using System.Text.Json;

namespace w4c_workflows.Services.Execution;

/// <summary>
/// Wire contract for a <c>task.run</c> job pulled off the tenant's jobs stream.
/// The control plane (step 9) enqueues these; the worker reads, executes and
/// acks them. Field names are flat Redis Stream entries so the contract is
/// transport-agnostic (Redis Streams now, RabbitMQ later).
/// </summary>
public sealed record TaskInvocation(
    string Type,
    string RunId,
    string TaskId,
    string TaskKey,
    string Language,
    string EntryFile,
    string? EntryFunction,
    IReadOnlyDictionary<string, string> Env,
    string? Input,
    string? WorkingDir,
    string TenantId,
    int Attempt,
    string? Server = null)
{
    public const string TypeValue = "task.run";

    private static readonly JsonSerializerOptions Json = new(JsonSerializerDefaults.Web);

    /// <summary>Parses a stream message into an invocation, throwing if a required field is missing.</summary>
    public static TaskInvocation FromFields(IReadOnlyDictionary<string, string> fields)
    {
        static string Get(IReadOnlyDictionary<string, string> fields, string key) =>
            fields.TryGetValue(key, out var value) && !string.IsNullOrEmpty(value)
                ? value
                : throw new InvalidOperationException($"missing required job field '{key}'");

        static int GetInt(IReadOnlyDictionary<string, string> fields, string key, int fallback) =>
            fields.TryGetValue(key, out var raw) && int.TryParse(raw, out var n) ? n : fallback;

        var env = fields.TryGetValue("env", out var envJson) && !string.IsNullOrWhiteSpace(envJson)
            ? JsonSerializer.Deserialize<Dictionary<string, string>>(envJson, Json) ?? new()
            : new Dictionary<string, string>();

        return new TaskInvocation(
            Get(fields, "type"),
            Get(fields, "run_id"),
            Get(fields, "task_id"),
            Get(fields, "task_key"),
            Get(fields, "language"),
            Get(fields, "entry_file"),
            fields.GetValueOrDefault("entry_function"),
            env,
            fields.GetValueOrDefault("input"),
            fields.GetValueOrDefault("working_dir"),
            Get(fields, "tenant_id"),
            GetInt(fields, "attempt", 1),
            fields.GetValueOrDefault("server"));
    }
}