# lambda_andreasknuth.py
import os
import boto3
import smtplib
import time
import traceback
from email.parser import BytesParser
from email.policy import default
from email.utils import getaddresses

s3 = boto3.client('s3')

# Environment variables (set these in the Lambda config)
SMTP_HOST = os.environ.get('MAILCOW_SMTP_HOST', 'mail.email-srvr.com')
SMTP_PORT = int(os.environ.get('MAILCOW_SMTP_PORT', '2525'))  # default to your mapped port
SMTP_USER = os.environ.get('SMTP_USER') or os.environ.get('MAILCOW_SMTP_USER')
SMTP_PASS = os.environ.get('SMTP_PASS') or os.environ.get('MAILCOW_SMTP_PASS')

# Metadata key/value to mark processed objects (only set when at least one recipient delivered)
PROCESSED_META_KEY = os.environ.get('PROCESSED_META_KEY', 'processed')
PROCESSED_META_VALUE = os.environ.get('PROCESSED_META_VALUE', 'true')

def domain_to_bucket(domain: str) -> str:
    return domain.replace('.', '-') + '-emails'

def bucket_to_domain(bucket: str) -> str:
    return bucket.replace('-emails', '').replace('-', '.')

def parse_raw_message(raw_bytes: bytes):
    try:
        parsed = BytesParser(policy=default).parsebytes(raw_bytes)
    except Exception:
        parsed = None
    return parsed

def mark_object_processed(bucket: str, key: str):
    try:
        head = s3.head_object(Bucket=bucket, Key=key)
        current_metadata = head.get('Metadata', {}) or {}
        if current_metadata.get(PROCESSED_META_KEY) == PROCESSED_META_VALUE:
            print(f"Object {key} in {bucket} already marked processed.")
            return
        new_meta = current_metadata.copy()
        new_meta[PROCESSED_META_KEY] = PROCESSED_META_VALUE
        # Copy object onto itself replacing metadata
        s3.copy_object(
            Bucket=bucket,
            Key=key,
            CopySource={'Bucket': bucket, 'Key': key},
            Metadata=new_meta,
            MetadataDirective='REPLACE'
        )
        print(f"Marked {bucket}/{key} as processed.")
    except Exception as e:
        print("Failed to mark processed metadata:", e)
        traceback.print_exc()

def lambda_handler(event, context):
    print("Event:", event)
    ses = None
    try:
        rec = event['Records'][0]
    except Exception as e:
        print("No Records in event:", e)
        return {'statusCode': 400, 'body': 'No Records'}

    # Determine bucket/key and initial recipients list
    recipients = []
    bucket = None
    key = None

    if 'ses' in rec:
        ses = rec['ses']
        msg_id = ses['mail']['messageId']
        recipients = ses['receipt'].get('recipients', [])
        # assume first recipient domain maps to bucket
        if recipients:
            domain = recipients[0].split('@', 1)[1]
            bucket = domain_to_bucket(domain)
            prefix = f"emails/{msg_id}"
            print(f"SES event: domain={domain}, bucket={bucket}, prefix={prefix}")
            resp_list = s3.list_objects_v2(Bucket=bucket, Prefix=prefix)
            if 'Contents' not in resp_list or not resp_list['Contents']:
                raise Exception(f"No S3 object under {prefix} in {bucket}")
            key = resp_list['Contents'][0]['Key']
        else:
            raise Exception("SES event but no recipients found")
    elif 's3' in rec:
        s3info = rec['s3']
        bucket = s3info['bucket']['name']
        key = s3info['object']['key']
        print(f"S3 event: bucket={bucket}, key={key}")
        # recipients will be parsed from message headers below
    else:
        raise Exception("Unknown event type")

    # Check if already processed (only to avoid unnecessary work; we still honor processed semantics)
    try:
        head = s3.head_object(Bucket=bucket, Key=key)
        if head.get('Metadata', {}).get(PROCESSED_META_KEY) == PROCESSED_META_VALUE:
            print(f"Object {key} in {bucket} already processed. Exiting.")
            return {'statusCode': 200, 'body': 'already processed'}
    except Exception as e:
        # If head_object fails, continue and try to process (log for debugging)
        print("head_object error (continuing):", e)

    # Get raw mail bytes
    resp = s3.get_object(Bucket=bucket, Key=key)
    raw_bytes = resp['Body'].read()
    print(f"Loaded {len(raw_bytes)} bytes from s3://{bucket}/{key}")

    parsed = parse_raw_message(raw_bytes)
    subj = parsed.get('subject', '(no subject)') if parsed else '(no subject)'
    frm_addr = None
    if parsed:
        from_addrs = getaddresses(parsed.get_all('from', []) or [])
        frm_addr = from_addrs[0][1] if from_addrs else None
    if not frm_addr:
        # fallback: try envelope sender if present in SES event
        frm_addr = (ses['mail'].get('source') if ses else None) or ('noreply@' + (bucket_to_domain(bucket) if bucket else 'localhost'))
    print(f"From: {frm_addr}, Subject: {subj}")

    # If recipients were not provided (S3 path), extract from headers
    if not recipients:
        if parsed:
            to_addrs = [addr for _n, addr in getaddresses(parsed.get_all('to', []) or [])]
            cc_addrs = [addr for _n, addr in getaddresses(parsed.get_all('cc', []) or [])]
            bcc_addrs = [addr for _n, addr in getaddresses(parsed.get_all('bcc', []) or [])]
            recipients = to_addrs + cc_addrs + bcc_addrs
            print("Recipients from headers:", recipients)
            # filter recipients to bucket domain (safety)
            expected_domain = bucket_to_domain(bucket)
            recipients = [r for r in recipients if r.lower().split('@')[-1] == expected_domain]
            print(f"Recipients after domain filter ({expected_domain}): {recipients}")
        else:
            print("No parsed headers and no recipients provided; nothing to do.")
            recipients = []

    # If after all we have no recipients, skip SMTP
    delivered = []
    refused = {}
    if recipients:
        # Prepare message string for sendmail (decode bytes safely)
        try:
            raw_message = raw_bytes.decode('utf-8')
        except Exception:
            raw_message = raw_bytes.decode('utf-8', errors='replace')

        # Determine a sensible local hostname (HELO). Prefer explicit ENV, else use domain of bucket (recipient domain).
        env_local = os.environ.get('SMTP_LOCAL_HOSTNAME')
        derived_local = bucket_to_domain(bucket) if bucket else None
        local_helo = env_local or derived_local or 'localhost'

        print(f"Attempting SMTP send to {len(recipients)} recipients via {SMTP_HOST}:{SMTP_PORT} with local_hostname={local_helo}")
        start = time.time()
        try:
            # Pass local_hostname so the server receives a proper FQDN in HELO/EHLO
            with smtplib.SMTP(SMTP_HOST, SMTP_PORT, timeout=30, local_hostname=local_helo) as smtp:
                smtp.ehlo()
                # Try STARTTLS; if it fails, continue (server might be implicit TLS port)
                try:
                    smtp.starttls()
                    smtp.ehlo()
                except Exception as e:
                    print("STARTTLS not available or failed (continuing):", e)

                if SMTP_USER and SMTP_PASS:
                    try:
                        smtp.login(SMTP_USER, SMTP_PASS)
                    except Exception as e:
                        print("SMTP login failed (continuing):", e)

                try:
                    send_result = smtp.sendmail(frm_addr, recipients, raw_message)
                    # sendmail returns dict of refused recipients
                    if isinstance(send_result, dict):
                        refused = send_result
                        delivered = [r for r in recipients if r not in refused]
                    else:
                        # Unexpected but treat all as delivered
                        delivered = recipients[:]
                        refused = {}
                except smtplib.SMTPRecipientsRefused as e:
                    print("SMTPRecipientsRefused:", e)
                    try:
                        refused = e.recipients
                    except Exception:
                        refused = {r: ('550', 'Recipient refused') for r in recipients}
                    delivered = [r for r in recipients if r not in refused]
                except Exception as e:
                    print("SMTP sendmail error:", e)
                    refused = {r: ('error', str(e)) for r in recipients}
                    delivered = []
        except Exception as e:
            print("Error connecting to SMTP host:", e)
            refused = {r: ('connect-error', str(e)) for r in recipients}
            delivered = []
        print(f"SMTP completed in {time.time()-start:.2f}s delivered={delivered} refused={refused}")
    else:
        print("No recipients to send to; skipping SMTP.")

    # Only mark as processed if at least one recipient was delivered successfully
    if delivered:
        try:
            mark_object_processed(bucket, key)
        except Exception as e:
            print("Failed to mark object processed after delivery:", e)
    else:
        print("No successful deliveries; NOT setting processed metadata so message can be re-evaluated later.")

    return {
        'statusCode': 200,
        'body': f"processed={bool(delivered)}, delivered={delivered}, refused_count={len(refused)}"
    }