package workflow

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"time"

	"switchboard-core/events"
	"switchboard-core/models"
	"switchboard-core/sandbox"
	"switchboard-core/store"

	"github.com/google/uuid"
)

// MaxConsecutiveAutomated is the cycle guard limit for automated stages.
const MaxConsecutiveAutomated = 10

// Engine orchestrates workflow instance lifecycle.
type Engine struct {
	stores store.Stores
	bus    *events.Bus
	runner *sandbox.Runner
}

// NewEngine creates a workflow engine.
func NewEngine(stores store.Stores, bus *events.Bus, runner *sandbox.Runner) *Engine {
	return &Engine{stores: stores, bus: bus, runner: runner}
}

// Start creates a new workflow instance and kicks off the first stage.
func (e *Engine) Start(ctx context.Context, workflowID string, initialData json.RawMessage, userID string) (*models.WorkflowInstance, error) {
	wf, err := e.stores.Workflows.GetByID(ctx, workflowID)
	if err != nil {
		return nil, fmt.Errorf("workflow not found: %w", err)
	}
	if !wf.IsActive {
		return nil, fmt.Errorf("workflow %q is not active", wf.Name)
	}

	ver, err := e.stores.Workflows.GetLatestVersion(ctx, workflowID)
	if err != nil {
		return nil, fmt.Errorf("no published version: %w", err)
	}

	var stages []models.WorkflowStage
	if err := json.Unmarshal(ver.Snapshot, &stages); err != nil {
		return nil, fmt.Errorf("corrupt version snapshot: %w", err)
	}
	if len(stages) == 0 {
		return nil, fmt.Errorf("workflow has no stages")
	}

	inst := &models.WorkflowInstance{
		WorkflowID:      workflowID,
		WorkflowVersion: ver.VersionNumber,
		CurrentStage:    stages[0].Name,
		StageData:       initialData,
		Status:          models.InstanceStatusActive,
		StartedBy:       userID,
		Metadata:        json.RawMessage(`{}`),
	}

	if wf.EntryMode == "public_link" {
		tok := uuid.New().String()
		inst.EntryToken = &tok
	}

	if err := e.stores.Workflows.CreateInstance(ctx, inst); err != nil {
		return nil, fmt.Errorf("create instance: %w", err)
	}

	// Create initial assignment if first stage has a team
	if stages[0].AssignmentTeamID != nil {
		a := &models.WorkflowAssignment{
			InstanceID: inst.ID,
			Stage:      stages[0].Name,
			TeamID:     *stages[0].AssignmentTeamID,
		}
		if err := e.stores.Workflows.CreateAssignment(ctx, a); err != nil {
			log.Printf("[workflow-engine] create initial assignment: %v", err)
		}
	}

	e.emit(ctx, "workflow.started", inst.ID, map[string]any{
		"workflow_id": workflowID,
		"instance_id": inst.ID,
		"started_by":  userID,
	})

	// If first stage is automated, process it
	if stages[0].StageMode == models.StageModeAutomated {
		if err := e.processAutomatedStage(ctx, inst, stages, 0); err != nil {
			log.Printf("[workflow-engine] automated stage error on start: %v", err)
		}
		// Re-read instance after automated processing
		inst, _ = e.stores.Workflows.GetInstance(ctx, inst.ID)
	}

	return inst, nil
}

// Advance moves an instance to the next stage.
func (e *Engine) Advance(ctx context.Context, instanceID string, stageData json.RawMessage, userID string) (*models.WorkflowInstance, error) {
	return e.advanceInternal(ctx, instanceID, stageData, userID, 0)
}

func (e *Engine) advanceInternal(ctx context.Context, instanceID string, stageData json.RawMessage, userID string, autoDepth int) (*models.WorkflowInstance, error) {
	inst, err := e.stores.Workflows.GetInstance(ctx, instanceID)
	if err != nil {
		return nil, fmt.Errorf("instance not found: %w", err)
	}
	if inst.Status != models.InstanceStatusActive {
		return nil, fmt.Errorf("instance is %s, not active", inst.Status)
	}

	ver, err := e.stores.Workflows.GetVersion(ctx, inst.WorkflowID, inst.WorkflowVersion)
	if err != nil {
		return nil, fmt.Errorf("version not found: %w", err)
	}

	var stages []models.WorkflowStage
	if err := json.Unmarshal(ver.Snapshot, &stages); err != nil {
		return nil, fmt.Errorf("corrupt snapshot: %w", err)
	}

	// Find current stage ordinal
	currentOrdinal := -1
	for _, s := range stages {
		if s.Name == inst.CurrentStage {
			currentOrdinal = s.Ordinal
			break
		}
	}
	if currentOrdinal < 0 {
		return nil, fmt.Errorf("current stage %q not found in snapshot", inst.CurrentStage)
	}
	currentStage := stages[currentOrdinal]

	// Merge stage data
	merged := mergeJSON(inst.StageData, stageData)

	// Resolve next stage
	nextOrdinal, err := ResolveNextStage(stages, currentOrdinal, merged)
	if err != nil {
		return nil, fmt.Errorf("resolve next stage: %w", err)
	}

	// Terminal — complete the instance
	if nextOrdinal >= len(stages) {
		if err := e.stores.Workflows.CompleteInstance(ctx, instanceID); err != nil {
			return nil, fmt.Errorf("complete: %w", err)
		}
		e.emit(ctx, "workflow.completed", instanceID, map[string]any{
			"instance_id": instanceID,
		})
		return e.stores.Workflows.GetInstance(ctx, instanceID)
	}

	nextStage := stages[nextOrdinal]

	// Advance in store
	if err := e.stores.Workflows.AdvanceStage(ctx, instanceID, nextStage.Name, merged); err != nil {
		return nil, fmt.Errorf("advance store: %w", err)
	}

	// Cancel old assignments for the previous stage
	oldAssignments, _ := e.stores.Workflows.ListAssignmentsByInstance(ctx, instanceID)
	for _, a := range oldAssignments {
		if a.Stage == currentStage.Name && (a.Status == models.AssignmentStatusUnassigned || a.Status == models.AssignmentStatusClaimed) {
			e.stores.Workflows.CancelAssignment(ctx, a.ID)
		}
	}

	// Create new assignment if next stage has a team
	if nextStage.AssignmentTeamID != nil {
		a := &models.WorkflowAssignment{
			InstanceID: instanceID,
			Stage:      nextStage.Name,
			TeamID:     *nextStage.AssignmentTeamID,
		}
		if err := e.stores.Workflows.CreateAssignment(ctx, a); err != nil {
			log.Printf("[workflow-engine] create assignment: %v", err)
		} else {
			e.emit(ctx, "workflow.assigned", a.TeamID, map[string]any{
				"instance_id":   instanceID,
				"stage":         nextStage.Name,
				"assignment_id": a.ID,
				"team_id":       a.TeamID,
			})
		}
	}

	e.emit(ctx, "workflow.advanced", instanceID, map[string]any{
		"instance_id":    instanceID,
		"previous_stage": currentStage.Name,
		"current_stage":  nextStage.Name,
	})

	// If next stage is automated, process it
	if nextStage.StageMode == models.StageModeAutomated {
		if err := e.processAutomatedStage(ctx, inst, stages, autoDepth+1); err != nil {
			log.Printf("[workflow-engine] automated stage error: %v", err)
		}
	}

	return e.stores.Workflows.GetInstance(ctx, instanceID)
}

// Cancel terminates an active instance and all its open assignments.
func (e *Engine) Cancel(ctx context.Context, instanceID string, userID string) error {
	inst, err := e.stores.Workflows.GetInstance(ctx, instanceID)
	if err != nil {
		return fmt.Errorf("instance not found: %w", err)
	}
	if inst.Status != models.InstanceStatusActive {
		return fmt.Errorf("instance is %s, not active", inst.Status)
	}

	if err := e.stores.Workflows.CancelInstance(ctx, instanceID); err != nil {
		return fmt.Errorf("cancel: %w", err)
	}

	// Cancel all open assignments
	assignments, _ := e.stores.Workflows.ListAssignmentsByInstance(ctx, instanceID)
	for _, a := range assignments {
		if a.Status == models.AssignmentStatusUnassigned || a.Status == models.AssignmentStatusClaimed {
			e.stores.Workflows.CancelAssignment(ctx, a.ID)
		}
	}

	e.emit(ctx, "workflow.cancelled", instanceID, map[string]any{
		"instance_id": instanceID,
		"cancelled_by": userID,
	})

	return nil
}

// ── Public Entry (v0.3.3) ───────────────────

// StartPublic creates an instance for a public_link workflow without authentication.
// The caller is identified as "public:<uuid>". Returns the instance including its entry_token.
func (e *Engine) StartPublic(ctx context.Context, workflowID string, initialData json.RawMessage) (*models.WorkflowInstance, error) {
	wf, err := e.stores.Workflows.GetByID(ctx, workflowID)
	if err != nil {
		return nil, fmt.Errorf("workflow not found: %w", err)
	}
	if wf.EntryMode != "public_link" {
		return nil, fmt.Errorf("workflow %q does not accept public entry", wf.Name)
	}
	anonymousID := "public:" + uuid.New().String()
	return e.Start(ctx, workflowID, initialData, anonymousID)
}

// ResumePublic returns an active instance by its entry token. No authentication required.
func (e *Engine) ResumePublic(ctx context.Context, entryToken string) (*models.WorkflowInstance, error) {
	inst, err := e.stores.Workflows.GetInstanceByToken(ctx, entryToken)
	if err != nil {
		return nil, fmt.Errorf("instance not found: %w", err)
	}
	if inst.Status != models.InstanceStatusActive {
		return nil, fmt.Errorf("instance is %s, not active", inst.Status)
	}
	return inst, nil
}

// AdvancePublic advances an instance identified by entry token. Only public-audience stages
// can be advanced this way. The original anonymous identity is used as the actor.
func (e *Engine) AdvancePublic(ctx context.Context, entryToken string, stageData json.RawMessage) (*models.WorkflowInstance, error) {
	inst, err := e.stores.Workflows.GetInstanceByToken(ctx, entryToken)
	if err != nil {
		return nil, fmt.Errorf("instance not found: %w", err)
	}
	if inst.Status != models.InstanceStatusActive {
		return nil, fmt.Errorf("instance is %s, not active", inst.Status)
	}

	// Load version snapshot to check audience
	ver, err := e.stores.Workflows.GetVersion(ctx, inst.WorkflowID, inst.WorkflowVersion)
	if err != nil {
		return nil, fmt.Errorf("version not found: %w", err)
	}
	var stages []models.WorkflowStage
	if err := json.Unmarshal(ver.Snapshot, &stages); err != nil {
		return nil, fmt.Errorf("corrupt snapshot: %w", err)
	}

	// Find current stage and validate audience
	for _, s := range stages {
		if s.Name == inst.CurrentStage {
			if s.Audience != models.AudiencePublic {
				return nil, fmt.Errorf("stage %q requires authenticated access", s.Name)
			}
			break
		}
	}

	return e.advanceInternal(ctx, inst.ID, stageData, inst.StartedBy, 0)
}

// emit publishes an event on the bus.
func (e *Engine) emit(_ context.Context, label, room string, payload map[string]any) {
	if e.bus == nil {
		return
	}
	e.bus.Publish(events.Event{
		Label:   label,
		Room:    room,
		Payload: events.MustJSON(payload),
		Ts:      time.Now().UnixMilli(),
	})
}

// mergeJSON merges b into a (shallow). Returns a if b is empty.
func mergeJSON(a, b json.RawMessage) json.RawMessage {
	if len(b) == 0 || string(b) == "{}" || string(b) == "null" {
		if len(a) == 0 {
			return json.RawMessage(`{}`)
		}
		return a
	}
	if len(a) == 0 || string(a) == "{}" || string(a) == "null" {
		return b
	}

	var ma, mb map[string]json.RawMessage
	if json.Unmarshal(a, &ma) != nil {
		return b
	}
	if json.Unmarshal(b, &mb) != nil {
		return a
	}
	for k, v := range mb {
		ma[k] = v
	}
	merged, err := json.Marshal(ma)
	if err != nil {
		return b
	}
	return merged
}