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|
use std::collections::HashMap;
/// Render REPL prompt
///
/// The template comprises plain text and `{...}`.
///
/// The syntax of `{...}`:
/// - `{var}` - When `var` has a value, replace `var` with the value and eval `template`
/// - `{?var <template>}` - Eval `template` when `var` is evaluated as true
/// - `{!var <template>}` - Eval `template` when `var` is evaluated as false
pub fn render_prompt(template: &str, variables: &HashMap<&str, String>) -> String {
let exprs = parse_template(template);
eval_exprs(&exprs, variables)
}
fn parse_template(template: &str) -> Vec<Expr> {
let chars: Vec<char> = template.chars().collect();
let mut exprs = vec![];
let mut current = vec![];
let mut balances = vec![];
for ch in chars.iter().cloned() {
if !balances.is_empty() {
if ch == '}' {
balances.pop();
if balances.is_empty() {
if !current.is_empty() {
let block = parse_block(&mut current);
exprs.push(block)
}
} else {
current.push(ch);
}
} else if ch == '{' {
balances.push(ch);
current.push(ch);
} else {
current.push(ch);
}
} else if ch == '{' {
balances.push(ch);
add_text(&mut exprs, &mut current);
} else {
current.push(ch)
}
}
add_text(&mut exprs, &mut current);
exprs
}
fn parse_block(current: &mut Vec<char>) -> Expr {
let value: String = current.drain(..).collect();
match value.split_once(' ') {
Some((name, tail)) => {
if let Some(name) = name.strip_prefix('?') {
let block_exprs = parse_template(tail);
Expr::Block(BlockType::Yes, name.to_string(), block_exprs)
} else if let Some(name) = name.strip_prefix('!') {
let block_exprs = parse_template(tail);
Expr::Block(BlockType::No, name.to_string(), block_exprs)
} else {
Expr::Text(format!("{{{value}}}"))
}
}
None => Expr::Variable(value),
}
}
fn eval_exprs(exprs: &[Expr], variables: &HashMap<&str, String>) -> String {
let mut output = String::new();
for part in exprs {
match part {
Expr::Text(text) => output.push_str(text),
Expr::Variable(variable) => {
let value = variables
.get(variable.as_str())
.cloned()
.unwrap_or_default();
output.push_str(&value);
}
Expr::Block(typ, variable, block_exprs) => {
let value = variables
.get(variable.as_str())
.cloned()
.unwrap_or_default();
match typ {
BlockType::Yes => {
if truly(&value) {
let block_output = eval_exprs(block_exprs, variables);
output.push_str(&block_output)
}
}
BlockType::No => {
if !truly(&value) {
let block_output = eval_exprs(block_exprs, variables);
output.push_str(&block_output)
}
}
}
}
}
}
output
}
fn add_text(exprs: &mut Vec<Expr>, current: &mut Vec<char>) {
if current.is_empty() {
return;
}
let value: String = current.drain(..).collect();
exprs.push(Expr::Text(value));
}
fn truly(value: &str) -> bool {
!(value.is_empty() || value == "0" || value == "false")
}
#[derive(Debug)]
enum Expr {
Text(String),
Variable(String),
Block(BlockType, String, Vec<Expr>),
}
#[derive(Debug)]
enum BlockType {
Yes,
No,
}
#[cfg(test)]
mod tests {
use super::*;
macro_rules! assert_render {
($template:expr, [$(($key:literal, $value:literal),)*], $expect:literal) => {
let data = HashMap::from([
$(($key, $value.into()),)*
]);
assert_eq!(render_prompt($template, &data), $expect);
};
}
#[test]
fn test_render() {
let prompt = "{?session {session}{?role /}}{role}{?session )}{!session >}";
assert_render!(prompt, [], ">");
assert_render!(prompt, [("role", "coder"),], "coder>");
assert_render!(prompt, [("session", "temp"),], "temp)");
assert_render!(
prompt,
[("session", "temp"), ("role", "coder"),],
"temp/coder)"
);
}
}
|
