//! Zig 0.17 reports container fields as parallel slices (`field_names`,
//! `field_types`, ...). `fieldAt` presents one field at a time, the shape the
//! encoders and decoders work with.

const std = @import("std");
const Type = std.builtin.Type;

pub const Field = struct {
    name: [:0]const u8,
    type: type,
    default_value_ptr: ?*const anyopaque,
};

pub const EnumField = struct {
    name: [:0]const u8,
    value: comptime_int,
};

fn FieldOf(comptime Info: type) type {
    return switch (Info) {
        Type.Struct, Type.Union => Field,
        Type.Enum => EnumField,
        else => @compileError("reflect.fieldAt: unsupported type info " ++ @typeName(Info)),
    };
}

pub fn fieldAt(comptime info: anytype, comptime i: usize) FieldOf(@TypeOf(info)) {
    return switch (@TypeOf(info)) {
        Type.Struct => .{
            .name = info.field_names[i],
            .type = info.field_types[i],
            .default_value_ptr = info.field_attrs[i].default_value_ptr,
        },
        Type.Union => .{
            .name = info.field_names[i],
            .type = info.field_types[i],
            .default_value_ptr = null,
        },
        Type.Enum => .{ .name = info.field_names[i], .value = info.field_values[i] },
        else => unreachable,
    };
}