(local pxl8 (require :pxl8))

(local FIREBALL_COLOR 218)

(var fireball-mesh nil)

(fn create-fireball-mesh []
  (let [verts []
        indices []
        radius 5
        rings 4
        segments 6
        core-color (+ FIREBALL_COLOR 6)
        spike-color (- FIREBALL_COLOR 1)]

    (table.insert verts {:x 0 :y radius :z 0 :nx 0 :ny 1 :nz 0 :color core-color :light 255})

    (for [ring 1 (- rings 1)]
      (let [phi (* (/ ring rings) math.pi)
            sin-phi (math.sin phi)
            cos-phi (math.cos phi)
            y (* radius cos-phi)
            ring-radius (* radius sin-phi)]
        (for [seg 0 (- segments 1)]
          (let [theta (* (/ seg segments) math.pi 2)
                x (* ring-radius (math.cos theta))
                z (* ring-radius (math.sin theta))
                nx (* sin-phi (math.cos theta))
                nz (* sin-phi (math.sin theta))]
            (table.insert verts {:x x :y y :z z :nx nx :ny cos-phi :nz nz :color core-color :light 255})))))

    (let [bottom-idx (length verts)]
      (table.insert verts {:x 0 :y (- radius) :z 0 :nx 0 :ny -1 :nz 0 :color core-color :light 255})

      (for [seg 0 (- segments 1)]
        (let [next-seg (% (+ seg 1) segments)]
          (table.insert indices 0)
          (table.insert indices (+ 1 next-seg))
          (table.insert indices (+ 1 seg))))

      (for [ring 0 (- rings 3)]
        (for [seg 0 (- segments 1)]
          (let [next-seg (% (+ seg 1) segments)
                curr-row (+ 1 (* ring segments))
                next-row (+ 1 (* (+ ring 1) segments))]
            (table.insert indices (+ curr-row seg))
            (table.insert indices (+ curr-row next-seg))
            (table.insert indices (+ next-row seg))
            (table.insert indices (+ curr-row next-seg))
            (table.insert indices (+ next-row next-seg))
            (table.insert indices (+ next-row seg)))))

      (let [last-ring-start (+ 1 (* (- rings 2) segments))]
        (for [seg 0 (- segments 1)]
          (let [next-seg (% (+ seg 1) segments)]
            (table.insert indices bottom-idx)
            (table.insert indices (+ last-ring-start seg))
            (table.insert indices (+ last-ring-start next-seg))))))

    (let [num-spikes 12
          spike-len 8
          base-size 1.2
          golden-ratio (/ (+ 1 (math.sqrt 5)) 2)]
      (for [i 0 (- num-spikes 1)]
        (let [y (- 1 (* (/ i (- num-spikes 1)) 2))
              r-at-y (math.sqrt (- 1 (* y y)))
              theta (* math.pi 2 i golden-ratio)
              nx (* r-at-y (math.cos theta))
              ny y
              nz (* r-at-y (math.sin theta))
              tx (if (> (math.abs ny) 0.9) 1 0)
              ty (if (> (math.abs ny) 0.9) 0 1)
              tz 0
              px (- (* ty nz) (* tz ny))
              py (- (* tz nx) (* tx nz))
              pz (- (* tx ny) (* ty nx))
              pl (math.sqrt (+ (* px px) (* py py) (* pz pz)))
              px (/ px pl) py (/ py pl) pz (/ pz pl)
              qx (- (* ny pz) (* nz py))
              qy (- (* nz px) (* nx pz))
              qz (- (* nx py) (* ny px))
              bx (* radius 0.8 nx)
              by (* radius 0.8 ny)
              bz (* radius 0.8 nz)
              sx (* (+ radius spike-len) nx)
              sy (* (+ radius spike-len) ny)
              sz (* (+ radius spike-len) nz)
              base-idx (length verts)]
          (table.insert verts {:x (+ bx (* base-size px) (* base-size qx))
                               :y (+ by (* base-size py) (* base-size qy))
                               :z (+ bz (* base-size pz) (* base-size qz))
                               :nx nx :ny ny :nz nz :color core-color :light 255})
          (table.insert verts {:x (+ bx (* base-size px) (* (- base-size) qx))
                               :y (+ by (* base-size py) (* (- base-size) qy))
                               :z (+ bz (* base-size pz) (* (- base-size) qz))
                               :nx nx :ny ny :nz nz :color core-color :light 255})
          (table.insert verts {:x (+ bx (* (- base-size) px) (* (- base-size) qx))
                               :y (+ by (* (- base-size) py) (* (- base-size) qy))
                               :z (+ bz (* (- base-size) pz) (* (- base-size) qz))
                               :nx nx :ny ny :nz nz :color core-color :light 255})
          (table.insert verts {:x (+ bx (* (- base-size) px) (* base-size qx))
                               :y (+ by (* (- base-size) py) (* base-size qy))
                               :z (+ bz (* (- base-size) pz) (* base-size qz))
                               :nx nx :ny ny :nz nz :color core-color :light 255})
          (table.insert verts {:x sx :y sy :z sz :nx nx :ny ny :nz nz :color spike-color :light 255})
          (table.insert indices base-idx)
          (table.insert indices (+ base-idx 1))
          (table.insert indices (+ base-idx 4))
          (table.insert indices (+ base-idx 1))
          (table.insert indices (+ base-idx 2))
          (table.insert indices (+ base-idx 4))
          (table.insert indices (+ base-idx 2))
          (table.insert indices (+ base-idx 3))
          (table.insert indices (+ base-idx 4))
          (table.insert indices (+ base-idx 3))
          (table.insert indices base-idx)
          (table.insert indices (+ base-idx 4)))))

    (set fireball-mesh (pxl8.create_mesh verts indices))))

(fn init [textures]
  (when (not fireball-mesh)
    (create-fireball-mesh)))

(fn render-fireball [x y z]
  (when fireball-mesh
    (pxl8.draw_mesh fireball-mesh {:x x :y y :z z
                                    :emissive true})))

{:FIREBALL_COLOR FIREBALL_COLOR
 :init init
 :render-fireball render-fireball}