# src/bg_shader.py
import time
import math
from typing import Optional
import numpy as np
from imgui_bundle import imgui, nanovg as nvg, hello_imgui

class BackgroundShader:
 def __init__(self):
  self.enabled = False
  self.start_time = time.time()
  self.ctx: Optional[nvg.Context] = None

 def render(self, width: float, height: float):
  if not self.enabled:
   return

  # In imgui-bundle, hello_imgui handles the background.
  # We can use the background_draw_list to draw primitives.
  # Since we don't have raw GLSL easily in Python without PyOpenGL,
  # we'll use a "faux-shader" approach with NanoVG or DrawList gradients.
  
  t = time.time() - self.start_time
  dl = imgui.get_background_draw_list()
  
  # Base deep sea color
  dl.add_rect_filled(imgui.ImVec2(0, 0), imgui.ImVec2(width, height), imgui.get_color_u32(imgui.ImVec4(0.01, 0.07, 0.20, 1.0)))
  
  # Layer 1: Slow moving large blobs (FBM approximation)
  for i in range(3):
   phase = t * (0.1 + i * 0.05)
   x = (math.sin(phase) * 0.5 + 0.5) * width
   y = (math.cos(phase * 0.8) * 0.5 + 0.5) * height
   radius = (0.4 + 0.2 * math.sin(t * 0.2)) * max(width, height)
   
   col = imgui.ImVec4(0.02, 0.26, 0.55, 0.3)
   dl.add_circle_filled(imgui.ImVec2(x, y), radius, imgui.get_color_u32(col), num_segments=32)

  # Layer 2: Shimmering caustics (Animated Lines)
  num_lines = 15
  for i in range(num_lines):
   offset = (t * 20.0 + i * (width / num_lines)) % width
   alpha = 0.1 * (1.0 + math.sin(t + i))
   col = imgui.get_color_u32(imgui.ImVec4(0.08, 0.60, 0.88, alpha))
   
   p1 = imgui.ImVec2(offset, 0)
   p2 = imgui.ImVec2(offset - 100, height)
   dl.add_line(p1, p2, col, thickness=2.0)

  # Vignette
  center = imgui.ImVec2(width/2, height/2)
  radius = max(width, height) * 0.8
  # Draw multiple concentric circles for a soft vignette
  for i in range(10):
   r = radius + (i * 50)
   alpha = (i / 10.0) * 0.5
   dl.add_circle(center, r, imgui.get_color_u32(imgui.ImVec4(0, 0, 0, alpha)), num_segments=64, thickness=60.0)

_bg: Optional[BackgroundShader] = None

def get_bg():
 global _bg
 if _bg is None:
  _bg = BackgroundShader()
 return _bg