package main

import (
	"context"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"fn-registry/functions/core"
	"fn-registry/functions/infra"

	"dag-engine/store"
)

// Executor orchestrates DAG parsing, validation, and execution.
type Executor struct {
	store   *store.DB
	dagsDir string
}

// NewExecutor creates a new executor.
func NewExecutor(s *store.DB, dagsDir string) *Executor {
	return &Executor{store: s, dagsDir: dagsDir}
}

// ExecuteDAG runs a DAG from a YAML file path and returns the run ID.
// It runs asynchronously: steps execute in topological order with parallel levels.
func (e *Executor) ExecuteDAG(ctx context.Context, dagPath string, trigger string) (string, error) {
	data, err := os.ReadFile(dagPath)
	if err != nil {
		return "", fmt.Errorf("read dag: %w", err)
	}

	dag, err := core.DagParse(data)
	if err != nil {
		return "", fmt.Errorf("parse dag: %w", err)
	}
	dag.FilePath = dagPath

	// Resolve env variables.
	dag = core.DagResolveEnv(dag, os.Environ())

	// Validate.
	result := core.DagValidate(dag)
	if !result.Valid {
		return "", fmt.Errorf("validate dag: %s", strings.Join(result.Errors, "; "))
	}

	// Create run record.
	runID := generateID()
	now := time.Now()
	run := &store.DagRun{
		ID:        runID,
		DagName:   dag.Name,
		DagPath:   dagPath,
		Status:    "running",
		Trigger:   trigger,
		StartedAt: now,
	}
	if err := e.store.CreateRun(run); err != nil {
		return "", fmt.Errorf("create run: %w", err)
	}

	// Topological sort.
	levels, err := core.DagTopoSort(dag.Steps)
	if err != nil {
		e.failRun(runID, err)
		return runID, err
	}

	// Setup DAGU_ENV temp file for inter-step communication.
	daguEnvFile, err := os.CreateTemp("", "dagu_env_*")
	if err != nil {
		e.failRun(runID, err)
		return runID, err
	}
	daguEnvPath := daguEnvFile.Name()
	daguEnvFile.Close()
	defer os.Remove(daguEnvPath)

	// Track step outputs for ${step_id.stdout} references.
	stepOutputs := make(map[string]string)

	// Execute levels.
	runFailed := false
	var runErr error

	for _, level := range levels {
		if runFailed {
			// Skip remaining levels, mark steps as skipped.
			for _, step := range level {
				e.recordStepSkipped(runID, step)
			}
			continue
		}

		var wg sync.WaitGroup
		var mu sync.Mutex
		levelFailed := false

		for _, step := range level {
			step := step
			wg.Add(1)
			go func() {
				defer wg.Done()

				mu.Lock()
				if levelFailed {
					mu.Unlock()
					e.recordStepSkipped(runID, step)
					return
				}
				mu.Unlock()

				err := e.executeStep(ctx, runID, dag, step, daguEnvPath, stepOutputs, &mu)
				if err != nil && !step.ContinueOn.Failure {
					mu.Lock()
					levelFailed = true
					runFailed = true
					runErr = fmt.Errorf("step %q failed: %w", stepName(step), err)
					mu.Unlock()
				}
			}()
		}
		wg.Wait()
	}

	// Run handlers.
	if runFailed {
		e.runHandlers(ctx, runID, dag, dag.HandlerOn.Failure, daguEnvPath, stepOutputs)
	} else {
		e.runHandlers(ctx, runID, dag, dag.HandlerOn.Success, daguEnvPath, stepOutputs)
	}
	e.runHandlers(ctx, runID, dag, dag.HandlerOn.Exit, daguEnvPath, stepOutputs)

	// Finalize run.
	fin := time.Now()
	status := "success"
	errMsg := ""
	if runFailed {
		status = "failed"
		if runErr != nil {
			errMsg = runErr.Error()
		}
	}
	e.store.UpdateRunStatus(runID, status, &fin, errMsg)

	return runID, runErr
}

// executeStep runs a single step, recording results in the store.
func (e *Executor) executeStep(ctx context.Context, runID string, dag core.DagDefinition, step core.DagStep, daguEnvPath string, outputs map[string]string, mu *sync.Mutex) error {
	stepID := generateID()
	now := time.Now()
	e.store.InsertStepResult(&store.DagStepResult{
		ID:        stepID,
		RunID:     runID,
		StepName:  stepName(step),
		Status:    "running",
		StartedAt: &now,
	})

	// Build environment.
	env := buildStepEnv(dag, step, daguEnvPath, outputs)

	// Determine command.
	command := step.Command
	if command == "" && step.Script != "" {
		command = step.Script
	}
	if command == "" {
		e.store.UpdateStepResult(stepID, "skipped", 0, "", "", nil, 0, "no command or script")
		return nil
	}

	// Resolve step-level ${VAR} references and ${step_id.stdout} patterns.
	mu.Lock()
	command = resolveStepRefs(command, outputs)
	mu.Unlock()

	// Determine working directory.
	dir := step.Dir
	if dir == "" {
		dir = dag.WorkingDir
	}

	shell := step.Shell
	if shell == "" {
		shell = dag.Shell
	}

	// Spawn process.
	handle, err := infra.ProcessSpawn(command, dir, env, shell)
	if err != nil {
		fin := time.Now()
		e.store.UpdateStepResult(stepID, "failed", -1, "", "", &fin, time.Since(now).Milliseconds(), err.Error())
		return err
	}

	// Wait for process.
	result, err := infra.ProcessWait(handle, step.TimeoutSec)
	fin := time.Now()
	duration := time.Since(now).Milliseconds()

	if err != nil && result.ExitCode == 0 {
		result.ExitCode = -1
	}

	status := "success"
	errMsg := ""
	if result.ExitCode != 0 || err != nil {
		status = "failed"
		if err != nil {
			errMsg = err.Error()
		}
	}

	e.store.UpdateStepResult(stepID, status, result.ExitCode, result.Stdout, result.Stderr, &fin, duration, errMsg)

	// Store output for ${step_id.stdout} references.
	if step.ID != "" || step.Output != "" {
		mu.Lock()
		key := step.ID
		if key == "" {
			key = step.Output
		}
		outputs[key] = strings.TrimSpace(result.Stdout)
		mu.Unlock()
	}

	// Read DAGU_ENV for inter-step env propagation.
	readDaguEnv(daguEnvPath, outputs)

	if status == "failed" {
		return fmt.Errorf("exit code %d", result.ExitCode)
	}
	return nil
}

func (e *Executor) runHandlers(ctx context.Context, runID string, dag core.DagDefinition, handlers []core.DagStep, daguEnvPath string, outputs map[string]string) {
	var mu sync.Mutex
	for _, step := range handlers {
		e.executeStep(ctx, runID, dag, step, daguEnvPath, outputs, &mu)
	}
}

func (e *Executor) failRun(runID string, err error) {
	fin := time.Now()
	e.store.UpdateRunStatus(runID, "failed", &fin, err.Error())
}

func (e *Executor) recordStepSkipped(runID string, step core.DagStep) {
	now := time.Now()
	e.store.InsertStepResult(&store.DagStepResult{
		ID:       generateID(),
		RunID:    runID,
		StepName: stepName(step),
		Status:   "skipped",
		StartedAt: &now,
	})
}

// --- helpers ---

func stepName(s core.DagStep) string {
	if s.Name != "" {
		return s.Name
	}
	return s.ID
}

func buildStepEnv(dag core.DagDefinition, step core.DagStep, daguEnvPath string, outputs map[string]string) []string {
	env := os.Environ()

	// Add DAG-level env.
	for k, v := range dag.Env {
		env = append(env, k+"="+v)
	}

	// Add step-level env.
	for k, v := range step.Env {
		env = append(env, k+"="+v)
	}

	// Add DAGU_ENV path.
	env = append(env, "DAGU_ENV="+daguEnvPath)

	return env
}

func resolveStepRefs(command string, outputs map[string]string) string {
	for k, v := range outputs {
		command = strings.ReplaceAll(command, "${"+k+".stdout}", v)
		command = strings.ReplaceAll(command, "$"+k+".stdout", v)
	}
	return command
}

func readDaguEnv(path string, outputs map[string]string) {
	data, err := os.ReadFile(path)
	if err != nil || len(data) == 0 {
		return
	}
	for _, line := range strings.Split(string(data), "\n") {
		line = strings.TrimSpace(line)
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		parts := strings.SplitN(line, "=", 2)
		if len(parts) == 2 {
			outputs[parts[0]] = parts[1]
		}
	}
}

// generateID creates a simple time-based unique ID.
func generateID() string {
	return fmt.Sprintf("%d-%04x", time.Now().UnixNano(), time.Now().Nanosecond()%0xFFFF)
}

// --- DAG listing helpers ---

// DagInfo summarizes a DAG file for listing.
type DagInfo struct {
	Name        string   `json:"name"`
	Description string   `json:"description,omitempty"`
	Schedule    []string `json:"schedule,omitempty"`
	Tags        []string `json:"tags,omitempty"`
	Type        string   `json:"type,omitempty"`
	FilePath    string   `json:"file_path"`
	Valid       bool     `json:"valid"`
	LastRun     *store.DagRun `json:"last_run,omitempty"`
}

// ListDAGs scans a directory for YAML files and returns parsed DAG info.
func (e *Executor) ListDAGs() ([]DagInfo, error) {
	entries, err := os.ReadDir(e.dagsDir)
	if err != nil {
		return nil, fmt.Errorf("read dags dir: %w", err)
	}

	var dags []DagInfo
	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}
		ext := filepath.Ext(entry.Name())
		if ext != ".yaml" && ext != ".yml" {
			continue
		}

		path := filepath.Join(e.dagsDir, entry.Name())
		data, err := os.ReadFile(path)
		if err != nil {
			continue
		}

		dag, err := core.DagParse(data)
		if err != nil {
			dags = append(dags, DagInfo{
				Name:     strings.TrimSuffix(entry.Name(), ext),
				FilePath: path,
				Valid:    false,
			})
			continue
		}

		info := DagInfo{
			Name:        dag.Name,
			Description: dag.Description,
			Schedule:    dag.Schedule,
			Tags:        dag.Tags,
			Type:        dag.Type,
			FilePath:    path,
			Valid:       true,
		}

		// Attach last run info.
		runs, _, _ := e.store.ListRuns(dag.Name, 1, 0)
		if len(runs) > 0 {
			info.LastRun = &runs[0]
		}

		dags = append(dags, info)
	}

	return dags, nil
}

// GetDAG returns detailed info for a specific DAG by name.
func (e *Executor) GetDAG(name string) (*DagInfo, *core.DagDefinition, *core.DagValidationResult, error) {
	// Find the YAML file.
	entries, err := os.ReadDir(e.dagsDir)
	if err != nil {
		return nil, nil, nil, err
	}

	for _, entry := range entries {
		ext := filepath.Ext(entry.Name())
		base := strings.TrimSuffix(entry.Name(), ext)
		if (ext != ".yaml" && ext != ".yml") || base != name {
			continue
		}

		path := filepath.Join(e.dagsDir, entry.Name())
		data, err := os.ReadFile(path)
		if err != nil {
			return nil, nil, nil, err
		}

		dag, err := core.DagParse(data)
		if err != nil {
			return nil, nil, nil, fmt.Errorf("parse: %w", err)
		}
		dag.FilePath = path

		validationResult := core.DagValidate(dag)

		info := &DagInfo{
			Name:        dag.Name,
			Description: dag.Description,
			Schedule:    dag.Schedule,
			Tags:        dag.Tags,
			Type:        dag.Type,
			FilePath:    path,
			Valid:       validationResult.Valid,
		}

		runs, _, _ := e.store.ListRuns(dag.Name, 1, 0)
		if len(runs) > 0 {
			info.LastRun = &runs[0]
		}

		return info, &dag, &validationResult, nil
	}

	return nil, nil, nil, fmt.Errorf("dag %q not found in %s", name, e.dagsDir)
}

// ValidateDAG parses and validates a DAG file, printing results.
func ValidateDAG(path string) error {
	data, err := os.ReadFile(path)
	if err != nil {
		return err
	}

	dag, err := core.DagParse(data)
	if err != nil {
		return fmt.Errorf("parse error: %w", err)
	}

	result := core.DagValidate(dag)

	log.Printf("DAG: %s", dag.Name)
	log.Printf("Steps: %d", len(dag.Steps))
	log.Printf("Schedule: %v", dag.Schedule)

	if result.Valid {
		log.Printf("Validation: PASS")
		log.Printf("Topological levels: %d", len(result.Levels))
		for i, level := range result.Levels {
			log.Printf("  Level %d: %v", i, level)
		}
	} else {
		log.Printf("Validation: FAIL")
		for _, e := range result.Errors {
			log.Printf("  ERROR: %s", e)
		}
	}
	for _, w := range result.Warnings {
		log.Printf("  WARNING: %s", w)
	}

	if !result.Valid {
		return fmt.Errorf("validation failed")
	}
	return nil
}