package rasterize

import (
	"bytes"
	"fmt"

	"github.com/pdfcpu/pdfcpu/pkg/api"
	"github.com/pdfcpu/pdfcpu/pkg/pdfcpu/model"
)

// RotatePDFPages applies clockwise rotations (degrees, multiples of 90) to each page.
// pageRotations is 1-indexed slice aligned with input pages: pageRotations[0] = page 1.
func RotatePDFPages(in []byte, pageRotations []int) ([]byte, error) {
	conf := model.NewDefaultConfiguration()
	conf.ValidationMode = model.ValidationRelaxed

	// pdfcpu's Rotate API takes a single rotation and a page selection. We group
	// pages by rotation value to minimize passes.
	groups := map[int][]int{}
	for i, r := range pageRotations {
		r = ((r % 360) + 360) % 360
		if r == 0 {
			continue
		}
		groups[r] = append(groups[r], i+1)
	}
	if len(groups) == 0 {
		out := make([]byte, len(in))
		copy(out, in)
		return out, nil
	}

	current := bytes.NewReader(in)
	var buf bytes.Buffer
	for rot, pages := range groups {
		buf.Reset()
		selectedPages := make([]string, len(pages))
		for i, p := range pages {
			selectedPages[i] = fmt.Sprintf("%d", p)
		}
		if err := api.Rotate(current, &buf, rot, selectedPages, conf); err != nil {
			return nil, fmt.Errorf("rotate %d°: %w", rot, err)
		}
		current = bytes.NewReader(append([]byte(nil), buf.Bytes()...))
	}
	out := make([]byte, current.Size())
	if _, err := current.ReadAt(out, 0); err != nil {
		return nil, err
	}
	return out, nil
}