NYXA/src/world/query.zig

const std = @import("std");
const World = @import("world.zig");
const Archetype = @import("archetype.zig");
const QueryFilters = @import("query_filters.zig");
const TypeID = @import("../template/type_id.zig").of;

/// ----------------------------------------------------
/// ----------------------------------------------------
pub fn Query(
    comptime Result: type,
    comptime Filters: QueryFilters,
) type {
    return struct {
        const Self = @This();

        const result_fields = std.meta.fields(Result);

        //
        // FIELDS
        //

        world: *World,
        arch_cursor: usize,
        row_cursor: usize,

        current_arch: ?*Archetype,
        current_row: usize,

        /// ----------------------------------------------------
        /// ----------------------------------------------------
        pub fn init(world: *World) Self {
            return .{
                .world = world,
                .arch_cursor = 0,
                .row_cursor = 0,

                .current_arch = null,
                .current_row = 0,
            };
        }

        /// ----------------------------------------------------
        /// ----------------------------------------------------
        fn matches(arch: *Archetype) bool {
            // --- REQUIRED COMPONENTS ---
            inline for (result_fields) |field| {
                // TODO: Clean this shit up
                const FieldT = field.type;
                const is_optional = @typeInfo(FieldT) == .optional;

                const PtrT = if (is_optional) @typeInfo(FieldT).optional.child else FieldT;
                const T = std.meta.Child(PtrT);

                if (!arch.type_map.contains(TypeID(T))) {
                    // --- SKIP OPTIONALS ---
                    if (!is_optional) {
                        return false;
                    }
                }
            }

            // --- WITH ---
            inline for (Filters.with) |T| {
                if (!arch.type_map.contains(TypeID(T))) {
                    return false;
                }
            }

            // --- WITHOUT ---
            inline for (Filters.without) |T| {
                if (arch.type_map.contains(TypeID(T))) {
                    return false;
                }
            }

            return true;
        }

        /// ----------------------------------------------------
        /// ----------------------------------------------------
        pub fn next(self: *Self) ?Result {
            while (self.arch_cursor < self.world.archetypes.items.len) {
                var arch = &self.world.archetypes.items[self.arch_cursor];

                // --- SKIP ARCHETYPES ---
                if (!matches(arch)) {
                    self.arch_cursor += 1;
                    self.row_cursor = 0;
                    continue;
                }

                // --- END ROWS ---
                if (self.row_cursor >= arch.entities.items.len) {
                    self.arch_cursor += 1;
                    self.row_cursor = 0;
                    continue;
                }

                const row = self.row_cursor;

                self.row_cursor += 1;
                self.current_arch = arch;
                self.current_row = row;

                var result: Result = undefined;

                inline for (result_fields) |field| {
                    // TODO: Clean this shit up
                    const FieldT = field.type;

                    const is_optional = @typeInfo(FieldT) == .optional;

                    const PtrT = if (is_optional) @typeInfo(FieldT).optional.child else FieldT;

                    const T = std.meta.Child(PtrT);

                    const ptr = arch.get(T, row);

                    if (is_optional) {
                        @field(result, field.name) = ptr;
                    } else {
                        @field(result, field.name) = ptr orelse return null;
                    }
                }

                return result;
            }

            return null;
        }

        /// ----------------------------------------------------
        /// ----------------------------------------------------
        pub fn entity(self: *const Self) u64 {
            return self.current_arch.?.entities.items[
                self.current_row
            ];
        }
    };
}