add Parallel helper (#60)

src/lang/std/std.ts

@@ -12,6 +12,7 @@ import {
   angledLineToY,
   closee,
   startSketchAt,
+  getCoordsFromPaths,
 } from './sketch'
 import {
   segLen,
@@ -27,6 +28,7 @@ import { Quaternion, Vector3 } from 'three'
 import { SketchGroup, ExtrudeGroup, Position, Rotation } from '../executor'
 
 import { InternalFn, InternalFnNames, InternalFirstArg } from './stdTypes'
+import { intersectionWithParallelLine } from 'sketch-helpers'
 
 const transform: InternalFn = <T extends SketchGroup | ExtrudeGroup>(
   { sourceRange }: InternalFirstArg,
@@ -79,6 +81,38 @@ const translate: InternalFn = <T extends SketchGroup | ExtrudeGroup>(
   }
 }
 
+const angledLineThatIntersects: InternalFn = (
+  { sourceRange, programMemory },
+  data: {
+    angle: number
+    intersectTag: string
+    offset?: number
+    tag?: string
+  },
+  previousSketch: SketchGroup
+) => {
+  if (!previousSketch) throw new Error('lineTo must be called after lineTo')
+  const intersectPath = previousSketch.value.find(
+    ({ name }) => name === data.intersectTag
+  )
+  if (!intersectPath) throw new Error('intersectTag must match a line')
+  const from = getCoordsFromPaths(
+    previousSketch,
+    previousSketch.value.length - 1
+  )
+  const to = intersectionWithParallelLine({
+    line1: [intersectPath.from, intersectPath.to],
+    line1Offset: data.offset || 0,
+    line2Point: from,
+    line2Angle: data.angle,
+  })
+  return lineTo.fn(
+    { sourceRange, programMemory },
+    { to, tag: data.tag },
+    previousSketch
+  )
+}
+
 const min: InternalFn = (_, a: number, b: number): number => Math.min(a, b)
 
 const legLen: InternalFn = (_, hypotenuse: number, leg: number): number =>
@@ -122,6 +156,7 @@ export const internalFns: { [key in InternalFnNames]: InternalFn } = {
   angledLineToX: angledLineToX.fn,
   angledLineOfYLength: angledLineOfYLength.fn,
   angledLineToY: angledLineToY.fn,
+  angledLineThatIntersects,
   startSketchAt,
   closee,
 }