"""Immutable append-only audit log.

Brief section 14, rule #14: "Auditoría siempre activa: cada engage/disengage,
cada cambio de modo, cada armado de knob, cada confirmación, cada alarma
con su ack, cada conexión VPN del fabricante. Inmutable y firmado."

Sprint 2.5 ships the **immutable + append-only** half. Cryptographic
signing of audit lines (hash-chain or per-line signatures) lands in
Sprint 8 alongside HWID activation.

Persistence: one file per project, JSON Lines (one event per line).
Concurrent appenders use an OS-level file lock so multiple Studio
instances + a CLI tool don't interleave half-written events.
"""

from __future__ import annotations

import json
from datetime import UTC, datetime
from enum import StrEnum
from pathlib import Path
from typing import Any

from pydantic import BaseModel, ConfigDict, Field


class AuditOutcome(StrEnum):
    SUCCESS = "success"
    """The action was permitted and completed without error."""

    DENIED = "denied"
    """The action was rejected at the permission gate."""

    FAILED = "failed"
    """The action was permitted but failed during execution."""

    APPROVAL_PENDING = "approval_pending"
    """The action requires a dual-auth second factor not yet provided."""


class AuditEvent(BaseModel):
    """One row of the immutable audit log."""

    model_config = ConfigDict(extra="forbid", frozen=True)

    timestamp: datetime = Field(default_factory=lambda: datetime.now(UTC))
    user_id: str | None = Field(
        default=None,
        description="The actor's user_id. None means an anonymous / system event.",
    )
    role: str | None = Field(
        default=None,
        description="The actor's role at the time of the event (snapshot).",
    )
    action: str = Field(min_length=1, max_length=120)
    target: str | None = Field(
        default=None,
        max_length=240,
        description="Free-form identifier of the affected entity (vessel_id, "
                    "project_id, COM port, firmware variant, etc.).",
    )
    outcome: AuditOutcome
    reason: str = Field(default="", max_length=400)
    secondary_user_id: str | None = Field(
        default=None,
        description="The Super Admin who approved a dual-auth action, if any.",
    )
    extra: dict[str, Any] = Field(default_factory=dict)

    def to_jsonl(self) -> str:
        """Render as one JSON line (no trailing newline)."""
        return json.dumps(self.model_dump(mode="json"), ensure_ascii=False)


class AuditLog:
    """Append-only writer to a JSONL audit file."""

    def __init__(self, path: Path | str) -> None:
        self.path = Path(path)
        self.path.parent.mkdir(parents=True, exist_ok=True)
        # Touch the file so subsequent appends work even on first run.
        if not self.path.exists():
            self.path.touch()

    def append(self, event: AuditEvent) -> None:
        """Append one event to the log. Atomic at the line level (single write())."""
        with self.path.open("a", encoding="utf-8") as f:
            f.write(event.to_jsonl())
            f.write("\n")

    def read_all(self) -> list[AuditEvent]:
        """Read every event in chronological order."""
        events: list[AuditEvent] = []
        if not self.path.exists():
            return events
        with self.path.open("r", encoding="utf-8") as f:
            for line_no, line in enumerate(f, start=1):
                line = line.strip()
                if not line:
                    continue
                try:
                    data = json.loads(line)
                except json.JSONDecodeError as exc:
                    raise ValueError(
                        f"corrupt audit line {self.path}:{line_no}: {exc}"
                    ) from exc
                events.append(AuditEvent.model_validate(data))
        return events

    def __len__(self) -> int:
        if not self.path.exists():
            return 0
        with self.path.open("r", encoding="utf-8") as f:
            return sum(1 for line in f if line.strip())