1 files changed, 165 insertions, 0 deletions

diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..02fbcd4
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,165 @@
+use clap::Parser;
+use pandoc::{
+  InputFormat,InputKind,OutputFormat,OutputKind,Pandoc
+};
+use pandoc_ast::Block;
+use std::borrow::Cow;
+use std::collections::HashMap;
+use lazy_static::lazy_static;
+use regex::{Captures,Regex};
+use std::fs;
+use std::io::Result;
+use std::path::PathBuf;
+
+const BASE: &str = "./";
+
+/// A tangler for Literate Programming in Pandoc
+#[derive(Parser, Debug)]
+#[clap(author, version, about, long_about = None)]
+struct Config {
+  /// Maximum substitution depth
+  #[clap(short, long, default_value_t = 10)]
+  depth: u32,
+  /// Base output directory [default: './']
+  #[clap(short, long)]
+  output: Option<PathBuf>,
+  /// Input files
+  input: Vec<PathBuf>,
+}
+
+type Blocks<'a> = HashMap<String,Cow<'a,str>>;
+
+fn build(
+  base: &Option<PathBuf>,
+  blocks: &Blocks,
+  max_depth: u32
+) {
+  lazy_static! {
+    static ref PATH: Regex =
+      Regex::new(
+        r"^(?:[[:word:]\.-]+/)*[[:word:]\.-]+\.[[:alpha:]]+$"
+      ).unwrap();
+    static ref MACRO: Regex =
+      Regex::new(
+        r"(?m)^([[:blank:]]*)<<([^>\s]+)>>"
+      ).unwrap();
+  }
+  blocks
+    .iter()
+    .for_each(|(path,code)| if PATH.is_match(path) { 
+      let mut current_depth = 0;
+      let mut code = code.clone();
+      while let Cow::Owned(new_code) = MACRO.replace_all(
+        &code,
+        |caps: &Captures| {
+          if current_depth < max_depth {
+            let block = blocks
+              .get(&caps[2])
+              .expect("Block not present")
+              .clone();
+            indent(block, caps[1].len())
+          } else {
+            eprintln!("Reached maximum depth, \
+                       output might be truncated.\n\
+                       Increase `--depth` accordingly.");
+            Cow::Owned(String::from(""))
+          }
+        }
+      ) {
+        code = Cow::from(new_code);
+        current_depth += 1;
+      }
+      let file = base
+        .clone()
+        .unwrap_or(PathBuf::from(BASE))
+        .join(path);
+      write_to_file(file, &code)
+        .expect("Unable to write to file");
+    })
+}
+
+fn indent<'a>(
+  input: Cow<'a,str>,
+  indent: usize
+) -> Cow<'a,str> {
+  if indent > 0 {
+    let prefix = format!("{:indent$}", "");
+    let size = input.len() + indent*input.lines().count();
+    let mut output = String::with_capacity(size);
+    input.lines().enumerate().for_each(|(i,line)| {
+      if i > 0 {
+        output.push('\n');
+      }
+      if !line.is_empty() {
+        output.push_str(&prefix);
+        output.push_str(line);
+      }
+    });
+    Cow::Owned(output)
+  } else {
+    input
+  }
+}
+
+fn write_to_file(
+  path: PathBuf, content: &str
+) -> std::io::Result<()> {
+  if path.is_relative() {
+    fs::create_dir_all(path.parent().unwrap())?;
+    fs::write(path, content)?;
+  } else { 
+    eprintln!(
+      "Absolute paths not supported: {}",
+      path.to_string_lossy()
+    )
+  }
+  Ok(())
+}
+
+
+fn main() -> Result<()> {
+  let config = Config::parse();
+  let mut pandoc = Pandoc::new();
+  pandoc.set_input(InputKind::Files(config.input));
+  pandoc.set_input_format(InputFormat::Markdown, vec![]);
+  pandoc.set_output(OutputKind::Pipe);
+  pandoc.set_output_format(OutputFormat::Json, vec![]);
+  pandoc.add_filter(
+    move |json| pandoc_ast::filter(json,
+      |pandoc| {
+        let mut blocks: Blocks = HashMap::new();
+        pandoc.blocks.iter().for_each(|block|
+          if let Block::CodeBlock((id,clss,attrs), code) = block {
+            if !id.is_empty() {
+              let key = {
+                let path = attrs.iter().find(|(k,_)| k == "path");
+                if let Some(path) = path {
+                  format!("{}{}", path.1, id) 
+                } else {
+                  id.to_string()
+                }
+              };
+              if clss.iter().any(|c| c == "override") {
+                blocks.insert(key, Cow::from(code));
+              } else {
+                blocks.entry(key)
+                      .and_modify(|s| {
+                        *s += "\n";
+                        *s += Cow::from(code)
+                      })
+                      .or_insert(Cow::from(code));
+              }
+            } else {
+              eprintln!("Ignoring code block without ID:");
+              eprintln!("{}", indent(Cow::from(code),4));
+            }
+          }
+        );
+        build(&config.output, &blocks, config.depth);
+        pandoc
+      }
+    )
+  );
+  pandoc.execute().unwrap();
+  Ok(())
+}
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