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

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

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

const CSS: &str = include_str!("../res/style.css");
const HTML_TEMPLATE: &str = include_str!("../res/template.html");

pub fn do_build(config: &crate::config::Config) -> Result<()> {
    let tmpdir = tempfile::tempdir().wrap_err("Could not create temporary directory")?;
    debug!(
        "Created temporary directory at: '{}'",
        tmpdir.path().display()
    );

    let template_path = tmpdir.path().join("template.html");
    trace!("Writing HTML template to: '{}'", template_path.display());
    std::fs::write(&template_path, HTML_TEMPLATE)
        .wrap_err("Could not save HTML template in temporary directory")?;

    let defaults_path = tmpdir.path().join("defaults.yaml");
    debug!("Generating file: '{}'", defaults_path.display());
    let defaults =
        std::fs::File::create(&defaults_path).wrap_err("Could not create defaults.yaml")?;
    serde_json::to_writer(defaults, &config.pandoc).wrap_err("Could not create defaults.yaml")?;

    let source_root = Path::new(&config.book.summary)
        .parent()
        .expect("Summary has no parent");
    let (summary, files) = process_summary(&config.book.summary, 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()
        )
    })?;

    let style_path = build_dir.join("style.css");
    debug!("Generating file: '{}'", style_path.display());
    std::fs::write(&style_path, CSS).wrap_err("Could not create style.css")?;

    // 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 level = source_dir
            .components()
            .skip_while(|c| matches!(c, std::path::Component::CurDir))
            .count();

        let summary = relativize_summary(&summary.source, level);
        let mut source = source.clone();
        source.meta.insert(
            "summary".to_string(),
            pandoc_ast::MetaValue::MetaBlocks(summary.blocks),
        );

        let style_path = std::iter::repeat(std::path::Component::ParentDir)
            .take(level)
            .collect::<PathBuf>()
            .join("style.css");

        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::Css(style_path.to_string()),
                pandoc::PandocOption::Defaults(defaults_path.clone()),
                pandoc::PandocOption::SectionDivs,
                pandoc::PandocOption::Standalone,
                pandoc::PandocOption::Template(template_path.clone()),
            ])
            .add_filter(move |source| {
                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);
                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: &[(&PandocMeta, &Path)],
    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 (child, file) in children {
        let title = match child.get("title").cloned() {
            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")),
    }
}

// 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
fn process_summary(file: &str, source_root: &Path) -> Result<(Summary, Vec<SourceFile>)> {
    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);

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

    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 mut source_files = Vec::new();

    for element in list.iter_mut() {
        process_summary_element(element, Path::new("./"), source_root, &mut source_files)?;
    }

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

fn process_summary_element(
    element: &mut Vec<pandoc_ast::Block>,
    parent: &Path,
    source_root: &Path,
    source_files: &mut Vec<SourceFile>,
) -> Result<()> {
    if element.len() != 1 && element.len() != 2 {
        // TODO: better error message?
        return Err(eyre!("Summary element does not contain a single list"));
    }

    trace!("Parsing summary element");
    let mut value = element.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 child_parent = match &item[0] {
        pandoc_ast::Inline::Link(_, _, target) => {
            let file = &target.0;
            Path::new(&file).with_extension("")
        }
        _ => {
            let title = item.clone();
            let id = AutoIdentifier::from(title.as_slice());
            parent.join(&id.0)
        }
    };
    trace!("Summary element is {:?}", child_parent);

    let previous_source_len = source_files.len();
    if let Some(children) = value.next() {
        for child in list_content(children)? {
            process_summary_element(child, &child_parent, source_root, source_files)?;
        }
    }

    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();
            source_files.push(parse_file(&file, source_root)?);
        }
        _ => {
            let title = item.clone();

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

            *item = vec![pandoc_ast::Inline::Link(
                (String::new(), vec!["generated".to_string()], vec![]),
                item.clone(),
                (
                    parent.join(&id.0).with_extension("html").to_string(),
                    String::new(),
                ),
            )];

            // TODO: this shows children recursively (and has a bug when in a subdirectory)
            let children_metadata = source_files[previous_source_len..source_files.len()]
                .iter()
                .map(|source| (&source.source.meta, source.path.as_ref()))
                .collect::<Vec<_>>();

            let source = generate_source(title, &children_metadata, 0)?;

            source_files.push(SourceFile {
                path: child_parent.with_extension("html"),
                source,
            });
        }
    }

    Ok(())
}

fn parse_file(file: &str, source_root: &Path) -> Result<SourceFile> {
    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(&source_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();
    let source = pandoc_ast::Pandoc::from_json(&raw_source);

    Ok(SourceFile {
        path: file.into(),
        source,
    })
}