src/writing_studio/services/diff_service.py

"""Text comparison and diff generation service."""

import difflib
from typing import Tuple

from writing_studio.utils.logging import logger


class DiffService:
    """Service for comparing texts and generating diffs."""

    def __init__(self):
        """Initialize the diff service."""
        self.html_differ = difflib.HtmlDiff()

    def generate_html_diff(
        self,
        original: str,
        revised: str,
        context: bool = True,
        numlines: int = 3,
    ) -> str:
        """
        Generate HTML diff highlighting differences between texts.

        Args:
            original: Original text
            revised: Revised text
            context: Show context lines
            numlines: Number of context lines

        Returns:
            HTML diff table
        """
        logger.info("Generating HTML diff")

        original_lines = original.splitlines()
        revised_lines = revised.splitlines()

        html_diff = self.html_differ.make_table(
            original_lines,
            revised_lines,
            fromdesc="Original",
            todesc="AI Revision",
            context=context,
            numlines=numlines,
        )

        return html_diff

    def generate_unified_diff(self, original: str, revised: str, lineterm: str = "\n") -> str:
        """
        Generate unified diff format.

        Args:
            original: Original text
            revised: Revised text
            lineterm: Line terminator

        Returns:
            Unified diff string
        """
        logger.info("Generating unified diff")

        original_lines = original.splitlines(keepends=True)
        revised_lines = revised.splitlines(keepends=True)

        diff = difflib.unified_diff(
            original_lines,
            revised_lines,
            fromfile="original",
            tofile="revised",
            lineterm=lineterm,
        )

        return "".join(diff)

    def get_similarity_ratio(self, original: str, revised: str) -> float:
        """
        Calculate similarity ratio between two texts.

        Args:
            original: Original text
            revised: Revised text

        Returns:
            Similarity ratio (0.0 to 1.0)
        """
        sequence_matcher = difflib.SequenceMatcher(None, original, revised)
        return sequence_matcher.ratio()

    def get_change_summary(self, original: str, revised: str) -> dict:
        """
        Get summary of changes between texts.

        Args:
            original: Original text
            revised: Revised text

        Returns:
            Dictionary with change statistics
        """
        original_lines = original.splitlines()
        revised_lines = revised.splitlines()

        differ = difflib.Differ()
        diff = list(differ.compare(original_lines, revised_lines))

        added = sum(1 for line in diff if line.startswith("+ "))
        removed = sum(1 for line in diff if line.startswith("- "))
        unchanged = sum(1 for line in diff if line.startswith("  "))

        similarity = self.get_similarity_ratio(original, revised)

        return {
            "lines_added": added,
            "lines_removed": removed,
            "lines_unchanged": unchanged,
            "similarity_ratio": similarity,
            "original_lines": len(original_lines),
            "revised_lines": len(revised_lines),
        }