use lazy_static::lazy_static;
use regex::Regex;
use serde::Deserialize;
use serde_yaml::Value;
use std::collections::{BTreeMap, HashMap};
use std::path::{Path, PathBuf};

lazy_static! {
    // Pattern that recognises a YAML block at the beginning of a file.
    static ref LEADING_YAML_PATTERN: Regex = Regex::new(r"^(?:\S*\n)*(?P<yaml>-{3,}\n([^.].*\n)*\.{3,}\n)(?P<text>(.*\n)*)$").unwrap();


    // Pattern that recognises a YAML block at the end of a file.
    static ref TRAILING_YAML_PATTERN: Regex = Regex::new(r"(?P<text>(.*\n)*)\n*(?P<yaml>-{3,}\n([^.].*\n)*\.{3,}\n)(?:\S*\n)*$").unwrap();
}

/// Errors from Markdown parsing.
#[derive(Debug, thiserror::Error)]
pub enum Error {
    #[error(transparent)]
    Regex(#[from] regex::Error),

    #[error("Markdown doesn't contain a YAML block for document metadata")]
    NoMetadata,

    #[error(transparent)]
    Yaml(#[from] serde_yaml::Error),
}

/// Document metadata.
///
/// This is expressed in the Markdown input file as an embedded YAML
/// block.
///
/// Note that this structure needs to be able to capture any metadata
/// block we can work with, in any input file. By being strict here we
/// make it easier to tell the user when a metadata block has, say, a
/// misspelled field.
#[derive(Debug, Default, Clone, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct YamlMetadata {
    title: String,
    subtitle: Option<String>,
    authors: Option<Vec<String>>,
    date: Option<String>,
    classes: Option<Vec<String>>,
    bibliography: Option<Vec<PathBuf>>,
    markdowns: Vec<PathBuf>,
    bindings: Option<Vec<PathBuf>>,
    documentclass: Option<String>,
    #[serde(default)]
    impls: BTreeMap<String, Vec<PathBuf>>,
    pandoc: Option<HashMap<String, Value>>,
}

impl YamlMetadata {
    #[cfg(test)]
    fn new(yaml_text: &str) -> Result<Self, Error> {
        let meta: Self = serde_yaml::from_str(yaml_text)?;
        Ok(meta)
    }

    /// Name of file with the Markdown for the subplot document.
    pub fn markdown(&self) -> &Path {
        &self.markdowns[0]
    }

    /// Title.
    pub fn title(&self) -> &str {
        &self.title
    }

    /// Subtitle.
    pub fn subtitle(&self) -> Option<&str> {
        self.subtitle.as_deref()
    }

    /// Date.
    pub fn date(&self) -> Option<&str> {
        self.date.as_deref()
    }

    /// Authors.
    pub fn authors(&self) -> Option<&[String]> {
        self.authors.as_deref()
    }

    /// Names of bindings files.
    pub fn bindings_filenames(&self) -> Option<&[PathBuf]> {
        self.bindings.as_deref()
    }

    /// Impls section.
    pub fn impls(&self) -> &BTreeMap<String, Vec<PathBuf>> {
        &self.impls
    }

    /// Bibliographies.
    pub fn bibliographies(&self) -> Option<&[PathBuf]> {
        self.bibliography.as_deref()
    }

    /// Classes..
    pub fn classes(&self) -> Option<&[String]> {
        self.classes.as_deref()
    }

    /// Documentclass.
    pub fn documentclass(&self) -> Option<&str> {
        self.documentclass.as_deref()
    }

    /// Pandoc metadata.
    pub fn pandoc(&self) -> Option<&HashMap<String, Value>> {
        if let Some(x) = &self.pandoc {
            Some(x)
        } else {
            None
        }
    }
}

#[cfg(test)]
mod test {
    use super::YamlMetadata;
    use std::path::{Path, PathBuf};

    #[test]
    fn full_meta() {
        let meta = YamlMetadata::new(
            "\
title: Foo Bar
date: today
classes: [json, text]
impls:
  python:
   - foo.py
   - bar.py
bibliography:
- foo.bib
- bar.bib
markdowns:
- test.md
bindings:
- foo.yaml
- bar.yaml
",
        )
        .unwrap();
        assert_eq!(meta.title, "Foo Bar");
        assert_eq!(meta.date.unwrap(), "today");
        assert_eq!(meta.classes.unwrap(), &["json", "text"]);
        assert_eq!(
            meta.bibliography.unwrap(),
            &[path("foo.bib"), path("bar.bib")]
        );
        assert_eq!(meta.markdowns, vec![Path::new("test.md")]);
        assert_eq!(
            meta.bindings.unwrap(),
            &[path("foo.yaml"), path("bar.yaml")]
        );
        assert!(!meta.impls.is_empty());
        for (k, v) in meta.impls.iter() {
            assert_eq!(k, "python");
            assert_eq!(v, &[path("foo.py"), path("bar.py")]);
        }
    }

    fn path(s: &str) -> PathBuf {
        PathBuf::from(s)
    }
}