using System.Collections.Generic;
using System.Data.Common;
using System.Threading.Tasks;
using GB5Shared.DTO.Framework.Login;
using GB5Shared.DTO.WorkFlow;
using static GB5Shared.DTO.WorkFlow.ContractsDTO;

namespace GB5Shared.WorkFlow.WorkFlowEngine
{
    public interface IWorkFlowEngine
    {
        /// <summary>
        /// Facts key injected by EventHandler when login.WipApprovalId > 0.
        /// When this key is true, CheckWorkFlowApplicability returns WORKFLOW.NONE,
        /// allowing the entity to be saved directly without triggering WIP again.
        /// </summary>
        const string WipApprovalFactKey = "__WipApproval";

        // ── Applicability check (primary — uses MWORKFLOWCONFIG) ──────────────

        /// <summary>
        /// Checks MWORKFLOWCONFIG to determine whether a workflow applies
        /// for the given context, and returns the resolved workflow id.
        ///
        /// Steps:
        ///  1. Query MWORKFLOWCONFIG filtered by EntityId / ClientId / OUId /
        ///     BizTransactionClassId / BizTransactionId (wildcards via -1).
        ///  2. For each candidate row (most-specific first) evaluate EVALCONDITION
        ///     against <see cref="WorkflowCheckContext.Facts"/>.
        ///  3. Return the first match.
        ///  4. If Facts["__WipApproval"] == true, returns WORKFLOW.NONE immediately
        ///     (WIP approval callback — skip all workflow checks).
        /// </summary>
        Task<WorkflowPreCheckResult> CheckWorkFlowApplicability(
            WorkflowCheckContext context,
            LoginDTO login,
            DbTransaction tx);

        // ── Start workflow ────────────────────────────────────────────────────

        /// <summary>
        /// For REGULAR: creates a workflow instance and tasks for the first approval level.
        /// For WIP (IsFormBasedApproval=true): inserts TWORKFLOWWIP, then creates the
        /// instance with ObjectId=WipId, then enters the first approval level.
        /// Returns a WorkflowStartResult describing what was started.
        /// </summary>
        Task<WorkflowStartResult> StartWorkflowAsync(
            WorkflowStartRequest request,
            LoginDTO login,
            DbTransaction tx);

        // ── Action handling ───────────────────────────────────────────────────

        /// <summary>
        /// Processes one or more approver actions (Approve / Reject / Return / Escalate).
        /// When all tasks at the current approval level are approved the engine
        /// automatically advances to the next level and creates tasks there.
        /// When no further levels exist the workflow is completed.
        /// For WIP instances at final approval: updates TWORKFLOWWIP.STATUS=Approved and
        /// returns WipDispatchInfo in WorkflowActionResult.PendingDispatches.
        /// Caller MUST dispatch after committing the transaction.
        /// </summary>
        Task<WorkflowActionResult> HandleActionsAsync(
            IEnumerable<WorkflowActionContext> actions,
            LoginDTO login,
            DbTransaction tx);

        // ── Cancel on delete / cancel on resubmit ─────────────────────────────

        /// <summary>
        /// Cancels any real pending (WORKFLOWSTATUS=0) workflow instance for the given
        /// entity+object — used when the underlying record is deleted, or is about to be
        /// resubmitted after an edit while its prior approval is still pending. Cancels the
        /// instance's TWORKFLOWTASK rows, the instance itself, its linked TWORKFLOWWIP row
        /// (if any), and writes one TWORKFLOWHISTORY entry (Action=Cancel) per cancelled
        /// instance. Safe no-op (returns 0) when nothing is pending, e.g. for a new record.
        /// </summary>
        Task<int> CancelPendingInstanceAsync(
            int entityId,
            int objectId,
            string reason,
            LoginDTO login,
            DbTransaction tx);

        // ── WIP post-dispatch update ─────────────────────────────────────────

        /// <summary>
        /// Called by EventHandler after the WIP approval callback saves the entity.
        /// Writes the real saved entity ID (e.g. TaskId) into TWORKFLOWWIP.OBJECTID
        /// while still inside the same transaction — so the update is atomic with the
        /// entity save and rolls back together if the BLL transaction later fails.
        /// </summary>
        Task UpdateWipObjectIdAsync(
            int wipId,
            int objectId,
            LoginDTO login,
            DbTransaction tx);

        // ── Auto-approve ─────────────────────────────────────────────────────

        /// <summary>
        /// Returns all pending tasks whose DUEON has passed and whose step
        /// has ISAUTOAPPROVE = 0 (0=Yes). Called by the background auto-approve job.
        /// </summary>
        Task<IReadOnlyList<OverdueAutoApproveTaskDTO>> GetOverdueAutoApproveTasksAsync(
            LoginDTO login,
            DbTransaction tx);

        // ── Delegation ────────────────────────────────────────────────────────

        /// <summary>
        /// Resolves the effective approver: if the principal has an active delegation
        /// record the delegate user-id is returned; otherwise the principal id is used.
        /// </summary>
        Task<int> ResolveEffectiveUserAsync(
            long userId,
            System.DateTime at,
            LoginDTO login,
            DbTransaction tx);
    }

    public interface IUserDelegationResolver
    {
        Task<IReadOnlyList<UserDelegation>> GetAsync(
            long userId,
            LoginDTO login,
            DbTransaction tx);
    }
}