update README.md, reorganize the code, remove main.cpp and restore sketch.ino after the compile, minor fixes

Author: umbynos

.gitignore

@@ -1,3 +1,3 @@
 cslt-tool
 .vscode
-build/
+lib*

README.md

@@ -1,33 +1,57 @@
 # cslt-tool
 
-cslt-tool is a convenient wrapper of [arduino-cli](https://github.com/arduino/arduino-cli), it compiles Arduino sketches outputting object files and a json file in a `build/` directory
-The json contains information regarding libraries and core to use in order to build the sketch. The result is achieved by parsing the verbose output of `arduino-cli`.
+`cslt-tool` is a convenient wrapper of [arduino-cli](https://github.com/arduino/arduino-cli), it compiles Arduino sketches outputting a precompiled library in the current working directory.
+It generates a json file in `extra/` folder that contains information regarding libraries and core to use in order to build the sketch. The result is achieved by parsing the verbose output of `arduino-cli` and by using [GNU ar](https://sourceware.org/binutils/docs/binutils/ar.html) to generate an archive of the object files.
 
-## Requisites
-In order to run this tool you have to install first the [arduino-cli](https://github.com/arduino/arduino-cli) and have `arduino-cli` binary in your path, otherwise `cslt-tool` won't work.
-Please use a version of the cli that has [this](https://github.com/arduino/arduino-cli/pull/1608) change, version > 0.20.2
+## Prequisites
+In order to run this tool you have to install first the [arduino-cli](https://github.com/arduino/arduino-cli) and have `arduino-cli` binary in your `$PATH`, otherwise `cslt-tool` won't work.
+Please use a version of the arduino CLI that has [this](https://github.com/arduino/arduino-cli/pull/1608) change (version > 0.20.2).
+
+Another requirement is o have [`gcc-ar`](https://sourceware.org/binutils/docs/binutils/ar.html) (installable with `apt-get install gcc`) in your `$PATH`.
 
 ## Build it
-In order to build it just use `go build`
+In order to build `cslt-tool` just use `go build`
 
 ## Usage
 `./cslt-tool compile -b <fqbn> <sketch_path>`
 
-This is an example execution:
-``` bash
-$ ./cslt-tool compile -b arduino:samd:mkrwan1310 /home/umberto/getdeveui
-INFO[0001] arduino-cli version: git-snapshot                  
-INFO[0001] running: arduino-cli compile -b arduino:samd:mkrwan1310 /home/umberto/getdeveui -v --format json 
-INFO[0002] copied file to /home/umberto/Nextcloud/8tb/Lavoro/cslt-tool/build/getdeveui.ino.cpp.o 
-INFO[0002] created new file in: /home/umberto/Nextcloud/8tb/Lavoro/cslt-tool/build/result.json
+For example, running `./cslt-tool compile -b arduino:samd:mkrwifi1010 sketch/sketch.ino` should produce a library with the following structure, in the current working directory:
 ```
-The structure of the `build` forder is the following:
+libsketch/
+├── examples
+│   └── sketch
+│       └── sketch.ino  <-- the actual sketch we are going to compile with the arduino-cli later
+├── extra
+│   └── result.json
+├── library.properties
+└── src
+    ├── cortex-m0plus
+    │   └── libsketch.a
+    └── libsketch.h
 ```
-build/
-├── getdeveui.ino.cpp.o
-└── result.json
+
+This is an example execution:
+``` bash
+$ ./cslt-tool compile -b arduino:samd:mkrwifi1010 sketch/sketch.ino
+INFO[0000] arduino-cli version: git-snapshot            
+INFO[0000] GNU ar (GNU Binutils) 2.37                   
+INFO[0000] the ino file path is sketch/sketch.ino 
+INFO[0000] created sketch/main.cpp 
+INFO[0000] replaced setup() and loop() functions in sketch/sketch.ino 
+INFO[0000] running: arduino-cli compile -b arduino:samd:mkrwifi1010 sketch/sketch.ino -v --format json 
+INFO[0000] running: arduino-cli compile -b arduino:samd:mkrwifi1010 sketch/sketch.ino --show-properties 
+INFO[0001] removed sketch/main.cpp 
+INFO[0001] created sketch/sketch.ino 
+INFO[0001] restored sketch/sketch.ino 
+INFO[0001] created libsketch/library.properties 
+INFO[0001] created libsketch/src/libsketch.h 
+INFO[0001] created libsketch/examples/sketch/sketch.ino 
+INFO[0001] running: gcc-ar rcs libsketch/src/cortex-m0plus/libsketch.a /tmp/arduino-sketch-E4D76B1781E9EB73A7B3491CAC68F374/sketch/sketch.ino.cpp.o 
+INFO[0001] created libsketch/src/cortex-m0plus/libsketch.a 
+INFO[0001] created libsketch/extra/result.json
 ```
-And the content of `build/result.json` is:
+
+And the content of `libsketch/extra/result.json` is:
 ```json
 {
  "coreInfo": {
@@ -36,9 +60,42 @@ And the content of `build/result.json` is:
  },
  "libsInfo": [
   {
-   "name": "MKRWAN",
-   "version": "1.1.0"
+   "name": "WiFiNINA",
+   "version": "1.8.13",
+   "provides_includes": [
+    "WiFiNINA.h"
+   ]
+  },
+  {
+   "name": "SPI",
+   "version": "1.0",
+   "provides_includes": [
+    "SPI.h"
+   ]
   }
  ]
 }
+```
+
+## How to compile the precompiled sketch
+In order to compile the sketch you have first to install manually the libraries and the core listed in the `<libsketch>/extra/result.json` file.
+
+You can install a library with `arduino-cli lib install LIBRARY[@VERSION_NUMBER]`.
+
+You can install a core with `arduino-cli core install PACKAGER:ARCH[@VERSION]`.
+
+After completing that operation you can compile it with:
+
+`arduino-cli compile -b <fqbn> <libsketch>/examples/sketch/sketch.ino --library <libsketch>`.
+
+It's important to use the `--library` flag to include the precompiled library generated with cslt-tool otherwise the arduino CLI won't find it.
+
+For example a legit execution looks like this:
+``` bash
+$ arduino-cli compile -b arduino:samd:mkrwifi1010 libsketch/examples/sketch/sketch.ino --library libsketch/
+
+Library libsketch has been declared precompiled:
+Using precompiled library in libsketch/src/cortex-m0plus
+Sketch uses 14636 bytes (5%) of program storage space. Maximum is 262144 bytes.
+Global variables use 3224 bytes (9%) of dynamic memory, leaving 29544 bytes for local variables. Maximum is 32768 bytes.
 ```