#5 variables are read from environment and propagated

src/config.rs

@@ -1,7 +1,7 @@
 use std::fs;
 use std::ffi::OsString;
 use serde::Deserialize;
-use std::collections::BTreeMap;
+use std::collections::{BTreeMap, HashMap};
 use csv::StringRecord;
 
 use crate::transformer::{Transformer, Expression};
@@ -60,6 +60,7 @@ fn get_input_columns_index_map(headers: &StringRecord) -> BTreeMap<String, usize
 fn step_to_expression(
     step: &Step,
     input_column_index_by_name: &BTreeMap<String, usize>,
+    variables: &HashMap<String, String>,
 ) -> Result<Option<Expression>, String> {
     match step {
         Step::Input {input} => match input_column_index_by_name.get(input) {
@@ -88,6 +89,7 @@ fn step_to_expression(
 fn column_to_expressions(
     column: &Column,
     input_column_index_by_name: &BTreeMap<String, usize>,
+    variables: &HashMap<String, String>,
 ) -> Result<Vec<Expression>, String> {
     match column {
         Column::Input(input_column_name) => {
@@ -96,6 +98,7 @@ fn column_to_expressions(
                     input: input_column_name.clone(),
                 },
                 &input_column_index_by_name,
+                &variables,
             );
 
             match maybe_some_expression? {
@@ -109,6 +112,7 @@ fn column_to_expressions(
                 |step| step_to_expression(
                     step,
                     &input_column_index_by_name,
+                    &variables,
                 ),
             ).collect();
 
@@ -118,13 +122,18 @@ fn column_to_expressions(
 }
 
 
-pub fn create_transformer(config: &Config, headers: &StringRecord) -> Result<Transformer, String> {
+pub fn create_transformer(
+    config: &Config,
+    headers: &StringRecord,
+    variables: &HashMap<String, String>,
+) -> Result<Transformer, String> {
     let input_columns_index_by_name = get_input_columns_index_map(headers);
 
     let maybe_columns: Result<Vec<Vec<Expression>>, String> = config.columns.values().map(
         |column| column_to_expressions(
             column,
             &input_columns_index_by_name,
+            &variables,
         ),
     ).collect();
 

src/main.rs

@@ -12,6 +12,7 @@ use worker::process;
 use config::parse_config_from_file;
 use serde::Serialize;
 use crate::printable_error::PrintableError;
+use std::collections::HashMap;
 
 
 const HELP: &str = r#"
@@ -46,10 +47,25 @@ fn format_error(error: &PrintableError, format: &ErrorFormat) -> String {
     }
 }
 
+// Fetch environment variables
+fn determine_variables() -> HashMap<String, String> {
+    let prefix = "YSV_VAR_";
+
+    env::vars().filter(
+        |(variable, value)| variable.starts_with(prefix)
+    ).map(
+        |(variable, value)| (
+            variable.replace(prefix, ""),
+            value,
+        )
+    ).collect()
+}
+
 
 fn run(file_path: &str) -> Result<(), PrintableError> {
+    let variables = determine_variables();
     let config = parse_config_from_file(file_path)?;
-    process(config);
+    process(config, variables);
     Ok(())
 }
 

src/worker.rs

@@ -3,6 +3,7 @@ use csv::{ByteRecord, Reader, Writer, ReaderBuilder};
 
 use crate::config::{Config, create_transformer};
 use crate::transformer::{Transformer, Expression};
+use std::collections::HashMap;
 
 
 fn apply_column(column: &Vec<Expression>, record: &ByteRecord) -> String {
@@ -31,7 +32,7 @@ fn transform(record: ByteRecord, transformer: &Transformer) -> ByteRecord {
 }
 
 
-pub fn process(config: Config) -> Result<(), String> {
+pub fn process(config: Config, variables: HashMap<String, String>) -> Result<(), String> {
     let mut reader = ReaderBuilder::new()
         .flexible(true)
         .from_reader(io::stdin());
@@ -40,7 +41,7 @@ pub fn process(config: Config) -> Result<(), String> {
 
     let headers = reader.headers().unwrap().clone();
 
-    let transformer = create_transformer(&config, &headers)?;
+    let transformer = create_transformer(&config, &headers, &variables)?;
 
     writer.write_record(&transformer.headers).unwrap();