// Copyright (c) 2026 Dominic Masters
//
// This software is released under the MIT License.
// https://opensource.org/licenses/MIT

"use strict";

// ChunkTerrain - JS port of the terrain-quad generation performed by
// tools/asset/chunk/__main__.py (build_terrain_verts / _tile_quad /
// _RAMP_CORNERS) so the editor's 3D preview can show the same geometry the
// Python compiler will bake into the chunk's terrain mesh, without waiting
// for a compile pass. Vertex layout matches DMF: interleaved [u, v, x, y, z].

const ChunkTerrain = (() => {
  const CHUNK_WIDTH  = 16;
  const CHUNK_HEIGHT = 16;
  const CHUNK_DEPTH  = 4;
  const TILE_COUNT   = CHUNK_WIDTH * CHUNK_HEIGHT * CHUNK_DEPTH;

  // World-space Z distance of one Z-layer/story, in world-float space.
  // Must match WORLD_LAYER_HEIGHT in src/dusk/rpg/overworld/worldpos.h.
  const WORLD_LAYER_HEIGHT = Math.SQRT1_2;

  const TILE_SHAPE_NULL           = 0;
  const TILE_SHAPE_GROUND         = 1;
  const TILE_SHAPE_RAMP_NORTH     = 2;
  const TILE_SHAPE_RAMP_EAST      = 3;
  const TILE_SHAPE_RAMP_SOUTH     = 4;
  const TILE_SHAPE_RAMP_WEST      = 5;
  const TILE_SHAPE_RAMP_NORTHEAST = 6;
  const TILE_SHAPE_RAMP_NORTHWEST = 7;
  const TILE_SHAPE_RAMP_SOUTHEAST = 8;
  const TILE_SHAPE_RAMP_SOUTHWEST = 9;
  const TILE_SHAPE_RAMP_NORTHEAST_INNER = 10;
  const TILE_SHAPE_RAMP_NORTHWEST_INNER = 11;
  const TILE_SHAPE_RAMP_SOUTHEAST_INNER = 12;
  const TILE_SHAPE_RAMP_SOUTHWEST_INNER = 13;

  // Per-shape corner heights as [sw, se, ne, nw] offsets from tile base Z.
  // NORTH=+Y, EAST=+X. Cardinal ramps: low face at 0, high face at 1.
  // Diagonal outer-corner ramps: only the named corner raised, rest at 0.
  // Diagonal inner-corner ramps: only the corner opposite the named one is
  // lowered to 0, the rest (including the named corner) stay raised at 1.
  const RAMP_CORNERS = {
    [TILE_SHAPE_GROUND]:         [0.0, 0.0, 0.0, 0.0],
    [TILE_SHAPE_RAMP_NORTH]:     [0.0, 0.0, 1.0, 1.0],
    [TILE_SHAPE_RAMP_SOUTH]:     [1.0, 1.0, 0.0, 0.0],
    [TILE_SHAPE_RAMP_EAST]:      [0.0, 1.0, 1.0, 0.0],
    [TILE_SHAPE_RAMP_WEST]:      [1.0, 0.0, 0.0, 1.0],
    [TILE_SHAPE_RAMP_NORTHEAST]: [0.0, 0.0, 1.0, 0.0],
    [TILE_SHAPE_RAMP_NORTHWEST]: [0.0, 0.0, 0.0, 1.0],
    [TILE_SHAPE_RAMP_SOUTHEAST]: [0.0, 1.0, 0.0, 0.0],
    [TILE_SHAPE_RAMP_SOUTHWEST]: [1.0, 0.0, 0.0, 0.0],
    [TILE_SHAPE_RAMP_NORTHEAST_INNER]: [0.0, 1.0, 1.0, 1.0],
    [TILE_SHAPE_RAMP_NORTHWEST_INNER]: [1.0, 0.0, 1.0, 1.0],
    [TILE_SHAPE_RAMP_SOUTHEAST_INNER]: [1.0, 1.0, 1.0, 0.0],
    [TILE_SHAPE_RAMP_SOUTHWEST_INNER]: [1.0, 1.0, 0.0, 1.0],
  };

  function tileIndex(x, y, z) {
    return x + y * CHUNK_WIDTH + z * CHUNK_WIDTH * CHUNK_HEIGHT;
  }

  // Six vertices (2 CCW triangles) for a quad with per-corner Z heights.
  // Corner order: SW=(fx,fy), SE=(fx+1,fy), NE=(fx+1,fy+1), NW=(fx,fy+1).
  function pushTileQuad(out, u0, u1, v0, v1, fx, fy, swZ, seZ, neZ, nwZ) {
    out.push(
      u0, v0, fx,     fy,     swZ,
      u1, v0, fx + 1, fy,     seZ,
      u1, v1, fx + 1, fy + 1, neZ,
      u0, v0, fx,     fy,     swZ,
      u1, v1, fx + 1, fy + 1, neZ,
      u0, v1, fx,     fy + 1, nwZ,
    );
  }

  // Generate terrain quads for every non-null tile in a flat tiles array
  // (length TILE_COUNT, indexed via tileIndex). Returns a Float32Array of
  // interleaved [u, v, x, y, z] vertices, matching DMF.VERTEX_FLOATS.
  function buildTerrainVerts(tiles) {
    const out = [];
    for(let z = 0; z < CHUNK_DEPTH; z++) {
      for(let y = 0; y < CHUNK_HEIGHT; y++) {
        for(let x = 0; x < CHUNK_WIDTH; x++) {
          const type = tiles[tileIndex(x, y, z)] || TILE_SHAPE_NULL;
          const corners = RAMP_CORNERS[type];
          if(!corners) continue;

          const u0 = x / CHUNK_WIDTH;
          const u1 = (x + 1) / CHUNK_WIDTH;
          const v0 = y / CHUNK_HEIGHT;
          const v1 = (y + 1) / CHUNK_HEIGHT;
          const [sw, se, ne, nw] = corners;

          pushTileQuad(
            out, u0, u1, v0, v1, x, y,
            (z + sw) * WORLD_LAYER_HEIGHT,
            (z + se) * WORLD_LAYER_HEIGHT,
            (z + ne) * WORLD_LAYER_HEIGHT,
            (z + nw) * WORLD_LAYER_HEIGHT
          );
        }
      }
    }
    return new Float32Array(out);
  }

  // Four edges (SW-SE, SE-NE, NE-NW, NW-SW) of a tile's quad as line
  // segments, lifted slightly above the terrain surface to avoid
  // z-fighting - same corner-height convention as pushTileQuad().
  function pushTileGridLines(out, fx, fy, swZ, seZ, neZ, nwZ) {
    const eps = 0.01;
    const sw = [fx,     fy,     swZ + eps];
    const se = [fx + 1, fy,     seZ + eps];
    const ne = [fx + 1, fy + 1, neZ + eps];
    const nw = [fx,     fy + 1, nwZ + eps];
    const edges = [sw, se, se, ne, ne, nw, nw, sw];
    for(const [x, y, z] of edges) out.push(0, 0, x, y, z);
  }

  // Generate grid-outline line segments for every non-null tile, following
  // the same per-corner heights as buildTerrainVerts() so lines hug ramps
  // instead of cutting through them. Returns a Float32Array of interleaved
  // [u, v, x, y, z] vertices meant to be drawn with gl.LINES (pairs).
  function buildGridLines(tiles) {
    const out = [];
    for(let z = 0; z < CHUNK_DEPTH; z++) {
      for(let y = 0; y < CHUNK_HEIGHT; y++) {
        for(let x = 0; x < CHUNK_WIDTH; x++) {
          const type = tiles[tileIndex(x, y, z)] || TILE_SHAPE_NULL;
          const corners = RAMP_CORNERS[type];
          if(!corners) continue;

          const [sw, se, ne, nw] = corners;
          pushTileGridLines(
            out, x, y,
            (z + sw) * WORLD_LAYER_HEIGHT,
            (z + se) * WORLD_LAYER_HEIGHT,
            (z + ne) * WORLD_LAYER_HEIGHT,
            (z + nw) * WORLD_LAYER_HEIGHT
          );
        }
      }
    }
    return new Float32Array(out);
  }

  return Object.freeze({
    CHUNK_WIDTH, CHUNK_HEIGHT, CHUNK_DEPTH, TILE_COUNT, WORLD_LAYER_HEIGHT,
    TILE_SHAPE_NULL, TILE_SHAPE_GROUND,
    TILE_SHAPE_RAMP_NORTH, TILE_SHAPE_RAMP_EAST,
    TILE_SHAPE_RAMP_SOUTH, TILE_SHAPE_RAMP_WEST,
    TILE_SHAPE_RAMP_NORTHEAST, TILE_SHAPE_RAMP_NORTHWEST,
    TILE_SHAPE_RAMP_SOUTHEAST, TILE_SHAPE_RAMP_SOUTHWEST,
    TILE_SHAPE_RAMP_NORTHEAST_INNER, TILE_SHAPE_RAMP_NORTHWEST_INNER,
    TILE_SHAPE_RAMP_SOUTHEAST_INNER, TILE_SHAPE_RAMP_SOUTHWEST_INNER,
    RAMP_CORNERS, tileIndex, buildTerrainVerts, buildGridLines,
  });
})();