use std::collections::HashMap;
use std::path::Path;
use std::sync::RwLock;

use git2::BranchType;
use git2::Repository;
use git2::Signature;
use git2::Tree;
use hyper::http::request::Parts;
use serde::Deserialize;
use sputnik::html_escape;

use crate::Branch;
use crate::Context;
use crate::Error;
use crate::Page;
use crate::Response;

pub trait Controller {
    /// Parse the URL into a Branch and file path or intercept the request handling.
    fn parse_url_path<'a>(
        &'a self,
        path: &'a str,
        parts: &Parts,
        repo: &Repository,
    ) -> Result<(Branch, &'a str), Result<Response, Error>>;

    /// Builds an absolute URL path from a given Git branch and file path.
    fn build_url_path<'a>(&self, branch: &Branch, path: &'a str) -> String;

    /// Returns some HTML info to display for the current page.
    fn user_info_html(&self, parts: &Parts) -> Option<String> {
        None
    }

    /// Returns the author/committer signature used to create commits.
    fn signature(&self, repo: &Repository, parts: &Parts) -> Result<Signature, Error>;

    /// Returns whether or not a request is authorized to read a file or list a directory.
    fn may_read_path(&self, ctx: &Context, parts: &Parts) -> bool;

    /// Returns whether or not a request is authorized to write a file.
    fn may_write_path(&self, context: &Context, parts: &Parts) -> bool;

    /// Returns whether or not a request is authorized to (re)move a file.
    fn may_move_path(&self, context: &Context, parts: &Parts) -> bool;

    fn edit_hint_html(&self, context: &Context) -> Option<String> {
        None
    }

    fn before_return_tree_page(
        &self,
        page: &mut Page,
        tree: Option<Tree>,
        context: &Context,
        parts: &Parts,
    );

    /// Executed before writing a file. Return an error to abort the writing process.
    fn before_write(&self, text: &str, ctx: &Context, parts: &mut Parts) -> Result<(), String> {
        Ok(())
    }

    /// Executed after successfully writing a file.
    fn after_write(&self, context: &Context, parts: &mut Parts) {}
}

pub struct SoloController(pub Branch);

impl SoloController {
    pub fn new(repo: &Repository) -> Self {
        Self(Branch(
            repo.find_reference("HEAD")
                .unwrap()
                .symbolic_target()
                .unwrap()
                .strip_prefix("refs/heads/")
                .unwrap()
                .to_owned(),
        ))
    }
}

const USERNAME_HEADER: &str = "Username";

impl Controller for SoloController {
    fn parse_url_path<'a>(
        &'a self,
        path: &'a str,
        parts: &Parts,
        repo: &Repository,
    ) -> Result<(Branch, &'a str), Result<Response, Error>> {
        if parts.headers.contains_key(USERNAME_HEADER) {
            return Err(Err(Error::BadRequest(format!(
                "unexpected header {} (only \
            allowed in multi-user mode), aborting to prevent accidental \
            information leakage",
                USERNAME_HEADER
            ))));
        }

        Ok((self.0.clone(), path))
    }

    fn build_url_path<'a>(&self, branch: &Branch, path: &'a str) -> String {
        format!("/{}", path)
    }

    fn signature(&self, repo: &Repository, parts: &Parts) -> Result<Signature, Error> {
        repo.signature().map_err(|e| Error::Internal(e.to_string()))
    }

    fn may_read_path(&self, ctx: &Context, parts: &Parts) -> bool {
        true
    }

    fn may_write_path(&self, _context: &Context, parts: &Parts) -> bool {
        true
    }

    fn may_move_path(&self, _context: &Context, parts: &Parts) -> bool {
        true
    }

    fn before_return_tree_page(
        &self,
        page: &mut Page,
        tree: Option<Tree>,
        context: &Context,
        parts: &Parts,
    ) {
        if tree.map(|t| t.len()).unwrap_or_default() == 0 {
            page.body.push_str("<p>create files by editing the URL, e.g. <a href='/hello-world.md'>/hello-world.md</a></p>");
        }
    }

    fn before_write(&self, text: &str, ctx: &Context, parts: &mut Parts) -> Result<(), String> {
        if let Some(ext) = ctx.path.extension() {
            validate_formats(text, ext)?;
        }
        Ok(())
    }
}

#[derive(Deserialize)]
#[serde(transparent)]
struct Identities(HashMap<String, Identity>);

pub struct MultiUserController {
    identities: RwLock<Identities>,
}

// using our own struct because git2::Signature isn't thread-safe
#[derive(Deserialize)]
struct Identity {
    name: String,
    email: String,
}

fn parse_identities(repo: &Repository) -> Option<Identities> {
    let rev = repo.revparse_single("refs/heads/gitpad").ok()?;
    let commit = rev.into_commit().ok()?;
    let tree = commit.tree().ok()?;
    let entry = tree.get_path(Path::new("users.toml")).ok()?;
    let blob = repo.find_blob(entry.id()).ok()?;
    toml::from_slice(blob.content()).ok()
}

impl MultiUserController {
    pub fn new(repo: &Repository) -> Self {
        Self {
            identities: RwLock::new(
                parse_identities(repo).unwrap_or_else(|| Identities(HashMap::new())),
            ),
        }
    }
}

const EMPTY_HOME_HINT: &str = "This is your home directory. Create files by editing the URL.";

fn username_from_parts(parts: &Parts) -> Option<&str> {
    parts
        .headers
        .get(USERNAME_HEADER)
        .and_then(|h| h.to_str().ok())
}

fn validate_formats(text: &str, extension: &str) -> Result<(), String> {
    if extension == "toml" {
        toml::from_str::<toml::Value>(text).map_err(|e| e.to_string())?;
    }
    Ok(())
}

fn multi_user_startpage(repo: &Repository) -> Result<Response, Error> {
    // TODO: add domain name to title?
    let mut page = Page {
        title: "GitPad".into(),
        ..Default::default()
    };

    let branches: Vec<_> = repo.branches(Some(BranchType::Local))?.collect();

    page.body.push_str("This GitPad instance has ");

    if branches.is_empty() {
        page.body.push_str("no branches yet.");
    } else {
        page.body.push_str("the following branches:");
        page.body.push_str("<ul>");
        for (branch, _) in repo.branches(Some(BranchType::Local))?.flatten() {
            page.body.push_str(&format!(
                "<li><a href='~{0}/'>~{0}</a></li>",
                html_escape(branch.name()?.unwrap())
            ));
        }
        page.body.push_str("</ul>");
    }

    Ok(page.into())
}

impl Controller for MultiUserController {
    fn parse_url_path<'a>(
        &'a self,
        path: &'a str,
        parts: &Parts,
        repo: &Repository,
    ) -> Result<(Branch, &'a str), Result<Response, Error>> {
        if !parts.headers.contains_key(USERNAME_HEADER) {
            return Err(Err(Error::BadRequest(format!(
                "expected header {} because of multi-user mode \
            (this shouldn't be happening because a reverse-proxy \
            should be used to set this header)",
                USERNAME_HEADER
            ))));
        }
        if path == "/" {
            return Err(multi_user_startpage(repo));
        }

        let mut iter = path.splitn(3, '/');
        iter.next();
        let rev = iter.next().unwrap();
        if !rev.starts_with('~') {
            return Err(Err(Error::NotFound(
                "branch name must be prefixed a tilde (~)".into(),
            )));
        }
        let rev = &rev[1..];
        if rev.trim().is_empty() {
            return Err(Err(Error::NotFound("invalid branch name".into())));
        }
        let rev = Branch(rev.to_owned());
        let unsanitized_path = match iter.next() {
            Some(value) => value,
            None => {
                return Err(Err(Error::MissingTrailingSlash(
                    parts.uri.path().to_string(),
                )))
            }
        };
        if unsanitized_path.is_empty() {
            let username = username_from_parts(parts).unwrap();
            if username != rev.0 {
                let mut page = Page::default();
                return Err(Ok(page.into()));
            }
        }
        Ok((rev, unsanitized_path))
    }

    fn build_url_path<'a>(&self, branch: &Branch, path: &'a str) -> String {
        format!("/~{}/{}", branch.0, path)
    }

    fn user_info_html(&self, parts: &Parts) -> Option<String> {
        let username = username_from_parts(parts).unwrap();
        Some(format!(
            "<a href='/~{0}/' title='your home directory'>~{0}</a>",
            html_escape(username)
        ))
    }

    fn before_return_tree_page(
        &self,
        page: &mut Page,
        tree: Option<Tree>,
        context: &Context,
        parts: &Parts,
    ) {
        let username = username_from_parts(parts).unwrap();
        if context.branch.0 == username && context.path.components().count() == 0 {
            match tree {
                None => page.body.push_str(EMPTY_HOME_HINT),
                Some(tree) => {
                    if tree.iter().count() == 0 {
                        page.body.push_str(EMPTY_HOME_HINT);
                    }
                }
            }
        }
    }

    fn signature(&self, _repo: &Repository, parts: &Parts) -> Result<Signature, Error> {
        // TODO: return proper error message if header missing
        let username = username_from_parts(parts).unwrap();
        if let Some(identity) = self.identities.read().unwrap().0.get(username) {
            Signature::now(identity.name.as_str(), &identity.email)
                .map_err(|e| e.to_string())
                .map_err(Error::Internal)
        } else {
            Signature::now(username, &format!("{}@localhost.invalid", username))
                .map_err(|e| e.to_string())
                .map_err(Error::Internal)
        }
    }

    fn may_read_path(&self, ctx: &Context, parts: &Parts) -> bool {
        let username = username_from_parts(parts).unwrap();
        return ctx.branch.0 == username;
    }

    fn may_write_path(&self, ctx: &Context, parts: &Parts) -> bool {
        let username = username_from_parts(parts).unwrap();
        return ctx.branch.0 == username;
    }

    fn may_move_path(&self, ctx: &Context, parts: &Parts) -> bool {
        ctx.branch.0 == username_from_parts(parts).unwrap()
    }

    fn edit_hint_html(&self, ctx: &Context) -> Option<String> {
        match (ctx.branch.0.as_str(), ctx.path.as_str()) {
            ("gitpad", "users.toml") => {
                return Some(include_str!("static/help_users.toml.html").into());
            }
            _ => {}
        }
        None
    }

    fn before_write(&self, text: &str, ctx: &Context, parts: &mut Parts) -> Result<(), String> {
        match (ctx.branch.0.as_str(), ctx.path.as_str()) {
            ("gitpad", "users.toml") => {
                parts
                    .extensions
                    .insert(toml::from_str::<Identities>(text).map_err(|e| e.to_string())?);
            }
            _ => {
                if let Some(ext) = ctx.path.extension() {
                    validate_formats(text, ext)?;
                }
            }
        }
        Ok(())
    }

    fn after_write(&self, ctx: &Context, parts: &mut Parts) {
        match (ctx.branch.0.as_str(), ctx.path.as_str()) {
            ("gitpad", "users.toml") => {
                *self.identities.write().unwrap() = parts.extensions.remove().unwrap();
            }
            _ => {}
        }
    }
}