using System.Text.RegularExpressions;
using NozCli.Core.Models;

namespace NozCli.Core.Client;

public static class NoteRenamer
{
    public record Result(List<string> UpdatedNotes, int LinksUpdated);

    /// Renames a note and rewrites all inbound wikilinks/markdown-links in one atomic sequence.
    /// Progress callback receives human-readable step descriptions.
    public static async Task<Result> ExecuteAsync(
        NozApiClient        api,
        string              oldSlug,
        string              newSlug,
        Action<string>?     onProgress = null,
        CancellationToken   ct         = default)
    {
        // 1. Fetch inbound edges before we change anything
        onProgress?.Invoke("Hole Graph-Daten…");
        var graph   = await api.GetGraphAsync(ct);
        var inbound = graph.Edges
            .Where(e => e.Target == oldSlug)
            .Select(e => e.Source)
            .Distinct()
            .ToList();

        // 2. Fetch the original note
        onProgress?.Invoke($"Lese {oldSlug}…");
        var original = await api.GetNoteAsync(oldSlug, ct);

        // 3. Patch frontmatter topic if the slug prefix (= topic) changes
        var patchedContent = PatchTopicIfNeeded(original.Markdown, oldSlug, newSlug);

        // 4. Create note under new slug
        onProgress?.Invoke($"Erstelle {newSlug}…");
        await api.PutNoteAsync(newSlug, patchedContent, ct);

        // 5. Update every note that links to the old slug
        var updatedNotes = new List<string>();
        foreach (var sourceSlug in inbound)
        {
            onProgress?.Invoke($"Aktualisiere Links in {sourceSlug}…");
            try
            {
                var src     = await api.GetNoteAsync(sourceSlug, ct);
                var updated = ReplaceReferences(src.Markdown, oldSlug, newSlug);
                if (updated != src.Markdown)
                {
                    await api.PutNoteAsync(sourceSlug, updated, ct);
                    updatedNotes.Add(sourceSlug);
                }
            }
            catch (HttpRequestException)
            {
                // Don't abort the whole rename if one note fails to update
                onProgress?.Invoke($"  ⚠ {sourceSlug} konnte nicht aktualisiert werden");
            }
        }

        // 6. Delete old slug — do this last so we never lose data on partial failure
        onProgress?.Invoke($"Lösche {oldSlug}…");
        await api.DeleteNoteAsync(oldSlug, ct);

        return new Result(updatedNotes, updatedNotes.Count);
    }

    // ── Slug reference replacement ────────────────────────────────────────────

    private static string ReplaceReferences(string markdown, string oldSlug, string newSlug)
    {
        // [[old-slug]] → [[new-slug]]
        // [[old-slug|Anzeigetext]] → [[new-slug|Anzeigetext]]
        markdown = Regex.Replace(
            markdown,
            @"\[\[" + Regex.Escape(oldSlug) + @"(\|[^\]]+)?\]\]",
            m => $"[[{newSlug}{m.Groups[1].Value}]]");

        // [text](/noosphere/old-slug) → [text](/noosphere/new-slug)
        // [text](/noosphere/old-slug#anchor) → [text](/noosphere/new-slug#anchor)
        markdown = Regex.Replace(
            markdown,
            @"\[([^\]]+)\]\(/noosphere/" + Regex.Escape(oldSlug) + @"(#[^\)]*)?\)",
            m => $"[{m.Groups[1].Value}](/noosphere/{newSlug}{m.Groups[2].Value})");

        return markdown;
    }

    // ── Frontmatter topic patch ───────────────────────────────────────────────

    private static string PatchTopicIfNeeded(string markdown, string oldSlug, string newSlug)
    {
        var oldTopic = FirstSegment(oldSlug);
        var newTopic = FirstSegment(newSlug);

        if (oldTopic == newTopic || oldTopic is null || newTopic is null)
            return markdown;

        // Only patch within the frontmatter block
        var (fmStart, fmEnd) = FindFrontmatterBounds(markdown);
        if (fmStart < 0) return markdown;

        var block   = markdown[fmStart..fmEnd];
        var patched = Regex.Replace(
            block,
            @"(?m)^(topic:\s*)" + Regex.Escape(oldTopic) + @"(\s*)$",
            $"$1{newTopic}$2");

        return markdown[..fmStart] + patched + markdown[fmEnd..];
    }

    private static string? FirstSegment(string slug)
    {
        var idx = slug.IndexOf('/');
        return idx > 0 ? slug[..idx] : null;
    }

    private static (int start, int end) FindFrontmatterBounds(string markdown)
    {
        if (!markdown.StartsWith("---", StringComparison.Ordinal)) return (-1, -1);
        var closeIdx = markdown.IndexOf("\n---", 3, StringComparison.Ordinal);
        if (closeIdx < 0) return (-1, -1);
        return (0, closeIdx + 4);  // include closing ---
    }
}