use std::path::{Path, PathBuf};

use eyre::{eyre, ContextCompat, Result, WrapErr};
use log::{debug, error, log_enabled, trace, warn};
use pandoc_ast::MutVisitor;

use crate::{
    filters,
    utils::{AutoIdentifier, PandocMeta, PandocOutputExt},
};

pub fn do_build(config: &crate::config::Config) -> Result<()> {
    let summary = Summary::try_from_file(&config.book.summary)?;
    let source_root = Path::new(&config.book.summary)
        .parent()
        .expect("Summary has no parent");
    let files = summary.collect_source_files(source_root)?;

    let build_dir = Path::new(&config.build.build_dir);
    trace!("Creating build directory: '{}'", build_dir.display());
    std::fs::create_dir_all(build_dir).wrap_err_with(|| {
        format!(
            "Could not create build directory: '{}'",
            build_dir.display()
        )
    })?;

    // Pre-create files so that we know which links to relativize
    for SourceFile { path, .. } in &files {
        let output_file = build_dir.join(path.with_extension("html"));

        let product_dir = build_dir.join(path.parent().expect("Source file has no parent"));
        trace!("Creating product directory: '{}'", product_dir.display());
        std::fs::create_dir_all(&product_dir).wrap_err_with(|| {
            format!(
                "Could not create build output directory: '{}'",
                product_dir.display()
            )
        })?;

        std::fs::OpenOptions::new()
            .write(true)
            .create(true)
            .open(&output_file)
            .wrap_err_with(|| {
                format!("Failed to create output file: '{}'", output_file.display())
            })?;
    }

    for SourceFile { path, source } in &files {
        let mut pandoc_command = pandoc::new();

        let output_file = build_dir.join(path.with_extension("html"));

        debug!("Generating file: '{}'", output_file.display());

        // To be captured in the filter
        let config_clone = config.clone();
        let source_dir = path
            .parent()
            .expect("Source file has no parent")
            .to_path_buf();
        let build_dir_clone = build_dir.to_path_buf();
        let summary_clone = summary.source.clone();

        pandoc_command
            .set_input(pandoc::InputKind::Pipe(source.to_json()))
            .set_input_format(pandoc::InputFormat::Json, vec![])
            .set_output(pandoc::OutputKind::File(output_file))
            .set_output_format(pandoc::OutputFormat::Html5, vec![])
            .add_options(&[pandoc::PandocOption::SelfContained])
            .add_filter(move |source| {
                let level = source_dir
                    .components()
                    .skip_while(|c| matches!(c, std::path::Component::CurDir))
                    .count();

                let mut insert_summary_filter = filters::InsertSummary {
                    level,
                    summary: &summary_clone,
                };

                let mut relativize_urls_filter = filters::RelativizeUrls {
                    config: &config_clone,
                    // TODO: other output formats
                    extension: "html",
                    build_dir: &build_dir_clone,
                    source_dir: &source_dir,
                };

                let mut source = pandoc_ast::Pandoc::from_json(&source);
                insert_summary_filter.walk_pandoc(&mut source);
                relativize_urls_filter.walk_pandoc(&mut source);
                source.to_json()
            });

        if log_enabled!(log::Level::Trace) {
            pandoc_command.set_show_cmdline(true);
        }

        pandoc_command
            .execute()
            .wrap_err_with(|| format!("Failed to generate output of: '{}'", path.display()))?;
    }

    Ok(())
}

// TODO: move that into generated.rs
fn generate_source(
    title: Vec<pandoc_ast::Inline>,
    children: Vec<(PandocMeta, PathBuf)>,
    level: usize,
) -> Result<pandoc_ast::Pandoc> {
    // TODO: make that text configurable
    let mut content = vec![pandoc_ast::Block::Para(vec![pandoc_ast::Inline::Str(
        "Here are the articles in this section:".to_string(),
    )])];

    for (mut child, file) in children {
        let title = match child.remove("title") {
            None => {
                warn!("Missing title for file: '{}'", file.display());
                vec![pandoc_ast::Inline::Str("Untitled page".to_string())]
            }
            Some(pandoc_ast::MetaValue::MetaInlines(inlines)) => inlines,
            Some(pandoc_ast::MetaValue::MetaString(s)) => {
                vec![pandoc_ast::Inline::Str(s)]
            }
            // TODO: check that other values are actually invalid
            _ => {
                error!("Invalid value for title");
                vec![pandoc_ast::Inline::Str("Untitled page".to_string())]
            }
        };

        let link_target = std::iter::repeat(std::path::Component::ParentDir)
            .take(level)
            .collect::<PathBuf>()
            .join(file);

        content.push(pandoc_ast::Block::Para(vec![pandoc_ast::Inline::Link(
            // TODO: attribute to recognize big links?
            (String::new(), vec![], vec![]),
            title,
            (
                link_target
                    .to_str()
                    .expect("Filename contains invalid unicode")
                    .to_string(),
                String::new(),
            ),
        )]));
    }

    let mut meta = PandocMeta::new();
    meta.insert(
        "title".to_string(),
        pandoc_ast::MetaValue::MetaInlines(title),
    );

    Ok(pandoc_ast::Pandoc {
        meta,
        blocks: content,
        pandoc_api_version: vec![1, 22],
    })
}

fn list_content(block: &mut pandoc_ast::Block) -> Result<&mut Vec<Vec<pandoc_ast::Block>>> {
    match block {
        pandoc_ast::Block::OrderedList(_, list) => Ok(list),
        pandoc_ast::Block::BulletList(list) => Ok(list),
        _ => Err(eyre!("Expected list in summary, found something else")),
    }
}

fn try_into_node_vec(vec: &mut Vec<Vec<pandoc_ast::Block>>) -> Result<Vec<Node>> {
    vec.iter_mut().map(Node::try_from_vec_block).collect()
}

// TODO: support separators like these:
// ---------

#[derive(Debug)]
pub struct Summary {
    source: pandoc_ast::Pandoc,
    nodes: Vec<Node>,
}

#[derive(Debug)]
struct SourceFile {
    path: PathBuf,
    source: pandoc_ast::Pandoc,
}

// TODO: move that into summary.rs
impl Summary {
    fn try_from_file(file: &str) -> Result<Self> {
        debug!("Parsing summary");
        let mut pandoc_command = pandoc::new();
        pandoc_command
            .add_input(file)
            .set_output_format(pandoc::OutputFormat::Json, vec![])
            .set_output(pandoc::OutputKind::Pipe);

        trace!("Launching pandoc command");

        if log_enabled!(log::Level::Trace) {
            pandoc_command.set_show_cmdline(true);
        }

        let output = pandoc_command
            .execute()
            .wrap_err("Could not execute pandoc")?
            .buffer();

        let document = pandoc_ast::Pandoc::from_json(&output);

        let summary: Self = document.try_into()?;
        if summary.has_files_missing(
            Path::new(file)
                .parent()
                .expect("Summary file has no parent"),
        ) {
            return Err(eyre!("Files from the summary are missing, aborting"));
        }

        Ok(summary)
    }

    fn has_files_missing(&self, root: &Path) -> bool {
        // Do not use `.any()` to prevent short-circuiting, we want to report all missing files
        self.nodes.iter().fold(false, |acc, node| {
            let missing = node.has_files_missing(root);
            acc || missing
        })
    }

    /// Get a list of source files.
    ///
    /// If a file is a generated file, generate it and store it in memory.
    fn collect_source_files(&self, root: &Path) -> Result<Vec<SourceFile>> {
        let mut result = Vec::new();

        for node in &self.nodes {
            node.collect_source_files(&mut result, root, Path::new("."), 0)?;
        }

        Ok(result)
    }
}

impl TryFrom<pandoc_ast::Pandoc> for Summary {
    type Error = eyre::Error;

    fn try_from(mut document: pandoc_ast::Pandoc) -> Result<Self, Self::Error> {
        if document.blocks.len() != 1 {
            return Err(eyre!("Summary does not contain a single list"));
        }

        let root = &mut document.blocks[0];

        let list = list_content(root)?;

        let nodes = list
            .iter_mut()
            .map(Node::try_from_vec_block)
            .collect::<Result<_>>()?;

        Ok(Summary {
            source: document,
            nodes,
        })
    }
}

#[derive(Debug)]
pub enum Node {
    Provided {
        file: String,
        children: Vec<Node>,
    },
    Generated {
        file: String,
        title: Vec<pandoc_ast::Inline>,
        children: Vec<Node>,
    },
}

impl Node {
    fn children(&self) -> &[Node] {
        match self {
            Node::Provided { children, .. } => children,
            Node::Generated { children, .. } => children,
        }
    }

    fn has_files_missing(&self, root: &Path) -> bool {
        if let Node::Provided { file, .. } = self {
            if !root.join(file).exists() {
                error!("File '{}' specified in summary does not exists", file);
                return true;
            }
        }

        // Do not use `.any()` to prevent short-circuiting, we want to report all missing files
        self.children().iter().fold(false, |acc, node| {
            let missing = node.has_files_missing(root);
            acc || missing
        })
    }

    fn collect_source_files(
        &self,
        result: &mut Vec<SourceFile>,
        root: &Path,
        parent: &Path,
        level: usize,
    ) -> Result<()> {
        let new_parent;
        let children_;
        let path;
        let source: Box<dyn FnOnce(_) -> _>;

        match self {
            Node::Provided { file, children } => {
                trace!("Parsing file: '{}'", file);

                // TODO: some filters here? not all filters, since we may want to filter generated
                // files too
                let mut pandoc_command = pandoc::new();
                pandoc_command
                    .add_input(&root.join(file))
                    .set_output(pandoc::OutputKind::Pipe)
                    .set_output_format(pandoc::OutputFormat::Json, vec![]);

                if log_enabled!(log::Level::Trace) {
                    pandoc_command.set_show_cmdline(true);
                }

                let raw_source = pandoc_command
                    .execute()
                    .wrap_err_with(|| format!("Failed to parse '{}'", file))?
                    .buffer();
                source = Box::new(move |_| Ok(pandoc_ast::Pandoc::from_json(&raw_source)));

                let file = Path::new(&file);
                let stem = file.file_stem().expect("No file name");
                let id =
                    AutoIdentifier::from(stem.to_str().wrap_err("Invalid unicode in file name")?);

                path = file.into();
                new_parent = file.parent().expect("Source file has no parent").join(&*id);
                children_ = children;
            }

            Self::Generated {
                file,
                title,
                children,
            } => {
                trace!("Found file to generate: '{}'", file);

                path = file.into();

                source = Box::new(move |direct_children| {
                    generate_source(title.clone(), direct_children, level)
                });
                new_parent = Path::new(file).with_extension("");
                children_ = children;
            }
        };

        let mut direct_children = Vec::with_capacity(children_.len());

        for child in children_ {
            child.collect_source_files(result, root, &new_parent, level + 1)?;
            let direct_child = result.last().unwrap();
            direct_children.push((direct_child.source.meta.clone(), direct_child.path.clone()));
        }

        result.push(SourceFile {
            path,
            source: source(direct_children)?,
        });

        Ok(())
    }

    // Wil also modify the block to linkify generated pages
    fn try_from_vec_block(value: &mut Vec<pandoc_ast::Block>) -> Result<Self> {
        if value.len() != 1 && value.len() != 2 {
            // TODO: better error message?
            return Err(eyre!("Summary does not contain a single list"));
        }

        let mut value = value.iter_mut();

        let item = match value.next().unwrap() {
            pandoc_ast::Block::Plain(inlines) => inlines,
            pandoc_ast::Block::Para(inlines) => inlines,
            _ => return Err(eyre!("List item is not a link or plain text")),
        };

        if item.is_empty() {
            return Err(eyre!("Summary list items cannot be empty"));
        }

        let children = if let Some(children) = value.next() {
            try_into_node_vec(list_content(children)?)?
        } else {
            vec![]
        };

        match &item[0] {
            pandoc_ast::Inline::Link(_, _, target) => {
                if item.len() != 1 {
                    return Err(eyre!("Summary list item not a single link or plain text"));
                }

                let file = target.0.clone();

                Ok(Node::Provided { file, children })
            }
            _ => {
                let title = item.clone();

                let id = AutoIdentifier::from(title.as_slice());

                // TODO: missing parent

                // Move generate page into this pass
                //let mut file = parent.join(&*id);
                //file.set_extension("md");

                // TODO: Attribute to style them differently
                *item = vec![pandoc_ast::Inline::Link(
                    (String::new(), vec!["generated".to_string()], vec![]),
                    item.clone(),
                    (id.0.clone(), String::new()),
                )];

                Ok(Node::Generated {
                    file: id.0,
                    title,
                    children,
                })
            }
        }
    }
}