval;
                for (; value <= end; value += interval) {
                        char buffer[128];
                        snprintf(buffer, sizeof(buffer), "%.0f", value);
                        StringChartLegend* legend
                                = new(std::nothrow) StringChartLegend(buffer, 1);
                        if (legend == NULL)
                                return count;
        
                        legends[count] = legend;
                        values[count++] = value;
                }

                return count;
        }

        // The range is so small that we need a fraction interval.

        // First find out how many places after the decimal point we need.
        int positions = 0;
        double factor = 1;
        while (rangeSpan * factor < maxLegends / 2) {
                factor *= 10;
                positions++;
        }

        double relativeFactor = 1;
        if (rangeSpan * factor / relativeFactor >= maxLegends) {
                relativeFactor = 2;
                if (rangeSpan * factor / relativeFactor >= maxLegends)
                        relativeFactor = 5;
        }

        // generate the legends
        int32 count = 0;
        double interval = relativeFactor / factor;
        double shiftedValue = ceil(start / interval);
        for (; shiftedValue * interval <= end; shiftedValue++) {
                double value = shiftedValue * interval;
                char buffer[128];
                snprintf(buffer, sizeof(buffer), "%.*f", positions, value);
                StringChartLegend* legend
                        = new(std::nothrow) StringChartLegend(buffer, 1);
                if (legend == NULL)
                        return count;

                legends[count] = legend;
                values[count++] = value;
        }

        return count;
}