Extract PNG read/write methods

src/character-card-parser.js

@@ -1,41 +1,80 @@
 const fs = require('fs');
 
+const encode = require('png-chunks-encode');
 const extract = require('png-chunks-extract');
 const PNGtext = require('png-chunk-text');
 
-const parse = async (cardUrl, format) => {
+/**
+ * Writes Character metadata to a PNG image buffer.
+ * @param {Buffer} image PNG image buffer
+ * @param {string} data Character data to write
+ * @returns {Buffer} PNG image buffer with metadata
+ */
+const write = (image, data) => {
+    const chunks = extract(image);
+    const tEXtChunks = chunks.filter(chunk => chunk.name === 'tEXt');
+
+    // Remove all existing tEXt chunks
+    for (let tEXtChunk of tEXtChunks) {
+        chunks.splice(chunks.indexOf(tEXtChunk), 1);
+    }
+    // Add new chunks before the IEND chunk
+    const base64EncodedData = Buffer.from(data, 'utf8').toString('base64');
+    chunks.splice(-1, 0, PNGtext.encode('chara', base64EncodedData));
+    const newBuffer = Buffer.from(encode(chunks));
+    return newBuffer;
+};
+
+/**
+ * Reads Character metadata from a PNG image buffer.
+ * @param {Buffer} image PNG image buffer
+ * @returns {string} Character data
+ */
+const read = (image) => {
+    const chunks = extract(image);
+
+    const textChunks = chunks.filter(function (chunk) {
+        return chunk.name === 'tEXt';
+    }).map(function (chunk) {
+        return PNGtext.decode(chunk.data);
+    });
+
+    if (textChunks.length === 0) {
+        console.error('PNG metadata does not contain any text chunks.');
+        throw new Error('No PNG metadata.');
+    }
+
+    let index = textChunks.findIndex((chunk) => chunk.keyword.toLowerCase() == 'chara');
+
+    if (index === -1) {
+        console.error('PNG metadata does not contain any character data.');
+        throw new Error('No PNG metadata.');
+    }
+
+    return Buffer.from(textChunks[index].text, 'base64').toString('utf8');
+};
+
+/**
+ * Parses a card image and returns the character metadata.
+ * @param {string} cardUrl Path to the card image
+ * @param {string} format File format
+ * @returns {string} Character data
+ */
+const parse = (cardUrl, format) => {
     let fileFormat = format === undefined ? 'png' : format;
 
     switch (fileFormat) {
         case 'png': {
             const buffer = fs.readFileSync(cardUrl);
-            const chunks = extract(buffer);
-
-            const textChunks = chunks.filter(function (chunk) {
-                return chunk.name === 'tEXt';
-            }).map(function (chunk) {
-                return PNGtext.decode(chunk.data);
-            });
-
-            if (textChunks.length === 0) {
-                console.error('PNG metadata does not contain any text chunks.');
-                throw new Error('No PNG metadata.');
-            }
-
-            let index = textChunks.findIndex((chunk) => chunk.keyword.toLowerCase() == 'chara');
-
-            if (index === -1) {
-                console.error('PNG metadata does not contain any character data.');
-                throw new Error('No PNG metadata.');
-            }
-
-            return Buffer.from(textChunks[index].text, 'base64').toString('utf8');
+            return read(buffer);
         }
-        default:
-            break;
     }
+
+    throw new Error('Unsupported format');
 };
 
 module.exports = {
-    parse: parse,
+    parse,
+    write,
+    read,
 };