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use crate::storage_id_type;

// This ID is used to map a handle to its actual data.
storage_id_type!(StorageId);

/// Defines if data uses a full memory chunk or a slice of it.
#[derive(Clone, Debug)]
pub enum StorageUtilization {
    /// Full memory chunk of specified size
    Full(usize),
    /// Slice of memory chunk with start index and size.
    Slice {
        /// The offset in bytes from the chunk start.
        offset: usize,
        /// The size of the slice in bytes.
        size: usize,
    },
}

/// Contains the [storage id](StorageId) of a resource and the way it is used.
#[derive(new, Clone, Debug)]
pub struct StorageHandle {
    /// Storage id.
    pub id: StorageId,
    /// How the storage is used.
    pub utilization: StorageUtilization,
}

impl StorageHandle {
    /// Returns the size the handle is pointing to in memory.
    pub fn size(&self) -> usize {
        match self.utilization {
            StorageUtilization::Full(size) => size,
            StorageUtilization::Slice { offset: _, size } => size,
        }
    }

    /// Returns the size the handle is pointing to in memory.
    pub fn offset(&self) -> usize {
        match self.utilization {
            StorageUtilization::Full(..) => panic!("full size slice not supported anymore"),
            StorageUtilization::Slice { offset, .. } => offset,
        }
    }
}

/// Storage types are responsible for allocating and deallocating memory.
pub trait ComputeStorage: Send {
    /// The resource associated type determines the way data is implemented and how
    /// it can be accessed by kernels.
    type Resource: Send;

    /// Returns the underlying resource for a specified storage handle
    fn get(&mut self, handle: &StorageHandle) -> Self::Resource;

    /// Allocates `size` units of memory and returns a handle to it
    fn alloc(&mut self, size: usize) -> StorageHandle;

    /// Deallocates the memory pointed by the given storage id.
    fn dealloc(&mut self, id: StorageId);

    /// Copy
    fn copy(&mut self, from: &StorageHandle, to: &StorageHandle);
}