NYXA/src/world/world.zig

// --- LIBS ---
const std = @import("std");
const Archetype = @import("archetype.zig");
const Signature = @import("signature.zig");
const EntityRecord = @import("entity_record.zig");
const QueryFilters = @import("query_filters.zig");
const Query = @import("query.zig").Query;
const TypeID = @import("../template/type_id.zig").of;
const Self = @This();

//
// FIELDS
//

archetypes: std.ArrayList(Archetype),
entity_map: std.AutoHashMap(u64, EntityRecord),
signature_map: std.AutoHashMap(u64, usize),
next_entity: u64,
alloc: std.mem.Allocator,

/// ----------------------------------------------------
/// ----------------------------------------------------
pub fn init(alloc: std.mem.Allocator) Self {
    return .{
        .archetypes = .empty,
        .entity_map = .init(alloc),
        .signature_map = .init(alloc),
        .next_entity = 1,
        .alloc = alloc,
    };
}

/// ----------------------------------------------------
/// ----------------------------------------------------
pub fn deinit(self: *Self) void {
    // --- ARCHETYPES ---
    for (self.archetypes.items) |*arch| {
        arch.deinit();
    }
    self.entity_map.deinit();
    self.archetypes.deinit(self.alloc);
    self.signature_map.deinit();
}

/// ----------------------------------------------------
/// ----------------------------------------------------
pub fn spawn(
    self: *Self,
    components: anytype,
) !void {
    _ = try self.spawnEntity(components);
}

/// ----------------------------------------------------
/// ----------------------------------------------------
pub fn despawn(
    self: *Self,
    entity: u64,
) void {
    const record = self.entity_map.get(entity) orelse return;
    if (self.archetypes.items[record.archetype_idx].remove(record.row)) |moved| {
        self.entity_map.getPtr(moved).?.row = record.row;
    }
    _ = self.entity_map.remove(entity);
}

/// ----------------------------------------------------
/// ----------------------------------------------------
pub fn spawnEntity(
    self: *Self,
    components: anytype,
) !u64 {
    const Components = @TypeOf(components);

    const fields = std.meta.fields(Components);

    // --- SIGNATURE ---
    var ids: [fields.len]u64 = undefined;
    inline for (fields, 0..) |field, i| {
        const component = @field(
            components,
            field.name,
        );
        ids[i] = TypeID(@TypeOf(component));
    }

    // --- SORT TYPE ID'S ---
    std.mem.sort(
        u64,
        &ids,
        {},
        std.sort.asc(u64),
    );

    const signature_hash = std.hash.Wyhash.hash(0, std.mem.sliceAsBytes(&ids));

    // --- FIND OR CREATE ARCHETYPE ---
    const archetype_idx =
        self.signature_map.get(signature_hash) orelse blk: {
            const sig_ids = try self.alloc.dupe(u64, &ids);

            var arch: Archetype = .init(.{ .ids = sig_ids }, self.alloc);

            // --- NEW COLUMNS ---
            inline for (fields) |field| {
                const component = @field(components, field.name);
                try arch.addColumn(@TypeOf(component));
            }

            // --- ADD ARCHETYPE ---
            try self.archetypes.append(
                self.alloc,
                arch,
            );

            // --- ADD SIGNATURE ---
            const idx = self.archetypes.items.len - 1;
            try self.signature_map.put(
                signature_hash,
                idx,
            );

            break :blk idx;
        };

    // --- NEW ENTITY ---
    const entity = self.next_entity;
    self.next_entity += 1;

    // --- ADD ROW ---
    var arch = &self.archetypes.items[archetype_idx];

    const row = arch.entities.items.len;

    try arch.add(
        entity,
        components,
    );

    // --- STORE ENTITY LOCATION ---
    try self.entity_map.put(entity, .{
        .archetype_idx = archetype_idx,
        .row = row,
    });

    return entity;
}

/// ----------------------------------------------------
/// ----------------------------------------------------
fn createEntity(self: *Self) u64 {
    const entity = self.next_entity;
    self.next_entity += 1;
    return entity;
}

/// ----------------------------------------------------
/// ----------------------------------------------------
fn createArchetype(
    self: *Self,
    comptime Components: type,
) !usize {
    const fields =
        std.meta.fields(Components);

    var ids = try self.alloc.alloc(
        u64,
        fields.len,
    );

    inline for (fields, 0..) |field, i| {
        ids[i] = TypeID(field.type);
    }

    const sig: Signature = .{
        .ids = ids,
    };

    var arch: Archetype = .init(
        sig,
        self.alloc,
    );

    inline for (fields) |field| {
        try arch.addColumn(
            field.type,
        );
    }

    try self.archetypes.append(
        self.alloc,
        arch,
    );

    return self.archetypes.items.len - 1;
}

/// ----------------------------------------------------
/// Example:
/// ```
/// var query = world.query(struct {
///   player: ?*Player,
///   pos: *Position,
///   vel: *Velocity,
/// }, .{});
/// while (query.next()) |entity| {
///   if (entity.player) |player| {}
/// }
/// ```
/// ----------------------------------------------------
pub fn query(
    self: *Self,
    comptime Result: type,
    comptime Filters: QueryFilters,
) Query(Result, Filters) {
    return .init(self);
}