From 8634dfd30d43d1daf57c60c1ccbc65fcc3282ee0 Mon Sep 17 00:00:00 2001
From: miripiruni <miripiruni@gmail.com>
Date: Wed, 17 May 2017 15:54:10 +0300
Subject: [PATCH] File: support prev map (issue #16)

---
 lib/file.js | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/lib/file.js b/lib/file.js
index 98b4cac..598441c 100644
--- a/lib/file.js
+++ b/lib/file.js
@@ -1,6 +1,7 @@
 var os = require('os'),
     path = require('path'),
     url = require('url'),
+    fs = require('fs'),
     mozilla = require('source-map'),
     SourceMapGenerator = mozilla.SourceMapGenerator,
     utils = require('./utils');
@@ -37,6 +38,60 @@ File.prototype = {
         return this;
     },
 
+    writeFileFromPrevMap: function (file, prev) {
+        if (prev === false) {
+            return this.writeFileContent(file);
+        }
+
+        if (prev) {
+            if (typeof prev === 'string') {
+                return prev;
+            }
+
+            if (typeof prev === 'function') {
+                var prevPath = prev(file);
+
+                if (prevPath && fs.existsSync && fs.existsSync(prevPath)) {
+                    return fs.readFileSync(prevPath, 'utf-8').toString().trim();
+                } else {
+                    throw new Error('Unable to load previous source map: ' + prevPath.toString());
+                }
+            }
+
+            if (prev instanceof mozilla.SourceMapConsumer) {
+                return mozilla.SourceMapGenerator.fromSourceMap(prev).toString();
+            }
+
+            if (prev instanceof mozilla.SourceMapGenerator) {
+                return prev.toString();
+            }
+
+            if (isMap(prev)) {
+                return JSON.stringify(prev);
+            }
+
+            throw new Error('Unsupported previous source map format: ' + prev.toString());
+
+        }
+
+        if (this.inline) {
+            return this.decodeInline(this.annotation);
+        }
+
+        if (this.annotation) {
+            var map = this.annotation;
+            if (file) {
+                map = path.join(path.dirname(file), map);
+            }
+
+            this.root = path.dirname(map);
+
+            return (fs.existsSync && fs.existsSync(map)) ?
+                fs.readFileSync(map, 'utf-8').toString().trim() :
+                false;
+        }
+    },
+
     writeLine: function (line) {
         this.write(line + '\n');
 
@@ -131,6 +186,12 @@ File.prototype = {
     }
 };
 
+
+function isMap(map) {
+    if (typeof map !== 'object') return false;
+    return typeof map.mappings === 'string' || typeof map._mappings === 'string';
+}
+
 function getLines(text) {
     return text.split(/\r\n|\r|\n/);
 }