"""Versioned Pattern Catalog — files-first source of truth (FR-U3; T02).

The catalog is a directory of one JSON file per Solution Pattern
(``<catalog_dir>/<pattern-id>.json``). Files originate the work; the State Hub
indexes them (ADR-001 / PRD §9). Identity is the pattern ``id`` (derived from the
source candidate key), so re-promoting the same detect candidate maps to the same
file — dedup is structural, not heuristic.

:meth:`Catalog.upsert` is the one write path and is **idempotent**:

* new id                       -> written as-is                  (``added``)
* same id, identical content   -> no write, no version bump      (``unchanged``)
* same id, only status/flags   -> updated in place, no bump      (``updated``)
* same id, content changed     -> version bumped, prior snapshot
                                  appended to ``<id>.history.jsonl`` (``versioned``)

History is append-only alongside the current file, so the catalog dir stays one
clean current file per pattern while every superseded version is recoverable.
"""

from __future__ import annotations

import json
import os
from datetime import datetime, timezone
from typing import Optional

from .schema import SolutionPattern

# Content fields that define a pattern's substance. Version, timestamps, status,
# and distribution_ready are metadata — changes to them never bump the version.
_CONTENT_KEYS = ("name", "polarity", "problem", "resolutions", "scope",
                 "provenance", "rendering_hints", "covers")

ADDED = "added"
UNCHANGED = "unchanged"
UPDATED = "updated"
VERSIONED = "versioned"


def _now() -> str:
    return datetime.now(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")


def _content(p: SolutionPattern) -> str:
    d = p.to_dict()
    return json.dumps({k: d[k] for k in _CONTENT_KEYS}, sort_keys=True)


class Catalog:
    """File-backed catalog of versioned :class:`SolutionPattern` artifacts."""

    def __init__(self, catalog_dir: str) -> None:
        self.dir = catalog_dir
        os.makedirs(self.dir, exist_ok=True)

    # --- paths --------------------------------------------------------------

    def _path(self, pattern_id: str) -> str:
        return os.path.join(self.dir, f"{pattern_id}.json")

    def _history_path(self, pattern_id: str) -> str:
        return os.path.join(self.dir, f"{pattern_id}.history.jsonl")

    # --- reads --------------------------------------------------------------

    def load(self, pattern_id: str) -> Optional[SolutionPattern]:
        path = self._path(pattern_id)
        if not os.path.exists(path):
            return None
        with open(path, encoding="utf-8") as fh:
            return SolutionPattern.from_json(fh.read())

    def list(self) -> list[SolutionPattern]:
        out: list[SolutionPattern] = []
        for name in sorted(os.listdir(self.dir)):
            if name.endswith(".json") and not name.endswith(".history.jsonl"):
                with open(os.path.join(self.dir, name), encoding="utf-8") as fh:
                    out.append(SolutionPattern.from_json(fh.read()))
        return out

    def history(self, pattern_id: str) -> list[dict]:
        path = self._history_path(pattern_id)
        if not os.path.exists(path):
            return []
        with open(path, encoding="utf-8") as fh:
            return [json.loads(line) for line in fh if line.strip()]

    def find_for(self, signal_key: str, locus: str = "") -> Optional[SolutionPattern]:
        """Best catalog pattern for a detect signal: exact id first, then ``covers``.

        Lets a signal that doesn't share a pattern's exact key (e.g. a
        ``recurring_error`` fingerprint) inherit the curated recommendation when a
        pattern declares it covers that text.
        """
        exact = self.load(SolutionPattern.make_id(signal_key))
        if exact is not None:
            return exact
        hay = f"{signal_key} {locus}".lower()
        for p in self.list():  # sorted by id -> deterministic
            if any(c.lower() in hay for c in p.covers):
                return p
        return None

    # --- the single write path ---------------------------------------------

    def upsert(self, pattern: SolutionPattern) -> str:
        """Insert or version-update a pattern. Returns the action taken."""
        existing = self.load(pattern.id)
        now = _now()

        if existing is None:
            pattern.created_at = pattern.created_at or now
            pattern.updated_at = now
            self._write(pattern)
            return ADDED

        if _content(existing) == _content(pattern):
            # substance unchanged — only persist a metadata (status/flag) change
            if (existing.status == pattern.status
                    and existing.distribution_ready == pattern.distribution_ready):
                return UNCHANGED
            existing.status = pattern.status
            existing.distribution_ready = pattern.distribution_ready
            existing.updated_at = now
            self._write(existing)
            return UPDATED

        # substance changed: archive the old version, bump, write the new one
        self._append_history(existing)
        pattern.version = SolutionPattern.bump_version(existing.version)
        pattern.created_at = existing.created_at or now
        pattern.updated_at = now
        self._write(pattern)
        return VERSIONED

    # --- internals ----------------------------------------------------------

    def _write(self, pattern: SolutionPattern) -> None:
        with open(self._path(pattern.id), "w", encoding="utf-8") as fh:
            fh.write(pattern.to_json())
            fh.write("\n")

    def _append_history(self, superseded: SolutionPattern) -> None:
        superseded.status = "superseded"
        with open(self._history_path(superseded.id), "a", encoding="utf-8") as fh:
            fh.write(json.dumps(superseded.to_dict(), sort_keys=True))
            fh.write("\n")