using System.Text.Json;
using System.Text.RegularExpressions;
using Api.Clients.Api.Contracts;
using Api.Services.Contracts;
using CvMatcher.Models.Responses;
using CvSearch.Data;
using CvSearch.Data.Entities;
using CvMatcher.Models.Settings;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Options;

namespace Api.Services;

/// <summary>
/// Creates and validates one-time job search tokens, and creates the corresponding search sessions.
/// Provider configuration is read from <c>cvSearch.JobProviders</c> at session-creation time and
/// snapshotted into <c>JobSearchSessionEntity.ProviderConfigJson</c> so subsequent config changes
/// do not affect already-queued sessions.
/// </summary>
public sealed class JobTokenService : IJobTokenService
{
    private readonly CvSearchDbContext _db;
    private readonly IRagApiClient _rag;
    private readonly JobSearchSettings _settings;
    private readonly ILogger<JobTokenService> _logger;

    public JobTokenService(
        CvSearchDbContext db,
        IRagApiClient rag,
        IOptions<JobSearchSettings> settings,
        ILogger<JobTokenService> logger)
    {
        _db = db;
        _rag = rag;
        _settings = settings.Value;
        _logger = logger;
    }

    /// <inheritdoc />
    public async Task<string?> CreateTokenAsync(string cvDocumentId, string email, string language, CancellationToken ct)
    {
        var hasEnabledProviders = await _db.JobProviders.AnyAsync(p => p.Enabled, ct);
        if (!hasEnabledProviders)
        {
            _logger.LogDebug("Job search token skipped — no enabled providers in cvSearch.JobProviders");
            return null;
        }

        var token = new JobSearchTokenEntity
        {
            Id = Guid.NewGuid().ToString("N"),
            CvDocumentId = cvDocumentId,
            Email = email,
            Language = language,
            ExpiresAt = DateTime.UtcNow.AddDays(_settings.TokenExpiryDays),
            Used = false,
            CreatedAt = DateTime.UtcNow
        };

        _db.JobSearchTokens.Add(token);
        await _db.SaveChangesAsync(ct);
        _logger.LogInformation("Job search token created. TokenId={TokenId}, CvDocumentId={CvDocumentId}", token.Id, cvDocumentId);
        return token.Id;
    }

    /// <inheritdoc />
    public async Task<string> TriggerStartAsync(string tokenId, CancellationToken ct)
    {
        var token = await _db.JobSearchTokens.FirstOrDefaultAsync(x => x.Id == tokenId, ct);
        if (token is null) return StartJobSearchStatus.NotFound;
        if (token.Used) return StartJobSearchStatus.AlreadyUsed;
        if (token.ExpiresAt <= DateTime.UtcNow) return StartJobSearchStatus.Expired;

        token.Used = true;
        await _db.SaveChangesAsync(ct);

        var cv = await _rag.GetDocumentAsync(token.CvDocumentId, ct);
        var keywords = cv is not null ? ExtractKeywords(cv.Text) : string.Empty;

        var enabledProviders = await _db.JobProviders
            .Where(p => p.Enabled)
            .OrderBy(p => p.DisplayOrder)
            .ToListAsync(ct);

        var providerConfigJson = JsonSerializer.Serialize(
            enabledProviders.Select(ToConfig).ToList(),
            new JsonSerializerOptions(JsonSerializerDefaults.Web));

        var session = new JobSearchSessionEntity
        {
            Id = Guid.NewGuid().ToString("N"),
            TokenId = token.Id,
            CvDocumentId = token.CvDocumentId,
            Email = token.Email,
            Language = token.Language,
            Status = JobSearchStatus.Pending,
            Keywords = keywords,
            ProviderConfigJson = providerConfigJson,
            CreatedAt = DateTime.UtcNow
        };

        _db.JobSearchSessions.Add(session);
        await _db.SaveChangesAsync(ct);
        _logger.LogInformation(
            "Job search session created. SessionId={SessionId}, Keywords={Keywords}, Providers={Providers}",
            session.Id, keywords, string.Join(", ", enabledProviders.Select(p => p.Name)));

        return StartJobSearchStatus.Started;
    }

    /// <summary>
    /// Maps a <see cref="JobProviderEntity"/> to the <see cref="JobProviderConfig"/> DTO used by
    /// <c>cv-search-job</c>. The <c>InitialKeywords</c> list is stored as a JSON array in the entity.
    /// </summary>
    private static JobProviderConfig ToConfig(JobProviderEntity entity)
    {
        List<string> keywords;
        try
        {
            keywords = JsonSerializer.Deserialize<List<string>>(entity.InitialKeywordsJson,
                new JsonSerializerOptions(JsonSerializerDefaults.Web)) ?? [];
        }
        catch
        {
            keywords = [];
        }

        return new JobProviderConfig
        {
            Name = entity.Name,
            Enabled = entity.Enabled,
            SearchUrlTemplate = entity.SearchUrlTemplate,
            JobLinkContains = entity.JobLinkContains,
            InitialKeywords = keywords,
            MaxResults = entity.MaxResults
        };
    }

    /// <summary>
    /// Extracts up to 10 meaningful keywords from the CV text using simple heuristics (no LLM).
    /// Samples the first 2000 characters (where title/role/skills usually appear), splits by
    /// whitespace and common delimiters, strips punctuation, and deduplicates.
    /// Works regardless of whether the PDF extractor preserves newlines.
    /// </summary>
    private static string ExtractKeywords(string cvText)
    {
        // Focus on the header area where name/title/skills typically appear
        var sample = cvText.Length > 2000 ? cvText[..2000] : cvText;

        var words = sample
            .Split([' ', '\n', '\r', '\t', '|', '/', ',', ';', '(', ')'], StringSplitOptions.RemoveEmptyEntries)
            .Select(w => Regex.Replace(w, @"[^\w\-]", "").Trim('-'))
            .Where(w => w.Length > 2)
            .Where(w => !Regex.IsMatch(w, @"^[\d\-]+$"))  // skip phone fragments and pure numbers
            .Where(w => !w.Contains('@') && !w.Contains('.'))  // skip emails and URLs
            .Distinct(StringComparer.OrdinalIgnoreCase)
            .Take(10)
            .ToList();

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