From bc3b2cd81d5237fb0628bf5ecce1ef7ac4f8b4ec Mon Sep 17 00:00:00 2001
From: Steven Hugg <hugg@fasterlight.com>
Date: Thu, 3 Feb 2022 09:24:00 -0600
Subject: [PATCH] ecs: with/if

---
 src/codemirror/ecs.js      |  4 ++--
 src/common/ecs/compiler.ts |  2 +-
 src/common/ecs/ecs.ts      | 27 +++++++++++++++++++--------
 3 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/src/codemirror/ecs.js b/src/codemirror/ecs.js
index 10b835a2..869f9eab 100644
--- a/src/codemirror/ecs.js
+++ b/src/codemirror/ecs.js
@@ -20,14 +20,14 @@
       'end', 'component', 'system', 'entity', 'scope', 'using', 'demo',
       'const', 'init', 'locals',
       'on', 'do', 'emit', 'limit',
-      'once', 'foreach', 'with', 'join'
+      'once', 'foreach', 'with', 'join', 'if',
     ];
     var keywords_list = [
       'processor',
       'byte', 'word', 'long',
       'include', 'seg', 'dc', 'ds', 'dv', 'hex', 'err', 'org', 'rorg', 'echo', 'rend',
       'align', 'subroutine', 'equ', 'eqm', 'set', 'mac', 'endm', 'mexit', 'ifconst',
-      'ifnconst', 'if', 'else', 'endif', 'eif', 'repeat', 'repend'
+      'ifnconst', 'else', 'endif', 'eif', 'repeat', 'repend'
     ];
 
     var directives = new Map();
diff --git a/src/common/ecs/compiler.ts b/src/common/ecs/compiler.ts
index f187d428..79823b65 100644
--- a/src/common/ecs/compiler.ts
+++ b/src/common/ecs/compiler.ts
@@ -212,7 +212,7 @@ export class ECSCompiler extends Tokenizer {
         let event = this.expectIdent().str;
         this.expectToken('do');
         let select = this.expectTokens(
-            ['once', 'foreach', 'join', 'with', 'select']).str as SelectType; // TODO: type check?
+            ['once', 'foreach', 'join', 'with', 'if', 'select']).str as SelectType; // TODO: type check?
         let query = undefined;
         let join = undefined;
         if (select != 'once') {
diff --git a/src/common/ecs/ecs.ts b/src/common/ecs/ecs.ts
index 38f6f466..18147ecb 100644
--- a/src/common/ecs/ecs.ts
+++ b/src/common/ecs/ecs.ts
@@ -111,7 +111,7 @@ export interface System extends SourceLocated {
     tempbytes?: number;
 }
 
-export type SelectType = 'once' | 'foreach' | 'join' | 'with' | 'select';
+export type SelectType = 'once' | 'foreach' | 'join' | 'with' | 'if' | 'select';
 
 export interface ActionBase extends SourceLocated {
     select: SelectType;
@@ -125,7 +125,7 @@ export interface ActionOnce extends ActionBase {
 }
 
 export interface ActionWithQuery extends ActionBase {
-    select: 'foreach' | 'join' | 'with' | 'select'
+    select: 'foreach' | 'join' | 'with' | 'if' | 'select'
     query: Query
     limit?: number
 }
@@ -529,14 +529,20 @@ class ActionEval {
                 this.jr = new QueryResult(this.scope, (this.action as ActionWithJoin).join);
                 state.x = this.jr;
                 break;
+            case 'if':
             case 'with':
                 if (state.x) {
                     let int = state.x.intersection(this.qr);
-                    // TODO: what if we filter 0 entities?
-                    if (int.entities.length == 0) throw new ECSError('queries do not intersect', this.action);
-                    let indofs = int.entities[0].id - state.x.entities[0].id;
-                    state.xofs += indofs; // TODO: should merge with filter
-                    state.x = int;
+                    if (int.entities.length == 0) {
+                        if (this.action.select == 'with')
+                            throw new ECSError('queries do not intersect', this.action);
+                        else
+                            break;
+                    } else {
+                        let indofs = int.entities[0].id - state.x.entities[0].id;
+                        state.xofs += indofs; // TODO: should merge with filter
+                        state.x = int;
+                    }
                 } else {
                     if (this.qr.entities.length != 1)
                         throw new ECSError(`query outside of loop must match exactly one entity`, this.action);
@@ -566,7 +572,7 @@ class ActionEval {
             if (action.select == 'join' && this.jr) {
                 let jentities = this.jr.entities;
                 if (jentities.length == 0)
-                    throw new ECSError(`join query doesn't match any entities`, action); // TODO 
+                    throw new ECSError(`join query doesn't match any entities`, (action as ActionWithJoin).join); // TODO 
                 let joinfield = this.getJoinField(action, this.qr.atypes, this.jr.atypes);
                 // TODO: what if only 1 item?
                 // TODO: should be able to access fields via Y reg
@@ -580,6 +586,8 @@ class ActionEval {
             if (action.limit) {
                 entities = entities.slice(0, action.limit);
             }
+            if (entities.length == 0 && action.select == 'if')
+                return '';
             if (entities.length == 0)
                 throw new ECSError(`query doesn't match any entities`, action.query); // TODO 
             this.qr.entities = entities;
@@ -587,6 +595,9 @@ class ActionEval {
             if (action.select == 'with' && entities.length > 1) {
                 code = this.wrapCodeInFilter(code);
             }
+            if (action.select == 'if' && entities.length > 1) {
+                code = this.wrapCodeInFilter(code);
+            }
             // define properties
             props['%elo'] = entities[0].id.toString();
             props['%ehi'] = entities[entities.length - 1].id.toString();