"""Shared, deterministic comparison summary for whole-document rewrites."""

from __future__ import annotations

import re
from collections import Counter
from difflib import SequenceMatcher
from typing import Any

_BLOCK_SPLIT_RE = re.compile(r"\n\s*\n+")
_HEADING_RE = re.compile(r"^(#{1,6})\s+(.+?)\s*$")


def visible_char_count(content: str) -> int:
    return len("".join(content.split()))


def _blocks(content: str) -> list[str]:
    return [block.strip() for block in _BLOCK_SPLIT_RE.split(content) if block.strip()]


def changed_block_count(original: str, rewritten: str) -> int:
    """Count affected Markdown blocks, not merely the net block-count delta."""
    before = _blocks(original)
    after = _blocks(rewritten)
    changed = 0
    for tag, before_start, before_end, after_start, after_end in SequenceMatcher(
        a=before,
        b=after,
        autojunk=False,
    ).get_opcodes():
        if tag != "equal":
            changed += max(before_end - before_start, after_end - after_start)
    return changed


def _headings(content: str) -> list[tuple[int, str]]:
    output: list[tuple[int, str]] = []
    for line in content.splitlines():
        match = _HEADING_RE.match(line.strip())
        if match:
            output.append((len(match.group(1)), match.group(2).strip()))
    return output


def _requested_optimizations(instruction: str) -> list[str]:
    keywords = (
        ("重复", "减少重复表述"),
        ("衔接", "改善段落衔接"),
        ("结构", "调整文章结构"),
        ("语气", "统一写作语气"),
        ("精炼", "压缩冗余内容"),
        ("润色", "改善表达流畅度"),
        ("扩写", "补充原文已有信息的说明"),
    )
    return [label for token, label in keywords if token in instruction] or ["按用户要求整体改写"]


def build_document_rewrite_summary(
    *,
    source_display_name: str,
    instruction: str,
    model_name: str,
    original: str,
    rewritten: str,
    validation_warnings: list[str] | None = None,
) -> dict[str, Any]:
    before_headings = _headings(original)
    after_headings = _headings(rewritten)
    before_titles = [title for _, title in before_headings]
    after_titles = [title for _, title in after_headings]
    before_counter = Counter(before_titles)
    after_counter = Counter(after_titles)
    added = list((after_counter - before_counter).elements())
    removed = list((before_counter - after_counter).elements())
    common_before = [title for title in before_titles if title in after_counter]
    common_after = [title for title in after_titles if title in before_counter]
    levels_before = {title: level for level, title in before_headings}
    levels_after = {title: level for level, title in after_headings}
    level_warnings = [
        f"标题「{title}」层级从 H{levels_before[title]} 调整为 H{levels_after[title]}"
        for title in levels_before.keys() & levels_after.keys()
        if levels_before[title] != levels_after[title]
    ]
    before_chars = visible_char_count(original)
    after_chars = visible_char_count(rewritten)
    return {
        "sourceDisplayName": source_display_name,
        "instruction": instruction,
        "modelName": model_name,
        "originalCharCount": before_chars,
        "rewrittenCharCount": after_chars,
        "charChangeRatio": round((after_chars - before_chars) / before_chars, 4) if before_chars else 0,
        "changedBlockCount": changed_block_count(original, rewritten),
        "headingCountBefore": len(before_headings),
        "headingCountAfter": len(after_headings),
        "headingChanges": {
            "added": added,
            "removed": removed,
            "reordered": common_before != common_after,
            "levelWarnings": level_warnings,
        },
        "requestedOptimizations": _requested_optimizations(instruction),
        "validationWarnings": validation_warnings or [],
    }


__all__ = ["build_document_rewrite_summary", "changed_block_count", "visible_char_count"]