#!/usr/bin/env python3
"""Fills in deploy/forum/app.yml from environment variables and writes the result (mode 600).

  render.py <template> <output>

Required: FORUM_BIND KNOWN_PROXY FORUM_ADMIN_EMAIL FORUM_SMTP_ADDRESS FORUM_SMTP_USER FORUM_SMTP_PASSWORD
Optional: FORUM_HOSTNAME (forum.seosoft.dk), FORUM_PORT (8082), FORUM_SMTP_PORT (587), FORUM_NOTIFICATION_EMAIL (FORUM_SMTP_USER),
          FORUM_WORKERS (4), FORUM_DB_SHARED_BUFFERS (512MB)
"""
import ipaddress
import os
import re
import sys

DEFAULTS = {
    "FORUM_HOSTNAME": "forum.seosoft.dk",
    "FORUM_PORT": "8082",
    "FORUM_SMTP_PORT": "587",
    "FORUM_WORKERS": "4",
    "FORUM_DB_SHARED_BUFFERS": "512MB",
}
# Values that end up unquoted in YAML or in nginx/docker syntax must look exactly like this.
FORMATS = {
    "FORUM_PORT": r"\d{1,5}",
    "FORUM_SMTP_PORT": r"\d{1,5}",
    "FORUM_WORKERS": r"\d{1,2}",
    "FORUM_DB_SHARED_BUFFERS": r"\d+[MG]B",
    "FORUM_HOSTNAME": r"[a-z0-9.-]+",
}


def value(name):
    v = os.environ.get(name) or DEFAULTS.get(name)
    if name == "FORUM_NOTIFICATION_EMAIL" and not v:
        v = os.environ.get("FORUM_SMTP_USER")
    if not v:
        sys.exit(f"ERROR: {name} is not set")
    if "\n" in v or "{{" in v:
        sys.exit(f"ERROR: {name} contains a line break or {{{{")
    if name in FORMATS and not re.fullmatch(FORMATS[name], v):
        sys.exit(f"ERROR: {name} has an unexpected format")
    if name in ("FORUM_BIND", "KNOWN_PROXY"):
        try:
            ipaddress.ip_network(v, strict=False) if name == "KNOWN_PROXY" else ipaddress.ip_address(v)
        except ValueError:
            sys.exit(f"ERROR: {name} is not an IP address" + (" or network" if name == "KNOWN_PROXY" else ""))
    # All free-text values sit in single-quoted YAML strings.
    return v.replace("'", "''")


def main():
    if len(sys.argv) != 3:
        sys.exit(__doc__)
    template, output = sys.argv[1], sys.argv[2]
    with open(template, encoding="utf-8") as f:
        text = f.read()
    names = sorted(set(re.findall(r"\{\{([A-Z_]+)\}\}", text)))
    text = re.sub(r"\{\{([A-Z_]+)\}\}", lambda m: value(m.group(1)), text)
    fd = os.open(output, os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600)
    with os.fdopen(fd, "w", encoding="utf-8") as f:
        f.write(text)
    print(f"{output}: {len(names)} values filled in")


if __name__ == "__main__":
    main()