---@class Obj
---@field model string
---@field texture string
---@field texture_size integer
---@field position Vector3
---@field triangles table
local Obj = {}

local Vector3 = require "types.vector3"

Obj.__index = Obj

local function string_split(str, delimiter)
  local res = {}
  local i = 0
  local f
  local match = '(.-)' .. delimiter .. '()'
  
  if string.find(str, delimiter) == nil then
    return {str}
  end
  
  for sub, j in string.gmatch(str, match) do
    i = i + 1
    res[i] = sub
    f = j
  end
  
  if i ~= 0 then
    res[i+1] = string.sub(str, f)
  end
  
  return res
end

---parses the obj file and triangulates it for drawing
---@param model string path to obj model
---@param texture {file: string, size: number}
---@param position Vector3?
---@return Obj
function Obj.create(model, texture, position)
  local pos
  if position ~= nil then
    pos = position
  else
    pos = Vector3()
  end
  local obj = {
    model = model,
    texture = texture.file,
    texture_size = texture.size,
    position = pos:copy(),

    triangles = {}
  }
  obj.position = obj.position:copy()
  setmetatable(obj, Obj)
  -- adapted from https://github.com/karai17/lua-obj/blob/master/obj_loader.lua
  -- Copyright (c) 2014 Landon Manning - LManning17@gmail.com - LandonManning.com
  -- MIT
  local file = file_read{file = obj.model}
  local lines = string_split(file, "\r?\n")
  local obj_data = {
    v = {},
    vt = {},
    f = {},
  }
  for _, line in ipairs(lines) do
    local l = string_split(line, "%s+")
    if l[1] == "v" then
      local v = {
        x = tonumber(l[2]),
        y = tonumber(l[3]),
        z = tonumber(l[4]),
      }
      table.insert(obj_data.v, v)
    elseif l[1] == "vt" then
      local vt = {
        x = tonumber(l[2]) * obj.texture_size,
        y = tonumber(l[3]) * obj.texture_size,
      }
      table.insert(obj_data.vt, vt)
    elseif l[1] == "f" then
      local f = {}
      for i = 2, #l do
        local split = string_split(l[i], "/")
        local v = {}

        v.v = tonumber(split[1])
        if split[2] ~= "" then v.vt = tonumber(split[2]) end
        -- v.vn = tonumber(split[3])

        table.insert(f, v)
      end
      table.insert(obj_data.f, f)
    end
  end
  for _, face in ipairs(obj_data.f) do
    for i = 2, #face - 1 do
      local triangle = {
        v0 = obj_data.v[face[1].v],
        v1 = obj_data.v[face[i].v],
        v2 = obj_data.v[face[i + 1].v],
        uv0 = obj_data.vt[face[1].vt],
        uv1 = obj_data.vt[face[i].vt],
        uv2 = obj_data.vt[face[i + 1].vt],
        texture = obj.texture
      }
      table.insert(obj.triangles, triangle)
    end
  end
  return obj
end

function Obj:draw()
  for _, triangle in ipairs(self.triangles) do
    local newt = util.shallow_copy(triangle)
    newt.v0 = Vector3(triangle.v0) + self.position
    newt.v1 = Vector3(triangle.v1) + self.position
    newt.v2 = Vector3(triangle.v2) + self.position
    draw_triangle(newt)
  end
end

return Obj