using Microsoft.EntityFrameworkCore;
using Purrse.Core.DTOs;
using Purrse.Core.Helpers;
using Purrse.Core.Interfaces.Services;
using Purrse.Core.Models;
using Purrse.Data;

namespace Purrse.Api.Services;

public class PayeeService : IPayeeService
{
    private readonly PurrseDbContext _db;

    public PayeeService(PurrseDbContext db)
    {
        _db = db;
    }

    public async Task<List<PayeeResponse>> GetAllAsync(Guid userId)
    {
        return await _db.Payees
            .Include(p => p.Aliases).Include(p => p.DefaultCategory)
            .Where(p => p.UserId == userId)
            .OrderBy(p => p.Name)
            .Select(p => new PayeeResponse(p.Id, p.Name, p.DefaultCategoryId, p.DefaultCategory != null ? p.DefaultCategory.Name : null, p.IsActive, p.Aliases.Select(a => new PayeeAliasResponse(a.Id, a.Alias)).ToList()))
            .ToListAsync();
    }

    public async Task<PayeeResponse?> GetByIdAsync(Guid userId, Guid payeeId)
    {
        var p = await _db.Payees.Include(p => p.Aliases).Include(p => p.DefaultCategory)
            .FirstOrDefaultAsync(p => p.Id == payeeId && p.UserId == userId);
        return p == null ? null : new PayeeResponse(p.Id, p.Name, p.DefaultCategoryId, p.DefaultCategory?.Name, p.IsActive, p.Aliases.Select(a => new PayeeAliasResponse(a.Id, a.Alias)).ToList());
    }

    public async Task<PayeeResponse> CreateAsync(Guid userId, CreatePayeeRequest request)
    {
        var payee = new Payee
        {
            Id = Guid.NewGuid(),
            UserId = userId,
            Name = request.Name,
            DefaultCategoryId = request.DefaultCategoryId
        };

        if (request.Aliases?.Any() == true)
        {
            foreach (var alias in request.Aliases)
                payee.Aliases.Add(new PayeeAlias { Id = Guid.NewGuid(), Alias = alias });
        }

        _db.Payees.Add(payee);
        await _db.SaveChangesAsync();

        await MatchUnlinkedTransactions(userId, payee);

        return new PayeeResponse(payee.Id, payee.Name, payee.DefaultCategoryId, null, true, payee.Aliases.Select(a => new PayeeAliasResponse(a.Id, a.Alias)).ToList());
    }

    public async Task<PayeeResponse> UpdateAsync(Guid userId, Guid payeeId, UpdatePayeeRequest request)
    {
        var payee = await _db.Payees.Include(p => p.Aliases)
            .FirstOrDefaultAsync(p => p.Id == payeeId && p.UserId == userId)
            ?? throw new KeyNotFoundException("Payee not found");

        payee.Name = request.Name;
        payee.DefaultCategoryId = request.DefaultCategoryId;
        payee.IsActive = request.IsActive;
        await _db.SaveChangesAsync();

        await NormalizeLinkedTransactions(payee);

        return new PayeeResponse(payee.Id, payee.Name, payee.DefaultCategoryId, null, payee.IsActive, payee.Aliases.Select(a => new PayeeAliasResponse(a.Id, a.Alias)).ToList());
    }

    public async Task DeleteAsync(Guid userId, Guid payeeId)
    {
        var payee = await _db.Payees.FirstOrDefaultAsync(p => p.Id == payeeId && p.UserId == userId)
            ?? throw new KeyNotFoundException("Payee not found");
        _db.Payees.Remove(payee);
        await _db.SaveChangesAsync();
    }

    public async Task AddAliasAsync(Guid userId, Guid payeeId, string alias)
    {
        var payee = await _db.Payees.Include(p => p.Aliases)
            .FirstOrDefaultAsync(p => p.Id == payeeId && p.UserId == userId)
            ?? throw new KeyNotFoundException("Payee not found");
        _db.PayeeAliases.Add(new PayeeAlias { Id = Guid.NewGuid(), PayeeId = payeeId, Alias = alias });
        await _db.SaveChangesAsync();

        // Reload aliases so the newly added one is included
        await _db.Entry(payee).Collection(p => p.Aliases).LoadAsync();
        await MatchUnlinkedTransactions(userId, payee);
    }

    public async Task RemoveAliasAsync(Guid userId, Guid payeeId, Guid aliasId)
    {
        var alias = await _db.PayeeAliases.FirstOrDefaultAsync(a => a.Id == aliasId && a.PayeeId == payeeId)
            ?? throw new KeyNotFoundException("Alias not found");
        _db.PayeeAliases.Remove(alias);
        await _db.SaveChangesAsync();
    }

    public async Task<Payee?> MatchPayeeAsync(Guid userId, string importedName)
    {
        if (string.IsNullOrEmpty(importedName)) return null;

        // Check exact match on name
        var exact = await _db.Payees.FirstOrDefaultAsync(p => p.UserId == userId && p.Name == importedName && p.IsActive);
        if (exact != null) return exact;

        // Check aliases
        var aliasMatch = await _db.PayeeAliases
            .Include(a => a.Payee)
            .FirstOrDefaultAsync(a => a.Payee.UserId == userId && a.Alias == importedName);
        if (aliasMatch != null) return aliasMatch.Payee;

        // Fuzzy match
        var payees = await _db.Payees.Include(p => p.Aliases)
            .Where(p => p.UserId == userId && p.IsActive).ToListAsync();

        Payee? bestMatch = null;
        double bestScore = 0;

        foreach (var payee in payees)
        {
            var score = StringSimilarityHelper.Calculate(importedName, payee.Name);
            if (score > bestScore) { bestScore = score; bestMatch = payee; }

            foreach (var alias in payee.Aliases)
            {
                score = StringSimilarityHelper.Calculate(importedName, alias.Alias);
                if (score > bestScore) { bestScore = score; bestMatch = payee; }
            }
        }

        return bestScore >= 0.85 ? bestMatch : null;
    }

    private async Task NormalizeLinkedTransactions(Payee payee)
    {
        var transactions = await _db.Transactions
            .Where(t => t.PayeeId == payee.Id && t.PayeeName != payee.Name)
            .ToListAsync();

        foreach (var txn in transactions)
            txn.PayeeName = payee.Name;

        if (transactions.Count > 0)
            await _db.SaveChangesAsync();
    }

    private async Task MatchUnlinkedTransactions(Guid userId, Payee payee)
    {
        var unlinked = await _db.Transactions
            .Include(t => t.Account)
            .Where(t => t.Account.UserId == userId && t.PayeeId == null && t.PayeeName != null)
            .ToListAsync();

        var matched = false;
        foreach (var txn in unlinked)
        {
            if (!IsMatch(txn.PayeeName!, payee))
                continue;

            txn.PayeeId = payee.Id;
            txn.PayeeName = payee.Name;

            if (txn.CategoryId == null && payee.DefaultCategoryId != null)
                txn.CategoryId = payee.DefaultCategoryId;

            matched = true;
        }

        if (matched)
            await _db.SaveChangesAsync();
    }

    private static bool IsMatch(string transactionPayeeName, Payee payee)
    {
        if (string.Equals(transactionPayeeName, payee.Name, StringComparison.OrdinalIgnoreCase))
            return true;

        foreach (var alias in payee.Aliases)
        {
            if (string.Equals(transactionPayeeName, alias.Alias, StringComparison.OrdinalIgnoreCase))
                return true;
        }

        if (StringSimilarityHelper.Calculate(transactionPayeeName, payee.Name) >= 0.85)
            return true;

        foreach (var alias in payee.Aliases)
        {
            if (StringSimilarityHelper.Calculate(transactionPayeeName, alias.Alias) >= 0.85)
                return true;
        }

        return false;
    }
}