package main

import (
	"bytes"
	"fmt"
	"hash/fnv"
	"log"
	"math"
	"os"
	"runtime/pprof"
	"sort"
	"strings"
	"sync"
	"time"
)

const measurementsFile = "measurements.txt"
const testFile = "dummy.txt"
const resultFile = "my_results.txt"
const benchFile = "results.txt"

const profile = false

var nGoRoutine = 64

const maxSeekLen = int64(100)

type partitionRange struct {
	start int64
	end   int64
}

type resultSet map[uint64]result

type fRS struct {
	v    []result
	keys []uint64
	size int
}

func newFRS() *fRS {
	const size = 50000
	return &fRS{v: make([]result, size), keys: make([]uint64, size)}
}

type result struct {
	name  []byte
	count float64
	min   float64
	max   float64
	rAvg  float64
}

var count = int64(0)

func main() {
	fmt.Printf("Starting with %d threads\n", nGoRoutine)
	var f *os.File
	if profile {
		f = startCpuProfile()
	}

	_ = os.Remove(testFile)
	start := time.Now()
	oneBRC()
	finish := time.Now()
	if profile {
		stopProfiling(f)
	}
	fmt.Printf("Total ellapsed time: %.2fs\n", finish.Sub(start).Seconds())
	fmt.Printf("Total computed records: %d\n", count)
	validate()
}

func oneBRC() {
	bits, err := os.ReadFile(measurementsFile)
	if err != nil {
		panic(err)
	}

	parts := createPartitions(bits, '\n', nGoRoutine)
	wg := &sync.WaitGroup{}
	results := make([]*fRS, len(parts))

	for i, part := range parts {
		wg.Add(1)
		go workerComputePartition(bits, part, i, results, wg)
	}
	wg.Wait()

	finalRS := make(resultSet)

	for _, rs := range results {
		finalRS.merge(rs.toResultSet())
	}

	os.WriteFile(resultFile, []byte(finalRS.String()), 0666)
}

func validate() {
	me, err := os.ReadFile(resultFile)
	if err != nil {
		panic(err)
	}

	ref, err := os.ReadFile(benchFile)
	if err != nil {
		panic(err)
	}

	meLines := bytes.Split(me, []byte{'\r', '\n'})
	refLines := bytes.Split(ref, []byte{'\r', '\n'})

	errs := 0
	for i, line := range meLines {
		refLine := string(refLines[i])
		meLine := string(line)
		if refLine != meLine {
			errs++
			fmt.Printf("Validation tripped: reference[%s]\tme[%s]\n", refLine, meLine)
		}
	}

	fmt.Printf("Validation passed: %v\n", errs == 0)
}

func startCpuProfile() *os.File {
	name := fmt.Sprintf("prof-%s.pprof", time.Now().Format("15-04-05"))
	f, err := os.Create(name)
	if err != nil {
		log.Fatal(err)
	}
	err = pprof.StartCPUProfile(f)
	if err != nil {
		log.Fatal(err)
	}
	return f
}

func stopProfiling(f *os.File) {
	pprof.StopCPUProfile()
	f.Close()
}

func workerComputePartition(aData []byte, wPart partitionRange, workerNumber int, container []*fRS, wg *sync.WaitGroup) {
	defer wg.Done()
	const delimiter = byte(';')

	rs := newFRS()

	alloc := make([]result, 500)
	aCnt := 0
	var di int
	var line []byte

	hasher := fnv.New64()

	var start = wPart.start
	var end int64
	for end = seekNextNewLine(aData, wPart, start); end <= wPart.end; end = seekNextNewLine(aData, wPart, start) {

		line = aData[start : end-2]
		//we know there will be at minimum 0.0, so we can skip 3 bytes
		for di = len(line) - 3; di > -1; di-- {
			if line[di] == delimiter {
				break
			}
		}

		if di < 0 {
			continue
		}

		temp := fParseFloat(line[di+1:][:len(line[di+1:])])

		hasher.Write(line[:di])
		key := hasher.Sum64()
		hasher.Reset()
		r, ok := rs.get(key)
		if !ok {
			r = alloc[aCnt]
			r.name = line[:di]
			r.min = math.MaxFloat64
			r.max = math.SmallestNonzeroFloat64
			aCnt++
		}
		r.count += 1.0

		r.rAvg = ((r.rAvg * (r.count - 1.0)) + temp) / r.count

		if temp > r.max {
			r.max = temp
		}

		if temp < r.min {
			r.min = temp
		}

		rs.put(key, r)
		start = end
		if end == wPart.end {
			break
		}
	}

	container[workerNumber] = rs
}

func fParseFloat(str []byte) float64 {
	switch len(str) {
	case 3:
		//x.x
		a := float64(fCharToInt(str[0]))
		b := float64(fCharToInt(str[2])) * 0.1
		return a + b
	case 4:
		//either xx.x or -x.x
		if str[0] == '-' {
			//-x.x
			a := float64(fCharToInt(str[1]))
			b := float64(fCharToInt(str[3])) * 0.1
			return -(a + b)
		} else {
			//xx.x
			a := float64(f2CharToInt(str[0], str[1]))
			b := float64(fCharToInt(str[3])) * 0.1
			return a + b
		}
	case 5:
		//-xx.x
		a := float64(f2CharToInt(str[1], str[2]))
		b := float64(fCharToInt(str[4])) * 0.1
		return -(a + b)
	default:
		panic(fmt.Errorf("bad float string: %s", string(str)))
	}
}

func fCharToInt(b byte) int {
	return int(b - '0')
}

func f2CharToInt(b1 byte, b2 byte) int {
	return int(((b1 - '0') * 10) + (b2 - '0'))
}

func seekNextNewLine(b []byte, part partitionRange, last int64) int64 {
	const step = 8
	for i := last + step; i < part.end; {
		switch b[i] {
		case '\n':
			return i + 1
		case '\r':
			return i + 2
		case ';': // this will be minimum [;0.0\r]
			i += 5
		default:
			i += 2
		}
	}
	return part.end
}

func createPartitions(data []byte, seekChar byte, nPart int) []partitionRange {
	if len(data) == 0 || nPart == 0 {
		return make([]partitionRange, nPart)
	}

	if nPart == 0 {
		return []partitionRange{}
	}

	si := int64(0)
	step := int64(len(data) / nPart)
	tLen := int64(len(data))

	partitions := make([]partitionRange, nPart)

	for i := 0; i < nPart; i++ {
		start := si

		end := si + step

		if start > tLen {
			return partitions[:len(partitions)-1]
		}

		if end > tLen {
			partitions[i] = partitionRange{start: start, end: tLen}
			return partitions
		}

		found := false
		seekForward := end + maxSeekLen
		//seek next new line
		for j := end; j < min(seekForward, tLen); j++ {
			if data[j] == seekChar {
				if end == tLen {
					//if the final character is also a split character we just return the rest of the chunk
					end = tLen
				} else {
					end = j + 1
				}
				found = true
				break
			}
		}

		if !found {
			//we'll start looking backward from the end point by the seek amount just in case we barely over-stepped
			seekBack := max(0, end-maxSeekLen)
			for j := end; j > seekBack; j-- {
				if data[j] == seekChar {
					end = j + 1
					found = true
					break
				}
			}
			if !found {
				fmt.Printf("Could not find split in range [%d, %d]\n%s", seekBack, seekForward, string(data)[seekBack:seekForward])
				panic("thread died")
			}
		}

		partitions[i] = partitionRange{start: start, end: end}
		si = end

	}

	return partitions
}

func (r *result) merge(other *result) {
	if other.max > r.max {
		r.max = other.max
	}

	if other.min < r.min {
		r.min = other.min
	}

	r.rAvg = ((r.rAvg * r.count) + (other.rAvg * other.count)) / (r.count + other.count)
	r.count += other.count
}

func (rs resultSet) merge(other resultSet) {
	for k, v := range other {
		tr, ok := rs[k]
		if !ok {
			rs[k] = v
			continue
		}

		tr.merge(&v)

		rs[k] = tr
	}
}

func (rs resultSet) String() string {
	keys := make([]string, 0, len(rs))

	for _, v := range rs {
		keys = append(keys, string(v.name))
	}

	sort.Strings(keys)
	b := &strings.Builder{}
	hasher := fnv.New64()

	for i, key := range keys {
		hasher.Write([]byte(key))
		r := rs[hasher.Sum64()]
		hasher.Reset()
		count += int64(r.count)
		b.WriteString(key)
		b.WriteString("=")
		b.WriteString(fmt.Sprintf("%.1f", r.min))
		b.WriteString("/")
		b.WriteString(fmt.Sprintf("%.1f", r.rAvg))
		b.WriteString("/")
		b.WriteString(fmt.Sprintf("%.1f", r.max))
		if i < len(keys)-1 {
			b.WriteString(",\r\n")
		}
	}
	return b.String()
}

func (f *fRS) get(key uint64) (result, bool) {
	p := f.v[f.keyMap(key)]
	return p, p.name != nil
}

func (f *fRS) put(key uint64, v result) {
	idx := f.keyMap(key)
	f.v[idx] = v
	f.keys[idx] = key
	f.size += 1
}

func (f *fRS) keyMap(key uint64) uint64 {
	//a := key & math.MaxUint32
	//b := (key >> 32) & math.MaxUint32
	return (key) % uint64(len(f.v))
}

func (f *fRS) getKeys() []uint64 {
	keys := make([]uint64, 0, f.size)
	for _, k := range f.keys {
		if k > 0 {
			keys = append(keys, k)
		}
	}
	return keys
}

func (f *fRS) toResultSet() resultSet {
	rs := make(resultSet)
	for _, key := range f.getKeys() {
		v, _ := f.get(key)
		rs[key] = v
	}
	return rs
}