From 53799feb75bdd8dfc577c95088cb0d76c226316c Mon Sep 17 00:00:00 2001
From: bas <bastien.billey@gmail.com>
Date: Fri, 17 Nov 2023 11:50:27 +0800
Subject: [PATCH] add LOWER function

---
 cmd/genji/doc/functions.go          |   3 +-
 internal/expr/functions/builtins.go |  48 ++++++++++++
 sqltests/SELECT/lower.sql           | 113 ++++++++++++++++++++++++++++
 3 files changed, 163 insertions(+), 1 deletion(-)
 create mode 100644 sqltests/SELECT/lower.sql

diff --git a/cmd/genji/doc/functions.go b/cmd/genji/doc/functions.go
index da77f5d6..a40f6ed7 100644
--- a/cmd/genji/doc/functions.go
+++ b/cmd/genji/doc/functions.go
@@ -15,7 +15,8 @@ var builtinDocs = functionDocs{
 	"sum":    "The sum function returns the sum of all values taken by the arg1 expression in a group.",
 	"avg":    "The avg function returns the average of all values taken by the arg1 expression in a group.",
 	"typeof": "The typeof function returns the type of arg1.",
-	"len":    "Then len function returns length of the arg1 expression if arg1 evals to string, array or document, either returns NULL.",
+	"len":    "The len function returns length of the arg1 expression if arg1 evals to string, array or document, either returns NULL.",
+	"lower":  "The lower function returns arg1 to lower-case if arg1 evals to string",
 }
 
 var mathDocs = functionDocs{
diff --git a/internal/expr/functions/builtins.go b/internal/expr/functions/builtins.go
index dd56a6ff..aaa0d8d2 100644
--- a/internal/expr/functions/builtins.go
+++ b/internal/expr/functions/builtins.go
@@ -2,6 +2,7 @@ package functions
 
 import (
 	"fmt"
+	"strings"
 
 	"github.com/cockroachdb/errors"
 	"github.com/genjidb/genji/document"
@@ -67,6 +68,13 @@ var builtinFunctions = Definitions{
 			return &Len{Expr: args[0]}, nil
 		},
 	},
+	"lower": &definition{
+		name: "lower",
+		arity: 1,
+		constructorFn: func(args ...expr.Expr) (expr.Function, error) {
+			return &Lower{Expr: args[0]}, nil
+		},
+	},
 }
 
 // BuiltinDefinitions returns a map of builtin functions.
@@ -717,3 +725,43 @@ func (s *Len) Params() []expr.Expr { return []expr.Expr{s.Expr} }
 func (s *Len) String() string {
 	return fmt.Sprintf("LEN(%v)", s.Expr)
 }
+
+// Lower is the LOWER function
+// It returns the lower-case version of a string
+type Lower struct {
+	Expr expr.Expr
+}
+
+func (s* Lower) Eval(env *environment.Environment) (types.Value, error) {
+	val, err := s.Expr.Eval(env)
+	if err != nil {
+		return nil, err
+	}
+
+	if val.Type() != types.TextValue {
+		return types.NewNullValue(), nil
+	}
+	
+	lowerCaseString := strings.ToLower(types.As[string](val))
+
+	return types.NewTextValue(lowerCaseString), nil
+}
+
+func (s *Lower) IsEqual(other expr.Expr) bool {
+	if other == nil {
+		return false
+	}
+
+	o, ok := other.(*Lower)
+	if !ok {
+		return false
+	}
+
+	return expr.Equal(s.Expr, o.Expr)
+}
+
+func (s *Lower) Params() []expr.Expr { return []expr.Expr{s.Expr} }
+
+func (s *Lower) String() string {
+	return fmt.Sprintf("LOWER(%v)", s.Expr)
+}
\ No newline at end of file
diff --git a/sqltests/SELECT/lower.sql b/sqltests/SELECT/lower.sql
new file mode 100644
index 00000000..2a120968
--- /dev/null
+++ b/sqltests/SELECT/lower.sql
@@ -0,0 +1,113 @@
+-- setup:
+CREATE TABLE test(
+    a TEXT,
+    b INT,
+    c BOOL,
+    d DOUBLE,
+    e ARRAY,
+    f (
+        ...
+    )
+);
+
+INSERT INTO test (a, b, c, d, e, f) VALUES (
+    "FOO",
+    42,
+    true,
+    42.42,
+    ["A", "b", "C", "d", "E"],
+    {
+        a: "HELLO",
+        b: "WorlD"
+    }
+);
+
+-- test: TEXT value
+SELECT LOWER(a) FROM test;
+/* result:
+{
+    "LOWER(a)": "foo" 
+}
+*/
+
+
+-- test: INT value
+SELECT LOWER(b) FROM test;
+/* result:
+{
+    "LOWER(b)": NULL 
+}
+*/
+
+
+-- test: BOOL value
+SELECT LOWER(c) FROM test;
+/* result:
+{
+    "LOWER(c)": NULL 
+}
+*/
+
+-- test: DOUBLE value
+SELECT LOWER(d) FROM test;
+/* result:
+{
+    "LOWER(d)": NULL 
+}
+*/
+
+-- test: ARRAY value
+SELECT LOWER(e) FROM test;
+/* result:
+{
+    "LOWER(e)": NULL 
+}
+*/
+
+-- test: DOCUMENT value
+SELECT LOWER(f) FROM test;
+/* result:
+{
+    "LOWER(f)": NULL 
+}
+*/
+
+-- test: cast INT
+SELECT LOWER(CAST(b as TEXT)) FROM test;
+/* result:
+{
+    "LOWER(CAST(b AS text))": "42" 
+}
+*/
+
+-- test: cast BOOL
+SELECT LOWER(CAST(c as TEXT)) FROM test;
+/* result:
+{
+    "LOWER(CAST(c AS text))": "true" 
+}
+*/
+
+-- test: cast DOUBLE
+SELECT LOWER(CAST(d as TEXT)) FROM test;
+/* result:
+{
+    "LOWER(CAST(d AS text))": "42.42" 
+}
+*/
+
+-- test: cast ARRAY
+SELECT LOWER(CAST(e as TEXT)) FROM test;
+/* result:
+{
+    "LOWER(CAST(e AS text))": "[\"a\", \"b\", \"c\", \"d\", \"e\"]" 
+}
+*/
+
+-- test: cast DOCUMENT
+SELECT LOWER(CAST(f as TEXT)) FROM test;
+/* result:
+{
+    "LOWER(CAST(f AS text))": "{\"a\": \"hello\", \"b\": \"world\"}" 
+}
+*/