Handle case when SQLStatement passed as parameter.

Closes felixfbecker#30.

index.js

@@ -7,8 +7,36 @@ class SQLStatement {
    * @param {any[]} values
    */
   constructor(strings, values) {
-    this.strings = strings
-    this.values = values
+    if (values.length === 0) {
+      this.strings = strings
+      this.values = values
+    } else {
+      this.strings = []
+      this.values = []
+      let prevOpened = false
+      const valuesLength = values.length
+      for (let i = 0; i < valuesLength; i++) {
+        if (prevOpened) {
+          this.strings[this.strings.length - 1] += strings[i]
+          prevOpened = false
+        } else {
+          this.strings.push(strings[i])
+        }
+        const value = values[i]
+        if (value instanceof SQLStatement) {
+          this.append(value)
+          prevOpened = true
+        } else {
+          this.values.push(value)
+        }
+      }
+      if (prevOpened) {
+        this.strings[this.strings.length - 1] += strings[valuesLength]
+        prevOpened = false
+      } else {
+        this.strings.push(strings[valuesLength])
+      }
+    }
   }
 
   /** Returns the SQL Statement for Sequelize */

test/unit.js

@@ -77,6 +77,45 @@ describe('SQL', () => {
     })
   })
 
+  describe('pass nested SQLStatement instances', () => {
+    it('should not handle nested SQLStatement as parameter', () => {
+      const nested = SQL`table_name`
+      const statement = SQL`SELECT * FROM ${nested}`
+      assert.equal(statement.sql, 'SELECT * FROM table_name')
+      assert.equal(statement.text, 'SELECT * FROM table_name')
+      assert.deepEqual(statement.values, [])
+    })
+
+    it('should merge SQLStatement instances parameters', () => {
+      const nested = SQL`SELECT id FROM table2 WHERE key = ${'value'}`
+      const statement = SQL`SELECT * FROM table1 WHERE id IN (${nested})`
+      assert.equal(statement.sql, 'SELECT * FROM table1 WHERE id IN (SELECT id FROM table2 WHERE key = ?)')
+      assert.equal(statement.text, 'SELECT * FROM table1 WHERE id IN (SELECT id FROM table2 WHERE key = $1)')
+      assert.deepEqual(statement.values, ['value'])
+    })
+
+    it('should merge SQLStatement instances parameters, 3 nested statements test', () => {
+      const s1 = SQL`SELECT id FROM table WHERE key=${'value1'}`
+      const s2 = SQL`SELECT id FROM table2 WHERE key=${'value0'} AND key2 IN (${s1})`
+      const s3 = SQL`SELECT id FROM table3 WHERE key=${'value2'} AND key3 IN (${s2})`
+      assert.equal(
+        s3.sql,
+        'SELECT id FROM table3 WHERE key=? AND key3 IN (SELECT id FROM table2 WHERE key=? AND key2 IN (SELECT id FROM table WHERE key=?))'
+      )
+      assert.equal(
+        s3.text,
+        'SELECT id FROM table3 WHERE key=$1 AND key3 IN (SELECT id FROM table2 WHERE key=$2 AND key2 IN (SELECT id FROM table WHERE key=$3))'
+      )
+      assert.deepEqual(s3.values, ['value2', 'value0', 'value1'])
+    })
+
+    it('should not handle nested SQLStatement as parameter, if passed first', () => {
+      const statement = SQL`${SQL`SELECT`} * FROM table`
+      assert.equal(statement.sql, 'SELECT * FROM table')
+      assert.deepEqual(statement.values, [])
+    })
+  })
+
   describe('setName()', () => {
 
     it('should set the name and return this', () => {