From af1a11872adaa0410695f0c1082e71108b76b1c4 Mon Sep 17 00:00:00 2001
From: Norbert Renner <norbert.renner@gmx.de>
Date: Mon, 4 Oct 2021 10:26:54 +0200
Subject: [PATCH] Initial client-side stats from BRouter StdPath.java

- `computeKinematic` and dependencies extracted from:
https://github.com/abrensch/brouter/blob/57da34d205d26f22b31f667facc99ab7507d468c/brouter-core/src/main/java/btools/router/StdPath.java
- transpiled with JSweet 3.0.0 - http://www.jsweet.org/jsweet-live-sandbox/
- manual cleanup
---
 js/util/StdPath.js | 146 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 146 insertions(+)
 create mode 100644 js/util/StdPath.js

diff --git a/js/util/StdPath.js b/js/util/StdPath.js
new file mode 100644
index 0000000..14e45ba
--- /dev/null
+++ b/js/util/StdPath.js
@@ -0,0 +1,146 @@
+(function () {
+    // Calculates time and energy stats
+    //
+    // from BRouter btools.router.StdPath
+
+    class BExpressionContextWay {
+        getMaxspeed() {
+            return 45.0;
+        }
+        getCostfactor() {
+            return 1.0;
+        }
+    }
+
+    class BExpressionContext {
+        getVariableValue(name, defaultValue) {
+            return defaultValue;
+        }
+    }
+
+    class RoutingContext {
+        constructor() {
+            this.expctxGlobal = new BExpressionContext();
+            this.expctxWay = new BExpressionContextWay();
+            this.bikeMode = true;
+            this.footMode = false;
+            this.totalMass = this.expctxGlobal.getVariableValue('totalMass', 90.0);
+            this.maxSpeed = this.expctxGlobal.getVariableValue('maxSpeed', this.footMode ? 6.0 : 45.0) / 3.6;
+            this.S_C_x = this.expctxGlobal.getVariableValue('S_C_x', 0.5 * 0.45);
+            this.defaultC_r = this.expctxGlobal.getVariableValue('C_r', 0.01);
+            this.bikerPower = this.expctxGlobal.getVariableValue('bikerPower', 100.0);
+        }
+    }
+
+    class StdPath {
+        constructor() {
+            this.totalTime = 0;
+            this.totalEnergy = 0;
+            this.elevation_buffer = 0;
+        }
+
+        /**
+         * Approximation to Math.exp for small negative arguments
+         * @param {number} e
+         * @return {number}
+         */
+        static exp(e) {
+            var x = e;
+            var f = 1.0;
+            while (e < -1.0) {
+                {
+                    e += 1.0;
+                    f *= 0.367879;
+                }
+            }
+            return f * (1.0 + x * (1.0 + x * (0.5 + x * (0.166667 + 0.0416667 * x))));
+        }
+
+        static solveCubic(a, c, d) {
+            var v = 8.0;
+            var findingStartvalue = true;
+            for (var i = 0; i < 10; i++) {
+                {
+                    var y = (a * v * v + c) * v - d;
+                    if (y < 0.1) {
+                        if (findingStartvalue) {
+                            v *= 2.0;
+                            continue;
+                        }
+                        break;
+                    }
+                    findingStartvalue = false;
+                    var y_prime = 3 * a * v * v + c;
+                    v -= y / y_prime;
+                }
+            }
+            return v;
+        }
+
+        resetState() {
+            this.totalTime = 0.0;
+            this.totalEnergy = 0.0;
+            this.elevation_buffer = 0.0;
+        }
+
+        calcIncline(dist) {
+            var min_delta = 3.0;
+            var shift;
+            if (this.elevation_buffer > min_delta) {
+                shift = -min_delta;
+            } else if (this.elevation_buffer < min_delta) {
+                shift = -min_delta;
+            } else {
+                return 0.0;
+            }
+            var decayFactor = StdPath.exp(-dist / 100.0);
+            var new_elevation_buffer = (this.elevation_buffer + shift) * decayFactor - shift;
+            var incline = (this.elevation_buffer - new_elevation_buffer) / dist;
+            this.elevation_buffer = new_elevation_buffer;
+            return incline;
+        }
+
+        computeKinematic(rc, dist, delta_h, detailMode) {
+            if (!detailMode) {
+                return;
+            }
+            this.elevation_buffer += delta_h;
+            var incline = this.calcIncline(dist);
+            var wayMaxspeed;
+            wayMaxspeed = rc.expctxWay.getMaxspeed() / 3.6;
+            if (wayMaxspeed === 0) {
+                wayMaxspeed = rc.maxSpeed;
+            }
+            wayMaxspeed = Math.min(wayMaxspeed, rc.maxSpeed);
+            var speed;
+            var f_roll = rc.totalMass * StdPath.GRAVITY * (rc.defaultC_r + incline);
+            if (rc.footMode || rc.expctxWay.getCostfactor() > 4.9) {
+                speed = rc.maxSpeed * 3.6;
+                speed = (speed * StdPath.exp(-3.5 * Math.abs(incline + 0.05))) / 3.6;
+            } else if (rc.bikeMode) {
+                speed = StdPath.solveCubic(rc.S_C_x, f_roll, rc.bikerPower);
+                speed = Math.min(speed, wayMaxspeed);
+            } else {
+                speed = wayMaxspeed;
+            }
+            var dt = dist / speed;
+            this.totalTime += dt;
+            var energy = dist * (rc.S_C_x * speed * speed + f_roll);
+            if (energy > 0.0) {
+                this.totalEnergy += energy;
+            }
+        }
+
+        getTotalTime() {
+            return this.totalTime;
+        }
+
+        getTotalEnergy() {
+            return this.totalEnergy;
+        }
+    }
+
+    StdPath.GRAVITY = 9.81;
+
+    BR.StdPath = StdPath;
+})();