const std = @import("std");

const SlabError = error{
    OutOfRange,
    SlotOccupied,
    EmptySlot,
    RemoveEmptySlot,
};

const SlabConfig = struct {
    safe: bool = true,
    dynamic: bool = true,
    size: comptime_int,
};

pub fn createSlab(comptime T: type, comptime cfg: SlabConfig) type {
    return struct {
        const Self = @This();
        allocator: std.mem.Allocator,
        data: []?T,

        pub fn init(allocator: ?std.mem.Allocator) !Self {
            if (comptime cfg.dynamic) {
                if (allocator == null) @compileError("Allocator is required for dynamic slab.");
                const data = try allocator.?.alloc(?T, cfg.size);
                for (data) |*slot| slot.* = null;
                return Self{
                    .allocator = allocator.?,
                    // .data = comptime @as(&T, &[_]?T{null} ** cfg.size),
                };
            } else {
                return Self{
                    .allocator = undefined,
                    .data = @memset(, elem),
                };
            }
        }

        inline fn checkOutOfRage(self: *Self, index: usize) !void {
            if (cfg.safe and index >= self.data.len) return SlabError.OutOfRange;
        }

        pub fn insertAt(self: *Self, index: usize, value: T) SlabError!void {
            try checkOutOfRage(index);
            if (self.data[index] != null) return SlabError.SlotOccupied;
            self.data[index] = value;
        }

        pub fn remove(self: *Self, index: usize) SlabError!void {
            if (comptime cfg.safe and self.data[index] == null) return SlabError.RemoveEmptySlot;
            self.data[index] = null;
        }

        pub fn get(self: *Self, index: usize) SlabError!*T {
            try checkOutOfRage(index);

            const maybe = self.data[index] orelse return SlabError.EmptySlot;
            return &maybe;
        }
    };
}

test "init" {
    const Slab = createSlab(u32, .{ .dynamic = false, .size = 3000, .safe = false });
    const slab = try Slab.init(null);
    try slab.insertAt(2500, 25);
    std.debug.print("{}\n", .{slab.get(2500)});
}