--[[                         .__               .__
         ____ ___  _________ |  |   ____  _____|__| ____   ____   ______
       _/ __ \\  \/  /\____ \|  |  /  _ \/  ___/  |/  _ \ /    \ /  ___/
       \  ___/ >    < |  |_> >  |_(  <_> )___ \|  (  <_> )   |  \\___ \
        \___  >__/\_ \|   __/|____/\____/____  >__|\____/|___|  /____  >
            \/      \/|__|                   \/               \/     \/

            Explosion API mod for Minetest (adapted to MineClone 2)

    This mod is based on the Minetest explosion API mod, but has been changed
    to have the same explosion mechanics as Minecraft and work with MineClone.
    The computation-intensive parts of the mod has been optimized to allow for
    larger explosions and faster world updating.

    This mod was created by Elias Astrom <ryvnf@riseup.net> and is released
    under the LGPLv2.1 license.
--]]


mcl_explosions = {}

local creative_mode = minetest.settings:get_bool("creative_mode")

-- Saved sphere explosion shapes for various radiuses
local sphere_shapes = {}

-- Saved node definitions in table using cid-keys for faster look-up.
local node_blastres = {}
local node_on_blast = {}
local node_walkable = {}

-- The step length for the rays (Minecraft uses 0.3)
local STEP_LENGTH = 0.3

-- How many rays to compute entity exposure to explosion
local N_EXPOSURE_RAYS = 16

minetest.register_on_mods_loaded(function()
  -- Store blast resistance values by content ids to improve performance.
  for name, def in pairs(minetest.registered_nodes) do
    node_blastres[minetest.get_content_id(name)] = def._mcl_blast_resistance or 0
    node_on_blast[minetest.get_content_id(name)] = def.on_blast
    node_walkable[minetest.get_content_id(name)] = def.walkable
  end
end)

-- Compute the rays which make up a sphere with radius.  Returns a list of rays
-- which can be used to trace explosions.  This function is not efficient
-- (especially for larger radiuses), so the generated rays for various radiuses
-- should be cached and reused.
--
-- Should be possible to improve by using a midpoint circle algorithm multiple
-- times to create the sphere, currently uses more of a brute-force approach.
local function compute_sphere_rays(radius)
  local rays = {}
  local sphere = {}

  for y = -radius, radius do
    for z = -radius, radius do
      for x = -radius, 0, 1 do
        local d = x * x + y * y + z * z
        if d <= radius * radius then
          local pos = { x = x, y = y, z = z }
          sphere[minetest.hash_node_position(pos)] = pos
          break
        end
      end
    end
  end

  for y = -radius, radius do
    for z = -radius, radius do
      for x = radius, 0, -1 do
        local d = x * x + y * y + z * z
        if d <= radius * radius then
          local pos = { x = x, y = y, z = z }
          sphere[minetest.hash_node_position(pos)] = pos
          break
        end
      end
    end
  end

  for x = -radius, radius do
    for z = -radius, radius do
      for y = -radius, 0, 1 do
        local d = x * x + y * y + z * z
        if d <= radius * radius then
          local pos = { x = x, y = y, z = z }
          sphere[minetest.hash_node_position(pos)] = pos
          break
        end
      end
    end
  end

  for x = -radius, radius do
    for z = -radius, radius do
      for y = radius, 0, -1 do
        local d = x * x + y * y + z * z
        if d <= radius * radius then
          local pos = { x = x, y = y, z = z }
          sphere[minetest.hash_node_position(pos)] = pos
          break
        end
      end
    end
  end

  for x = -radius, radius do
    for y = -radius, radius do
      for z = -radius, 0, 1 do
        local d = x * x + y * y + z * z
        if d <= radius * radius then
          local pos = { x = x, y = y, z = z }
          sphere[minetest.hash_node_position(pos)] = pos
          break
        end
      end
    end
  end

  for x = -radius, radius do
    for y = -radius, radius do
      for z = radius, 0, -1 do
        local d = x * x + y * y + z * z
        if d <= radius * radius then
          local pos = { x = x, y = y, z = z }
          sphere[minetest.hash_node_position(pos)] = pos
          break
        end
      end
    end
  end

  for _, pos in pairs(sphere) do
    rays[#rays + 1] = vector.normalize(pos)
  end

  return rays
end

-- Add particles from explosion
--
-- Parameters:
--   pos - The position of the explosion
--   radius - The radius of the explosion
local function add_particles(pos, radius)
  minetest.add_particlespawner({
    amount = 64,
    time = 0.125,
    minpos = pos,
    maxpos = pos,
    minvel = {x = -radius, y = -radius, z = -radius},
    maxvel = {x = radius, y = radius, z = radius},
    minacc = vector.new(),
    maxacc = vector.new(),
    minexptime = 0.5,
    maxexptime = 1.0,
    minsize = radius * 0.5,
    maxsize = radius * 1.0,
    texture = "tnt_smoke.png",
  })
end

-- Get position from hash.  This should be identical to
-- 'minetest.get_position_from_hash' but is used in case the hashing function
-- would change.
local function get_position_from_hash(hash)
  local pos = {}
  pos.x = (hash % 65536) - 32768
  hash  = math.floor(hash / 65536)
  pos.y = (hash % 65536) - 32768
  hash  = math.floor(hash / 65536)
  pos.z = (hash % 65536) - 32768
  return pos
end

-- Traces the rays of an explosion, and updates the environment.
--
-- Parameters:
--   pos - Where the rays in the explosion should start from
--   strength - The strength of each ray
--   raydirs - The directions for each ray
--   radius - The maximum distance each ray will go
--   drop_chance - The chance that destroyed nodes will drop their items
--
-- Note that this function has been optimized, it contains code which has been
-- inlined to avoid function calls and unnecessary table creation.  This was
-- measured to give a significant performance increase.
local function trace_explode(pos, strength, raydirs, radius, drop_chance)
  local vm = minetest.get_voxel_manip()

  local emin, emax = vm:read_from_map(vector.subtract(pos, radius),
    vector.add(pos, radius))
  local emin_x = emin.x
  local emin_y = emin.y
  local emin_z = emin.z

  local ystride = (emax.x - emin_x + 1)
  local zstride = ystride * (emax.y - emin_y + 1)
  local pos_x = pos.x
  local pos_y = pos.y
  local pos_z = pos.z

  local area = VoxelArea:new {
    MinEdge = emin,
    MaxEdge = emax
  }
  local data = vm:get_data()
  local destroy = {}

  -- Trace rays for environment destruction
  for i = 1, #raydirs do
    local rpos_x = pos.x
    local rpos_y = pos.y
    local rpos_z = pos.z
    local rdir_x = raydirs[i].x
    local rdir_y = raydirs[i].y
    local rdir_z = raydirs[i].z
    local rstr = (0.7 + math.random() * 0.6) * strength

    for r = 0, math.ceil(radius * (1.0 / STEP_LENGTH)) do
      local npos_x = math.floor(rpos_x + 0.5)
      local npos_y = math.floor(rpos_y + 0.5)
      local npos_z = math.floor(rpos_z + 0.5)
      local idx = (npos_z - emin_z) * zstride + (npos_y - emin_y) * ystride +
          npos_x - emin_x + 1

      local cid = data[idx]
      local br = node_blastres[cid]
      local hash = (npos_z + 32768) * 65536 * 65536 +
          (npos_y + 32768) * 65536 +
          npos_x + 32768

      rpos_x = rpos_x + STEP_LENGTH * rdir_x
      rpos_y = rpos_y + STEP_LENGTH * rdir_y
      rpos_z = rpos_z + STEP_LENGTH * rdir_z

      rstr = rstr - 0.75 * STEP_LENGTH - (br + 0.3) * STEP_LENGTH

      if rstr <= 0 then
        break
      end

      if cid ~= minetest.CONTENT_AIR then
        destroy[hash] = idx
      end
    end
  end

  -- Entities in radius of explosion
  local punch_radius = 2 * strength
  local objs = minetest.get_objects_inside_radius(pos, punch_radius)

  -- Trace rays for entity damage
  for _, obj in pairs(objs) do
    local ent = obj:get_luaentity()

    -- Ignore items to lower lag
    if obj:is_player() or (ent and ent.name ~= '__builtin.item') then
      local opos = obj:get_pos()
      local collisionbox = nil

      if obj:is_player() then
        collisionbox = { -0.3, 0.0, -0.3, 0.3, 1.77, 0.3 }
      elseif ent.name then
        local def = minetest.registered_entities[ent.name]
        collisionbox = def.collisionbox
      end

      if collisionbox then
        -- Create rays from random points in the collision box
        local x1 = collisionbox[1] * 2
        local y1 = collisionbox[2] * 2
        local z1 = collisionbox[3] * 2
        local x2 = collisionbox[4] * 2
        local y2 = collisionbox[5] * 2
        local z2 = collisionbox[6] * 2
        local x_len = math.abs(x2 - x1)
        local y_len = math.abs(y2 - y1)
        local z_len = math.abs(z2 - z1)

        -- Move object position to the center of its bounding box
        opos.x = opos.x + x1 + x2
        opos.y = opos.y + y1 + y2
        opos.z = opos.z + z1 + z2

        -- Count number of rays from collision box which are unobstructed
        local count = N_EXPOSURE_RAYS

        for i = 1, N_EXPOSURE_RAYS do
          local rpos_x = opos.x + math.random() * x_len - x_len / 2
          local rpos_y = opos.y + math.random() * y_len - y_len / 2
          local rpos_z = opos.z + math.random() * z_len - z_len / 2
          local rdir_x = pos.x - rpos_x
          local rdir_y = pos.y - rpos_y
          local rdir_z = pos.z - rpos_z
          local rdir_len = math.hypot(rdir_x, math.hypot(rdir_y, rdir_z))
          rdir_x = rdir_x / rdir_len
          rdir_y = rdir_y / rdir_len
          rdir_z = rdir_z / rdir_len

          for i=0, rdir_len / STEP_LENGTH do
            rpos_x = rpos_x + rdir_x * STEP_LENGTH
            rpos_y = rpos_y + rdir_y * STEP_LENGTH
            rpos_z = rpos_z + rdir_z * STEP_LENGTH
            local npos_x = math.floor(rpos_x + 0.5)
            local npos_y = math.floor(rpos_y + 0.5)
            local npos_z = math.floor(rpos_z + 0.5)
            local idx = (npos_z - emin_z) * zstride + (npos_y - emin_y) * ystride +
                npos_x - emin_x + 1


            local cid = data[idx]
            local walkable = node_walkable[cid]

            if walkable then
              count = count - 1
              break
            end
          end
        end

        -- Punch entity with damage depending on explosion exposure and
        -- distance to explosion
        local exposure = count / N_EXPOSURE_RAYS
        local punch_vec = vector.subtract(opos, pos)
        local punch_dir = vector.normalize(punch_vec)
        local impact = (1 - vector.length(punch_vec) / punch_radius) * exposure
        if impact < 0 then
          impact = 0
        end
        local damage = math.floor((impact * impact + impact) * 7 * strength + 1)
        obj:punch(obj, 10, { damage_groups = { full_punch_interval = 1,
            fleshy = damage, knockback = impact * 20.0 } }, punch_dir)

        if obj:is_player() then
          obj:add_player_velocity(vector.multiply(punch_dir, impact * 20))
        elseif ent.tnt_knockback then
          obj:add_velocity(vector.multiply(punch_dir, impact * 20))
        end
      end
    end
  end

  -- Remove destroyed blocks and drop items
  for hash, idx in pairs(destroy) do
    local do_drop = not creative_mode and math.random() <= drop_chance
    local on_blast = node_on_blast[data[idx]]
    local remove = true

    if do_drop or on_blast ~= nil then
      local npos = get_position_from_hash(hash)
      if on_blast ~= nil then
        remove = on_blast(npos, 1.0)
      else
        local name = minetest.get_name_from_content_id(data[idx])
        local drop = minetest.get_node_drops(name, "")

        for _, item in ipairs(drop) do
          if item ~= "string" then
            item = item:get_name() .. item:get_count()
          end
          minetest.add_item(npos, item)
        end
      end
    end
    if remove then
      data[idx] = minetest.CONTENT_AIR
    end
  end

  -- Log explosion
  minetest.log('action', 'Explosion at ' .. minetest.pos_to_string(pos) ..
    ' with strength ' .. strength .. ' and radius ' .. radius)

  -- Update environment
  vm:set_data(data)
  vm:write_to_map(data)
  vm:update_liquids()
end

-- Create an explosion with strength at pos.
--
-- Parameters:
--   pos - The position where the explosion originates from
--   strength - The blast strength of the explosion (a TNT explosion uses 4)
--   info - Table containing information about explosion.
--
-- Values in info:
--   drop_chance - If specified becomes the drop chance of all nodes in the
--                 explosion (defaults to 1.0 / strength)
--   no_sound    - If true then the explosion will not play a sound
--   no_particle - If true then the explosion will not create particles
function mcl_explosions.explode(pos, strength, info)
  -- The maximum blast radius (in the air)
  local radius = math.ceil(1.3 * strength / (0.3 * 0.75) * 0.3)

  if not sphere_shapes[radius] then
    sphere_shapes[radius] = compute_sphere_rays(radius)
  end
  shape = sphere_shapes[radius]

  trace_explode(pos, strength, shape, radius, (info and info.drop_chance) or 1 / strength)

  if not (info and info.no_sound) then
    add_particles(pos, radius)
  end
  if not (info and info.no_particle) then
    minetest.sound_play("tnt_explode", {
      pos = pos, gain = 1.0,
      max_hear_distance = strength * 16
    }, true)
  end
end