use std::collections::HashSet;
use std::{borrow::Cow, collections::BTreeMap, error::Error, time::Duration};

use chrono::NaiveDate;
use futures::{future::ready, stream::iter, StreamExt, TryStreamExt};
use lofty::file::{AudioFile, TaggedFileExt};
use lofty::tag::Accessor;
use log::info;
use regex::Regex;
use render::Renderer;
use serde::{Deserialize, Serialize};
use str_slug::slug;

pub mod de;
mod render;
pub mod s3;

/// The Index tracks the state from the last successful exection.
#[derive(Default, Serialize, Deserialize)]
pub struct Index {
    #[serde(default)]
    entries: BTreeMap<String, Entry>,
    #[serde(default)]
    templates: BTreeMap<String, Template>,
    #[serde(default)]
    rendered: BTreeMap<String, HashSet<String>>,
}

impl Index {
    pub fn contains_key(&self, key: &str) -> bool {
        self.entries.contains_key(key)
    }

    pub fn add(&mut self, entry: Entry) {
        self.entries.insert(entry.filename.to_owned(), entry);
    }

    pub fn remove(&mut self, filename: &str) {
        self.entries.remove(filename);
    }
}

/// Entry records the metadata about a file in the collection.
#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct Entry {
    pub filename: String,
    pub date: Option<NaiveDate>,
    pub etag: Option<String>,
    pub title: Option<String>,
    pub album: Option<String>,
    pub artist: Option<String>,
    pub size: i64,
    #[serde(with = "de::hms_duration")]
    pub duration: Duration,
    pub hidden: bool,
}

impl Entry {
    pub fn read_from(
        key: String,
        etag: Option<String>,
        size: i64,
        date: Option<NaiveDate>,
        mut file: std::fs::File,
    ) -> Result<Entry, Box<dyn Error>> {
        let tagged = lofty::read_from(&mut file)?;
        let tag = tagged.primary_tag();

        Ok(Entry {
            filename: key.to_string(),
            etag,
            date,
            title: tag.and_then(|t| t.title()).map(Cow::into_owned),
            artist: tag.and_then(|t| t.artist()).map(Cow::into_owned),
            album: tag.and_then(|t| t.album()).map(Cow::into_owned),
            size,
            duration: tagged.properties().duration(),
            hidden: false,
        })
    }
}

/// Templates are used to render content for the feed.
///
/// `partial` templates are never rendered, but may be included in other templates.
/// `index` templates are rendered once for the entire collection.
/// Non-index templates are rendered once per entry.
#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct Template {
    pub name: String,
    /// False if the template should be rendered for each entry.
    /// True if the template renders the list of all entries.
    #[serde(default)]
    pub index: bool,
    #[serde(default)]
    pub partial: bool,
    pub content_type: Option<String>,
    #[serde(default)]
    /// Only render this template for files that match this regex.
    pub filter: Option<String>,
    pub template: String,
}

impl Template {
    fn make_filename(&self, entry: &Entry) -> String {
        if self.index {
            self.name.to_string()
        } else {
            let (basename, extension) = self
                .name
                .rsplit_once(".")
                .unwrap_or_else(|| (&self.name, ".html"));
            let title = if let Some(title) = &entry.title {
                slug(title)
            } else {
                slug(
                    entry
                        .filename
                        .rsplit_once(".")
                        .unwrap_or_else(|| (&entry.filename, ""))
                        .0,
                )
            };
            if let Some(ref date) = entry.date {
                format!("{basename}/{date}-{title}.{extension}")
            } else {
                format!("{basename}/{title}.{extension}")
            }
        }
    }
}

pub struct MP32RSS {
    access: s3::Access,
    index: Index,
    index_etag: Option<String>,
}

impl MP32RSS {
    pub async fn open(access: s3::Access) -> Result<Self, Box<dyn Error>> {
        info!("Opening index file");
        let (index, index_etag) = access.fetch_index().await?;
        Ok(Self {
            access,
            index,
            index_etag,
        })
    }

    pub fn get_mut_entry(&mut self, filename: &str) -> Option<&mut Entry> {
        self.index.entries.get_mut(filename)
    }

    pub async fn sync(&mut self) -> Result<(), Box<dyn Error>> {
        info!("Saving index file");
        let new_etag = self
            .access
            .put_index(&self.index, self.index_etag.as_deref())
            .await?;
        self.index_etag = new_etag;
        Ok(())
    }

    pub async fn refresh(&mut self) -> Result<(), Box<dyn Error>> {
        info!("Syncing against files in bucket");

        // 2. List files in the bucket
        let objects = self.access.list_mp3s().await?;

        // 3. Find files missing in the index
        // 4. For each missing file, download and add to local index
        let new_entries: Vec<_> = iter(objects)
            .filter(|k| ready(!self.index.contains_key(k)))
            .then(|k| {
                info!("Found new file: {k}...");
                self.access.fetch_entry(k)
            })
            .try_collect()
            .await?;

        let mut new_filenames = HashSet::new();
        for entry in new_entries {
            new_filenames.insert(entry.filename.to_string());
            self.index.add(entry);
        }

        // 5. Generate files for each template and upload
        // 6. Upload each file
        //      Check the ETAG against the ETAG in the index object?
        self.render(|e| new_filenames.contains(&e.filename)).await?;

        // 7. Upload the index file
        //    If upload fails, abort (or retry from the beginning)
        self.sync().await
    }

    pub async fn delete(&mut self, filename: &str) -> Result<(), Box<dyn Error>> {
        self.index.remove(filename);
        self.access.remove_file(filename).await?;
        self.render(|e| e.filename == filename).await?;
        self.sync().await
    }

    pub fn templates(&self) -> impl Iterator<Item = &Template> {
        self.index.templates.values()
    }

    /// Add a new template and rerender.
    pub async fn add_template(
        &mut self,
        name: String,
        template: String,
        index: bool,
        partial: bool,
        content_type: Option<String>,
        filter: Option<String>,
    ) -> Result<(), Box<dyn Error>> {
        self.index.templates.insert(
            name.to_owned(),
            Template {
                name,
                template,
                index,
                partial,
                content_type,
                filter,
            },
        );
        self.render(|_| true).await?;
        self.sync().await
    }

    /// Add a new template and rerender.
    pub async fn delete_template(&mut self, name: &str) -> Result<(), Box<dyn Error>> {
        self.index.templates.remove(name);
        self.render(|_| true).await?;
        self.sync().await
    }

    /// Render all templates.
    ///
    // Filter limits rerendering to entries which return true.
    pub async fn render<F>(&mut self, filter: F) -> Result<(), Box<dyn Error>>
    where
        F: Fn(&Entry) -> bool,
    {
        let empty_set = HashSet::new();
        let mut renderer = Renderer::new(self.index.templates.values())?;

        for template in self.index.templates.values() {
            let existing_files = self
                .index
                .rendered
                .get(&template.name)
                .unwrap_or(&empty_set);
            let mut new_files = HashSet::new();

            if !template.partial {
                info!("Rendering template {}", template.name);
                let content_type = template.content_type.as_deref().unwrap_or("text/html");
                let file_regex = Regex::new(template.filter.as_deref().unwrap_or(".*"))?;
                let entries: Vec<_> = self
                    .index
                    .entries
                    .values()
                    .filter(|e| !e.hidden && file_regex.is_match(&e.filename))
                    .cloned()
                    .collect();
                renderer.set_entries(entries.clone());
                if template.index {
                    let filename = template.name.to_string();
                    let data = renderer.render_index(&template.name, &filename)?;
                    self.access.put_file(&filename, content_type, data).await?;
                    new_files.insert(filename);
                } else {
                    // Generate a file for each entry.
                    for entry in &entries {
                        let filename = template.make_filename(entry);
                        if filter(entry) {
                            let data = renderer.render_entry(&template.name, &filename, entry)?;
                            self.access.put_file(&filename, content_type, data).await?;
                            new_files.insert(filename);
                        } else if existing_files.contains(&filename) {
                            new_files.insert(filename);
                        }
                    }
                }
            }

            // Remove any orphaned files
            for filename in existing_files {
                if !new_files.contains(filename) {
                    info!("Removing rendered file {}", filename);
                    self.access.remove_file(filename).await?;
                }
            }

            // Update the list of rendered files.
            self.index
                .rendered
                .insert(template.name.to_string(), new_files);
        }

        // Remove renderings of any deleted templates
        for (template, files) in &self.index.rendered {
            if !self.index.templates.contains_key(template) {
                info!("Removing all rendered files for template {}", template);
                for filename in files {
                    self.access.remove_file(filename).await?;
                }
            }
        }
        self.index
            .rendered
            .retain(|k, _| self.index.templates.contains_key(k));

        self.sync().await
    }
}