"""Text diffs between stored versions or a version and the working copy."""

from __future__ import annotations

import difflib
import re
from typing import Any

_WS = re.compile(r"\s+")


def _lines(content: bytes) -> list[str]:
    return content.decode("utf-8", errors="replace").splitlines(keepends=True)


def _normalize(line: str, ignore_whitespace: bool, ignore_eol: bool) -> str:
    if ignore_whitespace:
        return _WS.sub(" ", line).strip()
    if ignore_eol:
        return line.rstrip("\r\n")
    return line


def hunks(
    a: bytes,
    b: bytes,
    context: int = 3,
    ignore_whitespace: bool = False,
    ignore_eol: bool = False,
) -> list[dict[str, Any]]:
    a_lines, b_lines = _lines(a), _lines(b)
    a_norm = [_normalize(x, ignore_whitespace, ignore_eol) for x in a_lines]
    b_norm = [_normalize(x, ignore_whitespace, ignore_eol) for x in b_lines]
    matcher = difflib.SequenceMatcher(None, a_norm, b_norm, autojunk=False)
    result = []
    for group in matcher.get_grouped_opcodes(context):
        first, last = group[0], group[-1]
        lines = []
        for tag, i1, i2, j1, j2 in group:
            if tag == "equal":
                lines += [{"op": " ", "text": x} for x in a_lines[i1:i2]]
                continue
            if tag in ("replace", "delete"):
                lines += [{"op": "-", "text": x} for x in a_lines[i1:i2]]
            if tag in ("replace", "insert"):
                lines += [{"op": "+", "text": x} for x in b_lines[j1:j2]]
        result.append({
            "old_start": first[1] + 1,
            "old_lines": last[2] - first[1],
            "new_start": first[3] + 1,
            "new_lines": last[4] - first[3],
            "lines": lines,
        })
    return result


def unified(hunk_list: list[dict[str, Any]], from_label: str, to_label: str) -> str:
    if not hunk_list:
        return ""
    out = [f"--- {from_label}\n", f"+++ {to_label}\n"]
    for h in hunk_list:
        out.append(f"@@ -{h['old_start']},{h['old_lines']} +{h['new_start']},{h['new_lines']} @@\n")
        for line in h["lines"]:
            text = line["text"]
            out.append(line["op"] + text + ("" if text.endswith("\n") else "\n\\ No newline at end of file\n"))
    return "".join(out)


def side_by_side_html(a: bytes, b: bytes, from_label: str, to_label: str, context: int = 3) -> str:
    return difflib.HtmlDiff(wrapcolumn=100).make_file(
        _lines(a), _lines(b), from_label, to_label, context=True, numlines=context
    )