#!/usr/bin/env python3
"""Install the lean Claude Code / Codex setup. Dry-run unless --apply is given."""

import argparse
import os
import shutil
import sys
import tempfile
from datetime import datetime
from pathlib import Path

ROOT = Path(__file__).resolve().parent.parent
LEAN = ROOT / "lean"
BEGIN = "<!-- lean-scaffold:begin -->"
END = "<!-- lean-scaffold:end -->"
SKILL = "lean-review"


class InstallError(Exception):
    pass


def block_text() -> str:
    body = (LEAN / "global" / "instructions.md").read_text(encoding="utf-8").strip()
    return f"{BEGIN}\n{body}\n{END}\n"


def split_block(text: str) -> tuple[str, str, str] | None:
    starts, ends = text.count(BEGIN), text.count(END)
    if starts == 0 and ends == 0:
        return None
    if starts != 1 or ends != 1 or text.index(BEGIN) > text.index(END):
        raise InstallError("malformed lean-scaffold markers; fix or remove them manually")
    head, rest = text.split(BEGIN, 1)
    _, tail = rest.split(END, 1)
    return head, BEGIN, tail.lstrip("\n")


def merged(existing: str | None) -> str:
    block = block_text()
    if existing is None or not existing.strip():
        return block
    parts = split_block(existing)
    if parts is None:
        return existing.rstrip("\n") + "\n\n" + block
    head, _, tail = parts
    return head + block + (("\n" + tail) if tail else "")


def without_block(existing: str) -> str:
    parts = split_block(existing)
    if parts is None:
        return existing
    head, _, tail = parts
    return (head.rstrip("\n") + ("\n\n" if head.strip() and tail else "") + tail).lstrip("\n")


def check_writable(path: Path) -> None:
    if path.is_symlink():
        raise InstallError(f"refusing symlink: {path}")
    if path.exists() and not path.is_file():
        raise InstallError(f"not a regular file: {path}")
    parent = path.parent
    while parent != parent.parent:
        if parent.is_symlink() and parent.name in {"skills", SKILL}:
            raise InstallError(f"refusing symlinked directory: {parent}")
        parent = parent.parent


def read_text(path: Path) -> str | None:
    check_writable(path)
    if not path.exists():
        return None
    try:
        return path.read_text(encoding="utf-8")
    except UnicodeDecodeError as err:
        raise InstallError(f"not UTF-8 text: {path}") from err


def backup_path(path: Path, now: datetime) -> Path:
    stamp = now.strftime("%Y%m%dT%H%M%S")
    candidate = path.with_name(f"{path.name}.bak-{stamp}")
    counter = 1
    while candidate.exists() or candidate.is_symlink():
        candidate = path.with_name(f"{path.name}.bak-{stamp}-{counter}")
        counter += 1
    return candidate


def write_file(path: Path, content: str, log: list[str], apply: bool, mode: int = 0o600) -> None:
    existing = read_text(path)
    if existing == content:
        log.append(f"unchanged  {path}")
        return
    if existing is None:
        log.append(f"create     {path}")
    else:
        target = backup_path(path, datetime.now())
        log.append(f"backup     {path} -> {target.name}")
        log.append(f"update     {path}")
    if not apply:
        return
    path.parent.mkdir(parents=True, exist_ok=True)
    if existing is not None:
        shutil.copy2(path, target, follow_symlinks=False)
        mode = path.stat().st_mode & 0o777
    fd, tmp = tempfile.mkstemp(dir=path.parent, prefix=f".{path.name}.")
    try:
        with os.fdopen(fd, "w", encoding="utf-8") as handle:
            handle.write(content)
        os.chmod(tmp, mode)
        os.replace(tmp, path)
    except BaseException:
        Path(tmp).unlink(missing_ok=True)
        raise


def require_dir(path: Path, label: str) -> Path:
    if not path.is_dir():
        raise InstallError(f"{label} is not an existing directory: {path}")
    return path.resolve()


def claude_home(arg: str | None) -> Path:
    return Path(arg or os.environ.get("CLAUDE_CONFIG_DIR") or Path.home() / ".claude")


def codex_home(arg: str | None) -> Path:
    return Path(arg or os.environ.get("CODEX_HOME") or Path.home() / ".codex")


def install_global(args: argparse.Namespace, log: list[str]) -> None:
    plans = []
    if not args.skip_claude:
        home = require_dir(claude_home(args.claude_home), "Claude home")
        plans.append((home / "CLAUDE.md", "block"))
        if not args.skip_skill:
            plans.append((home / "skills" / SKILL / "SKILL.md", "skill"))
    if not args.skip_codex:
        home = require_dir(codex_home(args.codex_home), "Codex home")
        plans.append((home / "AGENTS.md", "block"))
    for path, kind in plans:
        if kind == "block":
            write_file(path, merged(read_text(path)), log, args.apply)
            continue
        content = (LEAN / "skills" / SKILL / "SKILL.md").read_text(encoding="utf-8")
        existing = read_text(path)
        if existing not in (None, content) and not args.force:
            raise InstallError(f"{path} exists and differs; rerun with --force to back up and replace")
        write_file(path, content, log, args.apply)


def uninstall_global(args: argparse.Namespace, log: list[str]) -> None:
    homes = []
    if not args.skip_claude:
        homes.append(require_dir(claude_home(args.claude_home), "Claude home") / "CLAUDE.md")
    if not args.skip_codex:
        homes.append(require_dir(codex_home(args.codex_home), "Codex home") / "AGENTS.md")
    for path in homes:
        existing = read_text(path)
        if existing is None or split_block(existing) is None:
            log.append(f"absent     {path}")
            continue
        write_file(path, without_block(existing), log, args.apply)


def install_project(args: argparse.Namespace, log: list[str]) -> None:
    target = require_dir(Path(args.target), "project target")
    for name in ("AGENTS.md", "CLAUDE.md"):
        path = target / name
        content = (LEAN / "project" / name).read_text(encoding="utf-8")
        existing = read_text(path)
        if existing not in (None, content) and not args.force:
            raise InstallError(f"{path} exists and differs; rerun with --force to back up and replace")
        write_file(path, content, log, args.apply, mode=0o644)


def parser() -> argparse.ArgumentParser:
    top = argparse.ArgumentParser(description=__doc__)
    sub = top.add_subparsers(dest="command", required=True)
    for name in ("global", "uninstall", "project"):
        cmd = sub.add_parser(name)
        cmd.add_argument("--apply", action="store_true", help="write changes (default: dry-run)")
        cmd.add_argument("--force", action="store_true", help="replace differing files after backup")
        if name == "project":
            cmd.add_argument("target", help="existing project directory")
            continue
        cmd.add_argument("--claude-home", help="default: $CLAUDE_CONFIG_DIR or ~/.claude")
        cmd.add_argument("--codex-home", help="default: $CODEX_HOME or ~/.codex")
        cmd.add_argument("--skip-claude", action="store_true")
        cmd.add_argument("--skip-codex", action="store_true")
        cmd.add_argument("--skip-skill", action="store_true", help="do not install the lean-review skill")
    return top


def main(argv: list[str] | None = None) -> int:
    args = parser().parse_args(argv)
    log: list[str] = []
    handler = {"global": install_global, "uninstall": uninstall_global, "project": install_project}[args.command]
    try:
        if args.apply:
            handler(argparse.Namespace(**{**vars(args), "apply": False}), [])
        handler(args, log)
    except InstallError as err:
        print(f"error: {err}", file=sys.stderr)
        return 2
    print("\n".join(log))
    if not args.apply:
        print("dry-run: no files written; add --apply to write")
    return 0


if __name__ == "__main__":
    sys.exit(main())