/**
 * Tests for Diablo II v1.13c LightGrid and Environment engine.
 * Verifies mathematical parity against decompiled D2Client `dLightMap.c` and D2Common `D2Environment.cpp`.
 */

import { describe, it, expect } from 'vitest'
import {
  LightGrid,
  fastDistanceApprox,
  LIGHT_GRID_SIZE,
  SUB_TILES_PER_LIGHT_CELL,
} from '../src/game/engine/light-grid.ts'
import {
  Environment,
  NORMAL_ENV_CYCLES,
  ACT4_ENV_CYCLES,
  EnvCycleIndex,
} from '../src/game/engine/environment.ts'
import { COLLIDE_VISIBLE, COLLIDE_BLANK, type CollisionGrid } from '../src/game/d2map.ts'

describe('D2Client v1.13c dLightMap Fast Distance Approximation', () => {
  it('implements Alpha Max Plus Beta Min with <= 3.96% theoretical error', () => {
    // Exact cardinal distances
    expect(fastDistanceApprox(100, 0)).toBe((983 * 100) >> 10) // 95
    expect(fastDistanceApprox(0, 100)).toBe((983 * 100) >> 10) // 95
    expect(fastDistanceApprox(-100, 0)).toBe((983 * 100) >> 10)

    // 45 degree diagonal: dx = 100, dy = 100
    // Real hypot = sqrt(20000) ~ 141.42
    // Approx = (983 * 100 + 407 * 100) >> 10 = 139000 >> 10 = 135 (error ~4.5% integer vs float)
    const approx45 = fastDistanceApprox(100, 100)
    expect(approx45).toBe(135)
  })
})

describe('D2Client v1.13c LightGrid Attenuation & Blending', () => {
  it('correctly creates 48x48 cell buffers with proper dimensions', () => {
    const grid = new LightGrid()
    expect(grid.intensity.length).toBe(48 * 48)
    expect(grid.textureBuffer.length).toBe(48 * 48 * 4)
  })

  it('calculates linear falloff and attenuation matching 1.13c formula', () => {
    const grid = new LightGrid()
    grid.centerOnSubTile(200, 200)

    // Add a white light at the center: radius 32 sub-tiles, intensity 255
    grid.addLight({
      subTileX: 200,
      subTileY: 200,
      radius: 32,
      intensity: 255,
      red: 255,
      green: 255,
      blue: 255,
    })

    // Center cell (24, 24) should be brightest
    const centerIdx = 24 * LIGHT_GRID_SIZE + 24
    expect(grid.intensity[centerIdx]).toBeGreaterThan(200)
    expect(grid.red[centerIdx]).toBe(255)
    expect(grid.green[centerIdx]).toBe(255)
    expect(grid.blue[centerIdx]).toBe(255)

    // Cell at distance > 32 sub-tiles (4 cells away) should have 0 added intensity
    const farIdx = (24 + 5) * LIGHT_GRID_SIZE + 24
    expect(grid.intensity[farIdx]).toBe(0)
  })

  it('blocks light completely when obstacle factor >= 16', () => {
    const grid = new LightGrid()
    grid.centerOnSubTile(200, 200)

    // Artificially place an opaque obstacle in front of the light
    const targetCellIdx = 24 * LIGHT_GRID_SIZE + 25
    grid.obstacle[targetCellIdx] = 16

    grid.addLight({
      subTileX: 200,
      subTileY: 200,
      radius: 32,
      intensity: 255,
      red: 255,
      green: 200,
      blue: 100,
    })

    // Target cell was completely blocked
    expect(grid.intensity[targetCellIdx]).toBe(0)
  })

  it('performs intensity-weighted color blending when lights overlap', () => {
    const grid = new LightGrid()
    grid.centerOnSubTile(200, 200)

    // Light 1: Pure Red (255, 0, 0), Intensity 100
    grid.addLight({
      subTileX: 200,
      subTileY: 200,
      radius: 24,
      intensity: 100,
      red: 255,
      green: 0,
      blue: 0,
    })

    // Light 2: Pure Blue (0, 0, 255), Intensity 100 at same position
    grid.addLight({
      subTileX: 200,
      subTileY: 200,
      radius: 24,
      intensity: 100,
      red: 0,
      green: 0,
      blue: 255,
    })

    const centerIdx = 24 * LIGHT_GRID_SIZE + 24
    // Intensities sum up to ~180-200
    expect(grid.intensity[centerIdx]).toBeGreaterThan(150)
    // Red and Blue should be roughly equal (purple blend)
    const r = grid.red[centerIdx]!
    const b = grid.blue[centerIdx]!
    expect(Math.abs(r - b)).toBeLessThanOrEqual(5)
    expect(grid.green[centerIdx]).toBe(0)
  })

  it('performs 8.8 fixed point bilinear interpolation smoothly', () => {
    const grid = new LightGrid()
    grid.centerOnSubTile(200, 200)
    grid.addLight({
      subTileX: 200,
      subTileY: 200,
      radius: 40,
      intensity: 255,
      red: 255,
      green: 255,
      blue: 255,
    })

    // Sampling at exact sub-tile positions should yield smooth gradient
    const sample0 = grid.sampleBilinear(200, 200)
    const sample1 = grid.sampleBilinear(208, 200)
    const sample2 = grid.sampleBilinear(216, 200)

    expect(sample0.intensity).toBeGreaterThan(sample1.intensity)
    expect(sample1.intensity).toBeGreaterThan(sample2.intensity)
  })
})

describe('D2Common v1.13c Environment Day/Night Simulation', () => {
  it('indoor levels return constant ambient from Levels.txt', () => {
    const env = new Environment()
    // Level 8 (Den of Evil) is inside with Intensity 0 (total darkness without light sources)
    const ambientDen = env.tick(8, 1)
    expect(ambientDen.isInside).toBe(true)
    expect(ambientDen.intensity).toBe(0)

    // Level 50 (Harem Level 1) is inside with Intensity 128
    const ambientHarem = env.tick(50, 2)
    expect(ambientHarem.isInside).toBe(true)
    expect(ambientHarem.intensity).toBe(128)
  })

  it('outdoor levels follow solar angle sine curve', () => {
    const env = new Environment()
    // Start at noon
    env.setTime(EnvCycleIndex.Noon, 0)
    const noonAmbient = env.tick(2, 1) // Level 2 = Blood Moor
    expect(noonAmbient.isInside).toBe(false)
    expect(noonAmbient.intensity).toBeGreaterThan(120)
  })

  it('Act IV levels lerp towards canonical fixed target intensities', () => {
    const env = new Environment()
    // Level 103 = Pandemonium Fortress (target 128)
    env.currentIntensity = 120
    const ambient = env.tick(103, 4)
    expect(ambient.intensity).toBe(121) // Increments by 1 towards 128

    // Level 104 = Outer Steppes (target 64)
    env.currentIntensity = 100
    const ambientSteppes = env.tick(104, 4)
    expect(ambientSteppes.intensity).toBe(99) // Decrements by 1 towards 64
  })

  it('Rocky Summit (Level 120) has fixed intensity 200 and custom RGB tint', () => {
    const env = new Environment()
    const ambient = env.tick(120, 5)
    expect(ambient.intensity).toBe(200)
    expect(ambient.red).toBe(245)
    expect(ambient.green).toBe(240)
    expect(ambient.blue).toBe(255)
  })
})