"""Working-tree git diff collection shared by the CLI and gateway ``/diff``.

Surface-agnostic so the CLI (colored terminal) and gateway (fenced, truncated
messages) render the same data. Modes: ``working`` (unstaged + untracked),
``staged`` (``git diff --cached``), ``all`` (everything since HEAD plus untracked).
Untracked files are folded in via ``git diff --no-index /dev/null <file>`` so
brand-new files show as additions instead of being invisible.
"""

from __future__ import annotations

import os
import shutil
import subprocess
from contextlib import suppress
from typing import Dict, List

from hermes_cli._subprocess_compat import harden_git_argv, noninteractive_git_env, selected_git_env

_GIT_TIMEOUT = 15
_MAX_UNTRACKED_FILES = 50  # sanity cap so a node_modules explosion can't hang us

_MODE_ARGS = {
    "working": ["diff"],
    "staged": ["diff", "--cached"],
    "all": ["diff", "HEAD"],
}
VALID_MODES = tuple(_MODE_ARGS)


def _run(args: List[str], cwd: str, timeout: int = _GIT_TIMEOUT):
    """Run git, returning (returncode, stdout). Never raises on git failure.

    Hardened against a malicious repo's ``.git/config`` (GHSA-7x36-8jrh-v4pw):
    ``noninteractive_git_env`` disables fsmonitor/hooks/pager/editor/credential
    sinks, and ``harden_git_argv`` appends ``--no-ext-diff --no-textconv`` to
    the diff-rendering subcommands so attribute-scoped diff/textconv drivers
    can't execute either.
    """
    env = noninteractive_git_env(selected_git_env())
    command = shutil.which("git", path=env.get("PATH", ""))
    if command is None:
        return 127, ""
    proc = subprocess.run(
        [command, "-c", "core.quotePath=false", *harden_git_argv(args)],
        cwd=cwd, capture_output=True, text=True, timeout=timeout,
        encoding="utf-8", errors="replace",
        stdin=subprocess.DEVNULL, env=env,
    )
    return proc.returncode, proc.stdout


def _untracked_files(cwd: str) -> List[str]:
    code, out = _run(["ls-files", "--others", "--exclude-standard"], cwd)
    return [line for line in out.splitlines() if line.strip()] if code == 0 else []


def _untracked_diff(cwd: str, files: List[str]) -> str:
    """Render untracked files as new-file diffs via ``git diff --no-index``."""
    chunks: List[str] = []
    for rel in files[:_MAX_UNTRACKED_FILES]:
        with suppress(subprocess.TimeoutExpired, OSError):
            # --no-index exits 1 when the files differ — that's the success
            # path here, so ignore the return code and keep the output.
            _, out = _run(
                ["diff", "--no-ext-diff", "--no-index", "--", os.devnull, rel], cwd,
            )
            if out.strip():
                chunks.append(out.rstrip("\n"))
    if len(files) > _MAX_UNTRACKED_FILES:
        chunks.append(f"... ({len(files) - _MAX_UNTRACKED_FILES} more untracked files not shown)")
    return "\n".join(chunks)


def collect_working_diff(cwd: str, mode: str = "working",
                         paths: List[str] | None = None) -> Dict:
    """Collect a git diff of the working directory.

    Returns ``{"success", "stat", "diff", "untracked", "empty"}`` on success or
    ``{"success": False, "error": ...}`` when git is unavailable / not a repo.
    ``paths`` optionally restricts the diff to specific pathspecs (passed
    through to git verbatim, so quoted paths with spaces survive).
    """
    if mode not in VALID_MODES:
        return {"success": False,
                "error": f"Unknown mode '{mode}'. Use: {', '.join(VALID_MODES)}"}

    try:
        code, _ = _run(["rev-parse", "--is-inside-work-tree"], cwd, timeout=5)
    except (subprocess.TimeoutExpired, OSError) as e:
        return {"success": False, "error": f"git failed: {e}"}
    if code == 127:
        return {"success": False, "error": "git is not installed or not on PATH."}
    if code != 0:
        return {"success": False, "error": "Not a git repository."}

    # --no-ext-diff: a user-configured external differ (diff.external in
    # gitconfig, e.g. difftastic) replaces the unified-diff format that the
    # CLI/gateway renderers and truncation logic parse. Force the internal
    # diff engine so the collected output shape is stable for all users.
    # (_run's harden_git_argv also enforces this; explicit here for clarity.)
    base_args = [a for a in _MODE_ARGS[mode] if a != "diff"]
    base_args = ["diff", "--no-ext-diff", *base_args]
    pathspec = ["--", *paths] if paths else []
    try:
        _, stat_out = _run([*base_args, "--stat", *pathspec], cwd)
        _, diff_out = _run([*base_args, *pathspec], cwd, timeout=_GIT_TIMEOUT * 2)
        untracked = _untracked_files(cwd) if mode in ("working", "all") and not paths else []
        untracked_diff = _untracked_diff(cwd, untracked) if untracked else ""
    except subprocess.TimeoutExpired:
        return {"success": False, "error": "git diff timed out."}
    except OSError as e:
        return {"success": False, "error": f"git failed: {e}"}

    stat, diff = stat_out.strip(), diff_out.strip()
    if untracked_diff:
        diff = f"{diff}\n{untracked_diff}".strip()
    result = {"success": True, "stat": stat, "diff": diff, "untracked": untracked}
    if not stat and not diff and not untracked:
        result["empty"] = True
    return result