#![allow(clippy::nonstandard_macro_braces)] // clippy bug, see https://github.com/rust-lang/rust-clippy/issues/7434

use anyhow::Result;
use thiserror::Error;

use super::RVA;

// these are usize so that they're easy to work with for indexing within this
// module. generally, this module should work with RVA/u64 as its public
// interface.
const PAGE_SIZE: usize = 0x1000;
const PAGE_SHIFT: usize = 12;
const PAGE_MASK: usize = 0xFFF;

#[derive(Debug, Error)]
pub enum PageMapError {
    #[error("address not mapped")]
    NotMapped,
}

fn page(rva: RVA) -> usize {
    (rva as usize) >> PAGE_SHIFT
}

fn page_offset(rva: RVA) -> usize {
    (rva as usize) & PAGE_MASK
}

#[derive(Clone)]
struct Page<T: Default + Copy> {
    elements: [T; PAGE_SIZE],
}

impl<T: Default + Copy> Page<T> {
    fn new(items: &[T]) -> Page<T> {
        let mut page: Page<T> = Default::default();
        page.elements.copy_from_slice(items);
        page
    }
}

impl<T: Default + Copy> Default for Page<T> {
    fn default() -> Self {
        Page {
            elements: [Default::default(); PAGE_SIZE],
        }
    }
}

/// PageMap is a map-like data structure that stores `Copy` elements in pages of
/// 0x1000.
///
/// Its a good choice when representing lots of small elements that are found at
/// contiguous indices. At the moment, indices are `RVA`.
///
/// Lookups should be quick, as they boil down to just a couple dereferences.
#[derive(Clone)]
pub struct PageMap<T: Default + Copy> {
    pages: Vec<Option<Page<T>>>,
}

impl<T: Default + Copy> PageMap<T> {
    pub fn with_capacity(capacity: RVA) -> PageMap<T> {
        let page_count = page(capacity) + 1;
        let mut pages = Vec::with_capacity(page_count);
        pages.resize_with(page_count, || None);

        PageMap { pages }
    }

    pub fn from_items(items: &[T]) -> PageMap<T> {
        let capacity = crate::util::align(items.len() as u64, PAGE_SIZE as u64);
        let mut map = PageMap::with_capacity(capacity);
        map.writezx(0x0, items).unwrap();
        map
    }

    /// error if rva is not in a valid page.
    /// panic due to:
    ///   - rva must be page aligned.
    ///   - must be PAGE_SIZE number of items.
    fn write_page(&mut self, rva: RVA, items: &[T]) -> Result<()> {
        if page_offset(rva) != 0 {
            panic!("invalid map address");
        }
        if items.len() != PAGE_SIZE {
            panic!("invalid map buffer size");
        }
        if page(rva) > self.pages.len() - 1 {
            return Err(PageMapError::NotMapped.into());
        }

        self.pages[page(rva)] = Some(Page::new(items));

        Ok(())
    }

    /// map the given items at the given address.
    ///
    /// error if rva or items are not in a valid page.
    /// panic due to:
    ///   - rva must be page aligned.
    ///   - must be multiple of PAGE_SIZE number of items.
    ///
    /// see example under `get`.
    pub fn write(&mut self, rva: RVA, items: &[T]) -> Result<()> {
        if items.len() % PAGE_SIZE != 0 {
            panic!("items must be page aligned");
        }
        for (i, chunk) in items.chunks_exact(PAGE_SIZE).enumerate() {
            self.write_page(rva + (i * PAGE_SIZE) as u64, chunk)?;
        }
        Ok(())
    }

    /// map the default value (probably zero) at the given address for the given
    /// size.
    ///
    /// same error conditions as `map`.
    /// see example under `probe`.
    pub fn map_empty(&mut self, rva: RVA, size: usize) -> Result<()> {
        self.write(rva, &vec![Default::default(); size])
    }

    /// map the given items at the given address, padding with the default value
    /// until the next page. (map zero-extend).
    ///
    /// same error conditions as `map`.
    ///
    /// ```
    /// use lancelot::pagemap::PageMap;
    ///
    /// let mut d: PageMap<u32> = PageMap::with_capacity(0x2000);
    /// assert_eq!(d.get(0x0), None);
    /// assert_eq!(d.get(0x1), None);
    ///
    /// d.writezx(0x0, &[0x1, ]).expect("failed to write");
    /// assert_eq!(d.get(0x0), Some(0x1));
    /// assert_eq!(d.get(0x1), Some(0x0));
    /// ```
    pub fn writezx(&mut self, rva: RVA, items: &[T]) -> Result<()> {
        let empty_count = PAGE_SIZE - page_offset(items.len() as u64);
        let mut padded_items = Vec::with_capacity(items.len() + empty_count);
        padded_items.extend(items);
        padded_items.extend(&vec![Default::default(); empty_count]);
        self.write(rva, &padded_items)
    }

    /// is the given address mapped?
    ///
    /// ```
    /// use lancelot::pagemap::PageMap;
    ///
    /// let mut d: PageMap<u32> = PageMap::with_capacity(0x2000);
    /// assert_eq!(d.probe(0x0), false);
    /// assert_eq!(d.probe(0x1000), false);
    ///
    /// d.map_empty(0x0, 0x1000).expect("failed to map");
    /// assert_eq!(d.probe(0x0), true);
    /// assert_eq!(d.probe(0x1000), false);
    /// ```
    pub fn probe(&self, rva: RVA) -> bool {
        if page(rva) > self.pages.len() - 1 {
            return false;
        }

        self.pages[page(rva)].is_some()
    }

    /// fetch one item from the given address.
    /// if the address is not mapped, then the result is `None`.
    ///
    /// ```
    /// use lancelot::pagemap::PageMap;
    ///
    /// let mut d: PageMap<u32> = PageMap::with_capacity(0x2000);
    /// assert_eq!(d.get(0x0), None);
    /// assert_eq!(d.get(0x1000), None);
    ///
    /// d.write(0x1000, &[0x1; 0x1000]).expect("failed to map");
    /// assert_eq!(d.get(0x0), None);
    /// assert_eq!(d.get(0x1000), Some(0x1));
    ///
    /// d.write(0x0, &[0x2; 0x2000]).expect("failed to map");
    ///  assert_eq!(d.get(0x0), Some(0x2));
    ///  assert_eq!(d.get(0x1000), Some(0x2));
    /// ```
    pub fn get(&self, rva: RVA) -> Option<T> {
        if page(rva) > self.pages.len() - 1 {
            return None;
        }

        let page = match &self.pages[page(rva)] {
            // page is not mapped
            None => return None,
            // page is mapped
            Some(page) => page,
        };

        Some(page.elements[page_offset(rva)])
    }

    /// fetch one mutable item from the given address.
    ///
    /// ```
    /// use lancelot::pagemap::PageMap;
    ///
    /// let mut d: PageMap<u32> = PageMap::with_capacity(0x2000);
    /// d.map_empty(0x0, 0x1000).expect("failed to map");
    ///
    /// // address 0x0 starts at 0
    /// assert_eq!(d.get(0x0), Some(0x0));
    ///
    /// // set address 0x0 to 1
    /// let v = d.get_mut(0x0).expect("should be mapped");
    /// *v = 1;
    ///
    /// // address 0x0 is 1
    /// assert_eq!(d.get(0x0), Some(0x1));
    /// ```
    pub fn get_mut(&mut self, rva: RVA) -> Option<&mut T> {
        if page(rva) > self.pages.len() - 1 {
            return None;
        }

        let page = match &mut self.pages[page(rva)] {
            // page is not mapped
            None => return None,
            // page is mapped
            Some(page) => page,
        };

        Some(&mut page.elements[page_offset(rva)])
    }

    /// handle the simple slice case: when start and end fall within the same
    /// page. for example, reading a dword from address 0x10.
    ///
    /// ```
    /// use lancelot::pagemap::PageMap;
    ///
    /// let mut d: PageMap<u32> = PageMap::with_capacity(0x2000);
    /// d.map_empty(0x0, 0x1000).expect("failed to map");
    /// assert_eq!(d.slice(0x0, 0x2).unwrap(), [0x0, 0x0]);
    /// assert_eq!(d.slice(0x1000, 0x1002).is_err(), true);
    /// ```
    fn slice_into_simple<'a>(&self, start: RVA, buf: &'a mut [T]) -> Result<&'a [T]> {
        // precondition: page(start) == page(start + buf.len())

        if page(start) > self.pages.len() - 1 {
            return Err(PageMapError::NotMapped.into());
        }

        let page = match &self.pages[page(start)] {
            // page is not mapped
            None => return Err(PageMapError::NotMapped.into()),
            // page is mapped
            Some(page) => page,
        };

        let end = start + buf.len() as u64;
        let elements = &page.elements[page_offset(start)..page_offset(end)];
        buf.copy_from_slice(elements);

        Ok(buf)
    }

    /// handle the complex slice case: when start and end are on different
    /// pages. for example, reading a dword from address 0xFFE.
    ///
    /// ```
    /// use lancelot::pagemap::PageMap;
    ///
    /// let mut d: PageMap<u32> = PageMap::with_capacity(0x5000);
    /// d.map_empty(0x1000, 0x3000).expect("failed to map");
    ///
    /// // 0     unmapped
    /// //       unmapped
    /// // 1000  0 0 0 0
    /// //       0 0 0 0
    /// // 2000  0 0 0 0
    /// //       0 0 0 0
    /// // 3000  0 0 0 0
    /// //       0 0 0 0
    /// // 4000  unmapped
    /// //       unmapped
    /// // 5000  unmapped
    ///
    /// assert_eq!(d.slice(0x1FFC, 0x2000).unwrap(), [0x0, 0x0, 0x0, 0x0], "no overlap");
    /// assert_eq!(d.slice(0x1FFD, 0x2001).unwrap(), [0x0, 0x0, 0x0, 0x0], "overlap 1");
    /// assert_eq!(d.slice(0x1FFE, 0x2002).unwrap(), [0x0, 0x0, 0x0, 0x0], "overlap 2");
    /// assert_eq!(d.slice(0x1FFF, 0x2003).unwrap(), [0x0, 0x0, 0x0, 0x0], "overlap 3");
    /// assert_eq!(d.slice(0x2000, 0x2004).unwrap(), [0x0, 0x0, 0x0, 0x0], "overlap 4");
    ///
    /// assert_eq!(d.slice(0x1FFC, 0x3004).unwrap().len(), 0x1008, "4, page, 4");
    ///
    /// assert_eq!(d.slice(0x1FFC, 0x3000).unwrap().len(), 0x1004, "4, page");
    ///
    /// assert_eq!(d.slice(0x2000, 0x3004).unwrap().len(), 0x1004, "page, 4");
    /// ```
    fn slice_into_split<'a>(&self, start: RVA, buf: &'a mut [T]) -> Result<&'a [T]> {
        let end = start + buf.len() as u64;
        let start_page = page(start);
        let end_page = if page_offset(end) == 0 {
            page(end) - 1
        } else {
            page(end)
        };

        if end_page > self.pages.len() - 1 {
            return Err(PageMapError::NotMapped.into());
        }

        // ensure each page within the requested region is mapped.
        for page in start_page..=end_page {
            if !self.probe((page * PAGE_SIZE) as RVA) {
                return Err(PageMapError::NotMapped.into());
            }
        }

        let mut offset: usize = 0;

        // region one: from `start` to the end of its page
        // region two: any intermediate complete pages
        // region three: from start of final page until `end`

        // one.
        {
            let page = self.pages[page(start)].as_ref().expect("slice_into_split: one");
            let elements = &page.elements[page_offset(start)..];
            {
                let dst = &mut buf[offset..offset + elements.len()];
                dst.copy_from_slice(elements);
                offset += elements.len();
            }
        }

        // two.
        if page(start) != page(end) - 1 {
            let start_index = page(start) + 1;
            let end_index = page(end);
            for page_index in start_index..end_index {
                let page = self.pages[page_index].as_ref().expect("slice_into_split: two");
                let elements = &page.elements[..];
                {
                    let dst = &mut buf[offset..offset + elements.len()];
                    dst.copy_from_slice(elements);
                    offset += elements.len();
                }
            }
        }

        // three.
        if page_offset(end) != 0x0 {
            let page = self.pages[page(end)].as_ref().expect("slice_into_split: three");
            let elements = &page.elements[..page_offset(end)];
            {
                let dst = &mut buf[offset..offset + elements.len()];
                dst.copy_from_slice(elements);
            }
        }

        Ok(buf)
    }

    /// fetch the items found in the given range, placing them into the given
    /// slice. compared with `slice`, this routine avoids an allocation.
    ///
    /// errors:
    ///   - PageMapError::NotMapped: if any requested address is not mapped
    pub fn slice_into<'a>(&self, start: RVA, buf: &'a mut [T]) -> Result<&'a [T]> {
        let end = start + buf.len() as u64;
        if page(start) == page(end) {
            self.slice_into_simple(start, buf)
        } else {
            self.slice_into_split(start, buf)
        }
    }

    /// fetch the items found in the given range.
    ///
    /// errors:
    ///   - PageMapError::NotMapped: if any requested address is not mapped
    ///
    /// panic if:
    ///   - start > end
    ///
    /// ```
    /// use lancelot::pagemap::PageMap;
    ///
    /// let mut d: PageMap<u32> = PageMap::with_capacity(0x2000);
    /// d.map_empty(0x0, 0x1000).expect("failed to map");
    ///
    /// assert_eq!(d.slice(0x0, 0x2).unwrap(), [0x0, 0x0]);
    /// assert!(d.slice(0x0, 0x1000).is_ok(), "read page");
    /// assert!(d.slice(0x0, 0x1001).is_err(), "read more than a page");
    /// ```
    pub fn slice(&self, start: RVA, end: RVA) -> Result<Vec<T>> {
        if start > end {
            panic!("start > end");
        }

        if end - start > std::usize::MAX as u64 {
            panic!("slice too large")
        }

        let mut ret = vec![Default::default(); (end - start) as usize];
        self.slice_into(start, &mut ret)?;

        Ok(ret)
    }
}

impl<T: Default + Copy> std::fmt::Debug for PageMap<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        let mut was_allocated = false;

        writeln!(f, "regions:")?;
        for (i, page) in self.pages.iter().enumerate() {
            match page {
                Some(_) => {
                    if !was_allocated {
                        write!(f, "  - {:#x}", i * PAGE_SIZE)?;
                    }
                    was_allocated = true;
                }
                None => {
                    if was_allocated {
                        writeln!(f, "-{:#x} mapped", i * PAGE_SIZE)?;
                    }
                    was_allocated = false;
                }
            };
        }

        if was_allocated {
            writeln!(f, " - {:#x} mapped", self.pages.len() * PAGE_SIZE)?;
        }

        writeln!(f, "capacity: {:#x}", self.pages.len() * PAGE_SIZE)?;

        Ok(())
    }
}