#![no_std]

#[cfg(test)]
extern crate std;

mod rsdp;
mod sdt;

use core::ops::Deref;
use core::ptr::NonNull;
use rsdp::Rsdp;

#[derive(Debug)]
pub enum AcpiError
{
    RsdpIncorrectSignature,
    RsdpInvalidOemId,
    RsdpInvalidChecksum,
}

/// Describes a physical mapping created by `AcpiHandler::map_physical_region` and unmapped by
/// `AcpiHandler::unmap_physical_region`. The region mapped must be at least `mem::size_of::<T>()`
/// bytes, but may be bigger.
pub struct PhysicalMapping<T>
{
    pub physical_start  : usize,
    pub virtual_start   : NonNull<T>,
    pub mapped_length   : usize,    // Differs from `region_length` if padding is added to align to page boundaries
}

impl<T> Deref for PhysicalMapping<T>
{
    type Target = T;

    fn deref(&self) -> &T
    {
        unsafe
        {
            self.virtual_start.as_ref()
        }
    }
}

/// The kernel must provide an implementation of this trait for `acpi` to interface with. It has
/// utility methods `acpi` uses to for e.g. mapping physical memory, but also an interface for
/// `acpi` to tell the kernel about the tables it's parsing, such as how the kernel should
/// configure the APIC or PCI routing.
pub trait AcpiHandler
{
    /// Given a starting physical address, map a region of physical memory that contains a `T`
    /// somewhere in the virtual address space. The address doesn't have to be page-aligned, so
    /// the implementation may have to add padding to either end.
    fn map_physical_region<T>(&mut self, physical_address : usize) -> PhysicalMapping<T>;

    /// Unmap the given physical mapping. Safe because we consume the mapping, and so it can't be
    /// used after being passed to this function.
    fn unmap_physical_region<T>(&mut self, region : PhysicalMapping<T>);
}

/// This is the entry point of `acpi`. Given the **physical** address of the RSDP, it parses all
/// the SDTs in the RSDT, calling the relevant handlers in the implementation's `AcpiHandler`.
pub fn parse_acpi<T>(handler : &mut T, rsdp_address : usize) -> Result<(), AcpiError>
    where T : AcpiHandler
{
    let rsdp_mapping = handler.map_physical_region::<Rsdp>(rsdp_address);
    (*rsdp_mapping).validate()?;

    // TODO: map the RSDT
    // TODO: parse the RSDT

    handler.unmap_physical_region(rsdp_mapping);
    Ok(())
}