;; Functions to apply a heightmap to a world.
;;
;; Heightmaps are considered only as greyscale images, so colour is redundent (will be
;; ignored). Darker shades are higher.

(ns mw-engine.heightmap
  (:import [java.awt.image BufferedImage])
  (:use mw-engine.utils
        mw-engine.world
        mw-engine.drainage)
  (:require [fivetonine.collage.util :as collage :only [load-image]]
            [mikera.image.core :as imagez :only [filter-image get-pixels]]
            [mikera.image.filters :as filters]))

(defn tag-gradient
  "Set the `gradient` property of this `cell` of this `world` to the difference in
   altitude between its highest and lowest neghbours."
  [world cell]
  (let [heights (remove nil? (map #(:altitude %) (get-neighbours world cell)))
        highest (cond (empty? heights) 0 ;; shouldn't happen
                  true (apply max heights))
        lowest (cond (empty? heights) 0 ;; shouldn't
                 true (apply min heights))
        gradient (- highest lowest)]
    (merge cell {:gradient gradient})))

(defn tag-gradients
  "Set the `gradient` property of each cell in this `world` to the difference in
   altitude between its highest and lowest neghbours."
  [world]
  (map-world world tag-gradient))

(defn tag-altitude
  "Set the altitude of this cell from the corresponding pixel of this heightmap.
   If the heightmap you supply is smaller than the world, this will break.

   * `world` not actually used, but present to enable this function to be
     passed as an argument to `mw-engine.utils/map-world`, q.v.
   * `cell` a cell, as discussed in world.clj, q.v. Alternatively, a map;
   * `heightmap` an (ideally) greyscale image, whose x and y dimensions should
     exceed those of the world of which the `cell` forms part."
  ([world cell heightmap]
    (tag-altitude cell heightmap))
  ([cell heightmap]
    (merge cell
           {:altitude
            (+ (get-int cell :altitude)
               (- 256
                  (abs
                    (mod
                      (.getRGB heightmap
                        (get-int cell :x)
                        (get-int cell :y)) 256))))})))

(defn apply-heightmap
  "Apply the image file loaded from this path to this world, and return a world whose
  altitudes are modified (added to) by the altitudes in the heightmap. It is assumed that
  the heightmap is at least as large in x and y dimensions as the world.

  * `world` a world, as defined in `world.clj`, q.v.; if world is not supplied,
    a world the size of the heightmap will be created.
  * `imagepath` a file path or URL which indicates an image file."
  ([world imagepath]
    (let [heightmap (imagez/filter-image
                      (filters/grayscale)
                      (collage/load-image imagepath))]
      (map-world
        (map-world world tag-altitude (list heightmap))
        tag-gradient)))
   ([imagepath]
    (let [heightmap (imagez/filter-image
                      (filters/grayscale)
                      (collage/load-image imagepath))
          world (make-world (.getWidth heightmap) (.getHeight heightmap))]
      (map-world
        (map-world world tag-altitude (list heightmap))
        tag-gradient))))