using HrynCo.NotificationService.DAL.Abstract.Repositories;
using HrynCo.NotificationService.DAL.Abstract.Templates;
using HrynCo.NotificationService.DAL.EF.Entities;
using Microsoft.EntityFrameworkCore;

namespace HrynCo.NotificationService.DAL.EF.Repositories;

internal sealed class EmailTemplateRepository(NotificationDbContext db, TemplateMutationRunner mutations)
    : IEmailTemplateRepository, IEmailTemplateDefinitionRepository
{
    private IQueryable<EmailTemplateEntity> Languages => db.Templates
        .Include(t => t.Definition).ThenInclude(d => d.Service).Include(t => t.ServiceLanguage);
    private IQueryable<EmailTemplateDefinitionEntity> Definitions => db.TemplateDefinitions
        .Include(d => d.Service).ThenInclude(s => s.Languages)
        .Include(d => d.Languages).ThenInclude(t => t.ServiceLanguage);

    public async Task<IReadOnlyList<EmailTemplate>> GetAllAsync(string? serviceName = null, string? key = null, CancellationToken ct = default)
    {
        var query = Languages.AsNoTracking();
        if (!string.IsNullOrWhiteSpace(serviceName))
            query = query.Where(t => t.Definition.Service.Name == serviceName);
        if (!string.IsNullOrWhiteSpace(key))
            query = query.Where(t => t.Definition.Key == key);
        var entities = await query.OrderBy(t => t.Definition.Service.Name).ThenBy(t => t.Definition.Key)
            .ThenBy(t => t.ServiceLanguage.Code).ToListAsync(ct);
        return entities.Select(MapLanguage).ToList();
    }

    public Task<IReadOnlyList<EmailTemplate>> GetByServiceAsync(string serviceName, CancellationToken ct = default) =>
        GetAllAsync(serviceName, ct: ct);

    public async Task<EmailTemplate?> GetAsync(string serviceName, string key, string languageCode, CancellationToken ct = default)
    {
        var code = languageCode;
        var entity = await Languages.AsNoTracking().SingleOrDefaultAsync(t =>
            t.Definition.Service.Name == serviceName && t.Definition.Key == key && t.ServiceLanguage.Code == code, ct);
        return entity is null ? null : MapLanguage(entity);
    }

    public async Task<EmailTemplateDefinition?> GetDefinitionAsync(string serviceName, string key, CancellationToken ct = default)
    {
        var entity = await Definitions.AsNoTracking().SingleOrDefaultAsync(d => d.Service.Name == serviceName && d.Key == key, ct);
        return entity is null ? null : MapDefinition(entity);
    }

    public async Task<EmailTemplateDefinition?> GetDefinitionAsync(Guid serviceId, string key, CancellationToken ct = default)
    {
        var entity = await Definitions.AsNoTracking().SingleOrDefaultAsync(d => d.ServiceId == serviceId && d.Key == key, ct);
        return entity is null ? null : MapDefinition(entity);
    }

    public async Task<EmailTemplateDefinition?> UpsertDefinitionAsync(EmailTemplateDefinitionPatch patch, CancellationToken ct = default)
    {
        EmailTemplateDefinitionEntity? saved = null;
        await mutations.ExecuteAsync(async () =>
        {
            var service = await db.Services.Include(s => s.Languages).SingleOrDefaultAsync(s => s.Id == patch.ServiceId, ct);
            if (service is null)
                return;
            ValidatePatch(patch, service);
            var entity = await LoadForUpsertAsync(patch, service, ct);
            entity.Variables = MapVariables(patch.Variables);
            var removed = patch.RemoveLanguageCodes.ToHashSet(StringComparer.Ordinal);
            db.Templates.RemoveRange(entity.Languages.Where(t => removed.Contains(t.ServiceLanguage.Code)));
            // Omitted translations are retained. Only explicitly supplied content is changed.
            UpsertLanguages(entity, patch.Translations);
            Touch(entity);
            saved = entity;
        }, ct);
        return saved is null ? null : MapDefinition(saved);
    }

    private async Task<EmailTemplateDefinitionEntity> LoadForUpsertAsync(EmailTemplateDefinitionPatch patch, ServiceEntity service, CancellationToken ct)
    {
        var entity = await Definitions.SingleOrDefaultAsync(d => d.ServiceId == patch.ServiceId && d.Key == patch.Key, ct);
        if (patch.Revision is null)
        {
            if (entity is not null)
                throw new EmailTemplateWriteException("A definition with this service and key already exists. Read its revision before updating.");
            entity = new EmailTemplateDefinitionEntity { Service = service, ServiceId = service.Id, Key = patch.Key, Created = DateTimeOffset.UtcNow };
            db.TemplateDefinitions.Add(entity);
            return entity;
        }
        if (entity is null || entity.Revision != patch.Revision)
            throw new EmailTemplateWriteException("The definition is missing or its revision changed. Read it again before updating.");
        return entity;
    }

    private static void ValidatePatch(EmailTemplateDefinitionPatch patch, ServiceEntity service)
    {
        EmailTemplateValidation.ValidateDefinition(new EmailTemplateDefinition
        {
            ServiceId = service.Id, ServiceName = service.Name, Key = patch.Key,
            Variables = patch.Variables, Languages = patch.Translations
        });
        if (patch.Revision == Guid.Empty)
            throw new EmailTemplateWriteException("Revision must be null for creation or a nonempty revision from the last read for update.", false);
        var removed = patch.RemoveLanguageCodes;
        if (removed.Any(string.IsNullOrWhiteSpace) || removed.Distinct(StringComparer.Ordinal).Count() != removed.Count)
            throw new EmailTemplateWriteException("removeLanguageCodes must contain unique nonblank language codes.", false);
        var supplied = patch.Translations.Select(t => t.LanguageCode).ToHashSet(StringComparer.Ordinal);
        if (removed.Any(supplied.Contains))
            throw new EmailTemplateWriteException("A language cannot be supplied and removed in the same request.", false);
        var supported = service.Languages.Select(l => l.Code).ToHashSet(StringComparer.Ordinal);
        if (supplied.Concat(removed).Any(code => !supported.Contains(code)))
            throw new EmailTemplateWriteException("Every supplied or removed language must exactly match a code in this service's catalog.", false);
    }

    public async Task<IReadOnlyList<EmailTemplateDefinition>> GetDefinitionsAsync(Guid serviceId, CancellationToken ct = default)
    {
        var entities = await Definitions.AsNoTracking().Where(d => d.ServiceId == serviceId).OrderBy(d => d.Key).ToListAsync(ct);
        return entities.Select(MapDefinition).ToList();
    }

    public async Task<bool> DeleteDefinitionAsync(Guid serviceId, string key, Guid revision, CancellationToken ct = default)
    {
        var removed = false;
        await mutations.ExecuteAsync(async () =>
        {
            if (string.IsNullOrWhiteSpace(key) || key.Length > 100 || revision == Guid.Empty)
                throw new EmailTemplateWriteException("An exact key (at most 100 characters) and a nonempty revision are required.", false);
            var definition = await Definitions.SingleOrDefaultAsync(d => d.ServiceId == serviceId && d.Key == key, ct);
            if (definition is null)
                return;
            if (definition.Revision != revision)
                throw new EmailTemplateWriteException("The definition revision changed. Read it again before deleting.");
            db.TemplateDefinitions.Remove(definition);
            removed = true;
        }, ct);
        return removed;
    }

    public Task AddAsync(EmailTemplate template, CancellationToken ct = default) => mutations.ExecuteAsync(async () =>
    {
        ValidateLegacy(template);
        var definition = await FindDefinitionAsync(template.ServiceName, template.Key, ct);
        if (definition is null)
        {
            await RequireServiceLanguageAsync(template.ServiceName, template.LanguageCode, ct);
            definition = await CreateDefinitionAsync(template.ServiceName, template.Key, template.Variables, ct);
        }
        EnsureMatchingContract(definition, template.Variables);
        await RequireServiceLanguageAsync(template.ServiceName, template.LanguageCode, ct);
        var code = template.LanguageCode;
        if (definition.Languages.Any(t => t.ServiceLanguage.Code == code))
            throw new EmailTemplateWriteException("This language already exists for the template.");
        var language = NewLanguage(template, definition);
        definition.Languages.Add(language);
        db.Templates.Add(language);
        Touch(definition);
    }, ct);

    public Task UpdateAsync(EmailTemplate template, CancellationToken ct = default) => mutations.ExecuteAsync(async () =>
    {
        ValidateLegacy(template);
        var definition = await RequireDefinitionAsync(template.ServiceName, template.Key, ct);
        EnsureMatchingContract(definition, template.Variables);
        var language = definition.Languages.SingleOrDefault(t => t.Id == template.Id)
            ?? throw new EmailTemplateWriteException("The language changed or was removed. Reload the template.");
        SetContent(language, template);
        Touch(definition);
    }, ct);

    public Task DeleteAsync(EmailTemplate template, CancellationToken ct = default) => mutations.ExecuteAsync(async () =>
    {
        var definition = await RequireDefinitionAsync(template.ServiceName, template.Key, ct);
        var language = definition.Languages.SingleOrDefault(t => t.Id == template.Id)
            ?? throw new EmailTemplateWriteException("The language changed or was removed. Reload the template.");
        db.Templates.Remove(language);
        Touch(definition);
    }, ct);

    public Task SaveDefinitionAsync(EmailTemplateDefinition definition, bool isNew, CancellationToken ct = default) => mutations.ExecuteAsync(async () =>
    {
        EmailTemplateValidation.ValidateDefinition(definition);
        await ValidateServiceLanguagesAsync(definition, ct);
        var entity = await LoadForSaveAsync(definition, isNew, ct);
        entity.Variables = MapVariables(definition.Variables);
        SynchronizeLanguages(entity, definition.Languages);
        Touch(entity);
        definition.Id = entity.Id;
        definition.Revision = entity.Revision;
    }, ct);

    private async Task<EmailTemplateDefinitionEntity> LoadForSaveAsync(EmailTemplateDefinition model, bool isNew, CancellationToken ct)
    {
        var entity = await FindDefinitionAsync(model.ServiceName, model.Key, ct);
        if (isNew)
        {
            if (entity is not null)
                throw new EmailTemplateWriteException("A template with this service and key already exists.");
            return await CreateDefinitionAsync(model.ServiceName, model.Key, model.Variables, ct);
        }
        if (entity is null || entity.Id != model.Id || entity.Revision != model.Revision)
            throw new EmailTemplateWriteException("This template changed after you opened it. Reload before saving; your entered values are retained.");
        return entity;
    }

    private void SynchronizeLanguages(EmailTemplateDefinitionEntity definition, IReadOnlyList<EmailTemplate> languages)
    {
        var codes = languages.Select(t => t.LanguageCode).ToHashSet(StringComparer.Ordinal);
        db.Templates.RemoveRange(definition.Languages.Where(t => !codes.Contains(t.ServiceLanguage.Code)));
        UpsertLanguages(definition, languages);
    }

    private void UpsertLanguages(EmailTemplateDefinitionEntity definition, IReadOnlyList<EmailTemplate> languages)
    {
        foreach (var model in languages)
        {
            var code = model.LanguageCode;
            var entity = definition.Languages.SingleOrDefault(t => t.ServiceLanguage.Code == code);
            if (entity is null)
            {
                var language = NewLanguage(model, definition);
                definition.Languages.Add(language);
                db.Templates.Add(language);
            }
            else
                SetContent(entity, model);
        }
    }

    public async Task<IReadOnlyList<EmailTemplateDefinition>> GetDefinitionsAsync(string? serviceName = null, string? key = null, CancellationToken ct = default)
    {
        var query = Definitions.AsNoTracking();
        if (!string.IsNullOrWhiteSpace(serviceName))
            query = query.Where(d => d.Service.Name == serviceName);
        if (!string.IsNullOrWhiteSpace(key))
            query = query.Where(d => d.Key == key);
        var entities = await query.OrderBy(d => d.Service.Name).ThenBy(d => d.Key).ToListAsync(ct);
        return entities.Select(MapDefinition).ToList();
    }

    private async Task RequireServiceLanguageAsync(string serviceName, string code, CancellationToken ct)
    {
        if (!await db.ServiceLanguages.AnyAsync(l => l.Service.Name == serviceName && l.Code == code, ct))
            throw new EmailTemplateWriteException("Language is not in this service's catalog. Add it in the service editor first.", false);
    }

    private async Task ValidateServiceLanguagesAsync(EmailTemplateDefinition definition, CancellationToken ct)
    {
        var service = await db.Services.Include(s => s.Languages).SingleOrDefaultAsync(s => s.Name == definition.ServiceName
                && (definition.ServiceId == Guid.Empty || s.Id == definition.ServiceId), ct)
            ?? throw new EmailTemplateWriteException("Service does not exist. Create the service first.", false);
        var codes = service.Languages.Select(l => l.Code).ToHashSet(StringComparer.Ordinal);
        if (definition.Languages.Any(l => !codes.Contains(l.LanguageCode)))
            throw new EmailTemplateWriteException("Language is not in this service's catalog. Add it in the service editor first.", false);
    }

    private Task<EmailTemplateDefinitionEntity?> FindDefinitionAsync(string serviceName, string key, CancellationToken ct) =>
        Definitions.SingleOrDefaultAsync(d => d.Service.Name == serviceName && d.Key == key, ct);

    private async Task<EmailTemplateDefinitionEntity> RequireDefinitionAsync(string serviceName, string key, CancellationToken ct) =>
        await FindDefinitionAsync(serviceName, key, ct)
        ?? throw new EmailTemplateWriteException("The template was removed. Reload the template list.");

    private async Task<EmailTemplateDefinitionEntity> CreateDefinitionAsync(string serviceName, string key,
        IReadOnlyList<EmailTemplateVariable> variables, CancellationToken ct)
    {
        var service = await db.Services.Include(s => s.Languages).SingleOrDefaultAsync(s => s.Name == serviceName, ct)
            ?? throw new EmailTemplateWriteException("Service does not exist. Create the service and its language codes first.", false);
        var entity = new EmailTemplateDefinitionEntity
        {
            Service = service, Key = key, Variables = MapVariables(variables), Created = DateTimeOffset.UtcNow
        };
        db.TemplateDefinitions.Add(entity);
        return entity;
    }

    private static void ValidateLegacy(EmailTemplate template)
    {
        EmailTemplateValidation.ValidateIdentity(template.ServiceName, template.Key);
        EmailTemplateValidation.ValidateLanguage(template);
        EmailTemplateValidation.ValidateVariables(template.Variables);
    }

    private static void EnsureMatchingContract(EmailTemplateDefinitionEntity definition, IReadOnlyList<EmailTemplateVariable> variables)
    {
        var shared = definition.Variables.Select(v => new EmailTemplateVariable { Name = v.Name, Required = v.Required }).ToList();
        if (!EmailTemplateValidation.ContractsEqual(shared, variables))
            throw new EmailTemplateWriteException("Variables conflict with the shared template contract. Edit shared variables in the template editor.");
    }

    private static void Touch(EmailTemplateDefinitionEntity definition)
    {
        definition.Revision = Guid.NewGuid();
        definition.Updated = DateTimeOffset.UtcNow;
    }

    private static List<EmailTemplateVariableData> MapVariables(IReadOnlyList<EmailTemplateVariable> variables) =>
        variables.Select(v => new EmailTemplateVariableData { Name = v.Name, Required = v.Required }).ToList();

    private static EmailTemplateEntity NewLanguage(EmailTemplate model, EmailTemplateDefinitionEntity definition) => new()
    {
        Id = model.Id, Definition = definition, ServiceId = definition.Service.Id,
        ServiceLanguage = definition.Service.Languages.SingleOrDefault(l => l.Code == model.LanguageCode)
            ?? throw new EmailTemplateWriteException("Language is not in this service's catalog. Add it in the service editor first.", false),
        Subject = model.Subject, HtmlBody = model.HtmlBody, TextBody = model.TextBody, Created = model.Created
    };

    private static void SetContent(EmailTemplateEntity entity, EmailTemplate model)
    {
        entity.Subject = model.Subject;
        entity.HtmlBody = model.HtmlBody;
        entity.TextBody = model.TextBody;
        entity.Updated = DateTimeOffset.UtcNow;
    }

    private static EmailTemplate MapLanguage(EmailTemplateEntity entity) => new()
    {
        Id = entity.Id, ServiceName = entity.Definition.Service.Name, Key = entity.Definition.Key,
        LanguageCode = entity.ServiceLanguage.Code, Subject = entity.Subject, HtmlBody = entity.HtmlBody, TextBody = entity.TextBody,
        Variables = entity.Definition.Variables.Select(v => new EmailTemplateVariable { Name = v.Name, Required = v.Required }).ToList(),
        Created = entity.Created, Updated = entity.Updated
    };

    private static EmailTemplateDefinition MapDefinition(EmailTemplateDefinitionEntity entity) => new()
    {
        Id = entity.Id, ServiceId = entity.ServiceId, ServiceName = entity.Service.Name, Key = entity.Key, Revision = entity.Revision,
        Variables = entity.Variables.Select(v => new EmailTemplateVariable { Name = v.Name, Required = v.Required }).ToList(),
        Languages = entity.Languages.OrderBy(t => t.ServiceLanguage.Code).Select(MapLanguage).ToList(),
        Created = entity.Created, Updated = entity.Updated
    };
}