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const KUNIT: usize = 1024; // a kunit of memory is 1024 things (bytes, kilobytes, ...)
const PREFIXES: &str = "KMGTPE"; // prefixes for memory quantities KiB, MiB, GiB, ...

// Create a human-readable string representation of the memory size
pub fn memory_size(total: usize) -> String {
    if total < KUNIT {
        format!("{total} B")
    } else {
        // Compute the index in the prefixes string above
        let mut idx = 0;
        let mut d = KUNIT;
        let mut n = total / KUNIT;

        while n >= KUNIT {
            d *= KUNIT;
            idx += 1;
            n /= KUNIT;
        }

        let value = total as f64 / d as f64;

        let prefix =
        ////////////////////////////////////////////////////////////////////////
        // Famous last words: 1023 exabytes ought to be enough for anybody    //
        //                                                                    //
        // Corollary:                                                         //
        // unwrap() below shouldn't fail                                      //
        // The maximum representation for usize corresponds to 16 exabytes    //
        // anyway                                                             //
        ////////////////////////////////////////////////////////////////////////
            PREFIXES.chars().nth(idx).unwrap();

        format!("{:.1} {}iB", value, prefix)
    }
}

#[cfg(test)]
mod tests {

    use super::*;

    #[test]
    fn test_memory_size() {
        assert_eq!(memory_size(1023_usize), "1023 B");
        assert_eq!(memory_size(1024_usize), "1.0 KiB");
        assert_eq!(memory_size(1024 * 1024_usize), "1.0 MiB");
        assert_eq!(memory_size(2100 * 1024 * 1024_usize), "2.1 GiB");
        assert_eq!(memory_size(std::usize::MAX), "16.0 EiB");
    }
}