06/15 Phase 3 codes

app/services/messaging.py

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+"""Messaging business logic.
+
+Rules:
+- Buyer initiates; one conversation per (listing, buyer) pair.
+- Seller cannot open a conversation with themselves.
+- High contact-density messages are auto-flagged for moderation.
+- Notification email sent to recipient on each new message (async in Phase 4+;
+  for now sent inline — fast enough at low volume).
+"""
+from datetime import datetime
+from sqlalchemy.exc import IntegrityError
+from flask import current_app
+from app.extensions import db
+from app.models.messaging import Conversation, Message
+from app.services.contact import contact_density
+from app.services.email import send_email
+
+# Bodies with ≥ 3 contact signals get auto-flagged
+_FLAG_THRESHOLD = 3
+
+
+class MessagingError(ValueError):
+    pass
+
+
+def get_or_create_conversation(listing, buyer):
+    """Return existing conversation or create one. Raises if buyer == seller."""
+    if listing.user_id == buyer.id:
+        raise MessagingError("cannot message your own listing")
+
+    conv = Conversation.query.filter_by(
+        listing_id=listing.id, buyer_id=buyer.id).first()
+    if conv:
+        return conv, False
+
+    conv = Conversation(
+        listing_id=listing.id,
+        buyer_id=buyer.id,
+        seller_id=listing.user_id,
+    )
+    db.session.add(conv)
+    try:
+        db.session.commit()
+    except IntegrityError:
+        db.session.rollback()
+        conv = Conversation.query.filter_by(
+            listing_id=listing.id, buyer_id=buyer.id).first()
+    return conv, True
+
+
+def send_message(conversation, sender, body: str) -> Message:
+    """Append a message. Notify recipient. Returns the saved Message."""
+    body = body.strip()
+    if not body:
+        raise MessagingError("message cannot be empty")
+    if len(body) > 4000:
+        raise MessagingError("message too long (max 4000 chars)")
+
+    # verify sender is a participant
+    if sender.id not in (conversation.buyer_id, conversation.seller_id):
+        raise MessagingError("not a participant")
+
+    flagged = contact_density(body) >= _FLAG_THRESHOLD
+
+    msg = Message(
+        conversation_id=conversation.id,
+        sender_id=sender.id,
+        body=body,
+    )
+    db.session.add(msg)
+    conversation.last_message_at = datetime.utcnow()
+    db.session.commit()
+
+    if flagged:
+        current_app.logger.warning(
+            "High contact-density message id=%s conv=%s sender=%s",
+            msg.id, conversation.id, sender.id)
+
+    _notify_recipient(conversation, sender, msg)
+    return msg
+
+
+def mark_conversation_read(conversation, reader):
+    """Mark all messages NOT sent by reader as read."""
+    changed = False
+    for msg in conversation.messages:
+        if msg.sender_id != reader.id and msg.read_at is None:
+            msg.mark_read()
+            changed = True
+    if changed:
+        db.session.commit()
+
+
+def inbox(user, page=1, per_page=20):
+    """Conversations where user is buyer or seller, newest first."""
+    return (Conversation.query
+            .filter(db.or_(
+                Conversation.buyer_id == user.id,
+                Conversation.seller_id == user.id,
+            ))
+            .order_by(Conversation.last_message_at.desc().nullslast(),
+                      Conversation.created_at.desc())
+            .paginate(page=page, per_page=per_page, error_out=False))
+
+
+def total_unread(user) -> int:
+    """Total unread message count across all conversations (for nav badge)."""
+    convs = Conversation.query.filter(
+        db.or_(
+            Conversation.buyer_id == user.id,
+            Conversation.seller_id == user.id,
+        )
+    ).all()
+    return sum(c.unread_count(user) for c in convs)
+
+
+def _notify_recipient(conversation, sender, message):
+    recipient = (conversation.seller
+                 if sender.id == conversation.buyer_id
+                 else conversation.buyer)
+    try:
+        subject = f"New message about: {conversation.listing.title[:60]}"
+        body = (
+            f"Hi {recipient.display_name},\n\n"
+            f"{sender.display_name} sent you a message about "
+            f'"{conversation.listing.title}":\n\n'
+            f"{message.body[:500]}\n\n"
+            f"Reply at: /messages/{conversation.id}\n"
+        )
+        send_email(recipient.email, subject, body)
+    except Exception as exc:
+        current_app.logger.error("Message notification failed: %s", exc)