Mercurial > personal > weather-server

annotate weather_server/static/script.js @ 15:df3e0534c994

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Tighten up MADRegistry: - Use only one map for registry. - Make the user construct it, to avoid modifying global state.
author Paul Fisher <paul@pfish.zone>
date Fri, 11 Oct 2019 20:50:50 -0400
parents 4eaa9d69c4e2
children
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1 'use strict';
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2
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3 /**
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4 * Converts Celsius to Fahrenheit.
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5 * @param {number} tempC
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6 * @return {number} The temperature in Fahrenheit.
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7 */
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8 function cToF(tempC) {
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9 return tempC * 9 / 5 + 32;
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10 }
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11
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12 const MAGNUS_B = 17.62;
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13 const MAGNUS_C = 243.12;
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14
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15 /**
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16 * The gamma function to calculate dew point.
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17 *
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18 * @param {number} tempC The temperature, in degrees Celsius.
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19 * @param {number} rhPct The relative humidity, in percent.
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20 * @return {number} The value of the gamma function.
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21 */
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22 function gammaFn(tempC, rhPct) {
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23 return Math.log(rhPct / 100) + MAGNUS_B * tempC / (MAGNUS_C + tempC);
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24 }
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25
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26 /**
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27 * Calculates the dew point.
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28 *
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29 * @param {number} tempC The temperature, in degrees Celsius.
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30 * @param {number} rhPct The relative humidity, in percent.
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31 * @return {number} The dew point, in degrees Celsius.
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32 */
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33 function dewPointC(tempC, rhPct) {
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34 const gamma = gammaFn(tempC, rhPct);
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35 return MAGNUS_C * gamma / (MAGNUS_B - gamma);
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36 }
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37
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38 const HISTORY_SECONDS = 86400;
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39
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40 /**
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41 * Sets up everything.
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42 * @param {HTMLElement} tempElement The element where temperature data is.
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43 * @param {HTMLElement} dewPointElement The element where the dew point is.
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44 */
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45 async function setUp(tempElement, dewPointElement) {
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46 const nowTS = new Date().getTime() / 1000;
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47 const startTS = nowTS - HISTORY_SECONDS;
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48 const query = new URL(location.href);
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49 query.pathname = query.pathname + '/recent';
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50 query.search = '';
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51 query.searchParams.set('seconds', String(HISTORY_SECONDS));
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52 const results = await fetch(query.href);
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53 if (!results.ok) return;
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54 const data = await results.json();
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55 if (data.length === 0) return;
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56
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57 const tempsF = data.map(s => [s.sample_time, cToF(s.temp_c)]);
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58 const dewPointsF = data.map(
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59 s => [s.sample_time, cToF(dewPointC(s.temp_c, s.rh_pct))]);
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60 setUpElement(tempElement, [startTS, nowTS], tempsF);
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61 setUpElement(dewPointElement, [startTS, nowTS], dewPointsF);
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62 }
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63
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64 /**
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65 * Sets up charting for this element.
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66 * @param {HTMLElement} element The element to put a graph in.
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67 * @param {[number, number]} timeRange The `[start, end]` of the time range.
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68 * @param {[number, number][]} data The data to chart.
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69 */
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70 function setUpElement(element, timeRange, data) {
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71 element.insertBefore(document.createElement('canvas'), element.firstChild);
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72 element.classList.remove('plain');
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73 element.classList.add('fancy');
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74 const doDraw = () => redrawCanvas(element, data, timeRange);
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75 doDraw();
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76 addEventListener('resize', doDraw);
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77 }
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78
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79 /**
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80 *
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81 * @param {HTMLElement} element The parent element to put the `<canvas>` in.
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82 * @param {[number, number][]} data The data to chart.
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83 * @param {[number, number]} xRange The `[start, end]` of the X range to plot.
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84 */
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85 function redrawCanvas(element, data, xRange) {
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86 let canvas = element.getElementsByTagName('canvas')[0];
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87 if (!canvas) {
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88 canvas = document.createElement('canvas');
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89 element.insertBefore(canvas, element.firstChild);
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90 }
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91 const dpr = window.devicePixelRatio || 1;
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92 const cssSize = element.getBoundingClientRect();
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93 const pxSize = [cssSize.width * dpr, cssSize.height * dpr];
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94 canvas.width = pxSize[0];
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95 canvas.height = pxSize[1];
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96 const ctx = canvas.getContext('2d');
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97 ctx.clearRect(0, 0, pxSize[0], pxSize[1]);
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98 const computed = getComputedStyle(element);
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99 ctx.strokeStyle = computed.color;
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100 drawChart(ctx, data, xRange, pxSize);
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101 }
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102
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103 /** The height of the chart in degrees. */
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104 const CHART_RANGE_DEGREES = 15;
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105
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106 /**
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107 * Charts some data.
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108 *
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109 * @param {CanvasRenderingContext2D} ctx The context to draw in.
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110 * @param {[number, number][]} data The data to chart, as `[x, y]` pairs.
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111 * @param {[number, number]} xRange The bounds of the X axis to draw.
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112 * @param {[number, number]} size The `[width, height]` of the context.
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113 */
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114 function drawChart(ctx, data, xRange, size) {
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115 const yRange = calculateYRange(data.map(d => d[1]));
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116
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117 ctx.lineWidth = 1.5;
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118
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119 ctx.beginPath();
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120 const first = project(data[0], size, xRange, yRange);
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121 ctx.moveTo(...first);
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122 for (const pt of data) {
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123 const projected = project(pt, size, xRange, yRange);
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124 ctx.lineTo(...projected);
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125 }
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126 ctx.stroke();
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127 }
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128
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129 /**
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130 * Determines what the Y range of the chart should be.
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131 * @param {number[]} ys The Y values of the chart.
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132 * @return {[number, number]} The lowest and highest values of the range.
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133 */
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134 function calculateYRange(ys) {
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135 const yMax = Math.max(...ys);
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136 const yMin = Math.min(...ys);
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137 const yMid = (yMin + yMax) / 2;
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138 const lastY = ys[ys.length - 1];
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139
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140 // We want the last value to be, at most, at the top or bottom 1/4 line
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141 // of the chart.
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142
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143 // If the middle of the range is already close enough, just use that.
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144 if (CHART_RANGE_DEGREES / 4 <= Math.abs(yMid - lastY)) {
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145 return [yMid - CHART_RANGE_DEGREES / 2, yMid + CHART_RANGE_DEGREES / 2];
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146 }
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147 // Otherwise, clamp the chart range.
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148 if (lastY < yMid) {
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149 return [lastY - CHART_RANGE_DEGREES / 4, lastY + 3 * CHART_RANGE_DEGREES / 4];
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150 }
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151 return [lastY - 3 * CHART_RANGE_DEGREES / 4, lastY + CHART_RANGE_DEGREES / 4];
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152 }
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153
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154 /**
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155 * Projects a Cartesian coordinate into Canvas space.
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156 *
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157 * @param {[number, number]} coord The `[x, y]` coordinate to project.
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158 * @param {[number, number]} size The `[width, height]` of the context.
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159 * @param {[number, number]} xRange The range of X values in the context.
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160 * @param {[number, number]} yRange The range of Y values in the context.
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161 * @return {[number, number]} The `[x, y]` coordinate in Canvas space.
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162 */
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163 function project(coord, size, xRange, yRange) {
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164 const [x, y] = coord;
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165 const [xMin, xMax] = xRange;
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166 const xSpan = xMax - xMin;
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167 const [yMin, yMax] = yRange;
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168 const ySpan = yMax - yMin;
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169 const [xSize, ySize] = size;
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170 return [
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171 (x - xMin) / xSpan * xSize,
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172 (yMax- y) / ySpan * ySize,
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173 ]
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174 }