package hostcollect

import (
	"path/filepath"
	"sort"
	"strconv"
	"strings"

	"github.com/itworx/pulse/internal/host"
)

// pseudoFilesystems never describe usable capacity; reporting them would fill the
// filesystem list with kernel bookkeeping and push real volumes past the limit.
var pseudoFilesystems = map[string]struct{}{
	"autofs": {}, "bpf": {}, "binfmt_misc": {}, "cgroup": {}, "cgroup2": {},
	"configfs": {}, "debugfs": {}, "devpts": {}, "devtmpfs": {}, "efivarfs": {},
	"fuse.gvfsd-fuse": {}, "fusectl": {}, "hugetlbfs": {}, "mqueue": {}, "nsfs": {},
	"overlay": {}, "proc": {}, "pstore": {}, "ramfs": {}, "rpc_pipefs": {},
	"securityfs": {}, "selinuxfs": {}, "squashfs": {}, "sysfs": {}, "tmpfs": {},
	"tracefs": {},
}

type mountEntry struct {
	device string
	mount  string
	fsType string
}

// parseMounts reads /proc/mounts. Fields are space separated and the kernel escapes
// space, tab, newline and backslash inside the device and mount point as octal
// sequences, so an Unraid share called "/mnt/user/Media Backup" arrives as
// "/mnt/user/Media\040Backup" and must be unescaped before it can be used as a path.
func parseMounts(data []byte) []mountEntry {
	all := lines(data)
	entries := make([]mountEntry, 0, len(all))
	for _, line := range all {
		fields := strings.Fields(line)
		if len(fields) < 3 {
			continue
		}
		entries = append(entries, mountEntry{
			device: unescapeMountField(fields[0]),
			mount:  unescapeMountField(fields[1]),
			fsType: fields[2],
		})
	}
	return entries
}

func unescapeMountField(value string) string {
	if !strings.Contains(value, `\`) {
		return value
	}
	var builder strings.Builder
	builder.Grow(len(value))
	for index := 0; index < len(value); index++ {
		if value[index] == '\\' && index+3 < len(value) {
			if decoded, err := strconv.ParseUint(value[index+1:index+4], 8, 8); err == nil {
				builder.WriteByte(byte(decoded))
				index += 3
				continue
			}
		}
		builder.WriteByte(value[index])
	}
	return builder.String()
}

// filesystems reports capacity and inode usage per real mount point.
//
// It is disabled unless FilesystemRoot is configured. Inside a container the host's
// /proc/mounts lists host paths that do not exist in the container's mount namespace;
// calling statfs on the same string would either fail or — worse, for "/" — silently
// measure the container's own overlay and report it as the host's root filesystem.
// Mounting a host root read-only and pointing FilesystemRoot at it is an explicit,
// auditable decision rather than an accident of naming.
func (c *Collector) filesystems(warnings *warningSet) []host.RawFilesystem {
	if c.options.FilesystemRoot == "" {
		warnings.add(WarningFilesystemDisabled)
		return nil
	}
	data, err := readLimited(c.procPath("mounts"), maxFileBytes)
	if err != nil {
		warnings.add(WarningMountsUnavailable)
		return nil
	}
	seen := make(map[string]struct{})
	results := make([]host.RawFilesystem, 0, 16)
	failures := 0
	for _, entry := range parseMounts(data) {
		if _, pseudo := pseudoFilesystems[entry.fsType]; pseudo {
			continue
		}
		if entry.mount == "" || len(entry.mount) > 512 {
			continue
		}
		if _, duplicate := seen[entry.mount]; duplicate {
			continue
		}
		seen[entry.mount] = struct{}{}
		usage, statErr := c.options.StatFS(filepath.Join(c.options.FilesystemRoot, entry.mount))
		if statErr != nil {
			failures++
			continue
		}
		if usage.CapacityBytes == 0 {
			continue
		}
		if usage.UsedBytes > usage.CapacityBytes {
			usage.UsedBytes = usage.CapacityBytes
		}
		item := host.RawFilesystem{
			Mount:         entry.mount,
			Filesystem:    truncate(entry.fsType, 64),
			CapacityBytes: usage.CapacityBytes,
			UsedBytes:     usage.UsedBytes,
		}
		if usage.InodesTotal > 0 {
			used := usage.InodesUsed
			if used > usage.InodesTotal {
				used = usage.InodesTotal
			}
			item.Inodes = &host.RawInodes{Total: usage.InodesTotal, Used: used}
		}
		results = append(results, item)
	}
	if failures > 0 {
		warnings.add(WarningFilesystemPartial)
	}
	sort.Slice(results, func(i, j int) bool { return results[i].Mount < results[j].Mount })
	if len(results) > c.options.HostLimits.MaxFilesystems {
		results = results[:c.options.HostLimits.MaxFilesystems]
		warnings.add(WarningFilesystemTruncated)
	}
	if len(results) == 0 {
		return nil
	}
	return results
}