"""
app/utils/storage.py
---------------------
Storage abstraction for uploaded photo files (R2 object-storage migration).

Ported from the single-tenant tree (§22 Phase 1/2) with one multi-tenant
addition: per-tenant object-key prefixing. See "Tenant isolation" below.

One interface, backend selected by config ``STORAGE_BACKEND``:
  - ``local`` (default): files under ``app/static/uploads``, served via
    ``url_for('static', ...)``. **Byte-for-byte identical** to the behavior
    before this abstraction existed — MT-2 is a no-op.
  - ``s3``: Cloudflare R2 / any S3-compatible store. Private bucket; browser/API
    URLs are short-lived presigned GETs. Requires ``boto3`` and the ``R2_*``
    config keys. boto3 is imported lazily, so a ``local`` deploy needs neither.
    Inert until MT-8 flips STORAGE_BACKEND per tenant.

The stored **key** is always the relative path ``uploads/<subfolder>/<file>`` —
the exact string persisted in the DB (`Issue.photo_path`, `result_photos[]`,
`mobile_photo_paths[]`, `Inspection.form_data` image values,
`InspectionResult.photo_path`). It never changes between backends or between
tenants, so there is **no schema migration** and no data rewrite.

Tenant isolation
----------------
Every tenant's DB holds keys in the same ``uploads/...`` namespace, so on a
shared object store those keys would collide across tenants. The prefix
``t<tenant_id>/`` is therefore applied **inside the S3 backend, on the wire**
(``_object_key``) — never in the DB, never in a template, never in an API
payload. Callers stay tenant-agnostic; the DB stays portable.

  DB value:     uploads/issue_photos/ab12….jpg
  R2 object:    t3/uploads/issue_photos/ab12….jpg

The **local** backend deliberately does NOT prefix: its layout is the existing
on-disk tree, and prefixing would relocate every existing file (that is not a
no-op, and MT-2 must be one). Local mode therefore keeps today's shared
``app/static/uploads`` directory across tenants — an isolation weakness that
predates this module and is retired when a tenant moves to ``s3`` in MT-8.

Public module-level API (delegates to the active backend):

    save(file_obj, subfolder) -> key    # write an uploaded file, return its key
    media_url(key) -> str               # browser/API URL for a key ('' if falsy)
    read(key) -> bytes                  # raw bytes (e.g. PDF export image embed)
    exists(key) -> bool
    delete(key) -> None                 # best-effort file removal
    abs_local_path(key) -> str          # physical path under static/ (local backend)
    materialize_to_dir(keys) -> (base_dir, cleanup)

NOTE: extension / magic-byte validation stays in the CALLER (e.g. `_save_photo`,
`api/photos.upload_photo`) — this module only moves bytes and builds URLs.
"""

import os
import uuid
import logging

from flask import current_app, g, url_for

logger = logging.getLogger(__name__)


def _ext_of(filename):
    """Lower-case extension of a filename, defaulting to 'jpg' when absent."""
    name = filename or ''
    return name.rsplit('.', 1)[-1].lower() if '.' in name else 'jpg'


def tenant_key_prefix():
    """Object-key prefix isolating one tenant's media from another's.

    Returns ``'t<id>/'`` when multi-tenancy is enabled and a tenant is bound to
    the current context, else ``''``.

    The empty case covers three legitimate situations:
      - MULTI_TENANT_ENABLED is false (plain single-tenant deploy),
      - a cross-tenant cron/CLI context with no tenant bound,
      - request contexts exempt from the tenant middleware.

    Callers that must not silently write to an unprefixed key guard on this
    themselves — see ``S3Backend.save``.
    """
    if not current_app.config.get('MULTI_TENANT_ENABLED'):
        return ''
    tenant = getattr(g, 'tenant', None) if g else None
    return f't{tenant.id}/' if tenant is not None else ''


# ── Local filesystem backend (current behavior) ───────────────────────────────

class LocalBackend:
    """Files under ``app/static/uploads``, served by Flask/Nginx static route.

    No tenant prefixing — see module docstring ("Tenant isolation").
    """

    name = 'local'

    def _uploads_root(self):
        # config UPLOAD_FOLDER == <root>/app/static/uploads
        return current_app.config['UPLOAD_FOLDER']

    def _static_folder(self):
        # <root>/app/static — key 'uploads/...' resolves under here
        return os.path.join(current_app.root_path, 'static')

    def save(self, file_obj, subfolder):
        """Write ``file_obj`` under ``subfolder``; return the ``uploads/...`` key.

        Replicates the previous inline logic in `_save_photo` / `upload_photo`
        exactly: random uuid filename, `os.makedirs(exist_ok=True)`, same key.
        """
        ext      = _ext_of(file_obj.filename)
        filename = f'{uuid.uuid4().hex}.{ext}'
        dest_dir = os.path.join(self._uploads_root(), subfolder)
        os.makedirs(dest_dir, exist_ok=True)
        file_obj.save(os.path.join(dest_dir, filename))
        return f'uploads/{subfolder}/{filename}'

    def abs_local_path(self, key):
        return os.path.normpath(os.path.join(self._static_folder(), key))

    def media_url(self, key, external=False):
        if not key:
            return ''
        # external=True yields an absolute URL (scheme+host) for API responses
        # consumed off-origin (the iPad); templates call with external=False.
        return url_for('static', filename=key, _external=external)

    def read(self, key):
        with open(self.abs_local_path(key), 'rb') as fh:
            return fh.read()

    def exists(self, key):
        return bool(key) and os.path.isfile(self.abs_local_path(key))

    def delete(self, key):
        if not key:
            return
        try:
            path = self.abs_local_path(key)
            if os.path.isfile(path):
                os.remove(path)
        except OSError:
            pass

    def materialize_to_dir(self, keys):
        # Files already live under the static folder — no copy needed.
        return self._static_folder(), (lambda: None)


# ── Cloudflare R2 / S3-compatible backend ─────────────────────────────────────

_CONTENT_TYPES = {
    'jpg': 'image/jpeg', 'jpeg': 'image/jpeg',
    'png': 'image/png', 'gif': 'image/gif',
}


class S3Backend:
    """
    Cloudflare R2 (or any S3-compatible store). Objects are private; browser/API
    URLs are short-lived presigned GETs. The object key == tenant prefix + the
    DB path string (see module docstring).

    boto3 is imported lazily so a 'local' deployment doesn't require it installed.
    """

    name = 's3'

    def __init__(self):
        import boto3                              # lazy — only when s3 is active
        from botocore.config import Config as _BotoConfig

        cfg = current_app.config
        missing = [k for k in ('R2_ENDPOINT_URL', 'R2_ACCESS_KEY_ID',
                               'R2_SECRET_ACCESS_KEY', 'R2_BUCKET') if not cfg.get(k)]
        if missing:
            raise RuntimeError(f'STORAGE_BACKEND=s3 but missing config: {", ".join(missing)}')

        self.bucket    = cfg['R2_BUCKET']
        self.ttl       = int(cfg.get('R2_PRESIGN_TTL', 86400))
        self.fallback  = bool(cfg.get('R2_MEDIA_FALLBACK', False))
        self._client   = boto3.client(
            's3',
            endpoint_url          = cfg['R2_ENDPOINT_URL'],
            aws_access_key_id     = cfg['R2_ACCESS_KEY_ID'],
            aws_secret_access_key = cfg['R2_SECRET_ACCESS_KEY'],
            region_name           = 'auto',
            config                = _BotoConfig(signature_version='s3v4'),
        )
        # A LocalBackend for transition fallback (read/media_url when object absent).
        self._local = LocalBackend()

    # ── Key mapping ──────────────────────────────────────────────────────────

    def _object_key(self, key):
        """DB key -> on-the-wire object key (tenant-prefixed)."""
        return f'{tenant_key_prefix()}{key}'

    def _read_candidates(self, key):
        """Object keys to try when reading, most-specific first.

        The unprefixed key is retained as a fallback so objects written before a
        tenant prefix existed (or by a no-tenant context) stay readable.
        """
        prefixed = self._object_key(key)
        return [prefixed] if prefixed == key else [prefixed, key]

    def _content_type(self, key):
        return _CONTENT_TYPES.get(_ext_of(key), 'application/octet-stream')

    # ── Interface ────────────────────────────────────────────────────────────

    def save(self, file_obj, subfolder):
        ext = _ext_of(file_obj.filename)
        key = f'uploads/{subfolder}/{uuid.uuid4().hex}.{ext}'

        # Fail loudly rather than write a key that could collide with another
        # tenant's. A missing tenant here means the caller reached an upload
        # path outside tenant resolution — a bug, not a fallback case.
        if current_app.config.get('MULTI_TENANT_ENABLED') and not tenant_key_prefix():
            raise RuntimeError(
                'storage.save() called with STORAGE_BACKEND=s3 and no tenant '
                'bound — refusing to write an unprefixed object key.'
            )

        file_obj.stream.seek(0)
        body = file_obj.stream.read()
        self._client.put_object(
            Bucket=self.bucket, Key=self._object_key(key), Body=body,
            ContentType=_CONTENT_TYPES.get(ext, 'application/octet-stream'),
        )
        # The DB always stores the unprefixed key.
        return key

    def abs_local_path(self, key):
        # No local path for an S3 object; expose the local mirror path (may or may
        # not exist) so transition code / callers can still reference it.
        return self._local.abs_local_path(key)

    def media_url(self, key, external=False):
        if not key:
            return ''
        obj = self._object_key(key)
        if self.fallback and not self._head(obj):
            # Object not at the tenant-prefixed key — try the legacy unprefixed
            # key, then the local copy, during transition.
            if obj != key and self._head(key):
                obj = key
            elif self._local.exists(key):
                return self._local.media_url(key, external=external)
        # Presigned R2 URLs are always absolute; the external flag is moot.
        return self._client.generate_presigned_url(
            'get_object',
            Params={'Bucket': self.bucket, 'Key': obj},
            ExpiresIn=self.ttl,
        )

    def read(self, key):
        for candidate in self._read_candidates(key):
            try:
                resp = self._client.get_object(Bucket=self.bucket, Key=candidate)
                return resp['Body'].read()
            except Exception:
                continue
        # Transition safety: fall back to a local copy if present.
        if self._local.exists(key):
            return self._local.read(key)
        raise FileNotFoundError(f'storage: no object for key {key!r}')

    def _head(self, key):
        try:
            self._client.head_object(Bucket=self.bucket, Key=key)
            return True
        except Exception:
            return False

    def exists(self, key):
        if not key:
            return False
        return any(self._head(k) for k in self._read_candidates(key))

    def delete(self, key):
        if not key:
            return
        for candidate in self._read_candidates(key):
            try:
                self._client.delete_object(Bucket=self.bucket, Key=candidate)
            except Exception as e:
                logger.warning('S3 delete failed for %s: %s', candidate, e)

    def materialize_to_dir(self, keys):
        """Download the given keys to a temp dir mirroring the key layout.

        Returns (base_dir, cleanup); each key resolves at base_dir/key so tools
        that need real file paths (ReportLab/PIL) work unchanged. The temp tree
        uses the **DB** key layout (unprefixed) because that is what callers
        join against. Missing or unreadable keys are skipped — callers already
        guard with os.path.exists.
        """
        import tempfile
        import shutil

        base = tempfile.mkdtemp(prefix='jqc_media_')
        for key in {k for k in keys if k}:
            try:
                data = self.read(key)
            except Exception:
                continue                       # skip missing; caller guards existence
            dest = os.path.join(base, key)
            os.makedirs(os.path.dirname(dest), exist_ok=True)
            with open(dest, 'wb') as fh:
                fh.write(data)

        def _cleanup():
            shutil.rmtree(base, ignore_errors=True)

        return base, _cleanup


_BACKENDS = {
    'local': LocalBackend,
    's3':    S3Backend,
}


def get_backend():
    """Return the active storage backend (one cached instance per app)."""
    name = (current_app.config.get('STORAGE_BACKEND') or 'local').lower()
    cls  = _BACKENDS.get(name)
    if cls is None:
        logger.warning('Unknown STORAGE_BACKEND=%r — falling back to local', name)
        cls = LocalBackend
    cache_key = f'_storage_backend_{cls.name}'
    inst = current_app.extensions.get(cache_key)
    if inst is None:
        inst = cls()
        current_app.extensions[cache_key] = inst
    return inst


# ── Module-level convenience delegates ────────────────────────────────────────

def save(file_obj, subfolder):
    return get_backend().save(file_obj, subfolder)


def media_url(key, external=False):
    return get_backend().media_url(key, external=external)


def read(key):
    return get_backend().read(key)


def exists(key):
    return get_backend().exists(key)


def delete(key):
    return get_backend().delete(key)


def abs_local_path(key):
    return get_backend().abs_local_path(key)


def materialize_to_dir(keys):
    return get_backend().materialize_to_dir(keys)