using System.Text.Json;
using System.Text.Json.Serialization;
using System.Text.RegularExpressions;

namespace JobTrackerApi.Models;

public static class StructuredCvProfileJson
{
    private static readonly JsonSerializerOptions SerializerOptions = new(JsonSerializerDefaults.Web)
    {
        PropertyNameCaseInsensitive = true,
        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
    };

    private static readonly HashSet<string> NonLocationTokens = new(StringComparer.OrdinalIgnoreCase)
    {
        "python", "ruby", "sql", "mysql", "postgresql", "postgres", "sqlite", "javascript", "typescript",
        "react", "node", "node.js", "c#", ".net", "asp.net", "java", "azure", "aws", "gcp", "docker",
        "kubernetes", "terraform", "git", "github", "gitlab", "ci/cd", "rest", "graphql", "php", "golang", "go"
    };

    public static StructuredCvProfile Empty() => Normalize(new StructuredCvProfile());

    public static StructuredCvProfile Deserialize(string? json)
    {
        if (string.IsNullOrWhiteSpace(json)) return Empty();

        try
        {
            using var doc = JsonDocument.Parse(json);
            if (doc.RootElement.ValueKind == JsonValueKind.Array)
            {
                var sections = JsonSerializer.Deserialize<List<StructuredCvSection>>(json, SerializerOptions) ?? new List<StructuredCvSection>();
                return FromSections(sections);
            }

            if (doc.RootElement.ValueKind != JsonValueKind.Object) return Empty();
            var profile = JsonSerializer.Deserialize<StructuredCvProfile>(json, SerializerOptions) ?? new StructuredCvProfile();
            return Normalize(profile);
        }
        catch
        {
            return Empty();
        }
    }

    public static string Serialize(StructuredCvProfile? profile)
    {
        return JsonSerializer.Serialize(Normalize(profile), SerializerOptions);
    }

    public static StructuredCvProfile Merge(StructuredCvProfile? preferred, StructuredCvProfile? fallback)
    {
        var primary = Normalize(preferred);
        var secondary = Normalize(fallback);

        primary.Contact.FullName ??= secondary.Contact.FullName;
        primary.Contact.Headline ??= secondary.Contact.Headline;
        primary.Contact.Email ??= secondary.Contact.Email;
        primary.Contact.Phone ??= secondary.Contact.Phone;
        primary.Contact.Location ??= secondary.Contact.Location;
        primary.Contact.Website ??= secondary.Contact.Website;
        primary.Contact.LinkedIn ??= secondary.Contact.LinkedIn;

        primary.Summary = primary.Summary.Count == 0
            ? secondary.Summary
            : primary.Summary.Concat(secondary.Summary).Distinct(StringComparer.OrdinalIgnoreCase).ToList();
        if (primary.Jobs.Count == 0) primary.Jobs = secondary.Jobs;
        if (primary.Education.Count == 0) primary.Education = secondary.Education;
        if (primary.Certifications.Count == 0) primary.Certifications = secondary.Certifications;
        if (primary.Projects.Count == 0) primary.Projects = secondary.Projects;
        primary.Skills = primary.Skills.Count == 0
            ? secondary.Skills
            : primary.Skills.Concat(secondary.Skills).Distinct(StringComparer.OrdinalIgnoreCase).ToList();
        primary.Languages = primary.Languages.Count == 0
            ? secondary.Languages
            : primary.Languages
                .Concat(secondary.Languages)
                .GroupBy(language => language.Name ?? string.Empty, StringComparer.OrdinalIgnoreCase)
                .Select(group => group.First())
                .ToList();
        primary.Interests = primary.Interests.Count == 0
            ? secondary.Interests
            : primary.Interests.Concat(secondary.Interests).Distinct(StringComparer.OrdinalIgnoreCase).ToList();
        if (primary.OtherSections.Count == 0) primary.OtherSections = secondary.OtherSections;
        if (primary.Sections.Count == 0) primary.Sections = secondary.Sections;

        foreach (var entry in secondary.Metadata.Fields)
        {
            if (!primary.Metadata.Fields.ContainsKey(entry.Key))
            {
                primary.Metadata.Fields[entry.Key] = entry.Value;
            }
        }

        return Normalize(primary);
    }

    public static StructuredCvProfile FromSections(IEnumerable<StructuredCvSection>? sections)
    {
        var normalizedSections = NormalizeSections(sections);
        var profile = new StructuredCvProfile
        {
            Sections = normalizedSections,
        };

        foreach (var section in normalizedSections)
        {
            switch (section.Name.Trim().ToLowerInvariant())
            {
                case "contact":
                    ApplyContact(profile.Contact, section.Content);
                    break;
                case "professional summary":
                case "summary":
                    profile.Summary = SplitList(section.Content);
                    break;
                case "skills":
                case "core skills":
                case "technical skills":
                    profile.Skills = SplitList(section.Content);
                    break;
                case "languages":
                    profile.Languages = ParseLanguages(section.Content);
                    break;
                case "interests":
                    profile.Interests = SplitList(section.Content);
                    break;
                case "work experience":
                case "experience":
                case "employment history":
                    profile.Jobs = ParseJobs(section.Content);
                    break;
                case "education":
                    profile.Education = ParseEducation(section.Content);
                    break;
                case "certifications":
                case "certificates":
                    profile.Certifications = ParseCertifications(section.Content);
                    break;
                case "projects":
                case "selected projects":
                    profile.Projects = ParseProjects(section.Content);
                    break;
                default:
                    profile.OtherSections.Add(new StructuredCvOtherSection
                    {
                        Title = section.Name,
                        Items = SplitList(section.Content),
                    });
                    break;
            }
        }

        return Normalize(profile);
    }

    public static StructuredCvProfile Normalize(StructuredCvProfile? profile)
    {
        profile ??= new StructuredCvProfile();
        profile.Version = string.IsNullOrWhiteSpace(profile.Version) ? "1" : profile.Version.Trim();
        profile.Metadata ??= new StructuredCvMetadata();
        profile.Metadata.Fields ??= new Dictionary<string, StructuredCvFieldMetadata>();
        profile.Contact = NormalizeContact(profile.Contact);
        profile.Summary = CleanList(profile.Summary);
        profile.Jobs = (profile.Jobs ?? new List<StructuredCvJob>())
            .Select(NormalizeJob)
            .Where(job => !string.IsNullOrWhiteSpace(job.Title)
                || !string.IsNullOrWhiteSpace(job.Company)
                || job.Bullets.Count > 0)
            .ToList();
        profile.Education = (profile.Education ?? new List<StructuredCvEducation>())
            .Select(NormalizeEducation)
            .Where(education => !string.IsNullOrWhiteSpace(education.Qualification)
                || !string.IsNullOrWhiteSpace(education.Institution)
                || education.Details.Count > 0)
            .ToList();
        profile.Certifications = (profile.Certifications ?? new List<StructuredCvCertification>())
            .Select(NormalizeCertification)
            .Where(certification => !string.IsNullOrWhiteSpace(certification.Name)
                || !string.IsNullOrWhiteSpace(certification.Issuer)
                || certification.Details.Count > 0)
            .ToList();
        profile.Projects = (profile.Projects ?? new List<StructuredCvProject>())
            .Select(NormalizeProject)
            .Where(project => !string.IsNullOrWhiteSpace(project.Name)
                || !string.IsNullOrWhiteSpace(project.Role)
                || project.Bullets.Count > 0)
            .ToList();
        profile.Skills = CleanList(profile.Skills);
        profile.Languages = (profile.Languages ?? new List<StructuredCvLanguage>())
            .Select(NormalizeLanguage)
            .Where(language => !string.IsNullOrWhiteSpace(language.Name))
            .ToList();
        profile.Interests = CleanList(profile.Interests);
        profile.OtherSections = (profile.OtherSections ?? new List<StructuredCvOtherSection>())
            .Select(section => new StructuredCvOtherSection
            {
                Title = TrimOrNull(section?.Title),
                Items = CleanList(section?.Items),
            })
            .Where(section => !string.IsNullOrWhiteSpace(section.Title) || section.Items.Count > 0)
            .ToList();

        var normalizedSections = NormalizeSections(profile.Sections);
        profile.Sections = normalizedSections.Count > 0 ? normalizedSections : BuildSections(profile);
        return profile;
    }

    private static StructuredCvContact NormalizeContact(StructuredCvContact? contact)
    {
        contact ??= new StructuredCvContact();
        contact.FullName = TrimOrNull(contact.FullName);
        contact.Headline = TrimOrNull(contact.Headline);
        contact.Email = TrimOrNull(contact.Email);
        contact.Phone = TrimOrNull(contact.Phone);
        contact.Location = NormalizeLocationValue(contact.Location);
        contact.Website = NormalizeWebsite(contact.Website);
        contact.LinkedIn = NormalizeLinkedIn(contact.LinkedIn);
        return contact;
    }

    private static StructuredCvJob NormalizeJob(StructuredCvJob? job)
    {
        job ??= new StructuredCvJob();

        var title = NormalizeJobTitle(job.Title);
        var company = NormalizeCompanyName(job.Company);
        var location = NormalizeLocationValue(job.Location);

        if (!string.IsNullOrWhiteSpace(title) && company is null)
        {
            var atSplit = Regex.Match(title, @"^(?<title>.+?)\s+at\s+(?<company>.+)$", RegexOptions.IgnoreCase);
            if (atSplit.Success)
            {
                title = NormalizeJobTitle(atSplit.Groups["title"].Value);
                company = NormalizeCompanyName(atSplit.Groups["company"].Value);
            }
        }

        if (!string.IsNullOrWhiteSpace(title) && !string.IsNullOrWhiteSpace(company))
        {
            var titleLooksLikeCompany = LooksLikeCompanyName(title) && !LooksLikeJobTitle(title);
            var companyLooksLikeTitle = LooksLikeJobTitle(company) && !LooksLikeCompanyName(company);
            if (titleLooksLikeCompany && companyLooksLikeTitle)
            {
                (title, company) = (company, title);
            }
        }

        if (!string.IsNullOrWhiteSpace(title) && !LooksLikeJobTitle(title) && LooksLikeCompanyName(title))
        {
            if (company is null) company = title;
            title = null;
        }

        if (!string.IsNullOrWhiteSpace(company) && !LooksLikeCompanyName(company) && LooksLikeJobTitle(company) && title is null)
        {
            title = company;
            company = null;
        }

        job.Title = title;
        job.Company = company;
        job.Location = location;
        job.Start = NormalizeDateValue(job.Start);
        job.End = NormalizeDateValue(job.End);
        job.Bullets = CleanList(job.Bullets)
            .Select(NormalizeBullet)
            .Where(bullet => bullet is not null)
            .Select(bullet => bullet!)
            .Where(bullet => IsUsefulJobBullet(bullet, job.Title, job.Company))
            .ToList();
        job.Skills = CleanList(job.Skills);
        job.IsCurrent = job.IsCurrent || string.Equals(job.End, "present", StringComparison.OrdinalIgnoreCase) || string.Equals(job.End, "current", StringComparison.OrdinalIgnoreCase);
        return job;
    }

    private static string? NormalizeBullet(string? value)
    {
        if (string.IsNullOrWhiteSpace(value)) return null;
        return value.Trim().TrimStart('-', '•', '*', ' ');
    }

    private static bool IsUsefulJobBullet(string? value, string? title, string? company)
    {
        var trimmed = TrimOrNull(value);
        if (trimmed is null) return false;
        if (LooksLikeDateRange(trimmed) || LooksLikeSectionHeading(trimmed) || trimmed.StartsWith("Skills:", StringComparison.OrdinalIgnoreCase)) return false;
        if (title is not null && trimmed.Equals(title, StringComparison.OrdinalIgnoreCase)) return false;
        if (company is not null && trimmed.Equals(company, StringComparison.OrdinalIgnoreCase)) return false;
        if (trimmed.Length < 12 && !trimmed.Contains(' ')) return false;
        return true;
    }

    private static string? NormalizeJobTitle(string? value)
    {
        var trimmed = TrimOrNull(value);
        if (trimmed is null) return null;
        if (LooksLikeDateRange(trimmed) || LooksLikeSectionHeading(trimmed) || LooksLikeUrlOrEmail(trimmed)) return null;
        trimmed = Regex.Replace(trimmed, @"\s+", " ").Trim(' ', '|', ',', '-', ':');
        return string.IsNullOrWhiteSpace(trimmed) ? null : trimmed;
    }

    private static string? NormalizeCompanyName(string? value)
    {
        var trimmed = TrimOrNull(value);
        if (trimmed is null) return null;
        if (LooksLikeDateRange(trimmed) || LooksLikeSectionHeading(trimmed) || LooksLikeUrlOrEmail(trimmed)) return null;
        if (trimmed.StartsWith("Skills:", StringComparison.OrdinalIgnoreCase)) return null;
        if (trimmed.Contains('.') && trimmed.Contains(' ')) return null;
        trimmed = Regex.Replace(trimmed, @"\s+", " ").Trim(' ', '|', ',', '-', ':');
        return string.IsNullOrWhiteSpace(trimmed) ? null : trimmed;
    }

    private static string? NormalizeLocationValue(string? value)
    {
        var trimmed = TrimOrNull(value);
        if (trimmed is null) return null;
        if (LooksLikeDateRange(trimmed) || LooksLikeSectionHeading(trimmed) || LooksLikeUrlOrEmail(trimmed)) return null;
        if (trimmed.Any(char.IsDigit) || trimmed.Length > 80) return null;

        var normalized = Regex.Replace(trimmed, @"\s+[A-Z](?:\s+[A-Z]){2,}(?:\b.*)?$", string.Empty).Trim();
        normalized = Regex.Replace(normalized, @"\b(?:remote|hybrid)\b.*$", string.Empty, RegexOptions.IgnoreCase).Trim();
        normalized = Regex.Replace(normalized, @"\b(?:sales representative|developer|engineer|manager|consultant|analyst|designer|specialist|technician)\b.*$", string.Empty, RegexOptions.IgnoreCase).Trim();
        normalized = Regex.Replace(normalized, @"\s+", " ").Trim(' ', '|', ';', ':');
        var parts = normalized.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
        if (parts.Length == 0 || parts.Length > 4) return null;
        if (parts.Any(part => !Regex.IsMatch(part, @"^[\p{L}][\p{L}'’\-. ]+$"))) return null;
        if (parts.Any(LooksLikeSkillToken)) return null;

        return string.Join(", ", parts);
    }

    private static string? NormalizeWebsite(string? value)
    {
        var trimmed = TrimOrNull(value);
        if (trimmed is null) return null;
        if (trimmed.Contains("linkedin.com", StringComparison.OrdinalIgnoreCase)) return null;

        var candidate = trimmed;
        if (!candidate.Contains("://", StringComparison.Ordinal)) candidate = $"https://{candidate}";
        if (!Uri.TryCreate(candidate, UriKind.Absolute, out var uri)) return null;
        var host = uri.Host.Trim().Trim('.').ToLowerInvariant();
        if (string.IsNullOrWhiteSpace(host) || !Regex.IsMatch(host, @"^(?:[a-z0-9-]+\.)+[a-z]{2,}$", RegexOptions.IgnoreCase)) return null;
        return host;
    }

    private static string? NormalizeLinkedIn(string? value)
    {
        var trimmed = TrimOrNull(value);
        if (trimmed is null) return null;

        var candidate = trimmed;
        if (!candidate.Contains("://", StringComparison.Ordinal)) candidate = $"https://{candidate}";
        if (!Uri.TryCreate(candidate, UriKind.Absolute, out var uri)) return null;
        if (!uri.Host.Contains("linkedin.com", StringComparison.OrdinalIgnoreCase)) return null;

        var path = uri.AbsolutePath.TrimEnd('/');
        if (!Regex.IsMatch(path, @"^/(in|pub)/[^/]+(?:/[^/]+){0,2}$", RegexOptions.IgnoreCase)) return null;
        return $"https://www.linkedin.com{path}";
    }

    private static string? NormalizeDateValue(string? value)
    {
        var trimmed = TrimOrNull(value);
        return trimmed is not null && LooksLikeDateRange(trimmed) ? trimmed : null;
    }

    private static bool LooksLikeDateRange(string value)
    {
        return Regex.IsMatch(value, @"^(?:\d{1,2}/\d{1,2}/\d{4}|(?:Jan|January|Feb|February|Mar|March|Apr|April|May|Jun|June|Jul|July|Aug|August|Sep|Sept|September|Oct|October|Nov|November|Dec|December)\s+\d{4}|\d{4}|Present|Current)(?:\s*[-–]\s*(?:\d{1,2}/\d{1,2}/\d{4}|(?:Jan|January|Feb|February|Mar|March|Apr|April|May|Jun|June|Jul|July|Aug|August|Sep|Sept|September|Oct|October|Nov|November|Dec|December)\s+\d{4}|\d{4}|Present|Current))?$", RegexOptions.IgnoreCase);
    }

    private static bool LooksLikeUrlOrEmail(string value)
    {
        return value.Contains('@')
            || value.Contains("www.", StringComparison.OrdinalIgnoreCase)
            || value.Contains("http://", StringComparison.OrdinalIgnoreCase)
            || value.Contains("https://", StringComparison.OrdinalIgnoreCase);
    }

    private static bool LooksLikeSectionHeading(string value)
    {
        return value.Equals("Work Experience", StringComparison.OrdinalIgnoreCase)
            || value.Equals("Experience", StringComparison.OrdinalIgnoreCase)
            || value.Equals("Employment History", StringComparison.OrdinalIgnoreCase)
            || value.Equals("Education", StringComparison.OrdinalIgnoreCase)
            || value.Equals("Skills", StringComparison.OrdinalIgnoreCase)
            || value.Equals("Languages", StringComparison.OrdinalIgnoreCase)
            || value.Equals("Interests", StringComparison.OrdinalIgnoreCase)
            || value.Equals("Contact", StringComparison.OrdinalIgnoreCase)
            || value.Equals("Professional Summary", StringComparison.OrdinalIgnoreCase)
            || value.Equals("Summary", StringComparison.OrdinalIgnoreCase);
    }

    private static bool LooksLikeJobTitle(string value)
    {
        if (string.IsNullOrWhiteSpace(value) || LooksLikeDateRange(value) || LooksLikeUrlOrEmail(value)) return false;

        return Regex.IsMatch(value, @"\b(developer|engineer|manager|lead|architect|consultant|specialist|analyst|administrator|coordinator|director|designer|intern|officer|owner|founder|teacher|researcher|writer|editor|producer|assistant|technician|supervisor|head)\b", RegexOptions.IgnoreCase)
            || (value.Split(' ', StringSplitOptions.RemoveEmptyEntries).Length <= 6 && !LooksLikeCompanyName(value));
    }

    private static bool LooksLikeCompanyName(string value)
    {
        if (string.IsNullOrWhiteSpace(value) || LooksLikeDateRange(value) || LooksLikeUrlOrEmail(value)) return false;

        return Regex.IsMatch(value, @"\b(inc|llc|ltd|limited|plc|corp|corporation|company|group|university|college|council|municipality|kommune|bank|studio|agency|institute|hospital|school|technologies|technology|systems|solutions|consulting|consultants|partners|foundation|ministry|government)\b", RegexOptions.IgnoreCase)
            || value.Contains('&')
            || Regex.IsMatch(value, @"\b[A-Z]{2,}\b");
    }

    private static bool LooksLikeSkillToken(string value)
    {
        var normalized = TrimOrNull(value)?.Trim('.', ' ');
        return normalized is not null && NonLocationTokens.Contains(normalized);
    }

    private static bool LooksLikeQualification(string value)
    {
        return Regex.IsMatch(value, @"\b(level\s*\d+|nvq|btec|gcse|a-?level|diploma|certificate|certification|bachelor(?:'s)?|master(?:'s)?|phd|doctorate|mba|ba|bsc|msc|ma|associate|apprenticeship|degree|ict)\b", RegexOptions.IgnoreCase);
    }

    private static bool LooksLikeInstitutionName(string value)
    {
        return Regex.IsMatch(value, @"\b(university|college|school|academy|institute|faculty|campus|council|polytechnic)\b", RegexOptions.IgnoreCase);
    }

    private static string? NormalizeQualification(string? value)
    {
        var trimmed = TrimOrNull(value);
        if (trimmed is null) return null;
        if (LooksLikeDateRange(trimmed) || LooksLikeUrlOrEmail(trimmed) || LooksLikeSectionHeading(trimmed)) return null;
        trimmed = Regex.Replace(trimmed, @"\s+", " ").Trim(' ', '|', ';', ':');
        return string.IsNullOrWhiteSpace(trimmed) ? null : trimmed;
    }

    private static string? NormalizeInstitution(string? value)
    {
        var trimmed = TrimOrNull(value);
        if (trimmed is null) return null;
        if (LooksLikeDateRange(trimmed) || LooksLikeUrlOrEmail(trimmed) || LooksLikeSectionHeading(trimmed)) return null;
        trimmed = Regex.Replace(trimmed, @"\s+", " ").Trim(' ', '|', ';', ':');
        return string.IsNullOrWhiteSpace(trimmed) ? null : trimmed;
    }

    private static string? NormalizeQualificationLevel(string? explicitValue, string? qualificationText)
    {
        var candidate = TrimOrNull(explicitValue) ?? TrimOrNull(qualificationText);
        if (candidate is null) return null;

        if (Regex.IsMatch(candidate, @"\b(phd|doctorate|dphil)\b", RegexOptions.IgnoreCase)) return "PhD";
        if (Regex.IsMatch(candidate, @"\b(master(?:'s)?|msc|m\.sc|ma|m\.a|mba|meng|meng)\b", RegexOptions.IgnoreCase)) return "Master";
        if (Regex.IsMatch(candidate, @"\b(bachelor(?:'s)?|bsc|b\.sc|ba|b\.a|beng|llb|undergraduate degree)\b", RegexOptions.IgnoreCase)) return "Bachelor";
        if (Regex.IsMatch(candidate, @"\b(diploma|certificate|certification|nvq|btec|level\s*\d+|apprenticeship|associate degree)\b", RegexOptions.IgnoreCase)) return "Diploma/Certificate";
        if (Regex.IsMatch(candidate, @"\b(gcse|a-?level|secondary|high school|gymnasium)\b", RegexOptions.IgnoreCase)) return "Secondary";
        return "Other";
    }

    private static StructuredCvEducation NormalizeEducation(StructuredCvEducation? education)
    {
        education ??= new StructuredCvEducation();
        education.Qualification = NormalizeQualification(education.Qualification);
        education.QualificationLevel = NormalizeQualificationLevel(education.QualificationLevel, education.Qualification);
        education.Institution = NormalizeInstitution(education.Institution);
        education.Location = NormalizeLocationValue(education.Location);
        education.Start = NormalizeDateValue(education.Start);
        education.End = NormalizeDateValue(education.End);
        education.Details = CleanList(education.Details);

        if (!string.IsNullOrWhiteSpace(education.Qualification) && !string.IsNullOrWhiteSpace(education.Institution))
        {
            var qualificationLooksInstitutional = LooksLikeInstitutionName(education.Qualification) && !LooksLikeQualification(education.Qualification);
            var institutionLooksQualification = LooksLikeQualification(education.Institution) && !LooksLikeInstitutionName(education.Institution);
            if (qualificationLooksInstitutional && institutionLooksQualification)
            {
                (education.Qualification, education.Institution) = (education.Institution, education.Qualification);
                education.QualificationLevel = NormalizeQualificationLevel(education.QualificationLevel, education.Qualification);
            }
        }

        return education;
    }

    private static StructuredCvCertification NormalizeCertification(StructuredCvCertification? certification)
    {
        certification ??= new StructuredCvCertification();
        certification.Name = NormalizeQualification(certification.Name);
        certification.Issuer = NormalizeInstitution(certification.Issuer);
        certification.Location = NormalizeLocationValue(certification.Location);
        certification.Date = NormalizeDateValue(certification.Date);
        certification.Details = CleanList(certification.Details);
        return certification;
    }

    private static StructuredCvProject NormalizeProject(StructuredCvProject? project)
    {
        project ??= new StructuredCvProject();
        project.Name = NormalizeQualification(project.Name);
        project.Role = NormalizeJobTitle(project.Role);
        project.Location = NormalizeLocationValue(project.Location);
        project.Start = NormalizeDateValue(project.Start);
        project.End = NormalizeDateValue(project.End);
        project.Bullets = CleanList(project.Bullets)
            .Select(NormalizeBullet)
            .Where(bullet => bullet is not null)
            .Select(bullet => bullet!)
            .ToList();
        project.Skills = CleanList(project.Skills);
        return project;
    }

    private static StructuredCvLanguage NormalizeLanguage(StructuredCvLanguage? language)
    {
        language ??= new StructuredCvLanguage();

        var originalName = TrimOrNull(language.Name);
        var normalizedName = HumanLanguageCatalog.NormalizeLanguageName(originalName);
        var normalizedLevel = HumanLanguageCatalog.ExtractLevel(language.Level) ?? HumanLanguageCatalog.ExtractLevel(originalName);

        language.Name = normalizedName is not null && normalizedLevel is not null ? normalizedName : null;
        language.Level = normalizedLevel;
        language.Notes = TrimOrNull(language.Notes);
        return language;
    }

    private static List<StructuredCvSection> NormalizeSections(IEnumerable<StructuredCvSection>? sections)
    {
        return (sections ?? Array.Empty<StructuredCvSection>())
            .Select(section => new StructuredCvSection
            {
                Name = string.IsNullOrWhiteSpace(section?.Name) ? "General" : section.Name.Trim(),
                Content = section?.Content?.Trim() ?? string.Empty,
                WordCount = section?.WordCount is > 0 ? section.WordCount : CountWords(section?.Content),
            })
            .Where(section => !string.IsNullOrWhiteSpace(section.Content))
            .ToList();
    }

    private static List<StructuredCvSection> BuildSections(StructuredCvProfile profile)
    {
        var sections = new List<StructuredCvSection>();

        var contactLines = new List<string>();
        AddIf(contactLines, profile.Contact.FullName);
        AddIf(contactLines, profile.Contact.Headline);
        AddIf(contactLines, profile.Contact.Email);
        AddIf(contactLines, profile.Contact.Phone);
        AddIf(contactLines, profile.Contact.Location);
        AddIf(contactLines, profile.Contact.Website);
        AddIf(contactLines, profile.Contact.LinkedIn);
        AddSectionIfAny(sections, "Contact", contactLines);
        AddSectionIfAny(sections, "Professional Summary", profile.Summary);

        if (profile.Jobs.Count > 0)
        {
            var lines = new List<string>();
            foreach (var job in profile.Jobs)
            {
                AddIf(lines, $"### {job.Title}".Trim());
                var meta = string.Join(" | ", new[] { job.Company, job.Location, FormatDateRange(job.Start, job.End, job.IsCurrent) }.Where(value => !string.IsNullOrWhiteSpace(value)));
                AddIf(lines, meta);
                lines.AddRange(job.Bullets.Select(bullet => $"- {bullet}"));
                if (job.Skills.Count > 0)
                {
                    lines.Add($"Skills: {string.Join(", ", job.Skills)}");
                }
                if (lines.Count > 0 && !string.IsNullOrWhiteSpace(lines[^1])) lines.Add(string.Empty);
            }
            AddSectionIfAny(sections, "Work Experience", lines);
        }

        if (profile.Education.Count > 0)
        {
            var lines = new List<string>();
            foreach (var education in profile.Education)
            {
                AddIf(lines, $"### {education.Qualification}".Trim());
                var meta = string.Join(" | ", new[] { education.Institution, education.Location, FormatDateRange(education.Start, education.End, false) }.Where(value => !string.IsNullOrWhiteSpace(value)));
                AddIf(lines, meta);
                if (!string.IsNullOrWhiteSpace(education.QualificationLevel)) AddIf(lines, $"Level: {education.QualificationLevel}");
                lines.AddRange(education.Details.Select(detail => $"- {detail}"));
                if (lines.Count > 0 && !string.IsNullOrWhiteSpace(lines[^1])) lines.Add(string.Empty);
            }
            AddSectionIfAny(sections, "Education", lines);
        }

        if (profile.Certifications.Count > 0)
        {
            var lines = new List<string>();
            foreach (var certification in profile.Certifications)
            {
                AddIf(lines, $"### {certification.Name}".Trim());
                var meta = string.Join(" | ", new[] { certification.Issuer, certification.Location, certification.Date }.Where(value => !string.IsNullOrWhiteSpace(value)));
                AddIf(lines, meta);
                lines.AddRange(certification.Details.Select(detail => $"- {detail}"));
                if (lines.Count > 0 && !string.IsNullOrWhiteSpace(lines[^1])) lines.Add(string.Empty);
            }
            AddSectionIfAny(sections, "Certifications", lines);
        }

        if (profile.Projects.Count > 0)
        {
            var lines = new List<string>();
            foreach (var project in profile.Projects)
            {
                AddIf(lines, $"### {project.Name}".Trim());
                var meta = string.Join(" | ", new[] { project.Role, project.Location, FormatDateRange(project.Start, project.End, false) }.Where(value => !string.IsNullOrWhiteSpace(value)));
                AddIf(lines, meta);
                lines.AddRange(project.Bullets.Select(bullet => $"- {bullet}"));
                if (project.Skills.Count > 0) AddIf(lines, $"Skills: {string.Join(", ", project.Skills)}");
                if (lines.Count > 0 && !string.IsNullOrWhiteSpace(lines[^1])) lines.Add(string.Empty);
            }
            AddSectionIfAny(sections, "Projects", lines);
        }

        AddSectionIfAny(sections, "Skills", profile.Skills);

        if (profile.Languages.Count > 0)
        {
            AddSectionIfAny(sections, "Languages", profile.Languages.Select(language =>
            {
                var value = language.Name ?? string.Empty;
                if (!string.IsNullOrWhiteSpace(language.Level)) value += $": {language.Level}";
                if (!string.IsNullOrWhiteSpace(language.Notes)) value += $" ({language.Notes})";
                return value;
            }).ToList());
        }

        AddSectionIfAny(sections, "Interests", profile.Interests);

        foreach (var other in profile.OtherSections)
        {
            AddSectionIfAny(sections, other.Title ?? "Other", other.Items);
        }

        return NormalizeSections(sections);
    }

    private static void AddSectionIfAny(List<StructuredCvSection> sections, string name, IEnumerable<string>? lines)
    {
        var content = string.Join("\n", (lines ?? Array.Empty<string>()).Where(line => !string.IsNullOrWhiteSpace(line)).Select(line => line.Trim())).Trim();
        if (string.IsNullOrWhiteSpace(content)) return;
        sections.Add(new StructuredCvSection { Name = name, Content = content, WordCount = CountWords(content) });
    }

    private static void AddIf(List<string> lines, string? value)
    {
        if (!string.IsNullOrWhiteSpace(value)) lines.Add(value.Trim());
    }

    private static void ApplyContact(StructuredCvContact contact, string content)
    {
        var lines = content.Replace("\r\n", "\n").Split('\n', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
        contact.Email ??= Regex.Match(content, @"[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}", RegexOptions.IgnoreCase).Value.NullIfWhitespace();
        contact.Phone ??= Regex.Match(content, @"(?<!\w)(?:\+?\d[\d\s().-]{6,}\d)", RegexOptions.IgnoreCase).Value.NullIfWhitespace();

        foreach (var line in lines)
        {
            if (contact.LinkedIn is null && line.Contains("linkedin", StringComparison.OrdinalIgnoreCase))
            {
                contact.LinkedIn = line.Trim();
                continue;
            }

            if (contact.Website is null && (line.Contains("http", StringComparison.OrdinalIgnoreCase) || line.Contains("www.", StringComparison.OrdinalIgnoreCase) || line.Contains(".") && !line.Contains('@')))
            {
                contact.Website = line.Trim();
            }
        }

        var leftovers = lines.Where(line => !line.Contains('@') && !line.Contains("linkedin", StringComparison.OrdinalIgnoreCase) && !line.Equals(contact.Website, StringComparison.OrdinalIgnoreCase) && !line.Equals(contact.Phone, StringComparison.OrdinalIgnoreCase)).ToList();
        if (leftovers.Count > 0) contact.FullName ??= leftovers[0].Trim();
        if (leftovers.Count > 1) contact.Headline ??= leftovers[1].Trim();
        if (leftovers.Count > 2) contact.Location ??= leftovers[2].Trim();
    }

    private static List<StructuredCvLanguage> ParseLanguages(string content)
    {
        return SplitList(content)
            .Select(item =>
            {
                var name = item;
                string? level = null;
                string? notes = null;

                var colonIndex = item.IndexOf(':');
                if (colonIndex > 0)
                {
                    name = item[..colonIndex].Trim();
                    var remainder = item[(colonIndex + 1)..].Trim();
                    var noteMatch = Regex.Match(remainder, @"^(.*?)\s*\((.*?)\)$");
                    if (noteMatch.Success)
                    {
                        level = noteMatch.Groups[1].Value.NullIfWhitespace();
                        notes = noteMatch.Groups[2].Value.NullIfWhitespace();
                    }
                    else
                    {
                        level = remainder.NullIfWhitespace();
                    }
                }

                var normalizedLevel = HumanLanguageCatalog.ExtractLevel(level) ?? HumanLanguageCatalog.ExtractLevel(item);
                return new StructuredCvLanguage
                {
                    Name = normalizedLevel is not null ? HumanLanguageCatalog.NormalizeLanguageName(name) : null,
                    Level = normalizedLevel,
                    Notes = notes,
                };
            })
            .Where(language => !string.IsNullOrWhiteSpace(language.Name))
            .ToList();
    }

    private static List<StructuredCvJob> ParseJobs(string content)
    {
        var blocks = SplitBlocks(content);
        return blocks.Select(ParseJobBlock).Where(job => job is not null).Select(job => job!).ToList();
    }

    private static StructuredCvJob? ParseJobBlock(string block)
    {
        var lines = block.Replace("\r\n", "\n").Split('\n', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries).ToList();
        if (lines.Count == 0) return null;

        var job = new StructuredCvJob();
        if (lines[0].StartsWith("###", StringComparison.Ordinal)) lines[0] = lines[0].TrimStart('#', ' ');
        job.Title = lines[0].NullIfWhitespace();

        var metadata = lines.Skip(1).TakeWhile(line => !IsBullet(line)).ToList();
        var dateValue = metadata.Select(line => Regex.Match(line, @"(?:(?:\w+\s+)?\d{4}|Present|Current)(?:\s*[-–]\s*(?:(?:\w+\s+)?\d{4}|Present|Current))?", RegexOptions.IgnoreCase).Value.NullIfWhitespace()).FirstOrDefault(value => value is not null);
        if (!string.IsNullOrWhiteSpace(dateValue))
        {
            var parts = Regex.Split(dateValue, "\\s*[-–]\\s*");
            job.Start = parts.FirstOrDefault().NullIfWhitespace();
            job.End = parts.Skip(1).FirstOrDefault().NullIfWhitespace();
            job.IsCurrent = string.Equals(job.End, "present", StringComparison.OrdinalIgnoreCase) || string.Equals(job.End, "current", StringComparison.OrdinalIgnoreCase);
        }

        var metadataWithoutDates = metadata
            .Select(line => string.IsNullOrWhiteSpace(dateValue) ? line : line.Replace(dateValue, string.Empty))
            .Select(line => line.Trim(' ', '|', ',', '-'))
            .Where(line => !string.IsNullOrWhiteSpace(line))
            .ToList();
        if (metadataWithoutDates.Count > 0) job.Company = metadataWithoutDates[0].NullIfWhitespace();
        if (metadataWithoutDates.Count > 1) job.Location = metadataWithoutDates[1].NullIfWhitespace();

        job.Bullets = lines.Where(IsBullet).Select(line => line.Trim().TrimStart('-', '•', '*', ' ')).Where(line => !string.IsNullOrWhiteSpace(line)).ToList();
        job.Skills = lines
            .Where(line => line.StartsWith("Skills:", StringComparison.OrdinalIgnoreCase))
            .SelectMany(line => SplitList(line[(line.IndexOf(':') + 1)..]))
            .ToList();

        return string.IsNullOrWhiteSpace(job.Title) && string.IsNullOrWhiteSpace(job.Company) && job.Bullets.Count == 0 ? null : job;
    }

    private static List<StructuredCvEducation> ParseEducation(string content)
    {
        var blocks = SplitBlocks(content);
        return blocks.Select(ParseEducationBlock).Where(education => education is not null).Select(education => education!).ToList();
    }

    private static StructuredCvEducation? ParseEducationBlock(string block)
    {
        var lines = block.Replace("\r\n", "\n").Split('\n', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries).ToList();
        if (lines.Count == 0) return null;

        var education = new StructuredCvEducation();
        if (lines[0].StartsWith("###", StringComparison.Ordinal)) lines[0] = lines[0].TrimStart('#', ' ');
        education.Qualification = lines[0].NullIfWhitespace();

        var metadata = lines.Skip(1).TakeWhile(line => !IsBullet(line)).ToList();
        var dateValue = metadata.Select(line => Regex.Match(line, @"(?:(?:\w+\s+)?\d{4})(?:\s*[-–]\s*(?:(?:\w+\s+)?\d{4}|Present|Current))?", RegexOptions.IgnoreCase).Value.NullIfWhitespace()).FirstOrDefault(value => value is not null);
        if (!string.IsNullOrWhiteSpace(dateValue))
        {
            var parts = Regex.Split(dateValue, "\\s*[-–]\\s*");
            education.Start = parts.FirstOrDefault().NullIfWhitespace();
            education.End = parts.Skip(1).FirstOrDefault().NullIfWhitespace();
        }

        var metadataWithoutDates = metadata
            .Select(line => string.IsNullOrWhiteSpace(dateValue) ? line : line.Replace(dateValue, string.Empty))
            .Select(line => line.Trim(' ', '|', ',', '-'))
            .Where(line => !string.IsNullOrWhiteSpace(line))
            .ToList();
        if (metadataWithoutDates.Count > 0) education.Institution = metadataWithoutDates[0].NullIfWhitespace();
        if (metadataWithoutDates.Count > 1) education.Location = metadataWithoutDates[1].NullIfWhitespace();

        education.Details = lines.Skip(1).Where(IsBullet).Select(line => line.Trim().TrimStart('-', '•', '*', ' ')).Where(line => !string.IsNullOrWhiteSpace(line)).ToList();
        education.QualificationLevel = NormalizeQualificationLevel(null, education.Qualification);
        return string.IsNullOrWhiteSpace(education.Qualification) && string.IsNullOrWhiteSpace(education.Institution) && education.Details.Count == 0 ? null : education;
    }

    private static List<StructuredCvCertification> ParseCertifications(string content)
    {
        var blocks = SplitBlocks(content);
        return blocks.Select(ParseCertificationBlock).Where(certification => certification is not null).Select(certification => certification!).ToList();
    }

    private static StructuredCvCertification? ParseCertificationBlock(string block)
    {
        var lines = block.Replace("\r\n", "\n").Split('\n', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries).ToList();
        if (lines.Count == 0) return null;

        var certification = new StructuredCvCertification();
        if (lines[0].StartsWith("###", StringComparison.Ordinal)) lines[0] = lines[0].TrimStart('#', ' ');
        certification.Name = lines[0].NullIfWhitespace();

        var metadata = lines.Skip(1).TakeWhile(line => !IsBullet(line)).ToList();
        certification.Date = metadata.Select(line => Regex.Match(line, @"(?:(?:\w+\s+)?\d{4}|Present|Current)", RegexOptions.IgnoreCase).Value.NullIfWhitespace()).FirstOrDefault(value => value is not null);
        var metadataWithoutDates = metadata
            .Select(line => string.IsNullOrWhiteSpace(certification.Date) ? line : line.Replace(certification.Date, string.Empty))
            .Select(line => line.Trim(' ', '|', ',', '-'))
            .Where(line => !string.IsNullOrWhiteSpace(line))
            .ToList();
        if (metadataWithoutDates.Count > 0) certification.Issuer = metadataWithoutDates[0].NullIfWhitespace();
        if (metadataWithoutDates.Count > 1) certification.Location = metadataWithoutDates[1].NullIfWhitespace();
        certification.Details = lines.Skip(1).Where(IsBullet).Select(line => line.Trim().TrimStart('-', '•', '*', ' ')).Where(line => !string.IsNullOrWhiteSpace(line)).ToList();
        return string.IsNullOrWhiteSpace(certification.Name) && string.IsNullOrWhiteSpace(certification.Issuer) ? null : certification;
    }

    private static List<StructuredCvProject> ParseProjects(string content)
    {
        var blocks = SplitBlocks(content);
        return blocks.Select(ParseProjectBlock).Where(project => project is not null).Select(project => project!).ToList();
    }

    private static StructuredCvProject? ParseProjectBlock(string block)
    {
        var lines = block.Replace("\r\n", "\n").Split('\n', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries).ToList();
        if (lines.Count == 0) return null;

        var project = new StructuredCvProject();
        if (lines[0].StartsWith("###", StringComparison.Ordinal)) lines[0] = lines[0].TrimStart('#', ' ');
        project.Name = lines[0].NullIfWhitespace();
        var metadata = lines.Skip(1).TakeWhile(line => !IsBullet(line) && !line.StartsWith("Skills:", StringComparison.OrdinalIgnoreCase)).ToList();
        var dateValue = metadata.Select(line => Regex.Match(line, @"(?:(?:\w+\s+)?\d{4}|Present|Current)(?:\s*[-–]\s*(?:(?:\w+\s+)?\d{4}|Present|Current))?", RegexOptions.IgnoreCase).Value.NullIfWhitespace()).FirstOrDefault(value => value is not null);
        if (!string.IsNullOrWhiteSpace(dateValue))
        {
            var parts = Regex.Split(dateValue, "\\s*[-–]\\s*");
            project.Start = parts.FirstOrDefault().NullIfWhitespace();
            project.End = parts.Skip(1).FirstOrDefault().NullIfWhitespace();
        }

        var metadataWithoutDates = metadata
            .Select(line => string.IsNullOrWhiteSpace(dateValue) ? line : line.Replace(dateValue, string.Empty))
            .Select(line => line.Trim(' ', '|', ',', '-'))
            .Where(line => !string.IsNullOrWhiteSpace(line))
            .ToList();
        if (metadataWithoutDates.Count > 0) project.Role = metadataWithoutDates[0].NullIfWhitespace();
        if (metadataWithoutDates.Count > 1) project.Location = metadataWithoutDates[1].NullIfWhitespace();
        project.Bullets = lines.Where(IsBullet).Select(line => line.Trim().TrimStart('-', '•', '*', ' ')).Where(line => !string.IsNullOrWhiteSpace(line)).ToList();
        project.Skills = lines
            .Where(line => line.StartsWith("Skills:", StringComparison.OrdinalIgnoreCase))
            .SelectMany(line => SplitList(line[(line.IndexOf(':') + 1)..]))
            .ToList();
        return string.IsNullOrWhiteSpace(project.Name) && string.IsNullOrWhiteSpace(project.Role) && project.Bullets.Count == 0 ? null : project;
    }

    private static List<string> SplitBlocks(string content)
    {
        var normalized = content.Replace("\r\n", "\n").Trim();
        if (string.IsNullOrWhiteSpace(normalized)) return new List<string>();

        if (normalized.Contains("### ", StringComparison.Ordinal))
        {
            return Regex.Split(normalized, @"(?=^###\s+)" , RegexOptions.Multiline)
                .Select(block => block.Trim())
                .Where(block => !string.IsNullOrWhiteSpace(block))
                .ToList();
        }

        return Regex.Split(normalized, @"\n\s*\n")
            .Select(block => block.Trim())
            .Where(block => !string.IsNullOrWhiteSpace(block))
            .ToList();
    }

    private static bool IsBullet(string value)
    {
        var trimmed = value.TrimStart();
        return trimmed.StartsWith("-", StringComparison.Ordinal)
            || trimmed.StartsWith("•", StringComparison.Ordinal)
            || trimmed.StartsWith("*", StringComparison.Ordinal);
    }

    private static List<string> SplitList(string? content)
    {
        if (string.IsNullOrWhiteSpace(content)) return new List<string>();

        return content
            .Replace("\r\n", "\n")
            .Split('\n', StringSplitOptions.RemoveEmptyEntries)
            .SelectMany(line => line.Contains(',') && !line.TrimStart().StartsWith("-", StringComparison.Ordinal)
                ? line.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
                : new[] { line })
            .Select(item => item.Trim().TrimStart('-', '•', '*', ' '))
            .Where(item => !string.IsNullOrWhiteSpace(item))
            .Distinct(StringComparer.OrdinalIgnoreCase)
            .ToList();
    }

    private static List<string> CleanList(IEnumerable<string>? values)
    {
        return (values ?? Array.Empty<string>())
            .Select(value => value?.Trim() ?? string.Empty)
            .Where(value => !string.IsNullOrWhiteSpace(value))
            .Distinct(StringComparer.OrdinalIgnoreCase)
            .ToList();
    }

    private static int CountWords(string? content)
    {
        if (string.IsNullOrWhiteSpace(content)) return 0;
        return content.Trim().Split((char[]?)null, StringSplitOptions.RemoveEmptyEntries).Length;
    }

    private static string? TrimOrNull(string? value)
    {
        return string.IsNullOrWhiteSpace(value) ? null : value.Trim();
    }

    private static string? FormatDateRange(string? start, string? end, bool isCurrent)
    {
        if (string.IsNullOrWhiteSpace(start) && string.IsNullOrWhiteSpace(end)) return null;
        if (string.IsNullOrWhiteSpace(start)) return end;
        return $"{start} - {(isCurrent ? "Present" : end ?? "Present")}";
    }

    private static string? NullIfWhitespace(this string? value)
    {
        return string.IsNullOrWhiteSpace(value) ? null : value.Trim();
    }
}