package workflow

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
	"sync"
	"sync/atomic"
	"time"
)

// Engine is the main workflow execution engine
type Engine struct {
	workflow         *Workflow
	parallelExecutor *ParallelExecutor
	errorStrategy    ParallelErrorStrategy
	eventSequence    uint64    // Atomic counter for event sequence numbers
	stopOnce         sync.Once // Captures the first Stop_* node ID
	stopNodeID       string    // ID of the first Stop_* node that triggered stop
}

// NewEngine creates a new workflow engine with default options
func NewEngine(workflow *Workflow) (*Engine, error) {
	return NewEngineWithOptions(workflow, DefaultEngineOptions)
}

// NewEngineWithOptions creates a new workflow engine with custom options
func NewEngineWithOptions(workflow *Workflow, opts EngineOptions) (*Engine, error) {
	// Validate workflow is not nil
	if workflow == nil {
		return nil, fmt.Errorf("workflow cannot be nil")
	}

	// Validate workflow structure
	if err := workflow.Validate(); err != nil {
		return nil, fmt.Errorf("invalid workflow: %w", err)
	}

	return &Engine{
		workflow:         workflow,
		parallelExecutor: NewParallelExecutor(opts.MaxConcurrency),
		errorStrategy:    opts.ParallelErrorStrategy,
		eventSequence:    0,
	}, nil
}

// Execute starts workflow execution with the given context and initial variables
func (e *Engine) Execute(ctx context.Context, initialVars map[string]interface{}, adapters *Adapters) (*ExecutionResult, error) {
	// Validate required parameters
	if ctx == nil {
		return nil, fmt.Errorf("context cannot be nil")
	}
	if adapters == nil {
		return nil, fmt.Errorf("adapters cannot be nil")
	}

	// Create execution context
	execCtx := &ExecutionContext{
		Ctx:              ctx,
		WorkflowID:       generateWorkflowID(),
		Params:           make(map[string]interface{}),
		Variables:        make(map[string]interface{}),
		SystemVars:       make(map[string]interface{}),
		LocalVars:        make(map[string]interface{}),
		Artifacts:        make(map[string]string),
		Status:           StatusRunning,
		StartTime:        time.Now(),
		RunEventStream:   make(chan RunEvent, 500),
		ServiceAdapter:   adapters.Service,
		APIAdapter:       adapters.API,
		ComponentAdapter: adapters.Component,
		LLMAdapter:         adapters.LLM,
		LLMAdapterRegistry: adapters.LLMAdapterRegistry,
		FileAdapter:        adapters.File,
		DocAdapter:         adapters.Doc,
	}

	// Initialize parameter types from registry
	execCtx.ParamTypes = make(map[string]string)
	if paramDecls, err := e.workflow.Registry.GetParamDeclarations(); err == nil {
		for name, decl := range paramDecls {
			execCtx.ParamTypes[name] = decl.Type
		}
	}

	// Initialize variable types from registry
	execCtx.VarTypes = make(map[string]string)
	if varDecls, err := e.workflow.Registry.GetVariableDeclarations(); err == nil {
		for name, decl := range varDecls {
			execCtx.VarTypes[name] = decl.Type
		}
	}

	// Initialize parameters and variables from initialVars
	// Parameters are those defined in registry.Params (no $ prefix)
	// Variables are those with $ prefix
	for k, v := range initialVars {
		if strings.HasPrefix(k, "$") {
			execCtx.Variables[k] = v
		} else {
			// Check if this is a declared parameter
			if paramType, ok := execCtx.ParamTypes[k]; ok {
				// Apply type conversion for OBJECT params
				convertedValue := v
				if paramType == "OBJECT" {
					if str, isString := v.(string); isString {
						var obj map[string]interface{}
						if err := json.Unmarshal([]byte(str), &obj); err != nil {
							return nil, fmt.Errorf("failed to convert parameter %s to OBJECT: %w", k, err)
						}
						convertedValue = obj
					}
				}
				execCtx.Params[k] = convertedValue
			} else {
				// Not a declared parameter, treat as variable with $ prefix
				execCtx.Variables["$"+k] = v
			}
		}
	}

	// Apply registry param defaults for parameters not supplied by the caller (spec §3.2).
	// This runs after initialVars processing so explicit caller values always take precedence.
	if paramDecls, err := e.workflow.Registry.GetParamDeclarations(); err == nil {
		for name, decl := range paramDecls {
			if _, alreadySet := execCtx.Params[name]; !alreadySet && decl.Default != nil {
				if defaultVal, coerceErr := CoerceParamDefault(decl); coerceErr == nil && defaultVal != nil {
					execCtx.Params[name] = defaultVal
				}
			}
		}
	}

	// Execute workflow
	go e.executeWorkflow(execCtx)

	// Return result
	return &ExecutionResult{
		Context:        execCtx,
		RunEventStream: execCtx.RunEventStream,
	}, nil
}

// ExecuteWithRunParams starts workflow execution with run-level control parameters (v3.15+, spec §2.2).
// RunParams allow the caller to specify a workspace scope, a selective node list, an
// execution mode, and business-level input params without polluting the workflow's own registry.
//
// RunParams.Params (spec §1.7 runParams.params) are merged into the effective initial variables.
// They take precedence over initialVars for the same key, mirroring how the online platform
// passes declared registry params to the engine separately from internal engine state.
func (e *Engine) ExecuteWithRunParams(ctx context.Context, initialVars map[string]interface{}, adapters *Adapters, runParams RunParams) (*ExecutionResult, error) {
	// Merge RunParams.Params + initialVars → RunParams.Params wins (they are the caller-declared params).
	// RunParams.Params keys are bare names (e.g. "prompt") per the spec §1.7.
	// They are passed through unchanged so Execute()'s param-routing logic places them in
	// execCtx.Params[name], accessible via =name expressions (no $ prefix).
	merged := make(map[string]interface{}, len(initialVars)+len(runParams.Params))
	for k, v := range initialVars {
		merged[k] = v
	}
	for k, v := range runParams.Params {
		merged[k] = v
	}

	result, err := e.Execute(ctx, merged, adapters)
	if err != nil {
		return nil, err
	}
	// Attach RunParams to the execution context so downstream steps / adapters can inspect them.
	result.Context.RunParams = &runParams
	return result, nil
}

// executeWorkflow executes the workflow from the beginning
func (e *Engine) executeWorkflow(execCtx *ExecutionContext) {
	defer close(execCtx.RunEventStream)

	// Emit workflow_start RunEvent
	e.emitRunEvent(execCtx, RunEventWorkflowStart, nil, map[string]interface{}{
		"params": execCtx.Params,
	})

	// Find true entry nodes (spec §1.4C: unreferenced nodes, NOT always steps[0]).
	entryIDs := findEntryNodeIDs(e.workflow.Steps)
	if len(entryIDs) == 0 {
		e.fail(execCtx, fmt.Errorf("no entry nodes found in workflow"))
		return
	}

	var execErr error
	if len(entryIDs) == 1 {
		// Single entry: execute serially (common case)
		entry := e.findStepByID(entryIDs[0])
		execErr = e.executeStep(execCtx, entry)
	} else {
		// Multiple entry nodes: execute in parallel (spec §1.4C)
		execErr = e.executeChildren(execCtx, entryIDs)
	}
	if execErr != nil {
		e.fail(execCtx, execErr)
		return
	}

	// Terminal event: emit workflow_done AFTER all branches have finished.
	switch execCtx.Status {
	case StatusRunning:
		e.complete(execCtx)
	case StatusStopped:
		// Deferred from e.stop() — emit workflow_done now that every parallel
		// branch has returned, so all step events precede the terminal event.
		e.emitRunEvent(execCtx, RunEventWorkflowDone, nil, map[string]interface{}{
			"stop_id":     e.stopNodeID,
			"duration_ms": time.Since(execCtx.StartTime).Milliseconds(),
		})
	}
}

// executeStep executes a single step
func (e *Engine) executeStep(ctx ContextAccessor, step *Step) error {
	// Get base context
	baseCtx := ctx.GetBaseContext()

	// Short-circuit if this branch has been stopped or the workflow is paused.
	// For ChildExecutionContext (parallel branches), IsStopped() checks the
	// branch-local flag so sibling branches are NOT short-circuited.
	// For non-parallel paths, IsStopped() checks the global Status.
	// Pause is always a global check — all branches should pause.
	if ctx.IsStopped() || baseCtx.Status == StatusPaused {
		return nil
	}

	// Set current step ID using thread-safe method
	ctx.SetCurrentStepID(step.ID)

	// Collect file write targets for the step.start event and file_start RunEvents.
	// Expand {expr} templates in out-key paths (e.g. "/{_item.filePath}") so that
	// file_start carries the actual resolved path, not the raw template string.
	var fileTargets []string
	for target := range step.Out {
		if strings.HasPrefix(target, "/") {
			if expanded, err := e.interpolateFilePath(ctx, target); err == nil {
				fileTargets = append(fileTargets, expanded)
			} else {
				fileTargets = append(fileTargets, target)
			}
		}
	}
	if strings.HasPrefix(step.ID, "Write_") && step.Target != "" {
		// Try to evaluate the target path expression; fall back to the raw string
		evaluator := NewExpressionEvaluator(ctx)
		if targetVal, err := evaluator.EvaluateValue(step.Target); err == nil {
			if targetStr, ok := targetVal.(string); ok {
				fileTargets = append(fileTargets, targetStr)
			} else {
				fileTargets = append(fileTargets, step.Target)
			}
		} else {
			fileTargets = append(fileTargets, step.Target)
		}
	}

	// Check if condition
	stepType := e.getStepType(step.ID)
	stepTypePattern := string(stepType) + "_*"

	if step.If != "" {
		evaluator := NewExpressionEvaluator(ctx)
		var result interface{}
		var err error
		if strings.HasPrefix(step.If, "=") {
			result, err = evaluator.EvaluateValue(step.If)
		} else {
			result, err = evaluator.Evaluate(step.If)
		}
		if err != nil {
			return fmt.Errorf("failed to evaluate if condition: %w", err)
		}

		if !toBool(result) {
			// Emit step_skipped RunEvent (spec 3.12 §13.3)
			stepID := step.ID
			e.emitRunEvent(baseCtx, RunEventStepSkipped, &stepID, map[string]interface{}{
				"step_type": stepTypePattern,
				"reason":    "if_false",
			})

			// Skip this step and its children, move to next
			if step.Next != "" {
				// Handle special next values
				if step.Next == "RETURN" {
					return nil
				}
				if step.Next == "BREAK" {
					return ErrBreak
				}
				nextStep := e.findStepByID(step.Next)
				if nextStep != nil {
					return e.executeStep(ctx, nextStep)
				}
			}
			// No next - this branch is complete
			return nil
		}
	}

	// Emit step_start RunEvent (condition passed, about to execute)
	stepID := step.ID
	e.emitRunEvent(baseCtx, RunEventStepStart, &stepID, map[string]interface{}{
		"step_type": stepTypePattern,
	})

	// Emit file_start RunEvents for all file targets (spec 3.13 §13.3)
	// Batch-emitted immediately after step_start, before any llm_token
	for _, target := range fileTargets {
		path := strings.TrimPrefix(target, "/")
		e.emitRunEvent(baseCtx, RunEventFileStart, &stepID, map[string]interface{}{
			"path": path,
		})
	}

	stepStartTime := time.Now()

	var err error
	switch stepType {
	case StepTypeService:
		err = e.executeServiceStep(ctx, step)
	case StepTypeAPI:
		err = e.executeAPIStep(ctx, step)
	case StepTypeComponent:
		err = e.executeComponentStep(ctx, step)
	case StepTypeLLM:
		err = e.executeLLMStep(ctx, step)
	case StepTypeSet:
		err = e.executeSetStep(ctx, step)
	case StepTypeWrite:
		err = e.executeWriteStep(ctx, step)
	case StepTypeDownload:
		err = e.executeDownloadStep(ctx, step)
	case StepTypeUnzip:
		err = e.executeUnzipStep(ctx, step)
	case StepTypePause:
		// Pause_* has special routing semantics: executePauseStep blocks until
		// the workflow is resumed or times out, then handles step_done and next
		// routing internally (similar to how Stop_* handles workflow termination).
		pauseErr := e.executePauseStep(ctx, step, stepStartTime, stepTypePattern)
		if pauseErr == nil {
			return nil // executePauseStep handled step_done and next routing
		}
		// Non-nil error (e.g. context cancellation): emit step_error and handle onError
		e.emitRunEvent(baseCtx, RunEventStepError, &stepID, map[string]interface{}{
			"step_type":   stepTypePattern,
			"error":       buildErrorMap(pauseErr),
			"duration_ms": time.Since(stepStartTime).Milliseconds(),
		})
		if step.OnError != "" && e.isV310OrLater() {
			ctx.SetLocalVar("_error", buildErrorMap(pauseErr))
			errorStep := e.findStepByID(step.OnError)
			if errorStep == nil {
				ctx.DeleteLocalVar("_error")
				ctx.DeleteLocalVar("_meta")
				return fmt.Errorf("onError step not found: %s (referenced by %s)", step.OnError, step.ID)
			}
			onErrResult := e.executeStep(ctx, errorStep)
			ctx.DeleteLocalVar("_error")
			ctx.DeleteLocalVar("_meta")
			return onErrResult
		}
		return pauseErr
	case StepTypeBranch:
		err = e.executeBranchStep(ctx, step)
	case StepTypeLoop:
		err = e.executeLoopStep(ctx, step)
	case StepTypeStop:
		e.stop(ctx)
		return nil
	case StepTypeNoop:
		// Noop step does nothing, just executes children
		err = nil
	default:
		return fmt.Errorf("unknown step type: %s", step.ID)
	}

	if err != nil {
		// v3.16+: BREAK is a control flow signal, not an error — propagate without step_error
		if IsBreakError(err) {
			return err
		}

		// Emit step_error RunEvent (spec 3.12 §13.4)
		e.emitRunEvent(baseCtx, RunEventStepError, &stepID, map[string]interface{}{
			"step_type":   stepTypePattern,
			"error":       buildErrorMap(err),
			"duration_ms": time.Since(stepStartTime).Milliseconds(),
		})

		// v3.10+: If step has onError handler, jump there instead of failing
		if step.OnError != "" && e.isV310OrLater() {
			// _error is built from the error (structured if LLMError, generic otherwise)
			ctx.SetLocalVar("_error", buildErrorMap(err))

			// Execute the onError handler step
			errorStep := e.findStepByID(step.OnError)
			if errorStep == nil {
				ctx.DeleteLocalVar("_error")
				ctx.DeleteLocalVar("_meta")
				return fmt.Errorf("onError step not found: %s (referenced by %s)", step.OnError, step.ID)
			}

			onErrResult := e.executeStep(ctx, errorStep)

			// Clean up after onError handler completes
			ctx.DeleteLocalVar("_error")
			ctx.DeleteLocalVar("_meta")

			return onErrResult
		}

		return err
	}

	// Emit step_print RunEvent (spec 3.13 §5.2.12)
	// Order: file_done(×N) → step_print(0..1) → step_done
	// Only on successful execution; Stop_* nodes cannot have print
	if step.Print != "" && stepType != StepTypeStop {
		evaluator := NewExpressionEvaluator(ctx)
		printVal, err := evaluator.EvaluateValue(step.Print)
		if err == nil {
			var message string
			switch v := printVal.(type) {
			case string:
				message = v
			default:
				if b, jerr := json.Marshal(v); jerr == nil {
					message = string(b)
				} else {
					message = fmt.Sprintf("%v", v)
				}
			}
			e.emitRunEvent(baseCtx, RunEventStepPrint, &stepID, map[string]interface{}{
				"message": message,
			})
		}
	}

	// Emit step_done RunEvent (spec 3.12 §13.4)
	e.emitRunEvent(baseCtx, RunEventStepDone, &stepID, map[string]interface{}{
		"step_type":   stepTypePattern,
		"duration_ms": time.Since(stepStartTime).Milliseconds(),
	})

	// Execute children (parallel branches)
	// Skip for Loop_* and Branch_* which handle their own children/branches internally
	if len(step.Children) > 0 && stepType != StepTypeLoop && stepType != StepTypeBranch {
		if err := e.executeChildren(ctx, step.Children); err != nil {
			return err
		}
	}

	// Move to next step
	if step.Next != "" {
		// Handle special next values
		if step.Next == "RETURN" {
			// Return from current execution path (used in children/loops)
			return nil
		}
		if step.Next == "BREAK" {
			// v3.16+: Exit the entire enclosing loop
			return ErrBreak
		}

		nextStep := e.findStepByID(step.Next)
		if nextStep != nil {
			return e.executeStep(ctx, nextStep)
		}
		return fmt.Errorf("next step not found: %s", step.Next)
	}

	// No next step - this branch is complete
	// Children workflows ending here are considered complete
	// Main workflow completion is handled by executeWorkflow
	return nil
}

// getStepType extracts the step type from the ID prefix
func (e *Engine) getStepType(stepID string) StepType {
	if strings.HasPrefix(stepID, "Service_") {
		return StepTypeService
	} else if strings.HasPrefix(stepID, "API_") {
		return StepTypeAPI
	} else if strings.HasPrefix(stepID, "Component_") {
		return StepTypeComponent
	} else if strings.HasPrefix(stepID, "LLM_") {
		return StepTypeLLM
	} else if strings.HasPrefix(stepID, "Set_") {
		return StepTypeSet
	} else if strings.HasPrefix(stepID, "Write_") {
		return StepTypeWrite
	} else if strings.HasPrefix(stepID, "Download_") {
		return StepTypeDownload
	} else if strings.HasPrefix(stepID, "Unzip_") {
		return StepTypeUnzip
	} else if strings.HasPrefix(stepID, "Pause_") {
		return StepTypePause
	} else if strings.HasPrefix(stepID, "Branch_") {
		return StepTypeBranch
	} else if strings.HasPrefix(stepID, "Loop_") {
		return StepTypeLoop
	} else if strings.HasPrefix(stepID, "Stop_") {
		return StepTypeStop
	} else if strings.HasPrefix(stepID, "Noop_") {
		return StepTypeNoop
	}
	return ""
}

// findStepByID finds a step by its ID
func (e *Engine) findStepByID(stepID string) *Step {
	for i := range e.workflow.Steps {
		if e.workflow.Steps[i].ID == stepID {
			return &e.workflow.Steps[i]
		}
	}
	return nil
}

// stop stops the workflow (called when a Stop_* node executes).
// Multiple parallel branches may each reach their own Stop_* node;
// stopOnce ensures workflow_done is emitted exactly once.
func (e *Engine) stop(ctx ContextAccessor) {
	// Use thread-safe method to set status
	ctx.SetStatus(StatusStopped)

	baseCtx := ctx.GetBaseContext()

	// Capture the first Stop_* node ID. The actual workflow_done event is emitted
	// by executeWorkflow AFTER all parallel branches have finished, so the SSE
	// reader sees every step event before the terminal event.
	e.stopOnce.Do(func() {
		e.stopNodeID = baseCtx.CurrentStepID
	})
}

// complete marks the workflow as completed (reached end naturally, no Stop_* node)
func (e *Engine) complete(ctx ContextAccessor) {
	ctx.SetStatus(StatusCompleted)

	baseCtx := ctx.GetBaseContext()
	// Emit workflow_done so clients receive the same signal whether the workflow
	// terminated via Stop_* or ran off the end of the last step.
	e.emitRunEvent(baseCtx, RunEventWorkflowDone, nil, map[string]interface{}{
		"duration_ms": time.Since(baseCtx.StartTime).Milliseconds(),
	})
}

// fail fails the workflow
func (e *Engine) fail(ctx ContextAccessor, err error) {
	// Use thread-safe method to set status
	ctx.SetStatus(StatusFailed)

	baseCtx := ctx.GetBaseContext()

	// Emit workflow_failed RunEvent (spec 3.12 §13.4)
	e.emitRunEvent(baseCtx, RunEventWorkflowFailed, nil, map[string]interface{}{
		"failed_step_id": baseCtx.CurrentStepID,
		"error":          buildErrorMap(err),
		"duration_ms":    time.Since(baseCtx.StartTime).Milliseconds(),
	})
}

// Resume sends a resume signal to a workflow that is suspended at a Pause_* node (v3.15+).
// It is idempotent: a duplicate call with the same RequestID is silently ignored.
// Returns an error if the workflow is not currently paused, the token is invalid,
// or the resume signal has already been delivered.
func (e *Engine) Resume(execCtx *ExecutionContext, req ResumeRequest) error {
	execCtx.pauseMu.Lock()
	state := execCtx.PauseState
	execCtx.pauseMu.Unlock()

	if state == nil {
		// Emit pause_rejected for state_error (spec §11.5.4: non-paused state → rejected)
		e.emitRunEvent(execCtx, RunEventPauseRejected, nil, map[string]interface{}{
			"requestId":  req.RequestID,
			"reasonCode": "state_error",
		})
		return fmt.Errorf("workflow is not in paused state")
	}

	// Validate RunID if provided (spec §11.4.1: runId must identify the correct run)
	if req.RunID != "" && req.RunID != execCtx.WorkflowID {
		return fmt.Errorf("resume runId %q does not match workflow run %q", req.RunID, execCtx.WorkflowID)
	}

	state.mu.Lock()
	defer state.mu.Unlock()

	// Validate token before any idempotency check
	if req.Token != state.token {
		nodeID := state.nodeID
		e.emitRunEvent(execCtx, RunEventPauseRejected, &nodeID, map[string]interface{}{
			"nodeId":     state.nodeID,
			"requestId":  req.RequestID,
			"reasonCode": "invalid_token",
		})
		return fmt.Errorf("invalid resume token")
	}

	// Idempotency: duplicate RequestID → silent no-op
	if req.RequestID != "" && state.seenRequestIDs[req.RequestID] {
		return nil
	}

	// Reject if already resumed by a different request
	if state.resumed {
		nodeID := state.nodeID
		e.emitRunEvent(execCtx, RunEventPauseRejected, &nodeID, map[string]interface{}{
			"nodeId":     state.nodeID,
			"requestId":  req.RequestID,
			"reasonCode": "already_resumed",
		})
		return fmt.Errorf("workflow has already been resumed")
	}

	// Record request ID for idempotency before sending
	if req.RequestID != "" {
		state.seenRequestIDs[req.RequestID] = true
	}
	state.resumed = true

	// Send signal (buffered channel size 1, non-blocking)
	state.ch <- resumeSignal{Payload: req.Payload, RequestID: req.RequestID}
	return nil
}

// snapshotLocalVars copies known local variables from a ContextAccessor
// so they can be propagated to child contexts (e.g., _item/_index from loops)
func snapshotLocalVars(ctx ContextAccessor) map[string]interface{} {
	snapshot := make(map[string]interface{})
	for _, key := range []string{"_item", "_index", "_result", "_meta", "_error"} {
		if val, ok := ctx.GetLocalVar(key); ok {
			snapshot[key] = val
		}
	}
	return snapshot
}

// executeChildren executes child steps in parallel
func (e *Engine) executeChildren(parentCtx ContextAccessor, childIDs []string) error {
	if len(childIDs) == 0 {
		return nil
	}

	baseCtx := parentCtx.GetBaseContext()

	// Optimization: single child doesn't need parallelism
	if len(childIDs) == 1 {
		child := e.findStepByID(childIDs[0])
		if child == nil {
			return fmt.Errorf("child step not found: %s", childIDs[0])
		}
		return e.executeStep(parentCtx, child)
	}

	// Parallel execution for multiple children
	safeCtx := NewSafeExecutionContext(baseCtx)
	executor := e.getParallelExecutor()

	// Snapshot parent's local vars so child branches inherit them (e.g., _item/_index from loops)
	parentLocalVars := snapshotLocalVars(parentCtx)

	// Create branches for each child
	branches := make([]ParallelBranch, len(childIDs))
	for i, childID := range childIDs {
		id := childID

		branches[i] = ParallelBranch{
			ID: id,
			Fn: func(ctx context.Context) error {
				// Create child context with isolated local vars
				childCtx := NewChildExecutionContext(safeCtx)

				// Propagate parent's local vars (e.g., _item, _index from enclosing loop)
				for k, v := range parentLocalVars {
					childCtx.LocalVars[k] = v
				}

				// Check cancellation
				select {
				case <-ctx.Done():
					return ctx.Err()
				default:
				}

				child := e.findStepByID(id)
				if child == nil {
					return fmt.Errorf("child step not found: %s", id)
				}

				// Execute with child context
				if err := e.executeStep(childCtx, child); err != nil {
					return fmt.Errorf("child %s: %w", id, err)
				}

				return nil
			},
		}
	}

	// Execute all branches in parallel
	if err := executor.Execute(baseCtx.Ctx, branches, e.getErrorStrategy()); err != nil {
		return fmt.Errorf("parallel children execution failed: %w", err)
	}

	return nil
}

// getParallelExecutor returns the parallel executor
func (e *Engine) getParallelExecutor() *ParallelExecutor {
	return e.parallelExecutor
}

// getErrorStrategy returns the configured error strategy
func (e *Engine) getErrorStrategy() ParallelErrorStrategy {
	return e.errorStrategy
}

// isV310OrLater returns true if the workflow version is 3.10 or later
func (e *Engine) isV310OrLater() bool {
	v := e.workflow.Version
	return v == "3.10" || v == "3.12" || v == "3.13" || v == "3.14" || v == "3.15" || v == "3.16"
}

// buildErrorMap converts an error into a map suitable for _error local variable
func buildErrorMap(err error) map[string]interface{} {
	var llmErr *LLMError
	if errors.As(err, &llmErr) {
		return llmErr.ToMap()
	}
	// Generic error fallback
	return map[string]interface{}{
		"type":    "internal_error",
		"code":    "INTERNAL_ERROR",
		"message": err.Error(),
	}
}

// nextEventSequence returns the next event sequence number
func (e *Engine) nextEventSequence() uint64 {
	return atomic.AddUint64(&e.eventSequence, 1)
}

// emitRunEvent emits a structured RunEvent to the run_events stream (spec 3.12 Chapter 13).
// Uses a non-blocking send (fire-and-forget): events are dropped if the channel is full or closed.
// The send is wrapped in a recover to guard against "send on closed channel" panics that can
// occur when Resume emits a pause_rejected event after the workflow goroutine has already closed
// the stream (e.g. the workflow completed between the paused check and the emit call).
func (e *Engine) emitRunEvent(ctx *ExecutionContext, eventType RunEventType, stepID *string, payload map[string]interface{}) {
	if ctx.RunEventStream == nil {
		return
	}
	event := RunEvent{
		RunID:   ctx.WorkflowID,
		Seq:     e.nextEventSequence(),
		Ts:      time.Now().UTC().Format("2006-01-02T15:04:05.000Z07:00"),
		Type:    eventType,
		StepID:  stepID,
		Payload: payload,
	}
	// Recover from "send on closed channel" panic (can happen when Resume is called
	// after the workflow goroutine has closed RunEventStream).
	defer func() { recover() }() //nolint:errcheck
	select {
	case ctx.RunEventStream <- event:
	default:
		// fire-and-forget: drop silently if channel is full
	}
}

// Adapters holds all the adapters needed for workflow execution
type Adapters struct {
	Service            ServiceAdapter
	API                APIAdapter
	Component          ComponentAdapter
	LLM                LLMAdapter
	LLMAdapterRegistry *LLMAdapterRegistry // v3.16+: multi-provider registry (nil for pre-3.16)
	File               FileAdapter
	Doc                DocAdapter
}

// ExecutionResult holds the result of workflow execution
type ExecutionResult struct {
	Context        *ExecutionContext
	RunEventStream <-chan RunEvent // v3.12+: structured run_events stream (spec Chapter 13)
}

// Validate validates the workflow structure
func (w *Workflow) Validate() error {
	if w.Version != "3.6" && w.Version != "3.7" && w.Version != "3.8" && w.Version != "3.9" && w.Version != "3.10" && w.Version != "3.12" && w.Version != "3.13" && w.Version != "3.14" && w.Version != "3.15" && w.Version != "3.16" {
		return fmt.Errorf("unsupported workflow version: %s (expected 3.6, 3.7, 3.8, 3.9, 3.10, 3.12, 3.13, 3.14, 3.15, or 3.16)", w.Version)
	}

	if w.Name == "" {
		return fmt.Errorf("workflow name is required")
	}

	if len(w.Steps) == 0 {
		return fmt.Errorf("workflow must have at least one step")
	}

	// Validate registry
	if err := w.Registry.ValidateRegistry(); err != nil {
		return err
	}

	// IDE scenario validation (v3.9+): forbid Service_* nodes
	if w.WorkflowType == WorkflowTypeIDE {
		// Check that no Service_* nodes exist in steps
		for _, step := range w.Steps {
			if strings.HasPrefix(step.ID, "Service_") {
				return fmt.Errorf("IDE workflow (WorkflowType: IDE) cannot contain Service_* nodes: %s", step.ID)
			}
		}
		// Check that registry.services is empty
		if len(w.Registry.Services) > 0 {
			return fmt.Errorf("IDE workflow (WorkflowType: IDE) must have empty registry.services")
		}
	}

	// ── Phase 1: Build stepID set, check uniqueness and basic field constraints ──────────
	stepIDs := make(map[string]bool)
	for _, step := range w.Steps {
		if stepIDs[step.ID] {
			return fmt.Errorf("duplicate step ID: %s", step.ID)
		}
		// v3.16+: BREAK and RETURN are reserved keywords, cannot be used as stepId
		if step.ID == "BREAK" {
			return fmt.Errorf("'BREAK' is a reserved keyword and cannot be used as a step ID")
		}
		if step.ID == "RETURN" {
			return fmt.Errorf("'RETURN' is a reserved keyword and cannot be used as a step ID")
		}
		stepIDs[step.ID] = true

		// Stop_* must NOT have next or children (spec §2.3.4)
		if strings.HasPrefix(step.ID, "Stop_") {
			if step.Next != "" {
				return fmt.Errorf("step %s: Stop_* steps cannot have a 'next' field (spec §2.3.4)", step.ID)
			}
			if len(step.Children) > 0 {
				return fmt.Errorf("step %s: Stop_* steps cannot have 'children' (spec §2.3.4)", step.ID)
			}
		} else {
			// All other steps must declare a 'next' field
			if step.Next == "" {
				return fmt.Errorf("step %s must have a 'next' field (use 'RETURN' for child/loop steps)", step.ID)
			}
		}
	}

	// ── Phase 2: Reference integrity (spec §2.3.3) ────────────────────────────────────
	// Every next / children / cases / timeout.on / onError value must resolve to an
	// existing step ID (or the special sentinels "RETURN" / "BREAK").
	for _, step := range w.Steps {
		check := func(fieldName, target string) error {
			if target == "" || target == "RETURN" || target == "BREAK" {
				return nil
			}
			if !stepIDs[target] {
				return fmt.Errorf("step %s: %s references non-existent step %q", step.ID, fieldName, target)
			}
			return nil
		}
		if err := check("next", step.Next); err != nil {
			return err
		}
		for i, childID := range step.Children {
			if err := check(fmt.Sprintf("children[%d]", i), childID); err != nil {
				return err
			}
		}
		for i, c := range step.Cases {
			if len(c) == 2 {
				if err := check(fmt.Sprintf("cases[%d]", i), c[1]); err != nil {
					return err
				}
			}
		}
		if step.Timeout != nil {
			if err := check("timeout.on", step.Timeout.On); err != nil {
				return err
			}
		}
		if err := check("onError", step.OnError); err != nil {
			return err
		}
	}

	// ── Phase 2b: BREAK scope validation (v3.16+) ─────────────────────────────────────
	// BREAK is only valid inside a Loop_* children subtree.
	// Build the set of stepIDs that are transitively reachable from any Loop_* children entry.
	loopChildren := make(map[string]bool)
	for _, step := range w.Steps {
		if !strings.HasPrefix(step.ID, "Loop_") || len(step.Children) == 0 {
			continue
		}
		// BFS from this Loop_*'s children entries
		visited := make(map[string]bool)
		bfsQueue := make([]string, len(step.Children))
		copy(bfsQueue, step.Children)
		for _, id := range step.Children {
			visited[id] = true
		}
		for len(bfsQueue) > 0 {
			cur := bfsQueue[0]
			bfsQueue = bfsQueue[1:]
			loopChildren[cur] = true
			// Find the step and add its successors (skip RETURN/BREAK which terminate)
			for _, s := range w.Steps {
				if s.ID != cur {
					continue
				}
				succs := []string{s.Next, s.OnError}
				succs = append(succs, s.Children...)
				for _, c := range s.Cases {
					if len(c) == 2 {
						succs = append(succs, c[1])
					}
				}
				if s.Timeout != nil {
					succs = append(succs, s.Timeout.On)
				}
				for _, sid := range succs {
					if sid == "" || sid == "RETURN" || sid == "BREAK" || visited[sid] {
						continue
					}
					visited[sid] = true
					bfsQueue = append(bfsQueue, sid)
				}
				break
			}
		}
	}
	// Verify every step with next:"BREAK" is inside a Loop_* children subtree
	for _, step := range w.Steps {
		if step.Next == "BREAK" && !loopChildren[step.ID] {
			return fmt.Errorf("step %s: 'BREAK' is only valid inside a Loop_* children subtree", step.ID)
		}
		// Also check Branch cases that target BREAK-reachable steps
		for _, c := range step.Cases {
			if len(c) == 2 && c[1] == "BREAK" && !loopChildren[step.ID] {
				return fmt.Errorf("step %s: BREAK target in cases is only valid inside a Loop_* children subtree", step.ID)
			}
		}
	}

	// ── Phase 3: Entry node validation (spec §2.3.1) ──────────────────────────────────
	entryNodeIDs := findEntryNodeIDs(w.Steps)
	if len(entryNodeIDs) == 0 {
		return fmt.Errorf("workflow graph has no entry node: every step is referenced by another step, creating a cycle with no starting point")
	}

	// ── Phase 4: Reachability (spec §2.3.2) ───────────────────────────────────────────
	// All steps must be reachable from at least one entry node via BFS.
	reachable := make(map[string]bool)
	queue := make([]string, len(entryNodeIDs))
	copy(queue, entryNodeIDs)
	for _, id := range entryNodeIDs {
		reachable[id] = true
	}
	for len(queue) > 0 {
		curr := queue[0]
		queue = queue[1:]
		// Find step (linear scan is fine at validation time)
		for _, step := range w.Steps {
			if step.ID != curr {
				continue
			}
			successors := []string{step.Next, step.OnError}
			successors = append(successors, step.Children...)
			for _, c := range step.Cases {
				if len(c) == 2 {
					successors = append(successors, c[1])
				}
			}
			if step.Timeout != nil {
				successors = append(successors, step.Timeout.On)
			}
			for _, s := range successors {
				if s != "" && s != "RETURN" && s != "BREAK" && !reachable[s] {
					reachable[s] = true
					queue = append(queue, s)
				}
			}
			break
		}
	}
	for _, step := range w.Steps {
		if !reachable[step.ID] {
			return fmt.Errorf("step %s is unreachable from any entry node (spec §2.3.2)", step.ID)
		}
	}

	// Validate Download_* and Unzip_* field constraints (v3.14+)
	for _, step := range w.Steps {
		if strings.HasPrefix(step.ID, "Download_") {
			// source is required
			if step.Source == nil {
				return fmt.Errorf("step %s: 'source' is required for Download_* steps", step.ID)
			}
			// target and routeByExt/defaultDir are mutually exclusive; at least one is required
			hasTarget := step.Target != ""
			hasRoute := len(step.RouteByExt) > 0 || step.DefaultDir != ""
			if hasTarget && hasRoute {
				return fmt.Errorf("step %s: 'target' and 'routeByExt'/'defaultDir' are mutually exclusive for Download_* steps", step.ID)
			}
			if !hasTarget && !hasRoute {
				return fmt.Errorf("step %s: Download_* steps must specify either 'target' or 'routeByExt'/'defaultDir'", step.ID)
			}
		}

		if strings.HasPrefix(step.ID, "Unzip_") {
			// source is required
			if step.Source == nil {
				return fmt.Errorf("step %s: 'source' is required for Unzip_* steps", step.ID)
			}
			// routeByExt is required (may be empty map {} combined with defaultDir, but the field must be declared)
			if step.RouteByExt == nil {
				return fmt.Errorf("step %s: 'routeByExt' is required for Unzip_* steps (use {} with 'defaultDir' to route all files to one directory)", step.ID)
			}
		}

		if strings.HasPrefix(step.ID, "Pause_") {
			// resumeResultTarget is required (spec §5.1, §11.2.1)
			if step.ResumeResultTarget == "" {
				return fmt.Errorf("step %s: 'resumeResultTarget' is required for Pause_* steps", step.ID)
			}
			// children is not applicable for Pause_* (spec §5.1: 不适用)
			if len(step.Children) > 0 {
				return fmt.Errorf("step %s: 'children' is not supported on Pause_* steps (spec §5.1)", step.ID)
			}
			// If timeout is provided, sec must be > 0 and on must be non-empty (spec §11.2.2)
			if step.Timeout != nil {
				if step.Timeout.Sec <= 0 {
					return fmt.Errorf("step %s: timeout.sec must be > 0 for Pause_* steps", step.ID)
				}
				if step.Timeout.On == "" {
					return fmt.Errorf("step %s: timeout.on is required when timeout is configured for Pause_* steps", step.ID)
				}
			}
		}

		// v3.16+: Loop_* field constraints
		if strings.HasPrefix(step.ID, "Loop_") {
			hasWhile := step.While != ""
			hasSource := step.Source != nil
			// source is interface{} — also check string form
			if sourceStr, ok := step.Source.(string); ok && sourceStr == "" {
				hasSource = false
			}

			// while and source both present → ERROR
			if hasWhile && hasSource {
				return fmt.Errorf("step %s: 'while' and 'source' are mutually exclusive on Loop_* steps", step.ID)
			}
			// while without maxIterations → ERROR
			if hasWhile && step.MaxIterations == nil {
				return fmt.Errorf("step %s: 'maxIterations' is required when 'while' is used on Loop_* steps", step.ID)
			}
			// maxIterations < 1 → ERROR
			if step.MaxIterations != nil && *step.MaxIterations < 1 {
				return fmt.Errorf("step %s: 'maxIterations' must be >= 1, got %d", step.ID, *step.MaxIterations)
			}
			// while + mode:"parallel" → ERROR
			if hasWhile && step.Mode == "parallel" {
				return fmt.Errorf("step %s: 'while' mode requires mode 'serial', got 'parallel'", step.ID)
			}
		}

		// v3.16+: LLM_* model field validation
		if strings.HasPrefix(step.ID, "LLM_") && step.Model != "" {
			// model contains "/" but provider or modelId part is empty → ERROR
			if strings.Contains(step.Model, "/") {
				parts := strings.SplitN(step.Model, "/", 2)
				if parts[0] == "" || parts[1] == "" {
					return fmt.Errorf("step %s: 'model' with '/' must have non-empty provider and modelId (got %q)", step.ID, step.Model)
				}
			}
		}
	}

	return nil
}

// generateWorkflowID generates a unique workflow execution ID
func generateWorkflowID() string {
	return fmt.Sprintf("wf_%d", time.Now().UnixNano())
}

// findEntryNodeIDs returns the IDs of all "entry" nodes in a step list.
// An entry node is one whose ID does not appear in any other step's
// next / children / cases / timeout.on / onError fields.
// Spec §1.4C: the engine auto-identifies entry nodes; it MUST NOT always use steps[0].
func findEntryNodeIDs(steps []Step) []string {
	referenced := make(map[string]bool)
	for _, step := range steps {
		if step.Next != "" && step.Next != "RETURN" && step.Next != "BREAK" {
			referenced[step.Next] = true
		}
		for _, childID := range step.Children {
			referenced[childID] = true
		}
		for _, c := range step.Cases {
			if len(c) == 2 {
				referenced[c[1]] = true
			}
		}
		if step.Timeout != nil && step.Timeout.On != "" {
			referenced[step.Timeout.On] = true
		}
		if step.OnError != "" {
			referenced[step.OnError] = true
		}
	}
	var entries []string
	for _, step := range steps {
		if !referenced[step.ID] {
			entries = append(entries, step.ID)
		}
	}
	return entries
}