package postgres

import (
	"context"
	"fmt"
	"sync"
	"time"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgconn"
	"github.com/jackc/pgx/v5/pgxpool"

	"code.nochebuena.dev/einherjar/contracts/logging"
	"code.nochebuena.dev/einherjar/contracts/observability"
	"code.nochebuena.dev/einherjar/core/xerrors"
)

// Compile-time interface verification (I-8 / CT-5).
var _ Component = (*pgComponent)(nil)
var _ observability.Identifiable = (*pgComponent)(nil)
var _ Tx = (*pgTx)(nil)
var _ UnitOfWork = (*unitOfWork)(nil)

// New returns a Component backed by the given configuration.
// The pool is not created until OnInit is called.
func New(logger logging.Logger, cfg Config) Component {
	return &pgComponent{logger: logger, cfg: cfg}
}

// NewUnitOfWork returns a UnitOfWork backed by the given client.
func NewUnitOfWork(logger logging.Logger, client Provider) UnitOfWork {
	return &unitOfWork{logger: logger, client: client}
}

// ctxTxKey is the context key for the active transaction.
type ctxTxKey struct{}

// --- pgComponent ---

type pgComponent struct {
	logger logging.Logger
	cfg    Config
	pool   *pgxpool.Pool
	mu     sync.RWMutex
}

func (c *pgComponent) OnInit() error {
	poolCfg, err := c.buildPoolConfig()
	if err != nil {
		return xerrors.New(xerrors.ErrInvalidInput, "postgres: parse config").WithError(err)
	}
	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()
	pool, err := pgxpool.NewWithConfig(ctx, poolCfg)
	if err != nil {
		c.logger.Error("postgres: failed to create pool", err)
		return xerrors.New(xerrors.ErrInternal, "postgres: create pool").WithError(err)
	}
	c.mu.Lock()
	c.pool = pool
	c.mu.Unlock()
	return nil
}

func (c *pgComponent) OnStart() error {
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	if err := c.Ping(ctx); err != nil {
		return xerrors.New(xerrors.ErrUnavailable, "postgres: ping failed").WithError(err)
	}
	c.logger.Info("postgres: connected")
	return nil
}

func (c *pgComponent) OnStop() error {
	c.mu.Lock()
	defer c.mu.Unlock()
	if c.pool != nil {
		c.logger.Info("postgres: closing pool")
		c.pool.Close()
		c.pool = nil
	}
	return nil
}

func (c *pgComponent) Ping(ctx context.Context) error {
	c.mu.RLock()
	pool := c.pool
	c.mu.RUnlock()
	if pool == nil {
		return xerrors.New(xerrors.ErrInternal, "postgres: pool not initialized")
	}
	return pool.Ping(ctx)
}

func (c *pgComponent) GetExecutor(ctx context.Context) Executor {
	if tx, ok := ctx.Value(ctxTxKey{}).(Executor); ok {
		return tx
	}
	c.mu.RLock()
	pool := c.pool
	c.mu.RUnlock()
	return pool
}

func (c *pgComponent) BeginTx(ctx context.Context, opts pgx.TxOptions) (Tx, error) {
	c.mu.RLock()
	pool := c.pool
	c.mu.RUnlock()
	if pool == nil {
		return nil, xerrors.New(xerrors.ErrInternal, "postgres: pool not initialized")
	}
	tx, err := pool.BeginTx(ctx, opts)
	if err != nil {
		return nil, xerrors.New(xerrors.ErrInternal, "postgres: begin transaction").WithError(err)
	}
	return &pgTx{Tx: tx}, nil
}

func (c *pgComponent) Begin(ctx context.Context) (Tx, error) {
	return c.BeginTx(ctx, pgx.TxOptions{})
}

func (c *pgComponent) Stats() *pgxpool.Stat {
	c.mu.RLock()
	pool := c.pool
	c.mu.RUnlock()
	if pool == nil {
		return &pgxpool.Stat{}
	}
	return pool.Stat()
}

func (c *pgComponent) Exec(ctx context.Context, sql string, args ...any) (pgconn.CommandTag, error) {
	c.mu.RLock()
	pool := c.pool
	c.mu.RUnlock()
	return pool.Exec(ctx, sql, args...)
}

func (c *pgComponent) Query(ctx context.Context, sql string, args ...any) (pgx.Rows, error) {
	c.mu.RLock()
	pool := c.pool
	c.mu.RUnlock()
	return pool.Query(ctx, sql, args...)
}

func (c *pgComponent) QueryRow(ctx context.Context, sql string, args ...any) pgx.Row {
	c.mu.RLock()
	pool := c.pool
	c.mu.RUnlock()
	return pool.QueryRow(ctx, sql, args...)
}

func (c *pgComponent) HandleError(err error) error { return HandleError(err) }

func (c *pgComponent) HealthCheck(ctx context.Context) error { return c.Ping(ctx) }
func (c *pgComponent) Name() string                          { return "postgres" }
func (c *pgComponent) Priority() observability.Level         { return observability.LevelCritical }

func (c *pgComponent) buildPoolConfig() (*pgxpool.Config, error) {
	cfg, err := pgxpool.ParseConfig(c.cfg.DSN())
	if err != nil {
		return nil, err
	}
	cfg.MaxConns = int32(c.cfg.MaxConns)
	cfg.MinConns = int32(c.cfg.MinConns)
	if c.cfg.MaxConnLifetime != "" {
		d, err := time.ParseDuration(c.cfg.MaxConnLifetime)
		if err != nil {
			return nil, fmt.Errorf("PG_MAX_CONN_LIFETIME: %w", err)
		}
		cfg.MaxConnLifetime = d
	}
	if c.cfg.MaxConnIdleTime != "" {
		d, err := time.ParseDuration(c.cfg.MaxConnIdleTime)
		if err != nil {
			return nil, fmt.Errorf("PG_MAX_CONN_IDLE_TIME: %w", err)
		}
		cfg.MaxConnIdleTime = d
	}
	if c.cfg.HealthCheckPeriod != "" {
		d, err := time.ParseDuration(c.cfg.HealthCheckPeriod)
		if err != nil {
			return nil, fmt.Errorf("PG_HEALTH_CHECK_PERIOD: %w", err)
		}
		cfg.HealthCheckPeriod = d
	}
	return cfg, nil
}

// --- pgTx ---

type pgTx struct{ pgx.Tx }

func (t *pgTx) Exec(ctx context.Context, sql string, args ...any) (pgconn.CommandTag, error) {
	return t.Tx.Exec(ctx, sql, args...)
}

func (t *pgTx) Query(ctx context.Context, sql string, args ...any) (pgx.Rows, error) {
	return t.Tx.Query(ctx, sql, args...)
}

func (t *pgTx) QueryRow(ctx context.Context, sql string, args ...any) pgx.Row {
	return t.Tx.QueryRow(ctx, sql, args...)
}

func (t *pgTx) Commit(ctx context.Context) error   { return t.Tx.Commit(ctx) }
func (t *pgTx) Rollback(ctx context.Context) error { return t.Tx.Rollback(ctx) }

// --- unitOfWork ---

type unitOfWork struct {
	logger logging.Logger
	client Provider
}

func (u *unitOfWork) Do(ctx context.Context, fn func(ctx context.Context) error) error {
	tx, err := u.client.Begin(ctx)
	if err != nil {
		return xerrors.New(xerrors.ErrInternal, "postgres: begin transaction").WithError(err)
	}
	ctx = context.WithValue(ctx, ctxTxKey{}, tx)
	if err := fn(ctx); err != nil {
		if rbErr := tx.Rollback(ctx); rbErr != nil {
			u.logger.Error("postgres: rollback failed", rbErr)
		}
		return err
	}
	return tx.Commit(ctx)
}