package utils

import (
	"math"

	"github.com/gofiber/fiber/v2"
	"gorm.io/gorm"
)

const (
	// DefaultPageSize bounds a list request that doesn't ask for a specific
	// window. It is deliberately high: these endpoints previously returned
	// whole tables, so a small default would silently truncate results for
	// consoles that don't paginate yet. It exists to stop a growing table
	// from being loaded into memory wholesale, not to enforce a page size.
	DefaultPageSize = 500

	// MaxPageSize is the ceiling a caller can request, so a client can't opt
	// back into an unbounded scan by sending pagesize=999999.
	MaxPageSize = 1000
)

// Page is a validated pagination window. Build one with ParsePage rather than
// constructing it directly.
type Page struct {
	No     int // 1-based page number
	Size   int
	Offset int
}

// ParsePage reads ?pageno and ?pagesize off the request, matching the naming
// GetAdminBookings already established. Both are clamped into a safe range;
// absent or malformed values fall back to page 1 at DefaultPageSize rather
// than erroring, so a bad query string degrades instead of failing the call.
func ParsePage(c *fiber.Ctx) Page {
	no := c.QueryInt("pageno", 1)
	if no < 1 {
		no = 1
	}

	size := c.QueryInt("pagesize", DefaultPageSize)
	if size < 1 {
		size = DefaultPageSize
	}
	if size > MaxPageSize {
		size = MaxPageSize
	}

	return Page{No: no, Size: size, Offset: (no - 1) * size}
}

// Apply scopes a query to this page's window.
func (p Page) Apply(q *gorm.DB) *gorm.DB {
	return q.Offset(p.Offset).Limit(p.Size)
}

// Paginated writes one page of a larger result set, using the same response
// keys GetAdminBookings already returns. It keeps the {success, data, total}
// shape utils.List emits and only adds keys, so clients that ignore the new
// fields are unaffected. total is the count of all matching rows, not the
// length of data.
func Paginated(c *fiber.Ctx, data interface{}, total int64, p Page) error {
	return c.JSON(fiber.Map{
		"success":  true,
		"data":     data,
		"total":    total,
		"pageno":   p.No,
		"pagesize": p.Size,
		"pages":    int(math.Ceil(float64(total) / float64(p.Size))),
	})
}