using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.Json;

namespace StellaOps.Scanner.Reachability;

public sealed class ReachabilityGraphBuilder
{
    private const string GraphSchemaVersion = "1.0";
    private readonly HashSet<string> nodes = new(StringComparer.Ordinal);
    private readonly HashSet<ReachabilityEdge> edges = new();

    public ReachabilityGraphBuilder AddNode(string symbolId)
    {
        if (!string.IsNullOrWhiteSpace(symbolId))
        {
            nodes.Add(symbolId.Trim());
        }

        return this;
    }

    public ReachabilityGraphBuilder AddEdge(string from, string to, string kind = "call")
    {
        if (string.IsNullOrWhiteSpace(from) || string.IsNullOrWhiteSpace(to))
        {
            return this;
        }

        var edge = new ReachabilityEdge(from.Trim(), to.Trim(), string.IsNullOrWhiteSpace(kind) ? "call" : kind.Trim());
        edges.Add(edge);
        nodes.Add(edge.From);
        nodes.Add(edge.To);
        return this;
    }

    public string BuildJson(bool indented = true)
    {
        var payload = new ReachabilityGraphPayload
        {
            SchemaVersion = GraphSchemaVersion,
            Nodes = nodes.Select(id => new ReachabilityNode(id)).ToList(),
            Edges = edges.Select(edge => new ReachabilityEdgePayload(edge.From, edge.To, edge.Kind)).ToList()
        };

        var options = new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            WriteIndented = indented
        };

        return JsonSerializer.Serialize(payload, options);
    }

    public static ReachabilityGraphBuilder FromFixture(string variantPath)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(variantPath);
        var builder = new ReachabilityGraphBuilder();

        foreach (var fileName in new[] { "callgraph.static.json", "callgraph.framework.json" })
        {
            var path = Path.Combine(variantPath, fileName);
            if (!File.Exists(path))
            {
                continue;
            }

            using var stream = File.OpenRead(path);
            using var document = JsonDocument.Parse(stream);
            var root = document.RootElement;

            if (root.TryGetProperty("nodes", out var nodesElement) && nodesElement.ValueKind == JsonValueKind.Array)
            {
                foreach (var node in nodesElement.EnumerateArray())
                {
                    var sid = node.TryGetProperty("sid", out var sidElement)
                        ? sidElement.GetString()
                        : node.GetProperty("id").GetString();
                    builder.AddNode(sid ?? string.Empty);
                }
            }

            if (root.TryGetProperty("edges", out var edgesElement) && edgesElement.ValueKind == JsonValueKind.Array)
            {
                foreach (var edge in edgesElement.EnumerateArray())
                {
                    var from = edge.TryGetProperty("from", out var fromEl)
                        ? fromEl.GetString()
                        : edge.GetProperty("source").GetString();
                    var to = edge.TryGetProperty("to", out var toEl)
                        ? toEl.GetString()
                        : edge.GetProperty("target").GetString();
                    var kind = edge.TryGetProperty("kind", out var kindEl)
                        ? kindEl.GetString()
                        : edge.TryGetProperty("type", out var typeEl)
                            ? typeEl.GetString()
                            : "call";

                    builder.AddEdge(from ?? string.Empty, to ?? string.Empty, kind ?? "call");
                }
            }
        }

        return builder;
    }

    private sealed record ReachabilityEdge(string From, string To, string Kind);

    private sealed record ReachabilityNode(string Sid);

    private sealed record ReachabilityEdgePayload(string From, string To, string Kind);

    private sealed record ReachabilityGraphPayload
    {
        public string SchemaVersion { get; set; } = GraphSchemaVersion;
        public List<ReachabilityNode> Nodes { get; set; } = new();
        public List<ReachabilityEdgePayload> Edges { get; set; } = new();
    }
}