using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using PowderCoating.Application.Interfaces;
using Twilio;
using Twilio.Rest.Api.V2010.Account;
using Twilio.Types;

namespace PowderCoating.Infrastructure.Services;

public class SmsService : ISmsService
{
    private readonly IConfiguration _configuration;
    private readonly IWebHostEnvironment _env;
    private readonly ILogger<SmsService> _logger;

    /// <summary>
    /// Initializes a new instance of <see cref="SmsService"/>. Twilio credentials are read
    /// per call (not cached here) because they may be rotated without restarting the application,
    /// and Twilio's client initialization (<c>TwilioClient.Init</c>) is idempotent and cheap.
    /// <para>
    /// In non-production environments, all outbound messages are redirected to
    /// <c>Twilio:DevRedirectPhone</c> (if configured) so real customer numbers are never
    /// texted during development or staging. The original destination is prepended to the
    /// message body for traceability.
    /// </para>
    /// </summary>
    public SmsService(IConfiguration configuration, IWebHostEnvironment env, ILogger<SmsService> logger)
    {
        _configuration = configuration;
        _env = env;
        _logger = logger;
    }

    /// <summary>
    /// Sends an SMS message via the Twilio REST API and returns a success/error tuple.
    /// The method short-circuits with a logged warning (not an exception) when Twilio is not
    /// configured, so callers in notification workflows are not broken in development
    /// environments where Twilio credentials are absent. Phone numbers are normalized via
    /// <see cref="NormalizePhone"/> before sending because users enter phone numbers in many
    /// formats (with dashes, parentheses, spaces, or a leading "1") and Twilio requires strict
    /// E.164 format. The method returns the Twilio message SID on success so callers can log
    /// it for delivery tracking. Carrier regulations (TCPA in the US) require that the first
    /// SMS to a new number include opt-out instructions ("Reply STOP to unsubscribe") — this
    /// is enforced in the message body by the calling controller or notification service before
    /// this method is invoked; <see cref="SmsService"/> itself is transport-only and does not
    /// inspect or modify the message body.
    /// </summary>
    public async Task<(bool Success, string? ErrorMessage)> SendSmsAsync(string toPhone, string message)
    {
        var accountSid = _configuration["Twilio:AccountSid"];
        var authToken = _configuration["Twilio:AuthToken"];
        var fromNumber = _configuration["Twilio:FromNumber"];

        if (string.IsNullOrWhiteSpace(accountSid) || accountSid.StartsWith("your-") ||
            string.IsNullOrWhiteSpace(authToken) || authToken.StartsWith("your-") ||
            string.IsNullOrWhiteSpace(fromNumber) || fromNumber.Contains("XXXXXXXXXX"))
        {
            _logger.LogWarning("Twilio is not configured. SMS to {ToPhone} skipped.", toPhone);
            return (false, "Twilio not configured");
        }

        var normalizedPhone = NormalizePhone(toPhone);
        if (string.IsNullOrEmpty(normalizedPhone))
        {
            _logger.LogWarning("Invalid phone number: {ToPhone}", toPhone);
            return (false, "Invalid phone number");
        }

        // Non-production guard: redirect all messages to the dev phone so real customers
        // are never texted outside of production. Double-gated on environment name AND
        // the config value so a misconfigured prod deploy can't accidentally redirect.
        var devRedirect = _configuration["Twilio:DevRedirectPhone"];
        if (!_env.IsProduction() && !string.IsNullOrWhiteSpace(devRedirect))
        {
            var devPhone = NormalizePhone(devRedirect);
            if (!string.IsNullOrEmpty(devPhone))
            {
                _logger.LogWarning("Non-production environment: redirecting SMS from {Original} to dev number {Dev}", normalizedPhone, devPhone);
                message = $"[DEV → {normalizedPhone}] {message}";
                normalizedPhone = devPhone;
            }
        }

        try
        {
            TwilioClient.Init(accountSid, authToken);

            var smsMessage = await MessageResource.CreateAsync(
                to: new PhoneNumber(normalizedPhone),
                from: new PhoneNumber(fromNumber),
                body: message);

            _logger.LogInformation("SMS sent to {ToPhone}: SID={Sid}", normalizedPhone, smsMessage.Sid);
            return (true, null);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Exception sending SMS to {ToPhone}", normalizedPhone);
            return (false, ex.Message);
        }
    }

    /// <summary>
    /// Normalizes a phone number string to E.164 format (e.g., "+12025551234") required by
    /// Twilio. Strips all non-digit characters, then applies three rules in priority order:
    /// an 11-digit string starting with "1" is assumed to be a North American number with
    /// country code already included; a 10-digit string is assumed to be a US/Canada number
    /// and gets "+1" prepended; a string that already starts with "+" and has more than 10
    /// digits is treated as an international number and reformatted with "+". Numbers that
    /// do not match any pattern return null, causing <see cref="SendSmsAsync"/> to abort with
    /// a warning rather than sending to a malformed number (which would generate a Twilio 400
    /// error and count against the account's error rate).
    /// </summary>
    private static string? NormalizePhone(string phone)
    {
        if (string.IsNullOrWhiteSpace(phone))
            return null;

        // Strip everything except digits
        var digits = new string(phone.Where(char.IsDigit).ToArray());

        // Already E.164 with country code
        if (digits.Length == 11 && digits[0] == '1')
            return "+" + digits;

        // 10-digit US number — prepend +1
        if (digits.Length == 10)
            return "+1" + digits;

        // Already formatted (e.g. +44...)
        if (phone.StartsWith("+") && digits.Length > 10)
            return "+" + digits;

        return null;
    }
}