"""Unified diff generator for squid.conf changes.

Provides a small, pure-Python unified-diff renderer. We avoid Python's
``difflib.unified_diff`` because we want tight control over hunk sizing
and color classes used by the UI.
"""
from __future__ import annotations

import difflib
from typing import Iterable


def unified_diff(old: str, new: str, context: int = 3, lineterm: str = "\n") -> list[dict]:
    """Return a list of diff lines as dicts: {kind, text, old_lineno, new_lineno}.

    kind: 'equal' | 'add' | 'del' | 'hunk' | 'meta'
    """
    old_lines = old.splitlines(keepends=False)
    new_lines = new.splitlines(keepends=False)

    sm = difflib.SequenceMatcher(a=old_lines, b=new_lines, autojunk=False)
    out: list[dict] = []

    old_no = 0
    new_no = 0

    def push_meta(text: str):
        out.append({"kind": "meta", "text": text, "old_lineno": None, "new_lineno": None})

    push_meta("--- 当前配置 (existing)")
    push_meta("+++ 新配置 (proposed)")

    for tag, i1, i2, j1, j2 in sm.get_opcodes():
        if tag == "equal":
            # show context lines (limit to first/last of long equal runs)
            block = old_lines[i1:i2]
            if len(block) <= context * 2 + 1:
                for k, ln in enumerate(block):
                    old_no += 1
                    new_no += 1
                    out.append({
                        "kind": "equal", "text": ln,
                        "old_lineno": old_no, "new_lineno": new_no,
                    })
            else:
                # head
                for k in range(context):
                    old_no += 1; new_no += 1
                    out.append({
                        "kind": "equal", "text": old_lines[i1 + k],
                        "old_lineno": old_no, "new_lineno": new_no,
                    })
                out.append({
                    "kind": "meta", "text": f"... ({i2 - i1 - 2 * context} equal lines skipped) ...",
                    "old_lineno": None, "new_lineno": None,
                })
                old_no += (i2 - i1 - 2 * context)
                new_no += (i2 - i1 - 2 * context)
                # tail
                for k in range(i2 - context, i2):
                    old_no += 1; new_no += 1
                    out.append({
                        "kind": "equal", "text": old_lines[k],
                        "old_lineno": old_no, "new_lineno": new_no,
                    })
        elif tag == "replace":
            for ln in old_lines[i1:i2]:
                old_no += 1
                out.append({
                    "kind": "del", "text": ln,
                    "old_lineno": old_no, "new_lineno": None,
                })
            for ln in new_lines[j1:j2]:
                new_no += 1
                out.append({
                    "kind": "add", "text": ln,
                    "old_lineno": None, "new_lineno": new_no,
                })
        elif tag == "delete":
            for ln in old_lines[i1:i2]:
                old_no += 1
                out.append({
                    "kind": "del", "text": ln,
                    "old_lineno": old_no, "new_lineno": None,
                })
        elif tag == "insert":
            for ln in new_lines[j1:j2]:
                new_no += 1
                out.append({
                    "kind": "add", "text": ln,
                    "old_lineno": None, "new_lineno": new_no,
                })
    return out


def summarize(diff: list[dict]) -> dict:
    """Return {adds, dels, total_changed}."""
    adds = sum(1 for d in diff if d["kind"] == "add")
    dels = sum(1 for d in diff if d["kind"] == "del")
    return {"adds": adds, "dels": dels, "total_changed": adds + dels}


def render_html(diff: list[dict]) -> str:
    """Render diff to HTML with classes used by static/style.css."""
    parts = ['<div class="diff-container">']
    for d in diff:
        kind = d["kind"]
        text = d["text"]
        # escape HTML
        esc = (text.replace("&", "&amp;").replace("<", "&lt;").replace(">", "&gt;"))
        old_n = d.get("old_lineno") or ""
        new_n = d.get("new_lineno") or ""
        if kind == "add":
            parts.append(f'<div class="diff-line diff-add"><span class="diff-ln">{old_n:>4}</span><span class="diff-ln">{new_n:>4}</span> + {esc}</div>')
        elif kind == "del":
            parts.append(f'<div class="diff-line diff-del"><span class="diff-ln">{old_n:>4}</span><span class="diff-ln">{new_n:>4}</span> - {esc}</div>')
        elif kind == "equal":
            parts.append(f'<div class="diff-line diff-ctx"><span class="diff-ln">{old_n:>4}</span><span class="diff-ln">{new_n:>4}</span>   {esc}</div>')
        else:  # meta
            parts.append(f'<div class="diff-line diff-hunk">{esc}</div>')
    parts.append("</div>")
    return "\n".join(parts)