using System.Net.Http.Headers;
using System.Text;
using System.Text.Json;
using System.Text.RegularExpressions;
using FlatRender.ContentSvc.Domain.Entities;
using FlatRender.ContentSvc.Infrastructure.Data;
using FlatRender.ContentSvc.Models;
using Microsoft.EntityFrameworkCore;

namespace FlatRender.ContentSvc.Application.Services;

/// <summary>Thrown for expected/config errors (missing key, provider error) → mapped to 400 by the controller.</summary>
public class AiConfigException(string message) : Exception(message);

public class AiContentService(ContentDbContext db, IHttpClientFactory httpFactory)
{
    public static readonly Guid DefaultTenant = Guid.Parse("00000000-0000-0000-0000-000000000001");

    // ── Settings ──────────────────────────────────────────────────────────────

    public async Task<AiSettings> GetRawAsync(Guid tenantId)
    {
        return await db.AiSettings.FirstOrDefaultAsync(x => x.TenantId == tenantId)
               ?? new AiSettings { TenantId = tenantId };
    }

    public async Task<AiSettingsResponse> GetSettingsAsync(Guid tenantId)
    {
        var s = await GetRawAsync(tenantId);
        var key = s.ApiKey;
        var has = !string.IsNullOrWhiteSpace(key);
        var masked = has ? $"••••••••{key![Math.Max(0, key.Length - 4)..]}" : null;
        return new AiSettingsResponse(s.Provider, s.BaseUrl, s.Model, s.Enabled, has, masked,
            s.UpdatedAt == default ? null : s.UpdatedAt);
    }

    public async Task<AiSettingsResponse> UpdateSettingsAsync(Guid tenantId, UpdateAiSettingsRequest req)
    {
        var s = await db.AiSettings.FirstOrDefaultAsync(x => x.TenantId == tenantId);
        var isNew = s is null;
        s ??= new AiSettings { TenantId = tenantId };

        if (req.Provider is { } p) s.Provider = p;
        if (req.BaseUrl is { } b && !string.IsNullOrWhiteSpace(b)) s.BaseUrl = b.TrimEnd('/');
        if (req.Model is { } m && !string.IsNullOrWhiteSpace(m)) s.Model = m;
        if (req.Enabled is { } e) s.Enabled = e;
        // ApiKey: null = leave unchanged; non-null (incl. "") = set/clear.
        if (req.ApiKey is not null) s.ApiKey = string.IsNullOrWhiteSpace(req.ApiKey) ? null : req.ApiKey.Trim();
        s.UpdatedAt = DateTime.UtcNow;

        if (isNew) db.AiSettings.Add(s);
        await db.SaveChangesAsync();
        return await GetSettingsAsync(tenantId);
    }

    // ── Generation ──────────────────────────────────────────────────────────────

    public async Task<SeoPostResponse> GenerateSeoPostAsync(Guid tenantId, GenerateSeoPostRequest req, CancellationToken ct)
    {
        var s = await GetRawAsync(tenantId);
        if (!s.Enabled) throw new AiConfigException("AI generation is disabled. Enable it in AI settings.");
        if (string.IsNullOrWhiteSpace(s.ApiKey)) throw new AiConfigException("No OpenAI API key configured. Add one in AI settings.");
        if (string.IsNullOrWhiteSpace(req.Description)) throw new AiConfigException("A description is required.");

        var locale = (req.Locale ?? "fa").ToLowerInvariant();
        var langName = locale == "en" ? "English" : "Persian (Farsi)";

        var system =
            "You are a senior SEO content strategist and copywriter. Given a product/page description and metadata, " +
            "write an original, engaging, well-structured, SEO-optimized article. " +
            "Return ONLY a single valid JSON object (no markdown, no code fences) with EXACTLY these keys: " +
            "title, slug, meta_title, meta_description, keywords, short_description, content_html. " +
            "Rules: " +
            $"write all human-readable text in {langName}; " +
            "slug must be a short lowercase ASCII (a-z, 0-9, hyphens) URL slug derived from the topic, even when the article is in Persian; " +
            "meta_title <= 60 characters; meta_description <= 160 characters and compelling; " +
            "keywords = array of 5-8 relevant search keywords; " +
            "short_description = 1-2 sentence summary; " +
            "content_html = semantic HTML using <h2>, <h3>, <p>, <ul><li>, <strong> (no <html>/<body>/<h1>), 500-900 words, " +
            "naturally incorporating the keywords, with a short intro, scannable sections, and a closing call to action.";

        var sb = new StringBuilder();
        sb.AppendLine("Write an SEO article for the following:");
        if (!string.IsNullOrWhiteSpace(req.Title)) sb.AppendLine($"Working title: {req.Title}");
        if (!string.IsNullOrWhiteSpace(req.Type)) sb.AppendLine($"Content type: {req.Type}");
        if (req.Tags is { Length: > 0 }) sb.AppendLine($"Tags: {string.Join(", ", req.Tags)}");
        if (!string.IsNullOrWhiteSpace(req.Keyword)) sb.AppendLine($"Primary target keyword: {req.Keyword}");
        if (!string.IsNullOrWhiteSpace(req.Audience)) sb.AppendLine($"Target audience: {req.Audience}");
        sb.AppendLine($"Description / brief:\n{req.Description}");

        var payload = new
        {
            model = s.Model,
            messages = new object[]
            {
                new { role = "system", content = system },
                new { role = "user", content = sb.ToString() },
            },
            temperature = 0.7,
            response_format = new { type = "json_object" },
        };

        var http = httpFactory.CreateClient("openai");
        http.Timeout = TimeSpan.FromSeconds(90);
        using var msg = new HttpRequestMessage(HttpMethod.Post, $"{s.BaseUrl.TrimEnd('/')}/chat/completions")
        {
            Content = new StringContent(JsonSerializer.Serialize(payload), Encoding.UTF8, "application/json"),
        };
        msg.Headers.Authorization = new AuthenticationHeaderValue("Bearer", s.ApiKey);

        HttpResponseMessage resp;
        try { resp = await http.SendAsync(msg, ct); }
        catch (Exception ex) { throw new AiConfigException($"Could not reach the AI provider: {ex.Message}"); }

        var body = await resp.Content.ReadAsStringAsync(ct);
        if (!resp.IsSuccessStatusCode)
            throw new AiConfigException($"AI provider returned {(int)resp.StatusCode}: {Truncate(body, 300)}");

        string contentJson;
        try
        {
            using var doc = JsonDocument.Parse(body);
            contentJson = doc.RootElement.GetProperty("choices")[0].GetProperty("message").GetProperty("content").GetString() ?? "";
        }
        catch (Exception ex) { throw new AiConfigException($"Unexpected AI response shape: {ex.Message}"); }

        return ParsePost(contentJson, req);
    }

    private static SeoPostResponse ParsePost(string contentJson, GenerateSeoPostRequest req)
    {
        try
        {
            using var doc = JsonDocument.Parse(contentJson);
            var r = doc.RootElement;
            string Str(string k) => r.TryGetProperty(k, out var v) && v.ValueKind == JsonValueKind.String ? v.GetString()! : "";
            string[] Keywords()
            {
                if (r.TryGetProperty("keywords", out var v))
                {
                    if (v.ValueKind == JsonValueKind.Array)
                        return v.EnumerateArray().Where(e => e.ValueKind == JsonValueKind.String).Select(e => e.GetString()!).ToArray();
                    if (v.ValueKind == JsonValueKind.String)
                        return v.GetString()!.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
                }
                return [];
            }

            var title = Str("title");
            if (string.IsNullOrWhiteSpace(title)) title = req.Title ?? "Untitled";
            var slug = Slugify(Str("slug"));
            if (string.IsNullOrWhiteSpace(slug)) slug = Slugify(req.Keyword ?? title);
            if (string.IsNullOrWhiteSpace(slug)) slug = "post";

            return new SeoPostResponse(
                title,
                slug,
                Str("meta_title") is { Length: > 0 } mt ? mt : title,
                Str("meta_description"),
                Keywords(),
                Str("short_description"),
                Str("content_html")
            );
        }
        catch (Exception ex) { throw new AiConfigException($"Could not parse AI content as JSON: {ex.Message}"); }
    }

    private static string Slugify(string s)
    {
        if (string.IsNullOrWhiteSpace(s)) return "";
        s = s.Trim().ToLowerInvariant();
        s = Regex.Replace(s, @"[^a-z0-9]+", "-").Trim('-');
        return s.Length > 80 ? s[..80].Trim('-') : s;
    }

    private static string Truncate(string s, int n) => s.Length <= n ? s : s[..n] + "…";
}