<!-- =======================================================================================

ABC TRANSCRIPTION TOOLS SHARE LINK DECODER

=========================================================================================

PURPOSE

-------

Extract the original ABC text from a share link containing either:

?lzw=<payload> (LZ-String compression)

?def=<payload> (Deflate + Base64URL compression)

This module allows 3rd-party developers to decode ABC share links

generated by the ABC Transcription Tools.

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REQUIRED LIBRARIES

-----------------------------------------------------------------------------------------

1) For lzw= links:

Include lz-string.min.js

Uses: LZString.decompressFromEncodedURIComponent()

2) For def= links:

Include pako.min.js

Uses: pako.inflate()

Also requires:

- TextDecoder (modern browsers)

- atob() (standard browser API)

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HOW SHARE LINKS ARE ENCODED

-----------------------------------------------------------------------------------------

LZW MODE (standard / legacy):

lzw = LZString.compressToEncodedURIComponent(abcText)

DEF MODE (often shorter for larger ABC):

1) UTF8 encode ABC

2) Deflate bytes (pako.deflate)

3) Base64 encode

4) Convert to Base64URL:

'+' → '-'

'/' → '_'

strip trailing '='

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HOW TO USE THIS DECODER

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const result = decodeABCFromShareLink(url);

result = {

mode: "lzw" | "deflate",

abc: "<decoded ABC text>"

}

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ERROR / NULL HANDLING (IMPORTANT)

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In LZW mode:

- LZString.decompressFromEncodedURIComponent() may return NULL.

- NULL indicates a decoding failure.

Common causes:

• The URL was truncated (length limits, email wrapping, messaging apps)

• Characters were modified during copy/paste

• The wrong decompression function was used

In Deflate mode:

- Base64URL length errors indicate corruption or truncation.

- pako.inflate() throws if compressed bytes are invalid.

In either case:

- Treat failures as "invalid or corrupted share link".

======================================================================================= -->

<script>

/* =========================================================================================

Base64URL → Bytes Helpers (Used for def= decoding)

========================================================================================= */

/**

* Convert normal Base64 string to Uint8Array.

*/

function base64ToBytes(base64) {

const binary = atob(base64);

const len = binary.length;

const bytes = new Uint8Array(len);

for (let i = 0; i < len; i++) {

bytes[i] = binary.charCodeAt(i);

}

return bytes;

}

/**

* Convert Base64URL string to Uint8Array.

*

* Base64URL differences:

* '-' instead of '+'

* '_' instead of '/'

* '=' padding removed

*

* We reverse these changes before decoding.

*/

function base64URLToBytes(base64url) {

let base64 = base64url

.replace(/-/g, "+")

.replace(/_/g, "/");

// Restore required '=' padding

const pad = base64.length % 4;

if (pad === 2) base64 += "==";

else if (pad === 3) base64 += "=";

else if (pad !== 0) {

throw new Error("Invalid Base64URL length. Payload may be truncated or corrupted.");

}

return base64ToBytes(base64);

}

/* =========================================================================================

MAIN DECODER FUNCTION

========================================================================================= */

/**

* Decode ABC text from an ABC Tools share link.

*

* @param {string} urlOrQueryString

* Can be:

* - Full URL (https://...abctools.html?lzw=...)

* - Just the query string (?lzw=...&format=...)

*

* @returns {{ mode: "lzw"|"deflate", abc: string }}

*

* @throws Error if:

* - No payload parameter found

* - Required library missing

* - Decoding fails

*/

function decodeABCFromShareLink(urlOrQueryString) {

if (!urlOrQueryString) {

throw new Error("No URL or query string provided.");

}

// Extract query string if full URL was passed

let query = urlOrQueryString;

if (query.includes("?")) {

query = query.split("?")[1];

}

const params = new URLSearchParams(query);

const lzw = params.get("lzw");

const def = params.get("def");

/* -----------------------------------------------------------------------

LZW MODE

----------------------------------------------------------------------- */

if (lzw != null) {

if (typeof LZString === "undefined") {

throw new Error("LZString library not loaded. Required for lzw= decoding.");

}

const abc = LZString.decompressFromEncodedURIComponent(lzw);

// CRITICAL: null means decompression failed

if (abc === null) {

throw new Error(

"LZW decompression returned null.\n" +

"This indicates a corrupted or truncated share link.\n" +

"Verify the entire lzw= value is intact."

);

}

return { mode: "lzw", abc };

}

/* -----------------------------------------------------------------------

DEFLATE MODE

----------------------------------------------------------------------- */

if (def != null) {

if (typeof pako === "undefined") {

throw new Error("pako library not loaded. Required for def= decoding.");

}

if (typeof TextDecoder === "undefined") {

throw new Error("TextDecoder not available. Required for UTF-8 decoding.");

}

// Step 1: Base64URL → raw compressed bytes

const deflatedBytes = base64URLToBytes(def);

// Step 2: Inflate (DEFLATE decompression)

const inflatedBytes = pako.inflate(deflatedBytes);

// Step 3: UTF-8 decode to JS string

const abc = new TextDecoder().decode(inflatedBytes);

return { mode: "deflate", abc };

}

/* -----------------------------------------------------------------------

NO PAYLOAD FOUND

----------------------------------------------------------------------- */

throw new Error("No lzw= or def= parameter found in the URL.");

}

</script>