string-template-plus 0.4.3

/*!
# Introduction

This is a simple template tool that works with variable names and
[`HashMap`] of [`String`]. The [`Template`] can be parsed from [`str`]
and then you can render it using the variables in [`HashMap`] and any
shell commands running through [`Exec`].

# Features
- Parse the template from a `str` that's easy to write,
- Support for alternatives in case some variables are not present,
  Use `?` to separate the alternatives, uses whichever it can find first. If `?` is at the end, leaves it blank instead of erroring out.
- Support for literal strings inside the alternative options,
  You can use a literal string `"string"` enclosed in `"` as an alternative if you want to put something instead of blank at the end.
- Support for the date time format using `chrono`,
  You can use any format starting with `%` inside the variable placeholder `{}` to use a date time format supported by chrono.
- Support for any arbitrary commands, etc.
You can keep any command inside `$(` and `)` to run it and use the result in the template. You can use other format elements inside it.
- Support for iterating (incremented with -N) strings with the same template conditions,
- Limited formatting support like UPCASE, downcase, float significant digits, etc. Look into [`transformers`] for more info.


# Usages
Simple variables:
```rust
# use std::error::Error;
# use std::collections::HashMap;
# use std::path::PathBuf;
# use string_template_plus::{Render, RenderOptions, Template};
#
# fn main() -> Result<(), Box<dyn Error>> {
let templ = Template::parse_template("hello {name}").unwrap();
let mut vars: HashMap<String, String> = HashMap::new();
vars.insert("name".into(), "world".into());
let rendered = templ
.render(&RenderOptions {
variables: vars,
..Default::default()
            })
            .unwrap();
assert_eq!(rendered, "hello world");
# Ok(())
# }
```

Safe replace, blank if not present, or literal string if not present:
```rust
# use std::error::Error;
# use std::collections::HashMap;
# use std::path::PathBuf;
# use string_template_plus::{Render, RenderOptions, Template};
#
# fn main() -> Result<(), Box<dyn Error>> {
let templ = Template::parse_template("hello {name?} {lastname?\"User\"}").unwrap();
let vars: HashMap<String, String> = HashMap::new();
let rendered = templ
.render(&RenderOptions {
variables: vars,
..Default::default()
            })
            .unwrap();
assert_eq!(rendered, "hello  User");
# Ok(())
# }
```

Alternate, whichever variable it finds first will be replaced:
```rust
# use std::error::Error;
# use std::collections::HashMap;
# use std::path::PathBuf;
# use string_template_plus::{Render, RenderOptions, Template};
#
# fn main() -> Result<(), Box<dyn Error>> {
let templ = Template::parse_template("hello {nickname?name}").unwrap();
let mut vars: HashMap<String, String> = HashMap::new();
vars.insert("name".into(), "world".into());
let rendered = templ
.render(&RenderOptions {
variables: vars,
..Default::default()
            })
            .unwrap();
        assert_eq!(rendered, "hello world");
# Ok(())
# }
```

Calculations can be written in lisp like language, it supports simple
functions. Using lisp can also allow you to write more complex
logic. The lisp implementation is the one from
https://github.com/brundonsmith/rust_lisp refer to the README there
for the functionality.

To access the values in lisp you can use the following functions:
- `st+var` : the value as string,
- `st+num` the value as a number, and
- `st+has` true if value is present else false.

You need to quote the symbol to pass to the functions (e.g. (st+num
'total) or (st+num "total").

Else, you can just write the variables in braces like normal as well.

there are two use cases.
- Standalone use case: in the format of `=()` that'll be replaced with
  the results.
- Inside the `{}` that can be used as alternative to a variable, or
  with a transformer.

```rust
# use std::error::Error;
# use std::collections::HashMap;
# use std::path::PathBuf;
# use string_template_plus::{Render, RenderOptions, Template};
#
# fn main() -> Result<(), Box<dyn Error>> {
let templ = Template::parse_template("hello {nickname?name}. You've done =(/ (st+num 'task_done) (st+num 'task_total)) work. {=(- 1 (/ (st+num \"task_done\") (st+num 'task_total))):calc(*100):f(1)}% remains.").unwrap();
let mut vars: HashMap<String, String> = HashMap::new();
vars.insert("name".into(), "world".into());
vars.insert("task_done".into(), "1".into());
vars.insert("task_total".into(), "4".into());
let rendered = templ
.render(&RenderOptions {
variables: vars,
..Default::default()
            })
            .unwrap();
        assert_eq!(rendered, "hello world. You've done 0.25 work. 75.0% remains.");
# Ok(())
# }
```

Custom Commands:
```rust
# use std::error::Error;
# use std::collections::HashMap;
# use std::path::PathBuf;
# use string_template_plus::{Render, RenderOptions, Template};
#
# fn main() -> Result<(), Box<dyn Error>> {
let templ = Template::parse_template("L=$(printf \"%.2f\" {length})").unwrap();
let mut vars: HashMap<String, String> = HashMap::new();
vars.insert("length".into(), "12.342323".into());
let rendered = templ
.render(&RenderOptions {
wd: PathBuf::from("."),
variables: vars,
shell_commands: true,
            })
            .unwrap();
        assert_eq!(rendered, "L=12.34");
# Ok(())
# }
```

You can turn off Custom Commands for safety:
```rust
# use std::error::Error;
# use std::collections::HashMap;
# use std::path::PathBuf;
# use string_template_plus::{Render, RenderOptions, Template};
#
# fn main() -> Result<(), Box<dyn Error>> {
let templ = Template::parse_template("L=$(printf \"%.2f\" {length})").unwrap();
let mut vars: HashMap<String, String> = HashMap::new();
vars.insert("length".into(), "12.342323".into());
let rendered = templ
.render(&RenderOptions {
wd: PathBuf::from("."),
variables: vars,
shell_commands: false,
            })
            .unwrap();
        assert_eq!(rendered, "L=$(printf %.2f 12.342323)");
# Ok(())
# }
```

Date Time:
```rust
# use std::error::Error;
# use std::collections::HashMap;
# use std::path::PathBuf;
# use chrono::Local;
# use string_template_plus::{Render, RenderOptions, Template};
#
# fn main() -> Result<(), Box<dyn Error>> {
let templ = Template::parse_template("hello {name} at {%Y-%m-%d}").unwrap();
let timefmt = Local::now().format("%Y-%m-%d");
let output = format!("hello world at {}", timefmt);
let mut vars: HashMap<String, String> = HashMap::new();
vars.insert("name".into(), "world".into());
let rendered = templ
.render(&RenderOptions {
wd: PathBuf::from("."),
variables: vars,
shell_commands: false,
            })
            .unwrap();
        assert_eq!(rendered, output);
# Ok(())
# }
```

# Transformers:
Although there is no format strings, there are transformer functions that can format for a bit. I'm planning to add more format functions as the need arises.

To apply a tranformer to a variable provide it after [`VAR_TRANSFORM_SEP_CHAR`] (currently ":") to a variable template.

There are a few transformers available:

| Transformer | Funtion                        | Arguments | Function                  | Example                  |
|-------------|--------------------------------|-----------|---------------------------|--------------------------|
| f           | [`transformers::float_format`] | [.]N      | only N number of decimal  | {"1.12":f(.1)} ⇒ 1.1     |
| case        | [`transformers::string_case`]  | up        | UPCASE a string           | {"na":case(up)} ⇒ NA     |
| case        | [`transformers::string_case`]  | down      | downcase a string         | {"nA":case(down)} ⇒ na   |
| case        | [`transformers::string_case`]  | proper    | Upcase the first letter   | {"nA":case(proper)} ⇒ Na |
| case        | [`transformers::string_case`]  | title     | Title Case the string     | {"na":case(title)} ⇒ Na  |
| calc        | [`transformers::calc`]         | [+-*\/^]N | Airthmatic calculation    | {"1":calc(+1*2^2)} ⇒ 16  |
| calc        | [`transformers::calc`]         | [+-*\/^]N | Airthmatic calculation    | {"1":calc(+1,-1)} ⇒ 2,0  |
| count       | [`transformers::count`]        | str       | count str occurance       | {"nata":count(a)} ⇒ 2    |
| repl        | [`transformers::replace`]      | str1,str2 | replace str1 by str2      | {"nata":rep(a,o)} ⇒ noto |
| q           | [`transformers::quote`]        | [str1]    | quote with str1, or ""    | {"nata":q()} ⇒ "noto"    |
| take        | [`transformers::take`]         | str,N     | take Nth group sep by str | {"nata":take(a,2)} ⇒ "t" |
| trim        | [`transformers::trim`]         | str       | trim the string with str  | {"nata":trim(a)} ⇒ "nat" |

You can chain transformers ones after another for combined actions. For example, `count( ):calc(+1)` will give you total number of words in a sentence.

Examples are in individual functions in [`transformers`].

```rust
# use std::error::Error;
# use std::collections::HashMap;
# use std::path::PathBuf;
# use chrono::Local;
# use string_template_plus::{Render, RenderOptions, Template};
#
# fn main() -> Result<(), Box<dyn Error>> {
let mut vars: HashMap<String, String> = HashMap::new();
vars.insert("length".into(), "120.1234".into());
vars.insert("name".into(), "joHN".into());
vars.insert("job".into(), "assistant manager of company".into());
let options = RenderOptions {
variables: vars,
..Default::default()
        };
let cases = [
("L={length}", "L=120.1234"),
("L={length:calc(+100)}", "L=220.1234"),
("L={length:f(.2)} ({length:f(3)})", "L=120.12 (120.123)"),
("hi {name:case(up)}", "hi JOHN"),
(
 "hi {name:case(proper)}, {job:case(title)}",
 "hi John, Assistant Manager of Company",
),
 ("hi {name:case(down)}", "hi john"),
];

for (t, r) in cases {
 let templ = Template::parse_template(t).unwrap();
 let rendered = templ.render(&options).unwrap();
 assert_eq!(rendered, r);
 }
# Ok(())
# }
```

# Limitations
- You cannot use positional arguments in this template system, only named ones. `{}` will be replaced with empty string. Although you can use `"0"`, `"1"`, etc as variable names in the template and the render options variables.
- I haven't tested variety of names, although they should work try to keep the names identifier friendly.
- Currently doesn't have format specifiers, for now you can use the command options with `printf` bash command to format things the way you want, or use the transformers which have limited formatting capabilities.
Like a template `this is $(printf "%05.2f" {weight}) kg.` should be rendered with the correct float formatting.
*/
use anyhow::Error;
use chrono::Local;
use colored::Colorize;
use lazy_static::lazy_static;
use std::collections::HashMap;
use std::io::Read;
use std::path::PathBuf;
use subprocess::Exec;

pub mod errors;
pub mod lisp;
pub mod transformers;

/// Character to separate the variables. If the first variable is not present it'll use the one behind it and so on. Keep it at the end, if you want a empty string instead of error on missing variable.
pub static OPTIONAL_RENDER_CHAR: char = '?';
/// Character that should be in the beginning of the variable to determine it as datetime format.
pub static TIME_FORMAT_CHAR: char = '%';
/// Character that indicates that this is a lisp expression from here.
pub static LISP_START_CHAR: char = '=';
/// Character that separates variable with format
pub static VAR_TRANSFORM_SEP_CHAR: char = ':';
/// Quote characters to use to make a value literal instead of a variable. In combination with [`OPTIONAL_RENDER_CHAR`] it can be used as a default value when variable(s) is/are not present.
pub static LITERAL_VALUE_QUOTE_CHAR: char = '"';
/// Character to escape special meaning characters
pub static ESCAPE_CHAR: char = '\\';
/// Characters that should be replaced as themselves if presented as a variable
static LITERAL_REPLACEMENTS: [&str; 3] = [
    "",  // to replace {} as empty string.
    "{", // to replace {{} as {
    "}", // to replace {}} as }
];

/// Runs a command and returns the output of the command or the error
fn cmd_output(cmd: &str, wd: &PathBuf) -> Result<String, Error> {
    let mut out: String = String::new();
    Exec::shell(cmd)
        .cwd(wd)
        .stream_stdout()?
        .read_to_string(&mut out)?;
    Ok(out)
}

/// Parts that make up a [`Template`]. You can have literal strings, variables, time date format, command, or optional format with [`OPTIONAL_RENDER_CHAR`].
///
/// [`TemplatePart::Lit`] = Literal Strings like `"hi "` in `"hi {name}"`
/// [`TemplatePart::Var`] = Variable part like `"name"` in `"hi {name}"` and format specifier
/// [`TemplatePart::Time`] = Date time format like `"%F"` in `"Today: {%F}"`
/// [`TemplatePart::Cmd`] = Command like `"echo world"` in `"hello $(echo world)"`
/// [`TemplatePart::Any`] = Optional format like `"name?age"` in `"hello {name?age}"`
///
/// [`TemplatePart::Cmd`] and [`TemplatePart::Any`] can in turn contain other [`TemplatePart`] inside them. Haven't tested on nesting complex ones within each other though.
#[derive(Debug, Clone)]
pub enum TemplatePart {
    /// Literal string, keep them as they are
    Lit(String),
    /// Variable and format, uses the variable's value in the rendered String
    Var(String, String),
    /// DateTime format, use [`chrono::Local`] in the given format
    Time(String),
    /// Lisp expression to calculate with the transformer
    Lisp(String, String, Vec<(usize, usize)>),
    /// Shell Command, use the output of command in the rendered String
    Cmd(Vec<TemplatePart>),
    /// Multiple variables or [`TemplatePart`]s, use the first one that succeeds
    Any(Vec<TemplatePart>),
}

lazy_static! {
    pub static ref TEMPLATE_PAIRS_START: [char; 3] = ['{', '"', '('];
    pub static ref TEMPLATE_PAIRS_END: [char; 3] = ['}', '"', ')'];
    pub static ref TEMPLATE_PAIRS: HashMap<char, char> = TEMPLATE_PAIRS_START
        .iter()
        .zip(TEMPLATE_PAIRS_END.iter())
        .map(|(k, v)| (*k, *v))
        .collect();
}

impl TemplatePart {
    pub fn lit(part: &str) -> Self {
        Self::Lit(part.to_string())
    }
    pub fn var(part: &str) -> Self {
        if let Some((part, fstr)) = part.split_once(VAR_TRANSFORM_SEP_CHAR) {
            Self::Var(part.to_string(), fstr.to_string())
        } else {
            Self::Var(part.to_string(), "".to_string())
        }
    }

    pub fn lisp(part: &str) -> Self {
        let (part, fstr) = if let Some((part, fstr)) = part.split_once(VAR_TRANSFORM_SEP_CHAR) {
            (part.to_string(), fstr.to_string())
        } else {
            (part.to_string(), "".to_string())
        };
        let variables = part
            .match_indices("(st+")
            .filter_map(|(loc, _)| {
                let end = Self::find_end(')', &part, loc + 1).ok()?;
                part[loc..end].find(' ').map(|s| {
                    let p = &part[(s + 1 + loc)..end];
                    if p.starts_with('"') {
                        (s + 2 + loc, end - 1)
                    } else if p.starts_with('\'') {
                        (s + 2 + loc, end)
                    } else {
                        (s + 1 + loc, end)
                    }
                })
            })
            .collect();
        Self::Lisp(part, fstr, variables)
    }

    pub fn time(part: &str) -> Self {
        Self::Time(part.to_string())
    }

    /// Parse a [`&str`] into [`TemplatePart::Lit`], [`TemplatePart::Time`], or [`TemplatePart::Var`]
    pub fn maybe_var(part: &str) -> Self {
        if LITERAL_REPLACEMENTS.contains(&part) {
            Self::lit(part)
        } else if part.starts_with(LITERAL_VALUE_QUOTE_CHAR)
            && part.ends_with(LITERAL_VALUE_QUOTE_CHAR)
        {
            Self::lit(&part[1..(part.len() - 1)])
        } else if part.starts_with(TIME_FORMAT_CHAR) {
            Self::time(part)
        } else if part.starts_with(LISP_START_CHAR) {
            Self::lisp(&part[1..])
        } else {
            Self::var(part)
        }
    }

    pub fn cmd(parts: Vec<TemplatePart>) -> Self {
        Self::Cmd(parts)
    }

    pub fn parse_cmd(part: &str) -> Result<Self, errors::RenderTemplateError> {
        Self::tokenize(part).map(Self::cmd)
    }

    pub fn any(parts: Vec<TemplatePart>) -> Self {
        Self::Any(parts)
    }

    pub fn maybe_any(part: &str) -> Self {
        if part.contains(OPTIONAL_RENDER_CHAR) {
            let parts = part
                .split(OPTIONAL_RENDER_CHAR)
                .map(|s| s.trim())
                .map(Self::maybe_var)
                .collect();

            Self::any(parts)
        } else {
            Self::maybe_var(part)
        }
    }

    fn find_end(
        end: char,
        templ: &str,
        offset: usize,
    ) -> Result<usize, errors::RenderTemplateError> {
        if end == '"' {
            return templ[offset..].find(end).map(|i| i + offset).ok_or(
                errors::RenderTemplateError::InvalidFormat(
                    templ.to_string(),
                    "Quote not closed".to_string(),
                ),
            );
        }
        let mut nest: Vec<char> = Vec::new();
        for (i, c) in templ[offset..].chars().enumerate() {
            if c == end && nest.is_empty() {
                return Ok(offset + i);
            } else if TEMPLATE_PAIRS_START.contains(&c) {
                if c == '"' && nest.contains(&c) {
                    while Some('"') != nest.pop() {}
                    continue;
                }
                nest.push(c);
            } else if TEMPLATE_PAIRS_END.contains(&c) {
                if let Some(last) = nest.pop() {
                    if c != TEMPLATE_PAIRS[&last] {
                        return Err(errors::RenderTemplateError::InvalidFormat(
                            templ.to_string(),
                            format!("Extra {} at [{}] in template", c, offset + i),
                        ));
                    }
                } else {
                    return Err(errors::RenderTemplateError::InvalidFormat(
                        templ.to_string(),
                        format!("Extra {} at [{}] in template", c, offset + i),
                    ));
                }
            }
        }
        Err(errors::RenderTemplateError::InvalidFormat(
            templ.to_string(),
            format!(
                "Closing {} not found from [{}] onwards in template",
                end, offset,
            ),
        ))
    }
    pub fn tokenize(templ: &str) -> Result<Vec<Self>, errors::RenderTemplateError> {
        let mut parts: Vec<TemplatePart> = Vec::new();
        let mut last = 0usize;
        let mut i = 0usize;
        let mut escape = false;
        while i < templ.len() {
            if templ[i..].starts_with(ESCAPE_CHAR) && !escape {
                if i > last {
                    parts.push(Self::lit(&templ[last..i]));
                }
                i += 1;
                last = i;
                escape = true;
                continue;
            }
            if escape {
                parts.push(Self::lit(&templ[i..(i + 1)]));
                last = i + 1;
                i += 1;
                escape = false;
                continue;
            }
            if templ[i..].starts_with("$(") {
                let end = Self::find_end(')', templ, i + 2)?;
                if i > last {
                    parts.push(Self::lit(&templ[last..i]));
                }
                last = end + 1;
                parts.push(Self::parse_cmd(&templ[(i + 2)..end])?);
                i = end;
            } else if templ[i..].starts_with("=(") {
                let end = Self::find_end(')', templ, i + 2)?;
                if i > last {
                    parts.push(Self::lit(&templ[last..i]));
                }
                last = end + 1;
                // need to include the found ')' for lisp expr to be valid
                parts.push(Self::lisp(&templ[(i + 1)..=end]));
                i = end;
            } else if templ[i..].starts_with('{') {
                let end = Self::find_end('}', templ, i + 1)?;
                if i > last {
                    parts.push(Self::lit(&templ[last..i]));
                }
                last = end + 1;
                parts.push(Self::maybe_any(&templ[(i + 1)..end]));
                i = end;
            } else if templ[i..].starts_with('"') {
                let end = Self::find_end('"', templ, i + 1)?;
                if i > last {
                    parts.push(Self::lit(&templ[last..i]));
                }
                last = end + 1;
                parts.push(Self::lit(&templ[(i + 1)..end]));
                i = end;
            }
            i += 1;
        }
        if templ.len() > last {
            parts.push(Self::lit(&templ[last..]));
        }
        Ok(parts)
    }

    pub fn variables(&self) -> Vec<&str> {
        match self {
            TemplatePart::Var(v, _) => vec![v.as_str()],
            TemplatePart::Lisp(expr, _, vars) => vars.iter().map(|(s, e)| &expr[*s..*e]).collect(),
            TemplatePart::Any(any) => any.iter().flat_map(|p| p.variables()).collect(),
            TemplatePart::Cmd(cmd) => cmd.iter().flat_map(|p| p.variables()).collect(),
            _ => vec![],
        }
    }
}
impl ToString for TemplatePart {
    fn to_string(&self) -> String {
        match self {
            Self::Lit(s) => format!("{0}{1}{0}", LITERAL_VALUE_QUOTE_CHAR, s),
            Self::Var(s, _) => s.to_string(),
            Self::Time(s) => s.to_string(),
            Self::Lisp(e, _, _) => e.to_string(),
            Self::Cmd(v) => v
                .iter()
                .map(|p| p.to_string())
                .collect::<Vec<String>>()
                .join(""),
            Self::Any(v) => v
                .iter()
                .map(|p| p.to_string())
                .collect::<Vec<String>>()
                .join(OPTIONAL_RENDER_CHAR.to_string().as_str()),
        }
    }
}

/// Main Template that get's passed around, consists of `[Vec`] of [`TemplatePart`]
///
/// ```rust
/// # use std::error::Error;
/// # use std::collections::HashMap;
/// # use std::path::PathBuf;
/// # use string_template_plus::{Render, RenderOptions, Template};
/// #
/// # fn main() -> Result<(), Box<dyn Error>> {
///     let templ = Template::parse_template("hello {nickname?name}. You're $(printf \"%.1f\" {weight})kg").unwrap();
///     let mut vars: HashMap<String, String> = HashMap::new();
///     vars.insert("name".into(), "John".into());
///     vars.insert("weight".into(), "132.3423".into());
///     let rendered = templ
///         .render(&RenderOptions {
///             wd: PathBuf::from("."),
///             variables: vars,
///             shell_commands: true,
///         })
///         .unwrap();
///     assert_eq!(rendered, "hello John. You're 132.3kg");
/// # Ok(())
/// }
#[derive(Debug, Clone)]
pub struct Template {
    original: String,
    parts: Vec<TemplatePart>,
}

impl Template {
    /// Parses the template from string and makes a [`Template`]. Which you can render later./// Main Template that get's passed around, consists of `[Vec`] of [`TemplatePart`]
    ///
    /// ```rust
    /// # use std::error::Error;
    /// # use std::collections::HashMap;
    /// # use std::path::PathBuf;
    /// # use string_template_plus::{Render, RenderOptions, Template};
    /// #
    /// # fn main() -> Result<(), Box<dyn Error>> {
    ///     let templ = Template::parse_template("hello {nickname?name?}. You're $(printf \\\"%.1f\\\" {weight})kg").unwrap();
    ///     let parts = concat!("[Lit(\"hello \"), ",
    ///                  "Any([Var(\"nickname\", \"\"), Var(\"name\", \"\"), Lit(\"\")]), ",
    ///                  "Lit(\". You're \"), ",
    ///                  "Cmd([Lit(\"printf \"), Lit(\"\\\"\"), Lit(\"%.1f\"), Lit(\"\\\"\"), Lit(\" \"), Var(\"weight\", \"\")]), ",
    ///                  "Lit(\"kg\")]");
    ///     assert_eq!(parts, format!("{:?}", templ.parts()));
    /// # Ok(())
    /// }
    pub fn parse_template(templ_str: &str) -> Result<Template, Error> {
        let template_parts = TemplatePart::tokenize(templ_str)?;
        Ok(Self {
            original: templ_str.to_string(),
            parts: template_parts,
        })
    }

    pub fn parts(&self) -> &Vec<TemplatePart> {
        &self.parts
    }

    pub fn original(&self) -> &str {
        &self.original
    }

    /// Concatenated String if [`Template`] is only literal strings
    pub fn lit(&self) -> Option<String> {
        let mut lit = String::new();
        for part in &self.parts {
            if let TemplatePart::Lit(l) = part {
                lit.push_str(l);
            } else {
                return None;
            }
        }
        Some(lit)
    }
}

/// Provides the function to render the object with [`RenderOptions`] into [`String`]
pub trait Render {
    fn render(&self, op: &RenderOptions) -> Result<String, Error>;

    fn print(&self);
}

/// Options for the [`Template`] to render into [`String`]
#[derive(Default, Debug, Clone)]
pub struct RenderOptions {
    /// Working Directory for the Shell Commands
    pub wd: PathBuf,
    /// Variables to use for the template
    pub variables: HashMap<String, String>,
    /// Run Shell Commands for the output or not
    pub shell_commands: bool,
}

impl RenderOptions {
    pub fn render(&self, templ: &Template) -> Result<String, Error> {
        templ.render(self)
    }

    /// Makes a [`RenderIter<'a>`] that can generate incremented strings from the given [`Template`] and the [`RenderOptions`]. The Iterator will have `-N` appended where N is the number representing the number of instance.
    ///
    /// ```rust
    /// # use std::error::Error;
    /// # use std::collections::HashMap;
    /// # use string_template_plus::{Render, RenderOptions, Template};
    /// #
    /// # fn main() -> Result<(), Box<dyn Error>> {
    ///     let templ = Template::parse_template("hello {name}").unwrap();
    ///     let mut vars: HashMap<String, String> = HashMap::new();
    ///     vars.insert("name".into(), "world".into());
    ///     let options = RenderOptions {
    ///         variables: vars,
    ///         ..Default::default()
    ///     };
    ///     let mut names = options.render_iter(&templ);
    ///     assert_eq!("hello world-1", names.next().unwrap());
    ///     assert_eq!("hello world-2", names.next().unwrap());
    ///     assert_eq!("hello world-3", names.next().unwrap());
    /// # Ok(())
    /// # }
    pub fn render_iter<'a>(&'a self, templ: &'a Template) -> RenderIter<'a> {
        RenderIter {
            template: templ,
            options: self,
            count: 0,
        }
    }
}

/// Render option with [`Iterator`] support. You can use this to get
/// incremented render results. It'll add `-N` to the render
/// [`Template`] where `N` is the count (1,2,3...). It can be useful
/// to make files with a given template.
///
/// ```rust
/// # use std::error::Error;
/// # use std::collections::HashMap;
/// # use string_template_plus::{Render, RenderOptions, RenderIter, Template};
/// #
/// # fn main() -> Result<(), Box<dyn Error>> {
///     let templ = Template::parse_template("hello {name}").unwrap();
///     let mut vars: HashMap<String, String> = HashMap::new();
///     vars.insert("name".into(), "world".into());
///     let options = RenderOptions {
///         variables: vars,
///         ..Default::default()
///     };
///     let mut names = RenderIter::new(&templ, &options);
///     assert_eq!("hello world-1", names.next().unwrap());
///     assert_eq!("hello world-2", names.next().unwrap());
///     assert_eq!("hello world-3", names.next().unwrap());
/// # Ok(())
/// # }
#[derive(Debug, Clone)]
pub struct RenderIter<'a> {
    template: &'a Template,
    options: &'a RenderOptions,
    count: usize,
}

impl<'a> RenderIter<'a> {
    /// Creates a new [`RenderIter<'a>`] object
    pub fn new(template: &'a Template, options: &'a RenderOptions) -> Self {
        Self {
            template,
            options,
            count: 0,
        }
    }
}

impl<'a> Iterator for RenderIter<'a> {
    type Item = String;
    fn next(&mut self) -> Option<String> {
        self.template.render(self.options).ok().map(|t| {
            self.count += 1;
            format!("{}-{}", t, self.count)
        })
    }
}

impl Render for TemplatePart {
    fn render(&self, op: &RenderOptions) -> Result<String, Error> {
        match self {
            TemplatePart::Lit(l) => Ok(l.to_string()),
            TemplatePart::Var(v, f) => op
                .variables
                .get(v)
                .ok_or(errors::RenderTemplateError::VariableNotFound(v.to_string()))
                .map(|s| -> Result<String, Error> { Ok(transformers::apply_tranformers(s, f)?) })?,
            TemplatePart::Time(t) => Ok(Local::now().format(t).to_string()),
            TemplatePart::Lisp(e, f, _) => Ok(transformers::apply_tranformers(
                &lisp::calculate(&op.variables, e)?,
                f,
            )?),
            TemplatePart::Cmd(c) => {
                let cmd = c.render(op)?;
                if op.shell_commands {
                    cmd_output(&cmd, &op.wd)
                } else {
                    Ok(format!("$({cmd})"))
                }
            }
            TemplatePart::Any(a) => a.iter().find_map(|p| p.render(op).ok()).ok_or(
                errors::RenderTemplateError::AllVariablesNotFound(
                    a.iter().map(|p| p.to_string()).collect(),
                )
                .into(),
            ),
        }
    }
    /// Visualize what has been parsed so it's easier to debug
    fn print(&self) {
        match self {
            Self::Lit(s) => print!("{}", s),
            Self::Var(s, sf) => print!("{}", {
                if sf.is_empty() {
                    s.on_blue()
                } else {
                    format!("{}:{}", s, sf.on_bright_blue()).on_blue()
                }
            }),
            Self::Time(s) => print!("{}", s.on_yellow()),
            Self::Lisp(expr, sf, vars) => {
                let mut last = 0;
                for (s, e) in vars {
                    print!("{}", expr[last..*s].on_purple());
                    print!("{}", expr[*s..*e].on_blue());
                    last = *e;
                }
                print!("{}", expr[last..expr.len()].on_purple());
                if !sf.is_empty() {
                    print!("{}", format!(":{}", sf).on_bright_purple())
                }
            }
            Self::Cmd(v) => {
                // overline; so the literal values are detected
                print!("\x1B[53m");
                print!("{}", "$(".on_red());
                v.iter().for_each(|p| {
                    print!("\x1B[53m");
                    p.print();
                });
                print!("\x1B[53m");
                print!("{}", ")".on_red());
            }
            Self::Any(v) => {
                v[..(v.len() - 1)].iter().for_each(|p| {
                    // underline; so the literal values are detected
                    print!("\x1B[4m");
                    p.print();
                    print!("\x1B[4m");
                    print!("{}", OPTIONAL_RENDER_CHAR.to_string().on_yellow());
                });
                print!("\x1B[4m");
                v.iter().last().unwrap().print();
                print!("\x1B[0m");
            }
        }
    }
}

impl Render for Vec<TemplatePart> {
    fn render(&self, op: &RenderOptions) -> Result<String, Error> {
        self.iter()
            .map(|p| p.render(op))
            .collect::<Result<Vec<String>, Error>>()
            .map(|v| v.join(""))
    }

    fn print(&self) {
        self.iter().for_each(|p| p.print());
    }
}

impl Render for Template {
    fn render(&self, op: &RenderOptions) -> Result<String, Error> {
        self.parts.render(op)
    }

    fn print(&self) {
        self.parts.print();
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_lit() {
        let templ = Template::parse_template("hello name").unwrap();
        let mut vars: HashMap<String, String> = HashMap::new();
        vars.insert("name".into(), "world".into());
        let rendered = templ
            .render(&RenderOptions {
                variables: vars,
                ..Default::default()
            })
            .unwrap();
        assert_eq!(rendered, "hello name");
    }

    #[test]
    fn test_vars() {
        let templ = Template::parse_template("hello {name}").unwrap();
        let mut vars: HashMap<String, String> = HashMap::new();
        vars.insert("name".into(), "world".into());
        let rendered = templ
            .render(&RenderOptions {
                variables: vars,
                ..Default::default()
            })
            .unwrap();
        assert_eq!(rendered, "hello world");
    }

    #[test]
    fn test_vars_format() {
        let mut vars: HashMap<String, String> = HashMap::new();
        vars.insert("length".into(), "120.1234".into());
        vars.insert("name".into(), "joHN".into());
        vars.insert("job".into(), "assistant manager of company".into());
        let options = RenderOptions {
            variables: vars,
            ..Default::default()
        };
        let cases = [
            ("L={length}", "L=120.1234"),
            ("L={length:calc(+100)}", "L=220.1234"),
            ("L={length:count(.):calc(+1)}", "L=2"),
            ("L={length:f(.2)} ({length:f(3)})", "L=120.12 (120.123)"),
            ("hi {name:case(up)}", "hi JOHN"),
            (
                "hi {name:case(proper)}, {job:case(title)}",
                "hi John, Assistant Manager of Company",
            ),
            ("hi {name:case(down)}", "hi john"),
        ];

        for (t, r) in cases {
            let templ = Template::parse_template(t).unwrap();
            let rendered = templ.render(&options).unwrap();
            assert_eq!(rendered, r);
        }
    }

    #[test]
    #[should_panic]
    fn test_novars() {
        let templ = Template::parse_template("hello {name}").unwrap();
        let vars: HashMap<String, String> = HashMap::new();
        templ
            .render(&RenderOptions {
                variables: vars,
                ..Default::default()
            })
            .unwrap();
    }

    #[test]
    fn test_novars_opt() {
        let templ = Template::parse_template("hello {name?}").unwrap();
        let vars: HashMap<String, String> = HashMap::new();
        let rendered = templ
            .render(&RenderOptions {
                variables: vars,
                ..Default::default()
            })
            .unwrap();
        assert_eq!(rendered, "hello ");
    }

    #[test]
    fn test_optional() {
        let templ = Template::parse_template("hello {age?name}").unwrap();
        let mut vars: HashMap<String, String> = HashMap::new();
        vars.insert("name".into(), "world".into());
        let rendered = templ
            .render(&RenderOptions {
                variables: vars,
                ..Default::default()
            })
            .unwrap();
        assert_eq!(rendered, "hello world");
    }

    #[test]
    fn test_special_chars() {
        let templ = Template::parse_template("$hello {}? \\{\\}%").unwrap();
        let rendered = templ.render(&RenderOptions::default()).unwrap();
        assert_eq!(rendered, "$hello ? {}%");
    }

    #[test]
    fn test_special_chars2() {
        let templ = Template::parse_template("$hello {}? \"{\"\"}\"%").unwrap();
        let rendered = templ.render(&RenderOptions::default()).unwrap();
        assert_eq!(rendered, "$hello ? {}%");
    }

    #[test]
    fn test_optional_lit() {
        let templ = Template::parse_template("hello {age?\"20\"}").unwrap();
        let mut vars: HashMap<String, String> = HashMap::new();
        vars.insert("name".into(), "world".into());
        let rendered = templ
            .render(&RenderOptions {
                variables: vars,
                ..Default::default()
            })
            .unwrap();
        assert_eq!(rendered, "hello 20");
    }

    #[test]
    fn test_command() {
        let templ = Template::parse_template("hello $(echo {name})").unwrap();
        let mut vars: HashMap<String, String> = HashMap::new();
        vars.insert("name".into(), "world".into());
        let rendered = templ
            .render(&RenderOptions {
                wd: PathBuf::from("."),
                variables: vars,
                shell_commands: true,
            })
            .unwrap();
        assert_eq!(rendered, "hello world\n");
    }

    #[test]
    fn test_command_quote() {
        let templ = Template::parse_template("hello $(printf \\\"%s %d\\\" {name} {age})").unwrap();
        let mut vars: HashMap<String, String> = HashMap::new();
        vars.insert("name".into(), "world".into());
        vars.insert("age".into(), "1".into());
        let rendered = templ
            .render(&RenderOptions {
                wd: PathBuf::from("."),
                variables: vars,
                shell_commands: true,
            })
            .unwrap();
        assert_eq!(rendered, "hello world 1");
    }

    #[test]
    fn test_time() {
        let templ = Template::parse_template("hello {name} at {%Y-%m-%d}").unwrap();
        let timefmt = Local::now().format("%Y-%m-%d");
        let output = format!("hello world at {}", timefmt);
        let mut vars: HashMap<String, String> = HashMap::new();
        vars.insert("name".into(), "world".into());
        let rendered = templ
            .render(&RenderOptions {
                wd: PathBuf::from("."),
                variables: vars,
                shell_commands: false,
            })
            .unwrap();
        assert_eq!(rendered, output);
    }

    #[test]
    fn test_var_or_time() {
        let templ = Template::parse_template("hello {name} at {age?%Y-%m-%d}").unwrap();
        let timefmt = Local::now().format("%Y-%m-%d");
        let output = format!("hello world at {}", timefmt);
        let mut vars: HashMap<String, String> = HashMap::new();
        vars.insert("name".into(), "world".into());
        let rendered = templ
            .render(&RenderOptions {
                wd: PathBuf::from("."),
                variables: vars,
                shell_commands: false,
            })
            .unwrap();
        assert_eq!(rendered, output);
    }

    #[test]
    fn test_render_iter() {
        let templ = Template::parse_template("hello {name}").unwrap();
        let mut vars: HashMap<String, String> = HashMap::new();
        vars.insert("name".into(), "world".into());
        let options = RenderOptions {
            variables: vars,
            ..Default::default()
        };
        let mut names = options.render_iter(&templ);
        assert_eq!("hello world-1", names.next().unwrap());
        assert_eq!("hello world-2", names.next().unwrap());
        assert_eq!("hello world-3", names.next().unwrap());
    }
}