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

#include <build/cxx/rule>

#include <cstddef>  // size_t
#include <cstdlib>  // exit
#include <string>
#include <vector>
#include <iostream>

#include <ext/stdio_filebuf.h>

#include <build/scope>
#include <build/algorithm>
#include <build/process>
#include <build/timestamp>
#include <build/diagnostics>
#include <build/context>

using namespace std;

namespace build
{
  namespace cxx
  {
    // compile
    //
    recipe compile::
    match (target& t, bool single, std::string& hint) const
    {
      tracer tr ("cxx::compile::match");

      // @@ TODO:
      //
      // - check prerequisites: single source file
      // - check prerequisites: the rest are headers (issue warning at v=1?)
      // - if path already assigned, verify extension
      //
      // @@ Q:
      //
      // - if there is no .cxx, are we going to check if the one derived
      //   from target exist or can be built? If we do that, then it
      //   probably makes sense to try other rules first (two passes).
      //
      // - Wouldn't it make sense to cache source file? Careful: unloading
      //   of dependency info.
      //

      // See if we have a source file.
      //
      prerequisite* sp (nullptr);
      for (prerequisite& p: t.prerequisites)
      {
        if (p.type.id == typeid (cxx))
        {
          sp = &p;
          break;
        }
      }

      if (sp == nullptr)
      {
        trace (3, [&]{tr << "no c++ source file for target " << t;});
        return recipe ();
      }

      // Derive object file name from target name.
      //
      obj& o (dynamic_cast<obj&> (t));

      if (o.path ().empty ())
        o.path (o.directory / path (o.name + ".o"));

      // Resolve prerequisite to target and match it to a rule. We need
      // this in order to get the source file path for prerequisite
      // injections.
      //
      cxx* st (
        dynamic_cast<cxx*> (
          sp->target != nullptr ? sp->target : search (*sp)));

      if (st != nullptr)
      {
        if (st->recipe () || build::match (*st))
        {
          // Don't bother if the file does not exist.
          //
          if (st->mtime () != timestamp_nonexistent)
            inject_prerequisites (o, *st, sp->scope);
        }
      }

      return recipe (&update);
    }

    // Return the next make prerequisite starting from the specified
    // position and update position to point to the start of the
    // following prerequisite or l.size() if there are none left.
    //
    static string
    next (const string& l, size_t& p)
    {
      size_t n (l.size ());

      // Skip leading spaces.
      //
      for (; p != n && l[p] == ' '; p++) ;

      // Lines containing multiple prerequisites are 80 characters max.
      //
      string r;
      r.reserve (n);

      // Scan the next prerequisite while watching out for escape sequences.
      //
      for (; p != n && l[p] != ' '; p++)
      {
        char c (l[p]);

        if (c == '\\')
          c = l[++p];

        r += c;
      }

      // Skip trailing spaces.
      //
      for (; p != n && l[p] == ' '; p++) ;

      // Skip final '\'.
      //
      if (p == n - 1 && l[p] == '\\')
        p++;

      return r;
    }

    void compile::
    inject_prerequisites (obj& o, const cxx& s, scope& ds) const
    {
      tracer tr ("cxx::compile::inject_prerequisites");

      // We are using absolute source file path in order to get
      // absolute paths in the result.
      //
      const char* args[] = {
        "g++-4.9",
        "-std=c++14",
        "-I", src_root.string ().c_str (),
        "-MM",       //@@ -M
        "-MG",      // Treat missing headers as generated.
        "-MQ", "*", // Quoted target (older version can't handle empty name).
        s.path ().string ().c_str (),
        nullptr};

      if (verb >= 2)
        print_process (args);

      if (verb >= 5)
        tr << "target: " << o;

      try
      {
        process pr (args, false, false, true);

        __gnu_cxx::stdio_filebuf<char> fb (pr.in_ofd, ios_base::in);
        istream is (&fb);

        for (bool first (true); !is.eof (); )
        {
          string l;
          getline (is, l);

          if (is.fail () && !is.eof ())
          {
            cerr << "error: io error while parsing g++ -M output" << endl;
            throw error ();
          }

          size_t pos (0);

          if (first)
          {
            // Empty output should mean the wait() call below will return
            // false.
            //
            if (l.empty ())
              break;

            assert (l[0] == '*' && l[1] == ':' && l[2] == ' ');
            next (l, (pos = 3)); // Skip the source file.

            first = false;
          }

          while (pos != l.size ())
          {
            path file (next (l, pos));
            file.normalize ();

            if (verb >= 5)
              tr << "prerequisite path: " << file.string ();

            // If there is no extension (e.g., standard C++ headers),
            // then assume it is a header. Otherwise, let the standard
            // mechanism derive the type from the extension.
            //

            // @@ TODO:
            //

            // Split the name into its directory part, the name part, and
            // extension. Here we can assume the name part is a valid
            // filesystem name.
            //
            path d (file.directory ());
            string n (file.leaf ().base ().string ());
            const char* es (file.extension ());
            const string* e (&extension_pool.find (es != nullptr ? es : ""));

            // Find or insert.
            //
            auto r (ds.prerequisites.emplace (
                      hxx::static_type, move (d), move (n), e, ds));

            auto& p (const_cast<prerequisite&> (*r.first));

            // Update extension if the existing prerequisite has it
            // unspecified.
            //
            if (p.ext != e)
            {
              trace (4, [&]{
                  tracer::record r (tr);
                  r << "assuming prerequisite " << p << " is the same as the "
                    << "one with ";
                  if (e->empty ())
                    r << "no extension";
                  else
                    r << "extension " << *e;
                });

              p.ext = e;
            }

            // Resolve to target so that we can assign its path.
            //
            path_target& t (
              dynamic_cast<path_target&> (
                p.target != nullptr ? *p.target : *search (p)));

            if (t.path ().empty ())
              t.path (file);

            o.prerequisites.push_back (p);
          }
        }

        // We assume the child process issued some diagnostics.
        //
        if (!pr.wait ())
          throw error ();
      }
      catch (const process_error& e)
      {
        cerr << "error: unable to execute '" << args[0] << "': " <<
          e.what () << endl;

        // In a multi-threaded program that fork()'ed but did not exec(),
        // it is unwise to try to do any kind of cleanup (like unwinding
        // the stack and running destructors).
        //
        if (e.child ())
          exit (1);

        throw error ();
      }
    }

    target_state compile::
    update (target& t)
    {
      obj& o (dynamic_cast<obj&> (t));
      timestamp mt (o.mtime ());

      bool u (mt == timestamp_nonexistent);
      const cxx* s (nullptr);

      for (const prerequisite& p: t.prerequisites)
      {
        const target& pt (*p.target);

        // Assume all our prerequisites are mtime-based (checked in
        // match()).
        //
        if (!u)
        {
          const auto& mtp (dynamic_cast<const mtime_target&> (pt));
          timestamp mp (mtp.mtime ());

          // What do we do if timestamps are equal? This can happen, for
          // example, on filesystems that don't have subsecond resolution.
          // There is not much we can do here except detect the case where
          // the prerequisite was updated in this run which means the
          // target must be out of date.
          //
          if (mt < mp || mt == mp && mtp.state () == target_state::updated)
            u = true;
        }

        if (s == nullptr)
          s = dynamic_cast<const cxx*> (&pt);

        if (u && s != nullptr)
          break;
      }

      if (!u)
        return target_state::uptodate;

      // Translate paths to relative (to working directory) ones. This
      // results in easier to read diagnostics.
      //
      path ro (translate (o.path ()));
      path rs (translate (s->path ()));

      const char* args[] = {
        "g++-4.9",
        "-std=c++14",
        "-g",
        "-I", src_root.string ().c_str (),
        "-c",
        "-o", ro.string ().c_str (),
        rs.string ().c_str (),
        nullptr};

      if (verb >= 1)
        print_process (args);
      else
        cerr << "c++ " << *s << endl;

      try
      {
        process pr (args);

        if (!pr.wait ())
          return target_state::failed;

        // Should we go to the filesystem and get the new mtime? We
        // know the file has been modified, so instead just use the
        // current clock time. It has the advantage of having the
        // subseconds precision.
        //
        o.mtime (system_clock::now ());
        return target_state::updated;
      }
      catch (const process_error& e)
      {
        cerr << "error: unable to execute '" << args[0] << "': " <<
          e.what () << endl;

        // In a multi-threaded program that fork()'ed but did not exec(),
        // it is unwise to try to do any kind of cleanup (like unwinding
        // the stack and running destructors).
        //
        if (e.child ())
          exit (1);

        return target_state::failed;
      }
    }

    // link
    //
    recipe link::
    match (target& t, bool single, std::string& hint) const
    {
      // @@ TODO:
      //
      // - check prerequisites: object files, libraries
      // - if path already assigned, verify extension
      //
      // @@ Q:
      //
      // - if there is no .o, are we going to check if the one derived
      //   from target exist or can be built? If we do that, then it
      //   probably makes sense to try other rules first (two passes).
      //   What if there is a library. Probably ok if .a, not is .so.
      //

      // See if we have at least one object file.
      //
      prerequisite* op (nullptr);
      for (prerequisite& p: t.prerequisites)
      {
        if (p.type.id == typeid (obj))
        {
          op = &p;
          break;
        }
      }

      if (op == nullptr)
        return recipe ();

      // Derive executable file name from target name.
      //
      exe& e (dynamic_cast<exe&> (t));

      if (e.path ().empty ())
        e.path (e.directory / path (e.name));

      return recipe (&update);
    }

    target_state link::
    update (target& t)
    {
      // @@ Q:
      //
      // - what are we doing with libraries?
      //

      exe& e (dynamic_cast<exe&> (t));
      timestamp mt (e.mtime ());

      bool u (mt == timestamp_nonexistent);

      for (const prerequisite& p: t.prerequisites)
      {
        const target& pt (*p.target);

        // Assume all our prerequisites are mtime-based (checked in
        // match()).
        //
        const auto& mtp (dynamic_cast<const mtime_target&> (pt));
        timestamp mp (mtp.mtime ());

        // What do we do if timestamps are equal? This can happen, for
        // example, on filesystems that don't have subsecond resolution.
        // There is not much we can do here except detect the case where
        // the prerequisite was updated in this run which means the
        // target must be out of date.
        //
        if (mt < mp || mt == mp && mtp.state () == target_state::updated)
        {
          u = true;
          break;
        }
      }

      if (!u)
        return target_state::uptodate;

      // Translate paths to relative (to working directory) ones. This
      // results in easier to read diagnostics.
      //
      path re (translate (e.path ()));
      vector<path> ro;

      vector<const char*> args {"g++-4.9", "-std=c++14", "-g", "-o"};

      args.push_back (re.string ().c_str ());

      for (const prerequisite& p: t.prerequisites)
      {
        const obj& o (dynamic_cast<const obj&> (*p.target));
        ro.push_back (translate (o.path ()));
        args.push_back (ro.back ().string ().c_str ());
      }

      args.push_back (nullptr);

      if (verb >= 1)
        print_process (args);
      else
        cerr << "ld " << e << endl;

      try
      {
        process pr (args.data ());

        if (!pr.wait ())
          return target_state::failed;

        // Should we go to the filesystem and get the new mtime? We
        // know the file has been modified, so instead just use the
        // current clock time. It has the advantage of having the
        // subseconds precision.
        //
        e.mtime (system_clock::now ());
        return target_state::updated;
      }
      catch (const process_error& e)
      {
        cerr << "error: unable to execute '" << args[0] << "': " <<
          e.what () << endl;

        // In a multi-threaded program that fork()'ed but did not exec(),
        // it is unwise to try to do any kind of cleanup (like unwinding
        // the stack and running destructors).
        //
        if (e.child ())
          exit (1);

        return target_state::failed;
      }
    }
  }
}