//! CSS module exports.
//!
//! [CSS modules](https://github.com/css-modules/css-modules) are a way of locally scoping names in a
//! CSS file. This includes class names, ids, keyframe animation names, and any other places where the
//! [CustomIdent](super::values::ident::CustomIdent) type is used.
//!
//! CSS modules can be enabled using the `css_modules` option when parsing a style sheet. When the
//! style sheet is printed, hashes will be added to any declared names, and references to those names
//! will be updated accordingly. A map of the original names to compiled (hashed) names will be returned.

use crate::error::PrinterErrorKind;
use crate::properties::css_modules::{Composes, ComposesFrom};
use crate::selector::Selectors;
use data_encoding::{Encoding, Specification};
use lazy_static::lazy_static;
use parcel_selectors::SelectorList;
use serde::Serialize;
use std::collections::hash_map::DefaultHasher;
use std::collections::HashMap;
use std::hash::{Hash, Hasher};

/// A referenced name within a CSS module, e.g. via the `composes` property.
///
/// See [CssModuleExport](CssModuleExport).
#[derive(PartialEq, Debug, Clone, Serialize)]
#[serde(tag = "type", rename_all = "lowercase")]
pub enum CssModuleReference {
  /// A local reference.
  Local {
    /// The local (compiled) name for the reference.
    name: String,
  },
  /// A global reference.
  Global {
    /// The referenced global name.
    name: String,
  },
  /// A reference to an export in a different file.
  Dependency {
    /// The name to reference within the dependency.
    name: String,
    /// The dependency specifier for the referenced file.
    specifier: String,
  },
}

/// An exported value from a CSS module.
#[derive(PartialEq, Debug, Clone, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct CssModuleExport {
  /// The local (compiled) name for this export.
  pub name: String,
  /// Other names that are composed by this export.
  pub composes: Vec<CssModuleReference>,
  /// Whether the export is referenced in this file.
  pub is_referenced: bool,
}

/// A map of exported names to values.
pub type CssModuleExports = HashMap<String, CssModuleExport>;

lazy_static! {
  static ref ENCODER: Encoding = {
    let mut spec = Specification::new();
    spec
      .symbols
      .push_str("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890_-");
    spec.encoding().unwrap()
  };
}

pub(crate) struct CssModule<'a> {
  pub hash: &'a str,
  pub exports: &'a mut CssModuleExports,
}

impl<'a> CssModule<'a> {
  pub fn add_local(&mut self, exported: &str, local: &str) {
    self.exports.entry(exported.into()).or_insert_with(|| CssModuleExport {
      name: get_hashed_name(self.hash, local),
      composes: vec![],
      is_referenced: false,
    });
  }

  pub fn reference(&mut self, name: &str) {
    match self.exports.entry(name.into()) {
      std::collections::hash_map::Entry::Occupied(mut entry) => {
        entry.get_mut().is_referenced = true;
      }
      std::collections::hash_map::Entry::Vacant(entry) => {
        entry.insert(CssModuleExport {
          name: get_hashed_name(self.hash, name),
          composes: vec![],
          is_referenced: true,
        });
      }
    }
  }

  pub fn handle_composes(
    &mut self,
    selectors: &SelectorList<Selectors>,
    composes: &Composes,
  ) -> Result<(), PrinterErrorKind> {
    for sel in &selectors.0 {
      if sel.len() == 1 {
        match sel.iter_raw_match_order().next().unwrap() {
          parcel_selectors::parser::Component::Class(ref id) => {
            for name in &composes.names {
              let reference = match &composes.from {
                None => CssModuleReference::Local {
                  name: get_hashed_name(self.hash, name.0.as_ref()),
                },
                Some(ComposesFrom::Global) => CssModuleReference::Global {
                  name: name.0.as_ref().into(),
                },
                Some(ComposesFrom::File(file)) => CssModuleReference::Dependency {
                  name: name.0.to_string(),
                  specifier: file.to_string(),
                },
              };

              let export = self.exports.get_mut(&id.0.as_ref().to_owned()).unwrap();
              if !export.composes.contains(&reference) {
                export.composes.push(reference);
              }
            }
            continue;
          }
          _ => {}
        }
      }

      // The composes property can only be used within a simple class selector.
      return Err(PrinterErrorKind::InvalidComposesSelector);
    }

    Ok(())
  }
}

fn get_hashed_name(hash: &str, name: &str) -> String {
  // Hash must come first so that CSS grid identifiers work.
  // This is because grid lines may have an implicit -start or -end appended.
  format!("{}_{}", hash, name)
}

pub(crate) fn hash(s: &str) -> String {
  let mut hasher = DefaultHasher::new();
  s.hash(&mut hasher);
  let hash = hasher.finish() as u32;

  let hash = ENCODER.encode(&hash.to_le_bytes());
  if matches!(hash.as_bytes()[0], b'0'..=b'9') {
    format!("_{}", hash)
  } else {
    hash
  }
}