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//! Template parsing and expansion for destination paths.
use anyhow::{Result, anyhow};
use ariadne::{Color, Label, Report, ReportKind, Source};
use std::collections::HashSet;
/// Known template variables.
const KNOWN_VARIABLES: &[&str] = &[
// Date/time.
"year",
"month",
"day",
"hour",
"minute",
"second",
// File.
"filename",
"extension",
// EXIF.
"camera_make",
"camera_model",
"lens",
"iso",
"focal_length",
];
/// A segment of a parsed template.
#[derive(Debug, Clone, PartialEq)]
pub enum Segment {
/// Literal text to include as-is.
Literal(String),
/// A variable to be substituted.
Variable { name: String, span: (usize, usize) },
}
/// A parsed template ready for expansion.
#[derive(Debug, Clone)]
pub struct Template {
segments: Vec<Segment>,
source: String,
}
/// Context providing values for template variables.
#[derive(Debug, Default)]
pub struct TemplateContext {
pub year: String,
pub month: String,
pub day: String,
pub hour: String,
pub minute: String,
pub second: String,
pub filename: String,
pub extension: String,
pub camera_make: Option<String>,
pub camera_model: Option<String>,
pub lens: Option<String>,
pub iso: Option<String>,
pub focal_length: Option<String>,
}
impl Template {
/// Parse a template string into segments.
pub fn parse(input: &str) -> Result<Self> {
let mut segments = Vec::new();
let mut chars = input.char_indices().peekable();
let mut literal = String::new();
let mut errors: Vec<(usize, usize, String)> = Vec::new();
while let Some((i, c)) = chars.next() {
match c {
'\\' => {
// Escape sequence.
if let Some(&(_, next)) = chars.peek() {
if next == '{' || next == '}' {
chars.next();
literal.push(next);
} else {
// Not a valid escape, keep the backslash.
literal.push(c);
}
} else {
literal.push(c);
}
}
'{' => {
// Start of variable.
if !literal.is_empty() {
segments.push(Segment::Literal(std::mem::take(
&mut literal,
)));
}
let start = i;
let mut var_name = String::new();
let mut found_close = false;
for (j, ch) in chars.by_ref() {
if ch == '}' {
found_close = true;
let end = j + 1;
if var_name.is_empty() {
errors.push((
start,
end,
"Empty variable name.".to_string(),
));
} else {
segments.push(Segment::Variable {
name: var_name,
span: (start, end),
});
}
break;
} else if ch == '{' {
// Found another '{' before closing '}' - report and
// return immediately.
// Strip trailing non-identifier chars to suggest
// the likely variable.
let likely_var: String = var_name
.chars()
.take_while(|c| {
c.is_alphanumeric() || *c == '_'
})
.collect();
let suggestion = if likely_var.is_empty() {
String::new()
} else {
format!(": did you mean '{{{}}}'?", likely_var)
};
let msg = if suggestion.is_empty() {
"Missing '}'.".to_string()
} else {
format!("Missing '}}'{}", suggestion)
};
Self::report_errors(input, &[(start, j, msg)]);
return Err(anyhow!("Failed to parse template."));
} else {
var_name.push(ch);
}
}
if !found_close && errors.is_empty() {
errors.push((
start,
input.len(),
"Missing '}'.".to_string(),
));
}
}
'}' => {
// Unmatched closing brace.
errors.push((
i,
i + 1,
"Unexpected '}': missing '{'.".to_string(),
));
}
_ => {
literal.push(c);
}
}
}
if !literal.is_empty() {
segments.push(Segment::Literal(literal));
}
if !errors.is_empty() {
// Show only the first error to avoid confusing cascading errors.
Self::report_errors(input, &errors[..1]);
return Err(anyhow!("Failed to parse template."));
}
Ok(Self {
segments,
source: input.to_string(),
})
}
/// Validate that all variables in the template are known.
pub fn validate(&self) -> Result<()> {
let known: HashSet<&str> = KNOWN_VARIABLES.iter().copied().collect();
let mut errors: Vec<(usize, usize, String)> = Vec::new();
for segment in &self.segments {
if let Segment::Variable { name, span } = segment
&& !known.contains(name.as_str())
{
errors.push((
span.0,
span.1,
format!("Unknown variable '{}'.", name),
));
}
}
if !errors.is_empty() {
Self::report_errors(&self.source, &errors);
let available = KNOWN_VARIABLES.join(", ");
return Err(anyhow!(
"Template contains unknown variables. Available: {}",
available
));
}
Ok(())
}
/// Expand the template using the provided context.
pub fn expand(&self, ctx: &TemplateContext) -> String {
let mut result = String::new();
for segment in &self.segments {
match segment {
Segment::Literal(s) => result.push_str(s),
Segment::Variable { name, .. } => {
let value = match name.as_str() {
"year" => &ctx.year,
"month" => &ctx.month,
"day" => &ctx.day,
"hour" => &ctx.hour,
"minute" => &ctx.minute,
"second" => &ctx.second,
"filename" => &ctx.filename,
"extension" => &ctx.extension,
"camera_make" => {
ctx.camera_make.as_deref().unwrap_or("unknown")
}
"camera_model" => {
ctx.camera_model.as_deref().unwrap_or("unknown")
}
"lens" => ctx.lens.as_deref().unwrap_or("unknown"),
"iso" => ctx.iso.as_deref().unwrap_or("unknown"),
"focal_length" => {
ctx.focal_length.as_deref().unwrap_or("unknown")
}
_ => "unknown",
};
result.push_str(value);
}
}
}
result
}
/// Report parse errors using ariadne.
fn report_errors(source: &str, errors: &[(usize, usize, String)]) {
for (start, end, msg) in errors {
Report::build(ReportKind::Error, ("template", *start..*end))
.with_message("Invalid template format")
.with_label(
Label::new(("template", *start..*end))
.with_message(msg)
.with_color(Color::Red),
)
.finish()
.eprint(("template", Source::from(source)))
.ok();
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn parse_simple() {
let t = Template::parse("{year}/{month}/{day}").unwrap();
assert_eq!(t.segments.len(), 5);
}
#[test]
fn parse_with_literals() {
let t = Template::parse("photos/{year}-{month}-{day}/img").unwrap();
assert_eq!(t.segments.len(), 7);
}
#[test]
fn parse_escaped_braces() {
let t = Template::parse(r"literal\{brace\}").unwrap();
assert_eq!(t.segments.len(), 1);
assert_eq!(
t.segments[0],
Segment::Literal("literal{brace}".to_string())
);
}
#[test]
fn expand_template() {
let t =
Template::parse("{year}/{month}/{filename}.{extension}").unwrap();
let ctx = TemplateContext {
year: "2023".to_string(),
month: "08".to_string(),
day: "15".to_string(),
filename: "IMG_1234".to_string(),
extension: "jpg".to_string(),
..Default::default()
};
assert_eq!(t.expand(&ctx), "2023/08/IMG_1234.jpg");
}
#[test]
fn validate_unknown_variable() {
let t = Template::parse("{year}/{unknown}").unwrap();
assert!(t.validate().is_err());
}
#[test]
fn unclosed_brace_error() {
assert!(Template::parse("{year").is_err());
}
#[test]
fn unmatched_close_brace_error() {
assert!(Template::parse("year}").is_err());
}
}