package pipeline

import (
	"fmt"
	"strings"

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

func validateChunkResult(doc *source.SourceDocument, chunks []contracts.SourceChunk) error {
	sourceUnitIndexes := make(map[string]int, len(doc.Units))
	for index, unit := range doc.Units {
		sourceUnitIndexes[unit.ID] = index
	}

	seenChunkIDs := make(map[string]struct{}, len(chunks))
	for chunkIndex, chunk := range chunks {
		if strings.TrimSpace(chunk.ID) == "" {
			return fmt.Errorf("chunk[%d].id must not be empty", chunkIndex)
		}
		if _, ok := seenChunkIDs[chunk.ID]; ok {
			return fmt.Errorf("chunk id %q is duplicated", chunk.ID)
		}
		seenChunkIDs[chunk.ID] = struct{}{}

		if chunk.SourceID != doc.ID {
			return fmt.Errorf("chunk %q source_id %q does not match source document id %q", chunk.ID, chunk.SourceID, doc.ID)
		}
		if chunk.Index != chunkIndex {
			return fmt.Errorf("chunk %q index %d does not match returned order %d", chunk.ID, chunk.Index, chunkIndex)
		}
		if len(chunk.Units) == 0 {
			return fmt.Errorf("chunk %q units must not be empty", chunk.ID)
		}

		seenUnitIDs := make(map[string]struct{}, len(chunk.Units))
		previousSourceIndex := -1
		for unitIndex, unit := range chunk.Units {
			if strings.TrimSpace(unit.ID) == "" {
				return fmt.Errorf("chunk %q unit[%d].id must not be empty", chunk.ID, unitIndex)
			}
			if _, ok := seenUnitIDs[unit.ID]; ok {
				return fmt.Errorf("chunk %q repeats source unit %q", chunk.ID, unit.ID)
			}
			seenUnitIDs[unit.ID] = struct{}{}

			sourceIndex, ok := sourceUnitIndexes[unit.ID]
			if !ok {
				return fmt.Errorf("chunk %q source unit %q was not found in source document %q", chunk.ID, unit.ID, doc.ID)
			}
			if sourceIndex <= previousSourceIndex {
				return fmt.Errorf("chunk %q source units must appear in source document order", chunk.ID)
			}
			previousSourceIndex = sourceIndex
		}
	}

	return nil
}