//! Simple bump allocator arena.

const phys_memory = @import("mem/phys.zig");
const log = @import("debug.zig").log;
const mem = @import("mem.zig");

/// Bump allocator implementation.
pub const Arena = struct {
    phys_base: mem.PhysicalAddress,
    capacity: usize,
    len: usize,

    /// Creates a new `Arena` of given `cap`acity.
    ///
    /// Requires initialized physical memory management.
    pub fn init(cap: usize) ?Arena {
        const phys_base = phys_memory.alloc_pages(cap / mem.vmm.PAGE_SIZE) orelse return null;
        return .{ .phys_base = phys_base, .capacity = cap, .len = 0 };
    }

    /// Allocates an object of type `T` within this arena.
    ///
    /// # Panics
    ///
    /// Panics if the arena runs out of memory.
    pub fn create(self: *@This(), comptime T: type) *T {
        if (self.len + @sizeOf(T) > self.capacity) {
            log.panic("Out of memory. Cannot allocate {} bytes", .{@sizeOf(T)});
        }

        const v = self.phys_base.add(self.len).virtualize();
        const ptr = @as(*T, @ptrFromInt(v));
        self.len += @sizeOf(T);

        return ptr;
    }
};