pdfmerge/internal/pdf/contentstream/contentstream.go

package contentstream

import (
	"bytes"
	"fmt"
	"strings"

	"gitea.tecamino.com/paadi/pdfmerge/internal/pdf/core"
)

type ContentStreamOperation struct {
	Params  []core.PdfObject
	Operand string
}

type ContentStreamOperations []*ContentStreamOperation

// Check if the content stream operations are fully wrapped (within q ... Q)
func (s *ContentStreamOperations) isWrapped() bool {
	if len(*s) < 2 {
		return false
	}

	depth := 0
	for _, op := range *s {
		switch op.Operand {
		case "q":
			depth++
		case "Q":
			depth--
		default:
			if depth < 1 {
				return false
			}
		}
	}

	// Should end at depth == 0
	return depth == 0
}

// Wrap entire contents within q ... Q.  If unbalanced, then adds extra Qs at the end.
// Only does if needed. Ensures that when adding new content, one start with all states
// in the default condition.
func (s *ContentStreamOperations) WrapIfNeeded() *ContentStreamOperations {
	if len(*s) == 0 {
		// No need to wrap if empty.
		return s
	}
	if s.isWrapped() {
		return s
	}

	*s = append([]*ContentStreamOperation{{Operand: "q"}}, *s...)

	depth := 0
	for _, op := range *s {
		switch op.Operand {
		case "q":
			depth++
		case "Q":
			depth--
		}
	}

	for depth > 0 {
		*s = append(*s, &ContentStreamOperation{Operand: "Q"})
		depth--
	}

	return s
}

// Convert a set of content stream operations to a content stream byte presentation, i.e. the kind that can be
// stored as a PDF stream or string format.
func (s *ContentStreamOperations) Bytes() []byte {
	var buf bytes.Buffer

	for _, op := range *s {
		if op == nil {
			continue
		}

		if op.Operand == "BI" {
			// Inline image requires special handling.
			buf.WriteString(op.Operand + "\n")
			buf.WriteString(op.Params[0].DefaultWriteString())

		} else {
			// Default handler.
			for _, param := range op.Params {
				buf.WriteString(param.DefaultWriteString())
				buf.WriteString(" ")

			}

			buf.WriteString(op.Operand + "\n")
		}
	}

	return buf.Bytes()
}

// ExtractText parses and extracts all text data in content streams and returns as a string.
// Does not take into account Encoding table, the output is simply the character codes.
//
// Deprecated: More advanced text extraction is offered in package extractor with character encoding support.
func (s *ContentStreamParser) ExtractText() (string, error) {
	operations, err := s.Parse()
	if err != nil {
		return "", err
	}
	inText := false
	xPos, yPos := float64(-1), float64(-1)
	var txt strings.Builder
	for _, op := range *operations {
		switch op.Operand {
		case "BT":
			inText = true
		case "ET":
			inText = false
		}

		if op.Operand == "Td" || op.Operand == "TD" || op.Operand == "T*" {
			// Move to next line...
			txt.WriteString("\n")
		}
		if op.Operand == "Tm" {
			if len(op.Params) != 6 {
				continue
			}
			xfloat, ok := op.Params[4].(*core.PdfObjectFloat)
			if !ok {
				xint, ok := op.Params[4].(*core.PdfObjectInteger)
				if !ok {
					continue
				}
				xfloat = core.MakeFloat(float64(*xint))
			}
			yfloat, ok := op.Params[5].(*core.PdfObjectFloat)
			if !ok {
				yint, ok := op.Params[5].(*core.PdfObjectInteger)
				if !ok {
					continue
				}
				yfloat = core.MakeFloat(float64(*yint))
			}
			if yPos == -1 {
				yPos = float64(*yfloat)
			} else if yPos > float64(*yfloat) {
				txt.WriteString("\n")
				xPos = float64(*xfloat)
				yPos = float64(*yfloat)
				continue
			}
			if xPos == -1 {
				xPos = float64(*xfloat)
			} else if xPos < float64(*xfloat) {
				txt.WriteString("\t")
				xPos = float64(*xfloat)
			}
		}
		if inText && op.Operand == "TJ" {
			if len(op.Params) < 1 {
				continue
			}
			paramList, ok := op.Params[0].(*core.PdfObjectArray)
			if !ok {
				return "", fmt.Errorf("invalid parameter type, no array (%T)", op.Params[0])
			}
			for _, obj := range *paramList {
				switch v := obj.(type) {
				case *core.PdfObjectString:
					txt.WriteString(string(*v))
				case *core.PdfObjectFloat:
					if *v < -100 {
						txt.WriteString(" ")
					}
				case *core.PdfObjectInteger:
					if *v < -100 {
						txt.WriteString(" ")
					}
				}
			}
		} else if inText && op.Operand == "Tj" {
			if len(op.Params) < 1 {
				continue
			}
			param, ok := op.Params[0].(*core.PdfObjectString)
			if !ok {
				return "", fmt.Errorf("invalid parameter type, not string (%T)", op.Params[0])
			}
			txt.WriteString(string(*param))
		}
	}

	return txt.String(), nil
}