package inspur

import (
	"bufio"
	"bytes"
	"regexp"
	"sort"
	"strings"
	"time"

	"git.mchus.pro/mchus/logpile/internal/parser"
)

var explicitInspurTimestampRegex = regexp.MustCompile(`\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(?:\.\d+)?[+-]\d{2}:\d{2}`)

type inspurOffsetSample struct {
	local  time.Time
	offset int
}

// inspurTimezoneResolver handles dumps where timezone.conf is stale or the BMC
// timezone changed during the retained SEL history. Offset-bearing IDL/syslog
// timestamps are authoritative; timezone.conf remains the fallback.
type inspurTimezoneResolver struct {
	fallback *time.Location
	samples  []inspurOffsetSample
}

func inferInspurTimezoneResolver(files []parser.ExtractedFile, fallback *time.Location) *inspurTimezoneResolver {
	if fallback == nil {
		fallback = parser.DefaultArchiveLocation()
	}
	r := &inspurTimezoneResolver{fallback: fallback}
	seen := make(map[string]struct{})
	preferIDL := false
	for _, f := range files {
		if strings.Contains(strings.ToLower(f.Path), "idl") {
			preferIDL = true
			break
		}
	}

	for pass := 0; pass < 2; pass++ {
		idlOnly := preferIDL && pass == 0
		if pass == 1 && (!preferIDL || len(r.samples) > 0) {
			break
		}
		for _, f := range files {
			path := strings.ToLower(f.Path)
			if idlOnly && !strings.Contains(path, "idl") {
				continue
			}
			if !strings.Contains(path, "/log/") && !strings.Contains(path, "idl") {
				continue
			}
			scanner := bufio.NewScanner(bytes.NewReader(f.Content))
			scanner.Buffer(make([]byte, 64*1024), 1024*1024)
			for scanner.Scan() {
				matches := explicitInspurTimestampRegex.FindAllString(scanner.Text(), -1)
				if len(matches) == 0 {
					continue
				}
				// idl.log is itself a syslog stream. Its outer timestamp can retain
				// an obsolete BMC offset while the embedded IDL record has the offset
				// that was active for the hardware event. Prefer the embedded value.
				raw := matches[len(matches)-1]
				ts, err := time.Parse(time.RFC3339Nano, raw)
				if err != nil || ts.Year() < 2000 {
					continue
				}
				_, offset := ts.Zone()
				local := time.Date(ts.Year(), ts.Month(), ts.Day(), ts.Hour(), ts.Minute(), ts.Second(), 0, time.UTC)
				// One sample per local day and offset is sufficient to identify BMC
				// timezone eras while bounding memory on very large rotated logs.
				key := local.Format("2006-01-02") + "|" + strings.TrimSpace(raw[len(raw)-6:])
				if _, ok := seen[key]; ok {
					continue
				}
				seen[key] = struct{}{}
				r.samples = append(r.samples, inspurOffsetSample{local: local, offset: offset})
			}
		}
	}

	sort.Slice(r.samples, func(i, j int) bool { return r.samples[i].local.Before(r.samples[j].local) })
	return r
}

func (r *inspurTimezoneResolver) locationFor(local time.Time) *time.Location {
	if r == nil || len(r.samples) == 0 {
		if r != nil && r.fallback != nil {
			return r.fallback
		}
		return parser.DefaultArchiveLocation()
	}

	best := r.samples[0]
	bestDistance := absDuration(local.Sub(best.local))
	for _, sample := range r.samples[1:] {
		distance := absDuration(local.Sub(sample.local))
		if distance < bestDistance {
			best = sample
			bestDistance = distance
		}
	}
	return time.FixedZone(formatUTCOffset(best.offset), best.offset)
}

func absDuration(v time.Duration) time.Duration {
	if v < 0 {
		return -v
	}
	return v
}

func formatUTCOffset(offset int) string {
	sign := "+"
	if offset < 0 {
		sign = "-"
		offset = -offset
	}
	return "UTC" + sign + twoDigits(offset/3600) + ":" + twoDigits((offset%3600)/60)
}

func twoDigits(v int) string {
	return string([]byte{'0' + byte(v/10), '0' + byte(v%10)})
}