// file      : build/variable -*- C++ -*-
// copyright : Copyright (c) 2014-2015 Code Synthesis Tools CC
// license   : MIT; see accompanying LICENSE file

#ifndef BUILD_VARIABLE
#define BUILD_VARIABLE

#include <string>
#include <memory>        // unique_ptr
#include <utility>       // move()
#include <cassert>
#include <functional>    // hash
#include <typeindex>
#include <unordered_set>

#include <build/path>
#include <build/name>
#include <build/prefix-map>

namespace build
{
  class scope;
  struct value;

  struct value_type
  {
    std::type_index id;
    value* (*const factory) ();
  };

  // variable
  //
  // The two variables are considered the same if they have the same name.
  //
  struct variable
  {
    explicit
    variable (std::string n): name (std::move (n)), type (nullptr) {}

    std::string name;
    const value_type* type; // If NULL, then this variable has no fixed type.
  };

  inline bool
  operator== (const variable& x, const variable& y) {return x.name == y.name;}

  typedef std::reference_wrapper<const variable> variable_cref;

  // value
  //
  struct value
  {
    typedef build::scope scope_type;

    virtual
    ~value () = default;

    value (scope_type& s): scope (s) {}

    scope_type& scope; // Scope to which this value belongs.
  };
  typedef std::unique_ptr<value> value_ptr;

  struct list_value: value
  {
    list_value (scope_type& s, names d): value (s), data (std::move (d)) {}

    list_value (scope_type& s, std::string d)
        : value (s)
    {
      data.emplace_back (std::move (d));
    }

    // Note: stored in name as a directory.
    //
    list_value (scope_type& s, path d)
        : value (s)
    {
      data.emplace_back (std::move (d));
    }

    names data;
  };
  typedef std::unique_ptr<list_value> list_value_ptr;

  // value_proxy
  //
  struct value_proxy
  {
    explicit operator bool () const {return p != nullptr && *p != nullptr;}
    explicit operator value_ptr& () const {return *p;}

    // Get interface. See available specializations below.
    //
    template <typename T>
    T
    as () const = delete;

    // Set interface.
    //
    const value_proxy&
    operator= (value_ptr v) const
    {
      assert (v == nullptr || &v->scope == s);
      *p = std::move (v);
      return *this;
    }

    const value_proxy&
    operator= (std::string v) const
    {
      // In most cases this is used to initialize a new variable, so
      // don't bother trying to optimize for the case where p is not
      // NULL.
      //
      p->reset (new list_value (*s, std::move (v)));
      return *this;
    }

    // Note: stored in name as a directory.
    //
    const value_proxy&
    operator= (path v) const
    {
      p->reset (new list_value (*s, std::move (v)));
      return *this;
    }

    // Implementation details.
    //
    explicit
    value_proxy (value_ptr* p, scope* s): p (p), s (s) {}

  protected:
    value_ptr* p;
    scope* s;
  };

  template <>
  list_value& value_proxy::
  as<list_value&> () const;

  template <>
  const std::string& value_proxy::
  as<const std::string&> () const;

  // Note: get the name's directory.
  //
  template <>
  const path& value_proxy::
  as<const path&> () const;
}

namespace std
{
  template <>
  struct hash<build::variable>: hash<string>
  {
    size_t
    operator() (const build::variable& v) const noexcept
    {
      return hash<string>::operator() (v.name);
    }
  };
}

namespace build
{
  // variable_pool
  //
  struct variable_set: std::unordered_set<variable>
  {
    // @@ Need to check/set type?
    //
    const variable&
    find (std::string name) {return *emplace (std::move (name)).first;}
  };

  extern variable_set variable_pool;

  // variable_map
  //
  template <>
  struct compare_prefix<variable_cref>: compare_prefix<std::string>
  {
    typedef compare_prefix<std::string> base;

    explicit
    compare_prefix (char d): base (d) {}

    bool
    operator() (const variable& x, const variable& y) const
    {
      return base::operator() (x.name, y.name);
    }

    bool
    prefix (const variable& p, const variable& k) const
    {
      return base::prefix (p.name, k.name);
    }
  };

  struct variable_map: prefix_map<variable_cref, value_ptr, '.'>
  {
    typedef prefix_map<variable_cref, value_ptr, '.'> base;

    value_proxy
    operator[] (const std::string& v)
    {
      return operator[] (variable_pool.find (v));
    }

    value_proxy
    operator[] (const variable& v)
    {
      return value_proxy (&base::operator[] (v), &scope_);
    }

    explicit
    variable_map (scope& s): scope_ (s) {}

  private:
    scope& scope_; // Scope to which this map belongs (and all its value).
  };
}

#endif // BUILD_VARIABLE