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

"use strict";

// DMF - Dusk Mesh Format
//
// Header (12 bytes):
//   [0-3]   "DMF\0"  magic
//   [4-7]   uint32   version (little-endian)
//   [8-11]  uint32   vertCount (little-endian)
//
// Followed by vertCount vertices, each 20 bytes:
//   [0-7]   float32[2]  uv  (little-endian)
//   [8-19]  float32[3]  pos (little-endian)

const DMF = (() => {
  const MAGIC          = [0x44, 0x4d, 0x46, 0x00]; // "DMF\0"
  const VERSION        = 1;
  const HEADER_SIZE    = 12;
  const VERTEX_FLOATS  = 5; // uv[2] + pos[3]
  const VERTEX_SIZE    = VERTEX_FLOATS * 4;

  // Decode a DMF ArrayBuffer into { version, vertexCount, floats }, where
  // floats is a Float32Array of tightly interleaved [u, v, x, y, z] per
  // vertex - ready to hand straight to gl.bufferData().
  function decode(buffer) {
    const bytes = new Uint8Array(buffer);
    const view  = new DataView(buffer);

    if(bytes.length < HEADER_SIZE) throw new Error("File too small to be a valid DMF");
    if(
      bytes[0] !== MAGIC[0] || bytes[1] !== MAGIC[1] ||
      bytes[2] !== MAGIC[2] || bytes[3] !== MAGIC[3]
    ) {
      throw new Error("Invalid DMF magic bytes - not a DMF file");
    }

    const version = view.getUint32(4, true);
    if(version !== VERSION) {
      throw new Error(`Unsupported DMF version: ${version}`);
    }

    const vertexCount = view.getUint32(8, true);
    const expected = HEADER_SIZE + vertexCount * VERTEX_SIZE;
    if(bytes.length < expected) {
      throw new Error(`DMF vertex data truncated (expected ${expected} bytes, got ${bytes.length})`);
    }

    const floats = new Float32Array(vertexCount * VERTEX_FLOATS);
    for(let i = 0; i < floats.length; i++) {
      floats[i] = view.getFloat32(HEADER_SIZE + i * 4, true);
    }

    return { version, vertexCount, floats };
  }

  return Object.freeze({
    decode,
    VERSION, HEADER_SIZE, VERTEX_FLOATS, VERTEX_SIZE,
  });
})();