Add support for pseudo-diff format in preview

[andrewimeson]

Is your feature request related to a problem? Please describe.

The current dnscontrol preview output is great for viewing on the CLI or in GitHub Actions runs, but it can't be colorized in a GitHub/Gitea Pull Request comment (that I can figure out, at least)

Describe the solution you'd like

An option like --diff-format=diff to synthesize a patch-style diff that could be included in a \```diff codeblock and thus be automatically rendered with colors symbolizing addition, removal, and changes.

Describe alternatives you've considered

1. Just giving up on colorized output and setting NO_COLOR or stripping out the ANSI color sequences in the CI step that posts the comment.
2. Building my own output by taking the JSON report and spitting out markdown formatted text with the changed domain and changes summarized under "Added", "Changed", and "Deleted" subheadings

Additional context

Relates to #2499

[andrewimeson]

For now I'm using this Python script that Grok and I wrote together to list changes grouped by zone and then change type (addition, modification, deletion).

## Summary of DNS Changes

### example.com

#### Additions

-  home.example.com A 192.0.2.22 proxy=false ttl=1

#### Modifications

-  example.com TXT ("bacon is very good" ttl=1) -> ("bacon is excellent" ttl=1) id=0588b382d5a7675bf2158e30b3e215fd

#!/usr/bin/env python3
import json
import sys
from collections import defaultdict


def main():
    if len(sys.argv) != 2:
        print("Usage: ./preview_zone_markdown.py <input_json_file>")
        print("Generate a markdown-formatted summary of dnscontrol changes")
        sys.exit(1)

    filename = sys.argv[1]

    try:
        with open(filename, "r", encoding="utf-8") as f:
            data = json.load(f)
    except FileNotFoundError:
        print(f"Error: File '{filename}' not found.")
        sys.exit(1)
    except json.JSONDecodeError as e:
        print(f"Error: Invalid JSON in '{filename}': {e}")
        sys.exit(1)
    except Exception as e:
        print(f"Error reading file: {e}")
        sys.exit(1)

    output_lines = []

    # Group by domain to handle possible multiple entries per domain
    domains_data = defaultdict(lambda: {"details": [], "corrections": 0})

    for entry in data:
        if entry.get("corrections", 0) <= 0:
            continue
        domain = entry.get("domain")
        if not domain:
            continue
        domains_data[domain]["corrections"] += entry.get("corrections", 0)
        details = entry.get("correction_details", [])
        domains_data[domain]["details"].extend(details)

    output_lines.append("## Summary of DNS Changes\n")
    # Sort domains alphabetically for consistent output
    for domain in sorted(domains_data.keys()):
        details = domains_data[domain]["details"]
        if not details:
            continue

        groups = defaultdict(list)

        for detail in details:
            stripped = detail.strip()
            if stripped.startswith("+ "):
                clean = stripped.removeprefix("+ CREATE")
                groups["Addition"].append(clean)
            elif stripped.startswith("± "):
                clean = stripped.removeprefix("± MODIFY")
                groups["Modification"].append(clean)
            elif stripped.startswith("- "):
                clean = stripped.removeprefix("- DELETE")
                groups["Deletion"].append(clean)
            else:
                groups["Modification"].append(stripped)

        # Output domain header
        output_lines.append(f"### {domain}\n")

        for change_type in ["Addition", "Modification", "Deletion"]:
            items = groups[change_type]
            if items:
                output_lines.append(f"#### {change_type}s\n")
                for item in items:
                    output_lines.append(f"- {item}")
                output_lines.append("")

        output_lines.append("")

    markdown_output = "\n".join(output_lines).strip()
    print(markdown_output)


if __name__ == "__main__":
    main()

[tlimoncelli]

Hi there!

I'd definitely be open to a PR that adds a --diff-format=diff option as you suggested. Sounds like a useful feature! As a stretch goal, it could automatically enable this feature if the CI env variable is set.