package server

import (
	"fmt"
	"net/url"
	"strconv"
	"strings"
	"time"
)

const (
	defaultWindow = 15 * time.Minute
	// maxWindow matches the table TTL; anything wider scans nothing extra
	// but signals a client bug, so reject it.
	maxWindow    = 72 * time.Hour
	defaultLimit = 100
	maxLimit     = 1000
	tailLimit    = 500
)

// filterColumns maps API query parameters to the column expression they filter
// on. Only these names are ever accepted; values are always bound parameters.
var filterColumns = []struct {
	param  string
	column string
}{
	{"namespace", "namespace"},
	{"host", "host"},
	{"pod", "pod"},
	{"container", "container"},
	{"app", "labels['app']"},
	{"severity", "severity"},
	{"stream", "stream"},
	{"source", "source"},
}

const selectColumns = "timestamp, toUnixTimestamp64Milli(timestamp) AS ts_ms, host, source, namespace, pod, container, stream, severity, message, labels, fields"

type timeRange struct {
	since time.Time
	until time.Time
}

// parseTimeRange enforces server-side time bounds: missing bounds default to a
// 15m window ending now, and windows wider than maxWindow are rejected so a
// query can never run unbounded over the store.
func parseTimeRange(sinceStr, untilStr string, now time.Time) (timeRange, error) {
	until := now
	if untilStr != "" {
		t, err := parseTime(untilStr, now)
		if err != nil {
			return timeRange{}, fmt.Errorf("invalid until: %w", err)
		}
		until = t
	}
	since := until.Add(-defaultWindow)
	if sinceStr != "" {
		t, err := parseTime(sinceStr, now)
		if err != nil {
			return timeRange{}, fmt.Errorf("invalid since: %w", err)
		}
		since = t
	}
	if !since.Before(until) {
		return timeRange{}, fmt.Errorf("since (%s) must be before until (%s)", since.UTC().Format(time.RFC3339), until.UTC().Format(time.RFC3339))
	}
	if until.Sub(since) > maxWindow {
		return timeRange{}, fmt.Errorf("time window %s exceeds maximum %s", until.Sub(since), maxWindow)
	}
	return timeRange{since: since, until: until}, nil
}

// parseTime accepts RFC3339, "2006-01-02 15:04:05", unix seconds/millis, and
// relative durations like "15m" / "6h" / "1d" (meaning that long ago).
func parseTime(s string, now time.Time) (time.Time, error) {
	if t, err := time.Parse(time.RFC3339, s); err == nil {
		return t, nil
	}
	if t, err := time.Parse("2006-01-02 15:04:05", s); err == nil {
		return t.UTC(), nil
	}
	if n, err := strconv.ParseInt(s, 10, 64); err == nil {
		if n > 1e12 {
			return time.UnixMilli(n).UTC(), nil
		}
		return time.Unix(n, 0).UTC(), nil
	}
	if d, err := parseDuration(strings.TrimPrefix(s, "-")); err == nil {
		return now.Add(-d), nil
	}
	return time.Time{}, fmt.Errorf("unrecognised time %q", s)
}

func parseDuration(s string) (time.Duration, error) {
	if strings.HasSuffix(s, "d") {
		n, err := strconv.Atoi(strings.TrimSuffix(s, "d"))
		if err != nil {
			return 0, err
		}
		return time.Duration(n) * 24 * time.Hour, nil
	}
	return time.ParseDuration(s)
}

func parseLimit(s string, def int) (int, error) {
	if s == "" {
		return def, nil
	}
	n, err := strconv.Atoi(s)
	if err != nil || n < 1 {
		return 0, fmt.Errorf("invalid limit %q", s)
	}
	if n > maxLimit {
		n = maxLimit
	}
	return n, nil
}

func parseOffset(s string) (int, error) {
	if s == "" {
		return 0, nil
	}
	n, err := strconv.Atoi(s)
	if err != nil || n < 0 {
		return 0, fmt.Errorf("invalid offset %q", s)
	}
	return n, nil
}

// validateSQLFragment gates the raw WHERE fragment. Real safety comes from the
// readonly ClickHouse user and the parameterized outer query; this only blocks
// statement separators.
func validateSQLFragment(frag string) error {
	if strings.Contains(frag, ";") {
		return fmt.Errorf("sql fragment must not contain ';'")
	}
	return nil
}

// encodeStringArray renders a ClickHouse Array(String) parameter value.
func encodeStringArray(items []string) string {
	var b strings.Builder
	b.WriteByte('[')
	for i, it := range items {
		if i > 0 {
			b.WriteByte(',')
		}
		b.WriteByte('\'')
		b.WriteString(strings.ReplaceAll(strings.ReplaceAll(it, `\`, `\\`), `'`, `\'`))
		b.WriteByte('\'')
	}
	b.WriteByte(']')
	return b.String()
}

// whereClause builds the parameterized WHERE clause shared by the endpoints.
// The time bounds are always present and always bound parameters, so no
// filter or raw sql fragment can widen the scanned range.
func whereClause(tr timeRange, form url.Values, params map[string]string, exclusiveSince bool) (string, error) {
	var conds []string
	params["since_ms"] = strconv.FormatInt(tr.since.UnixMilli(), 10)
	params["until_ms"] = strconv.FormatInt(tr.until.UnixMilli(), 10)
	sinceOp := ">="
	if exclusiveSince {
		sinceOp = ">"
	}
	conds = append(conds,
		"timestamp "+sinceOp+" fromUnixTimestamp64Milli({since_ms:Int64})",
		"timestamp < fromUnixTimestamp64Milli({until_ms:Int64})",
	)

	for _, f := range filterColumns {
		if v := form.Get(f.param); v != "" {
			p := "f_" + f.param
			params[p] = v
			conds = append(conds, fmt.Sprintf("%s = {%s:String}", f.column, p))
		}
	}

	if q := strings.TrimSpace(form.Get("q")); q != "" {
		tokens := strings.Fields(q)
		params["q_tokens"] = encodeStringArray(tokens)
		conds = append(conds, "arrayAll(t -> positionCaseInsensitive(message, t) > 0, {q_tokens:Array(String)})")
	}

	if frag := strings.TrimSpace(form.Get("sql")); frag != "" {
		if err := validateSQLFragment(frag); err != nil {
			return "", err
		}
		conds = append(conds, "( "+frag+" )")
	}

	return strings.Join(conds, "\n  AND "), nil
}

func buildQuerySQL(where string, limit, offset int) string {
	return fmt.Sprintf(
		"SELECT %s\nFROM logs.raw\nWHERE %s\nORDER BY timestamp DESC\nLIMIT %d OFFSET %d\nFORMAT JSON",
		selectColumns, where, limit, offset)
}

func buildTailSQL(where string) string {
	return fmt.Sprintf(
		"SELECT %s\nFROM logs.raw\nWHERE %s\nORDER BY timestamp ASC\nLIMIT %d\nFORMAT JSON",
		selectColumns, where, tailLimit)
}

func buildFacetsSQL(where string) string {
	facet := func(name, expr string) string {
		return fmt.Sprintf(
			"SELECT * FROM (SELECT '%s' AS facet, %s AS value, count() AS n FROM logs.raw WHERE %s GROUP BY value ORDER BY n DESC LIMIT 20)",
			name, expr, where)
	}
	return facet("namespace", "namespace") +
		"\nUNION ALL\n" + facet("app", "labels['app']") +
		"\nUNION ALL\n" + facet("host", "host") +
		"\nFORMAT JSON"
}