package shared

import (
	"fmt"
	"strings"

	"gitea.maximumdirect.net/eric/notarius/internal/core/source"
)

// CitedText resolves cited source ranges in document order, including each
// source unit once, and joins the resulting text with newlines.
func CitedText(doc *source.SourceDocument, refs []source.SourceRef) (string, error) {
	if doc == nil {
		return "", fmt.Errorf("source document must not be nil")
	}

	included := make([]bool, len(doc.Units))
	for _, ref := range refs {
		if err := source.ValidateRef(doc, ref); err != nil {
			return "", fmt.Errorf("resolve cited source range: %w", err)
		}
		start, _ := source.UnitIndex(doc, ref.StartUnitID)
		end, _ := source.UnitIndex(doc, ref.EndUnitID)
		for index := start; index <= end; index++ {
			included[index] = true
		}
	}

	parts := make([]string, 0, len(doc.Units))
	for index, unit := range doc.Units {
		if included[index] {
			parts = append(parts, unit.Text)
		}
	}
	return strings.Join(parts, "\n"), nil
}