// Copyright (c) 2021, Erik C. Thauvin. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be found
// in the LICENSE file.

library dcat;

import 'dart:convert';
import 'dart:io';

const libName = 'dcat';
const exitFailure = 1;
const exitSuccess = 0;

/// Concatenates files in [paths] to [stdout]
///
/// The parameters are similar to the [GNU cat utility](https://www.gnu.org/software/coreutils/manual/html_node/cat-invocation.html#cat-invocation).
/// Specify a [log] for debugging purpose.
Future<int> cat(List<String> paths,
    {List<String>? log,
    bool showEnds = false,
    bool numberNonBlank = false,
    bool showLineNumbers = false,
    bool showTabs = false,
    bool squeezeBlank = false}) async {
  var lineNumber = 1;
  var returnCode = 0;
  log?.clear();
  if (paths.isEmpty) {
    final lines = await _readStdin();
    await _writeLines(lines, lineNumber, log, showEnds, showLineNumbers,
        numberNonBlank, showTabs, squeezeBlank);
  } else {
    for (final path in paths) {
      try {
        final Stream<String> lines;
        if (path == '-') {
          lines = await _readStdin();
        } else {
          lines = utf8.decoder
              .bind(File(path).openRead())
              .transform(const LineSplitter());
        }
        lineNumber = await _writeLines(lines, lineNumber, log, showEnds,
            showLineNumbers, numberNonBlank, showTabs, squeezeBlank);
      } on FileSystemException catch (e) {
        final String? osMessage = e.osError?.message;
        final String message;
        if (osMessage != null && osMessage.isNotEmpty) {
          message = osMessage;
        } else {
          message = e.message;
        }
        returnCode = await printError(message, path: path);
      } on FormatException {
        returnCode = await printError('Binary file not supported.', path: path);
      } catch (e) {
        returnCode = await printError(e.toString(), path: path);
      }
    }
  }
  return returnCode;
}

/// Prints the [appName], [path] and error [message] to [stderr].
Future<int> printError(String message,
    {String appName = libName, String path = ''}) async {
  if (path.isNotEmpty) {
    stderr.writeln('$libName: $path: $message');
  } else {
    stderr.write('$libName: $message');
  }
  return exitFailure;
}

/// Reads from stdin.
Future<Stream<String>> _readStdin() async =>
    stdin.transform(utf8.decoder).transform(const LineSplitter());

/// Writes lines to stdout.
Future<int> _writeLines(Stream<String> lines, int lineNumber,
    [List<String>? log,
    bool showEnds = false,
    bool showLineNumbers = false,
    bool showNonBlank = false,
    bool showTabs = false,
    bool squeezeBlank = false]) async {
  var emptyLine = 0;
  final sb = StringBuffer();
  await for (final line in lines) {
    sb.clear();
    if (squeezeBlank && line.isEmpty) {
      if (++emptyLine >= 2) {
        continue;
      }
    } else {
      emptyLine = 0;
    }
    if (showNonBlank || showLineNumbers) {
      sb.write('${lineNumber++}: ');
    }
    if (showTabs) {
      sb.write(line.replaceAll('\t', '^I'));
    } else {
      sb.write(line);
    }
    if (showEnds) {
      sb.write('\$');
    }

    log?.add(sb.toString());
    stdout.writeln(sb);
  }
  return lineNumber;
}