hamkadr/src/JobsMedical.Web/Services/RecommendationService.cs

using JobsMedical.Web.Data;
using JobsMedical.Web.Models;
using Microsoft.EntityFrameworkCore;

namespace JobsMedical.Web.Services;

public record Recommendation(Shift Shift, double Score, List<string> Reasons);

/// <summary>
/// Stage 1 of the recommendation engine: a transparent, rule-based pattern engine.
/// It scores open shifts against a visitor's explicit preferences AND their recent behavior
/// (which roles/facilities/shift-types they keep engaging with), and returns the top matches
/// each with a human-readable reason. No ML/AI infra required — works from the first visit,
/// and every result is explainable. Behavioral data logged now feeds the ML stages later.
/// </summary>
public class RecommendationService
{
    private readonly AppDbContext _db;
    private readonly InterestService _interest;

    public RecommendationService(AppDbContext db, InterestService interest)
    {
        _db = db;
        _interest = interest;
    }

    // Tunable weights — the whole point of a pattern engine is that these are legible.
    private const double WRolePref = 40, WRoleBehavior = 15;
    private const double WCityPref = 20;
    private const double WShiftTypePref = 15, WShiftTypeBehavior = 8;
    private const double WPayMeetsExpectation = 10;
    private const double WFacilityAffinity = 12;
    private const double WFreshness = 5, WSoon = 6;
    private const double PenaltyDismissedFacility = 60;

    public async Task<List<Recommendation>> GetForVisitorAsync(int take = 6)
    {
        var today = DateOnly.FromDateTime(DateTime.UtcNow);
        var prefs = await _interest.GetPreferencesAsync();
        var events = await _interest.RecentEventsAsync(150);

        var candidates = await _db.Shifts
            .Include(s => s.Facility).ThenInclude(f => f.City)
            .Include(s => s.Role)
            .Where(s => s.Status == ShiftStatus.Open && s.Date >= today)
            .ToListAsync();

        // Cold start: no preferences and no behavior → just show the freshest opportunities.
        if (prefs is null && events.Count == 0)
        {
            return candidates
                .OrderBy(s => s.Date).ThenBy(s => s.StartTime)
                .Take(take)
                .Select(s => new Recommendation(s, 0, new() { "جدیدترین فرصت‌ها" }))
                .ToList();
        }

        // Derive behavioral affinities from the event log (shift events only — jobs are separate).
        var shiftEvents = events.Where(e => e.ShiftId is not null).ToList();
        var eventShiftIds = shiftEvents.Select(e => e.ShiftId!.Value).Distinct().ToList();
        var eventShifts = candidates.Where(s => eventShiftIds.Contains(s.Id))
            .Concat(await _db.Shifts.Include(s => s.Role)
                .Where(s => eventShiftIds.Contains(s.Id)).ToListAsync())
            .DistinctBy(s => s.Id)
            .ToDictionary(s => s.Id);

        var positive = new[] { InterestEventType.View, InterestEventType.Click,
                               InterestEventType.Save, InterestEventType.Apply };

        var roleAffinity = TopBy(shiftEvents, positive, eventShifts, s => s.RoleId);
        var shiftTypeAffinity = TopBy(shiftEvents, positive, eventShifts, s => (int)s.ShiftType);
        var facilityAffinity = TopBy(shiftEvents, positive, eventShifts, s => s.FacilityId);

        var dismissedFacilities = shiftEvents
            .Where(e => e.EventType is InterestEventType.Dismiss or InterestEventType.HideFacility)
            .Select(e => eventShifts.TryGetValue(e.ShiftId!.Value, out var s) ? s.FacilityId : 0)
            .Where(id => id != 0).ToHashSet();

        var results = new List<Recommendation>();
        foreach (var s in candidates)
        {
            double score = 0;
            var reasons = new List<string>();

            if (prefs?.RoleId is int pr && pr == s.RoleId)
            { score += WRolePref; reasons.Add($"متناسب با نقش مورد علاقه شما ({s.Role.Name})"); }
            else if (roleAffinity.Contains(s.RoleId))
            { score += WRoleBehavior; reasons.Add($"چون به فرصت‌های «{s.Role.Name}» علاقه نشان دادی"); }

            if (prefs?.CityId is int pc && pc == s.Facility.CityId)
            { score += WCityPref; reasons.Add($"در شهر مورد علاقه شما ({s.Facility.City.Name})"); }

            if (prefs?.PreferredShiftType is ShiftType pst && pst == s.ShiftType)
            { score += WShiftTypePref; reasons.Add($"نوع شیفت دلخواه شما ({ShiftTypeLabel(s.ShiftType)})"); }
            else if (shiftTypeAffinity.Contains((int)s.ShiftType))
            { score += WShiftTypeBehavior; reasons.Add($"شبیه شیفت‌هایی که دیده‌ای ({ShiftTypeLabel(s.ShiftType)})"); }

            if (prefs?.MinPay is long min && s.PayAmount is long pay && pay >= min)
            { score += WPayMeetsExpectation; reasons.Add("حقوق بالاتر از حد انتظار شما"); }

            if (facilityAffinity.Contains(s.FacilityId))
            { score += WFacilityAffinity; reasons.Add($"از مرکزی که قبلاً به آن علاقه نشان دادی ({s.Facility.Name})"); }

            if (dismissedFacilities.Contains(s.FacilityId))
                score -= PenaltyDismissedFacility;

            // Sooner shifts and freshly posted ones get a small nudge.
            var daysOut = s.Date.DayNumber - today.DayNumber;
            if (daysOut <= 3) score += WSoon;
            if ((DateTime.UtcNow - s.CreatedAt).TotalDays <= 2) score += WFreshness;

            if (reasons.Count == 0) reasons.Add("پیشنهاد بر اساس فعالیت شما");
            results.Add(new Recommendation(s, score, reasons));
        }

        return results
            .Where(r => r.Score > 0)
            .OrderByDescending(r => r.Score).ThenBy(r => r.Shift.Date)
            .Take(take)
            .ToList();
    }

    /// <summary>Keys the visitor engaged with most (positive events), top 3.</summary>
    private static HashSet<int> TopBy(
        List<InterestEvent> events, InterestEventType[] positive,
        Dictionary<int, Shift> shiftById, Func<Shift, int> key)
    {
        return events
            .Where(e => e.ShiftId is not null && positive.Contains(e.EventType)
                        && shiftById.ContainsKey(e.ShiftId.Value))
            .GroupBy(e => key(shiftById[e.ShiftId!.Value]))
            .OrderByDescending(g => g.Count())
            .Take(3)
            .Select(g => g.Key)
            .ToHashSet();
    }

    private static string ShiftTypeLabel(ShiftType t) => t switch
    {
        ShiftType.Day => "صبح",
        ShiftType.Evening => "عصر",
        ShiftType.Night => "شب",
        _ => "آنکال",
    };
}