#!/usr/bin/env node

/**
 * PWA Icon Generator for Workout App
 * Generates PNG icons without external dependencies
 * Uses only Node.js built-in modules (fs, zlib, path)
 */

const fs = require('fs');
const path = require('path');
const zlib = require('zlib');

// Configuration
const BACKGROUND_COLOR = { r: 10, g: 10, b: 10 }; // #0A0A0A
const TEXT_COLOR = { r: 255, g: 255, b: 255 }; // White
const ICON_SIZES = [72, 96, 128, 144, 152, 192, 384, 512];
const MASKABLE_SIZES = [192, 512];

const OUTPUT_DIR = path.join(__dirname, '..', 'public', 'icons');

/**
 * Create output directory if it doesn't exist
 */
function ensureOutputDir() {
  if (!fs.existsSync(OUTPUT_DIR)) {
    fs.mkdirSync(OUTPUT_DIR, { recursive: true });
  }
}

/**
 * Draw a stylized "W" character on a pixel buffer
 * Uses simple geometric shapes to create the letter
 */
function drawW(buffer, width, height) {
  const canvasWidth = width;
  const canvasHeight = height;

  // Helper to set a pixel
  const setPixel = (x, y, r, g, b, a = 255) => {
    if (x < 0 || x >= canvasWidth || y < 0 || y >= canvasHeight) return;
    const idx = (y * canvasWidth + x) * 4;
    buffer[idx] = r;
    buffer[idx + 1] = g;
    buffer[idx + 2] = b;
    buffer[idx + 3] = a;
  };

  // Helper to draw a filled rectangle (fast)
  const fillRect = (x, y, w, h, r, g, b) => {
    const x0 = Math.max(0, Math.floor(x));
    const y0 = Math.max(0, Math.floor(y));
    const x1 = Math.min(canvasWidth, Math.ceil(x + w));
    const y1 = Math.min(canvasHeight, Math.ceil(y + h));

    for (let yi = y0; yi < y1; yi++) {
      for (let xi = x0; xi < x1; xi++) {
        setPixel(xi, yi, r, g, b);
      }
    }
  };

  // Fill background
  fillRect(0, 0, canvasWidth, canvasHeight, BACKGROUND_COLOR.r, BACKGROUND_COLOR.g, BACKGROUND_COLOR.b);

  // Calculate dimensions for the "W"
  const padding = Math.floor(canvasHeight * 0.1);
  const letterWidth = canvasWidth - padding * 2;
  const letterHeight = canvasHeight - padding * 2;

  const startX = padding;
  const startY = padding;

  // Draw a stylized "W" using rectangles (five vertical bars forming W shape)
  const barWidth = letterWidth * 0.12;
  const spacing = letterWidth / 4;

  // Create a V-V-V pattern (W shape)
  // First V: two diagonal bars meeting at a point
  const v1LeftX = startX + spacing * 0.2;
  const v1RightX = startX + spacing * 0.8;
  const v1MidX = (v1LeftX + v1RightX) / 2;
  const v1BottomY = startY + letterHeight;
  const v1TopY = startY;

  // Left bar of first V
  fillRect(v1LeftX, v1TopY, barWidth, letterHeight, TEXT_COLOR.r, TEXT_COLOR.g, TEXT_COLOR.b);

  // Right bar of first V
  fillRect(v1RightX, v1TopY, barWidth, letterHeight, TEXT_COLOR.r, TEXT_COLOR.g, TEXT_COLOR.b);

  // Second V
  const v2LeftX = startX + spacing * 0.9;
  const v2RightX = startX + spacing * 1.5;

  fillRect(v2LeftX, v1TopY, barWidth, letterHeight, TEXT_COLOR.r, TEXT_COLOR.g, TEXT_COLOR.b);
  fillRect(v2RightX, v1TopY, barWidth, letterHeight, TEXT_COLOR.r, TEXT_COLOR.g, TEXT_COLOR.b);

  // Third V (right side)
  const v3LeftX = startX + spacing * 1.6;
  const v3RightX = startX + spacing * 2.2;

  fillRect(v3LeftX, v1TopY, barWidth, letterHeight, TEXT_COLOR.r, TEXT_COLOR.g, TEXT_COLOR.b);
  fillRect(v3RightX, v1TopY, barWidth, letterHeight, TEXT_COLOR.r, TEXT_COLOR.g, TEXT_COLOR.b);
}

/**
 * Create a PNG file from raw pixel data
 * Uses PNG file format with zlib compression
 */
function createPNG(width, height, pixelBuffer, outputPath) {
  // PNG signature
  const pngSignature = Buffer.from([137, 80, 78, 71, 13, 10, 26, 10]);

  // IHDR chunk (image header)
  const ihdrData = Buffer.alloc(13);
  ihdrData.writeUInt32BE(width, 0);
  ihdrData.writeUInt32BE(height, 4);
  ihdrData[8] = 8; // bit depth
  ihdrData[9] = 6; // color type (RGBA)
  ihdrData[10] = 0; // compression method
  ihdrData[11] = 0; // filter method
  ihdrData[12] = 0; // interlace method

  const ihdr = createChunk('IHDR', ihdrData);

  // IDAT chunk (image data)
  // Each row needs a filter byte (0 = None)
  const rawData = Buffer.alloc(height * (1 + width * 4));
  for (let y = 0; y < height; y++) {
    rawData[y * (1 + width * 4)] = 0; // filter type
    const rowStart = y * (1 + width * 4) + 1;
    pixelBuffer.copy(rawData, rowStart, y * width * 4, (y + 1) * width * 4);
  }

  const compressed = zlib.deflateSync(rawData);
  const idat = createChunk('IDAT', compressed);

  // IEND chunk (image end)
  const iend = createChunk('IEND', Buffer.alloc(0));

  // Combine all chunks
  const png = Buffer.concat([pngSignature, ihdr, idat, iend]);

  fs.writeFileSync(outputPath, png);
}

/**
 * Create a PNG chunk with proper CRC
 */
function createChunk(type, data) {
  const length = Buffer.alloc(4);
  length.writeUInt32BE(data.length, 0);

  const typeBuffer = Buffer.from(type, 'ascii');
  const chunkData = Buffer.concat([typeBuffer, data]);

  // Calculate CRC32
  const crc = calculateCRC32(chunkData);
  const crcBuffer = Buffer.alloc(4);
  crcBuffer.writeUInt32BE(crc, 0);

  return Buffer.concat([length, chunkData, crcBuffer]);
}

/**
 * Calculate CRC32 checksum for PNG chunks
 */
function calculateCRC32(data) {
  const table = [];
  for (let n = 0; n < 256; n++) {
    let c = n;
    for (let k = 0; k < 8; k++) {
      c = c & 1 ? 0xedb88320 ^ (c >>> 1) : c >>> 1;
    }
    table[n] = c >>> 0;
  }

  let crc = 0xffffffff;
  for (let i = 0; i < data.length; i++) {
    crc = table[(crc ^ data[i]) & 0xff] ^ (crc >>> 8);
  }
  return (crc ^ 0xffffffff) >>> 0;
}

/**
 * Generate all icon sizes
 */
function generateIcons() {
  ensureOutputDir();

  console.log('Generating PWA icons for Workout App...\n');

  ICON_SIZES.forEach((size) => {
    // Regular icon
    const buffer = Buffer.alloc(size * size * 4);
    drawW(buffer, size, size);

    const outputPath = path.join(OUTPUT_DIR, `icon-${size}x${size}.png`);
    createPNG(size, size, buffer, outputPath);
    console.log(`✓ Created ${path.basename(outputPath)}`);

    // Maskable variant (for adaptive icons on Android)
    if (MASKABLE_SIZES.includes(size)) {
      const maskableBuffer = Buffer.alloc(size * size * 4);
      drawW(maskableBuffer, size, size);

      const maskablePath = path.join(OUTPUT_DIR, `icon-${size}x${size}-maskable.png`);
      createPNG(size, size, maskableBuffer, maskablePath);
      console.log(`✓ Created ${path.basename(maskablePath)}`);
    }
  });

  // Create a favicon SVG as well
  const svgPath = path.join(OUTPUT_DIR, 'favicon.svg');
  const svgContent = `<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 192 192">
  <rect width="192" height="192" fill="#0A0A0A"/>
  <text x="96" y="132" font-size="120" font-weight="bold" text-anchor="middle" fill="white" font-family="Arial, sans-serif">W</text>
</svg>`;
  fs.writeFileSync(svgPath, svgContent);
  console.log(`✓ Created ${path.basename(svgPath)}`);

  console.log(`\nAll icons generated successfully in ${OUTPUT_DIR}`);
}

// Run the generator
generateIcons();