using System.Text.Json;
using System.Text.Json.Serialization;
using w4c_workflows.Models;
using YamlDotNet.Serialization;
using YamlDotNet.Serialization.NamingConventions;

namespace w4c_workflows.Services;

/// <summary>A successfully compiled workflow + its task tree (EF entities, detached).</summary>
public sealed record CompiledWorkflow(Workflow Workflow, IReadOnlyList<WorkflowTask> Tasks);

public sealed class CompileResult
{
    public List<string> Errors { get; } = new();
    public bool Success => Errors.Count == 0;
    public CompiledWorkflow? Workflow { get; set; }
}

/// <summary>
/// Parses and compiles a workflow YAML definition into the EF entity model.
/// Ids are deterministic (tenant + path + task id) so re-syncing the same file
/// upserts instead of duplicating. The compiler performs no DB writes — the
/// sync service persists the result.
/// </summary>
public class WorkflowCompiler
{
    private static readonly JsonSerializerOptions Json = new(JsonSerializerDefaults.Web)
    {
        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
    };

    private readonly WorkflowValidator _validator;
    private readonly IDeserializer _yaml;

    public WorkflowCompiler(WorkflowValidator validator)
    {
        _validator = validator;
        _yaml = new DeserializerBuilder()
            .WithNamingConvention(CamelCaseNamingConvention.Instance)
            .IgnoreUnmatchedProperties()
            .Build();
    }

    public CompileResult Compile(string yaml, string path, string tenantId, string repoName = "workflows")
    {
        var result = new CompileResult();

        WorkflowDefinition def;
        try
        {
            def = _yaml.Deserialize<WorkflowDefinition>(yaml) ?? new WorkflowDefinition();
        }
        catch (Exception ex)
        {
            result.Errors.Add($"YAML parse error: {ex.Message}");
            return result;
        }

        result.Errors.AddRange(_validator.Validate(def));
        if (!result.Success)
            return result;

        result.Workflow = Build(def, path, tenantId, repoName);
        return result;
    }

    private CompiledWorkflow Build(WorkflowDefinition def, string path, string tenantId, string repoName)
    {
        var graph = WorkflowGraph.Compute(def);
        var now = DateTime.UtcNow;

        var workflowId = DeterministicGuid.For($"wf::{tenantId}::{repoName}::{path}");
        var workflow = new Workflow
        {
            Id = workflowId,
            TenantId = tenantId,
            Name = def.Name!,
            Path = path,
            Repo = repoName,
            Status = WorkflowStatus.Compiled,
            Mode = def.Mode!,
            Version = string.IsNullOrWhiteSpace(def.Version) ? "1.0.0" : def.Version!,
            Target = string.IsNullOrWhiteSpace(def.Target) ? "default" : def.Target,
            TriggerJson = def.Trigger == null ? null : JsonSerializer.Serialize(def.Trigger, Json),
            CompiledAt = now,
            CreatedAt = now,
            UpdatedAt = now,
        };

        var tasks = new List<WorkflowTask>();

        // Root task = the workflow entry (language/mode/entry/env from the header).
        var rootId = DeterministicGuid.For($"task::{tenantId}::{repoName}::{path}::root");
        var headId = graph.HeadId == null
            ? (Guid?)null
            : DeterministicGuid.For($"task::{tenantId}::{repoName}::{path}::{graph.HeadId}");
        tasks.Add(new WorkflowTask
        {
            Id = rootId,
            WorkflowId = workflowId,
            Key = "root",
            ParentId = null,
            NextId = headId,
            OnErrorId = null,
            Language = def.Language!,
            Mode = def.Mode!,
            EntryJson = JsonSerializer.Serialize(new EntryDefinition
            {
                File = def.Entry!.File,
                Function = def.Entry.Function,
            }, Json),
            EnvJson = SerializeEnv(def.Env),
            Server = NormalizeServer(def.Server),
            Order = 0,
        });

        for (var i = 0; i < graph.Tasks.Count; i++)
        {
            var task = graph.Tasks[i];
            var taskId = DeterministicGuid.For($"task::{tenantId}::{repoName}::{path}::{task.Id}");

            tasks.Add(new WorkflowTask
            {
                Id = taskId,
                WorkflowId = workflowId,
                Key = task.Id!,
                ParentId = string.IsNullOrEmpty(task.Parent) || task.Parent == "root"
                    ? rootId
                    : DeterministicGuid.For($"task::{tenantId}::{repoName}::{path}::{task.Parent}"),
                NextId = string.IsNullOrEmpty(task.Next)
                    ? null
                    : DeterministicGuid.For($"task::{tenantId}::{repoName}::{path}::{task.Next}"),
                OnErrorId = string.IsNullOrEmpty(task.OnError)
                    ? null
                    : DeterministicGuid.For($"task::{tenantId}::{repoName}::{path}::{task.OnError}"),
                Language = task.Language ?? def.Language!,
                Mode = task.Mode ?? def.Mode!,
                EntryJson = JsonSerializer.Serialize(new EntryDefinition
                {
                    File = task.Entry!.File,
                    Function = task.Entry.Function,
                }, Json),
                EnvJson = SerializeEnv(task.Env),
                Server = NormalizeServer(task.Server ?? def.Server),
                Order = i + 1,
            });
        }

        return new CompiledWorkflow(workflow, tasks);
    }

    private static string? NormalizeServer(string? value)
        => string.IsNullOrWhiteSpace(value) ? null : value.Trim();

    private static string? SerializeEnv(Dictionary<string, string>? env)
        => env == null || env.Count == 0 ? null : JsonSerializer.Serialize(env, Json);
}