package pipeline

import (
	"fmt"
	"strings"

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

func validateAndCanonicalizeChunkResult(doc *source.SourceDocument, chunks []contracts.SourceChunk) ([]contracts.SourceChunk, error) {
	if len(chunks) == 0 {
		return nil, fmt.Errorf("chunks must not be empty")
	}

	sourceUnitIndexes := make(map[int]int, len(doc.Units))
	sourceUnits := make(map[int]source.SourceUnit, len(doc.Units))
	for index, unit := range doc.Units {
		sourceUnitIndexes[unit.ID] = index
		sourceUnits[unit.ID] = unit
	}

	canonicalChunks := make([]contracts.SourceChunk, 0, len(chunks))
	seenChunkIDs := make(map[string]struct{}, len(chunks))
	for chunkIndex, chunk := range chunks {
		if strings.TrimSpace(chunk.ID) == "" {
			return nil, fmt.Errorf("chunk[%d].id must not be empty", chunkIndex)
		}
		if _, ok := seenChunkIDs[chunk.ID]; ok {
			return nil, fmt.Errorf("chunk id %q is duplicated", chunk.ID)
		}
		seenChunkIDs[chunk.ID] = struct{}{}

		if chunk.SourceID != doc.ID {
			return nil, 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 nil, fmt.Errorf("chunk %q index %d does not match returned order %d", chunk.ID, chunk.Index, chunkIndex)
		}
		startIndex, ok := sourceUnitIndexes[chunk.StartUnitID]
		if !ok {
			return nil, fmt.Errorf("chunk %q start_unit_id %d was not found in source document %q", chunk.ID, chunk.StartUnitID, doc.ID)
		}
		endIndex, ok := sourceUnitIndexes[chunk.EndUnitID]
		if !ok {
			return nil, fmt.Errorf("chunk %q end_unit_id %d was not found in source document %q", chunk.ID, chunk.EndUnitID, doc.ID)
		}
		if startIndex > endIndex {
			return nil, fmt.Errorf("chunk %q start_unit_id %d appears after end_unit_id %d", chunk.ID, chunk.StartUnitID, chunk.EndUnitID)
		}
		if len(chunk.Units) == 0 {
			return nil, fmt.Errorf("chunk %q units must not be empty", chunk.ID)
		}
		if len(chunk.Content) == 0 {
			return nil, fmt.Errorf("chunk %q content must not be empty", chunk.ID)
		}
		if strings.TrimSpace(chunk.MediaType) == "" {
			return nil, fmt.Errorf("chunk %q media_type must not be empty", chunk.ID)
		}

		seenUnitIDs := make(map[int]struct{}, len(chunk.Units))
		previousSourceIndex := -1
		canonicalUnits := make([]source.SourceUnit, 0, len(chunk.Units))
		for unitIndex, unit := range chunk.Units {
			if unit.ID <= 0 {
				return nil, fmt.Errorf("chunk %q unit[%d].id must be positive", chunk.ID, unitIndex)
			}
			if _, ok := seenUnitIDs[unit.ID]; ok {
				return nil, fmt.Errorf("chunk %q repeats source unit %d", chunk.ID, unit.ID)
			}
			seenUnitIDs[unit.ID] = struct{}{}

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

		canonicalChunks = append(canonicalChunks, contracts.SourceChunk{
			ID:          chunk.ID,
			SourceID:    chunk.SourceID,
			Index:       chunk.Index,
			StartUnitID: chunk.StartUnitID,
			EndUnitID:   chunk.EndUnitID,
			Content:     append([]byte(nil), chunk.Content...),
			MediaType:   chunk.MediaType,
			Units:       canonicalUnits,
			Metadata:    cloneMetadata(chunk.Metadata),
		})
	}

	return canonicalChunks, nil
}

func cloneSourceUnit(unit source.SourceUnit) source.SourceUnit {
	return source.SourceUnit{
		ID:       unit.ID,
		Kind:     unit.Kind,
		Text:     unit.Text,
		Metadata: cloneMetadata(unit.Metadata),
	}
}