io/writer.hpp

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/*
 
Copyright 2025 Matthew Tolman
 
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 
   http://www.apache.org/licenses/LICENSE-2.0
 
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
 
*/
 
#ifndef MTCORE_WRITER_HPP
#define MTCORE_WRITER_HPP
 
#include "mtcore/colls/result.hpp"
#include "mtcore/colls/slice.hpp"
#include "mtcore/colls/slice_algo.hpp"
#include "mtcore/traits.hpp"
#include <functional>
#include <ostream>


namespace mtcore::io {
  template<typename T>
  struct Formatter;
 
  struct FormatOptions;
 
  template<WriterImpl Impl>
  struct Writer;

  template<WriterImpl Impl>
  struct Writer {
    using WriteElem = typename Impl::WriteElem;
    using ErrType   = typename Impl::ErrType;
 
    Impl underlying;

    Result<size_t, ErrType> write(const Slice<std::remove_const_t<WriteElem>> &s) { return write(s.to_const()); }

    Result<size_t, ErrType> write(const Slice<std::add_const_t<WriteElem>> &s) { return underlying.write(s); }

    Result<size_t, ErrType> write(const std::remove_const_t<WriteElem> &one) {
      auto s = Slice<std::add_const_t<WriteElem>>{&one, 1};
      return write_all(s);
    }

    Result<void, ErrType> flush() {
      if constexpr (is_flushable<Impl>) {
        return underlying.flush();
      }
      return success();
    }

    void deinit(Allocator &allocator)
      requires(AllocatorDeinit<Impl>)
    {
      underlying.deinit(allocator);
    }

    void deinit()
      requires(DefaultDeinit<Impl>)
    {
      underlying.deinit();
    }

    [[nodiscard]] size_t bytes_written() const { return underlying.bytes_written(); }

    Result<size_t, ErrType> write_all(const Slice<std::remove_const_t<WriteElem>> &s) {
      return write_all(s.to_const());
    }

    [[nodiscard]] size_t bytes_written() const
      requires(WriterImplBytes<Impl>)
    {
      return underlying.bytes_written();
    }
 
    [[nodiscard]] auto written() const
      requires(WriterImplWritten<Impl>)
    {
      return underlying.written();
    }
 
    void reset()
      requires(WriterImplResettable<Impl>)
    {
      underlying.reset();
    }

    Result<size_t, ErrType> write_all(const Slice<std::add_const_t<WriteElem>> &s) {
      auto r = underlying.write(s);
      if (r.is_error()) {
        return r.error();
      }
      // if we're dealing with a write-through writer, we have to rely on the final check in the stack
      // as there will be transformations, so we can't check for out of room here
      if constexpr (!is_write_through<Impl>) {
        if (r.value() != s.size()) {
          return error(ErrType::OUT_OF_ROOM);
        }
      }
      return success(r.value());
    }

    Result<void, ErrType> write_n_times(const Slice<std::remove_const_t<WriteElem>> &s, size_t n) {
      return write_n_times(s.to_const(), n);
    }

    Result<size_t, ErrType> write_n_times(const Slice<std::add_const_t<WriteElem>> &s, size_t n) {
      for (size_t i = 0; i < n; ++i) {
        auto r = write_all(s);
        if (r.is_error()) {
          return r.error();
        }
      }
      return success(n);
    }

    Result<size_t, ErrType> write_n_times(const std::remove_const_t<WriteElem> &one, size_t n) {
      auto s = Slice<std::add_const_t<WriteElem>>{&one, 1};
      for (size_t i = 0; i < n; ++i) {
        auto r = write_all(s);
        if (r.is_error()) {
          return r.error();
        }
      }
      return success(n);
    }
  };

  enum class SliceWriteError {
    OUT_OF_ROOM,  // necessary for writers
  };

  enum class VoidWriteError {
    OUT_OF_ROOM,
  };

  enum class OstreamWriteErr {
    OUT_OF_ROOM,
  };
 
  namespace impl {
    template<typename T>
    struct SliceWriterImpl {
      static_assert(!std::is_const_v<T>, "Cannot write to const pointer!");
      Slice<T> out;
      size_t curWriteIndex = 0;
 
      using WriteElem = T;
      using ErrType   = SliceWriteError;
 
      Result<size_t, ErrType> write(Slice<std::add_const_t<T>> bytes) {
        size_t i = 0;
        for (; i < bytes.size() && curWriteIndex < out.size(); ++i, ++curWriteIndex) {
          out[curWriteIndex] = bytes[i];
        }
        return success(i);
      }
 
      [[nodiscard]] size_t bytes_written() const { return curWriteIndex; }
 
      [[nodiscard]] Slice<T> written() const { return out.sub(0, bytes_written()); }
 
      void reset() {
        curWriteIndex = 0;
#ifndef NDEBUG
        if constexpr (std::is_same_v<T, char>) {
          memset(out.head, 0, out.len * sizeof(char));
        }
#endif
      }
    };
 
    template<typename T>
    struct VoidWriterImpl {
      using WriteElem = T;
      using ErrType   = VoidWriteError;
      Result<size_t, ErrType> write(Slice<std::add_const_t<T>> elems) { return success(elems.size()); }
    };
 
    template<WriterImpl WI>
    struct EnsureWriteable : std::true_type {};
    static_assert(EnsureWriteable<VoidWriterImpl<char>>::value);
 
    template<typename T>
    struct OstreamWriterImpl {
      using WriteElem = T;
      using ErrType   = OstreamWriteErr;
      std::ostream &os;
 
      Result<size_t, OstreamWriteErr> write(Slice<std::add_const_t<T>> elems) {
        for (size_t i = 0; i < elems.size(); ++i) {
          os << elems[i];
        }
        return success(elems.size());
      }
    };
 
    template<typename InType, WriterImpl WI, typename Err = typename io::Writer<WI>::ErrType,
             typename FuncType = std::function<Result<size_t, Err>(io::Writer<WI> &, Slice<std::add_const_t<InType>>)>>
    struct WriteTransformer {
      static constexpr bool IsWriteThrough = true;
      using WriteElem                      = InType;
      using ErrType                        = Err;
      io::Writer<WI> &underlying;
      FuncType mapper;

      void deinit(Allocator &allocator)
        requires(AllocatorDeinit<WI>)
      {
        underlying.deinit(allocator);
      }

      void deinit()
        requires(DefaultDeinit<WI>)
      {
        underlying.deinit();
      }

      [[nodiscard]] size_t bytes_written() const
        requires(WriterImplBytes<WI>)
      {
        return underlying.bytes_written();
      }

      [[nodiscard]] Slice<typename WI::WriteElem> written() const
        requires(WriterImplWritten<WI>)
      {
        return underlying.written();
      }

      [[nodiscard]] size_t reset() const
        requires(WriterImplResettable<WI>)
      {
        return underlying.reset();
      }

      Result<size_t, ErrType> write(Slice<std::add_const_t<InType>> elems) { return mapper(underlying, elems); }
    };
  }  // namespace impl

  template<typename T, WriterImpl WI, typename Err = typename io::Writer<WI>::ErrType,
           typename FuncType = std::function<Result<size_t, Err>(io::Writer<WI> &, Slice<std::add_const_t<T>>)>>
  io::Writer<impl::WriteTransformer<T, WI, Err, FuncType>> write_transformer(io::Writer<WI> &writer, FuncType mapper) {
    return io::Writer<impl::WriteTransformer<T, WI, Err, FuncType>>{writer, mapper};
  }

  template<typename T>
  io::Writer<impl::SliceWriterImpl<T>> slice_writer(Slice<T> out) {
    return io::Writer<impl::SliceWriterImpl<T>>{.underlying = impl::SliceWriterImpl<T>{.out = out}};
  }

  template<typename T>
  io::Writer<impl::VoidWriterImpl<T>> void_writer() {
    return io::Writer<impl::VoidWriterImpl<T>>{};
  }

  template<Formattable T>
  auto ostream_writer(std::ostream &os) {
    return io::Writer<impl::OstreamWriterImpl<T>>{.underlying = impl::OstreamWriterImpl<T>{os}};
  }
}  // namespace mtcore::io
 
#include "../colls/result.hpp"
#include "format.hpp"
 
namespace mtcore::io {
  template<WriterImpl WI, typename Arg>
  Result<size_t, typename Writer<WI>::ErrType> format(Writer<WI> &writer, const FormatOptions &opts, Arg arg) {
    return Formatter<Arg>::fmt(writer, opts, arg);
  }

  template<WriterImpl WI, typename... Args>
  Result<size_t, typename Writer<WI>::ErrType> print(Writer<WI> &writer, const char *fmt, const Args &...args) {
    return print(writer, slice_from(fmt), args...);
  }
 
  namespace impl {
    template<WriterImpl WI, typename A, typename... Args>
    Result<size_t, typename Writer<WI>::ErrType> print(size_t written, Writer<WI> &writer, Slice<const char> fmt,
                                                       const A &curArg, const Args &...args);
 
    template<WriterImpl WI>
    Result<size_t, typename Writer<WI>::ErrType> print(size_t written, Writer<WI> &writer, Slice<const char> fmt);
  }  // namespace impl

  template<WriterImpl WI, typename... Args>
  Result<size_t, typename Writer<WI>::ErrType> print(Writer<WI> &writer, const Slice<const char> &fmt,
                                                     const Args &...args) {
    return impl::print(0, writer, fmt, args...);
  }
 
  namespace impl {
    struct NextEscape {
      enum class EscapeType { CHAR, FORMAT };
      EscapeType type;
      size_t startIndex;
      size_t endIndex;
      Slice<const char> escaped;
    };
 
    inline Optional<NextEscape> next_escape(Slice<const char> fmt) {
      static constexpr auto printStartChars = "{";
      static constexpr auto printStart      = slice_from(printStartChars);
      static constexpr auto printEndChars   = "}";
      static constexpr auto printEnd        = slice_from(printEndChars);
      static constexpr auto esc             = '\\';
 
      for (size_t i = 0; i < fmt.size(); ++i) {
        if (fmt[i] == esc) {
          ensure(i + 1 < fmt.size(), "INVALID FORMAT STRING! EXPECTED CHARACTER AFTER '\\'");
          return NextEscape{NextEscape::EscapeType::CHAR, i, i + 1, fmt.sub(i + 1, 1)};
        }
        else if (slices::starts_with(printStart, fmt.sub(i))) {
          auto endOpt = slices::first_index_not_proceeded_by('\\', printEnd, fmt.sub(i + printStart.size()));
          ensure(endOpt.has_value(), "INVALID FORMAT STRING! UNTERMINATED FORMATTING SPECIFIER! EXPECTED '}'");
          auto escaped = fmt.sub(i + printStart.size(), endOpt.value());
          auto end     = endOpt.value() + i + printStart.size();
          return NextEscape{NextEscape::EscapeType::FORMAT, i, end, escaped};
        }
      }
      return nullopt;
    }
 
    template<WriterImpl WI>
    Result<size_t, typename Writer<WI>::ErrType> print(size_t written, Writer<WI> &writer, Slice<const char> fmt) {
      if (fmt.empty()) {
        return written;
      }
 
      using WriteAllRes = Result<size_t, typename Writer<WI>::ErrType>;
      for (size_t i = 0; !fmt.empty() && i < 1000; ++i) {
        auto s = next_escape(fmt);
        if (!s.has_value()) {
          written += fmt.size();
          writer.write_all(fmt);
          break;
        }
 
        NextEscape ne = s.value();
        auto prefix   = fmt.sub(0, ne.startIndex);
        if (!prefix.empty()) {
          WriteAllRes pRes = writer.write_all(prefix);
          if (pRes.is_error()) {
            return pRes.error();
          }
          written += prefix.size();
        }
 
        ensure(ne.type == NextEscape::EscapeType::CHAR, "Missing argument for format specifier");
        WriteAllRes escRes = writer.write_all(ne.escaped);
        if (escRes.is_error()) {
          return escRes.error();
        }
        written += ne.escaped.size();
        fmt = fmt.sub(ne.endIndex + 1);
      }
      return written;
    }
 
    template<WriterImpl WI, typename A, typename... Args>
    Result<size_t, typename Writer<WI>::ErrType> print(size_t written, Writer<WI> &writer, Slice<const char> fmt,
                                                       const A &curArg, const Args &...args) {
      using PrintRes    = Result<size_t, typename Writer<WI>::ErrType>;
      using WriteAllRes = Result<size_t, typename Writer<WI>::ErrType>;
      for (size_t i = 0; !fmt.empty() && i < 1000; ++i) {
        auto s = next_escape(fmt);
        ensure(s.has_value(), "Missing format specifier for argument");
 
        NextEscape ne = s.value();
        auto prefix   = fmt.sub(0, ne.startIndex);
        if (!prefix.empty()) {
          WriteAllRes pRes = writer.write_all(prefix);
          if (pRes.is_error()) {
            return pRes.error();
          }
          written += prefix.size();
        }
 
        if (ne.type == NextEscape::EscapeType::CHAR) {
          WriteAllRes escRes = writer.write_all(ne.escaped);
          if (escRes.is_error()) {
            return escRes.error();
          }
          written += ne.escaped.size();
          fmt = fmt.sub(ne.endIndex + 1);
        }
        else {
          PrintRes fRes = format(writer, FormatOptions{ne.escaped}, curArg);
          if (fRes.is_error()) {
            return fRes.error();
          }
          written += fRes.value();
          return print(written, writer, fmt.sub(ne.endIndex + 1), args...);
        }
      }
      unreachable("Missing Format Specifier for Argument");
    }
  }  // namespace impl
}  // namespace mtcore::io
 
#endif  // MTCORE_WRITER_HPP