use std::cell::RefCell;
use std::collections::{BTreeMap, BTreeSet};
use std::rc::Rc;
use std::sync::Arc;

use crate::authority::SourceAuthority;
use crate::package_config::{PackageConfig, Source};
use crate::registry::{PackageStore, checksum};
use avril_core::Error;
use url::Url;

use crate::local_packages::{
    PackageMapping, Resolution, declared_name, package_mapping, select_binding,
};

/// A remote mapping step: an already-decided resolution, or an export of
/// a directory by key. The adapters acquire (`export`) or reuse prepared
/// metadata (`resolve_export_meta`) afterwards.
enum RemoteStep {
    Done(Resolution),
    Export(Url, String),
}

struct Package {
    requested: Url,
    directory: Url,
    identity: (Url, String),
    config: PackageConfig,
    source: String,
    url: Url,
    bindings: RefCell<Option<BTreeMap<String, Source>>>,
}

impl Package {
    fn region(&self, name: &str) -> Option<&Url> {
        if name.starts_with(self.directory.as_str()) {
            Some(&self.directory)
        } else if name.starts_with(self.requested.as_str()) {
            Some(&self.requested)
        } else {
            None
        }
    }
}

#[derive(Clone)]
struct Owner {
    package: Rc<Package>,
    region: Url,
}

pub struct RemotePackages {
    authority: SourceAuthority,
    store: Arc<PackageStore>,
    packages: RefCell<BTreeMap<Url, Rc<Package>>>,
    owners: RefCell<BTreeMap<String, Option<Owner>>>,
    authorities: RefCell<BTreeMap<(Url, String), BTreeSet<Url>>>,
}

impl RemotePackages {
    pub fn new(authority: SourceAuthority, store: Arc<PackageStore>) -> Self {
        Self {
            authority,
            store,
            packages: RefCell::default(),
            owners: RefCell::default(),
            authorities: RefCell::default(),
        }
    }

    fn check(&self, package: &Package) -> Result<(), Error> {
        if let Some(urls) = self.authorities.borrow().get(&package.identity) {
            for url in urls {
                self.store
                    .check_acquired_remote(url.as_str(), &self.authority)
                    .map_err(|error| Error::Module(error.to_string()))?;
            }
        }
        self.store
            .check_acquired_remote(package.url.as_str(), &self.authority)
            .map_err(|error| Error::Module(error.to_string()))
    }

    async fn load(&self, directory: &Url) -> Result<Rc<Package>, Error> {
        let config_url = directory
            .join("avril.conf")
            .map_err(|error| Error::Module(error.to_string()))?;
        self.authority
            .check_remote_module(&config_url)
            .map_err(|error| Error::Module(error.to_string()))?;
        if let Some(package) = self.packages.borrow().get(directory).cloned() {
            self.check(&package)?;
            return Ok(package);
        }
        let source = self
            .store
            .remote_config(config_url.as_str())
            .await
            .map_err(|error| Error::Module(error.to_string()))?;
        let base = Url::parse(
            &self
                .store
                .remote_base(config_url.as_str())
                .map_err(|error| Error::Module(error.to_string()))?,
        )
        .map_err(|error| Error::Module(error.to_string()))?;
        let config = PackageConfig::parse(&source, &base)
            .map_err(|error| Error::Module(error.render(config_url.as_str(), &source)))?;
        let package = Rc::new(Package {
            requested: directory.clone(),
            directory: base.join("./").unwrap(),
            identity: (base, checksum(source.as_bytes())),
            config,
            source,
            url: config_url,
            bindings: RefCell::default(),
        });
        self.check(&package)?;
        Ok(self
            .packages
            .borrow_mut()
            .entry(directory.clone())
            .or_insert(package)
            .clone())
    }

    pub async fn bindings(
        &self,
        config: &PackageConfig,
    ) -> Result<BTreeMap<String, Source>, crate::config::Error> {
        config
            .bindings(|source| async move {
                match source {
                    Source::Local(directory) => declared_name(&directory, &self.authority),
                    Source::Http(directory) => self
                        .load(&directory)
                        .await
                        .map(|package| package.config.name.clone())
                        .map_err(|error| error.to_string()),
                    Source::Jsr(_) => unreachable!(),
                    Source::Npm(_) => unreachable!(),
                }
            })
            .await
    }

    fn owner(&self, name: &str) -> Option<Owner> {
        self.owners.borrow().get(name).cloned().flatten()
    }

    fn claim(&self, name: &str, owner: Option<Owner>) -> Result<(), Error> {
        let mut owners = self.owners.borrow_mut();
        if let Some(previous) = owners.get(name) {
            let same = match (previous, &owner) {
                (None, None) => true,
                (Some(previous), Some(owner)) => {
                    previous.package.identity == owner.package.identity
                        && previous.region == owner.region
                }
                _ => false,
            };
            if !same {
                let label = |owner: &Option<Owner>| {
                    owner
                        .as_ref()
                        .map(|owner| owner.package.url.as_str())
                        .unwrap_or("plain HTTP module")
                        .to_owned()
                };
                return Err(Error::Module(format!(
                    "Conflicting remote package ownership for {name}: {} versus {}",
                    label(previous),
                    label(&owner)
                )));
            }
        }
        if let Some(owner) = &owner {
            self.check(&owner.package)?;
            self.authorities
                .borrow_mut()
                .entry(owner.package.identity.clone())
                .or_default()
                .insert(owner.package.url.clone());
        }
        owners.entry(name.to_owned()).or_insert(owner);
        Ok(())
    }

    async fn owner_for(&self, name: &str, mut directory: Url) -> Result<Owner, Error> {
        let mut seen = BTreeSet::new();
        loop {
            if !seen.insert(directory.clone()) {
                return Err(Error::Module(format!(
                    "Cyclic remote package boundary for {name}: {directory}"
                )));
            }
            let package = self.load(&directory).await?;
            let region = package
                .region(name)
                .ok_or_else(|| {
                    Error::Module(format!("Module is outside its remote package: {name}"))
                })?
                .clone();
            let length = region.as_str().len();
            let child = package
                .config
                .dependencies
                .iter()
                .filter_map(|dependency| match &dependency.source {
                    Source::Http(directory)
                        if name.starts_with(directory.as_str())
                            && directory.as_str().len() > length =>
                    {
                        Some(directory)
                    }
                    _ => None,
                })
                .max_by_key(|directory| directory.as_str().len())
                .cloned();
            match child {
                Some(child) => directory = child,
                None => return Ok(Owner { package, region }),
            }
        }
    }

    pub async fn import(&self, name: &str, referrer: &str, local: &[Url]) -> Result<(), Error> {
        if name.starts_with(self.store.options().jsr_registry.as_str()) {
            return self.claim(name, None);
        }
        let owner = self.owner(referrer);
        let mut selected = owner
            .as_ref()
            .filter(|owner| name.starts_with(owner.region.as_str()))
            .map(|owner| (owner.region.as_str().len(), owner.package.requested.clone()));
        let declarations: Vec<_> = match &owner {
            Some(owner) => {
                self.check(&owner.package)?;
                owner
                    .package
                    .config
                    .dependencies
                    .iter()
                    .filter_map(|dependency| match &dependency.source {
                        Source::Http(directory) => Some(directory.clone()),
                        _ => None,
                    })
                    .collect()
            }
            None => local.to_vec(),
        };
        for directory in declarations {
            let length = directory.as_str().len();
            if name.starts_with(directory.as_str())
                && selected
                    .as_ref()
                    .is_none_or(|(previous, _)| length > *previous)
            {
                selected = Some((length, directory));
            }
        }
        let owner = match selected {
            Some((_, directory)) => Some(self.owner_for(name, directory).await?),
            None => None,
        };
        self.claim(name, owner)
    }

    pub async fn export(
        &self,
        directory: &Url,
        key: &str,
        specifier: &str,
    ) -> Result<Resolution, Error> {
        let package = self.load(directory).await?;
        let name = self.export_target(&package, key, specifier)?;
        let owner = self.owner_for(&name, directory.clone()).await?;
        self.claim(&name, Some(owner))?;
        Ok(Resolution::Remote(name))
    }

    pub async fn initialize(&self, name: &str) -> Result<(), Error> {
        let owner = self
            .owners
            .borrow_mut()
            .entry(name.to_owned())
            .or_default()
            .clone();
        if let Some(owner) = owner {
            let package = owner.package;
            self.check(&package)?;
            if package.bindings.borrow().is_none() {
                let bindings = self.bindings(&package.config).await.map_err(|error| {
                    Error::Module(error.render(package.url.as_str(), &package.source))
                })?;
                self.check(&package)?;
                *package.bindings.borrow_mut() = Some(bindings);
            }
        }
        Ok(())
    }

    /// Shared synchronous decision over an owned remote package: what its
    /// own imports/scopes select, falling back to its prepared bindings.
    /// `None` selects nothing: the caller resolves the raw specifier, so
    /// the prepared path still never initializes or loads packages.
    fn classify(
        &self,
        package: &Rc<Package>,
        specifier: &str,
        referrer: &str,
    ) -> Result<Option<RemoteStep>, Error> {
        let url = Url::parse(
            &self
                .store
                .remote_base(referrer)
                .map_err(|error| Error::Module(error.to_string()))?,
        )
        .unwrap();
        match package_mapping(&package.config, specifier, &url)
            .map_err(|error| Error::Module(error.to_string()))?
        {
            Some(PackageMapping::Specifier(target)) => {
                Ok(Some(RemoteStep::Done(Resolution::Specifier(target))))
            }
            Some(PackageMapping::Export(key)) => {
                Ok(Some(RemoteStep::Export(package.requested.clone(), key)))
            }
            None => match select_binding(package.bindings.borrow().as_ref(), specifier) {
                Some((key, Source::Http(directory))) => {
                    Ok(Some(RemoteStep::Export(directory, key)))
                }
                _ => Ok(None),
            },
        }
    }

    pub fn type_override(&self, specifier: &str, referrer: &str) -> Result<Option<String>, Error> {
        let Some(owner) = self.owner(referrer) else {
            return Ok(None);
        };
        self.check(&owner.package)?;
        let referrer_url =
            Url::parse(referrer).map_err(|error| Error::Module(error.to_string()))?;
        let result = owner
            .package
            .config
            .types
            .imports
            .resolve(specifier, &referrer_url)
            .map_err(|error| Error::Module(error.to_string()))?;
        self.check(&owner.package)?;
        Ok(result)
    }

    pub fn type_globals(&self, referrer: &str) -> Result<Vec<String>, Error> {
        let Some(owner) = self.owner(referrer) else {
            return Ok(Vec::new());
        };
        self.check(&owner.package)?;
        let globals = owner.package.config.types.globals.clone();
        self.check(&owner.package)?;
        Ok(globals)
    }

    pub async fn resolve(
        &self,
        specifier: &str,
        referrer: &str,
    ) -> Result<Option<Resolution>, Error> {
        let Some(owner) = self.owner(referrer) else {
            return Ok(None);
        };
        let package = owner.package;
        self.initialize(referrer).await?;
        self.check(&package)?;
        match self.classify(&package, specifier, referrer)? {
            None => Ok(None),
            Some(RemoteStep::Done(resolution)) => Ok(Some(resolution)),
            Some(RemoteStep::Export(directory, key)) => {
                self.export(&directory, &key, specifier).await.map(Some)
            }
        }
    }

    pub fn resolve_export_meta(
        &self,
        directory: &Url,
        key: &str,
        specifier: &str,
    ) -> Result<Resolution, Error> {
        let package = self
            .packages
            .borrow()
            .get(directory)
            .cloned()
            .ok_or_else(|| {
                Error::Module(format!("Package metadata is not prepared: {directory}"))
            })?;
        self.export_target(&package, key, specifier)
            .map(Resolution::Remote)
    }

    fn export_target(
        &self,
        package: &Package,
        key: &str,
        specifier: &str,
    ) -> Result<String, Error> {
        self.check(package)?;
        if package.config.exports.is_empty() {
            return Err(Error::Module(format!(
                "Dependency {specifier:?} has no exports: {}",
                package.url
            )));
        }
        let export = package.config.exports.get(key).ok_or_else(|| {
            Error::Module(format!(
                "Package has no export {key:?} for {specifier:?}: {}",
                package.url
            ))
        })?;
        self.authority
            .check_remote_module(&export.target)
            .map_err(|error| Error::Module(error.to_string()))?;
        Ok(export.target.to_string())
    }

    pub fn resolve_import_meta(
        &self,
        specifier: &str,
        referrer: &str,
    ) -> Result<Option<Resolution>, Error> {
        let Some(owner) = self.owner(referrer) else {
            return Ok(None);
        };
        let package = owner.package;
        self.check(&package)?;
        match self.classify(&package, specifier, referrer)? {
            None => Ok(None),
            Some(RemoteStep::Done(resolution)) => Ok(Some(resolution)),
            Some(RemoteStep::Export(directory, key)) => self
                .resolve_export_meta(&directory, &key, specifier)
                .map(Some),
        }
    }

    pub fn metadata(&self, name: &str) -> Result<Option<serde_json::Value>, Error> {
        let Some(owner) = self.owner(name) else {
            return Ok(None);
        };
        let package = owner.package;
        self.check(&package)?;
        let exports: BTreeMap<_, _> = package
            .config
            .exports
            .iter()
            .map(|(key, export)| (key, export.target.as_str()))
            .collect();
        let bindings = package.bindings.borrow();
        let dependencies: BTreeMap<_, _> = bindings
            .as_ref()
            .into_iter()
            .flatten()
            .map(|(name, source)| {
                (
                    name,
                    match source {
                        Source::Http(url) => serde_json::json!(url.as_str()),
                        Source::Jsr(request) => serde_json::json!(request.specifier),
                        Source::Npm(request) => serde_json::json!(request.request_key()),
                        Source::Local(directory) => serde_json::json!(directory),
                    },
                )
            })
            .collect();
        Ok(Some(serde_json::json!({
            "config": package.identity.0.as_str(), "name": package.config.name, "version": package.config.version,
            "description": package.config.description, "exports": exports, "dependencies": dependencies
        })))
    }
}