use crate::{FileWrapper, ProcResult};

use procfs_core::process::PageInfo;

use std::{

    io::{BufReader, Read, Seek, SeekFrom},

    mem::size_of,

    ops::{Bound, RangeBounds},

};

impl super::Process {

    /// Returns a struct that can be used to access information in the `/proc/pid/pagemap` file.

    pub fn pagemap(&self) -> ProcResult<PageMap> {

        let path = self.root.join("pagemap");

        let file = FileWrapper::open(&path)?;

        Ok(PageMap::from_file_wrapper(file))

    }

}

/// Parses page table entries accessing `/proc/<pid>/pagemap`.

pub struct PageMap {

    reader: BufReader<FileWrapper>,

}

impl PageMap {

    pub(crate) fn from_file_wrapper(file: FileWrapper) -> Self {

        Self {

            reader: BufReader::new(file),

        }

    }

    /// Retrieves information in the page table entry for the page at index `page_index`.

    ///

    /// Some mappings are not accessible, and will return an Err: `vsyscall`

    pub fn get_info(&mut self, page_index: usize) -> ProcResult<PageInfo> {

        self.get_range_info(page_index..page_index + 1)

            .map(|mut vec| vec.pop().unwrap())

    }

    /// Retrieves information in the page table entry for the pages with index in range `page_range`.

    pub fn get_range_info(&mut self, page_range: impl RangeBounds<usize>) -> ProcResult<Vec<PageInfo>> {

        // `start` is always included

        let start = match page_range.start_bound() {

            Bound::Included(v) => *v,

            Bound::Excluded(v) => *v + 1,

            Bound::Unbounded => 0,

        };

        // `end` is always excluded

        let end = match page_range.end_bound() {

            Bound::Included(v) => *v + 1,

            Bound::Excluded(v) => *v,

            Bound::Unbounded => std::usize::MAX / crate::page_size() as usize,

        };

        let start_position = (start * size_of::<u64>()) as u64;

        self.reader.seek(SeekFrom::Start(start_position))?;

        let mut page_infos = Vec::with_capacity((end - start) as usize);

        for _ in start..end {

            let mut info_bytes = [0; size_of::<u64>()];

            self.reader.read_exact(&mut info_bytes)?;

            page_infos.push(PageInfo::parse_info(u64::from_ne_bytes(info_bytes)));

        }

        Ok(page_infos)

    }

}