package common

import (
	"fmt"
	"regexp"
	"sort"
	"strconv"
	"strings"

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

// Part is an atomic unit for transfer during backup / restore.
//
// Each source file can be split into parts with up to MaxPartSize sizes.
type Part struct {
	// Path is the path to file for backup.
	Path string

	// FileSize is the size of the whole file for the given part.
	FileSize uint64

	// Offset is offset in the file to backup.
	Offset uint64

	// Size is the size of the part to backup starting from Offset.
	Size uint64

	// ActualSize is the actual size of the part.
	//
	// The part is considered broken if it isn't equal to Size.
	// Such a part must be removed from remote storage.
	ActualSize uint64
}

func (p *Part) key() string {
	// Do not use p.FileSize in the key, since it cannot be properly initialized when resuming the restore for partially restored file
	return fmt.Sprintf("%s%016X%016X%016X", p.Path, p.Offset, p.Size, p.ActualSize)
}

// String returns human-readable representation of the part.
func (p *Part) String() string {
	return fmt.Sprintf("part{path: %q, file_size: %d, offset: %d, size: %d}", p.Path, p.FileSize, p.Offset, p.Size)
}

// RemotePath returns remote path for the part p and the given prefix.
func (p *Part) RemotePath(prefix string) string {
	for strings.HasSuffix(prefix, "/") {
		prefix = prefix[:len(prefix)-1]
	}
	return fmt.Sprintf("%s/%s/%016X_%016X_%016X", prefix, p.Path, p.FileSize, p.Offset, p.Size)
}

var partNameRegexp = regexp.MustCompile(`^(.+)[/\\]([0-9A-F]{16})_([0-9A-F]{16})_([0-9A-F]{16})$`)

// ParseFromRemotePath parses p from remotePath.
//
// Returns true on success.
func (p *Part) ParseFromRemotePath(remotePath string) bool {
	tmp := partNameRegexp.FindStringSubmatch(remotePath)
	if len(tmp) != 5 {
		return false
	}
	path := tmp[1]
	for strings.HasPrefix(path, "/") {
		path = path[1:]
	}
	fileSize, err := strconv.ParseUint(tmp[2], 16, 64)
	if err != nil {
		logger.Panicf("BUG: cannot parse fileSize from %q: %s", tmp[2], err)
	}
	offset, err := strconv.ParseUint(tmp[3], 16, 64)
	if err != nil {
		logger.Panicf("BUG: cannot parse offset from %q: %s", tmp[3], err)
	}
	size, err := strconv.ParseUint(tmp[4], 16, 64)
	if err != nil {
		logger.Panicf("BUG: cannot parse size from %q: %s", tmp[4], err)
	}
	p.Path = path
	p.FileSize = fileSize
	p.Offset = offset
	p.Size = size
	return true
}

// MaxPartSize is the maximum size for each part.
//
// The MaxPartSize reduces bandwidth usage during retires on network errors
// when transferring multi-TB files.
const MaxPartSize = 1024 * 1024 * 1024

// SortParts sorts parts by (Path, Offset)
func SortParts(parts []Part) {
	sort.Slice(parts, func(i, j int) bool {
		a := parts[i]
		b := parts[j]
		if a.Path != b.Path {
			return a.Path < b.Path
		}
		return a.Offset < b.Offset
	})
}

// PartsDifference returns a - b
func PartsDifference(a, b []Part) []Part {
	m := make(map[string]bool, len(b))
	for _, p := range b {
		k := p.key()
		m[k] = true
	}
	var d []Part
	for _, p := range a {
		k := p.key()
		if !m[k] {
			d = append(d, p)
		}
	}
	return d
}

// PartsIntersect returns the intersection of a and b
func PartsIntersect(a, b []Part) []Part {
	m := make(map[string]bool, len(a))
	for _, p := range a {
		k := p.key()
		m[k] = true
	}
	var d []Part
	for _, p := range b {
		k := p.key()
		if m[k] {
			d = append(d, p)
		}
	}
	return d
}

// EnforceSpecialsCopy enforces copying of special parts from src to toCopy without checking whether
// part is already present in dst.
func EnforceSpecialsCopy(src, toCopy []Part) []Part {
	// `parts.json` files must be copied from src to dst without checking whether they already exist in dst.
	// This is needed because size and paths for those files can be the same even if the contents differ.
	// See: https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5005
	filtered := make(map[Part]bool)
	for _, pt := range src {
		if strings.HasPrefix(pt.Path, "data") && strings.HasSuffix(pt.Path, "parts.json") {
			filtered[pt] = false
		}
	}

	for _, pt := range toCopy {
		if _, ok := filtered[pt]; ok {
			filtered[pt] = true
		}
	}

	for pt, ok := range filtered {
		if !ok {
			toCopy = append(toCopy, pt)
		}
	}

	return toCopy
}