using System.Text.Json.Nodes;
using w4c_workflows.Models.Credentials;
using w4c_workflows.Models.Nodes;
using w4c_workflows.Services.Nodes.Interpolation;
using w4c_workflows.Services.Security;

namespace w4c_workflows.Services.Nodes;

/// <summary>Ambient data a node run needs beyond the graph itself.</summary>
public sealed record NodeRunEnvironment
{
    public string TenantId { get; init; } = string.Empty;
    public string RunId { get; init; } = string.Empty;

    /// <summary>Workflow variables exposed to expressions as <c>$env</c>.</summary>
    public JsonObject Variables { get; init; } = new();

    /// <summary>Decrypted credentials keyed by the blueprint alias the step uses.</summary>
    public IReadOnlyDictionary<string, CredentialData> Credentials { get; init; } =
        new Dictionary<string, CredentialData>();

    /// <summary>Directory code-executing nodes (<c>core.code</c>) resolve their entry file from.</summary>
    public string? WorkingDirectory { get; init; }

    /// <summary>
    /// Run-scoped mutable state shared by all nodes of one run. Loop nodes use it
    /// to remember their iteration cursor; it is created fresh per run.
    /// </summary>
    public IDictionary<string, object?> State { get; init; } = new Dictionary<string, object?>();

    /// <summary>
    /// Invokes another workflow in-process from a <c>core.executeWorkflow</c>
    /// node. Null when the host does not support sub-workflows (e.g. a bare
    /// <see cref="NodeGraphRunner"/> in a unit test); the node then fails cleanly.
    /// </summary>
    public ISubWorkflowInvoker? SubWorkflows { get; init; }

    /// <summary>Nesting depth of this run: 0 top-level, +1 per sub-workflow call.</summary>
    public int Depth { get; init; }

    /// <summary>
    /// Workflow ids from the root run down to (and including) this run, used to
    /// reject recursive sub-workflow cycles before they can loop forever.
    /// </summary>
    public IReadOnlyList<Guid> Ancestry { get; init; } = Array.Empty<Guid>();

    public IServiceProvider? Services { get; init; }
}

/// <summary>Result of running a node graph, with per-node outputs and a run-level failure.</summary>
public sealed record NodeGraphRunResult
{
    public required IReadOnlyDictionary<string, IReadOnlyList<IReadOnlyList<FlowItem>>> OutputsByNode { get; init; }

    /// <summary>Node ids in the order they were executed.</summary>
    public required IReadOnlyList<string> ExecutionOrder { get; init; }

    public NodeFailure? Failure { get; init; }

    public bool Succeeded => Failure == null;

    /// <summary>Items emitted by a node on a given output port (empty when absent).</summary>
    public IReadOnlyList<FlowItem> OutputOf(string nodeId, int port = 0)
        => OutputsByNode.TryGetValue(nodeId, out var ports) && port >= 0 && port < ports.Count
            ? ports[port]
            : Array.Empty<FlowItem>();
}

/// <summary>
/// Drives a <see cref="NodeGraph"/> to completion: accumulates items on each
/// input port, fires a node once every incoming edge has delivered, resolves the
/// node's parameters per item, runs the registered executor, stamps provenance
/// on produced items and forwards them along the outgoing edges.
///
/// Invariants guaranteed by <see cref="NodeGraphCompiler"/>: exactly one entry
/// node and no cycles, so a node fires exactly once.
///
/// The class is split across partial files by responsibility:
/// <c>NodeGraphRunner.Invocation.cs</c> (parameter/context resolution + executor
/// invocation), <c>NodeGraphRunner.Routing.cs</c> (edge propagation, listeners,
/// error ports) and <c>NodeGraphRunner.Shaping.cs</c> (result shaping).
/// </summary>
public sealed partial class NodeGraphRunner
{
    private readonly NodeExecutorRegistry _executors;
    private readonly NodeParameterInterpolator _interpolator;
    private readonly NodePermissionPolicy? _permissions;
    private readonly ILogger<NodeGraphRunner>? _logger;

    public NodeGraphRunner(
        NodeExecutorRegistry executors,
        NodeParameterInterpolator interpolator,
        ILogger<NodeGraphRunner>? logger = null,
        NodePermissionPolicy? permissions = null)
    {
        _executors = executors;
        _interpolator = interpolator;
        _logger = logger;
        _permissions = permissions;
    }

    public async Task<NodeGraphRunResult> RunAsync(
        NodeGraph graph,
        IReadOnlyList<FlowItem> seed,
        NodeRunEnvironment? environment = null,
        INodeRunListener? listener = null,
        CancellationToken ct = default)
    {
        environment ??= new NodeRunEnvironment();

        var outputs = new Dictionary<string, List<IReadOnlyList<FlowItem>>>(StringComparer.Ordinal);
        var order = new List<string>();
        // Loop-back edges do not count toward readiness: they re-trigger the loop
        // node after its body has run, rather than being a normal predecessor.
        var incoming = graph.Nodes.ToDictionary(
            n => n.Id,
            n => graph.EdgesTo(n.Id).Count(e => !e.IsLoopBack),
            StringComparer.Ordinal);
        var arrived = graph.Nodes.ToDictionary(n => n.Id, _ => 0, StringComparer.Ordinal);
        var inputs = graph.Nodes.ToDictionary(n => n.Id, NewInputPorts, StringComparer.Ordinal);
        var exhausted = new HashSet<string>(StringComparer.Ordinal);
        var queued = new HashSet<string>(StringComparer.Ordinal);
        // Per-node invocation count: 0 on the first pass, incremented on every
        // re-trigger (a loop-back edge), so loop bodies see a real iteration
        // index through $runIndex / NodeExecutionContext.RunIndex.
        var invocations = graph.Nodes.ToDictionary(n => n.Id, _ => 0, StringComparer.Ordinal);

        inputs[graph.EntryNodeId][0].AddRange(seed);
        var ready = new Queue<string>();
        ready.Enqueue(graph.EntryNodeId);
        queued.Add(graph.EntryNodeId);

        var hasLoops = graph.Edges.Any(e => e.IsLoopBack);
        var maxSteps = hasLoops
            ? Math.Max(1024, graph.Nodes.Count * 256)
            : Math.Max(64, graph.Nodes.Count * 64);
        var steps = 0;

        while (ready.Count > 0)
        {
            ct.ThrowIfCancellationRequested();
            if (++steps > maxSteps)
                return Failure(outputs, order, new NodeFailure("node graph exceeded its execution budget", "budget"));

            var nodeId = ready.Dequeue();
            queued.Remove(nodeId);
            var node = graph.Require(nodeId);

            if (!_executors.CanRun(node.Blueprint.Type))
                return Failure(outputs, order,
                    new NodeFailure($"no executor is installed for node type '{node.Blueprint.Type}'", "missing_executor"));

            order.Add(nodeId);
            var nodeInputs = inputs[nodeId].Select(port => (IReadOnlyList<FlowItem>)port).ToList();
            await NotifyStarted(listener, node, nodeInputs, ct);

            // Node permissions are enforced right before invocation, so a graph
            // persisted before a policy change still cannot run a barred node.
            // A denial is a normal node failure: it routes to the error output or
            // fails the run, exactly like an executor error.
            var permission = _permissions?.Evaluate(node.Blueprint, environment.TenantId);
            var runIndex = invocations[nodeId]++;
            var outcome = permission is { Allowed: false }
                ? NodeExecutionOutcome.Failed(
                    permission.Reason ?? $"node type '{node.Blueprint.Type}' is not permitted",
                    permission.Code ?? "node_not_permitted")
                : await InvokeAsync(node, nodeInputs, environment, outputs, graph, runIndex, ct);
            var nodeFailure = outcome.Failure;
            IReadOnlyList<IReadOnlyList<FlowItem>>? errorPorts = null;
            if (!outcome.Succeeded)
            {
                var errorPort = node.ErrorOutputIndex;
                // A failure is only "handled" when an error branch is actually
                // wired (an edge leaves the error port) or the node opted into
                // continueOnFail. A blueprint that merely declares an error port
                // (e.g. core.httpRequest) must not silently swallow the failure:
                // with no branch the run fails, so the message reaches
                // WorkflowRun.Error instead of only the per-node TaskRun row.
                var errorHandled = node.ContinueOnFail
                    || (errorPort >= 0 && graph.EdgesFrom(node.Id, errorPort).Any());
                if (!errorHandled)
                {
                    await NotifyFinished(listener, node, Array.Empty<IReadOnlyList<FlowItem>>(), nodeFailure, ct);
                    return Failure(outputs, order, outcome.Failure!);
                }
                errorPorts = BuildErrorOutputs(node, nodeInputs, outcome.Failure!, errorPort);
            }

            var ports = StampAndNormalize(errorPorts ?? outcome.Outputs, node, runIndex);
            outputs[nodeId] = ports;
            await NotifyFinished(listener, node, ports, nodeFailure, ct);

            if (outcome.LoopComplete)
                exhausted.Add(nodeId);

            Propagate(graph, nodeId, ports, inputs, arrived, incoming, ready, queued, exhausted, outcome.LoopComplete);

            // Consume this node's inputs so a loop can gather them again next
            // iteration; cleared after use, never before.
            arrived[nodeId] = 0;
            foreach (var port in inputs[nodeId])
                port.Clear();
        }

        _logger?.LogDebug("Node graph run finished: {Count} nodes executed", order.Count);
        return new NodeGraphRunResult { OutputsByNode = Freeze(outputs), ExecutionOrder = order };
    }
}