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,
    };

    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;
        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;
                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 ??= new StructuredCvContact();
        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.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 StructuredCvJob NormalizeJob(StructuredCvJob? job)
    {
        job ??= new StructuredCvJob();
        job.Title = TrimOrNull(job.Title);
        job.Company = TrimOrNull(job.Company);
        job.Location = TrimOrNull(job.Location);
        job.Start = TrimOrNull(job.Start);
        job.End = TrimOrNull(job.End);
        job.Bullets = CleanList(job.Bullets);
        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 StructuredCvEducation NormalizeEducation(StructuredCvEducation? education)
    {
        education ??= new StructuredCvEducation();
        education.Qualification = TrimOrNull(education.Qualification);
        education.Institution = TrimOrNull(education.Institution);
        education.Location = TrimOrNull(education.Location);
        education.Start = TrimOrNull(education.Start);
        education.End = TrimOrNull(education.End);
        education.Details = CleanList(education.Details);
        return education;
    }

    private static StructuredCvLanguage NormalizeLanguage(StructuredCvLanguage? language)
    {
        language ??= new StructuredCvLanguage();
        language.Name = TrimOrNull(language.Name);
        language.Level = TrimOrNull(language.Level);
        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);
                lines.AddRange(education.Details.Select(detail => $"- {detail}"));
                if (lines.Count > 0 && !string.IsNullOrWhiteSpace(lines[^1])) lines.Add(string.Empty);
            }
            AddSectionIfAny(sections, "Education", 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();
                    }
                }

                return new StructuredCvLanguage { Name = name.NullIfWhitespace(), Level = level, 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 => line.Replace(dateValue ?? string.Empty, string.Empty).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 => line.Replace(dateValue ?? string.Empty, string.Empty).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();
        return string.IsNullOrWhiteSpace(education.Qualification) && string.IsNullOrWhiteSpace(education.Institution) && education.Details.Count == 0 ? null : education;
    }

    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();
    }
}