Move file_wrapper and make testable. (#1085)

* WIP Move file_wrapper and make testable.

* More tests, get text_editor compiling

* Back to working

* Run formatter

---------

Co-authored-by: kallanreed <kallanreed@outlook.com>

firmware/application/file_wrapper.hpp

@@ -0,0 +1,342 @@
+/*
+ * Copyright (C) 2023 Kyle Reed
+ *
+ * This file is part of PortaPack.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __FILE_WRAPPER_HPP__
+#define __FILE_WRAPPER_HPP__
+
+#include "circular_buffer.hpp"
+#include "file.hpp"
+#include "optional.hpp"
+
+#include <memory>
+#include <string>
+
+enum class LineEnding : uint8_t {
+    LF,
+    CRLF
+};
+
+/* TODO:
+ * - CRLF handling.
+ */
+
+/* BufferType requires the following members
+ * Size size()
+ * Result<Size> read(void* data, Size bytes_to_read)
+ * Result<Offset> seek(uint32_t offset)
+ */
+
+/* Wraps a buffer and provides an API for accessing lines efficiently. */
+template <typename BufferType, uint32_t CacheSize>
+class BufferWrapper {
+   public:
+    using Offset = uint32_t;
+    using Line = uint32_t;
+    using Column = uint32_t;
+    using Range = struct {
+        // Offset of the line start.
+        Offset start;
+        // Offset of one past the line end.
+        Offset end;
+    };
+
+    BufferWrapper(BufferType* buffer)
+        : wrapped_{buffer} {
+        initialize();
+    }
+    virtual ~BufferWrapper() {}
+
+    /* Prevent copies */
+    BufferWrapper(const BufferWrapper&) = delete;
+    BufferWrapper& operator=(const BufferWrapper&) = delete;
+
+    Optional<std::string> get_text(Line line, Column col, Offset length) {
+        auto range = line_range(line);
+        int32_t to_read = length;
+
+        if (!range)
+            return {};
+
+        // Don't read past end of line.
+        if (range->start + col + to_read >= range->end)
+            to_read = range->end - col - range->start;
+
+        if (to_read <= 0)
+            return {};
+
+        return read(range->start + col, to_read);
+    }
+
+    /* Gets the size of the buffer in bytes. */
+    File::Size size() const { return wrapped_->size(); }
+
+    /* Get the count of the lines in the buffer. */
+    uint32_t line_count() const { return line_count_; }
+
+    /* Gets the range of the line if valid. */
+    Optional<Range> line_range(Line line) {
+        ensure_cached(line);
+
+        auto offset = offset_for_line(line);
+        if (!offset)
+            return {};
+
+        auto start = *offset == 0 ? start_offset_ : (newlines_[*offset - 1] + 1);
+        auto end = newlines_[*offset] + 1;
+
+        return Range{start, end};
+    }
+
+    /* Gets the length of the line, or 0 if invalid. */
+    Offset line_length(Line line) {
+        auto range = line_range(line);
+
+        if (range)
+            return range->end - range->start;
+
+        return 0;
+    }
+
+    /* Gets the index of the first line in the cache.
+     * Only really useful for unit testing or diagnostics. */
+    Offset start_line() { return start_line_; };
+
+   protected:
+    BufferWrapper() {}
+
+    void set_buffer(BufferType* buffer) {
+        wrapped_ = buffer;
+        initialize();
+    }
+
+   private:
+    /* Number of newline offsets to cache. */
+    static constexpr Offset max_newlines = CacheSize;
+
+    /* Size of stack buffer used for reading/writing. */
+    static constexpr size_t buffer_size = 512;
+
+    void initialize() {
+        start_offset_ = 0;
+        start_line_ = 0;
+        line_count_ = 0;
+        newlines_.clear();
+
+        // Special case for empty files to keep them consistent.
+        if (size() == 0) {
+            line_count_ = 1;
+            newlines_.push_back(0);
+            return;
+        }
+
+        Offset offset = 0;
+        auto result = next_newline(offset);
+
+        while (result) {
+            ++line_count_;
+            if (newlines_.size() < max_newlines)
+                newlines_.push_back(*result);
+            offset = *result + 1;
+            result = next_newline(offset);
+        }
+    }
+
+    Optional<std::string> read(Offset offset, Offset length) {
+        if (offset + length > size())
+            return {};
+
+        std::string buffer;
+        buffer.resize(length);
+        wrapped_->seek(offset);
+
+        auto result = wrapped_->read(&buffer[0], length);
+        if (result.is_error())
+            // TODO: better error handling.
+            return std::string{"[Bad Read]"};
+
+        buffer.resize(*result);
+        return buffer;
+    }
+
+    /* Returns the offset of the line in the newline cache if valid. */
+    Optional<Offset> offset_for_line(Line line) const {
+        if (line >= line_count_)
+            return {};
+
+        Offset actual = line - start_line_;
+        if (actual >= newlines_.size())  // NB: underflow wrap.
+            return {};
+
+        return actual;
+    }
+
+    /* Ensure specified line is in the newline cache. */
+    void ensure_cached(Line line) {
+        if (line >= line_count_)
+            return;
+
+        auto result = offset_for_line(line);
+        if (result)
+            return;
+
+        if (line < start_line_) {
+            while (line < start_line_ && start_offset_ >= 2) {
+                // start_offset_ - 1 should be a newline. Need to
+                // find the new value for start_offset_. start_line_
+                // has to be > 0 to get into this block so there should
+                // always be one newline before start_offset_.
+                auto offset = previous_newline(start_offset_ - 2);
+                newlines_.push_front(start_offset_ - 1);
+
+                if (!offset) {
+                    // Must be at beginning.
+                    start_line_ = 0;
+                    start_offset_ = 0;
+                } else {
+                    // Found an previous newline, the new start_line_
+                    // starts at the newline offset + 1.
+                    start_line_--;
+                    start_offset_ = *offset + 1;
+                }
+            }
+        } else {
+            while (line >= start_line_ + newlines_.size()) {
+                auto offset = next_newline(newlines_.back() + 1);
+                if (offset) {
+                    start_line_++;
+                    start_offset_ = newlines_.front() + 1;
+                    newlines_.push_back(*offset);
+                } /* else at the EOF. */
+            }
+        }
+    }
+
+    /* Helpers for finding the prev/next newline. */
+    Optional<Offset> previous_newline(Offset offset) {
+        char buffer[buffer_size];
+        auto to_read = buffer_size;
+
+        do {
+            if (offset < to_read) {
+                // NB: Char at 'offset' was read in the previous iteration.
+                to_read = offset;
+                offset = 0;
+            } else
+                offset -= to_read;
+
+            wrapped_->seek(offset);
+
+            auto result = wrapped_->read(buffer, to_read);
+            if (result.is_error())
+                break;
+
+            // Find newlines in the buffer backwards.
+            for (int32_t i = *result - 1; i >= 0; --i) {
+                switch (buffer[i]) {
+                    case '\n':
+                        return offset + i;
+                }
+            }
+
+            if (offset == 0)
+                break;
+
+        } while (true);
+
+        return {};  // Didn't find one.
+    }
+
+    Optional<Offset> next_newline(Offset offset) {
+        // EOF, no more newlines to find.
+        if (offset >= size())
+            return {};
+
+        char buffer[buffer_size];
+        wrapped_->seek(offset);
+
+        while (true) {
+            auto result = wrapped_->read(buffer, buffer_size);
+            if (result.is_error())
+                return {};
+
+            // Find newlines in the buffer.
+            for (Offset i = 0; i < *result; ++i) {
+                switch (buffer[i]) {
+                    case '\n':
+                        return offset + i;
+                }
+            }
+
+            offset += *result;
+
+            if (*result < buffer_size)
+                break;
+        }
+
+        // For consistency, treat the end of the file as a "newline".
+        return size() - 1;
+    }
+
+    BufferType* wrapped_{};
+
+    /* Total number of lines in the buffer. */
+    Offset line_count_{0};
+
+    /* The offset and line of the newlines cache. */
+    Offset start_offset_{0};
+    Offset start_line_{0};
+
+    LineEnding line_ending_{LineEnding::LF};
+    CircularBuffer<Offset, max_newlines + 1> newlines_{};
+};
+
+/* A BufferWrapper over a file. */
+class FileWrapper : public BufferWrapper<File, 64> {
+   public:
+    template <typename T>
+    using Result = File::Result<T>;
+    using Error = File::Error;
+    static Result<std::unique_ptr<FileWrapper>> open(const std::filesystem::path& path) {
+        auto fw = std::unique_ptr<FileWrapper>(new FileWrapper());
+        auto error = fw->file_.open(path);
+
+        if (error)
+            return *error;
+
+        fw->initialize();
+        return fw;
+    }
+
+   private:
+    FileWrapper() {}
+    void initialize() {
+        set_buffer(&file_);
+    }
+
+    File file_{};
+};
+
+template <uint32_t CacheSize = 64, typename T>
+BufferWrapper<T, CacheSize> wrap_buffer(T& buffer) {
+    return {&buffer};
+}
+
+#endif  // __FILE_WRAPPER_HPP__