package handlers

import (
	"time"
	"unicode/utf8"
)

// maxRenderedBodyBytes caps how many bytes of a stored event
// body reach the event log page. Bodies come from the
// unauthenticated receiver under the 1 MB ingest cap and
// renderTemplate buffers a whole page before writing it, so
// an uncapped page of paginationPerPage events is tens of
// megabytes of resident memory per concurrent viewer.
const maxRenderedBodyBytes = 8192

// eventLogColumns is the event log's projection. The casts to
// blob are load-bearing: they make substr and length count
// bytes rather than characters, so the cap bounds the page in
// bytes whatever the payload's encoding. Cutting in SQLite
// rather than in Go is the point of the projection — an
// oversized body never becomes a Go string at all.
const eventLogColumns = "id, created_at, method, content_type, " +
	"substr(cast(body as blob), 1, ?) AS body, " +
	"length(cast(body as blob)) AS body_bytes"

// EventLogView is the display-safe projection of an event for
// the event log page, alongside DeliveryView and TargetView.
// It carries a capped body plus the true stored size, so the
// page can mark a body as truncated without ever holding the
// whole thing.
type EventLogView struct {
	ID          string
	CreatedAt   time.Time
	Method      string
	ContentType string

	// Body holds at most maxRenderedBodyBytes bytes of the
	// stored body.
	Body string

	// BodyBytes is the true size of the stored body.
	BodyBytes int64

	// BodyTruncated reports that the stored body was larger
	// than the cap, so the page owes the reader a marker.
	BodyTruncated bool

	Deliveries []DeliveryView
}

// BodyShownBytes is how many body bytes the page is actually
// rendering, which the truncation marker reports beside the
// true size.
func (v EventLogView) BodyShownBytes() int {
	return len(v.Body)
}

// eventLogRow is one row of the event log projection. Its
// body column arrives already cut to the cap by SQLite, with
// the true size beside it.
type eventLogRow struct {
	ID          string
	CreatedAt   time.Time
	Method      string
	ContentType string
	Body        []byte
	BodyBytes   int64
}

// view projects a loaded row for rendering.
func (r *eventLogRow) view() EventLogView {
	body := r.Body
	truncated := r.BodyBytes > int64(len(body))

	// Only a cut body can have been left mid-sequence by
	// this query. A whole body is passed through exactly as
	// stored, however malformed.
	if truncated {
		body = trimPartialRune(body)
	}

	return EventLogView{
		ID:            r.ID,
		CreatedAt:     r.CreatedAt,
		Method:        r.Method,
		ContentType:   r.ContentType,
		Body:          string(body),
		BodyBytes:     r.BodyBytes,
		BodyTruncated: truncated,
	}
}

// trimPartialRune drops a trailing UTF-8 sequence that the
// byte-wise cut left incomplete, so a multi-byte rune severed
// at the cap does not surface as a mojibake tail.
//
// Bytes that are merely invalid UTF-8 are left exactly as
// stored: this service receives binary payloads, and rewriting
// them would misreport what was delivered. The distinction is
// utf8.FullRune's — it reports a complete sequence for an
// invalid encoding too, since that decodes to a width-1 error
// rune, so only a valid prefix still waiting for its
// continuation bytes is removed. A tail with no rune start in
// its last utf8.UTFMax bytes cannot be an incomplete sequence
// either, and is likewise left alone.
func trimPartialRune(b []byte) []byte {
	for i := len(b) - 1; i >= 0 && len(b)-i <= utf8.UTFMax; i-- {
		if !utf8.RuneStart(b[i]) {
			continue
		}

		if utf8.FullRune(b[i:]) {
			return b
		}

		return b[:i]
	}

	return b
}