using System.Collections.Generic;
using UnityEngine;

/// <summary>
/// Utility functions for building and querying puzzle step dependency graphs.
/// </summary>
public static class PuzzleGraphUtility
{
    /// <summary>
    /// Builds a dependency graph: for each step, lists the steps it depends on.
    /// </summary>
    /// <param name="steps">All puzzle steps.</param>
    /// <returns>Dictionary mapping each step to the list of steps it depends on.</returns>
    public static Dictionary<PuzzleStepSO, List<PuzzleStepSO>> BuildDependencyGraph(IEnumerable<PuzzleStepSO> steps)
    {
        var graph = new Dictionary<PuzzleStepSO, List<PuzzleStepSO>>();
        foreach (var step in steps)
        {
            graph[step] = new List<PuzzleStepSO>();
        }
        foreach (var step in steps)
        {
            foreach (var unlocked in step.unlocks)
            {
                if (!graph.ContainsKey(unlocked))
                    graph[unlocked] = new List<PuzzleStepSO>();
                graph[unlocked].Add(step);
            }
        }
        return graph;
    }

    /// <summary>
    /// Finds initial steps (no dependencies).
    /// </summary>
    /// <param name="graph">Dependency graph.</param>
    /// <returns>List of steps with no dependencies.</returns>
    public static List<PuzzleStepSO> FindInitialSteps(Dictionary<PuzzleStepSO, List<PuzzleStepSO>> graph)
    {
        var initial = new List<PuzzleStepSO>();
        foreach (var kvp in graph)
        {
            if (kvp.Value.Count == 0)
                initial.Add(kvp.Key);
        }
        return initial;
    }

    /// <summary>
    /// Finds all steps unlocked by a given step.
    /// </summary>
    /// <param name="step">The step to check unlocks for.</param>
    /// <param name="allSteps">All puzzle steps.</param>
    /// <returns>List of steps unlocked by the given step.</returns>
    public static List<PuzzleStepSO> FindUnlocks(PuzzleStepSO step, IEnumerable<PuzzleStepSO> allSteps)
    {
        var unlocks = new List<PuzzleStepSO>();
        foreach (var s in allSteps)
        {
            if (s.unlocks.Contains(step))
                unlocks.Add(s);
        }
        return unlocks;
    }
}