RealCV/src/TrueCV.Infrastructure/Services/CompanyVerifierService.cs

using System.Text.Json;
using FuzzySharp;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using TrueCV.Application.DTOs;
using TrueCV.Application.Helpers;
using TrueCV.Application.Interfaces;
using TrueCV.Application.Models;
using TrueCV.Domain.Entities;
using TrueCV.Infrastructure.Data;
using TrueCV.Infrastructure.ExternalApis;

namespace TrueCV.Infrastructure.Services;

public sealed class CompanyVerifierService : ICompanyVerifierService
{
    private readonly CompaniesHouseClient _companiesHouseClient;
    private readonly IDbContextFactory<ApplicationDbContext> _dbContextFactory;
    private readonly ILogger<CompanyVerifierService> _logger;

    private const int FuzzyMatchThreshold = 70;
    private const int CacheExpirationDays = 30;

    // SIC codes for tech/software companies
    private static readonly HashSet<string> TechSicCodes = new()
    {
        "62011", "62012", "62020", "62030", "62090", // Computer programming and consultancy
        "63110", "63120", // Data processing, hosting
        "58210", "58290", // Publishing of computer games, other software
        "61100", "61200", "61300", "61900" // Telecommunications
    };

    public CompanyVerifierService(
        CompaniesHouseClient companiesHouseClient,
        IDbContextFactory<ApplicationDbContext> dbContextFactory,
        ILogger<CompanyVerifierService> logger)
    {
        _companiesHouseClient = companiesHouseClient;
        _dbContextFactory = dbContextFactory;
        _logger = logger;
    }

    public async Task<CompanyVerificationResult> VerifyCompanyAsync(
        string companyName,
        DateOnly? startDate,
        DateOnly? endDate,
        string? jobTitle = null)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(companyName);

        _logger.LogDebug("Verifying company: {CompanyName}", companyName);
        var flags = new List<CompanyVerificationFlag>();

        // Try to find a cached match first
        var cachedMatch = await FindCachedMatchAsync(companyName);
        if (cachedMatch is not null)
        {
            _logger.LogDebug("Found cached company match for: {CompanyName}", companyName);
            return CreateResultFromCache(cachedMatch, companyName, startDate, endDate, jobTitle, flags);
        }

        // Search Companies House
        try
        {
            var searchResponse = await _companiesHouseClient.SearchCompaniesAsync(companyName);

            if (searchResponse?.Items is null || searchResponse.Items.Count == 0)
            {
                _logger.LogDebug("No companies found for: {CompanyName}", companyName);
                return CreateUnverifiedResult(companyName, startDate, endDate, jobTitle, "No matching company found in Companies House");
            }

            // Find best fuzzy match
            var bestMatch = FindBestMatch(companyName, searchResponse.Items);

            if (bestMatch is null)
            {
                _logger.LogDebug("No fuzzy match above threshold for: {CompanyName}", companyName);
                return CreateUnverifiedResult(companyName, startDate, endDate, jobTitle,
                    $"No company name matched above {FuzzyMatchThreshold}% threshold");
            }

            var match = bestMatch.Value;

            // Fetch full company details for additional data
            var companyDetails = await _companiesHouseClient.GetCompanyAsync(match.Item.CompanyNumber);

            // Cache the matched company with full details
            await CacheCompanyAsync(match.Item, companyDetails);

            _logger.LogInformation(
                "Verified company {ClaimedName} matched to {MatchedName} with score {Score}%",
                companyName, match.Item.Title, match.Score);

            // Run all verification checks
            var incorporationDate = DateHelpers.ParseDate(match.Item.DateOfCreation);
            var dissolutionDate = DateHelpers.ParseDate(match.Item.DateOfCessation);
            var companyStatus = match.Item.CompanyStatus;
            var companyType = match.Item.CompanyType;
            var sicCodes = companyDetails?.SicCodes ?? match.Item.SicCodes;
            var accountsCategory = companyDetails?.Accounts?.LastAccounts?.Type;

            // Check 1: Employment before company incorporation
            CheckIncorporationDate(flags, startDate, incorporationDate, match.Item.Title);

            // Check 2: Employment at dissolved company
            CheckDissolutionDate(flags, endDate, dissolutionDate, companyStatus, match.Item.Title);

            // Check 3: Dormant company check
            CheckDormantCompany(flags, accountsCategory, jobTitle, match.Item.Title);

            // Check 4: Company size vs job title
            CheckCompanySizeVsRole(flags, accountsCategory, jobTitle, match.Item.Title);

            // Check 5: SIC code vs job title mismatch
            CheckSicCodeMismatch(flags, sicCodes, jobTitle, match.Item.Title);

            // Check 6: Job title plausibility for PLCs
            var (jobPlausible, jobNotes) = CheckJobTitlePlausibility(jobTitle, companyType);
            if (jobPlausible == false)
            {
                flags.Add(new CompanyVerificationFlag
                {
                    Type = "ImplausibleJobTitle",
                    Severity = "Critical",
                    Message = jobNotes ?? "Job title requires verification",
                    ScoreImpact = -15
                });
            }

            return new CompanyVerificationResult
            {
                ClaimedCompany = companyName,
                MatchedCompanyName = match.Item.Title,
                MatchedCompanyNumber = match.Item.CompanyNumber,
                MatchScore = match.Score,
                IsVerified = true,
                VerificationNotes = $"Matched with {match.Score}% confidence",
                ClaimedStartDate = startDate,
                ClaimedEndDate = endDate,
                CompanyType = companyType,
                CompanyStatus = companyStatus,
                IncorporationDate = incorporationDate,
                DissolutionDate = dissolutionDate,
                AccountsCategory = accountsCategory,
                SicCodes = sicCodes,
                ClaimedJobTitle = jobTitle,
                JobTitlePlausible = jobPlausible,
                JobTitleNotes = jobNotes,
                Flags = flags
            };
        }
        catch (CompaniesHouseRateLimitException ex)
        {
            _logger.LogWarning(ex, "Rate limit hit while verifying company: {CompanyName}", companyName);
            return CreateUnverifiedResult(companyName, startDate, endDate, jobTitle,
                "Verification temporarily unavailable due to rate limiting");
        }
    }

    public async Task<List<CompanySearchResult>> SearchCompaniesAsync(string query)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(query);

        _logger.LogDebug("Searching companies for query: {Query}", query);

        var response = await _companiesHouseClient.SearchCompaniesAsync(query);

        if (response?.Items is null)
        {
            return [];
        }

        return response.Items.Select(item => new CompanySearchResult
        {
            CompanyNumber = item.CompanyNumber,
            CompanyName = item.Title,
            CompanyStatus = item.CompanyStatus ?? "Unknown",
            IncorporationDate = DateHelpers.ParseDate(item.DateOfCreation),
            AddressSnippet = item.AddressSnippet
        }).ToList();
    }

    public async Task<bool?> VerifyDirectorAsync(
        string companyNumber,
        string candidateName,
        DateOnly? startDate,
        DateOnly? endDate)
    {
        if (string.IsNullOrWhiteSpace(companyNumber) || string.IsNullOrWhiteSpace(candidateName))
        {
            return null;
        }

        try
        {
            var officers = await _companiesHouseClient.GetOfficersAsync(companyNumber);

            if (officers?.Items is null || officers.Items.Count == 0)
            {
                _logger.LogDebug("No officers found for company {CompanyNumber}", companyNumber);
                return null;
            }

            // Normalize candidate name for comparison
            var normalizedCandidate = NormalizeName(candidateName);

            foreach (var officer in officers.Items)
            {
                // Check if officer role is director-like
                var role = officer.OfficerRole?.ToLowerInvariant() ?? "";
                if (!role.Contains("director") && !role.Contains("secretary"))
                {
                    continue;
                }

                // Fuzzy match the name
                var normalizedOfficer = NormalizeName(officer.Name);
                var matchScore = Fuzz.Ratio(normalizedCandidate, normalizedOfficer);

                if (matchScore >= 80) // High threshold for name matching
                {
                    // Check date overlap
                    var appointedOn = DateHelpers.ParseDate(officer.AppointedOn);
                    var resignedOn = DateHelpers.ParseDate(officer.ResignedOn);

                    // If no claimed dates, just check if names match
                    if (!startDate.HasValue && !endDate.HasValue)
                    {
                        _logger.LogDebug(
                            "Found matching director {OfficerName} for candidate {CandidateName} at company {CompanyNumber}",
                            officer.Name, candidateName, companyNumber);
                        return true;
                    }

                    // Check if employment period overlaps with directorship
                    var datesOverlap = DatesOverlap(
                        startDate, endDate,
                        appointedOn, resignedOn);

                    if (datesOverlap)
                    {
                        _logger.LogDebug(
                            "Verified director {OfficerName} matches candidate {CandidateName} with overlapping dates",
                            officer.Name, candidateName);
                        return true;
                    }
                }
            }

            _logger.LogDebug(
                "No matching director found for candidate {CandidateName} at company {CompanyNumber}",
                candidateName, companyNumber);
            return false;
        }
        catch (CompaniesHouseRateLimitException)
        {
            _logger.LogWarning("Rate limit hit while verifying director for company {CompanyNumber}", companyNumber);
            return null;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error verifying director for company {CompanyNumber}", companyNumber);
            return null;
        }
    }

    private static string NormalizeName(string name)
    {
        if (string.IsNullOrWhiteSpace(name)) return "";

        // Companies House often stores names as "SURNAME, Firstname"
        // Convert to "Firstname Surname" format for comparison
        var normalized = name.ToUpperInvariant().Trim();

        if (normalized.Contains(','))
        {
            var parts = normalized.Split(',', 2);
            if (parts.Length == 2)
            {
                normalized = $"{parts[1].Trim()} {parts[0].Trim()}";
            }
        }

        return normalized;
    }

    private static bool DatesOverlap(DateOnly? start1, DateOnly? end1, DateOnly? start2, DateOnly? end2)
    {
        // If no dates, assume overlap
        if (!start1.HasValue && !end1.HasValue) return true;
        if (!start2.HasValue && !end2.HasValue) return true;

        // Use default dates for missing values
        var s1 = start1 ?? DateOnly.MinValue;
        var e1 = end1 ?? DateOnly.MaxValue;
        var s2 = start2 ?? DateOnly.MinValue;
        var e2 = end2 ?? DateOnly.MaxValue;

        // Check overlap: periods overlap if one starts before the other ends
        return s1 <= e2 && s2 <= e1;
    }

    #region Verification Checks

    private static void CheckIncorporationDate(
        List<CompanyVerificationFlag> flags,
        DateOnly? claimedStartDate,
        DateOnly? incorporationDate,
        string companyName)
    {
        if (claimedStartDate.HasValue && incorporationDate.HasValue)
        {
            if (claimedStartDate.Value < incorporationDate.Value)
            {
                flags.Add(new CompanyVerificationFlag
                {
                    Type = "EmploymentBeforeIncorporation",
                    Severity = "Critical",
                    Message = $"Claimed employment at '{companyName}' starting {claimedStartDate:MMM yyyy} is before company incorporation date {incorporationDate:MMM yyyy}",
                    ScoreImpact = -20
                });
            }
        }
    }

    private static void CheckDissolutionDate(
        List<CompanyVerificationFlag> flags,
        DateOnly? claimedEndDate,
        DateOnly? dissolutionDate,
        string? companyStatus,
        string companyName)
    {
        var isDissolvedStatus = companyStatus?.ToLowerInvariant() is "dissolved" or "liquidation" or "administration";

        if (dissolutionDate.HasValue && isDissolvedStatus)
        {
            // Allow 3 month buffer for wind-down
            var bufferDate = dissolutionDate.Value.AddMonths(3);

            if (claimedEndDate.HasValue && claimedEndDate.Value > bufferDate)
            {
                flags.Add(new CompanyVerificationFlag
                {
                    Type = "EmploymentAtDissolvedCompany",
                    Severity = "Critical",
                    Message = $"Claimed employment at '{companyName}' until {claimedEndDate:MMM yyyy} but company was dissolved on {dissolutionDate:MMM yyyy}",
                    ScoreImpact = -20
                });
            }
            else if (!claimedEndDate.HasValue) // Current employment at dissolved company
            {
                flags.Add(new CompanyVerificationFlag
                {
                    Type = "CurrentEmploymentAtDissolvedCompany",
                    Severity = "Critical",
                    Message = $"Claims current employment at '{companyName}' but company was dissolved on {dissolutionDate:MMM yyyy}",
                    ScoreImpact = -25
                });
            }
        }
    }

    private static void CheckDormantCompany(
        List<CompanyVerificationFlag> flags,
        string? accountsCategory,
        string? jobTitle,
        string companyName)
    {
        if (string.IsNullOrWhiteSpace(accountsCategory)) return;

        var isDormant = accountsCategory.ToLowerInvariant().Contains("dormant");
        if (!isDormant) return;

        // Directors can maintain dormant companies, but other roles are suspicious
        var title = jobTitle?.ToLowerInvariant() ?? "";
        var isDirectorRole = title.Contains("director") || title.Contains("company secretary");

        if (!isDirectorRole)
        {
            flags.Add(new CompanyVerificationFlag
            {
                Type = "EmploymentAtDormantCompany",
                Severity = "Warning",
                Message = $"Claimed active employment as '{jobTitle}' at '{companyName}' which files dormant accounts",
                ScoreImpact = -10
            });
        }
    }

    private static void CheckCompanySizeVsRole(
        List<CompanyVerificationFlag> flags,
        string? accountsCategory,
        string? jobTitle,
        string companyName)
    {
        if (string.IsNullOrWhiteSpace(accountsCategory) || string.IsNullOrWhiteSpace(jobTitle)) return;

        var category = accountsCategory.ToLowerInvariant();
        var title = jobTitle.ToLowerInvariant();

        // Micro-entity: < 10 employees, < £632k turnover
        var isMicroEntity = category.Contains("micro");

        // Check for senior management roles at micro companies
        var isSeniorRole = title.Contains("vp") ||
                          title.Contains("vice president") ||
                          title.Contains("head of") ||
                          title.Contains("chief") ||
                          title.Contains("director of") ||
                          title.Contains("senior director");

        // At micro companies, having many senior roles is suspicious
        if (isMicroEntity && isSeniorRole)
        {
            flags.Add(new CompanyVerificationFlag
            {
                Type = "SeniorRoleAtMicroCompany",
                Severity = "Warning",
                Message = $"Claimed senior role '{jobTitle}' at '{companyName}' which files micro-entity accounts (typically <10 employees)",
                ScoreImpact = -10
            });
        }
    }

    private static void CheckSicCodeMismatch(
        List<CompanyVerificationFlag> flags,
        List<string>? sicCodes,
        string? jobTitle,
        string companyName)
    {
        if (sicCodes is null || sicCodes.Count == 0 || string.IsNullOrWhiteSpace(jobTitle)) return;

        var title = jobTitle.ToLowerInvariant();

        // Check if this is a tech role
        var isTechRole = title.Contains("software") ||
                        title.Contains("developer") ||
                        title.Contains("engineer") ||
                        title.Contains("programmer") ||
                        title.Contains("data scientist") ||
                        title.Contains("data analyst") ||
                        title.Contains("devops") ||
                        title.Contains("cloud") ||
                        title.Contains("machine learning") ||
                        title.Contains("ai ") ||
                        title.Contains("frontend") ||
                        title.Contains("backend") ||
                        title.Contains("full stack") ||
                        title.Contains("fullstack");

        if (isTechRole)
        {
            // Check if company has any tech SIC codes
            var hasTechSic = sicCodes.Any(s => TechSicCodes.Contains(s));

            if (!hasTechSic)
            {
                // Get the primary SIC code description (simplified - just show code)
                var primarySic = sicCodes.FirstOrDefault() ?? "Unknown";

                flags.Add(new CompanyVerificationFlag
                {
                    Type = "SicCodeMismatch",
                    Severity = "Info",
                    Message = $"Tech role '{jobTitle}' at '{companyName}' (SIC: {primarySic}) - company is not registered as a technology business",
                    ScoreImpact = -5
                });
            }
        }
    }

    private static (bool? IsPlausible, string? Notes) CheckJobTitlePlausibility(string? jobTitle, string? companyType)
    {
        if (string.IsNullOrWhiteSpace(jobTitle) || string.IsNullOrWhiteSpace(companyType))
        {
            return (null, null);
        }

        var title = jobTitle.Trim().ToLowerInvariant();
        var type = companyType.Trim().ToLowerInvariant();

        // Check if this is a PLC (Public Limited Company) - these are large companies
        var isPlc = type.Contains("plc") || type.Contains("public limited");

        // Check for C-suite / very senior roles
        var isCsuiteRole = title.Contains("ceo") ||
                          title.Contains("chief executive") ||
                          title.Contains("cto") ||
                          title.Contains("chief technology") ||
                          title.Contains("cfo") ||
                          title.Contains("chief financial") ||
                          title.Contains("coo") ||
                          title.Contains("chief operating") ||
                          title.Contains("cio") ||
                          title.Contains("chief information") ||
                          title.Contains("managing director") ||
                          title == "md" ||
                          title.Contains("chairman") ||
                          title.Contains("chairwoman") ||
                          title.Contains("chairperson") ||
                          title.Contains("president");

        // Check for board-level roles
        var isBoardRole = title.Contains("board member") ||
                         title.Contains("non-executive director") ||
                         title.Contains("executive director") ||
                         (title == "director" && !title.Contains("of"));

        if (isPlc && (isCsuiteRole || isBoardRole))
        {
            return (false, $"Claimed senior role '{jobTitle}' at a PLC requires verification - C-suite positions at public companies are publicly disclosed");
        }

        // Check for VP/SVP at PLCs (also usually disclosed)
        var isVpRole = title.Contains("vice president") ||
                      title.Contains("vp ") ||
                      title.StartsWith("vp") ||
                      title.Contains("svp") ||
                      title.Contains("senior vice president") ||
                      title.Contains("evp") ||
                      title.Contains("executive vice president");

        if (isPlc && isVpRole)
        {
            return (false, $"Claimed VP-level role '{jobTitle}' at a PLC - senior positions at public companies should be verifiable");
        }

        return (true, null);
    }

    #endregion

    #region Helper Methods

    private async Task<CompanyCache?> FindCachedMatchAsync(string companyName)
    {
        var cutoffDate = DateTime.UtcNow.AddDays(-CacheExpirationDays);

        await using var dbContext = await _dbContextFactory.CreateDbContextAsync();

        var cachedCompanies = await dbContext.CompanyCache
            .Where(c => c.CachedAt >= cutoffDate)
            .ToListAsync();

        if (cachedCompanies.Count == 0)
        {
            return null;
        }

        var matches = cachedCompanies
            .Select(c => new { Company = c, Score = Fuzz.Ratio(companyName.ToUpperInvariant(), c.CompanyName.ToUpperInvariant()) })
            .Where(m => m.Score >= FuzzyMatchThreshold)
            .OrderByDescending(m => m.Score)
            .FirstOrDefault();

        return matches?.Company;
    }

    private static (CompaniesHouseSearchItem Item, int Score)? FindBestMatch(
        string companyName,
        List<CompaniesHouseSearchItem> items)
    {
        var normalizedSearch = companyName.ToUpperInvariant();

        var matches = items
            .Select(item => (Item: item, Score: Fuzz.Ratio(normalizedSearch, item.Title.ToUpperInvariant())))
            .Where(m => m.Score >= FuzzyMatchThreshold)
            .OrderByDescending(m => m.Score)
            .ToList();

        return matches.Count > 0 ? matches[0] : null;
    }

    private async Task CacheCompanyAsync(CompaniesHouseSearchItem item, CompaniesHouseCompany? details)
    {
        await using var dbContext = await _dbContextFactory.CreateDbContextAsync();

        var existingCache = await dbContext.CompanyCache
            .FirstOrDefaultAsync(c => c.CompanyNumber == item.CompanyNumber);

        var sicCodes = details?.SicCodes ?? item.SicCodes;
        var sicCodesJson = sicCodes != null ? JsonSerializer.Serialize(sicCodes) : null;
        var accountsCategory = details?.Accounts?.LastAccounts?.Type;

        if (existingCache is not null)
        {
            existingCache.CompanyName = item.Title;
            existingCache.Status = item.CompanyStatus ?? "Unknown";
            existingCache.CompanyType = item.CompanyType;
            existingCache.IncorporationDate = DateHelpers.ParseDate(item.DateOfCreation);
            existingCache.DissolutionDate = DateHelpers.ParseDate(item.DateOfCessation);
            existingCache.AccountsCategory = accountsCategory;
            existingCache.SicCodesJson = sicCodesJson;
            existingCache.CachedAt = DateTime.UtcNow;
        }
        else
        {
            var cacheEntry = new CompanyCache
            {
                CompanyNumber = item.CompanyNumber,
                CompanyName = item.Title,
                Status = item.CompanyStatus ?? "Unknown",
                CompanyType = item.CompanyType,
                IncorporationDate = DateHelpers.ParseDate(item.DateOfCreation),
                DissolutionDate = DateHelpers.ParseDate(item.DateOfCessation),
                AccountsCategory = accountsCategory,
                SicCodesJson = sicCodesJson,
                CachedAt = DateTime.UtcNow
            };

            dbContext.CompanyCache.Add(cacheEntry);
        }

        await dbContext.SaveChangesAsync();
    }

    private CompanyVerificationResult CreateResultFromCache(
        CompanyCache cached,
        string claimedCompany,
        DateOnly? startDate,
        DateOnly? endDate,
        string? jobTitle,
        List<CompanyVerificationFlag> flags)
    {
        var matchScore = Fuzz.Ratio(
            claimedCompany.ToUpperInvariant(),
            cached.CompanyName.ToUpperInvariant());

        var sicCodes = !string.IsNullOrEmpty(cached.SicCodesJson)
            ? JsonSerializer.Deserialize<List<string>>(cached.SicCodesJson)
            : null;

        // Run all verification checks
        CheckIncorporationDate(flags, startDate, cached.IncorporationDate, cached.CompanyName);
        CheckDissolutionDate(flags, endDate, cached.DissolutionDate, cached.Status, cached.CompanyName);
        CheckDormantCompany(flags, cached.AccountsCategory, jobTitle, cached.CompanyName);
        CheckCompanySizeVsRole(flags, cached.AccountsCategory, jobTitle, cached.CompanyName);
        CheckSicCodeMismatch(flags, sicCodes, jobTitle, cached.CompanyName);

        var (jobPlausible, jobNotes) = CheckJobTitlePlausibility(jobTitle, cached.CompanyType);
        if (jobPlausible == false)
        {
            flags.Add(new CompanyVerificationFlag
            {
                Type = "ImplausibleJobTitle",
                Severity = "Critical",
                Message = jobNotes ?? "Job title requires verification",
                ScoreImpact = -15
            });
        }

        return new CompanyVerificationResult
        {
            ClaimedCompany = claimedCompany,
            MatchedCompanyName = cached.CompanyName,
            MatchedCompanyNumber = cached.CompanyNumber,
            MatchScore = matchScore,
            IsVerified = true,
            VerificationNotes = $"Matched from cache with {matchScore}% confidence",
            ClaimedStartDate = startDate,
            ClaimedEndDate = endDate,
            CompanyType = cached.CompanyType,
            CompanyStatus = cached.Status,
            IncorporationDate = cached.IncorporationDate,
            DissolutionDate = cached.DissolutionDate,
            AccountsCategory = cached.AccountsCategory,
            SicCodes = sicCodes,
            ClaimedJobTitle = jobTitle,
            JobTitlePlausible = jobPlausible,
            JobTitleNotes = jobNotes,
            Flags = flags
        };
    }

    private static CompanyVerificationResult CreateUnverifiedResult(
        string companyName,
        DateOnly? startDate,
        DateOnly? endDate,
        string? jobTitle,
        string reason)
    {
        return new CompanyVerificationResult
        {
            ClaimedCompany = companyName,
            MatchedCompanyName = null,
            MatchedCompanyNumber = null,
            MatchScore = 0,
            IsVerified = false,
            VerificationNotes = reason,
            ClaimedStartDate = startDate,
            ClaimedEndDate = endDate,
            ClaimedJobTitle = jobTitle
        };
    }

    #endregion
}