Compile select expressions

Cargo.lock

@@ -15,8 +15,16 @@ version = "0.1.0"
 dependencies = [
  "lazy_static",
  "regex",
+ "serde",
+ "serde_json",
 ]
 
+[[package]]
+name = "itoa"
+version = "0.4.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dd25036021b0de88a0aff6b850051563c6516d0bf53f8638938edbb9de732736"
+
 [[package]]
 name = "lazy_static"
 version = "1.4.0"
@@ -45,3 +53,26 @@ name = "regex-syntax"
 version = "0.6.23"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "24d5f089152e60f62d28b835fbff2cd2e8dc0baf1ac13343bef92ab7eed84548"
+
+[[package]]
+name = "ryu"
+version = "1.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "71d301d4193d031abdd79ff7e3dd721168a9572ef3fe51a1517aba235bd8f86e"
+
+[[package]]
+name = "serde"
+version = "1.0.125"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "558dc50e1a5a5fa7112ca2ce4effcb321b0300c0d4ccf0776a9f60cd89031171"
+
+[[package]]
+name = "serde_json"
+version = "1.0.64"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "799e97dc9fdae36a5c8b8f2cae9ce2ee9fdce2058c57a93e6099d919fd982f79"
+dependencies = [
+ "itoa",
+ "ryu",
+ "serde",
+]

Cargo.toml

@@ -9,3 +9,5 @@ edition = "2018"
 [dependencies]
 lazy_static = "1.4.0"
 regex = "1.4.5"
+serde = "1.0.125"
+serde_json = "1.0.64"

src/compiler.rs

@@ -0,0 +1,86 @@
+use serde_json::{json, Value};
+
+use crate::error::CompilerError;
+use crate::parser::{Field, Identifier, Select};
+
+#[derive(Debug, PartialEq)]
+pub struct Query {
+    pub source: Identifier,
+    pub body: Value,
+}
+
+impl Query {
+    pub fn new(source: Identifier, body: Value) -> Self {
+        Self { source, body }
+    }
+}
+
+pub fn compile(expr: Select) -> Result<Query, CompilerError> {
+    let mut source = false;
+    let field_names: Vec<Value> = expr
+        .fields
+        .iter()
+        .map(|f| match f {
+            Field::Star => {
+                source = true;
+                Value::String("*".to_string())
+            }
+            Field::Named(name) => Value::String(name.clone()),
+        })
+        .collect();
+
+    let body = json!({
+        "query": { "match_all":{} },
+        "_source": source,
+        "fields": Value::Array(field_names)
+    });
+
+    Ok(Query::new(expr.source, body))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::lexer::scan;
+    use crate::parser::parse;
+
+    fn _compile(input: &str) -> Result<Query, CompilerError> {
+        let tokens = scan(input).unwrap();
+        let select = parse(tokens).unwrap();
+        compile(select)
+    }
+
+    #[test]
+    fn it_compiles_a_simple_select() {
+        assert_eq!(
+            _compile("SELECT * FROM bar").unwrap(),
+            Query::new(
+                Identifier::new("bar"),
+                json!({
+                    "query": {
+                        "match_all": {}
+                    },
+                    "fields": ["*"],
+                    "_source": true
+                })
+            )
+        )
+    }
+
+    #[test]
+    fn it_compiles_a_select_with_specific_fields() {
+        assert_eq!(
+            _compile("SELECT foo FROM bar").unwrap(),
+            Query::new(
+                Identifier::new("bar"),
+                json!({
+                    "query": {
+                        "match_all": {}
+                    },
+                    "fields": ["foo"],
+                    "_source": false
+                })
+            )
+        )
+    }
+}

src/error.rs

@@ -53,3 +53,30 @@ impl From<ParserError> for std::io::Error {
         Self::new(std::io::ErrorKind::InvalidInput, e.message)
     }
 }
+
+#[derive(Debug, PartialEq)]
+pub struct CompilerError {
+    message: String,
+}
+
+impl CompilerError {
+    pub fn new(message: &str) -> Self {
+        Self {
+            message: message.to_string(),
+        }
+    }
+}
+
+impl Display for CompilerError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", &self.message)
+    }
+}
+
+impl Error for CompilerError {}
+
+impl From<CompilerError> for std::io::Error {
+    fn from(e: CompilerError) -> Self {
+        Self::new(std::io::ErrorKind::InvalidInput, e.message)
+    }
+}

src/lib.rs

@@ -1,3 +1,4 @@
+pub mod compiler;
 pub mod error;
 pub mod lexer;
 pub mod parser;