package logstorage

import (
	"fmt"
	"html"
	"strconv"
	"strings"
	"unsafe"

	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
)

// pipeExtract processes '| extract (field, format)' pipe.
//
// See https://docs.victoriametrics.com/victorialogs/logsql/#extract-pipe
type pipeExtract struct {
	field string
	steps []extractFormatStep

	stepsStr string
}

func (pe *pipeExtract) String() string {
	return fmt.Sprintf("extract(%s, %s)", quoteTokenIfNeeded(pe.field), pe.stepsStr)
}

func (pe *pipeExtract) updateNeededFields(neededFields, unneededFields fieldsSet) {
	neededFields.add(pe.field)

	for _, step := range pe.steps {
		if step.field != "" {
			unneededFields.remove(step.field)
		}
	}
}

func (pe *pipeExtract) newPipeProcessor(workersCount int, stopCh <-chan struct{}, _ func(), ppBase pipeProcessor) pipeProcessor {
	shards := make([]pipeExtractProcessorShard, workersCount)
	for i := range shards {
		shards[i] = pipeExtractProcessorShard{
			pipeExtractProcessorShardNopad: pipeExtractProcessorShardNopad{
				ef: newExtractFormat(pe.steps),
			},
		}
	}

	pep := &pipeExtractProcessor{
		pe:     pe,
		stopCh: stopCh,
		ppBase: ppBase,

		shards: shards,
	}
	return pep
}

type pipeExtractProcessor struct {
	pe     *pipeExtract
	stopCh <-chan struct{}
	ppBase pipeProcessor

	shards []pipeExtractProcessorShard
}

type pipeExtractProcessorShard struct {
	pipeExtractProcessorShardNopad

	// The padding prevents false sharing on widespread platforms with 128 mod (cache line size) = 0 .
	_ [128 - unsafe.Sizeof(pipeExtractProcessorShardNopad{})%128]byte
}

type pipeExtractProcessorShardNopad struct {
	ef *extractFormat
}

func (pep *pipeExtractProcessor) writeBlock(workerID uint, br *blockResult) {
	if len(br.timestamps) == 0 {
		return
	}

	shard := &pep.shards[workerID]
	c := br.getColumnByName(pep.pe.field)
	values := c.getValues(br)

	ef := shard.ef
	for _, v := range values {
		ef.apply(v)
		/*		for i, result := range ef.results {
					rcs[i].addValue(result)
				}
		*/
	}
}

func (pep *pipeExtractProcessor) flush() error {
	return nil
}

type extractFormat struct {
	// steps contains steps for extracting fields from string
	steps []extractFormatStep

	// matches contains matches for every step in steps
	matches []string

	// fields contains matches for non-empty fields
	fields []extractField
}

type extractField struct {
	name  string
	value *string
}

type extractFormatStep struct {
	prefix string
	field  string
}

func newExtractFormat(steps []extractFormatStep) *extractFormat {
	if len(steps) == 0 {
		logger.Panicf("BUG: steps cannot be empty")
	}

	matches := make([]string, len(steps))

	var fields []extractField
	for i, step := range steps {
		if step.field != "" {
			fields = append(fields, extractField{
				name:  step.field,
				value: &matches[i],
			})
		}
	}
	if len(fields) == 0 {
		logger.Panicf("BUG: fields cannot be empty")
	}

	ef := &extractFormat{
		steps:   steps,
		matches: matches,
		fields:  fields,
	}
	return ef
}

func (ef *extractFormat) apply(s string) {
	clear(ef.matches)

	steps := ef.steps

	if prefix := steps[0].prefix; prefix != "" {
		n := strings.Index(s, prefix)
		if n < 0 {
			// Mismatch
			return
		}
		s = s[n+len(prefix):]
	}

	matches := ef.matches
	for i := range steps {
		nextPrefix := ""
		if i + 1 < len(steps) {
			nextPrefix = steps[i+1].prefix
		}

		us, nOffset, ok := tryUnquoteString(s)
		if ok {
			// Matched quoted string
			matches[i] = us
			s = s[nOffset:]
			if !strings.HasPrefix(s, nextPrefix) {
				// Mismatch
				return
			}
			s = s[len(nextPrefix):]
		} else {
			// Match unquoted string until the nextPrefix
			if nextPrefix == "" {
				matches[i] = s
				return
			}
			n := strings.Index(s, nextPrefix)
			if n < 0 {
				// Mismatch
				return
			}
			matches[i] = s[:n]
			s = s[n+len(nextPrefix):]
		}
	}
}

func tryUnquoteString(s string) (string, int, bool) {
	if len(s) == 0 {
		return s, 0, false
	}
	if s[0] != '"' && s[0] != '`' {
		return s, 0, false
	}
	qp, err := strconv.QuotedPrefix(s)
	if err != nil {
		return s, 0, false
	}
	us, err := strconv.Unquote(qp)
	if err != nil {
		return s, 0, false
	}
	return us, len(qp), true
}

func parseExtractFormatSteps(s string) ([]extractFormatStep, error) {
	var steps []extractFormatStep

	hasNamedField := false

	n := strings.IndexByte(s, '<')
	if n < 0 {
		return nil, fmt.Errorf("missing <...> fields")
	}
	prefix := s[:n]
	s = s[n+1:]
	for {
		n := strings.IndexByte(s, '>')
		if n < 0 {
			return nil, fmt.Errorf("missing '>' for <%s", s)
		}
		field := s[:n]
		s = s[n+1:]

		if field == "_" || field == "*" {
			field = ""
		}
		steps = append(steps, extractFormatStep{
			prefix: prefix,
			field:  field,
		})
		if !hasNamedField && field != "" {
			hasNamedField = true
		}
		if len(s) == 0 {
			break
		}

		n = strings.IndexByte(s, '<')
		if n < 0 {
			steps = append(steps, extractFormatStep{
				prefix: s,
			})
			break
		}
		if n == 0 {
			return nil, fmt.Errorf("missing delimiter after <%s>", field)
		}
		prefix = s[:n]
		s = s[n+1:]
	}

	if !hasNamedField {
		return nil, fmt.Errorf("missing named fields like <name>")
	}

	for i := range steps {
		step := &steps[i]
		step.prefix = html.UnescapeString(step.prefix)
	}

	return steps, nil
}