// registrar.go — turn catalogd's manifest list into DuckDB views.
//
// Refresh() reads /catalog/list, runs CREATE OR REPLACE VIEW for
// every manifest, drops views for manifests that disappeared, and
// skips any whose updated_at hasn't changed since the prior refresh
// (per kickoff D5.3 spec — "don't re-CREATE on every request,
// Opus review flagged that as the perf cliff").
//
// Identifier safety: all view names are double-quoted in SQL with
// internal " escaped to "" — catalogd accepts user-supplied dataset
// names that wouldn't pass SQL bare-identifier rules (hyphens,
// digit-leading, reserved words). Quoting makes them unambiguous.
package queryd

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"strings"
	"time"

	"git.agentview.dev/profit/golangLAKEHOUSE/internal/catalogd"
)

// CatalogLister is what registrar needs from the catalog client —
// only List, no Register. Defined as an interface so unit tests can
// inject a fake without spinning up a real catalogd.
type CatalogLister interface {
	List(ctx context.Context) ([]*catalogd.Manifest, error)
}

// Execer is the subset of *sql.DB that registrar actually uses.
// Same testability win — unit tests can record the SQL strings
// without booting DuckDB. *sql.DB satisfies this directly.
type Execer interface {
	ExecContext(ctx context.Context, query string, args ...any) (sql.Result, error)
}

// Registrar holds the running view state and the dependencies needed
// to refresh it.
type Registrar struct {
	exec    Execer
	catalog CatalogLister
	bucket  string

	// known tracks the current view names + the updated_at we last
	// rebuilt them from. Used by Refresh to skip unchanged views and
	// drop ones that disappeared from the catalog.
	known map[string]time.Time
}

// NewRegistrar builds a fresh registrar. bucket is the S3 bucket
// name used to construct s3:// URLs for read_parquet().
func NewRegistrar(exec Execer, catalog CatalogLister, bucket string) *Registrar {
	return &Registrar{
		exec:    exec,
		catalog: catalog,
		bucket:  bucket,
		known:   make(map[string]time.Time),
	}
}

// RefreshStats reports what Refresh did — for logs + tests.
type RefreshStats struct {
	Created int
	Updated int
	Dropped int
	Skipped int
}

// Refresh syncs DuckDB's view catalog with catalogd's manifest list.
// Returns counts of {Created, Updated, Dropped, Skipped} so the
// caller can decide whether to log loudly.
//
// Per scrum C1 (Opus + Kimi convergent): drop pass runs BEFORE create
// pass so a failure in one view's CREATE doesn't block another view's
// DROP. Per-iteration errors are collected and the refresh continues
// — a single poison manifest must not block the whole catalog from
// re-syncing. The collected errors are joined into the return value;
// callers see "everything that happened to fail this round."
func (r *Registrar) Refresh(ctx context.Context) (RefreshStats, error) {
	var stats RefreshStats

	manifests, err := r.catalog.List(ctx)
	if err != nil {
		return stats, fmt.Errorf("registrar list: %w", err)
	}

	wantNames := make(map[string]struct{}, len(manifests))
	for _, m := range manifests {
		wantNames[m.Name] = struct{}{}
	}

	var errs []error

	// 1. Drop views whose manifests disappeared. Run first so the
	//    create pass can't block removals on a poison-create error.
	for name := range r.known {
		if _, still := wantNames[name]; still {
			continue
		}
		if err := r.dropView(ctx, name); err != nil {
			errs = append(errs, err)
			continue
		}
		delete(r.known, name)
		stats.Dropped++
	}

	// 2. Create / update views for current manifests.
	for _, m := range manifests {
		prior, exists := r.known[m.Name]
		if exists && prior.Equal(m.UpdatedAt) {
			stats.Skipped++
			continue
		}
		if err := r.createOrReplaceView(ctx, m); err != nil {
			errs = append(errs, err)
			continue
		}
		if exists {
			stats.Updated++
		} else {
			stats.Created++
		}
		r.known[m.Name] = m.UpdatedAt
	}

	if len(errs) > 0 {
		return stats, errors.Join(errs...)
	}
	return stats, nil
}

// createOrReplaceView builds the DuckDB SQL for one manifest and
// runs it. G0 manifests have exactly one Object per dataset; if more
// land later (G2 multi-part), `read_parquet([...])` accepts a list.
func (r *Registrar) createOrReplaceView(ctx context.Context, m *catalogd.Manifest) error {
	if len(m.Objects) == 0 {
		return fmt.Errorf("registrar: manifest %q has no objects", m.Name)
	}
	urls := make([]string, len(m.Objects))
	for i, obj := range m.Objects {
		urls[i] = fmt.Sprintf("'%s'", sqlEscape(buildS3URL(r.bucket, obj.Key)))
	}
	var fromExpr string
	if len(urls) == 1 {
		fromExpr = "read_parquet(" + urls[0] + ")"
	} else {
		fromExpr = "read_parquet([" + strings.Join(urls, ", ") + "])"
	}
	sql := fmt.Sprintf("CREATE OR REPLACE VIEW %s AS SELECT * FROM %s",
		quoteIdent(m.Name), fromExpr)
	if _, err := r.exec.ExecContext(ctx, sql); err != nil {
		return fmt.Errorf("create view %q: %w", m.Name, err)
	}
	return nil
}

func (r *Registrar) dropView(ctx context.Context, name string) error {
	sql := "DROP VIEW IF EXISTS " + quoteIdent(name)
	if _, err := r.exec.ExecContext(ctx, sql); err != nil {
		return fmt.Errorf("drop view %q: %w", name, err)
	}
	return nil
}

// quoteIdent wraps a SQL identifier in double quotes and escapes
// internal " by doubling. This is the SQL-standard rule — works in
// every engine that accepts quoted identifiers.
func quoteIdent(name string) string {
	return `"` + strings.ReplaceAll(name, `"`, `""`) + `"`
}

// buildS3URL composes the s3://bucket/key URL DuckDB's httpfs
// extension consumes. Keys aren't URL-escaped because read_parquet
// accepts S3-style literal paths.
func buildS3URL(bucket, key string) string {
	return "s3://" + bucket + "/" + key
}