package nodes

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"time"

	"github.com/redis/go-redis/v9"

	dbx "github.com/wangjia/pangolin/server/internal/db"
	"github.com/wangjia/pangolin/server/internal/mtls"
	"github.com/wangjia/pangolin/server/internal/store"
)

// ErrInvalidTransition is returned when the requested status transition is not
// permitted by the lifecycle state machine, or when the node's current state
// does not match any valid "from" state (optimistic-lock conflict or illegal move).
var ErrInvalidTransition = errors.New("nodes: invalid lifecycle transition")

// nodeEvent mirrors the nine ENUM values in the node_events.event column (migration 6).
type nodeEvent string

const (
	eventProvisioned      nodeEvent = "provisioned"
	eventMarkedUp         nodeEvent = "marked_up"
	eventDraining         nodeEvent = "draining"
	eventProbeFail        nodeEvent = "probe_fail"
	eventBlockedSuspect   nodeEvent = "blocked_suspect"
	eventBlockedConfirmed nodeEvent = "blocked_confirmed"
	eventDestroyed        nodeEvent = "destroyed"
)

// transitionSpec describes one allowed status move for a Lifecycle method.
// When a method accepts multiple "from" states, specs are tried in order.
type transitionSpec struct {
	from  string
	to    string
	event nodeEvent
}

// Lifecycle drives the node lifecycle state machine.
//
// State machine (doc/04 §3):
//
//	provisioning → probing → up → draining → down → destroyed
//	                     ↘ destroyed (bad IP)
//	                                  ↘ down (skip draining, confirmed block)
//
// Each method executes a single MySQL transaction that:
//  1. UPDATE nodes SET status=<to> WHERE uuid=? AND status=<from>  (optimistic lock)
//  2. INSERT node_events(node_id, event, detail JSON, at)
//  3. BumpVersion(ctx, tx)  — increments the directory_version singleton
//
// MarkDestroyed additionally (after commit) calls mtls.CRL.Revoke and deletes
// the Redis keys node:load:{uuid} and node:cmdq:{uuid}.
//
// Called by #15 (block-detection / drain scheduler) and #14 (provisioning).
type Lifecycle struct {
	db      *sql.DB
	dialect dbx.Dialect
	crl     *mtls.CRL     // for MarkDestroyed post-commit hook
	rdb     redis.Cmdable // for MarkDestroyed post-commit cleanup
}

// NewLifecycle constructs a Lifecycle.
//   - db:  MySQL connection pool (from store.Open)
//   - crl: mTLS revocation manager (task 5b, mtls.NewCRL)
//   - rdb: Redis client or Cmdable (for post-destroy key cleanup)
func NewLifecycle(db *sql.DB, crl *mtls.CRL, rdb redis.Cmdable) *Lifecycle {
	return &Lifecycle{db: db, dialect: dbx.DialectForDB(db), crl: crl, rdb: rdb}
}

// BumpVersion atomically increments the directory_version singleton within tx.
// Delegates to the canonical store.BumpDirectoryVersion (dialect-aware).
func BumpVersion(ctx context.Context, tx *sql.Tx, d dbx.Dialect) error {
	return store.BumpDirectoryVersion(ctx, tx, d)
}

// MarkProbing transitions a node from provisioning → probing.
// Writes a "provisioned" event.
// Called by #14 after the VM passes initial reachability checks.
func (l *Lifecycle) MarkProbing(ctx context.Context, nodeUUID string, detail map[string]any) error {
	return l.transact(ctx, nodeUUID, []transitionSpec{
		{from: "provisioning", to: "probing", event: eventProvisioned},
	}, detail)
}

// MarkUp transitions a node from probing → up, admitting it to the directory.
// Writes a "marked_up" event.
// Called by #15 after initial probes confirm the node is reachable.
func (l *Lifecycle) MarkUp(ctx context.Context, nodeUUID string, detail map[string]any) error {
	return l.transact(ctx, nodeUUID, []transitionSpec{
		{from: "probing", to: "up", event: eventMarkedUp},
	}, detail)
}

// MarkDraining transitions a node from up → draining, removing it from the
// live directory while letting existing connections finish.
// Writes a "draining" event.
// The subsequent draining→down transition is driven by the #15 scheduler timer.
// Called by #15 on sustained suspect signals.
func (l *Lifecycle) MarkDraining(ctx context.Context, nodeUUID string, detail map[string]any) error {
	return l.transact(ctx, nodeUUID, []transitionSpec{
		{from: "up", to: "draining", event: eventDraining},
	}, detail)
}

// MarkDown transitions a node from draining → down or (fast-path) up → down.
// Both paths write a "blocked_confirmed" event.
// The up → down fast-path skips draining when block is immediately confirmed (#15).
// The draining → down path is driven by the drain timer in #15 scheduler.
func (l *Lifecycle) MarkDown(ctx context.Context, nodeUUID string, detail map[string]any) error {
	return l.transact(ctx, nodeUUID, []transitionSpec{
		{from: "draining", to: "down", event: eventBlockedConfirmed},
		{from: "up", to: "down", event: eventBlockedConfirmed},
	}, detail)
}

// MarkDestroyed permanently retires a node.
// Valid from-states:
//   - probing  → destroyed ("probe_fail" event):  bad IP, never entered the pool.
//   - down     → destroyed ("destroyed" event):    normal retirement after draining.
//
// After the DB transaction commits, two post-commit hooks run:
//  1. mtls.CRL.Revoke(nodeUUID)       — marks the node's cert as revoked in Redis.
//  2. Redis DEL node:load:{uuid} and node:cmdq:{uuid} — evicts runtime state.
//
// Called by #14 (failed initial probe) and #15 (retirement scheduler).
func (l *Lifecycle) MarkDestroyed(ctx context.Context, nodeUUID string, detail map[string]any) error {
	if err := l.transact(ctx, nodeUUID, []transitionSpec{
		{from: "probing", to: "destroyed", event: eventProbeFail},
		{from: "down", to: "destroyed", event: eventDestroyed},
	}, detail); err != nil {
		return err
	}

	// Post-commit: revoke mTLS certificate.
	if l.crl != nil {
		if err := l.crl.Revoke(ctx, nodeUUID); err != nil {
			return fmt.Errorf("lifecycle.MarkDestroyed: revoke cert: %w", err)
		}
	}

	// Post-commit: delete runtime Redis keys.
	if l.rdb != nil {
		if err := l.rdb.Del(ctx,
			nodeLoadKeyPrefix+nodeUUID,
			cmdQueuePrefix+nodeUUID,
		).Err(); err != nil {
			return fmt.Errorf("lifecycle.MarkDestroyed: redis del: %w", err)
		}
	}

	return nil
}

// MarkBlockedSuspect does NOT change the node's status.
// It lowers the routing weight to 10, writes a "blocked_suspect" event, and
// bumps the directory version so clients receive a re-weighted catalogue.
//
// Called by #15 on the first domestic-probe failure streak ("疑似" judgement).
func (l *Lifecycle) MarkBlockedSuspect(ctx context.Context, nodeUUID string, detail map[string]any) error {
	tx, err := l.db.BeginTx(ctx, nil)
	if err != nil {
		return fmt.Errorf("lifecycle.MarkBlockedSuspect: begin: %w", err)
	}
	defer tx.Rollback() //nolint:errcheck // no-op after Commit

	// Resolve the node's internal ID — fail fast if UUID is unknown.
	var nodeID int64
	if err := tx.QueryRowContext(ctx,
		`SELECT id FROM nodes WHERE uuid = ?`, nodeUUID,
	).Scan(&nodeID); err == sql.ErrNoRows {
		return ErrInvalidTransition
	} else if err != nil {
		return fmt.Errorf("lifecycle.MarkBlockedSuspect: resolve id: %w", err)
	}

	// Lower routing weight to 10 (idempotent if already ≤ 10).
	if _, err := tx.ExecContext(ctx,
		`UPDATE nodes SET weight = 10 WHERE uuid = ?`, nodeUUID,
	); err != nil {
		return fmt.Errorf("lifecycle.MarkBlockedSuspect: update weight: %w", err)
	}

	// Write the blocked_suspect event.
	detailJSON, err := json.Marshal(detail)
	if err != nil {
		return fmt.Errorf("lifecycle.MarkBlockedSuspect: marshal detail: %w", err)
	}
	if _, err := tx.ExecContext(ctx,
		`INSERT INTO node_events (node_id, event, detail, at) VALUES (?, ?, ?, ?)`,
		nodeID, string(eventBlockedSuspect), detailJSON, time.Now().UTC(),
	); err != nil {
		return fmt.Errorf("lifecycle.MarkBlockedSuspect: insert event: %w", err)
	}

	// Bump directory version.
	if err := BumpVersion(ctx, tx, l.dialect); err != nil {
		return err
	}

	return tx.Commit()
}

// transact attempts each spec in order, all within a single transaction.
//
// The first spec whose UPDATE affects ≥ 1 row "wins": the corresponding event
// is inserted, the directory version is bumped, and the transaction is committed.
//
// If no spec matches (all return 0 rows affected), the transaction is rolled back
// and ErrInvalidTransition is returned.  A 0-row result means either:
//   - The node is in a state that is not a valid "from" for this method (illegal move).
//   - A concurrent writer already advanced the node past the expected "from" state
//     (optimistic-lock conflict: the first writer won; the second sees ErrInvalidTransition).
func (l *Lifecycle) transact(
	ctx context.Context,
	nodeUUID string,
	specs []transitionSpec,
	detail map[string]any,
) error {
	detailJSON, err := json.Marshal(detail)
	if err != nil {
		return fmt.Errorf("lifecycle.transact: marshal detail: %w", err)
	}

	tx, err := l.db.BeginTx(ctx, nil)
	if err != nil {
		return fmt.Errorf("lifecycle.transact: begin: %w", err)
	}
	defer tx.Rollback() //nolint:errcheck // no-op after Commit

	for _, spec := range specs {
		res, err := tx.ExecContext(ctx,
			`UPDATE nodes SET status = ? WHERE uuid = ? AND status = ?`,
			spec.to, nodeUUID, spec.from,
		)
		if err != nil {
			return fmt.Errorf("lifecycle.transact [%s→%s]: %w", spec.from, spec.to, err)
		}
		n, err := res.RowsAffected()
		if err != nil {
			return fmt.Errorf("lifecycle.transact RowsAffected: %w", err)
		}
		if n == 0 {
			continue // from-state mismatch; try next spec
		}

		// Transition succeeded — resolve the internal node_id for the event row.
		var nodeID int64
		if err := tx.QueryRowContext(ctx,
			`SELECT id FROM nodes WHERE uuid = ?`, nodeUUID,
		).Scan(&nodeID); err != nil {
			return fmt.Errorf("lifecycle.transact: resolve node_id after [%s→%s]: %w",
				spec.from, spec.to, err)
		}

		// Insert the event record.
		if _, err := tx.ExecContext(ctx,
			`INSERT INTO node_events (node_id, event, detail, at) VALUES (?, ?, ?, ?)`,
			nodeID, string(spec.event), detailJSON, time.Now().UTC(),
		); err != nil {
			return fmt.Errorf("lifecycle.transact: insert event [%s→%s]: %w",
				spec.from, spec.to, err)
		}

		// Bump the global directory version.
		if err := BumpVersion(ctx, tx, l.dialect); err != nil {
			return err
		}

		return tx.Commit()
	}

	// No spec matched → illegal transition from the node's current state.
	return ErrInvalidTransition
}