stream.h

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#pragma once
// SPDX-FileCopyrightText: 2025 Nessan Fitzmaurice <nzznfitz+gh@icloud.com>
// SPDX-License-Identifier: MIT

 
#include <iostream>
#include <string>
 
namespace utilities {

static std::size_t
read_line(std::istream& s, std::string& line, std::string_view comment_begin = "#")
{
    // Lambda that trims a string in-place from leading/trailing space characters.
    auto trim = [](std::string& str) {
        str.erase(str.begin(), std::find_if(str.begin(), str.end(), [](int ch) { return !std::isspace(ch); }));
        str.erase(std::find_if(str.rbegin(), str.rend(), [](int ch) { return !std::isspace(ch); }).base(), str.end());
    };
 
    // Zap any existing content in the output parameter.
    line.clear();
 
    // We keep trying to read content until we hit the end-of-file (there are other early exits below).
    while (!s.eof()) {
 
        // Standard read-a-line from a stream.
        std::getline(s, line);
 
        // Remove any trailing comment (starts with the comment_begin).
        if (!comment_begin.empty()) {
            auto begin = line.find_first_of(comment_begin);
            if (begin != std::string::npos) line.erase(begin, line.length() - begin);
        }
 
        // Remove leading & trailing blanks.
        trim(line);
 
        // If after all that  we haven't captured anything skip on to try the next line.
        std::size_t n = line.length();
        if (n == 0) continue;
 
        // Handle continuation lines (we know that n != 0).
        if (line[n - 1] == '\\') {
            // Replace the continuation character with a space
            line[n - 1] = ' ';
 
            // Trim--we'll add one space back if there is a non-empty continuation.
            trim(line);
 
            // Recurse ...
            std::string continuation;
            read_line(s, continuation, comment_begin);
            if (!continuation.empty()) {
                line += " ";
                line += continuation;
            }
        }
 
        // If we have captured some content in `line` we can go home.
        if (!line.empty()) break;
    }
 
    return line.length();
}

inline std::string
read_line(std::istream& s, std::string_view comment_begin = "#")
{
    std::string retval;
    read_line(s, retval, comment_begin);
    return retval;
}

inline std::istream&
rewind(std::istream& is)
{
    is.clear();
    is.seekg(0, std::istream::beg);
    return is;
}

inline std::size_t
line_count(std::istream& is, std::string_view comment_begin = "#")
{
    std::size_t retval = 0;
    std::string line;
    if (comment_begin.empty()) {
        while (std::getline(is, line)) ++retval;
    }
    else {
        while (read_line(is, line, comment_begin)) ++retval;
    }
    rewind(is);
    return retval;
}
 
} // namespace utilities