// Copyright 2016 The Servo Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! A crate to create static string caches at compiletime.
//!
//! # Examples
//!
//! With static atoms:
//!
//! In `Cargo.toml`:
//!
//! ```toml
//! [package]
//! build = "build.rs"
//!
//! [dependencies]
//! string_cache = "0.8"
//!
//! [build-dependencies]
//! string_cache_codegen = "0.5"
//! ```
//!
//! In `build.rs`:
//!
//! ```no_run
//! extern crate string_cache_codegen;
//!
//! use std::env;
//! use std::path::Path;
//!
//! fn main() {
//!     string_cache_codegen::AtomType::new("foo::FooAtom", "foo_atom!")
//!         .atoms(&["foo", "bar"])
//!         .write_to_file(&Path::new(&env::var("OUT_DIR").unwrap()).join("foo_atom.rs"))
//!         .unwrap()
//! }
//! ```
//!
//! In `lib.rs`:
//!
//! ```ignore
//! extern crate string_cache;
//!
//! mod foo {
//!     include!(concat!(env!("OUT_DIR"), "/foo_atom.rs"));
//! }
//! ```
//!
//! The generated code will define a `FooAtom` type and a `foo_atom!` macro.
//! The macro can be used in expression or patterns, with strings listed in `build.rs`.
//! For example:
//!
//! ```ignore
//! fn compute_something(input: &foo::FooAtom) -> u32 {
//!     match *input {
//!         foo_atom!("foo") => 1,
//!         foo_atom!("bar") => 2,
//!         _ => 3,
//!     }
//! }
//! ```
//!

#![recursion_limit = "128"]

use quote::quote;
use std::collections::HashSet;
use std::fs::File;
use std::io::{self, BufWriter, Write};
use std::path::Path;

/// A builder for a static atom set and relevant macros
pub struct AtomType {
    path: String,
    atom_doc: Option<String>,
    static_set_doc: Option<String>,
    macro_name: String,
    macro_doc: Option<String>,
    atoms: HashSet<String>,
}

impl AtomType {
    /// Constructs a new static atom set builder
    ///
    /// `path` is a path within a crate of the atom type that will be created.
    /// e.g. `"FooAtom"` at the crate root or `"foo::Atom"` if the generated code
    /// is included in a `foo` module.
    ///
    /// `macro_name` must end with `!`.
    ///
    /// For example, `AtomType::new("foo::FooAtom", "foo_atom!")` will generate:
    ///
    /// ```ignore
    /// pub type FooAtom = ::string_cache::Atom<FooAtomStaticSet>;
    /// pub struct FooAtomStaticSet;
    /// impl ::string_cache::StaticAtomSet for FooAtomStaticSet {
    ///     // ...
    /// }
    /// #[macro_export]
    /// macro_rules foo_atom {
    ///    // Expands to: $crate::foo::FooAtom { … }
    /// }
    /// ```
    pub fn new(path: &str, macro_name: &str) -> Self {
        assert!(macro_name.ends_with("!"), "`macro_name` must end with '!'");
        AtomType {
            path: path.to_owned(),
            macro_name: macro_name[..macro_name.len() - "!".len()].to_owned(),
            atom_doc: None,
            static_set_doc: None,
            macro_doc: None,
            atoms: HashSet::new(),
        }
    }

    /// Add some documentation to the generated Atom type alias.
    ///
    /// This can help the user know that the type uses interned strings.
    ///
    /// Note that `docs` should not contain the `///` at the front of normal docs.
    pub fn with_atom_doc(&mut self, docs: &str) -> &mut Self {
        self.atom_doc = Some(docs.to_owned());
        self
    }

    /// Add some documentation to the generated static set.
    ///
    /// This can help the user know that this type is zero-sized and just references a static
    /// lookup table, or point them to the `Atom` type alias for more info.
    ///
    /// Note that `docs` should not contain the `///` at the front of normal docs.
    pub fn with_static_set_doc(&mut self, docs: &str) -> &mut Self {
        self.static_set_doc = Some(docs.to_owned());
        self
    }

    /// Add some documentation to the generated macro.
    ///
    /// Note that `docs` should not contain the `///` at the front of normal docs.
    pub fn with_macro_doc(&mut self, docs: &str) -> &mut Self {
        self.macro_doc = Some(docs.to_owned());
        self
    }

    /// Adds an atom to the builder
    pub fn atom(&mut self, s: &str) -> &mut Self {
        self.atoms.insert(s.to_owned());
        self
    }

    /// Adds multiple atoms to the builder
    pub fn atoms<I>(&mut self, iter: I) -> &mut Self
    where
        I: IntoIterator,
        I::Item: AsRef<str>,
    {
        self.atoms
            .extend(iter.into_iter().map(|s| s.as_ref().to_owned()));
        self
    }

    /// Write generated code to `destination`.
    pub fn write_to<W>(&mut self, mut destination: W) -> io::Result<()>
    where
        W: Write,
    {
        destination.write_all(
            self.to_tokens()
                .to_string()
                // Insert some newlines to make the generated code slightly easier to read.
                .replace(" [ \"", "[\n\"")
                .replace("\" , ", "\",\n")
                .replace(" ( \"", "\n( \"")
                .replace("; ", ";\n")
                .as_bytes(),
        )
    }

    fn to_tokens(&mut self) -> proc_macro2::TokenStream {
        // `impl Default for Atom` requires the empty string to be in the static set.
        // This also makes sure the set in non-empty,
        // which would cause divisions by zero in rust-phf.
        self.atoms.insert(String::new());

        let atoms: Vec<&str> = self.atoms.iter().map(|s| &**s).collect();
        let hash_state = phf_generator::generate_hash(&atoms);
        let phf_generator::HashState { key, disps, map } = hash_state;
        let (disps0, disps1): (Vec<_>, Vec<_>) = disps.into_iter().unzip();
        let atoms: Vec<&str> = map.iter().map(|&idx| atoms[idx]).collect();
        let empty_string_index = atoms.iter().position(|s| s.is_empty()).unwrap() as u32;
        let indices = 0..atoms.len() as u32;

        let hashes: Vec<u32> = atoms
            .iter()
            .map(|string| {
                let hash = phf_shared::hash(string, &key);
                (hash.g ^ hash.f1) as u32
            })
            .collect();

        let mut path_parts = self.path.rsplitn(2, "::");
        let type_name = path_parts.next().unwrap();
        let module = match path_parts.next() {
            Some(m) => format!("$crate::{}", m),
            None => format!("$crate"),
        };
        let atom_doc = match self.atom_doc {
            Some(ref doc) => quote!(#[doc = #doc]),
            None => quote!(),
        };
        let static_set_doc = match self.static_set_doc {
            Some(ref doc) => quote!(#[doc = #doc]),
            None => quote!(),
        };
        let macro_doc = match self.macro_doc {
            Some(ref doc) => quote!(#[doc = #doc]),
            None => quote!(),
        };
        let new_term =
            |string: &str| proc_macro2::Ident::new(string, proc_macro2::Span::call_site());
        let static_set_name = new_term(&format!("{}StaticSet", type_name));
        let type_name = new_term(type_name);
        let macro_name = new_term(&*self.macro_name);
        let module = module.parse::<proc_macro2::TokenStream>().unwrap();
        let atom_prefix = format!("ATOM_{}_", type_name.to_string().to_uppercase());
        let const_names: Vec<_> = atoms
            .iter()
            .map(|atom| {
                let mut name = atom_prefix.clone();
                for c in atom.chars() {
                    name.push_str(&format!("_{:02X}", c as u32))
                }
                new_term(&name)
            })
            .collect();

        quote! {
            #atom_doc
            pub type #type_name = ::string_cache::Atom<#static_set_name>;

            #static_set_doc
            #[derive(PartialEq, Eq, PartialOrd, Ord)]
            pub struct #static_set_name;

            impl ::string_cache::StaticAtomSet for #static_set_name {
                fn get() -> &'static ::string_cache::PhfStrSet {
                    static SET: ::string_cache::PhfStrSet = ::string_cache::PhfStrSet {
                        key: #key,
                        disps: &[#((#disps0, #disps1)),*],
                        atoms: &[#(#atoms),*],
                        hashes: &[#(#hashes),*]
                    };
                    &SET
                }
                fn empty_string_index() -> u32 {
                    #empty_string_index
                }
            }

            #(
                pub const #const_names: #type_name = #type_name::pack_static(#indices);
            )*

            #macro_doc
            #[macro_export]
            macro_rules! #macro_name {
                #(
                    (#atoms) => { #module::#const_names };
                )*
            }
        }
    }

    /// Create a new file at `path` and write generated code there.
    ///
    /// Typical usage:
    /// `.write_to_file(&Path::new(&env::var("OUT_DIR").unwrap()).join("foo_atom.rs"))`
    pub fn write_to_file(&mut self, path: &Path) -> io::Result<()> {
        self.write_to(BufWriter::new(File::create(path)?))
    }
}
