feat(2020-day-12): give the ferry directions

developher-net · developher-net · commit 8a0b041100dc · 2020-12-21T00:54:42.000-08:00
diff --git a/2020/day-12/ferry.js b/2020/day-12/ferry.js
@@ -1,9 +1,77 @@
-const move = () => {
-  return
+const parseCommand = (command) => {
+  return {
+    cmd: command.slice(0, 1),
+    unit: Number(command.slice(1))
+  }
 }
 
-const route = () => {
-  return
+const move = ({
+  position = {
+    x: 0,
+    y: 0,
+    d: 90 // Default to facing east
+  },
+  command
+}) => {
+  // Movement subfunctions
+  const mv = {
+    N: (u) => { // North
+      position.y += u
+    },
+    S: (u) => { // South
+      position.y -= u
+    },
+    E: (u) => { // East
+      position.x += u
+    },
+    W: (u) => { // West
+      position.x -= u
+    },
+    L: (u) => { // Turn Left
+      position.d -= u
+      position.d = position.d % 360
+    },
+    R: (u) => { // Turn Right
+      position.d += u
+      position.d = position.d % 360
+    },
+    F: (u) => { // Forward
+      // TODO: replace with vector positioning of arbitrary angles
+      switch (position.d) {
+        case 0 :
+          mv.N(u)
+          break
+        case 90 :
+          mv.E(u)
+          break
+        case 180 :
+          mv.S(u)
+          break
+        case 270 :
+          mv.W(u)
+          break
+        default :
+          console.debug('Position', position)
+          console.debug('Forward', u)
+          throw new Error('Non-cardinal compass direction')
+      }
+    }
+  }
+
+  console.debug('Received', command, position)
+  const operation = parseCommand(command)
+  mv[operation.cmd](operation.unit)
+  return position
+}
+
+const route = ({ instructions }) => {
+  return instructions.reduce(
+    (position, command) => {
+      console.debug('Routing position', position)
+      console.debug('Routing command', command)
+      return move({ position, command })
+    }, { x: 0, y: 0, d: 90 }
+  )
 }
 
 module.exports = {
diff --git a/2020/day-12/ferry.test.js b/2020/day-12/ferry.test.js
@@ -1,6 +1,6 @@
 /* eslint-env mocha */
 const { expect } = require('chai')
-const { distance } = require('../../2018/day-06')
+const { distance } = require('../../2018/day-06/coordinates')
 const { move, route } = require('./ferry')
 
 describe('--- Day 11: Seating System ---', () => {
@@ -51,11 +51,29 @@ describe('--- Day 11: Seating System ---', () => {
           move({ position: origin, command })
         ).to.deep.equal({ x: 0, y: 0, d: 180 })
       })
-      it('can move forward', () => {
+      it('can move forward in the direction it is pointing', () => {
         const command = 'F10'
         expect(
           move({ position: origin, command })
         ).to.deep.equal({ x: 10, y: 0, d: 90 })
+        expect(
+          move({ position: { x: 0, y: 0, d: 0 }, command })
+        ).to.deep.equal({ x: 0, y: 10, d: 0 })
+        expect(
+          move({ position: { x: 0, y: 0, d: 270 }, command })
+        ).to.deep.equal({ x: -10, y: 0, d: 270 })
+        expect(
+          move({ position: { x: 0, y: 0, d: 180 }, command })
+        ).to.deep.equal({ x: 0, y: -10, d: 180 })
+      })
+      it('cannot handle non-cardoma; directions', () => {
+        expect(() => {
+          move({ position: { x: 0, y: 0, d: 13 }, command: 'F10' })
+        }).to.throw('Non-cardinal compass direction')
+      })
+      it('defaults to 0,0 facing East', () => {
+        expect(move({ command: 'F10' }))
+          .to.deep.equal({ x: 10, y: 0, d: 90 })
       })
     })
     describe('route()', () => {
@@ -70,7 +88,8 @@ describe('--- Day 11: Seating System ---', () => {
         const result = route({ instructions })
         expect(result)
           .to.deep.equal({ x: 17, y: -8, d: 180 })
-        expect(distance(result.x, result.y)).to.equal(25)
+        // manhattan distance from origin
+        expect(distance({ x: 0, y: 0 }, result)).to.equal(25)
       })
     })
   })
