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//! Template engine for Rust.
//!
//! For more details on the idea behind `Template::Nest` read:
//! - <https://metacpan.org/pod/Template::Nest#DESCRIPTION>
//! - <https://pypi.org/project/template-nest/>
//! # Examples
//!
//! More examples in `examples/` directory.
//!
//! Place these files in `templates` directory:
//! `templates/00-simple-page.html`:
//! ```html
//! <!DOCTYPE html>
//! <html lang="en">
//! <head>
//! <meta charset="utf-8">
//! <meta name="viewport" content="width=device-width, initial-scale=1">
//! <title>Simple Page</title>
//! </head>
//! <body>
//! <p>A fairly simple page to test the performance of Template::Nest.</p>
//! <p><!--% variable %--></p>
//! <!--% simple_component %-->
//! </body>
//! </html>
//! ```
//!
//! `templates/00-simple-page.html`:
//! ```html
//! <p><!--% variable %--></p>
//! ```
//!
//! Those templates can be used in a template hash which is passed to
//! TemplateNest::render to render a page:
//! ```rust
//! use template_nest::TemplateNest;
//! use template_nest::{filling, Filling};
//! use std::collections::HashMap;
//!
//! let nest = TemplateNest::new("templates").unwrap();
//! let simple_page = filling!(
//! "TEMPLATE": "00-simple-page",
//! "variable": "Simple Variable",
//! "simple_component": {
//! "TEMPLATE":"01-simple-component",
//! "variable": "Simple Variable in Simple Component"
//! }
//! );
//! println!("{}", nest.render(&simple_page).unwrap());
//! ```
use std::collections::{HashMap, HashSet};
use std::path::PathBuf;
use std::{fs, io};
use regex::Regex;
use thiserror::Error;
/// Represents a variable in a template hash, can be a string, another template
/// hash or an array of template hash.
pub enum Filling {
Text(String),
List(Vec<Filling>),
Template(HashMap<String, Filling>),
}
impl Filling {
/// inserts into a Template, returns an Err if the enum if not of Template
/// variant.
pub fn insert(&mut self, variable: String, to_insert: Filling) -> Result<(), &'static str> {
match self {
Filling::Template(ref mut map) => {
map.insert(variable, to_insert);
Ok(())
}
_ => Err("Cannot insert into non-Template variant"),
}
}
/// push into a List, returns an Err if the enum if not of List variant.
pub fn push(&mut self, to_push: Filling) -> Result<(), &'static str> {
match self {
Filling::List(ref mut list) => {
list.push(to_push);
Ok(())
}
_ => Err("Cannot push into non-List variant"),
}
}
}
#[derive(Error, Debug)]
pub enum TemplateNestError {
#[error("expected template directory at `{0}`")]
TemplateDirNotFound(String),
#[error("expected template file at `{0}`")]
TemplateFileNotFound(String),
#[error("error reading: `{0}`")]
TemplateFileReadError(#[from] io::Error),
#[error("encountered hash with no name label (name label: `{0}`)")]
NoNameLabel(String),
#[error("encountered hash with invalid name label type (name label: `{0}`)")]
InvalidNameLabel(String),
#[error("bad params in template hash, variable not present in template file: `{0}`")]
BadParams(String),
}
/// Renders a template hash to produce an output.
pub struct TemplateNest<'a> {
/// Delimiters used in the template. It is a tuple of two strings,
/// representing the start and end delimiters.
pub delimiters: (&'a str, &'a str),
/// Name label used to identify the template to be used.
pub label: &'a str,
/// Template extension, appended on label to identify the template.
pub extension: &'a str,
/// Directory where templates are located.
pub directory: PathBuf,
/// Prepend & Append a string to every template which is helpful in
/// identifying which template the output text came from.
pub show_labels: bool,
/// Used in conjunction with show_labels. If the template is HTML then use
/// '<!--', '-->'.
pub comment_delimiters: (&'a str, &'a str),
/// Intended to improve readability when inspecting nested templates.
pub fixed_indent: bool,
/// If True, then an attempt to populate a template with a variable that
/// doesn't exist (i.e. name not found in template file) results in an
/// error.
pub die_on_bad_params: bool,
/// Escapes a token delimiter, i.e. if set to '\' then prefixing the token
/// delimiters with '\' means it won't be considered a variable.
///
/// <!--% token %--> => is a variable
/// \<!--% token %--> => is not a variable. ('\' is removed from output)
pub token_escape_char: &'a str,
/// Provide a hash of default values that are substituted if template hash
/// does not provide a value.
pub defaults: HashMap<String, Filling>,
}
/// Represents an indexed template file.
struct TemplateFileIndex {
/// Contents of the file.
contents: String,
/// Variables in the template file.
variables: Vec<TemplateFileVariable>,
/// Variable names in the template file.
variable_names: HashSet<String>,
}
/// Represents the variables in a template file.
struct TemplateFileVariable {
name: String,
/// Start & End positions of the complete variable string. i.e. including
/// the delimeters.
start_position: usize,
end_position: usize,
/// Indent level of the variable.
indent_level: usize,
/// If true then this variable was escaped with token_escape_char, we just
/// need to remove the escape character.
escaped_token: bool,
}
impl Default for TemplateNest<'_> {
fn default() -> Self {
TemplateNest {
label: "TEMPLATE",
extension: "html",
show_labels: false,
fixed_indent: false,
die_on_bad_params: false,
directory: "templates".into(),
delimiters: ("<!--%", "%-->"),
comment_delimiters: ("<!--", "-->"),
token_escape_char: "",
defaults: HashMap::new(),
}
}
}
impl TemplateNest<'_> {
/// Creates a new instance of TemplateNest with the specified directory.
pub fn new(directory_str: &str) -> Result<Self, TemplateNestError> {
let directory = PathBuf::from(directory_str);
if !directory.is_dir() {
return Err(TemplateNestError::TemplateDirNotFound(
directory_str.to_string(),
));
}
Ok(Self {
directory,
..Default::default()
})
}
/// Given a template name, returns the "index" of the template file, it
/// contains the contents of the file and all the variables that are
/// present.
fn index(&self, template_name: &str) -> Result<TemplateFileIndex, TemplateNestError> {
let file = self
.directory
.join(format!("{}.{}", template_name, self.extension));
if !file.is_file() {
return Err(TemplateNestError::TemplateFileNotFound(
file.display().to_string(),
));
}
let contents = match fs::read_to_string(&file) {
Ok(file_contents) => file_contents,
Err(err) => {
return Err(TemplateNestError::TemplateFileReadError(err));
}
};
let mut variable_names = HashSet::new();
let mut variables = vec![];
// Capture all the variables in the template.
let re = Regex::new(&format!("{}(.+?){}", self.delimiters.0, self.delimiters.1)).unwrap();
for cap in re.captures_iter(&contents) {
let whole_capture = cap.get(0).unwrap();
let start_position = whole_capture.start();
// If token_escape_char is set then look behind for it and if we
// find the escape char then we're only going to remove the escape
// char and not remove this variable.
//
// The variable can be at the beginning of the file, that will mean
// calculating escape_char_start results in an overflow.
if !self.token_escape_char.is_empty() && start_position > self.token_escape_char.len() {
let escape_char_start = start_position - self.token_escape_char.len();
if &contents[escape_char_start..start_position] == self.token_escape_char {
variables.push(TemplateFileVariable {
indent_level: 0,
name: "".to_string(),
escaped_token: true,
start_position: escape_char_start,
end_position: escape_char_start + self.token_escape_char.len(),
});
continue;
}
}
// If fixed_indent is enable then record the indent level for this
// variable. To get the indent level we look at each character in
// reverse from the start position of the variable until we find a
// newline character.
let indent_level = match self.fixed_indent {
true => {
let newline_position = &contents[..start_position].rfind('\n').unwrap_or(0);
start_position - newline_position - 1
}
false => 0,
};
let variable_name = cap[1].trim();
variable_names.insert(variable_name.to_string());
variables.push(TemplateFileVariable {
indent_level,
start_position,
end_position: whole_capture.end(),
name: variable_name.to_string(),
escaped_token: false,
});
}
let file_index = TemplateFileIndex {
variable_names,
contents,
variables,
};
Ok(file_index)
}
/// Given a TemplateHash, it parses the TemplateHash and renders a String
/// output.
pub fn render(&self, filling: &Filling) -> Result<String, TemplateNestError> {
match filling {
Filling::Text(text) => Ok(text.to_string()),
Filling::List(list) => {
let mut render = "".to_string();
for f in list {
render.push_str(&self.render(f)?);
}
Ok(render)
}
Filling::Template(template_hash) => {
let template_label: &Filling = template_hash
.get(self.label)
.ok_or(TemplateNestError::NoNameLabel(self.label.to_string()))?;
// template_name must contain a string, it cannot be a template hash or
// a vec of template hash.
if let Filling::Text(name) = template_label {
let template_index = self.index(name)?;
// Check for bad params.
if self.die_on_bad_params {
for name in template_hash.keys() {
// If a variable in template_hash is not present in
// the template file and it's not the template label
// then it's a bad param.
if !template_index.variable_names.contains(name) && name != self.label {
return Err(TemplateNestError::BadParams(name.to_string()));
}
}
}
let mut rendered = String::from(&template_index.contents);
// Iterate through all variables in reverse. We do this because we
// don't want to mess up all the indexed positions.
for var in template_index.variables.iter().rev() {
// If the variable was escaped then we just remove the token, not the variable.
if var.escaped_token {
rendered.replace_range(var.start_position..var.end_position, "");
continue;
}
// If the variable doesn't exist in template hash then
// replace it by an empty string.
let mut render = "".to_string();
// Look for the variable in template_hash, if it's not
// provided then we look at defaults HashMap, and then
// considering variable namespacing.
if let Some(value) = template_hash
.get(&var.name)
.or_else(|| self.defaults.get(&var.name))
{
let mut r: String = self.render(value)?;
// If fixed_indent is set then get the indent level
// and replace all newlines in the rendered string.
if self.fixed_indent && var.indent_level != 0 {
let replacement = format!("\n{}", " ".repeat(var.indent_level));
r = r.replace('\n', &replacement);
}
render.push_str(&r);
}
rendered.replace_range(var.start_position..var.end_position, &render);
}
// Add lables to the rendered string if show_labels is true.
if self.show_labels {
rendered.replace_range(
0..0,
&format!(
"{} BEGIN {} {}\n",
self.comment_delimiters.0, name, self.comment_delimiters.1
),
);
rendered.replace_range(
rendered.len()..rendered.len(),
&format!(
"{} END {} {}\n",
self.comment_delimiters.0, name, self.comment_delimiters.1
),
);
}
// Trim trailing without cloning `rendered'.
let len_withoutcrlf = rendered.trim_end().len();
rendered.truncate(len_withoutcrlf);
Ok(rendered)
} else {
Err(TemplateNestError::InvalidNameLabel(self.label.to_string()))
}
}
}
}
}
// The below macros are adapted from the json-rust macros (https://docs.rs/json/latest/json/#macros)
#[macro_export]
macro_rules! filling_list {
//[] => ($crate::JsonValue::new_array());
[] => { "".to_string() };
// Handles for token tree items
[@ITEM($( $i:expr, )*) $item:tt, $( $cont:tt )+] => {
$crate::filling_list!(
@ITEM($( $i, )* $crate::filling_text!($item), )
$( $cont )*
)
};
(@ITEM($( $i:expr, )*) $item:tt,) => ({
$crate::filling_list!(@END $( $i, )* $crate::filling_text!($item), )
});
(@ITEM($( $i:expr, )*) $item:tt) => ({
$crate::filling_list!(@END $( $i, )* $crate::filling_text!($item), )
});
// Handles for expression items
[@ITEM($( $i:expr, )*) $item:expr, $( $cont:tt )+] => {
$crate::filling_list!(
@ITEM($( $i, )* $crate::filling_text!($item), )
$( $cont )*
)
};
(@ITEM($( $i:expr, )*) $item:expr,) => ({
$crate::filling_list!(@END $( $i, )* $crate::filling_text!($item), )
});
(@ITEM($( $i:expr, )*) $item:expr) => ({
$crate::filling_list!(@END $( $i, )* $crate::filling_text!($item), )
});
// Construct the actual array
(@END $( $i:expr, )*) => ({
let size = 0 $( + {let _ = &$i; 1} )*;
let mut vec: Vec<Filling> = Vec::with_capacity(size);
$(
vec.push($i);
)*
$crate::Filling::List( vec )
});
// Entry point to the macro
($( $cont:tt )+) => {
$crate::filling_list!(@ITEM() $($cont)*)
};
}
/// Helper macro for converting types into `Filling::Text`. It's used internally
/// by the `filling!` and `filling_list!` macros.
#[macro_export]
macro_rules! filling_text {
//( null ) => { $crate::Null };
( null ) => { "".to_string() };
( [$( $token:tt )*] ) => {
// 10
$crate::filling_list![ $( $token )* ]
};
( {$( $token:tt )*} ) => {
$crate::filling!{ $( $token )* }
};
{ $value:expr } => { $crate::Filling::Text($value.to_string()) };
}
/// Helper macro for creating instances of `Filling`.
#[macro_export]
macro_rules! filling {
{} => { "".to_string() };
// Handles for different types of keys
(@ENTRY($( $k:expr => $v:expr, )*) $key:ident: $( $cont:tt )*) => {
$crate::filling!(@ENTRY($( $k => $v, )*) stringify!($key) => $($cont)*)
};
(@ENTRY($( $k:expr => $v:expr, )*) $key:literal: $( $cont:tt )*) => {
$crate::filling!(@ENTRY($( $k => $v, )*) $key => $($cont)*)
};
(@ENTRY($( $k:expr => $v:expr, )*) [$key:expr]: $( $cont:tt )*) => {
$crate::filling!(@ENTRY($( $k => $v, )*) $key => $($cont)*)
};
// Handles for token tree values
(@ENTRY($( $k:expr => $v:expr, )*) $key:expr => $value:tt, $( $cont:tt )+) => {
$crate::filling!(
@ENTRY($( $k => $v, )* $key => $crate::filling_text!($value), )
$( $cont )*
)
};
(@ENTRY($( $k:expr => $v:expr, )*) $key:expr => $value:tt,) => ({
$crate::filling!(@END $( $k => $v, )* $key => $crate::filling_text!($value), )
});
(@ENTRY($( $k:expr => $v:expr, )*) $key:expr => $value:tt) => ({
$crate::filling!(@END $( $k => $v, )* $key => $crate::filling_text!($value), )
});
// Handles for expression values
(@ENTRY($( $k:expr => $v:expr, )*) $key:expr => $value:expr, $( $cont:tt )+) => {
$crate::filling!(
@ENTRY($( $k => $v, )* $key => $crate::filling_text!($value), )
$( $cont )*
)
};
(@ENTRY($( $k:expr => $v:expr, )*) $key:expr => $value:expr,) => ({
$crate::filling!(@END $( $k => $v, )* $key => $crate::filling_text!($value), )
});
(@ENTRY($( $k:expr => $v:expr, )*) $key:expr => $value:expr) => ({
$crate::filling!(@END $( $k => $v, )* $key => $crate::filling_text!($value), )
});
// Construct the actual object
(@END $( $k:expr => $v:expr, )*) => ({
let mut params : HashMap<String, Filling> = Default::default();
$(
params.insert($k.to_string(), $v);
)*
let template = $crate::Filling::Template( params );
template
});
// Entry point to the macro
($key:tt: $( $cont:tt )+) => {
$crate::filling!(@ENTRY() $key: $($cont)*)
};
// Legacy macro
($( $k:expr => $v:expr, )*) => {
$crate::filling!(@END $( $k => $crate::filling_text!($v), )*)
};
($( $k:expr => $v:expr ),*) => {
$crate::filling!(@END $( $k => $crate::filling_text!($v), )*)
};
}