src/lib/services/picletMetadata.ts

import type { PicletInstance } from '$lib/db/schema';

const METADATA_KEY = 'snaplings-piclet-v1';

interface PicletMetadata {
  version: 1;
  data: Omit<PicletInstance, 'id' | 'rosterPosition' | 'isInRoster' | 'caughtAt'>;
  checksum?: string;
}

/**
 * Extract piclet metadata from a PNG image
 */
export async function extractPicletMetadata(file: File): Promise<PicletInstance | null> {
  try {
    const arrayBuffer = await file.arrayBuffer();
    const bytes = new Uint8Array(arrayBuffer);
    
    // Check PNG signature
    if (!isPNG(bytes)) {
      return null;
    }
    
    // Find tEXt chunks
    const chunks = parsePNGChunks(bytes);
    const textChunk = chunks.find(chunk => 
      chunk.type === 'tEXt' && 
      chunk.keyword === METADATA_KEY
    );
    
    if (!textChunk || !textChunk.text) {
      return null;
    }
    
    // Parse metadata
    const metadata: PicletMetadata = JSON.parse(textChunk.text);
    
    // Validate version
    if (metadata.version !== 1) {
      console.warn('Unsupported piclet metadata version:', metadata.version);
      return null;
    }
    
    // Create PicletInstance from metadata
    const piclet: PicletInstance = {
      ...metadata.data,
      caughtAt: new Date(), // Use current date for import
      isInRoster: false,
      rosterPosition: undefined
    };
    
    return piclet;
  } catch (error) {
    console.error('Failed to extract piclet metadata:', error);
    return null;
  }
}

/**
 * Embed piclet metadata into a PNG image
 */
export async function embedPicletMetadata(imageBlob: Blob, piclet: PicletInstance): Promise<Blob> {
  const arrayBuffer = await imageBlob.arrayBuffer();
  const bytes = new Uint8Array(arrayBuffer);
  
  // Prepare metadata
  const metadata: PicletMetadata = {
    version: 1,
    data: {
      typeId: piclet.typeId,
      nickname: piclet.nickname,
      primaryType: piclet.primaryType,
      secondaryType: piclet.secondaryType,
      currentHp: piclet.maxHp, // Reset to full HP for sharing
      maxHp: piclet.maxHp,
      level: piclet.level,
      xp: piclet.xp,
      attack: piclet.attack,
      defense: piclet.defense,
      fieldAttack: piclet.fieldAttack,
      fieldDefense: piclet.fieldDefense,
      speed: piclet.speed,
      baseHp: piclet.baseHp,
      baseAttack: piclet.baseAttack,
      baseDefense: piclet.baseDefense,
      baseFieldAttack: piclet.baseFieldAttack,
      baseFieldDefense: piclet.baseFieldDefense,
      baseSpeed: piclet.baseSpeed,
      moves: piclet.moves,
      nature: piclet.nature,
      bst: piclet.bst,
      tier: piclet.tier,
      role: piclet.role,
      variance: piclet.variance,
      imageUrl: piclet.imageUrl,
      imageData: piclet.imageData,
      imageCaption: piclet.imageCaption,
      concept: piclet.concept,
      imagePrompt: piclet.imagePrompt
    }
  };
  
  // Create tEXt chunk
  const textChunk = createTextChunk(METADATA_KEY, JSON.stringify(metadata));
  
  // Insert chunk after IHDR
  const newBytes = insertChunkAfterIHDR(bytes, textChunk);
  
  return new Blob([newBytes], { type: 'image/png' });
}

/**
 * Check if bytes represent a PNG file
 */
function isPNG(bytes: Uint8Array): boolean {
  const pngSignature = [137, 80, 78, 71, 13, 10, 26, 10];
  if (bytes.length < 8) return false;
  
  for (let i = 0; i < 8; i++) {
    if (bytes[i] !== pngSignature[i]) return false;
  }
  
  return true;
}

/**
 * Parse PNG chunks
 */
function parsePNGChunks(bytes: Uint8Array): any[] {
  const chunks = [];
  let pos = 8; // Skip PNG signature
  
  while (pos < bytes.length) {
    // Read chunk length
    const length = readUInt32BE(bytes, pos);
    pos += 4;
    
    // Read chunk type
    const type = String.fromCharCode(...bytes.slice(pos, pos + 4));
    pos += 4;
    
    // Read chunk data
    const data = bytes.slice(pos, pos + length);
    pos += length;
    
    // Skip CRC
    pos += 4;
    
    // Parse tEXt chunks
    if (type === 'tEXt') {
      const nullIndex = data.indexOf(0);
      if (nullIndex !== -1) {
        const keyword = String.fromCharCode(...data.slice(0, nullIndex));
        const text = String.fromCharCode(...data.slice(nullIndex + 1));
        chunks.push({ type, keyword, text });
      }
    } else {
      chunks.push({ type, data });
    }
    
    if (type === 'IEND') break;
  }
  
  return chunks;
}

/**
 * Create a tEXt chunk
 */
function createTextChunk(keyword: string, text: string): Uint8Array {
  const keywordBytes = new TextEncoder().encode(keyword);
  const textBytes = new TextEncoder().encode(text);
  
  // Create chunk data: keyword + null + text
  const data = new Uint8Array(keywordBytes.length + 1 + textBytes.length);
  data.set(keywordBytes);
  data[keywordBytes.length] = 0; // null separator
  data.set(textBytes, keywordBytes.length + 1);
  
  // Create full chunk: length + type + data + crc
  const chunk = new Uint8Array(4 + 4 + data.length + 4);
  
  // Length
  writeUInt32BE(chunk, 0, data.length);
  
  // Type: 'tEXt'
  chunk[4] = 116; // t
  chunk[5] = 69;  // E
  chunk[6] = 88;  // X
  chunk[7] = 116; // t
  
  // Data
  chunk.set(data, 8);
  
  // CRC
  const crc = calculateCRC(chunk.slice(4, 8 + data.length));
  writeUInt32BE(chunk, 8 + data.length, crc);
  
  return chunk;
}

/**
 * Insert chunk after IHDR
 */
function insertChunkAfterIHDR(bytes: Uint8Array, newChunk: Uint8Array): Uint8Array {
  // Find IHDR chunk end
  let ihdrEnd = 8; // PNG signature
  ihdrEnd += 4; // IHDR length
  ihdrEnd += 4; // IHDR type
  const ihdrLength = readUInt32BE(bytes, 8);
  ihdrEnd += ihdrLength; // IHDR data
  ihdrEnd += 4; // IHDR CRC
  
  // Create new array
  const result = new Uint8Array(bytes.length + newChunk.length);
  
  // Copy up to IHDR end
  result.set(bytes.slice(0, ihdrEnd));
  
  // Insert new chunk
  result.set(newChunk, ihdrEnd);
  
  // Copy rest
  result.set(bytes.slice(ihdrEnd), ihdrEnd + newChunk.length);
  
  return result;
}

/**
 * Read 32-bit unsigned integer (big endian)
 */
function readUInt32BE(bytes: Uint8Array, offset: number): number {
  return (bytes[offset] << 24) | 
         (bytes[offset + 1] << 16) | 
         (bytes[offset + 2] << 8) | 
         bytes[offset + 3];
}

/**
 * Write 32-bit unsigned integer (big endian)
 */
function writeUInt32BE(bytes: Uint8Array, offset: number, value: number): void {
  bytes[offset] = (value >>> 24) & 0xff;
  bytes[offset + 1] = (value >>> 16) & 0xff;
  bytes[offset + 2] = (value >>> 8) & 0xff;
  bytes[offset + 3] = value & 0xff;
}

/**
 * Calculate CRC32 for PNG chunk
 */
function calculateCRC(bytes: Uint8Array): number {
  const crcTable = getCRCTable();
  let crc = 0xffffffff;
  
  for (let i = 0; i < bytes.length; i++) {
    crc = crcTable[(crc ^ bytes[i]) & 0xff] ^ (crc >>> 8);
  }
  
  return crc ^ 0xffffffff;
}

/**
 * Get CRC table (cached)
 */
let crcTable: Uint32Array | null = null;
function getCRCTable(): Uint32Array {
  if (crcTable) return crcTable;
  
  crcTable = new Uint32Array(256);
  for (let i = 0; i < 256; i++) {
    let c = i;
    for (let j = 0; j < 8; j++) {
      c = (c & 1) ? 0xedb88320 ^ (c >>> 1) : c >>> 1;
    }
    crcTable[i] = c;
  }
  
  return crcTable;
}