using Microsoft.AspNetCore.Hosting;
using PlotLine.Models;

namespace PlotLine.Services;

public interface IHelpService
{
    IReadOnlyList<HelpArticle> GetAllArticles();
    HelpArticle? GetByContextKey(string contextKey);
    HelpArticle? GetByRelativePath(string relativePath);
    IReadOnlyList<HelpCoverageItem> GetCoverage();
}

public sealed class HelpService(IWebHostEnvironment environment) : IHelpService
{
    private readonly object cacheLock = new();
    private IReadOnlyList<HelpArticle>? cachedArticles;

    public IReadOnlyList<HelpArticle> GetAllArticles()
    {
        if (cachedArticles is not null)
        {
            return cachedArticles;
        }

        lock (cacheLock)
        {
            cachedArticles ??= LoadArticles();
            return cachedArticles;
        }
    }

    public HelpArticle? GetByContextKey(string contextKey)
    {
        if (string.IsNullOrWhiteSpace(contextKey))
        {
            return null;
        }

        return GetAllArticles().FirstOrDefault(x => string.Equals(x.ContextKey, contextKey, StringComparison.OrdinalIgnoreCase));
    }

    public HelpArticle? GetByRelativePath(string relativePath)
    {
        if (string.IsNullOrWhiteSpace(relativePath))
        {
            return null;
        }

        var normalisedPath = relativePath.Replace('\\', '/');
        return GetAllArticles().FirstOrDefault(x => string.Equals(x.RelativePath, normalisedPath, StringComparison.OrdinalIgnoreCase));
    }

    public IReadOnlyList<HelpCoverageItem> GetCoverage() =>
        GetAllArticles()
            .Select(x => new HelpCoverageItem
            {
                ContextKey = x.ContextKey,
                FilePath = x.RelativePath,
                IsValid = x.IsValid,
                ValidationIssues = x.ValidationIssues
            })
            .OrderBy(x => x.ContextKey)
            .ThenBy(x => x.FilePath)
            .ToList();

    private IReadOnlyList<HelpArticle> LoadArticles()
    {
        var articleRoot = Path.Combine(environment.ContentRootPath, "Help", "Articles");
        if (!Directory.Exists(articleRoot))
        {
            return [];
        }

        return Directory
            .EnumerateFiles(articleRoot, "*.md", SearchOption.AllDirectories)
            .OrderBy(x => x, StringComparer.OrdinalIgnoreCase)
            .Select(path => ParseArticle(articleRoot, path))
            .ToList();
    }

    private static HelpArticle ParseArticle(string articleRoot, string filePath)
    {
        var rawContent = File.ReadAllText(filePath);
        var relativePath = Path.GetRelativePath(articleRoot, filePath).Replace('\\', '/');
        var metadata = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
        var markdownContent = rawContent;
        var issues = new List<string>();

        if (rawContent.StartsWith("---", StringComparison.Ordinal))
        {
            using var reader = new StringReader(rawContent);
            _ = reader.ReadLine();
            var frontMatterLines = new List<string>();
            string? line;
            var frontMatterClosed = false;

            while ((line = reader.ReadLine()) is not null)
            {
                if (line.Trim() == "---")
                {
                    frontMatterClosed = true;
                    break;
                }

                frontMatterLines.Add(line);
            }

            if (frontMatterClosed)
            {
                metadata = ParseFrontMatter(frontMatterLines);
                markdownContent = reader.ReadToEnd().TrimStart();
            }
            else
            {
                issues.Add("Front matter was opened but not closed.");
            }
        }
        else
        {
            issues.Add("Front matter is missing.");
        }

        var article = new HelpArticle
        {
            Title = GetValue(metadata, "title"),
            Category = GetValue(metadata, "category"),
            Tags = SplitTags(GetValue(metadata, "tags")),
            ContextKey = GetValue(metadata, "contextKey"),
            Micro = GetValue(metadata, "micro"),
            QuickTitle = GetValue(metadata, "quickTitle"),
            QuickSummary = GetValue(metadata, "quickSummary"),
            Screenshot = GetValue(metadata, "screenshot"),
            MarkdownContent = markdownContent,
            RelativePath = relativePath
        };

        issues.AddRange(Validate(article));
        article.ValidationIssues = issues;
        return article;
    }

    private static Dictionary<string, string> ParseFrontMatter(IEnumerable<string> lines)
    {
        var metadata = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
        foreach (var line in lines)
        {
            var separatorIndex = line.IndexOf(':');
            if (separatorIndex <= 0)
            {
                continue;
            }

            var key = line[..separatorIndex].Trim();
            var value = line[(separatorIndex + 1)..].Trim().Trim('"');
            metadata[key] = value;
        }

        return metadata;
    }

    private static IReadOnlyList<string> Validate(HelpArticle article)
    {
        var issues = new List<string>();
        if (string.IsNullOrWhiteSpace(article.Title)) issues.Add("Title is required.");
        if (string.IsNullOrWhiteSpace(article.ContextKey)) issues.Add("ContextKey is required.");
        if (string.IsNullOrWhiteSpace(article.QuickTitle)) issues.Add("QuickTitle is required.");
        if (string.IsNullOrWhiteSpace(article.QuickSummary)) issues.Add("QuickSummary is required.");
        return issues;
    }

    private static string GetValue(IReadOnlyDictionary<string, string> metadata, string key) =>
        metadata.TryGetValue(key, out var value) ? value : string.Empty;

    private static IReadOnlyList<string> SplitTags(string tags) =>
        string.IsNullOrWhiteSpace(tags)
            ? []
            : tags.Split(',', StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries);
}