Read N Characters Given read4 II - Call

lcpy gen -n 158   # by problem number
lcpy gen -s read_n_characters_given_read4_ii   # by problem name

    Parameter:  char[] buf4
    Returns:    int

buf4[] is a destination, not a source. The results from read4 will be copied to buf4[].

File file("abcde"); // File is "abcde", initially file pointer (fp) points to 'a'
char[] buf4 = new char[4]; // Create buffer with enough space
read4(buf4); // read4 returns 4. Now buf4 = "abcd", fp points to 'e'
read4(buf4); // read4 returns 1. Now buf4 = "e", fp points to end of file
read4(buf4); // read4 returns 0. Now buf4 = "", fp points to end of file

    Parameters:  char[] buf, int n
    Returns:     int

buf[] is a destination, not a source. You will need to write the results to buf[].

Input: file = "abc", queries = [1,2,1]
Output: [1,2,0]
Explanation:
sol.read(buf, 1); // buf should contain "a". We read a total of 1 character from the file, so return 1.
sol.read(buf, 2); // Now buf should contain "bc". We read a total of 2 characters, so return 2.
sol.read(buf, 1); // We have reached the end of file, no more characters can be read. So return 0.

Input: file = "abc", queries = [4,1]
Output: [3,0]
Explanation:
sol.read(buf, 4); // buf should contain "abc". We read a total of 3 characters, so return 3.
sol.read(buf, 1); // We have reached the end of file, no more characters can be read. So return 0.

class File:
    # Test-harness API: backs the read4 interface with the file content
    def __init__(self, content: str) -> None:
        self.content = content
        self.pos = 0

    def read4(self, buf4: list[str]) -> int:
        # Reads up to 4 consecutive characters into buf4 and returns the
        # number of characters actually read; read4 keeps its own file
        # pointer across calls
        chunk = self.content[self.pos : self.pos + 4]
        self.pos += len(chunk)
        for i, char in enumerate(chunk):
            buf4[i] = char
        return len(chunk)


class Solution:
    # Time: O(n) per read call
    # Space: O(1), the internal 4-character buffer is reused across calls
    def __init__(self) -> None:
        self.buf4: list[str] = [""] * 4
        self.i = 0  # next unread position inside buf4
        self.size = 0  # number of valid characters currently in buf4

    def read(self, buf: list[str], n: int, file: File) -> int:
        count = 0
        while count < n:
            if self.i == self.size:
                self.size = file.read4(self.buf4)
                self.i = 0
                if self.size == 0:
                    break
            while count < n and self.i < self.size:
                buf[count] = self.buf4[self.i]
                self.i += 1
                count += 1
        return count