;;;; cl-ballistics.lisp

(in-package #:cl-ballistics)

;;; "cl-ballistics" goes here. Hacks and glory await!

;;; Constant definitions
(defconstant +gravity+ -32.194)

(defconstant +standard-pressure+ 29.92)

(defconstant +to-radians+ (/ pi 180))

(defconstant +to-degrees+ (/ 180 pi))

(defconstant +standard-altitude+ 0)

(defconstant +standard-temperature+ 32)

(defconstant +standard-humidity+ 1)

;;; Atmospheric Functions

(defun calc-fp (pressure)
  (declare (real pressure))
  (/ (- pressure +standard-pressure+) +standard-pressure+))

(defun calc-fr (temperature pressure relative-humidity)
  (declare (real temperature pressure relative-humidity))
  (let ((vpw (- (* 4e-6 (expt temperature 3))
                (+ (* 4e-4 (expt temperature 2))
                   (* 0.0234 temperature))
                0.2517)))
    (* 0.995
       (/ pressure (* (- pressure 0.3783)
                      relative-humidity
                      vpw)))))

(defun calc-ft (temperature altitude)
  (declare (real temperature altitude))
  (let ((tstd (+ (* -0.0036 altitude) 59)))
    (/ (- temperature tstd)
       (- 459.6 tstd))))

(defun calc-fa (altitude)
  (declare (real altitude))
  (/ 1 (+ (* -4e-15 (expt altitude 3))
          (* 4e-10 (expt altitude 2))
          (* -3e-5 altitude)
          1)))

(defun atmospheric-correction (drag-coefficient &optional (altitude +standard-altitude+) (pressure +standard-pressure+) (temperature +standard-temperature+) (relative-humidity +standard-humidity+))
  (declare (real drag-coefficient altitude pressure temperature relative-humidity))
  (let* ((altitude-correction (calc-fa altitude))
         (temperature-correction (calc-ft temperature altitude))
         (humidity-correction (calc-fr temperature pressure relative-humidity))
         (pressure-correction (calc-fp pressure))
         (correction-factor (* altitude-correction
                               (- (+ 1 temperature-correction)
                                  pressure-correction)
                               humidity-correction)))
    (* drag-coefficient correction-factor)))

(export 'atmospheric-correction)

;;; G-function retardation

;;; Angular conversion functions

(defun degrees-to-moa (degrees)
  (declare (real degrees))
  (* degrees 60))

(defun degrees-to-radians (degrees)
  (declare (real degrees))
  (* degrees +to-radians+))

(defun moa-to-degrees (moa)
  (declare (real moa))
  (/ moa 60))

(defun moa-to-radians (moa)
  (declare (real moa))
  (degrees-to-radians (moa-to-degrees moa)))

(defun radians-to-degrees (radians)
  (declare (real radians))
  (* radians +to-degrees+))

(defun radians-to-moa (radians)
  (declare (real radians))
  (degrees-to-moa (radians-to-degrees radians)))

(export '(degrees-to-moa
          degrees-to-radians
          moa-to-degrees
          moa-to-radians
          radians-to-degrees
          radians-to-moa))

;;; Windage functions

(defun windage (wind-speed vi xx tv)
  (declare (real wind-speed vi xx tv))
  (let ((wind-speed-inches-per-second (* wind-speed 17.60)))
    (* wind-speed-inches-per-second (/ (- tv xx) vi))))

(defun head-wind (wind-speed wind-angle)
  (declare (real wind-speed wind-angle))
  (* (cos (degrees-to-radians wind-angle))
     wind-speed))

(defun cross-wind (wind-speed wind-angle)
  (* (sin (degrees-to-radians wind-angle))
     wind-speed))

(export '(windage
          head-wind
          cross-wind))

;;; Bore angle functions


;;; Solving


;;; Retrieving Data