using System.Text.RegularExpressions;
using Microsoft.EntityFrameworkCore;
using OTSSignsOrchestrator.Server.Data;

namespace OTSSignsOrchestrator.Server.Services;

public class AbbreviationService
{
    private static readonly HashSet<string> StopWords = new(StringComparer.OrdinalIgnoreCase)
    {
        "inc", "llc", "ltd", "co", "corp", "group", "signs", "digital",
        "media", "the", "and", "of", "a"
    };

    private readonly OrchestratorDbContext _db;
    private readonly ILogger<AbbreviationService> _logger;

    public AbbreviationService(OrchestratorDbContext db, ILogger<AbbreviationService> logger)
    {
        _db = db;
        _logger = logger;
    }

    public async Task<string> GenerateAsync(string companyName)
    {
        var words = Regex.Split(companyName.Trim(), @"\s+")
            .Select(w => Regex.Replace(w, @"[^a-zA-Z0-9]", ""))
            .Where(w => w.Length > 0 && !StopWords.Contains(w))
            .ToList();

        if (words.Count == 0)
            throw new InvalidOperationException(
                $"Cannot generate abbreviation from company name '{companyName}' — no usable words after filtering.");

        string abbrev;
        if (words.Count >= 3)
        {
            // Take first letter of first 3 words
            abbrev = string.Concat(words.Take(3).Select(w => w[0]));
        }
        else if (words.Count == 2)
        {
            // First letter of each word + second char of last word
            abbrev = $"{words[0][0]}{words[1][0]}{(words[1].Length > 1 ? words[1][1] : words[0][1])}";
        }
        else
        {
            // Single word — take up to 3 chars
            abbrev = words[0].Length >= 3 ? words[0][..3] : words[0].PadRight(3, 'X');
        }

        abbrev = Regex.Replace(abbrev.ToUpperInvariant(), @"[^A-Z0-9]", "");
        if (abbrev.Length > 3) abbrev = abbrev[..3];

        // Check uniqueness
        if (!await _db.Customers.AnyAsync(c => c.Abbreviation == abbrev))
        {
            _logger.LogInformation("Generated abbreviation {Abbrev} for '{CompanyName}'", abbrev, companyName);
            return abbrev;
        }

        // Collision — try suffix 2–9
        var prefix = abbrev[..2];
        for (var suffix = 2; suffix <= 9; suffix++)
        {
            var candidate = $"{prefix}{suffix}";
            if (!await _db.Customers.AnyAsync(c => c.Abbreviation == candidate))
            {
                _logger.LogInformation("Generated abbreviation {Abbrev} (collision resolved) for '{CompanyName}'",
                    candidate, companyName);
                return candidate;
            }
        }

        throw new InvalidOperationException(
            $"All abbreviation variants for '{companyName}' are taken ({prefix}2–{prefix}9).");
    }
}