package claudewatcher

import (
	"context"
	"errors"
	"fmt"

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

// CursorStore tracks how far the watcher has ingested into each
// session JSONL file. Keyed by (host, file_path) so the same `~/.claude`
// path on different hosts doesn't collide and resumability survives
// pod restarts. Idempotent Init lives alongside the rest of the
// claudewatcher schema; no separate migration framework.
type CursorStore struct {
	pool *pgxpool.Pool
}

// NewCursorStore opens a pool against dsn. Caller closes the store.
func NewCursorStore(ctx context.Context, dsn string) (*CursorStore, error) {
	pool, err := pgxpool.New(ctx, dsn)
	if err != nil {
		return nil, fmt.Errorf("pgxpool: %w", err)
	}
	if err := pool.Ping(ctx); err != nil {
		pool.Close()
		return nil, fmt.Errorf("ping: %w", err)
	}
	return &CursorStore{pool: pool}, nil
}

// NewCursorStoreFromPool wraps an existing pool (so the watcher can
// share the brain DSN pool with vectorstore/graphstore without a
// second connection set). Caller must NOT close the wrapped pool via
// the store — close the pool directly.
func NewCursorStoreFromPool(pool *pgxpool.Pool) *CursorStore {
	return &CursorStore{pool: pool}
}

// Close releases the underlying connection pool when this store owns
// it. No-op when the pool was injected via NewCursorStoreFromPool —
// pgxpool.Close is idempotent so we lean on that.
func (s *CursorStore) Close() {
	if s.pool != nil {
		s.pool.Close()
	}
}

// Init creates the claude_session_cursors table when missing.
func (s *CursorStore) Init(ctx context.Context) error {
	const ddl = `
CREATE TABLE IF NOT EXISTS claude_session_cursors (
    host         TEXT NOT NULL,
    file_path    TEXT NOT NULL,
    byte_offset  BIGINT NOT NULL DEFAULT 0,
    last_seen_at TIMESTAMPTZ NOT NULL DEFAULT now(),
    PRIMARY KEY (host, file_path)
);
CREATE INDEX IF NOT EXISTS claude_session_cursors_host_idx
    ON claude_session_cursors (host);
`
	_, err := s.pool.Exec(ctx, ddl)
	return err
}

// GetOffset returns the last recorded byte offset for (host, filePath).
// Missing rows are reported as offset=0, ok=false so the caller can
// distinguish "never ingested" from "ingested at the start of the
// file" (both produce identical behaviour but the metric is useful).
func (s *CursorStore) GetOffset(ctx context.Context, host, filePath string) (int64, bool, error) {
	if host == "" || filePath == "" {
		return 0, false, errors.New("host and file_path are required")
	}
	var offset int64
	err := s.pool.QueryRow(ctx, `
        SELECT byte_offset FROM claude_session_cursors WHERE host = $1 AND file_path = $2
    `, host, filePath).Scan(&offset)
	if errors.Is(err, pgx.ErrNoRows) {
		return 0, false, nil
	}
	if err != nil {
		return 0, false, fmt.Errorf("query: %w", err)
	}
	return offset, true, nil
}

// SetOffset writes the new offset for (host, filePath). Used after
// every successful parse + ingest batch so a crash mid-file rewinds
// only to the last committed checkpoint.
func (s *CursorStore) SetOffset(ctx context.Context, host, filePath string, offset int64) error {
	if host == "" || filePath == "" {
		return errors.New("host and file_path are required")
	}
	if offset < 0 {
		return errors.New("offset must be >= 0")
	}
	_, err := s.pool.Exec(ctx, `
        INSERT INTO claude_session_cursors (host, file_path, byte_offset, last_seen_at)
        VALUES ($1, $2, $3, now())
        ON CONFLICT (host, file_path) DO UPDATE
        SET byte_offset = EXCLUDED.byte_offset,
            last_seen_at = now()
    `, host, filePath, offset)
	if err != nil {
		return fmt.Errorf("upsert offset: %w", err)
	}
	return nil
}