using System.Text.Json.Nodes;
using Microsoft.Extensions.Logging;
using StellaOps.Notify.Models;
using StellaOps.Notify.Storage.Mongo.Repositories;

namespace StellaOps.Notifier.WebService.Services;

/// <summary>
/// Default implementation of INotifyTemplateService with locale fallback and version tracking.
/// </summary>
public sealed class NotifyTemplateService : INotifyTemplateService
{
    private const string DefaultLocale = "en-us";

    private readonly INotifyTemplateRepository _repository;
    private readonly INotifyTemplateRenderer _renderer;
    private readonly TimeProvider _timeProvider;
    private readonly ILogger<NotifyTemplateService> _logger;

    public NotifyTemplateService(
        INotifyTemplateRepository repository,
        INotifyTemplateRenderer renderer,
        TimeProvider timeProvider,
        ILogger<NotifyTemplateService> logger)
    {
        _repository = repository ?? throw new ArgumentNullException(nameof(repository));
        _renderer = renderer ?? throw new ArgumentNullException(nameof(renderer));
        _timeProvider = timeProvider ?? TimeProvider.System;
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }

    public async Task<NotifyTemplate?> GetByKeyAsync(
        string tenantId,
        string key,
        string locale,
        NotifyChannelType? channelType = null,
        CancellationToken cancellationToken = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(tenantId);
        ArgumentException.ThrowIfNullOrWhiteSpace(key);

        locale = NormalizeLocale(locale);

        var allTemplates = await _repository.ListAsync(tenantId, cancellationToken).ConfigureAwait(false);

        // Filter by key
        var matching = allTemplates.Where(t => t.Key.Equals(key, StringComparison.OrdinalIgnoreCase));

        // Filter by channel type if specified
        if (channelType.HasValue)
        {
            matching = matching.Where(t => t.ChannelType == channelType.Value);
        }

        var candidates = matching.ToArray();

        // Try exact locale match
        var exactMatch = candidates.FirstOrDefault(t =>
            t.Locale.Equals(locale, StringComparison.OrdinalIgnoreCase));

        if (exactMatch is not null)
        {
            return exactMatch;
        }

        // Try language-only match (e.g., "en" from "en-us")
        var languageCode = locale.Split('-')[0];
        var languageMatch = candidates.FirstOrDefault(t =>
            t.Locale.StartsWith(languageCode, StringComparison.OrdinalIgnoreCase));

        if (languageMatch is not null)
        {
            _logger.LogDebug("Template {Key} not found for locale {Locale}, using {FallbackLocale}.",
                key, locale, languageMatch.Locale);
            return languageMatch;
        }

        // Fall back to default locale
        var defaultMatch = candidates.FirstOrDefault(t =>
            t.Locale.Equals(DefaultLocale, StringComparison.OrdinalIgnoreCase));

        if (defaultMatch is not null)
        {
            _logger.LogDebug("Template {Key} not found for locale {Locale}, using default locale.",
                key, locale);
            return defaultMatch;
        }

        // Return any available template for the key
        return candidates.FirstOrDefault();
    }

    public Task<NotifyTemplate?> GetByIdAsync(
        string tenantId,
        string templateId,
        CancellationToken cancellationToken = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(tenantId);
        ArgumentException.ThrowIfNullOrWhiteSpace(templateId);

        return _repository.GetAsync(tenantId, templateId, cancellationToken);
    }

    public async Task<IReadOnlyList<NotifyTemplate>> ListAsync(
        string tenantId,
        string? keyPrefix = null,
        string? locale = null,
        NotifyChannelType? channelType = null,
        CancellationToken cancellationToken = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(tenantId);

        var allTemplates = await _repository.ListAsync(tenantId, cancellationToken).ConfigureAwait(false);

        IEnumerable<NotifyTemplate> filtered = allTemplates;

        if (!string.IsNullOrWhiteSpace(keyPrefix))
        {
            filtered = filtered.Where(t => t.Key.StartsWith(keyPrefix, StringComparison.OrdinalIgnoreCase));
        }

        if (!string.IsNullOrWhiteSpace(locale))
        {
            var normalizedLocale = NormalizeLocale(locale);
            filtered = filtered.Where(t => t.Locale.Equals(normalizedLocale, StringComparison.OrdinalIgnoreCase));
        }

        if (channelType.HasValue)
        {
            filtered = filtered.Where(t => t.ChannelType == channelType.Value);
        }

        return filtered.OrderBy(t => t.Key).ThenBy(t => t.Locale).ToArray();
    }

    public async Task<NotifyTemplate> UpsertAsync(
        NotifyTemplate template,
        string updatedBy,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(template);
        ArgumentException.ThrowIfNullOrWhiteSpace(updatedBy);

        var now = _timeProvider.GetUtcNow();

        // Check for existing template to preserve creation metadata
        var existing = await _repository.GetAsync(template.TenantId, template.TemplateId, cancellationToken)
            .ConfigureAwait(false);

        var updatedTemplate = NotifyTemplate.Create(
            templateId: template.TemplateId,
            tenantId: template.TenantId,
            channelType: template.ChannelType,
            key: template.Key,
            locale: template.Locale,
            body: template.Body,
            renderMode: template.RenderMode,
            format: template.Format,
            description: template.Description,
            metadata: template.Metadata,
            createdBy: existing?.CreatedBy ?? updatedBy,
            createdAt: existing?.CreatedAt ?? now,
            updatedBy: updatedBy,
            updatedAt: now);

        await _repository.UpsertAsync(updatedTemplate, cancellationToken).ConfigureAwait(false);

        _logger.LogInformation(
            "Template {TemplateId} (key={Key}, locale={Locale}) upserted by {UpdatedBy}.",
            updatedTemplate.TemplateId, updatedTemplate.Key, updatedTemplate.Locale, updatedBy);

        return updatedTemplate;
    }

    public async Task DeleteAsync(
        string tenantId,
        string templateId,
        CancellationToken cancellationToken = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(tenantId);
        ArgumentException.ThrowIfNullOrWhiteSpace(templateId);

        await _repository.DeleteAsync(tenantId, templateId, cancellationToken).ConfigureAwait(false);

        _logger.LogInformation("Template {TemplateId} deleted from tenant {TenantId}.", templateId, tenantId);
    }

    public Task<TemplatePreviewResult> PreviewAsync(
        NotifyTemplate template,
        JsonNode? samplePayload,
        TemplateRenderOptions? options = null,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(template);

        options ??= new TemplateRenderOptions();

        // Apply redaction to payload if allowlist is specified
        var redactedFields = new List<string>();
        var processedPayload = samplePayload;

        if (options.RedactionAllowlist is { Count: > 0 })
        {
            processedPayload = ApplyRedaction(samplePayload, options.RedactionAllowlist, redactedFields);
        }

        // Render body
        var renderedBody = _renderer.Render(template, processedPayload, options);

        // Render subject if present in metadata
        string? renderedSubject = null;
        if (template.Metadata.TryGetValue("subject", out var subjectTemplate))
        {
            var subjectTemplateObj = NotifyTemplate.Create(
                templateId: "subject-preview",
                tenantId: template.TenantId,
                channelType: template.ChannelType,
                key: "subject",
                locale: template.Locale,
                body: subjectTemplate);
            renderedSubject = _renderer.Render(subjectTemplateObj, processedPayload, options);
        }

        // Build provenance link if requested
        string? provenanceLink = null;
        if (options.IncludeProvenance && !string.IsNullOrWhiteSpace(options.ProvenanceBaseUrl))
        {
            provenanceLink = $"{options.ProvenanceBaseUrl.TrimEnd('/')}/templates/{template.TemplateId}";
        }

        var result = new TemplatePreviewResult
        {
            RenderedBody = renderedBody,
            RenderedSubject = renderedSubject,
            RenderMode = template.RenderMode,
            Format = options.FormatOverride ?? template.Format,
            RedactedFields = redactedFields,
            ProvenanceLink = provenanceLink
        };

        return Task.FromResult(result);
    }

    private static JsonNode? ApplyRedaction(JsonNode? payload, IReadOnlySet<string> allowlist, List<string> redactedFields)
    {
        if (payload is not JsonObject obj)
        {
            return payload;
        }

        var result = new JsonObject();

        foreach (var (key, value) in obj)
        {
            if (allowlist.Contains(key))
            {
                result[key] = value?.DeepClone();
            }
            else
            {
                result[key] = "[REDACTED]";
                redactedFields.Add(key);
            }
        }

        return result;
    }

    private static string NormalizeLocale(string? locale)
    {
        return string.IsNullOrWhiteSpace(locale) ? DefaultLocale : locale.ToLowerInvariant();
    }
}