#!/usr/bin/env python3
"""Open one review artifact in a reusable right-side Herdr mcat pane."""

from __future__ import annotations

import argparse
import base64
import fcntl
import hashlib
import json
import os
import re
import secrets
import shutil
import subprocess
import tempfile
import time
from contextlib import contextmanager
from dataclasses import dataclass
from pathlib import Path
from typing import Callable, Mapping, Sequence

PANE_LABEL = "artifact presenter"
VIEWER_PROCESS_NAME = "mcat"
PANE_READY_ATTEMPTS = 40
PANE_READY_DELAY_SECONDS = 0.05
PANE_SHELL_STABLE_CHECKS = 2
VIEWER_START_ATTEMPTS = 40
SAFE_COMMAND_TOKEN = re.compile(r"^[A-Za-z0-9_./=-]+$")
VIEWER_LAUNCH_SCRIPT = """#!/usr/bin/env python3
import base64
import os
import sys
from pathlib import Path


def decode(value: str) -> str:
    return base64.urlsafe_b64decode(value.encode("ascii")).decode("utf-8")


acknowledgment, token, viewer, artifact = map(decode, sys.argv[1:])
Path(acknowledgment).write_text(token, encoding="utf-8")
os.execv(viewer, [viewer, artifact])
"""

RunCommand = Callable[..., subprocess.CompletedProcess[str]]
FindExecutable = Callable[[str], str | None]


@dataclass(frozen=True)
class PresentationResult:
    status: str
    artifact: Path
    pane_id: str | None = None
    reason: str | None = None

    def message(self) -> str:
        if self.status == "artifact-only":
            return f"artifact-only: {self.reason}; {self.artifact}"
        return f"{self.status}: pane {self.pane_id}; {self.artifact}"


def run_json(
    executable: str,
    args: Sequence[str],
    run: RunCommand,
) -> dict[str, object]:
    completed = run(
        [executable, *args],
        check=True,
        capture_output=True,
        text=True,
    )
    value = json.loads(completed.stdout)
    if not isinstance(value, dict):
        raise ValueError("Herdr returned a non-object response")
    return value


def panes_with_label(response: Mapping[str, object]) -> list[str]:
    result = response.get("result")
    if not isinstance(result, dict):
        return []
    panes = result.get("panes")
    if not isinstance(panes, list):
        return []
    pane_ids: list[str] = []
    for pane in panes:
        if not isinstance(pane, dict) or pane.get("label") != PANE_LABEL:
            continue
        pane_id = pane.get("pane_id")
        if isinstance(pane_id, str) and pane_id:
            pane_ids.append(pane_id)
    return pane_ids


def created_pane_id(response: Mapping[str, object]) -> str:
    result = response.get("result")
    pane = result.get("pane") if isinstance(result, dict) else None
    pane_id = pane.get("pane_id") if isinstance(pane, dict) else None
    if not isinstance(pane_id, str) or not pane_id:
        raise ValueError("Herdr split response is missing result.pane.pane_id")
    return pane_id


@dataclass(frozen=True)
class PaneProcessState:
    shell_pid: int
    foreground_pids: frozenset[int]
    foreground_names: frozenset[str]

    @property
    def shell_is_ready(self) -> bool:
        return self.shell_pid in self.foreground_pids

    @property
    def viewer_is_active(self) -> bool:
        return VIEWER_PROCESS_NAME in self.foreground_names


def pane_process_state(response: Mapping[str, object]) -> PaneProcessState:
    result = response.get("result")
    process_info = result.get("process_info") if isinstance(result, dict) else None
    if not isinstance(process_info, dict):
        raise ValueError("Herdr process response is missing process info")

    shell_pid = process_info.get("shell_pid")
    processes = process_info.get("foreground_processes")
    if not isinstance(shell_pid, int) or not isinstance(processes, list):
        raise ValueError("Herdr process response is missing shell state")

    pids: set[int] = set()
    names: set[str] = set()
    for process in processes:
        if not isinstance(process, dict):
            continue
        pid = process.get("pid")
        name = process.get("name")
        if isinstance(pid, int):
            pids.add(pid)
        if isinstance(name, str) and name:
            names.add(name)
    return PaneProcessState(shell_pid, frozenset(pids), frozenset(names))


def prepare_pane_for_command(
    herdr: str,
    pane_id: str,
    run: RunCommand,
    *,
    allow_startup_transition: bool,
) -> None:
    viewer_closed = False
    stable_shell_checks = 0
    for attempt in range(PANE_READY_ATTEMPTS):
        response = run_json(herdr, ["pane", "process-info", "--pane", pane_id], run)
        state = pane_process_state(response)
        if state.shell_is_ready:
            stable_shell_checks += 1
            if stable_shell_checks >= PANE_SHELL_STABLE_CHECKS:
                return
        else:
            stable_shell_checks = 0
        if state.viewer_is_active:
            if not viewer_closed:
                run(
                    [herdr, "pane", "send-keys", pane_id, "q"],
                    check=True,
                    capture_output=True,
                    text=True,
                )
                viewer_closed = True
        elif (
            state.foreground_pids
            and not state.shell_is_ready
            and not viewer_closed
            and not allow_startup_transition
        ):
            processes = ", ".join(sorted(state.foreground_names)) or "unknown"
            raise ValueError(f"pane is running an unrelated foreground process: {processes}")

        if attempt + 1 < PANE_READY_ATTEMPTS:
            time.sleep(PANE_READY_DELAY_SECONDS)

    raise ValueError("pane shell did not become ready for the artifact command")


def encode_argument(value: str) -> str:
    return base64.urlsafe_b64encode(value.encode("utf-8")).decode("ascii")


@contextmanager
def lock_pane(pane_id: str):
    runtime_directory = Path(os.environ.get("XDG_RUNTIME_DIR", tempfile.gettempdir()))
    lock_directory = runtime_directory / "pi-artifact-presenter-locks"
    lock_directory.mkdir(mode=0o700, exist_ok=True)
    lock_name = hashlib.sha256(pane_id.encode("utf-8")).hexdigest() + ".lock"
    descriptor = os.open(
        lock_directory / lock_name,
        os.O_CREAT | os.O_RDWR | os.O_CLOEXEC,
        0o600,
    )
    with os.fdopen(descriptor, "w") as handle:
        fcntl.flock(handle, fcntl.LOCK_EX)
        try:
            yield
        finally:
            fcntl.flock(handle, fcntl.LOCK_UN)


def run_mcat(
    herdr: str,
    mcat: str,
    pane_id: str,
    artifact: Path,
    run: RunCommand,
    *,
    reused: bool = False,
) -> None:
    with lock_pane(pane_id):
        prepare_pane_for_command(
            herdr,
            pane_id,
            run,
            allow_startup_transition=not reused,
        )

        token = secrets.token_hex(12)
        with tempfile.TemporaryDirectory(
            prefix="pi-artifact-presenter-",
            dir="/tmp",
        ) as acknowledgment_directory:
            temporary = Path(acknowledgment_directory)
            acknowledgment = temporary / "viewer-started"
            launcher = temporary / "launch-viewer.py"
            launcher.write_text(VIEWER_LAUNCH_SCRIPT, encoding="utf-8")
            command_parts = [
                "python3",
                str(launcher),
                encode_argument(str(acknowledgment)),
                encode_argument(token),
                encode_argument(mcat),
                encode_argument(str(artifact)),
            ]
            if not all(SAFE_COMMAND_TOKEN.fullmatch(part) for part in command_parts):
                raise ValueError("viewer launcher produced an unsafe terminal token")
            command = " ".join(command_parts)
            run(
                [herdr, "pane", "send-text", pane_id, command + "\r"],
                check=True,
                capture_output=True,
                text=True,
            )
            for attempt in range(VIEWER_START_ATTEMPTS):
                try:
                    if acknowledgment.read_text(encoding="utf-8") == token:
                        return
                except FileNotFoundError:
                    pass
                if attempt + 1 < VIEWER_START_ATTEMPTS:
                    time.sleep(PANE_READY_DELAY_SECONDS)

        raise ValueError("artifact command was delivered but did not start")


def present_in_workspace(
    artifact: Path,
    herdr: str,
    mcat: str,
    workspace_id: str,
    source_pane_id: str,
    run: RunCommand,
) -> PresentationResult:
    try:
        pane_list = run_json(herdr, ["pane", "list", "--workspace", workspace_id], run)
        existing_panes = panes_with_label(pane_list)
    except (json.JSONDecodeError, OSError, subprocess.SubprocessError, ValueError) as error:
        return PresentationResult("artifact-only", artifact, reason=f"could not list Herdr panes: {error}")

    for existing_pane in existing_panes:
        try:
            run_mcat(herdr, mcat, existing_pane, artifact, run, reused=True)
            return PresentationResult("reused", artifact, pane_id=existing_pane)
        except (OSError, subprocess.SubprocessError, ValueError):
            try:
                run(
                    [herdr, "pane", "rename", existing_pane, f"{PANE_LABEL} stale"],
                    check=False,
                    capture_output=True,
                    text=True,
                )
            except OSError:
                pass

    try:
        split = run_json(
            herdr,
            [
                "pane",
                "split",
                "--pane",
                source_pane_id,
                "--direction",
                "right",
                "--cwd",
                str(artifact.parent),
                "--no-focus",
            ],
            run,
        )
        pane_id = created_pane_id(split)
    except (json.JSONDecodeError, OSError, subprocess.SubprocessError, ValueError) as error:
        return PresentationResult("artifact-only", artifact, reason=f"could not create Herdr viewer: {error}")

    try:
        run(
            [herdr, "pane", "rename", pane_id, PANE_LABEL],
            check=True,
            capture_output=True,
            text=True,
        )
        run_mcat(herdr, mcat, pane_id, artifact, run)
        return PresentationResult("opened", artifact, pane_id=pane_id)
    except (OSError, subprocess.SubprocessError, ValueError) as error:
        try:
            run(
                [herdr, "pane", "close", pane_id],
                check=False,
                capture_output=True,
                text=True,
            )
        except OSError:
            pass
        return PresentationResult("artifact-only", artifact, reason=f"could not initialize Herdr viewer: {error}")


def present_document(
    document: Path,
    *,
    env: Mapping[str, str] = os.environ,
    which: FindExecutable = shutil.which,
    run: RunCommand = subprocess.run,
) -> PresentationResult:
    artifact = document.expanduser().resolve()
    if not artifact.is_file():
        raise ValueError(f"artifact is not a file: {artifact}")

    herdr = which("herdr")
    mcat = which("mcat")
    workspace_id = env.get("HERDR_WORKSPACE_ID")
    source_pane_id = env.get("HERDR_PANE_ID")
    if not herdr:
        return PresentationResult("artifact-only", artifact, reason="herdr is unavailable")
    if not mcat:
        return PresentationResult("artifact-only", artifact, reason="mcat is unavailable")
    if not workspace_id or not source_pane_id:
        return PresentationResult("artifact-only", artifact, reason="not running in a Herdr pane")

    with lock_pane(f"workspace:{workspace_id}"):
        return present_in_workspace(
            artifact,
            herdr,
            mcat,
            workspace_id,
            source_pane_id,
            run,
        )


def create_parser() -> argparse.ArgumentParser:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("artifact", type=Path, help="Local file to present with mcat")
    return parser


def main() -> int:
    args = create_parser().parse_args()
    try:
        result = present_document(args.artifact)
    except ValueError as error:
        print(error, file=os.sys.stderr)
        return 2
    print(result.message())
    return 0


if __name__ == "__main__":
    raise SystemExit(main())