// Adapted from https://github.com/ordpool-space/ordpool-parser/tree/ce04d7a5b6bb1cf37b9fdadd77ba430f5bd6e7d6/src
// Utils functions to decode ord inscriptions

export const OP_FALSE = 0x00;
export const OP_IF = 0x63;
export const OP_0 = 0x00;

export const OP_PUSHBYTES_3 = 0x03; //  3 -- not an actual opcode, but used in documentation --> pushes the next 3 bytes onto the stack.
export const OP_PUSHDATA1 = 0x4c;   // 76 -- The next byte contains the number of bytes to be pushed onto the stack.
export const OP_PUSHDATA2 = 0x4d;   // 77 -- The next two bytes contain the number of bytes to be pushed onto the stack in little endian order.
export const OP_PUSHDATA4 = 0x4e;   // 78 -- The next four bytes contain the number of bytes to be pushed onto the stack in little endian order.
export const OP_ENDIF = 0x68;       // 104 -- Ends an if/else block.

export const OP_1NEGATE = 0x4f;            // 79 -- The number -1 is pushed onto the stack.
export const OP_RESERVED = 0x50;           // 80 -- Transaction is invalid unless occuring in an unexecuted OP_IF branch
export const OP_PUSHNUM_1 = 0x51;          // 81 -- also known as OP_1
export const OP_PUSHNUM_2 = 0x52;          // 82 -- also known as OP_2
export const OP_PUSHNUM_3 = 0x53;          // 83 -- also known as OP_3
export const OP_PUSHNUM_4 = 0x54;          // 84 -- also known as OP_4
export const OP_PUSHNUM_5 = 0x55;          // 85 -- also known as OP_5
export const OP_PUSHNUM_6 = 0x56;          // 86 -- also known as OP_6
export const OP_PUSHNUM_7 = 0x57;          // 87 -- also known as OP_7
export const OP_PUSHNUM_8 = 0x58;          // 88 -- also known as OP_8
export const OP_PUSHNUM_9 = 0x59;          // 89 -- also known as OP_9
export const OP_PUSHNUM_10 = 0x5a;         // 90 -- also known as OP_10
export const OP_PUSHNUM_11 = 0x5b;         // 91 -- also known as OP_11
export const OP_PUSHNUM_12 = 0x5c;         // 92 -- also known as OP_12
export const OP_PUSHNUM_13 = 0x5d;         // 93 -- also known as OP_13
export const OP_PUSHNUM_14 = 0x5e;         // 94 -- also known as OP_14
export const OP_PUSHNUM_15 = 0x5f;         // 95 -- also known as OP_15
export const OP_PUSHNUM_16 = 0x60;         // 96 -- also known as OP_16

export const OP_RETURN = 0x6a;             // 106 -- a standard way of attaching extra data to transactions is to add a zero-value output with a scriptPubKey consisting of OP_RETURN followed by data

//////////////////////////// Helper ///////////////////////////////

/**
 * Inscriptions may include fields before an optional body. Each field consists of two data pushes, a tag and a value.
 * Currently, there are six defined fields:
 */
export const knownFields = {
  // content_type, with a tag of 1, whose value is the MIME type of the body.
  content_type: 0x01,

  // pointer, with a tag of 2, see pointer docs: https://docs.ordinals.com/inscriptions/pointer.html
  pointer: 0x02,

  // parent, with a tag of 3, see provenance docs: https://docs.ordinals.com/inscriptions/provenance.html
  parent: 0x03,

  // metadata, with a tag of 5, see metadata docs: https://docs.ordinals.com/inscriptions/metadata.html
  metadata: 0x05,

  // metaprotocol, with a tag of 7, whose value is the metaprotocol identifier.
  metaprotocol: 0x07,

  // content_encoding, with a tag of 9, whose value is the encoding of the body.
  content_encoding: 0x09,

  // delegate, with a tag of 11, see delegate docs: https://docs.ordinals.com/inscriptions/delegate.html
  delegate: 0xb
}

/**
 * Retrieves the value for a given field from an array of field objects.
 * It returns the value of the first object where the tag matches the specified field.
 *
 * @param fields - An array of objects containing tag and value properties.
 * @param field - The field number to search for.
 * @returns The value associated with the first matching field, or undefined if no match is found.
 */
export function getKnownFieldValue(fields: { tag: number; value: Uint8Array }[], field: number): Uint8Array | undefined {
  const knownField = fields.find(x =>
    x.tag === field);

  if (knownField === undefined) {
    return undefined;
  }

  return knownField.value;
}

/**
 * Retrieves the values for a given field from an array of field objects.
 * It returns the values of all objects where the tag matches the specified field.
 *
 * @param fields - An array of objects containing tag and value properties.
 * @param field - The field number to search for.
 * @returns An array of Uint8Array values associated with the matching fields. If no matches are found, an empty array is returned.
 */
export function getKnownFieldValues(fields: { tag: number; value: Uint8Array }[], field: number): Uint8Array[] {
  const knownFields = fields.filter(x =>
    x.tag === field
  );

  return knownFields.map(field => field.value);
}

/**
 * Searches for the next position of the ordinal inscription mark (0063036f7264)
 * within the raw transaction data, starting from a given position.
 *
 * This function looks for a specific sequence of 6 bytes that represents the start of an ordinal inscription.
 * If the sequence is found, the function returns the index immediately following the inscription mark.
 * If the sequence is not found, the function returns -1, indicating no inscription mark was found.
 *
 * Note: This function uses a simple hardcoded approach based on the fixed length of the inscription mark.
 *
 * @returns The position immediately after the inscription mark, or -1 if not found.
 */
export function getNextInscriptionMark(raw: Uint8Array, startPosition: number): number {

  // OP_FALSE
  // OP_IF
  // OP_PUSHBYTES_3: This pushes the next 3 bytes onto the stack.
  // 0x6f, 0x72, 0x64: These bytes translate to the ASCII string "ord"
  const inscriptionMark = new Uint8Array([OP_FALSE, OP_IF, OP_PUSHBYTES_3, 0x6f, 0x72, 0x64]);

  for (let index = startPosition; index <= raw.length - 6; index++) {
    if (raw[index] === inscriptionMark[0] &&
      raw[index + 1] === inscriptionMark[1] &&
      raw[index + 2] === inscriptionMark[2] &&
      raw[index + 3] === inscriptionMark[3] &&
      raw[index + 4] === inscriptionMark[4] &&
      raw[index + 5] === inscriptionMark[5]) {
      return index + 6;
    }
  }

  return -1;
}

/////////////////////////////// Reader ///////////////////////////////

/**
 * Reads a specified number of bytes from a Uint8Array starting from a given pointer.
 *
 * @param raw - The Uint8Array from which bytes are to be read.
 * @param pointer - The position in the array from where to start reading.
 * @param n - The number of bytes to read.
 * @returns A tuple containing the read bytes as Uint8Array and the updated pointer position.
 */
export function readBytes(raw: Uint8Array, pointer: number, n: number): [Uint8Array, number] {
  const slice = raw.slice(pointer, pointer + n);
  return [slice, pointer + n];
}

/**
 * Reads data based on the Bitcoin script push opcode starting from a specified pointer in the raw data.
 * Handles different opcodes and direct push (where the opcode itself signifies the number of bytes to push).
 *
 * @param raw - The raw transaction data as a Uint8Array.
 * @param pointer - The current position in the raw data array.
 * @returns A tuple containing the read data as Uint8Array and the updated pointer position.
 */
export function readPushdata(raw: Uint8Array, pointer: number): [Uint8Array, number] {

  let [opcodeSlice, newPointer] = readBytes(raw, pointer, 1);
  const opcode = opcodeSlice[0];

  // Handle the special case of OP_0 (0x00) which pushes an empty array (interpreted as zero)
  // fixes #18
  if (opcode === OP_0) {
    return [new Uint8Array(), newPointer];
  }

  // Handle the special case of OP_1NEGATE (-1)
  if (opcode === OP_1NEGATE) {
    // OP_1NEGATE pushes the value -1 onto the stack, represented as 0x81 in Bitcoin Script
    return [new Uint8Array([0x81]), newPointer];
  }

  // Handle minimal push numbers OP_PUSHNUM_1 (0x51) to OP_PUSHNUM_16 (0x60)
  // which are used to push the values 0x01 (decimal 1) through 0x10 (decimal 16) onto the stack.
  // To get the value, we can subtract OP_RESERVED (0x50) from the opcode to get the value to be pushed.
  if (opcode >= OP_PUSHNUM_1 && opcode <= OP_PUSHNUM_16) {
    // Convert opcode to corresponding byte value
    const byteValue = opcode - OP_RESERVED;
    return [Uint8Array.from([byteValue]), newPointer];
  }

  // Handle direct push of 1 to 75 bytes (OP_PUSHBYTES_1 to OP_PUSHBYTES_75)
  if (1 <= opcode && opcode <= 75) {
    return readBytes(raw, newPointer, opcode);
  }

  let numBytes: number;
  switch (opcode) {
    case OP_PUSHDATA1: numBytes = 1; break;
    case OP_PUSHDATA2: numBytes = 2; break;
    case OP_PUSHDATA4: numBytes = 4; break;
    default:
      throw new Error(`Invalid push opcode ${opcode} at position ${pointer}`);
  }

  let [dataSizeArray, nextPointer] = readBytes(raw, newPointer, numBytes);
  let dataSize = littleEndianBytesToNumber(dataSizeArray);
  return readBytes(raw, nextPointer, dataSize);
}

//////////////////////////// Conversion ////////////////////////////

/**
 * Converts a Uint8Array containing UTF-8 encoded data to a normal a UTF-16 encoded string.
 *
 * @param bytes - The Uint8Array containing UTF-8 encoded data.
 * @returns The corresponding UTF-16 encoded JavaScript string.
 */
export function bytesToUnicodeString(bytes: Uint8Array): string {
  const decoder = new TextDecoder('utf-8');
  return decoder.decode(bytes);
}

/**
 * Convert a Uint8Array to a string by treating each byte as a character code.
 * It avoids interpreting bytes as UTF-8 encoded sequences.
 * --> Again: it ignores UTF-8 encoding, which is necessary for binary content!
 *
 * Note: This method is different from just using `String.fromCharCode(...combinedData)` which can
 * cause a "Maximum call stack size exceeded" error for large arrays due to the limitation of
 * the spread operator in JavaScript. (previously the parser broke here, because of large content)
 *
 * @param bytes - The byte array to convert.
 * @returns The resulting string where each byte value is treated as a direct character code.
 */
export function bytesToBinaryString(bytes: Uint8Array): string {
  let resultStr = '';
  for (let i = 0; i < bytes.length; i++) {
    resultStr += String.fromCharCode(bytes[i]);
  }
  return resultStr;
}

/**
 * Converts a hexadecimal string to a Uint8Array.
 *
 * @param hex - A string of hexadecimal characters.
 * @returns A Uint8Array representing the hex string.
 */
export function hexToBytes(hex: string): Uint8Array {
  const bytes = new Uint8Array(hex.length / 2);
  for (let i = 0, j = 0; i < hex.length; i += 2, j++) {
    bytes[j] = parseInt(hex.slice(i, i + 2), 16);
  }
  return bytes;
}

/**
 * Converts a Uint8Array to a hexadecimal string.
 *
 * @param bytes - A Uint8Array to convert.
 * @returns A string of hexadecimal characters representing the byte array.
 */
export function bytesToHex(bytes: Uint8Array): string {
  if (!bytes) {
    return null;
  }
  return Array.from(bytes, byte => byte.toString(16).padStart(2, '0')).join('');
}

/**
 * Converts a little-endian byte array to a JavaScript number.
 *
 * This function interprets the provided bytes in little-endian format, where the least significant byte comes first.
 * It constructs an integer value representing the number encoded by the bytes.
 *
 * @param byteArray - An array containing the bytes in little-endian format.
 * @returns The number represented by the byte array.
 */
export function littleEndianBytesToNumber(byteArray: Uint8Array): number {
  let number = 0;
  for (let i = 0; i < byteArray.length; i++) {
    // Extract each byte from byteArray, shift it to the left by 8 * i bits, and combine it with number.
    // The shifting accounts for the little-endian format where the least significant byte comes first.
    number |= byteArray[i] << (8 * i);
  }
  return number;
}

/**
 * Concatenates multiple Uint8Array objects into a single Uint8Array.
 *
 * @param arrays - An array of Uint8Array objects to concatenate.
 * @returns A new Uint8Array containing the concatenated results of the input arrays.
 */
export function concatUint8Arrays(arrays: Uint8Array[]): Uint8Array {
  if (arrays.length === 0) {
      return new Uint8Array();
  }

  const totalLength = arrays.reduce((sum, arr) => sum + arr.length, 0);
  const result = new Uint8Array(totalLength);
  let offset = 0;

  for (const array of arrays) {
      result.set(array, offset);
      offset += array.length;
  }

  return result;
}

////////////////////////////// Inscription ///////////////////////////

export interface Inscription {
  body?: Uint8Array;
  is_cropped?: boolean;
  body_length?: number;
  content_type?: Uint8Array;
  content_type_str?: string;
  delegate_txid?: string;
}

/**
 * Extracts fields from the raw data until OP_0 is encountered.
 *
 * @param raw - The raw data to read.
 * @param pointer - The current pointer where the reading starts.
 * @returns An array of fields and the updated pointer position.
 */
export function extractFields(raw: Uint8Array, pointer: number): [{ tag: number; value: Uint8Array }[], number] {

  const fields: { tag: number; value: Uint8Array }[] = [];
  let newPointer = pointer;
  let slice: Uint8Array;

  while (newPointer < raw.length &&
    // normal inscription - content follows now
    (raw[newPointer] !== OP_0) &&
    // delegate - inscription has no further content and ends directly here
    (raw[newPointer] !== OP_ENDIF)
  ) {

    // tags are encoded by ord as single-byte data pushes, but are accepted by ord as either single-byte pushes, or as OP_NUM data pushes.
    // tags greater than or equal to 256 should be encoded as little endian integers with trailing zeros omitted.
    // see: https://github.com/ordinals/ord/issues/2505
    [slice, newPointer] = readPushdata(raw, newPointer);
    const tag = slice.length === 1 ? slice[0] : littleEndianBytesToNumber(slice);

    [slice, newPointer] = readPushdata(raw, newPointer);
    const value = slice;

    fields.push({ tag, value });
  }

  return [fields, newPointer];
}


/**
 * Extracts inscription data starting from the current pointer.
 * @param raw - The raw data to read.
 * @param pointer - The current pointer where the reading starts.
 * @returns The parsed inscription or nullx
 */
export function extractInscriptionData(raw: Uint8Array, pointer: number): Inscription | null {

  try {

    let fields: { tag: number; value: Uint8Array }[];
    let newPointer: number;
    let slice: Uint8Array;

    [fields, newPointer] = extractFields(raw, pointer);

    // Now we are at the beginning of the body
    // (or at the end of the raw data if there's no body)
    if (newPointer < raw.length && raw[newPointer] === OP_0) {
      newPointer++; // Skip OP_0
    }

    // Collect body data until OP_ENDIF
    const data: Uint8Array[] = [];
    while (newPointer < raw.length && raw[newPointer] !== OP_ENDIF) {
      [slice, newPointer] = readPushdata(raw, newPointer);
      data.push(slice);
    }

    const combinedLengthOfAllArrays = data.reduce((acc, curr) => acc + curr.length, 0);
    let combinedData = new Uint8Array(combinedLengthOfAllArrays);

    // Copy all segments from data into combinedData, forming a single contiguous Uint8Array
    let idx = 0;
    for (const segment of data) {
      combinedData.set(segment, idx);
      idx += segment.length;
    }

    const contentTypeRaw = getKnownFieldValue(fields, knownFields.content_type);
    let contentType: string;

    if (!contentTypeRaw) {
      contentType = 'undefined';
    } else {
      contentType = bytesToUnicodeString(contentTypeRaw);
    }

    return {
      content_type_str: contentType,
      body: combinedData.slice(0, 100_000), // Limit body to 100 kB for now
      is_cropped: combinedData.length > 100_000,
      body_length: combinedData.length,
      delegate_txid: getKnownFieldValue(fields, knownFields.delegate) ? bytesToHex(getKnownFieldValue(fields, knownFields.delegate).reverse()) : null
    };

  } catch (ex) {
    return null;
  }
}