package task

import (
	"database/sql"
	"encoding/json"
	"fmt"
	"sync"
	"time"

	_ "github.com/mattn/go-sqlite3"
)

// Store manages task state persistence with SQLite.
type Store struct {
	mu sync.Mutex
	db *sql.DB
}

// NewStore creates a new task store.
func NewStore(dbPath string) (*Store, error) {
	db, err := sql.Open("sqlite3", dbPath)
	if err != nil {
		return nil, fmt.Errorf("open task db: %w", err)
	}

	if err := initTaskDB(db); err != nil {
		return nil, fmt.Errorf("init task db: %w", err)
	}

	return &Store{db: db}, nil
}

func initTaskDB(db *sql.DB) error {
	schema := `
	CREATE TABLE IF NOT EXISTS tasks (
		id TEXT PRIMARY KEY,
		request_id TEXT NOT NULL,
		session_id TEXT,
		app_id TEXT NOT NULL,
		tenant_id TEXT NOT NULL,
		logical_model TEXT NOT NULL,
		actual_model TEXT,
		priority INTEGER NOT NULL DEFAULT 2,
		state TEXT NOT NULL,
		stream INTEGER NOT NULL DEFAULT 0,
		created_at TEXT NOT NULL,
		started_at TEXT,
		completed_at TEXT,
		cancel_reason TEXT,
		error_message TEXT,
		input_tokens INTEGER DEFAULT 0,
		output_tokens INTEGER DEFAULT 0,
		node_id TEXT,
		degraded INTEGER DEFAULT 0
	);
	CREATE INDEX IF NOT EXISTS idx_tasks_state ON tasks(state);
	CREATE INDEX IF NOT EXISTS idx_tasks_app ON tasks(app_id);
	CREATE INDEX IF NOT EXISTS idx_tasks_tenant ON tasks(tenant_id);`
	_, err := db.Exec(schema)
	return err
}

// Save persists a task to the database.
func (s *Store) Save(t *Task) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	var startedAt, completedAt interface{}
	if t.StartedAt != nil {
		startedAt = t.StartedAt.Format(time.RFC3339)
	}
	if t.CompletedAt != nil {
		completedAt = t.CompletedAt.Format(time.RFC3339)
	}

	streamInt := 0
	if t.Stream {
		streamInt = 1
	}
	degradedInt := 0
	if t.Degraded {
		degradedInt = 1
	}

	_, err := s.db.Exec(
		`INSERT OR REPLACE INTO tasks
		(id, request_id, session_id, app_id, tenant_id, logical_model, actual_model, priority, state, stream, created_at, started_at, completed_at, cancel_reason, error_message, input_tokens, output_tokens, node_id, degraded)
		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
		t.ID, t.RequestID, t.SessionID, t.AppID, t.TenantID, t.LogicalModel, t.ActualModel,
		int(t.Priority), string(t.State), streamInt, t.CreatedAt.Format(time.RFC3339),
		startedAt, completedAt, t.CancelReason, t.ErrorMessage,
		t.InputTokens, t.OutputTokens, t.NodeID, degradedInt,
	)
	return err
}

// Get retrieves a task by ID.
func (s *Store) Get(id string) (*Task, error) {
	s.mu.Lock()
	defer s.mu.Unlock()

	var (
		requestID, sessionID, appID, tenantID, logicalModel, actualModel, state  string
		priority                                                                 int
		streamInt                                                                int
		createdAtStr, startedAt, completedAt, cancelReason, errorMessage, nodeID sql.NullString
		inputTokens, outputTokens, degradedInt                                   int
	)

	err := s.db.QueryRow(
		`SELECT request_id, session_id, app_id, tenant_id, logical_model, actual_model, priority, state, stream, created_at, started_at, completed_at, cancel_reason, error_message, input_tokens, output_tokens, node_id, degraded FROM tasks WHERE id = ?`,
		id,
	).Scan(&requestID, &sessionID, &appID, &tenantID, &logicalModel, &actualModel, &priority, &state, &streamInt, &createdAtStr, &startedAt, &completedAt, &cancelReason, &errorMessage, &inputTokens, &outputTokens, &nodeID, &degradedInt)

	if err == sql.ErrNoRows {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}

	t := &Task{
		ID:           id,
		RequestID:    requestID,
		SessionID:    sessionID,
		AppID:        appID,
		TenantID:     tenantID,
		LogicalModel: logicalModel,
		ActualModel:  actualModel,
		Priority:     TaskPriority(priority),
		State:        TaskState(state),
		Stream:       streamInt == 1,
		InputTokens:  inputTokens,
		OutputTokens: outputTokens,
		NodeID:       nodeID.String,
		Degraded:     degradedInt == 1,
		CancelReason: cancelReason.String,
		ErrorMessage: errorMessage.String,
		cancelCh:     make(chan struct{}),
	}
	t.CreatedAt, _ = time.Parse(time.RFC3339, createdAtStr.String)
	if startedAt.Valid {
		tt, _ := time.Parse(time.RFC3339, startedAt.String)
		t.StartedAt = &tt
	}
	if completedAt.Valid {
		tt, _ := time.Parse(time.RFC3339, completedAt.String)
		t.CompletedAt = &tt
	}

	return t, nil
}

// RecoverPendingTasks marks RUNNING/STREAMING tasks as FAILED on startup.
func (s *Store) RecoverPendingTasks() (int, error) {
	s.mu.Lock()
	defer s.mu.Unlock()

	result, err := s.db.Exec(
		`UPDATE tasks SET state = 'FAILED', error_message = 'gateway restart' WHERE state IN ('RUNNING', 'STREAMING', 'QUEUED')`)
	if err != nil {
		return 0, err
	}
	n, _ := result.RowsAffected()
	return int(n), nil
}

// Close closes the database connection.
func (s *Store) Close() error {
	return s.db.Close()
}

// Ensure json is imported for future use.
var _ = json.Marshal