pub const Global = struct {
    linkage: Linkage = .external,
    preemption: Preemption = .dso_preemptable,
    visibility: Visibility = .default,
    dll_storage_class: DllStorageClass = .default,
    unnamed_addr: UnnamedAddr = .default,
    addr_space: AddrSpace = .default,
    externally_initialized: ExternallyInitialized = .default,
    type: Type,
    partition: String = .none,
    dbg: Metadata = .none,
    kind: union(enum) {
        alias: Alias.Index,
        variable: Variable.Index,
        function: Function.Index,
        replaced: Global.Index,
    },

    pub const Index = enum(u32) {
        none = std.math.maxInt(u32),
        _,

        pub fn unwrap(self: Index, builder: *const Builder) Index {
            var cur = self;
            while (true) {
                const replacement = cur.getReplacement(builder);
                if (replacement == .none) return cur;
                cur = replacement;
            }
        }

        pub fn eql(self: Index, other: Index, builder: *const Builder) bool {
            return self.unwrap(builder) == other.unwrap(builder);
        }

        pub fn ptr(self: Index, builder: *Builder) *Global {
            return &builder.globals.values()[@intFromEnum(self.unwrap(builder))];
        }

        pub fn ptrConst(self: Index, builder: *const Builder) *const Global {
            return &builder.globals.values()[@intFromEnum(self.unwrap(builder))];
        }

        pub fn name(self: Index, builder: *const Builder) StrtabString {
            return builder.globals.keys()[@intFromEnum(self.unwrap(builder))];
        }

        pub fn strtab(self: Index, builder: *const Builder) struct {
            offset: u32,
            size: u32,
        } {
            const name_index = self.name(builder).toIndex() orelse return .{
                .offset = 0,
                .size = 0,
            };

            return .{
                .offset = builder.strtab_string_indices.items[name_index],
                .size = builder.strtab_string_indices.items[name_index + 1] -
                    builder.strtab_string_indices.items[name_index],
            };
        }

        pub fn typeOf(self: Index, builder: *const Builder) Type {
            return self.ptrConst(builder).type;
        }

        pub fn toConst(self: Index) Constant {
            return @enumFromInt(@intFromEnum(Constant.first_global) + @intFromEnum(self));
        }

        pub fn setLinkage(self: Index, linkage: Linkage, builder: *Builder) void {
            self.ptr(builder).linkage = linkage;
            self.updateDsoLocal(builder);
        }

        pub fn setVisibility(self: Index, visibility: Visibility, builder: *Builder) void {
            self.ptr(builder).visibility = visibility;
            self.updateDsoLocal(builder);
        }

        pub fn setDllStorageClass(self: Index, class: DllStorageClass, builder: *Builder) void {
            self.ptr(builder).dll_storage_class = class;
        }

        pub fn setUnnamedAddr(self: Index, unnamed_addr: UnnamedAddr, builder: *Builder) void {
            self.ptr(builder).unnamed_addr = unnamed_addr;
        }

        pub fn setDebugMetadata(self: Index, dbg: Metadata, builder: *Builder) void {
            self.ptr(builder).dbg = dbg;
        }

        const FormatData = struct {
            global: Index,
            builder: *const Builder,
        };
        fn format(
            data: FormatData,
            comptime _: []const u8,
            _: std.fmt.FormatOptions,
            writer: anytype,
        ) @TypeOf(writer).Error!void {
            try writer.print("@{}", .{
                data.global.unwrap(data.builder).name(data.builder).fmt(data.builder),
            });
        }
        pub fn fmt(self: Index, builder: *const Builder) std.fmt.Formatter(format) {
            return .{ .data = .{ .global = self, .builder = builder } };
        }

        pub fn rename(self: Index, new_name: StrtabString, builder: *Builder) Allocator.Error!void {
            try builder.ensureUnusedGlobalCapacity(new_name);
            self.renameAssumeCapacity(new_name, builder);
        }

        pub fn takeName(self: Index, other: Index, builder: *Builder) Allocator.Error!void {
            try builder.ensureUnusedGlobalCapacity(.empty);
            self.takeNameAssumeCapacity(other, builder);
        }

        pub fn replace(self: Index, other: Index, builder: *Builder) Allocator.Error!void {
            try builder.ensureUnusedGlobalCapacity(.empty);
            self.replaceAssumeCapacity(other, builder);
        }

        pub fn delete(self: Index, builder: *Builder) void {
            self.ptr(builder).kind = .{ .replaced = .none };
        }

        fn updateDsoLocal(self: Index, builder: *Builder) void {
            const self_ptr = self.ptr(builder);
            switch (self_ptr.linkage) {
                .private, .internal => {
                    self_ptr.visibility = .default;
                    self_ptr.dll_storage_class = .default;
                    self_ptr.preemption = .implicit_dso_local;
                },
                .extern_weak => if (self_ptr.preemption == .implicit_dso_local) {
                    self_ptr.preemption = .dso_local;
                },
                else => switch (self_ptr.visibility) {
                    .default => if (self_ptr.preemption == .implicit_dso_local) {
                        self_ptr.preemption = .dso_local;
                    },
                    else => self_ptr.preemption = .implicit_dso_local,
                },
            }
        }

        fn renameAssumeCapacity(self: Index, new_name: StrtabString, builder: *Builder) void {
            const old_name = self.name(builder);
            if (new_name == old_name) return;
            const index = @intFromEnum(self.unwrap(builder));
            _ = builder.addGlobalAssumeCapacity(new_name, builder.globals.values()[index]);
            builder.globals.swapRemoveAt(index);
            if (!old_name.isAnon()) return;
            builder.next_unnamed_global = @enumFromInt(@intFromEnum(builder.next_unnamed_global) - 1);
            if (builder.next_unnamed_global == old_name) return;
            builder.getGlobal(builder.next_unnamed_global).?.renameAssumeCapacity(old_name, builder);
        }

        fn takeNameAssumeCapacity(self: Index, other: Index, builder: *Builder) void {
            const other_name = other.name(builder);
            other.renameAssumeCapacity(.empty, builder);
            self.renameAssumeCapacity(other_name, builder);
        }

        fn replaceAssumeCapacity(self: Index, other: Index, builder: *Builder) void {
            if (self.eql(other, builder)) return;
            builder.next_replaced_global = @enumFromInt(@intFromEnum(builder.next_replaced_global) - 1);
            self.renameAssumeCapacity(builder.next_replaced_global, builder);
            self.ptr(builder).kind = .{ .replaced = other.unwrap(builder) };
        }

        fn getReplacement(self: Index, builder: *const Builder) Index {
            return switch (builder.globals.values()[@intFromEnum(self)].kind) {
                .replaced => |replacement| replacement,
                else => .none,
            };
        }
    };
}