# -*- coding: utf-8 -*-
"""Deterministic diff service for document chat proposals."""

import difflib
import hashlib
import re
from typing import List

from core.document_chat.schemas import DiffItem, DiffResult


class DiffService:
    """Build paragraph/line diffs, falling back to full-content comparison."""

    _COMPLEX_PATTERNS = (
        re.compile(r"<table[\s>]", re.IGNORECASE),
        re.compile(r"</table>", re.IGNORECASE),
        re.compile(r"!\[[^\]]*\]\("),
        re.compile(r"<表格开始>|<表格结束>"),
    )

    def build_diff(self, old_content: str, new_content: str) -> DiffResult:
        old_text = old_content or ""
        new_text = new_content or ""
        old_hash = self.hash_content(old_text)
        new_hash = self.hash_content(new_text)

        if self._is_complex(old_text) or self._is_complex(new_text):
            return DiffResult(
                old_content_hash=old_hash,
                new_content_hash=new_hash,
                diff=[DiffItem(type="full_content", old_text=old_text, new_text=new_text)],
                diff_granularity="full_content",
            )

        old_units = self._split_units(old_text)
        new_units = self._split_units(new_text)
        matcher = difflib.SequenceMatcher(a=old_units, b=new_units, autojunk=False)
        diff_items: List[DiffItem] = []

        for tag, i1, i2, j1, j2 in matcher.get_opcodes():
            old_part = "\n".join(old_units[i1:i2])
            new_part = "\n".join(new_units[j1:j2])
            if tag == "equal":
                diff_items.append(DiffItem(type="equal", old_text=old_part, new_text=new_part))
            elif tag == "insert":
                diff_items.append(DiffItem(type="insert", old_text="", new_text=new_part))
            elif tag == "delete":
                diff_items.append(DiffItem(type="delete", old_text=old_part, new_text=""))
            elif tag == "replace":
                diff_items.append(DiffItem(type="replace", old_text=old_part, new_text=new_part))

        return DiffResult(
            old_content_hash=old_hash,
            new_content_hash=new_hash,
            diff=diff_items,
            diff_granularity="line",
        )

    @staticmethod
    def hash_content(content: str) -> str:
        digest = hashlib.sha256((content or "").encode("utf-8")).hexdigest()
        return f"sha256:{digest}"

    def _is_complex(self, content: str) -> bool:
        if not content:
            return False
        if any(pattern.search(content) for pattern in self._COMPLEX_PATTERNS):
            return True
        lines = [line for line in content.splitlines() if line.strip()]
        table_like_lines = sum(1 for line in lines if line.count("|") >= 2)
        return table_like_lines >= 2

    @staticmethod
    def _split_units(content: str) -> List[str]:
        if not content:
            return []
        paragraphs = [part.strip() for part in re.split(r"\n\s*\n", content.strip()) if part.strip()]
        if len(paragraphs) > 1:
            return paragraphs
        return [line.rstrip() for line in content.splitlines() if line.strip()]