module SimpleCov::CLI::Diff

def compute_row(fname, current_payload, baseline_payload, threshold)
  deltas = CRITERIA.to_h { |c| [c, pct_for(c, current_payload) - pct_for(c, baseline_payload)] }
  floor = [threshold.abs, EPSILON].max
  return nil unless deltas.values.any? { |delta| delta.abs > floor }
  {
    file: fname,
    status: status_for(current_payload, baseline_payload),
    line_delta: deltas[:lines],
    branch_delta: deltas[:branches],
    method_delta: deltas[:methods]
  }
end

def compute_rows(current, baseline, threshold)
  files = current.keys | baseline.keys
  files.filter_map { |fname| compute_row(fname, current[fname], baseline[fname], threshold) }
end

def delta_parts(row, color)
  [
    format_delta(row[:line_delta], "lines", color),
    (format_delta(row[:branch_delta], "branches", color) if row[:branch_delta].abs > EPSILON),
    (format_delta(row[:method_delta], "methods", color)  if row[:method_delta].abs > EPSILON)
  ].compact
end

def emit_json(stdout, rows)
  stdout.puts(JSON.pretty_generate(rows))
end

def emit_text(stdout, rows, color)
  return stdout.puts("simplecov diff: no per-file coverage changes") if rows.empty?
  rows.each { |row| stdout.puts(format_row(row, color)) }
end

def format_delta(delta, label, color)
  sign = delta.positive? ? "+" : ""
  text = format("%<sign>s%<delta>6.2f%% %<label>s", sign: sign, delta: delta, label: label)
  SimpleCov::Color.colorize(text, delta.negative? ? :red : :green, enabled: color)
end

def format_row(row, color)
  line = "  #{delta_parts(row, color).join('  ')}  #{row[:file]}"
  suffix = STATUS_SUFFIX[row[:status]]
  suffix ? "#{line}  #{suffix}" : line
end

def load_coverage(path, stderr)
  return normalize_keys(JSON.parse(File.read(path)).fetch("coverage", {})) if File.exist?(path)
  stderr.puts("simplecov diff: #{path} not found")
  nil
end

def normalize_keys(coverage)
  coverage.transform_keys { |key| key.delete_prefix("/") }
end

def option_parser(opts)
  OptionParser.new do |o|
    o.on("--input PATH")         { |v| opts[:input] = v }
    o.on("--fail-on-drop")       { opts[:fail_on_drop] = true }
    o.on("--json")               { opts[:json] = true }
    o.on("--threshold N", Float) { |v| opts[:threshold] = v }
    o.on("--no-color")           { opts[:no_color] = true }
  end
end

def parse(args, stderr)
  opts = parse_flags(args)
  return stderr.puts("simplecov diff: missing baseline argument") && nil if opts[:rest].empty?
  opts[:baseline] = load_coverage(opts[:rest].first, stderr) or return nil
  opts[:current]  = load_coverage(opts[:input], stderr) or return nil
  opts
end

def parse_flags(args)
  opts = {input: SimpleCov::CLI.default_input, fail_on_drop: false, json: false, threshold: 0.0, no_color: false}
  opts.merge(rest: option_parser(opts).parse(args))
end

def pct_for(criterion, payload)
  fields = CRITERION_FIELDS.fetch(criterion)
  return 0.0 unless payload.is_a?(Hash) && payload[fields[:total]].to_i.positive?
  payload[fields[:pct]].to_f
end

def run(args, stdout:, stderr:, **)
  opts = parse(args, stderr)
  return 1 unless opts
  rows = compute_rows(opts[:current], opts[:baseline], opts[:threshold])
  rows.sort_by! { |row| row[:line_delta] }
  if opts[:json]
    emit_json(stdout, rows)
  else
    emit_text(stdout, rows, SimpleCov::CLI.color_enabled?(opts, stdout))
  end
  opts[:fail_on_drop] && rows.any? { |row| row[:line_delta].negative? } ? 1 : 0
end

def status_for(current_payload, baseline_payload)
  return "added"   if baseline_payload.nil?
  return "removed" if current_payload.nil?
  "changed"
end