From 2a85d768a56687d7dd9f70a683185ee6928fcceb Mon Sep 17 00:00:00 2001
From: Zaid Abdulla <zaid@genieacs.com>
Date: Mon, 17 Aug 2020 10:01:45 -0700
Subject: [PATCH] Implement COALESCE function

---
 lib/common/boolean-expression.ts | 15 ++++++++++++++-
 lib/common/expression-parser.ts  |  2 +-
 lib/common/expression.ts         | 24 +++++++++++++++++++++++-
 3 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/lib/common/boolean-expression.ts b/lib/common/boolean-expression.ts
index e6aa62e..0ec808f 100644
--- a/lib/common/boolean-expression.ts
+++ b/lib/common/boolean-expression.ts
@@ -586,6 +586,13 @@ function normalizeCallback(exp: Expression): Expression {
   if (!Array.isArray(exp)) return exp;
   const op = exp[0];
 
+  if (op === "FUNC" && exp[1] === "COALESCE") {
+    const res: Expression[] = ["CASE"];
+    for (let i = 2; i < exp.length; ++i)
+      res.push(normalizeCallback(["IS NOT NULL", exp[i]]), exp[i]);
+    return normalizeCallback(res);
+  }
+
   if (op === "CASE") {
     const res = [] as [Expression, Expression][];
     for (let i = 1; i < exp.length; i += 2) {
@@ -765,7 +772,13 @@ function normalizeCallback(exp: Expression): Expression {
 
 export function normalize(expr: Expression): Expression {
   expr = map(expr, normalizeCallback);
-  if (expr instanceof Polynomial) expr = JSON.parse(expr.toString());
+  if (expr instanceof Polynomial) {
+    expr = JSON.parse(expr.toString());
+  } else if (Array.isArray(expr) && expr[0] === "CASE") {
+    expr = expr.map((e) =>
+      e instanceof Polynomial ? JSON.parse(e.toString()) : e
+    );
+  }
   return expr;
 }
 
diff --git a/lib/common/expression-parser.ts b/lib/common/expression-parser.ts
index b23e73d..07833f1 100644
--- a/lib/common/expression-parser.ts
+++ b/lib/common/expression-parser.ts
@@ -215,7 +215,7 @@ const lang = parsimmon.createLanguage({
         .regexp(/([a-zA-Z0-9_]+)/, 1)
         .skip(parsimmon.optWhitespace)
         .desc("function"),
-      r.ValueExpression.sepBy(
+      r.Expression.sepBy(
         parsimmon.string(",").skip(parsimmon.optWhitespace)
       ).wrap(
         parsimmon.string("(").skip(parsimmon.optWhitespace),
diff --git a/lib/common/expression.ts b/lib/common/expression.ts
index 97dc82a..7b84bf8 100644
--- a/lib/common/expression.ts
+++ b/lib/common/expression.ts
@@ -93,6 +93,17 @@ function toNumber(a: boolean | number | string): number {
   }
 }
 
+function toString(a: boolean | number | string): string {
+  switch (typeof a) {
+    case "string":
+      return a;
+    case "number":
+      return a.toString();
+    case "boolean":
+      return (+a).toString();
+  }
+}
+
 export function evaluateCallback(exp: Expression): Expression {
   if (!Array.isArray(exp)) return exp;
   if (exp[0] === "CASE") {
@@ -101,6 +112,17 @@ export function evaluateCallback(exp: Expression): Expression {
       if (exp[i]) return exp[i + 1];
     }
     return null;
+  } else if (exp[0] === "FUNC" && exp[1] === "COALESCE") {
+    const args: Expression[] = [];
+    for (let i = 2; i < exp.length; ++i) {
+      const e = exp[i];
+      if (e == null) continue;
+      args.push(e);
+      if (!Array.isArray(e)) break;
+    }
+    if (!args.length) return null;
+    if (args.length === 1) return args[0];
+    return ["FUNC", "COALESCE", ...args];
   } else if (exp[0] === "AND") {
     for (let i = 1; i < exp.length; ++i)
       if (!Array.isArray(exp[i]) && exp[i] != null && !exp[i]) return false;
@@ -223,7 +245,7 @@ export function evaluateCallback(exp: Expression): Expression {
   } else if (exp[0] === "||") {
     return reduce(exp, (a, b) => {
       if (a == null || b == null) return null;
-      if (!isArray(a) && !isArray(b)) return `${a}${b}`;
+      if (!isArray(a) && !isArray(b)) return toString(a) + toString(b);
       return REDUCE_SKIP;
     });
   }