AxisHelper.js

import { SCALES, BIG_DATE_SCALES } from "../date/TLDate";
import TLError from "../core/TLError";

/*  AxisHelper
    Strategies for laying out the timenav
    markers and time axis
    Intended as a private class -- probably only known to TimeScale
    Get them using the exported getBestHelper function
================================================== */
class AxisHelper {
    constructor(options) {
		if (options) {
            this.scale = options.scale;
	        this.minor = options.minor;
	        this.major = options.major;
		} else {
            throw new TLError("axis_helper_no_options_err")
        }
       
    }
    
    getPixelsPerTick(pixels_per_milli) {
        return pixels_per_milli * this.minor.factor;
    }

    getMajorTicks(timescale) {
		return this._getTicks(timescale, this.major)
    }

    getMinorTicks(timescale) {
        return this._getTicks(timescale, this.minor)
    }

    _getTicks(timescale, option) {
        var factor_scale = timescale._scaled_padding * option.factor;
        var first_tick_time = timescale._earliest - factor_scale;
        var last_tick_time = timescale._latest + factor_scale;
        var ticks = []
        for (var i = first_tick_time; i < last_tick_time; i += option.factor) {
            ticks.push(timescale.getDateFromTime(i).floor(option.name));
        }

        return {
            name: option.name,
            ticks: ticks
        }

    }

}
var HELPERS = {};

var setHelpers = function(scale_type, scales) {
    HELPERS[scale_type] = [];
    
    for (var idx = 0; idx < scales.length - 1; idx++) {
        var minor = scales[idx];
        var major = scales[idx+1];
        HELPERS[scale_type].push(new AxisHelper({
            scale: minor[3],
            minor: { name: minor[0], factor: minor[1]},
            major: { name: major[0], factor: major[1]}
        }));
    }
};

setHelpers('human', SCALES);
setHelpers('cosmological', BIG_DATE_SCALES);


export function getBestHelper(ts,optimal_tick_width) {
    if (typeof(optimal_tick_width) != 'number' ) {
        optimal_tick_width = 100;
    }
    var ts_scale = ts.getScale();
    var helpers = HELPERS[ts_scale];
    
    if (!helpers) {
        throw new TLError("axis_helper_scale_err", ts_scale);
    }
    
    var prev = null;
    for (var idx = 0; idx < helpers.length; idx++) {
        var curr = helpers[idx];
        var pixels_per_tick = curr.getPixelsPerTick(ts._pixels_per_milli);
        if (pixels_per_tick > optimal_tick_width)  {
            if (prev == null) return curr;
            var curr_dist = Math.abs(optimal_tick_width - pixels_per_tick);
            var prev_dist = Math.abs(optimal_tick_width - pixels_per_tick);
            if (curr_dist < prev_dist) {
                return curr;
            } else {
                return prev;
            }
        }
        prev = curr;
    }
    return helpers[helpers.length - 1]; // last resort           
}