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use std::cell::RefCell;
use std::collections::HashMap;
use std::fs;
use std::ops::Range;
use std::path::Path;

use regex::{Captures, Regex};

use crate::{FhttpError, Result};
use crate::path_utils::{RelativePath, canonicalize, CanonicalizedPathBuf};

pub fn load_file_recursively<P: AsRef<Path>>(path: P) -> Result<String> {
    RecursiveFileLoader::new().load_file_recursively(canonicalize(path.as_ref())?)
}

struct RecursiveFileLoader {
    resolved_paths: RefCell<HashMap<CanonicalizedPathBuf, String>>,
    resolution_stack: RefCell<Vec<CanonicalizedPathBuf>>,
}

impl RecursiveFileLoader {
    fn new() -> Self {
        RecursiveFileLoader {
            resolved_paths: RefCell::new(HashMap::new()),
            resolution_stack: RefCell::new(Vec::new()),
        }
    }

    fn load_file_recursively(
        &self,
        path: CanonicalizedPathBuf,
    ) -> Result<String> {
        self.get_text_for_path(path)
    }

    fn find_includes(
        &self,
        source_path: &CanonicalizedPathBuf,
        text: &str,
    ) -> Result<Vec<Include>> {
        lazy_static! {
            static ref RE_ENV: Regex = Regex::new(r##"(?m)\$\{include\("([^"]*)"\)}"##).unwrap();
        };

        let reversed_captures: Result<Vec<Include>> = RE_ENV.captures_iter(text)
            .collect::<Vec<Captures>>()
            .into_iter()
            .rev()
            .map(|capture| {
                let group = capture.get(0).unwrap();
                let range = group.start()..group.end();
                let path = capture.get(1).unwrap().as_str();
                let path = source_path.get_dependency_path(path)?;

                Ok(
                    Include {
                        range,
                        path,
                    }
                )
            })
            .collect();

        reversed_captures
    }

    fn get_text_for_path(
        &self,
        path: CanonicalizedPathBuf,
    ) -> Result<String> {
        if let Some(content) = self.resolved_paths.borrow().get(&path) {
            return Ok(content.clone())
        }

        if self.resolution_stack.borrow().contains(&path) {
            let stack = self.resolution_stack.borrow();
            let last = stack.last().unwrap().to_str();
            return Err(FhttpError::new(format!(
                "cyclic dependency detected between '{}' and '{}'",
                last,
                path.to_str(),
            )))
        } else {
            self.resolution_stack.borrow_mut().push(path.clone());
        }

        let mut content = fs::read_to_string(&path)
            .map_err(|_| FhttpError::new(format!("error reading file {}", path.to_str())))?;

        let includes = self.find_includes(&path, &content)?;
        for include in includes {
            let text = self.get_text_for_path(include.path)?;
            let end_index = match text.chars().last() {
                Some('\n') => text.len() - 1,
                _ => text.len(),
            };
            content.replace_range(include.range, &text[0..end_index]);
        }

        self.resolved_paths.borrow_mut().insert(path, content.clone());
        self.resolution_stack.borrow_mut().pop();

        Ok(content)
    }
}

#[derive(Debug)]
struct Include {
    range: Range<usize>,
    path: CanonicalizedPathBuf,
}

#[cfg(test)]
mod test {
    use std::str::FromStr;

    use indoc::indoc;

    use crate::test_utils::root;

    use super::*;

    #[test]
    fn should_load_files_recursively() {
        let result = load_file_recursively(
            &root().join("resources/nested_file_includes/normal/start.txt")
        );

        let expectation = String::from_str(
            indoc!{r##"
                START
                LEVEL-1
                LEVEL-2
                LEVEL-3
                LEVEL-3
            "##}
        ).unwrap();

        assert_eq!(result, Ok(expectation));
    }

    #[test]
    fn should_detect_cyclic_dependencies() {
        let one = root().join("resources/nested_file_includes/cyclic_dependency/level-1.txt");
        let three = root().join("resources/nested_file_includes/cyclic_dependency/level-3.txt");
        let result = load_file_recursively(
            &root().join("resources/nested_file_includes/cyclic_dependency/start.txt")
        );

        assert_eq!(
            result,
            Err(FhttpError::new(
                format!(
                    "cyclic dependency detected between '{}' and '{}'",
                    three.to_str(),
                    one.to_str(),
                )
            ))
        );
    }
}