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

namespace TrueCV.Infrastructure.Jobs;

public sealed class ProcessCVCheckJob
{
    private readonly ApplicationDbContext _dbContext;
    private readonly IFileStorageService _fileStorageService;
    private readonly ICVParserService _cvParserService;
    private readonly ICompanyVerifierService _companyVerifierService;
    private readonly IEducationVerifierService _educationVerifierService;
    private readonly ITimelineAnalyserService _timelineAnalyserService;
    private readonly IAuditService _auditService;
    private readonly ILogger<ProcessCVCheckJob> _logger;

    private const int BaseScore = 100;
    private const int UnverifiedCompanyPenalty = 10;
    private const int ImplausibleJobTitlePenalty = 15;
    private const int CompanyVerificationFlagPenalty = 5; // Base penalty for company flags, actual from flag.ScoreImpact
    private const int RapidProgressionPenalty = 10;
    private const int EarlyCareerSeniorRolePenalty = 10;
    private const int GapMonthPenalty = 1;
    private const int MaxGapPenalty = 10;
    private const int OverlapMonthPenalty = 2;
    private const int DiplomaMillPenalty = 25;
    private const int SuspiciousInstitutionPenalty = 15;
    private const int UnverifiedEducationPenalty = 5;
    private const int EducationDatePenalty = 10;

    public ProcessCVCheckJob(
        ApplicationDbContext dbContext,
        IFileStorageService fileStorageService,
        ICVParserService cvParserService,
        ICompanyVerifierService companyVerifierService,
        IEducationVerifierService educationVerifierService,
        ITimelineAnalyserService timelineAnalyserService,
        IAuditService auditService,
        ILogger<ProcessCVCheckJob> logger)
    {
        _dbContext = dbContext;
        _fileStorageService = fileStorageService;
        _cvParserService = cvParserService;
        _companyVerifierService = companyVerifierService;
        _educationVerifierService = educationVerifierService;
        _timelineAnalyserService = timelineAnalyserService;
        _auditService = auditService;
        _logger = logger;
    }

    public async Task ExecuteAsync(Guid cvCheckId, CancellationToken cancellationToken)
    {
        _logger.LogInformation("Starting CV check processing for: {CheckId}", cvCheckId);

        var cvCheck = await _dbContext.CVChecks
            .FirstOrDefaultAsync(c => c.Id == cvCheckId, cancellationToken);

        if (cvCheck is null)
        {
            _logger.LogError("CV check not found: {CheckId}", cvCheckId);
            return;
        }

        try
        {
            // Step 1: Update status to Processing
            cvCheck.Status = CheckStatus.Processing;
            cvCheck.ProcessingStage = "Downloading CV";
            await _dbContext.SaveChangesAsync(cancellationToken);

            _logger.LogDebug("CV check {CheckId} status updated to Processing", cvCheckId);

            // Step 2: Download file from blob
            await using var fileStream = await _fileStorageService.DownloadAsync(cvCheck.BlobUrl);

            _logger.LogDebug("Downloaded CV file for check {CheckId}", cvCheckId);

            // Step 3: Parse CV
            cvCheck.ProcessingStage = "Parsing CV";
            await _dbContext.SaveChangesAsync(cancellationToken);

            var cvData = await _cvParserService.ParseAsync(fileStream, cvCheck.OriginalFileName, cancellationToken);

            _logger.LogDebug(
                "Parsed CV for check {CheckId}: {EmploymentCount} employment entries",
                cvCheckId, cvData.Employment.Count);

            // Step 4: Save extracted data
            cvCheck.ExtractedDataJson = JsonSerializer.Serialize(cvData, JsonDefaults.CamelCaseIndented);
            cvCheck.ProcessingStage = "Verifying Employment";
            await _dbContext.SaveChangesAsync(cancellationToken);

            // Step 5: Verify each employment entry (parallelized with rate limiting)
            // Skip freelance entries as they cannot be verified against company registries
            var verificationTasks = cvData.Employment
                .Where(e => !IsFreelance(e.CompanyName))
                .Select(async employment =>
                {
                    var result = await _companyVerifierService.VerifyCompanyAsync(
                        employment.CompanyName,
                        employment.StartDate,
                        employment.EndDate,
                        employment.JobTitle);

                    _logger.LogDebug(
                        "Verified {Company}: {IsVerified} (Score: {Score}%), JobTitle: {JobTitle}, Plausible: {Plausible}",
                        employment.CompanyName, result.IsVerified, result.MatchScore,
                        employment.JobTitle, result.JobTitlePlausible);

                    return result;
                });

            var verificationResults = (await Task.WhenAll(verificationTasks)).ToList();

            // Add freelance entries as auto-verified (skipped)
            foreach (var employment in cvData.Employment.Where(e => IsFreelance(e.CompanyName)))
            {
                verificationResults.Add(new CompanyVerificationResult
                {
                    ClaimedCompany = employment.CompanyName,
                    IsVerified = true,
                    MatchScore = 100,
                    VerificationNotes = "Freelance/self-employed - verification skipped",
                    ClaimedJobTitle = employment.JobTitle,
                    JobTitlePlausible = true
                });

                _logger.LogDebug("Skipped verification for freelance entry: {Company}", employment.CompanyName);
            }

            // Step 5b: Verify director claims against Companies House officers
            cvCheck.ProcessingStage = "Verifying Directors";
            await _dbContext.SaveChangesAsync(cancellationToken);

            await VerifyDirectorClaims(cvData.FullName, verificationResults, cancellationToken);

            // Step 6: Verify education entries
            cvCheck.ProcessingStage = "Verifying Education";
            await _dbContext.SaveChangesAsync(cancellationToken);
            var educationResults = _educationVerifierService.VerifyAll(
                cvData.Education,
                cvData.Employment);

            _logger.LogDebug(
                "Education verification for check {CheckId}: {Count} entries verified ({Recognised} recognised, {DiplomaMill} diploma mills)",
                cvCheckId,
                educationResults.Count,
                educationResults.Count(e => e.IsVerified),
                educationResults.Count(e => e.IsDiplomaMill));

            // Step 7: Analyse timeline
            cvCheck.ProcessingStage = "Analysing Timeline";
            await _dbContext.SaveChangesAsync(cancellationToken);

            var timelineAnalysis = _timelineAnalyserService.Analyse(cvData.Employment);

            _logger.LogDebug(
                "Timeline analysis for check {CheckId}: {GapCount} gaps, {OverlapCount} overlaps",
                cvCheckId, timelineAnalysis.Gaps.Count, timelineAnalysis.Overlaps.Count);

            // Step 8: Calculate veracity score
            cvCheck.ProcessingStage = "Calculating Score";
            await _dbContext.SaveChangesAsync(cancellationToken);
            var (score, flags) = CalculateVeracityScore(verificationResults, educationResults, timelineAnalysis, cvData);

            _logger.LogDebug("Calculated veracity score for check {CheckId}: {Score}", cvCheckId, score);

            // Step 9: Create CVFlag records
            foreach (var flag in flags)
            {
                if (!Enum.TryParse<FlagCategory>(flag.Category, out var category))
                {
                    _logger.LogWarning("Unknown flag category: {Category}, defaulting to Timeline", flag.Category);
                    category = FlagCategory.Timeline;
                }

                if (!Enum.TryParse<FlagSeverity>(flag.Severity, out var severity))
                {
                    _logger.LogWarning("Unknown flag severity: {Severity}, defaulting to Info", flag.Severity);
                    severity = FlagSeverity.Info;
                }

                var cvFlag = new CVFlag
                {
                    Id = Guid.NewGuid(),
                    CVCheckId = cvCheckId,
                    Category = category,
                    Severity = severity,
                    Title = flag.Title,
                    Description = flag.Description,
                    ScoreImpact = flag.ScoreImpact
                };

                _dbContext.CVFlags.Add(cvFlag);
            }

            // Step 10: Generate veracity report
            cvCheck.ProcessingStage = "Generating Report";
            await _dbContext.SaveChangesAsync(cancellationToken);

            var report = new VeracityReport
            {
                OverallScore = score,
                ScoreLabel = GetScoreLabel(score),
                EmploymentVerifications = verificationResults,
                EducationVerifications = educationResults,
                TimelineAnalysis = timelineAnalysis,
                Flags = flags,
                GeneratedAt = DateTime.UtcNow
            };

            cvCheck.ReportJson = JsonSerializer.Serialize(report, JsonDefaults.CamelCaseIndented);
            cvCheck.VeracityScore = score;

            // Step 11: Update status to Completed
            cvCheck.Status = CheckStatus.Completed;
            cvCheck.ProcessingStage = null; // Clear stage on completion
            cvCheck.CompletedAt = DateTime.UtcNow;
            await _dbContext.SaveChangesAsync(cancellationToken);

            _logger.LogInformation(
                "CV check {CheckId} completed successfully with score {Score}",
                cvCheckId, score);

            await _auditService.LogAsync(cvCheck.UserId, AuditActions.CVProcessed, "CVCheck", cvCheckId, $"Score: {score}");
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error processing CV check {CheckId}", cvCheckId);

            try
            {
                cvCheck.Status = CheckStatus.Failed;
                // Use CancellationToken.None to ensure failure status is saved even if original token is cancelled
                await _dbContext.SaveChangesAsync(CancellationToken.None);
            }
            catch (DbUpdateConcurrencyException)
            {
                // Record was deleted during processing - nothing to update
                _logger.LogWarning("CV check {CheckId} was deleted during processing", cvCheckId);
                return;
            }

            throw;
        }
    }

    private static (int Score, List<FlagResult> Flags) CalculateVeracityScore(
        List<CompanyVerificationResult> verifications,
        List<EducationVerificationResult> educationResults,
        TimelineAnalysisResult timeline,
        CVData cvData)
    {
        var score = BaseScore;
        var flags = new List<FlagResult>();

        // Penalty for unverified companies (deduplicated by company name)
        var unverifiedByCompany = verifications
            .Where(v => !v.IsVerified)
            .GroupBy(v => v.ClaimedCompany, StringComparer.OrdinalIgnoreCase)
            .ToList();

        foreach (var companyGroup in unverifiedByCompany)
        {
            score -= UnverifiedCompanyPenalty;
            var firstInstance = companyGroup.First();
            var instanceCount = companyGroup.Count();

            var description = instanceCount > 1
                ? $"Could not verify employment at '{firstInstance.ClaimedCompany}' ({instanceCount} roles). {firstInstance.VerificationNotes}"
                : $"Could not verify employment at '{firstInstance.ClaimedCompany}'. {firstInstance.VerificationNotes}";

            flags.Add(new FlagResult
            {
                Category = FlagCategory.Employment.ToString(),
                Severity = FlagSeverity.Warning.ToString(),
                Title = "Unverified Company",
                Description = description,
                ScoreImpact = -UnverifiedCompanyPenalty
            });
        }

        // Process company verification flags (incorporation date, dissolution, dormant, etc.)
        // Deduplicate by (company, flag type) to avoid penalizing same issue multiple times
        var processedCompanyFlags = new HashSet<(string Company, string FlagType)>(
            new CompanyFlagComparer());

        foreach (var verification in verifications.Where(v => v.Flags.Count > 0))
        {
            foreach (var companyFlag in verification.Flags)
            {
                var key = (verification.ClaimedCompany, companyFlag.Type);
                if (!processedCompanyFlags.Add(key))
                {
                    // Already processed this flag for this company, skip
                    continue;
                }

                var penalty = Math.Abs(companyFlag.ScoreImpact);
                score -= penalty;

                var severity = companyFlag.Severity switch
                {
                    "Critical" => FlagSeverity.Critical,
                    "Warning" => FlagSeverity.Warning,
                    _ => FlagSeverity.Info
                };

                flags.Add(new FlagResult
                {
                    Category = FlagCategory.Employment.ToString(),
                    Severity = severity.ToString(),
                    Title = companyFlag.Type switch
                    {
                        "EmploymentBeforeIncorporation" => "Employment Before Company Existed",
                        "EmploymentAtDissolvedCompany" => "Employment at Dissolved Company",
                        "CurrentEmploymentAtDissolvedCompany" => "Current Employment at Dissolved Company",
                        "EmploymentAtDormantCompany" => "Employment at Dormant Company",
                        "SeniorRoleAtMicroCompany" => "Senior Role at Micro Company",
                        "SicCodeMismatch" => "Role/Industry Mismatch",
                        "ImplausibleJobTitle" => "Implausible Job Title",
                        "UnverifiedDirectorClaim" => "Unverified Director Claim",
                        _ => companyFlag.Type
                    },
                    Description = companyFlag.Message,
                    ScoreImpact = -penalty
                });
            }
        }

        // Check for rapid career progression
        CheckRapidCareerProgression(cvData.Employment, flags, ref score);

        // Check for early career senior roles (relative to education end date)
        CheckEarlyCareerSeniorRoles(cvData.Employment, cvData.Education, flags, ref score);

        // Check for frequent job changes (informational only)
        CheckFrequentJobChanges(cvData.Employment, flags);

        // Informational flags (no penalty - provide context for recruiters)
        AddCareerSpanFlag(cvData.Employment, flags);
        AddCurrentEmploymentStatusFlag(cvData.Employment, flags);
        AddLongTenureFlags(cvData.Employment, flags);
        AddManagementExperienceFlag(cvData.Employment, flags);
        AddCompanySizePatternFlag(verifications, flags);
        AddCareerTrajectoryFlag(cvData.Employment, flags);
        AddPLCExperienceFlag(verifications, flags);
        AddVerifiedDirectorFlag(verifications, flags);

        // Penalty for diploma mills (critical)
        foreach (var edu in educationResults.Where(e => e.IsDiplomaMill))
        {
            score -= DiplomaMillPenalty;

            flags.Add(new FlagResult
            {
                Category = FlagCategory.Education.ToString(),
                Severity = FlagSeverity.Critical.ToString(),
                Title = "Diploma Mill Detected",
                Description = $"'{edu.ClaimedInstitution}' is a known diploma mill. {edu.VerificationNotes}",
                ScoreImpact = -DiplomaMillPenalty
            });
        }

        // Penalty for suspicious institutions
        foreach (var edu in educationResults.Where(e => e.IsSuspicious && !e.IsDiplomaMill))
        {
            score -= SuspiciousInstitutionPenalty;

            flags.Add(new FlagResult
            {
                Category = FlagCategory.Education.ToString(),
                Severity = FlagSeverity.Warning.ToString(),
                Title = "Suspicious Institution",
                Description = $"'{edu.ClaimedInstitution}' has suspicious characteristics. {edu.VerificationNotes}",
                ScoreImpact = -SuspiciousInstitutionPenalty
            });
        }

        // Penalty for unverified education (not recognised, but not flagged as fake)
        // Skip unknown/empty institutions as there's nothing to verify
        foreach (var edu in educationResults.Where(e => !e.IsVerified && !e.IsDiplomaMill && !e.IsSuspicious && e.Status == "Unknown"
            && !string.IsNullOrWhiteSpace(e.ClaimedInstitution)
            && !e.ClaimedInstitution.Equals("Unknown Institution", StringComparison.OrdinalIgnoreCase)
            && !e.ClaimedInstitution.Equals("Unknown", StringComparison.OrdinalIgnoreCase)))
        {
            score -= UnverifiedEducationPenalty;

            flags.Add(new FlagResult
            {
                Category = FlagCategory.Education.ToString(),
                Severity = FlagSeverity.Info.ToString(),
                Title = "Unverified Institution",
                Description = $"Could not verify '{edu.ClaimedInstitution}'. {edu.VerificationNotes}",
                ScoreImpact = -UnverifiedEducationPenalty
            });
        }

        // Penalty for implausible education dates
        foreach (var edu in educationResults.Where(e => !e.DatesArePlausible))
        {
            score -= EducationDatePenalty;

            flags.Add(new FlagResult
            {
                Category = FlagCategory.Education.ToString(),
                Severity = FlagSeverity.Warning.ToString(),
                Title = "Education Date Issues",
                Description = $"Date issues for '{edu.ClaimedInstitution}': {edu.DatePlausibilityNotes}",
                ScoreImpact = -EducationDatePenalty
            });
        }

        // Penalty for gaps (max -10 per gap)
        foreach (var gap in timeline.Gaps)
        {
            var gapPenalty = Math.Min(gap.Months * GapMonthPenalty, MaxGapPenalty);
            score -= gapPenalty;

            var severity = gap.Months >= 6 ? FlagSeverity.Warning : FlagSeverity.Info;

            flags.Add(new FlagResult
            {
                Category = FlagCategory.Timeline.ToString(),
                Severity = severity.ToString(),
                Title = "Employment Gap",
                Description = $"{gap.Months} month gap in employment from {gap.StartDate:MMM yyyy} to {gap.EndDate:MMM yyyy}",
                ScoreImpact = -gapPenalty
            });
        }

        // Note overlaps - these are often legitimate (part-time, consulting, transitions)
        // Only flag as informational, no score penalty
        foreach (var overlap in timeline.Overlaps)
        {
            flags.Add(new FlagResult
            {
                Category = FlagCategory.Timeline.ToString(),
                Severity = FlagSeverity.Info.ToString(),
                Title = "Concurrent Employment",
                Description = $"Worked at both '{overlap.Company1}' and '{overlap.Company2}' simultaneously for {overlap.Months} months ({overlap.OverlapStart:MMM yyyy} to {overlap.OverlapEnd:MMM yyyy})",
                ScoreImpact = 0
            });
        }

        // Deduplicate flags based on Title + Description
        var uniqueFlags = flags
            .GroupBy(f => (f.Title, f.Description))
            .Select(g => g.First())
            .ToList();

        // Recalculate score based on unique flags
        var uniqueScore = BaseScore + uniqueFlags.Sum(f => f.ScoreImpact);

        // Ensure score doesn't go below 0
        uniqueScore = Math.Max(0, uniqueScore);

        return (uniqueScore, uniqueFlags);
    }

    private static string GetScoreLabel(int score)
    {
        return score switch
        {
            >= 90 => "Excellent",
            >= 75 => "Good",
            >= 60 => "Fair",
            >= 40 => "Poor",
            _ => "Very Poor"
        };
    }

    private static bool IsFreelance(string companyName)
    {
        if (string.IsNullOrWhiteSpace(companyName)) return false;

        var name = companyName.Trim().ToLowerInvariant();
        return name == "freelance" ||
               name == "freelancer" ||
               name == "self-employed" ||
               name == "self employed" ||
               name.StartsWith("freelance ") ||
               name.StartsWith("self-employed ") ||
               name.Contains("(freelance)") ||
               name.Contains("(self-employed)");
    }

    private async Task VerifyDirectorClaims(
        string candidateName,
        List<CompanyVerificationResult> verificationResults,
        CancellationToken cancellationToken)
    {
        // Find all director claims at verified companies - use ToList() to avoid modifying during enumeration
        var directorCandidates = verificationResults
            .Select((result, index) => (result, index))
            .Where(x => x.result.IsVerified && !string.IsNullOrEmpty(x.result.MatchedCompanyNumber))
            .ToList();

        foreach (var (result, index) in directorCandidates)
        {
            var jobTitle = result.ClaimedJobTitle?.ToLowerInvariant() ?? "";

            // Check if this is a director claim
            var isDirectorClaim = jobTitle.Contains("director") ||
                                  jobTitle.Contains("company secretary") ||
                                  jobTitle == "md" ||
                                  jobTitle.Contains("managing director");

            if (!isDirectorClaim) continue;

            _logger.LogDebug(
                "Verifying director claim for {Candidate} at {Company}",
                candidateName, result.MatchedCompanyName);

            var isVerifiedDirector = await _companyVerifierService.VerifyDirectorAsync(
                result.MatchedCompanyNumber!,
                candidateName,
                result.ClaimedStartDate,
                result.ClaimedEndDate);

            if (isVerifiedDirector == false)
            {
                // Add a flag for unverified director claim
                var flags = (result.Flags ?? []).ToList();
                flags.Add(new CompanyVerificationFlag
                {
                    Type = "UnverifiedDirectorClaim",
                    Severity = "Critical",
                    Message = $"Claimed director role at '{result.MatchedCompanyName}' but candidate name not found in Companies House officers list",
                    ScoreImpact = -20
                });

                // Update the result with the new flag
                verificationResults[index] = result with { Flags = flags };

                _logger.LogWarning(
                    "Director claim not verified for {Candidate} at {Company}",
                    candidateName, result.MatchedCompanyName);
            }
            else if (isVerifiedDirector == true)
            {
                _logger.LogInformation(
                    "Director claim verified for {Candidate} at {Company}",
                    candidateName, result.MatchedCompanyName);
            }
        }
    }

    private static void CheckRapidCareerProgression(
        List<EmploymentEntry> employment,
        List<FlagResult> flags,
        ref int score)
    {
        // Group employment by company and check for rapid promotions
        var byCompany = employment
            .Where(e => !string.IsNullOrWhiteSpace(e.CompanyName) && e.StartDate.HasValue)
            .GroupBy(e => e.CompanyName.ToLowerInvariant())
            .Where(g => g.Count() > 1);

        foreach (var companyGroup in byCompany)
        {
            var orderedRoles = companyGroup.OrderBy(e => e.StartDate).ToList();

            for (int i = 1; i < orderedRoles.Count; i++)
            {
                var prevRole = orderedRoles[i - 1];
                var currRole = orderedRoles[i];

                var prevSeniority = GetSeniorityLevel(prevRole.JobTitle);
                var currSeniority = GetSeniorityLevel(currRole.JobTitle);

                // Check for jump of 3+ seniority levels
                var seniorityJump = currSeniority - prevSeniority;
                if (seniorityJump >= 3)
                {
                    // Calculate time between roles
                    var monthsBetween = ((currRole.StartDate!.Value.Year - prevRole.StartDate!.Value.Year) * 12) +
                                       (currRole.StartDate!.Value.Month - prevRole.StartDate!.Value.Month);

                    // If jumped 3+ levels in less than 2 years, flag it
                    if (monthsBetween < 24)
                    {
                        score -= RapidProgressionPenalty;

                        flags.Add(new FlagResult
                        {
                            Category = FlagCategory.Employment.ToString(),
                            Severity = FlagSeverity.Warning.ToString(),
                            Title = "Rapid Career Progression",
                            Description = $"Promoted from '{prevRole.JobTitle}' to '{currRole.JobTitle}' at '{companyGroup.First().CompanyName}' in {monthsBetween} months - unusually fast progression",
                            ScoreImpact = -RapidProgressionPenalty
                        });
                    }
                }
            }
        }
    }

    private static void CheckEarlyCareerSeniorRoles(
        List<EmploymentEntry> employment,
        List<EducationEntry> education,
        List<FlagResult> flags,
        ref int score)
    {
        // Find the latest education end date to estimate career start
        var latestEducationEnd = education
            .Where(e => e.EndDate.HasValue)
            .Select(e => e.EndDate!.Value)
            .DefaultIfEmpty(DateOnly.MinValue)
            .Max();

        if (latestEducationEnd == DateOnly.MinValue)
        {
            // No education dates available, skip check
            return;
        }

        foreach (var emp in employment.Where(e => e.StartDate.HasValue))
        {
            var monthsAfterEducation = ((emp.StartDate!.Value.Year - latestEducationEnd.Year) * 12) +
                                       (emp.StartDate!.Value.Month - latestEducationEnd.Month);

            // Check if this is a senior role started within 2 years of finishing education
            if (monthsAfterEducation < 24 && monthsAfterEducation >= 0)
            {
                var seniority = GetSeniorityLevel(emp.JobTitle);

                // Flag if they're claiming a senior role (level 4+) very early in career
                if (seniority >= 4)
                {
                    score -= EarlyCareerSeniorRolePenalty;

                    flags.Add(new FlagResult
                    {
                        Category = FlagCategory.Employment.ToString(),
                        Severity = FlagSeverity.Warning.ToString(),
                        Title = "Early Career Senior Role",
                        Description = $"Claimed senior role '{emp.JobTitle}' at '{emp.CompanyName}' only {monthsAfterEducation} months after completing education",
                        ScoreImpact = -EarlyCareerSeniorRolePenalty
                    });
                }
            }
        }
    }

    private const int ShortTenureMonths = 18;
    private const int MinShortTenuresForFlag = 3;

    private static void CheckFrequentJobChanges(
        List<EmploymentEntry> employment,
        List<FlagResult> flags)
    {
        // Group employment by normalized company name (to combine roles at same employer)
        var employerTenures = employment
            .Where(e => !string.IsNullOrWhiteSpace(e.CompanyName) && e.StartDate.HasValue)
            .Where(e => !IsFreelance(e.CompanyName)) // Exclude freelance
            .GroupBy(e => NormalizeCompanyForGrouping(e.CompanyName))
            .Select(g =>
            {
                // Calculate total tenure at this employer (sum of all roles)
                var totalMonths = 0;
                foreach (var role in g)
                {
                    if (role.StartDate.HasValue)
                    {
                        var endDate = role.EndDate ?? DateOnly.FromDateTime(DateTime.Today);
                        var months = ((endDate.Year - role.StartDate.Value.Year) * 12) +
                                    (endDate.Month - role.StartDate.Value.Month);
                        totalMonths += Math.Max(0, months);
                    }
                }

                return new
                {
                    CompanyGroup = g.Key,
                    DisplayName = g.First().CompanyName,
                    TotalMonths = totalMonths,
                    RoleCount = g.Count()
                };
            })
            .Where(t => t.TotalMonths > 0) // Exclude zero-tenure entries
            .ToList();

        if (employerTenures.Count == 0) return;

        // Find short tenures (less than 18 months) at different companies
        var shortTenures = employerTenures
            .Where(t => t.TotalMonths < ShortTenureMonths)
            .ToList();

        // Calculate average tenure across unique employers
        var avgTenureMonths = employerTenures.Average(t => t.TotalMonths);
        var avgTenureYears = avgTenureMonths / 12.0;

        // If 3+ different companies with short tenure, flag it (informational only)
        if (shortTenures.Count >= MinShortTenuresForFlag)
        {
            var shortTenureCompanies = string.Join(", ", shortTenures.Take(5).Select(t => $"{t.DisplayName} ({t.TotalMonths}mo)"));
            var moreCount = shortTenures.Count > 5 ? $" and {shortTenures.Count - 5} more" : "";

            flags.Add(new FlagResult
            {
                Category = FlagCategory.Timeline.ToString(),
                Severity = FlagSeverity.Info.ToString(),
                Title = "Frequent Job Changes",
                Description = $"Candidate has {shortTenures.Count} employers with tenure under {ShortTenureMonths} months: {shortTenureCompanies}{moreCount}. Average tenure: {avgTenureYears:F1} years across {employerTenures.Count} employers.",
                ScoreImpact = 0 // Informational only, no penalty
            });
        }
        // Even without frequent changes, note average tenure if it's low
        else if (avgTenureMonths < 24 && employerTenures.Count >= 3)
        {
            flags.Add(new FlagResult
            {
                Category = FlagCategory.Timeline.ToString(),
                Severity = FlagSeverity.Info.ToString(),
                Title = "Average Tenure",
                Description = $"Average tenure: {avgTenureYears:F1} years across {employerTenures.Count} employers.",
                ScoreImpact = 0 // Informational only
            });
        }
    }

    /// <summary>
    /// Normalizes company name for grouping purposes.
    /// Groups companies like "BMW UK", "BMW Group", "BMW (UK) Ltd" together.
    /// </summary>
    private static string NormalizeCompanyForGrouping(string companyName)
    {
        if (string.IsNullOrWhiteSpace(companyName)) return "";

        var name = companyName.ToLowerInvariant().Trim();

        // Remove common suffixes
        var suffixes = new[] { " limited", " ltd", " plc", " llp", " inc", " corporation", " corp",
                              " uk", " (uk)", " u.k.", " group", " holdings", " services" };
        foreach (var suffix in suffixes)
        {
            if (name.EndsWith(suffix))
            {
                name = name[..^suffix.Length].Trim();
            }
        }

        // Remove parenthetical content
        name = System.Text.RegularExpressions.Regex.Replace(name, @"\([^)]*\)", "").Trim();

        // Take first significant word(s) as the company identifier
        // This helps group "Unilever Bestfood" with "Unilever UK"
        var words = name.Split(' ', StringSplitOptions.RemoveEmptyEntries);
        if (words.Length >= 1)
        {
            // Use first word if it's substantial (4+ chars), or first two words
            if (words[0].Length >= 4)
            {
                return words[0];
            }
            else if (words.Length >= 2)
            {
                return words[0] + " " + words[1];
            }
        }

        return name;
    }

    #region Informational Flags (No Penalty)

    /// <summary>
    /// Adds a flag showing total career span from earliest to latest employment.
    /// </summary>
    private static void AddCareerSpanFlag(List<EmploymentEntry> employment, List<FlagResult> flags)
    {
        var datedEmployment = employment
            .Where(e => e.StartDate.HasValue)
            .ToList();

        if (datedEmployment.Count == 0) return;

        var earliestStart = datedEmployment.Min(e => e.StartDate!.Value);
        var latestEnd = datedEmployment
            .Select(e => e.EndDate ?? DateOnly.FromDateTime(DateTime.Today))
            .Max();

        var totalMonths = ((latestEnd.Year - earliestStart.Year) * 12) + (latestEnd.Month - earliestStart.Month);
        var years = totalMonths / 12;
        var months = totalMonths % 12;

        var spanText = years > 0
            ? (months > 0 ? $"{years} years {months} months" : $"{years} years")
            : $"{months} months";

        var label = years switch
        {
            >= 20 => "Extensive Career",
            >= 10 => "Established Professional",
            >= 5 => "Experienced",
            >= 2 => "Early-Mid Career",
            _ => "Early Career"
        };

        flags.Add(new FlagResult
        {
            Category = FlagCategory.Timeline.ToString(),
            Severity = FlagSeverity.Info.ToString(),
            Title = "Career Span",
            Description = $"{label}: {spanText} of professional experience ({earliestStart:MMM yyyy} to {(latestEnd == DateOnly.FromDateTime(DateTime.Today) ? "present" : latestEnd.ToString("MMM yyyy"))})",
            ScoreImpact = 0
        });
    }

    /// <summary>
    /// Adds a flag showing current employment status.
    /// </summary>
    private static void AddCurrentEmploymentStatusFlag(List<EmploymentEntry> employment, List<FlagResult> flags)
    {
        var currentRole = employment.FirstOrDefault(e => e.IsCurrent || !e.EndDate.HasValue);

        if (currentRole != null)
        {
            var startText = currentRole.StartDate.HasValue
                ? $" since {currentRole.StartDate.Value:MMM yyyy}"
                : "";

            flags.Add(new FlagResult
            {
                Category = FlagCategory.Employment.ToString(),
                Severity = FlagSeverity.Info.ToString(),
                Title = "Current Status",
                Description = $"Currently employed at {currentRole.CompanyName}{startText}",
                ScoreImpact = 0
            });
        }
        else
        {
            var lastRole = employment
                .Where(e => e.EndDate.HasValue)
                .OrderByDescending(e => e.EndDate)
                .FirstOrDefault();

            if (lastRole?.EndDate != null)
            {
                var monthsSince = ((DateTime.Today.Year - lastRole.EndDate.Value.Year) * 12) +
                                  (DateTime.Today.Month - lastRole.EndDate.Value.Month);

                if (monthsSince > 0)
                {
                    flags.Add(new FlagResult
                    {
                        Category = FlagCategory.Employment.ToString(),
                        Severity = FlagSeverity.Info.ToString(),
                        Title = "Current Status",
                        Description = $"Currently available - last role ended {lastRole.EndDate.Value:MMM yyyy} ({monthsSince} months ago)",
                        ScoreImpact = 0
                    });
                }
            }
        }
    }

    /// <summary>
    /// Highlights roles with particularly long tenure (5+ years).
    /// </summary>
    private static void AddLongTenureFlags(List<EmploymentEntry> employment, List<FlagResult> flags)
    {
        const int longTenureMonths = 60; // 5 years

        var longTenures = employment
            .Where(e => e.StartDate.HasValue)
            .Select(e =>
            {
                var endDate = e.EndDate ?? DateOnly.FromDateTime(DateTime.Today);
                var months = ((endDate.Year - e.StartDate!.Value.Year) * 12) + (endDate.Month - e.StartDate.Value.Month);
                return new { Entry = e, Months = months };
            })
            .Where(x => x.Months >= longTenureMonths)
            .OrderByDescending(x => x.Months)
            .ToList();

        if (longTenures.Count > 0)
        {
            var longest = longTenures[0];
            var years = longest.Months / 12;

            if (longTenures.Count == 1)
            {
                flags.Add(new FlagResult
                {
                    Category = FlagCategory.Employment.ToString(),
                    Severity = FlagSeverity.Info.ToString(),
                    Title = "Long Tenure",
                    Description = $"{years} years at {longest.Entry.CompanyName} - demonstrates commitment and stability",
                    ScoreImpact = 0
                });
            }
            else
            {
                var companies = string.Join(", ", longTenures.Take(3).Select(t => $"{t.Entry.CompanyName} ({t.Months / 12}y)"));
                flags.Add(new FlagResult
                {
                    Category = FlagCategory.Employment.ToString(),
                    Severity = FlagSeverity.Info.ToString(),
                    Title = "Long Tenure",
                    Description = $"{longTenures.Count} roles with 5+ year tenure: {companies}",
                    ScoreImpact = 0
                });
            }
        }
    }

    /// <summary>
    /// Indicates management vs individual contributor experience.
    /// </summary>
    private static void AddManagementExperienceFlag(List<EmploymentEntry> employment, List<FlagResult> flags)
    {
        var managementKeywords = new[] { "manager", "head of", "director", "lead", "team lead", "supervisor", "chief", "vp", "vice president" };

        var managementRoles = employment
            .Where(e => !string.IsNullOrWhiteSpace(e.JobTitle))
            .Where(e => managementKeywords.Any(kw => e.JobTitle!.ToLowerInvariant().Contains(kw)))
            .ToList();

        var totalRoles = employment.Count(e => !string.IsNullOrWhiteSpace(e.JobTitle));
        if (totalRoles == 0) return;

        if (managementRoles.Count > 0)
        {
            var recentManagement = managementRoles
                .OrderByDescending(e => e.StartDate ?? DateOnly.MinValue)
                .Take(2)
                .Select(e => e.JobTitle)
                .ToList();

            flags.Add(new FlagResult
            {
                Category = FlagCategory.Employment.ToString(),
                Severity = FlagSeverity.Info.ToString(),
                Title = "Management Experience",
                Description = $"{managementRoles.Count} of {totalRoles} roles include management responsibility. Recent: {string.Join(", ", recentManagement)}",
                ScoreImpact = 0
            });
        }
        else
        {
            flags.Add(new FlagResult
            {
                Category = FlagCategory.Employment.ToString(),
                Severity = FlagSeverity.Info.ToString(),
                Title = "Individual Contributor",
                Description = "All roles appear to be individual contributor positions - no management titles detected",
                ScoreImpact = 0
            });
        }
    }

    /// <summary>
    /// Shows pattern of company sizes (startup/SME/corporate).
    /// </summary>
    private static void AddCompanySizePatternFlag(List<CompanyVerificationResult> verifications, List<FlagResult> flags)
    {
        var verifiedWithAccounts = verifications
            .Where(v => v.IsVerified && !string.IsNullOrWhiteSpace(v.AccountsCategory))
            .ToList();

        if (verifiedWithAccounts.Count < 2) return;

        var sizeGroups = verifiedWithAccounts
            .GroupBy(v => v.AccountsCategory?.ToLowerInvariant() switch
            {
                "micro-entity" or "micro" => "Micro/Startup",
                "small" => "Small",
                "medium" or "audit-exempt-subsidiary" => "Medium",
                "full" or "group" or "dormant" => "Large",
                _ => "Unknown"
            })
            .Where(g => g.Key != "Unknown")
            .ToDictionary(g => g.Key, g => g.Count());

        if (sizeGroups.Count == 0) return;

        var dominant = sizeGroups.OrderByDescending(kv => kv.Value).First();
        var total = sizeGroups.Values.Sum();
        var percentage = (dominant.Value * 100) / total;

        string pattern;
        if (percentage >= 70)
        {
            pattern = dominant.Key switch
            {
                "Micro/Startup" => "Startup/Early-stage focus",
                "Small" => "Small business specialist",
                "Medium" => "SME experience",
                "Large" => "Large corporate experience",
                _ => "Mixed company sizes"
            };
        }
        else if (sizeGroups.Count >= 3)
        {
            pattern = "Diverse company sizes - experience across startups to corporates";
        }
        else
        {
            pattern = $"Mix of {string.Join(" and ", sizeGroups.Keys)}";
        }

        flags.Add(new FlagResult
        {
            Category = FlagCategory.Employment.ToString(),
            Severity = FlagSeverity.Info.ToString(),
            Title = "Company Size Pattern",
            Description = $"{pattern} ({string.Join(", ", sizeGroups.Select(kv => $"{kv.Key}: {kv.Value}"))})",
            ScoreImpact = 0
        });
    }

    /// <summary>
    /// Shows career trajectory direction (upward/lateral/step-down).
    /// </summary>
    private static void AddCareerTrajectoryFlag(List<EmploymentEntry> employment, List<FlagResult> flags)
    {
        var orderedRoles = employment
            .Where(e => e.StartDate.HasValue && !string.IsNullOrWhiteSpace(e.JobTitle))
            .OrderBy(e => e.StartDate)
            .ToList();

        if (orderedRoles.Count < 3) return;

        var seniorityLevels = orderedRoles.Select(e => GetSeniorityLevel(e.JobTitle)).ToList();

        // Calculate average progression per transition
        var transitions = new List<int>();
        for (int i = 1; i < seniorityLevels.Count; i++)
        {
            transitions.Add(seniorityLevels[i] - seniorityLevels[i - 1]);
        }

        var avgProgression = transitions.Average();
        var firstLevel = seniorityLevels.First();
        var lastLevel = seniorityLevels.Last();
        var netChange = lastLevel - firstLevel;

        string trajectory;
        string description;

        if (avgProgression > 0.3 && netChange > 0)
        {
            trajectory = "Upward";
            var firstTitle = orderedRoles.First().JobTitle;
            var lastTitle = orderedRoles.Last().JobTitle;
            description = $"Career shows upward progression from {firstTitle} to {lastTitle} (net +{netChange} seniority levels)";
        }
        else if (avgProgression < -0.3 && netChange < 0)
        {
            trajectory = "Step-down";
            description = $"Recent roles at lower seniority than earlier career (may indicate work-life balance choice, industry change, or consulting)";
        }
        else
        {
            trajectory = "Lateral";
            description = $"Career shows lateral movement - consistent seniority level across {orderedRoles.Count} roles";
        }

        flags.Add(new FlagResult
        {
            Category = FlagCategory.Employment.ToString(),
            Severity = FlagSeverity.Info.ToString(),
            Title = $"Career Trajectory: {trajectory}",
            Description = description,
            ScoreImpact = 0
        });
    }

    /// <summary>
    /// Highlights experience at publicly listed companies (PLCs).
    /// </summary>
    private static void AddPLCExperienceFlag(List<CompanyVerificationResult> verifications, List<FlagResult> flags)
    {
        var plcRoles = verifications
            .Where(v => v.IsVerified)
            .Where(v => !string.IsNullOrWhiteSpace(v.CompanyType) &&
                       (v.CompanyType.ToLowerInvariant().Contains("plc") ||
                        v.CompanyType.ToLowerInvariant().Contains("public-limited")))
            .ToList();

        if (plcRoles.Count > 0)
        {
            var companies = string.Join(", ", plcRoles.Select(v => v.MatchedCompanyName).Distinct().Take(4));
            var moreText = plcRoles.Select(v => v.MatchedCompanyName).Distinct().Count() > 4 ? " and others" : "";

            flags.Add(new FlagResult
            {
                Category = FlagCategory.Employment.ToString(),
                Severity = FlagSeverity.Info.ToString(),
                Title = "Public Company Experience",
                Description = $"{plcRoles.Count} role(s) at PLC/publicly listed companies: {companies}{moreText}",
                ScoreImpact = 0
            });
        }
    }

    /// <summary>
    /// Positively highlights when director claims are verified by Companies House.
    /// </summary>
    private static void AddVerifiedDirectorFlag(List<CompanyVerificationResult> verifications, List<FlagResult> flags)
    {
        // Look for director roles that DON'T have an UnverifiedDirectorClaim flag
        // (meaning they were either verified or not checked)
        var directorRoles = verifications
            .Where(v => v.IsVerified && !string.IsNullOrWhiteSpace(v.ClaimedJobTitle))
            .Where(v =>
            {
                var title = v.ClaimedJobTitle!.ToLowerInvariant();
                return title.Contains("director") || title.Contains("company secretary") ||
                       title == "md" || title.Contains("managing director");
            })
            .Where(v => !v.Flags.Any(f => f.Type == "UnverifiedDirectorClaim"))
            .ToList();

        // Only flag if we have verified directors (i.e., they were checked and confirmed)
        // We can't distinguish "verified" from "not checked" without more context
        // So we'll be conservative and only mention if there are director roles without red flags
        if (directorRoles.Count > 0)
        {
            var companies = string.Join(", ", directorRoles.Select(v => v.MatchedCompanyName).Distinct().Take(3));

            flags.Add(new FlagResult
            {
                Category = FlagCategory.Employment.ToString(),
                Severity = FlagSeverity.Info.ToString(),
                Title = "Director Experience",
                Description = $"Director/senior officer role(s) at: {companies}",
                ScoreImpact = 0
            });
        }
    }

    #endregion

    private static int GetSeniorityLevel(string? jobTitle)
    {
        if (string.IsNullOrWhiteSpace(jobTitle)) return 0;

        var title = jobTitle.ToLowerInvariant();

        // Level 6: C-suite
        if (title.Contains("ceo") || title.Contains("cto") || title.Contains("cfo") ||
            title.Contains("coo") || title.Contains("cio") || title.Contains("chief") ||
            title.Contains("managing director") || title == "md" ||
            title.Contains("president") || title.Contains("chairman") ||
            title.Contains("chairwoman") || title.Contains("chairperson"))
        {
            return 6;
        }

        // Level 5: VP / Executive
        if (title.Contains("vice president") || title.Contains("vp ") ||
            title.StartsWith("vp") || title.Contains("svp") ||
            title.Contains("executive director") || title.Contains("executive vice"))
        {
            return 5;
        }

        // Level 4: Director / Head
        if (title.Contains("director") || title.Contains("head of"))
        {
            return 4;
        }

        // Level 3: Senior / Lead / Principal / Manager
        if (title.Contains("senior") || title.Contains("lead") ||
            title.Contains("principal") || title.Contains("manager") ||
            title.Contains("team lead") || title.Contains("staff"))
        {
            return 3;
        }

        // Level 2: Mid-level (no junior, no senior)
        if (!title.Contains("junior") && !title.Contains("trainee") &&
            !title.Contains("intern") && !title.Contains("graduate") &&
            !title.Contains("entry") && !title.Contains("assistant"))
        {
            return 2;
        }

        // Level 1: Junior / Entry-level
        return 1;
    }

    /// <summary>
    /// Comparer for deduplicating company flags by (company name, flag type).
    /// Uses case-insensitive comparison for company names.
    /// </summary>
    private sealed class CompanyFlagComparer : IEqualityComparer<(string Company, string FlagType)>
    {
        public bool Equals((string Company, string FlagType) x, (string Company, string FlagType) y)
        {
            return string.Equals(x.Company, y.Company, StringComparison.OrdinalIgnoreCase) &&
                   string.Equals(x.FlagType, y.FlagType, StringComparison.OrdinalIgnoreCase);
        }

        public int GetHashCode((string Company, string FlagType) obj)
        {
            return HashCode.Combine(
                obj.Company?.ToUpperInvariant() ?? "",
                obj.FlagType?.ToUpperInvariant() ?? "");
        }
    }
}