package textencoding

import (
	"errors"
)

// CID represents a character identifier.
type CID uint16

// CMap maps character codes to CIDs.
type CMap interface {
	CharacterCodesToCID(charcodes []byte) ([]CID, error)
}

// CMapIdentityH is a representation of the /Identity-H cmap.
type CMapIdentityH struct {
}

// CharacterCodesToCID converts charcodes to CIDs for the Identity CMap, which maps
// 2-byte character codes (from the raw data) from 0-65535 to the same 2-byte CID value.
func (cmap CMapIdentityH) CharacterCodesToCID(raw []byte) ([]CID, error) {
	if len(raw)%2 != 0 {
		return nil, errors.New("Range error")
	}

	var charcode uint16
	cids := []CID{}

	for i := 0; i < len(raw); i += 2 {
		b1 := uint16(raw[i])
		b2 := uint16(raw[i+1])
		charcode = (b1 << 8) | b2

		cids = append(cids, CID(charcode))
	}

	return cids, nil
}