explaination.txt

Let's walk through an example using the file "example.txt" with the following content:

		Hello World!
		This is a test file.
		End of file.

Here's a detailed step-by-step walkthrough of what happens when the `main` function is called:

1.Initialization in `main` function:
	* The file "example.txt" is opened for reading, and the file descriptor is stored in `fd`.
	* A variable `count` is initialized to keep track of the line numbers.
2.Reading the file line by line:
	* The `while` loop begins, and `get_next_line(fd)` is called for the first time.
3.Inside `get_next_line` function:
	* Checks are performed to ensure `fd` is valid, `read(fd, NULL, 0)` doesn't return an error,
	and `BUFFER_SIZE` is positive.
	* If `basin_buffer` is not already initialized (it's `NULL` the first time), 
	it's allocated `BUFFER_SIZE + 1` bytes and initialized with zeros using `ft_calloc`.
	* If there's no newline (`\n`) in `basin_buffer`, `read_from_file` is called to read from the file.
4.Inside `read_from_file` function:
	* A buffer `cup_buffer` is allocated `BUFFER_SIZE + 1` bytes and initialized with zeros.
	* The file is read into `cup_buffer` in chunks of `BUFFER_SIZE` bytes until a newline is encountered 
	or there are no more bytes to read.
	* After each read, `cup_buffer` is appended to `basin_buffer` using `append_buffer`.
	* For our example, let's assume `BUFFER_SIZE` is large enough to read the whole file in one go.
	The `basin_buffer` after reading the file will be:

		Hello World!\nThis is a test file.\nEnd of file.

	* The loop breaks because a newline is encountered.
5.Back in `get_next_line` function:
	* The line is extracted from `basin_buffer` using `extract_line`.
6.Inside `extract_line` function:
	* The function finds the position of the first newline (if it exists) or the end of the string.
	* It allocates enough memory for the line, copies characters up to the newline or end of the string,
	and adds a null terminator.
	* For our example, `line` will be `Hello World!\n`.
7.Back in `get_next_line` function:
	* The remaining part of `basin_buffer` is obtained using `obtain_remaining`.
8.Inside `obtain_remaining` function:
	* The function finds the part of `basin_buffer` after the extracted line.
	* It allocates enough memory for the remaining part, copies the characters, and adds a null terminator.
	* For our example, `basin_buffer` will be updated to:

		This is a test file.\nEnd of file.

	* The old `basin_buffer` is freed to prevent memory leaks.
9.Back in `get_next_line` function:
	* The extracted line `Hello World!\n` is returned to the `main` function.
10.Back in `main` function:
	* The returned line is printed with the line number `1`.
	* The memory for `line` is freed.
	* The loop continues, and `get_next_line` is called again.

The process repeats for the remaining lines in the file until `get_next_line` returns `NULL`, 
indicating the end of the file.
The loop then breaks, the file descriptor is closed, and the program ends.

The key part of this process is the interplay between `get_next_line`, `extract_line`, `obtain_remaining`, 
and `read_from_file`.
They work together to read from the file, manage the buffer, and extract lines efficiently, 
handling memory and ensuring that each line, including the last one, is correctly processed and returned.

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Continuing from where the first call to `get_next_line` returned "Hello World!\n", 
the `main` function is still in the loop, and `get_next_line` will be called again. Let's walk through the subsequent calls:

11.Second call to `get_next_line` function:
	* The validity checks for `fd` and `BUFFER_SIZE` are performed again.
	* This time, `basin_buffer` is not empty; it contains:

		This is a test file.\nEnd of file.

	* The function checks if there's a newline (`\n`) in `basin_buffer`. 
	There is, so it doesn't call `read_from_file` again.
	* The line is extracted from `basin_buffer` using `extract_line`.
12.Inside `extract_line` function:
	* The function finds the first newline and extracts "This is a test file.\n".
	* `basin_buffer` is now:

      End of file.

13.Back in `get_next_line` function:
	* The remaining part of `basin_buffer` is obtained using `obtain_remaining`.
14.Inside `obtain_remaining` function:
	* The function updates `basin_buffer` to contain only "End of file.".
	* The old `basin_buffer` is freed.
15.Back in `main` function:
	* The line "This is a test file.\n" is printed with the line number `2`.
	* The memory for `line` is freed.
	* The loop continues, and `get_next_line` is called again.
16.Third call to `get_next_line` function:
	* Similar checks are performed.
	* `basin_buffer` now contains "End of file." without a newline at the end.
	* The function realizes it's the end of the buffer and file, so it prepares to return the last line.
	* `extract_line` is called to get the line "End of file.".
17.Inside `extract_line` function:
	* The function extracts "End of file." as there's no newline indicating further content.
18.Back in `get_next_line` function:
	* The remaining part of `basin_buffer` is obtained using `obtain_remaining`, 
	but as there's no more content, `basin_buffer` is now set to `NULL`.
19.Back in `main` function:
	* The line "End of file." is printed with the line number `3`.
	* The memory for `line` is freed.
	* The loop attempts another `get_next_line` call.
20.Fourth call to `get_next_line` function:
	* `get_next_line` sees that `basin_buffer` is `NULL` and there's no more content to read from the file.
	* It returns `NULL`.
21.Back in `main` function:
	* The loop breaks as `get_next_line` returned `NULL`.
	* The file descriptor is closed with `close(fd)`.
	* The program ends as it reaches the return statement in `main`.

Throughout this process, the code ensures that memory is managed properly: buffers are allocated and freed appropriately, 
and lines are read efficiently from the file, 
respecting the `BUFFER_SIZE` and handling lines that span multiple buffer lengths or end right at the buffer's edge. 
The static `basin_buffer` ensures that the state is maintained across multiple calls to `get_next_line`, 
allowing the function to pick up right where it left off in the previous call.