import { Color } from "../engine/render/Color"
import type { SkyConfig } from "../engine/render/Sky"
import type { Mesh, Vertex } from "../engine/scene/Mesh"

type Corner = [number, number, number]

/** Axis-aligned solid. Blocks the player horizontally while their feet are
 *  below `top`; if `standable`, its `top` also counts as ground to land on. */
export type Aabb = {
  minX: number
  maxX: number
  minZ: number
  maxZ: number
  top: number
  standable: boolean
}

/** The playground: geometry split by texture, its collision solids, where the
 *  NPC stands, and the sky to draw behind it. */
export type Level = {
  floor: Mesh
  walls: Mesh
  crate: Mesh
  colliders: Aabb[]
  npcPosition: { x: number; y: number; z: number }
  sky: SkyConfig
}

const ARENA = 12
const WALL_HEIGHT = 5
const CRATE = { x: -2, z: -2, half: 1, top: 1 }

export function buildLevel(): Level {
  const floor = mesh()
  quadGrid(floor, [-ARENA, 0, -ARENA], [ARENA, 0, -ARENA], [ARENA, 0, ARENA], [-ARENA, 0, ARENA], 12, 12, 16)

  const walls = mesh()
  const h = WALL_HEIGHT
  // Inward-facing perimeter, no ceiling so the sky shows above.
  quadGrid(walls, [-ARENA, 0, -ARENA], [ARENA, 0, -ARENA], [ARENA, h, -ARENA], [-ARENA, h, -ARENA], 12, 2.5, 12)
  quadGrid(walls, [ARENA, 0, ARENA], [-ARENA, 0, ARENA], [-ARENA, h, ARENA], [ARENA, h, ARENA], 12, 2.5, 12)
  quadGrid(walls, [ARENA, 0, -ARENA], [ARENA, 0, ARENA], [ARENA, h, ARENA], [ARENA, h, -ARENA], 12, 2.5, 12)
  quadGrid(walls, [-ARENA, 0, ARENA], [-ARENA, 0, -ARENA], [-ARENA, h, -ARENA], [-ARENA, h, ARENA], 12, 2.5, 12)

  const crate = mesh()
  box(crate, CRATE.x, CRATE.z, CRATE.half, CRATE.top)

  const colliders: Aabb[] = [
    wall(-ARENA, ARENA, -ARENA, -ARENA + 1),
    wall(-ARENA, ARENA, ARENA - 1, ARENA),
    wall(ARENA - 1, ARENA, -ARENA, ARENA),
    wall(-ARENA, -ARENA + 1, -ARENA, ARENA),
    {
      minX: CRATE.x - CRATE.half,
      maxX: CRATE.x + CRATE.half,
      minZ: CRATE.z - CRATE.half,
      maxZ: CRATE.z + CRATE.half,
      top: CRATE.top,
      standable: true,
    },
  ]

  const sky: SkyConfig = {
    zenith: Color.rgb(58, 108, 196),
    horizon: Color.rgb(178, 198, 226),
    sun: Color.rgb(255, 246, 214),
    sunDir: { x: 0.3, y: 0.5, z: -0.8 },
    sunSize: 0.04,
  }

  return { floor, walls, crate, colliders, npcPosition: { x: 2, y: 0, z: -1 }, sky }
}

function mesh(): Mesh {
  return { vertices: [], indices: [] }
}

function wall(minX: number, maxX: number, minZ: number, maxZ: number): Aabb {
  return { minX, maxX, minZ, maxZ, top: WALL_HEIGHT, standable: false }
}

/** A quad tessellated into an n*n grid so affine texture warp stays per-tile.
 *  Corners run a (uv 0,0) -> b (us,0) -> c (us,vs) -> d (0,vs). */
function quadGrid(m: Mesh, a: Corner, b: Corner, c: Corner, d: Corner, us: number, vs: number, n: number): void {
  const base = m.vertices.length
  const row = n + 1
  for (let i = 0; i <= n; i++) {
    const t = i / n
    for (let j = 0; j <= n; j++) {
      const s = j / n
      const wa = (1 - s) * (1 - t)
      const wb = s * (1 - t)
      const wc = s * t
      const wd = (1 - s) * t
      m.vertices.push({
        pos: {
          x: a[0] * wa + b[0] * wb + c[0] * wc + d[0] * wd,
          y: a[1] * wa + b[1] * wb + c[1] * wc + d[1] * wd,
          z: a[2] * wa + b[2] * wb + c[2] * wc + d[2] * wd,
        },
        uv: { x: us * s, y: vs * t },
      })
    }
  }
  for (let i = 0; i < n; i++) {
    for (let j = 0; j < n; j++) {
      const p = base + i * row + j
      m.indices.push(p, p + 1, p + row + 1, p, p + row + 1, p + row)
    }
  }
}

/** A box centered at (cx, cz) on the floor: top face plus four sides, one uv
 *  tile per face. No bottom (never seen). */
function box(m: Mesh, cx: number, cz: number, half: number, top: number): void {
  const x0 = cx - half
  const x1 = cx + half
  const z0 = cz - half
  const z1 = cz + half
  quad(m, [x0, top, z0], [x1, top, z0], [x1, top, z1], [x0, top, z1])
  quad(m, [x0, 0, z0], [x1, 0, z0], [x1, top, z0], [x0, top, z0])
  quad(m, [x1, 0, z1], [x0, 0, z1], [x0, top, z1], [x1, top, z1])
  quad(m, [x1, 0, z0], [x1, 0, z1], [x1, top, z1], [x1, top, z0])
  quad(m, [x0, 0, z1], [x0, 0, z0], [x0, top, z0], [x0, top, z1])
}

function quad(m: Mesh, a: Corner, b: Corner, c: Corner, d: Corner): void {
  const base = m.vertices.length
  const corners: [Corner, [number, number]][] = [
    [a, [0, 0]],
    [b, [1, 0]],
    [c, [1, 1]],
    [d, [0, 1]],
  ]
  for (const [pos, uv] of corners) {
    const vertex: Vertex = { pos: { x: pos[0], y: pos[1], z: pos[2] }, uv: { x: uv[0], y: uv[1] } }
    m.vertices.push(vertex)
  }
  m.indices.push(base, base + 1, base + 2, base, base + 2, base + 3)
}