package main

// What the journal verb may be asked (the operator's direction 2026-10-07, recorded in novox/hq): a time
// window, a priority and a fixed text, beside the unit and how many lines.
//
// **Nothing a caller says reaches a shell, and nothing is read as an option.** journalctl is run with an
// argv of its own words (execRunner), under `sudo -n` for the system journal (issue 255) — so a value that
// journalctl read as an option would be root's option. Every value is therefore held to the forms
// journalctl reads for it and given as `--name=value`, one word: a relative "-30min" is the value of
// --since, never a flag. A value in any other form is refused naming the forms, before anything runs.

import (
	"fmt"
	"regexp"
	"strconv"
	"strings"
	"time"
)

const (
	// MostLines is the most lines one answer carries: well below what the runtime carries back in one reply.
	MostLines = 2000
	// DefaultLines is how many when the caller does not say.
	DefaultLines = 100
	// MatchScan is how many of the window's last lines a match is looked for in.
	MatchScan = 50000
	// LongestLine is where one line is cut, so a single runaway line cannot fill the answer.
	LongestLine = 4096
	// LongestMatch is the longest text a match may be.
	LongestMatch = 256
)

// JournalQuery is what a journal read is narrowed by.
type JournalQuery struct {
	Lines    int
	Since    string
	Until    string
	Match    string
	Priority string
}

// relative is a time journalctl reads relative to now: -30min, +1h, 2h30min ago, and the day words.
var relative = regexp.MustCompile(`^(now|today|yesterday|tomorrow|[+-]?([0-9]+(usec|us|msec|ms|seconds|second|sec|s|minutes|minute|min|m|hours|hour|hr|h|days|day|d|weeks|week|w|months|month|M|years|year|y))+|([0-9]+(usec|us|msec|ms|seconds|second|sec|s|minutes|minute|min|m|hours|hour|hr|h|days|day|d|weeks|week|w|months|month|M|years|year|y) ?)+ago)$`)

// localDate is a date, or a date and a time, in the machine's own zone, as journalctl reads it.
var localDate = regexp.MustCompile(`^[0-9]{4}-[0-9]{2}-[0-9]{2}( [0-9]{2}:[0-9]{2}(:[0-9]{2})?)?$`)

// priorities are journalctl's priority names, and the words people use for them.
var priorities = map[string]int{
	"emerg": 0, "emergency": 0, "panic": 0, "alert": 1, "crit": 2, "critical": 2, "err": 3, "error": 3,
	"warning": 4, "warn": 4, "notice": 5, "info": 6, "debug": 7,
}

// when is one bound of the window as journalctl is given it, and the absolute time it names when it is
// one: an RFC 3339 time becomes seconds since the epoch, which every journalctl reads whatever its version.
func when(name, v string, ceil bool) (string, *time.Time, error) {
	if t, err := time.Parse(time.RFC3339Nano, v); err == nil {
		s := t.Unix()
		if ceil && t.Nanosecond() > 0 {
			s++
		}
		return "@" + strconv.FormatInt(s, 10), &t, nil
	}
	if relative.MatchString(v) || localDate.MatchString(v) {
		return v, nil, nil
	}
	return "", nil, fmt.Errorf("%s %q: an RFC 3339 time (2026-10-07T09:30:00Z), a time relative to now "+
		"(-30min, -2h, 1h ago, yesterday) or a local date (2026-10-07 09:30)", name, v)
}

// valid is the query with its defaults applied and every value held to its forms.
func (q JournalQuery) valid() (JournalQuery, error) {
	switch {
	case q.Lines == 0:
		q.Lines = DefaultLines
	case q.Lines < 0:
		return q, fmt.Errorf("lines %d: at least 1", q.Lines)
	case q.Lines > MostLines:
		q.Lines = MostLines
	}
	var since, until *time.Time
	var err error
	if q.Since != "" {
		if _, since, err = when("since", q.Since, false); err != nil {
			return q, err
		}
	}
	if q.Until != "" {
		if _, until, err = when("until", q.Until, true); err != nil {
			return q, err
		}
	}
	if since != nil && until != nil && until.Before(*since) {
		return q, fmt.Errorf("the window ends (%s) before it starts (%s)", q.Until, q.Since)
	}
	if q.Priority != "" {
		p := strings.ToLower(q.Priority)
		if n, ok := priorities[p]; ok {
			q.Priority = strconv.Itoa(n)
		} else if len(p) != 1 || p[0] < '0' || p[0] > '7' {
			return q, fmt.Errorf("priority %q: 0-7, or emerg, alert, crit, err, warning, notice, info, debug", q.Priority)
		}
	}
	if len(q.Match) > LongestMatch {
		return q, fmt.Errorf("a match is at most %d bytes", LongestMatch)
	}
	if strings.ContainsAny(q.Match, "\n\r\x00") {
		return q, fmt.Errorf("a match is one line of text")
	}
	return q, nil
}

// argv is journalctl's words for a valid query: each value inside the word of its own option.
func (q JournalQuery) argv(unit string, lines int) []string {
	args := []string{"--no-pager", "--output=short-iso", "--unit=" + unit}
	if q.Since != "" {
		v, _, _ := when("since", q.Since, false)
		args = append(args, "--since="+v)
	}
	if q.Until != "" {
		v, _, _ := when("until", q.Until, true)
		args = append(args, "--until="+v)
	}
	if q.Priority != "" {
		args = append(args, "--priority="+q.Priority)
	}
	return append(args, "--lines="+strconv.Itoa(lines))
}

// journalQuery is the query a call's arguments say. A number may come as a JSON number or as its text:
// the seat's schema carries every argument as a string.
func journalQuery(a map[string]any) (JournalQuery, error) {
	q := JournalQuery{}
	switch v := a["lines"].(type) {
	case nil:
	case float64:
		if v != float64(int(v)) {
			return q, fmt.Errorf("lines %v: a whole number", v)
		}
		q.Lines = int(v)
	case string:
		if strings.TrimSpace(v) != "" {
			n, err := strconv.Atoi(strings.TrimSpace(v))
			if err != nil {
				return q, fmt.Errorf("lines %q: a whole number", v)
			}
			q.Lines = n
		}
	default:
		return q, fmt.Errorf("lines: a whole number")
	}
	for name, into := range map[string]*string{"since": &q.Since, "until": &q.Until, "match": &q.Match, "priority": &q.Priority} {
		switch v := a[name].(type) {
		case nil:
		case string:
			if name == "match" {
				*into = v
			} else {
				*into = strings.TrimSpace(v)
			}
		case float64:
			if name != "priority" {
				return q, fmt.Errorf("%s: text", name)
			}
			*into = strconv.FormatFloat(v, 'f', -1, 64)
		default:
			return q, fmt.Errorf("%s: text", name)
		}
	}
	return q, nil
}