// file      : libbuild2/rule.hxx -*- C++ -*-
// license   : MIT; see accompanying LICENSE file

#ifndef LIBBUILD2_RULE_HXX
#define LIBBUILD2_RULE_HXX

#include <libbuild2/types.hxx>
#include <libbuild2/forward.hxx>
#include <libbuild2/utility.hxx>

#include <libbuild2/action.hxx>
#include <libbuild2/target.hxx>
#include <libbuild2/recipe.hxx>

#include <libbuild2/export.hxx>

namespace build2
{
  // Rule interface (see also simple_rule below for a simplified version).
  //
  // Once a rule is registered (for a scope), it is treated as immutable. If
  // you need to modify some state (e.g., counters or some such), then make
  // sure things are MT-safe.
  //
  // Note: match() is only called once but may not be followed by apply().
  //
  // The match_extra argument is used to pass additional information that is
  // only needed by some rule implementations. It is also a way for us to
  // later pass more information without breaking source compatibility.
  //
  struct match_extra
  {
  };

  class LIBBUILD2_SYMEXPORT rule
  {
  public:
    virtual bool
    match (action, target&, const string& hint, match_extra&) const = 0;

    virtual recipe
    apply (action, target&, match_extra&) const = 0;

    rule () = default;

    virtual
    ~rule ();

    rule (const rule&) = delete;
    rule& operator= (const rule&) = delete;
  };

  // Simplified interface for rules that don't care about the extras.
  //
  class LIBBUILD2_SYMEXPORT simple_rule: public rule
  {
  public:
    virtual bool
    match (action, target&, const string& hint) const = 0;

    virtual recipe
    apply (action, target&) const = 0;

    virtual bool
    match (action, target&, const string&, match_extra&) const override;

    virtual recipe
    apply (action, target&, match_extra&) const override;
  };

  // Fallback rule that only matches if the file exists. It will also match
  // an mtime_target provided it has a set timestamp.
  //
  class LIBBUILD2_SYMEXPORT file_rule: public simple_rule
  {
  public:
    virtual bool
    match (action, target&, const string&) const override;

    virtual recipe
    apply (action, target&) const override;

    file_rule () {}
    static const file_rule instance;
  };

  class LIBBUILD2_SYMEXPORT alias_rule: public simple_rule
  {
  public:
    virtual bool
    match (action, target&, const string&) const override;

    virtual recipe
    apply (action, target&) const override;

    alias_rule () {}
    static const alias_rule instance;
  };

  // Note that this rule ignores the dry_run flag; see mkdir() in filesystem
  // for the rationale.
  //
  class LIBBUILD2_SYMEXPORT fsdir_rule: public simple_rule
  {
  public:
    virtual bool
    match (action, target&, const string&) const override;

    virtual recipe
    apply (action, target&) const override;

    static target_state
    perform_update (action, const target&);

    static target_state
    perform_clean (action, const target&);

    // Sometimes, as an optimization, we want to emulate execute_direct()
    // of fsdir{} without the overhead of switching to the execute phase.
    //
    static void
    perform_update_direct (action, const target&);

    fsdir_rule () {}
    static const fsdir_rule instance;
  };

  // Fallback rule that always matches and does nothing.
  //
  class LIBBUILD2_SYMEXPORT noop_rule: public simple_rule
  {
  public:
    virtual bool
    match (action, target&, const string&) const override;

    virtual recipe
    apply (action, target&) const override;

    noop_rule () {}
    static const noop_rule instance;
  };

  // Ad hoc rule.
  //
  // Note: not exported.
  //
  class adhoc_rule: public rule
  {
  public:
    location_value loc;     // Buildfile location of the recipe.
    size_t         braces;  // Number of braces in multi-brace tokens.

    adhoc_rule (const char* name, const location& l, size_t b)
      : loc (l),
        braces (b),
        rule_match (name, static_cast<const rule&> (*this)) {}

    // Set the rule text, handle any recipe-specific attributes, and return
    // true if the recipe builds anything in the build/recipes/ directory and
    // therefore requires cleanup.
    //
    virtual bool
    recipe_text (context&, const target&, string&&, attributes&) = 0;

  public:
    // Some of the operations come in compensating pairs, such as update and
    // clean, install and uninstall. An ad hoc rule implementation may choose
    // to provide a fallback implementation of a compensating operation if it
    // is providing the other half (passed in the fallback argument).
    //
    // The default implementation calls rule::match() if fallback is absent
    // and returns false if fallback is present. So an implementation that
    // doesn't care about this semantics can implement the straight rule
    // interface.
    //
    virtual bool
    match (action, target&, const string&, match_extra&,
           optional<action> fallback) const;

    virtual bool
    match (action, target&, const string&, match_extra&) const override;

    // Dump support.
    //
    virtual void
    dump_attributes (ostream&) const;

    virtual void
    dump_text (ostream&, string& indentation) const = 0;

    // Implementation details.
    //
  public:
    // The name in rule_match is used as a hint and as a name in diagnostics.
    // The former does not apply to us (but will apply to ad hoc rules) while
    // latter does. As a result, we use special-looking "<ad hoc X recipe>"
    // names.
    //
    build2::rule_match rule_match;

    static const dir_path recipes_build_dir;

    // Scope operation callback that cleans up ad hoc recipe builds.
    //
    static target_state
    clean_recipes_build (action, const scope&, const dir&);
  };

  // A mix-in interface for ad hoc rules that support recipes with deadlines.
  //
  class adhoc_rule_with_deadline
  {
  public:
    virtual
    ~adhoc_rule_with_deadline ();

    // Return empty recipe if one with the deadline cannot be provided for
    // this action. In this case the caller may fallback to the normal
    // apply().
    //
    virtual recipe
    apply (action, target&, match_extra&, const optional<timestamp>&) const = 0;
  };
}

#endif // LIBBUILD2_RULE_HXX