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// sources.rs
// Copyright 2022 Matti Hänninen
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.

use std::{
  borrow::Cow,
  collections::HashMap,
  fs,
  io::{self, Read},
  rc::Rc,
};

use crate::{cli, error::Error};

#[derive(Debug)]
pub struct Source {
  pub content: String,
  pub file: Option<String>,
}

pub fn load_sources(
  source_args: &[cli::SourceArg],
  template_args: &[cli::TemplateArg],
) -> Result<Vec<Source>, Error> {
  let context = Context::from(template_args);
  let mut result = Vec::new();
  for source_arg in source_args.iter() {
    let (file, raw_content) = load_content(source_arg)?;
    let content = render_source(&context, raw_content.as_ref());
    result.push(Source { content, file });
  }
  Ok(result)
}

fn load_content(
  source_arg: &cli::SourceArg,
) -> Result<(Option<String>, Cow<'_, str>), Error> {
  use cli::SourceArg::*;
  match source_arg {
    Pipe => {
      let stdin = io::stdin();
      let mut handle = stdin.lock();
      let mut buffer = String::new();
      handle
        .read_to_string(&mut buffer)
        .map_err(|_| Error::CannotReadStdIn)?;
      Ok((None, Cow::Owned(buffer)))
    }
    Expr(e) => Ok((None, Cow::Borrowed(e.as_str()))),
    File(f) => {
      let mut file = fs::File::open(f)
        .map_err(|_| Error::CannotReadFile(f.to_string_lossy().to_string()))?;
      let mut buffer = String::new();
      file
        .read_to_string(&mut buffer)
        .map_err(|_| Error::CannotReadFile(f.to_string_lossy().to_string()))?;
      Ok((Some(f.to_string_lossy().to_string()), Cow::Owned(buffer)))
    }
  }
}

// XXX(soija) This needs work
// This rendering has the following limitations:
// - does not catch '#nr[...]' exprs without value arg (nREPL catches this though)
// - is not easy to extend supporting '#nr[<var> <default>]'
// - let alone '#nr[<var-1> ... <var-n> <default>]'
// - does not captures values from environment variables (e.g. NR_VAR_1)
fn render_source(context: &Context, source: &str) -> String {
  let after_shebang = if source.starts_with("#!") {
    match source.split_once('\n') {
      Some((_, remaining)) => remaining,
      None => "",
    }
  } else {
    source
  }
  .trim();
  if let Some(ref regex) = context.regex {
    let mut fragments = Vec::<Rc<str>>::new();
    let mut remaining = after_shebang;
    while let Some(captures) = regex.captures(remaining) {
      let full_match = captures.get(0).unwrap();
      let (upto, after) = remaining.split_at(full_match.end());
      let (before, _) = upto.split_at(full_match.start());
      fragments.push(before.to_string().into());
      let value = context
        .table
        .get(captures.get(1).unwrap().as_str())
        .unwrap();
      fragments.push(value.clone());
      remaining = after;
    }
    fragments.push(remaining.to_string().into());
    fragments.join("")
  } else {
    after_shebang.into()
  }
}

#[derive(Debug)]
struct Context {
  table: HashMap<Rc<str>, Rc<str>>,
  regex: Option<regex::Regex>,
}

impl From<&[cli::TemplateArg]> for Context {
  fn from(template_args: &[cli::TemplateArg]) -> Self {
    let table = template_args.iter().fold(HashMap::new(), |mut m, a| {
      if let Some(ref n) = a.name {
        m.insert(n.clone(), a.value.clone());
      }
      if let Some(i) = a.pos {
        m.insert((i + 1).to_string().into(), a.value.clone());
      }
      m
    });
    let regex = if table.is_empty() {
      None
    } else {
      let keys = table
        .keys()
        .map(|s| regex::escape(s))
        .collect::<Vec<String>>();
      let key_union = keys.join("|");
      let pat = format!(r#"#nr\s*\[\s*({})\s*\]"#, key_union,);
      // XXX(soija) Once https://github.com/rust-lang/rust/issues/79524 lands, use
      // intersperse.
      /*
      let pat = format!(
          r#"#nr\s*\[\s*({})\s*\]"#,
          table
              .keys()
              .map(|k| regex::escape(k))
              .intersperse("|".to_string())
              .collect::<String>(),
      );
      */
      Some(regex::Regex::new(&pat).unwrap())
    };
    Self { table, regex }
  }
}