// Package scheduler — system_builtins.go
//
// v0.28.6: Built-in system functions registered at startup.
// These mirror the background goroutines in main.go but run as visible,
// scheduled, auditable tasks. The goroutines remain as fallback until
// system tasks are validated in production.
package scheduler

import (
	"context"
	"fmt"
	"log"
	"time"

	"git.gobha.me/xcaliber/chat-switchboard/database"
	"git.gobha.me/xcaliber/chat-switchboard/store"
	"git.gobha.me/xcaliber/chat-switchboard/taskutil"
)

// RegisterBuiltins registers all built-in system functions.
// Called once from main.go at startup.
func RegisterBuiltins() {
	taskutil.RegisterSystemFunc("session_cleanup",
		"Remove expired anonymous visitor sessions",
		sessionCleanup)

	taskutil.RegisterSystemFunc("staleness_check",
		"Mark idle workflow instances as stale",
		stalenessCheck)

	taskutil.RegisterSystemFunc("retention_sweep",
		"Delete completed workflow instances past retention policy",
		retentionSweep)

	taskutil.RegisterSystemFunc("health_prune",
		"Prune provider health windows older than 7 days",
		healthPrune)
}

// ── session_cleanup ─────────────────────────

func sessionCleanup(ctx context.Context, stores store.Stores) (string, error) {
	if stores.Sessions == nil {
		return "skipped: session store not available", nil
	}
	// Default: expire sessions older than 7 days
	cutoff := time.Now().UTC().AddDate(0, 0, -7)
	n, err := stores.Sessions.DeleteExpired(ctx, cutoff)
	if err != nil {
		return "", fmt.Errorf("session cleanup failed: %w", err)
	}
	msg := fmt.Sprintf("cleaned up %d expired sessions (cutoff: %s)", n, cutoff.Format(time.RFC3339))
	if n > 0 {
		log.Printf("[system_task] %s", msg)
	}
	return msg, nil
}

// ── staleness_check ─────────────────────────

func stalenessCheck(ctx context.Context, stores store.Stores) (string, error) {
	// Default: 48 hours idle → stale
	cutoff := time.Now().UTC().Add(-48 * time.Hour)
	res, err := database.DB.ExecContext(ctx, database.Q(`
		UPDATE channels
		SET workflow_status = 'stale'
		WHERE type = 'workflow'
		  AND workflow_status = 'active'
		  AND last_activity_at < $1
	`), cutoff)
	if err != nil {
		return "", fmt.Errorf("staleness sweep failed: %w", err)
	}
	n, _ := res.RowsAffected()
	msg := fmt.Sprintf("marked %d idle workflow instances as stale (cutoff: %s)", n, cutoff.Format(time.RFC3339))
	if n > 0 {
		log.Printf("[system_task] %s", msg)
	}
	return msg, nil
}

// ── retention_sweep ─────────────────────────

func retentionSweep(ctx context.Context, stores store.Stores) (string, error) {
	if database.IsSQLite() {
		return "skipped: retention enforcement requires PostgreSQL (JSON operators)", nil
	}
	cutoff := time.Now().UTC().Add(-48 * time.Hour)
	res, err := database.DB.ExecContext(ctx, database.Q(`
		DELETE FROM channels
		WHERE type = 'workflow'
		  AND workflow_status IN ('completed', 'archived')
		  AND workflow_id IS NOT NULL
		  AND last_activity_at < $1
		  AND workflow_id IN (
		    SELECT id FROM workflows
		    WHERE retention IS NOT NULL
		      AND retention->>'mode' = 'delete'
		      AND (retention->>'delete_after_days')::int > 0
		      AND channels.last_activity_at < now() - ((retention->>'delete_after_days')::int || ' days')::interval
		  )
	`), cutoff)
	if err != nil {
		return "", fmt.Errorf("retention enforcement failed: %w", err)
	}
	n, _ := res.RowsAffected()
	msg := fmt.Sprintf("deleted %d expired workflow instances (retention policy)", n)
	if n > 0 {
		log.Printf("[system_task] %s", msg)
	}
	return msg, nil
}

// ── health_prune ────────────────────────────

func healthPrune(ctx context.Context, stores store.Stores) (string, error) {
	cutoff := time.Now().UTC().Add(-7 * 24 * time.Hour)
	res, err := database.DB.ExecContext(ctx, database.Q(`
		DELETE FROM health_windows WHERE window_start < $1
	`), cutoff)
	if err != nil {
		return "", fmt.Errorf("health prune failed: %w", err)
	}
	n, _ := res.RowsAffected()
	msg := fmt.Sprintf("pruned %d old health windows (cutoff: %s)", n, cutoff.Format(time.RFC3339))
	if n > 0 {
		log.Printf("[system_task] %s", msg)
	}
	return msg, nil
}