using DataModel.Database;
using DataModel.Database.Common;
using Microsoft.EntityFrameworkCore;

namespace Processor;

public static class SectionProcessor
{
    /// <summary>
    /// Load one layer of the tree by using the specified depth:
    /// </summary>
    public static IAsyncEnumerable<Section> LoadLayer(DataContext db, int depth)
    {
        return db.Sections.Where(n => n.Depth == depth).OrderBy(n => n.Id).AsAsyncEnumerable();
    }

    /// <summary>
    /// Determine how deep the tree is.
    /// </summary>
    public static async ValueTask<int> GetDepth(DataContext db)
    {
        if(!await db.Sections.AnyAsync())
        {
            return 0;
        }

        return await db.Sections.MaxAsync(s => s.Depth);
    }
    
    /// <summary>
    /// Compute the new sections key and its depth, then store the section in the database.
    /// </summary>
    public static async Task<Section> AddSection(DataContext db, string text, string? parentKey)
    {
        // Remove any whitespaces from the section name, regardless of how many e.g. spaces the user typed:
        var key = string.Join('_', text.Split(' ', StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries)).ToUpperInvariant();
        
        // Check, if this key already exists:
        if (await db.Sections.AnyAsync(n => n.DataKey == key))
        {
            var rng = new Random();
            while (await db.Sections.AnyAsync(n => n.DataKey == key))
            {
                // Add a random number to the end of the key:
                key += $"_{rng.Next(1, 10_000)}";
            }
        }

        // In the case, when the user adds a section to the root, handle the insert differently:
        if (string.IsNullOrEmpty(parentKey))
        {
            var rootSection = new Section
            {
                Depth = 0,
                DataKey = key,
                Parent = null,
                Name = text.Trim(),
                TextElements = new(),
            };

            db.Sections.Add(rootSection);
            await db.SaveChangesAsync();
            return rootSection;
        }

        // Read the parent from the database:
        var parent = await db.Sections.FirstOrDefaultAsync(n => n.DataKey == parentKey);
        if (parent is null)
            throw new ArgumentException($"The section's parent with key {parentKey} does not exist in the database.");

        // Add the new section to the database:
        var section = new Section
        {
            Name = text.Trim(),
            DataKey = key,
            Parent = parent,
            TextElements = new(),
            Depth = parent.Depth + 1,
        };
        
        db.Sections.Add(section);
        await db.SaveChangesAsync();
        return section;
    }

    public static async Task RemoveSection(DataContext db, string selectedKey)
    {
        // Remove the section from the database:
        var section2Delete = await db.Sections.FirstOrDefaultAsync(n => n.DataKey == selectedKey);
        if (section2Delete is null)
            throw new ArgumentException($"The section with key {selectedKey} does not exist in the database.");
        
        // Next, remove all children of the section, and the children's children, etc.:
        var children = await db.Sections.Where(n => n.Parent == section2Delete).ToListAsync();
        foreach (var child in children)
            await RemoveSection(db, child.DataKey);

        db.Sections.Remove(section2Delete);
        await db.SaveChangesAsync();
    }
    
    public static async Task<int> NumberChildren(DataContext db, string selectedKey)
    {
        // Read the section from the database:
        var section = await db.Sections.FirstOrDefaultAsync(n => n.DataKey == selectedKey);
        if (section is null)
            throw new ArgumentException($"The section with key {selectedKey} does not exist in the database.");
        
        return await db.Sections.CountAsync(n => n.Parent == section);
    }
}