#!/usr/bin/env python3
"""Install a skill from a GitHub repo path into $AGENTS_HOME/skills."""

from __future__ import annotations

import argparse
from dataclasses import dataclass
import os
import shutil
import subprocess
import sys
import tempfile
import urllib.error
import urllib.parse
import zipfile

from github_utils import github_request
DEFAULT_REF = "main"


@dataclass
class Args:
    url: str | None = None
    repo: str | None = None
    path: list[str] | None = None
    ref: str = DEFAULT_REF
    dest: str | None = None
    name: str | None = None
    method: str = "auto"


@dataclass
class Source:
    owner: str
    repo: str
    ref: str
    paths: list[str]
    repo_url: str | None = None


class InstallError(Exception):
    pass


def _agents_home() -> str:
    return os.path.expanduser("~/.agents")


def _tmp_root() -> str:
    base = os.path.join(tempfile.gettempdir(), "agents")
    os.makedirs(base, exist_ok=True)
    return base


def _request(url: str) -> bytes:
    return github_request(url, "agents-skill-install")


def _parse_github_url(url: str, default_ref: str) -> tuple[str, str, str, str | None]:
    parsed = urllib.parse.urlparse(url)
    if parsed.netloc != "github.com":
        raise InstallError("Only GitHub URLs are supported for download mode.")
    parts = [p for p in parsed.path.split("/") if p]
    if len(parts) < 2:
        raise InstallError("Invalid GitHub URL.")
    owner, repo = parts[0], parts[1]
    ref = default_ref
    subpath = ""
    if len(parts) > 2:
        if parts[2] in ("tree", "blob"):
            if len(parts) < 4:
                raise InstallError("GitHub URL missing ref or path.")
            ref = parts[3]
            subpath = "/".join(parts[4:])
        else:
            subpath = "/".join(parts[2:])
    return owner, repo, ref, subpath or None


def _download_repo_zip(owner: str, repo: str, ref: str, dest_dir: str) -> str:
    zip_url = f"https://codeload.github.com/{owner}/{repo}/zip/{ref}"
    zip_path = os.path.join(dest_dir, "repo.zip")
    try:
        payload = _request(zip_url)
    except urllib.error.HTTPError as exc:
        raise InstallError(f"Download failed: HTTP {exc.code}") from exc
    with open(zip_path, "wb") as file_handle:
        file_handle.write(payload)
    with zipfile.ZipFile(zip_path, "r") as zip_file:
        _safe_extract_zip(zip_file, dest_dir)
        top_levels = {name.split("/")[0] for name in zip_file.namelist() if name}
    if not top_levels:
        raise InstallError("Downloaded archive was empty.")
    if len(top_levels) != 1:
        raise InstallError("Unexpected archive layout.")
    return os.path.join(dest_dir, next(iter(top_levels)))


def _run_git(args: list[str]) -> None:
    result = subprocess.run(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True)
    if result.returncode != 0:
        raise InstallError(result.stderr.strip() or "Git command failed.")


def _safe_extract_zip(zip_file: zipfile.ZipFile, dest_dir: str) -> None:
    dest_root = os.path.realpath(dest_dir)
    for info in zip_file.infolist():
        extracted_path = os.path.realpath(os.path.join(dest_dir, info.filename))
        if extracted_path == dest_root or extracted_path.startswith(dest_root + os.sep):
            continue
        raise InstallError("Archive contains files outside the destination.")
    zip_file.extractall(dest_dir)


def _validate_relative_path(path: str) -> None:
    if os.path.isabs(path) or os.path.normpath(path).startswith(".."):
        raise InstallError("Skill path must be a relative path inside the repo.")


def _validate_skill_name(name: str) -> None:
    altsep = os.path.altsep
    if not name or os.path.sep in name or (altsep and altsep in name):
        raise InstallError("Skill name must be a single path segment.")
    if name in (".", ".."):
        raise InstallError("Invalid skill name.")


def _git_sparse_checkout(repo_url: str, ref: str, paths: list[str], dest_dir: str) -> str:
    repo_dir = os.path.join(dest_dir, "repo")
    clone_cmd = [
        "git",
        "clone",
        "--filter=blob:none",
        "--depth",
        "1",
        "--sparse",
        "--single-branch",
        "--branch",
        ref,
        repo_url,
        repo_dir,
    ]
    try:
        _run_git(clone_cmd)
    except InstallError:
        _run_git(
            [
                "git",
                "clone",
                "--filter=blob:none",
                "--depth",
                "1",
                "--sparse",
                "--single-branch",
                repo_url,
                repo_dir,
            ]
        )
    _run_git(["git", "-C", repo_dir, "sparse-checkout", "set", *paths])
    _run_git(["git", "-C", repo_dir, "checkout", ref])
    return repo_dir


def _validate_skill(path: str) -> None:
    if not os.path.isdir(path):
        raise InstallError(f"Skill path not found: {path}")
    skill_md = os.path.join(path, "SKILL.md")
    if not os.path.isfile(skill_md):
        raise InstallError("SKILL.md not found in selected skill directory.")


def _copy_skill(src: str, dest_dir: str) -> None:
    os.makedirs(os.path.dirname(dest_dir), exist_ok=True)
    if os.path.exists(dest_dir):
        raise InstallError(f"Destination already exists: {dest_dir}")
    shutil.copytree(src, dest_dir)


def _build_repo_url(owner: str, repo: str) -> str:
    return f"https://github.com/{owner}/{repo}.git"


def _build_repo_ssh(owner: str, repo: str) -> str:
    return f"git@github.com:{owner}/{repo}.git"


def _prepare_repo(source: Source, method: str, tmp_dir: str) -> str:
    if method in ("download", "auto"):
        try:
            return _download_repo_zip(source.owner, source.repo, source.ref, tmp_dir)
        except InstallError as exc:
            if method == "download":
                raise
            err_msg = str(exc)
            if "HTTP 401" in err_msg or "HTTP 403" in err_msg or "HTTP 404" in err_msg:
                pass
            else:
                raise
    if method in ("git", "auto"):
        repo_url = source.repo_url or _build_repo_url(source.owner, source.repo)
        try:
            return _git_sparse_checkout(repo_url, source.ref, source.paths, tmp_dir)
        except InstallError:
            repo_url = _build_repo_ssh(source.owner, source.repo)
            return _git_sparse_checkout(repo_url, source.ref, source.paths, tmp_dir)
    raise InstallError("Unsupported method.")


def _resolve_source(args: Args) -> Source:
    if args.url:
        owner, repo, ref, url_path = _parse_github_url(args.url, args.ref)
        if args.path is not None:
            paths = list(args.path)
        elif url_path:
            paths = [url_path]
        else:
            paths = []
        if not paths:
            raise InstallError("Missing --path for GitHub URL.")
        return Source(owner=owner, repo=repo, ref=ref, paths=paths)

    if not args.repo:
        raise InstallError("Provide --repo or --url.")
    if "://" in args.repo:
        return _resolve_source(
            Args(url=args.repo, repo=None, path=args.path, ref=args.ref)
        )

    repo_parts = [p for p in args.repo.split("/") if p]
    if len(repo_parts) != 2:
        raise InstallError("--repo must be in owner/repo format.")
    if not args.path:
        raise InstallError("Missing --path for --repo.")
    paths = list(args.path)
    return Source(
        owner=repo_parts[0],
        repo=repo_parts[1],
        ref=args.ref,
        paths=paths,
    )


def _default_dest() -> str:
    return os.path.join(_agents_home(), "skills")


def _parse_args(argv: list[str]) -> Args:
    parser = argparse.ArgumentParser(description="Install a skill from GitHub.")
    parser.add_argument("--repo", help="owner/repo")
    parser.add_argument("--url", help="https://github.com/owner/repo[/tree/ref/path]")
    parser.add_argument(
        "--path",
        nargs="+",
        help="Path(s) to skill(s) inside repo",
    )
    parser.add_argument("--ref", default=DEFAULT_REF)
    parser.add_argument("--dest", help="Destination skills directory")
    parser.add_argument(
        "--name", help="Destination skill name (defaults to basename of path)"
    )
    parser.add_argument(
        "--method",
        choices=["auto", "download", "git"],
        default="auto",
    )
    return parser.parse_args(argv, namespace=Args())


def main(argv: list[str]) -> int:
    args = _parse_args(argv)
    try:
        source = _resolve_source(args)
        source.ref = source.ref or args.ref
        if not source.paths:
            raise InstallError("No skill paths provided.")
        for path in source.paths:
            _validate_relative_path(path)
        dest_root = args.dest or _default_dest()
        tmp_dir = tempfile.mkdtemp(prefix="skill-install-", dir=_tmp_root())
        try:
            repo_root = _prepare_repo(source, args.method, tmp_dir)
            installed = []
            for path in source.paths:
                skill_name = args.name if len(source.paths) == 1 else None
                skill_name = skill_name or os.path.basename(path.rstrip("/"))
                _validate_skill_name(skill_name)
                if not skill_name:
                    raise InstallError("Unable to derive skill name.")
                dest_dir = os.path.join(dest_root, skill_name)
                if os.path.exists(dest_dir):
                    raise InstallError(f"Destination already exists: {dest_dir}")
                skill_src = os.path.join(repo_root, path)
                _validate_skill(skill_src)
                _copy_skill(skill_src, dest_dir)
                installed.append((skill_name, dest_dir))
        finally:
            if os.path.isdir(tmp_dir):
                shutil.rmtree(tmp_dir, ignore_errors=True)
        for skill_name, dest_dir in installed:
            print(f"Installed {skill_name} to {dest_dir}")
        return 0
    except InstallError as exc:
        print(f"Error: {exc}", file=sys.stderr)
        return 1


if __name__ == "__main__":
    raise SystemExit(main(sys.argv[1:]))
