"""Git diff scanning: changed files, dirs, and per-file added-line ranges."""
from __future__ import annotations

import re
import subprocess
from pathlib import PurePosixPath


_HCL_SUFFIXES = (".tf", ".tf.json", ".hcl")
_HUNK_RE = re.compile(r"^@@ -\d+(?:,\d+)? \+(\d+)(?:,(\d+))? @@")


def _run_git_diff(repo: str, base: str, head: str) -> str:
    result = subprocess.run(
        [
            "git", "-C", repo,
            "-c", "diff.noprefix=false",
            "-c", "color.ui=never",
            "diff", "--no-ext-diff", "--unified=0", f"{base}...{head}"
        ],
        capture_output=True, text=True, check=False,
    )
    if result.returncode != 0:
        raise RuntimeError(f"git diff failed: {result.stderr.strip()}")
    return result.stdout


def _iter_file_blocks(diff_text: str):
    """Yield (path, block_text) for each file section in a unified diff."""
    current_path: str | None = None
    buf: list[str] = []
    for line in diff_text.splitlines():
        if line.startswith("diff --git "):
            if current_path is not None:
                yield current_path, "\n".join(buf)
            current_path = None
            buf = []
        elif line.startswith("+++ b/"):
            current_path = line[len("+++ b/"):]
        if current_path is not None:
            buf.append(line)
    if current_path is not None:
        yield current_path, "\n".join(buf)


def changed_files(repo: str, base: str, head: str) -> list[str]:
    out: list[str] = []
    for path, _ in _iter_file_blocks(_run_git_diff(repo, base, head)):
        if path.endswith(_HCL_SUFFIXES):
            out.append(path)
    return out


def is_terragrunt_file(path: str) -> bool:
    return PurePosixPath(path).name == "terragrunt.hcl"


def changed_dirs(repo: str, base: str, head: str) -> set[str]:
    return {str(PurePosixPath(p).parent) for p in changed_files(repo, base, head)}


def changed_line_ranges(
    repo: str, base: str, head: str, path: str,
) -> list[tuple[int, int]]:
    """Return inclusive (start, end) line ranges of *added* lines in `path`."""
    ranges: list[tuple[int, int]] = []
    for fpath, block in _iter_file_blocks(_run_git_diff(repo, base, head)):
        if fpath != path:
            continue
        cur: int | None = None
        run_start: int | None = None
        run_end: int | None = None
        for line in block.splitlines():
            m = _HUNK_RE.match(line)
            if m:
                if run_start is not None:
                    ranges.append((run_start, run_end))  # type: ignore[arg-type]
                    run_start = run_end = None
                cur = int(m.group(1))
                continue
            if cur is None:
                continue
            if line.startswith("+") and not line.startswith("+++"):
                if run_start is None:
                    run_start = cur
                run_end = cur
                cur += 1
            elif line.startswith("-") and not line.startswith("---"):
                continue
            else:
                if run_start is not None:
                    ranges.append((run_start, run_end))  # type: ignore[arg-type]
                    run_start = run_end = None
                cur += 1
        if run_start is not None:
            ranges.append((run_start, run_end))  # type: ignore[arg-type]
    return ranges