package handlers

import (
	"encoding/json"
	"net/http"
	"slices"
	"strings"
	"time"
	"unicode/utf8"

	"github.com/dustin/go-humanize"
	"sneak.berlin/go/webhooker/internal/database"
)

// 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 or set of request headers never becomes a Go
// string at all.
const eventLogColumns = "id, created_at, method, content_type, " +
	"resubmitted_from_id, entrypoint_id, " +
	"substr(cast(headers as blob), 1, ?) AS headers, " +
	"length(cast(headers as blob)) AS headers_bytes, " +
	"substr(cast(body as blob), 1, ?) AS body, " +
	"length(cast(body as blob)) AS body_bytes"

// eventColumns is eventLogColumns for the event's own page, which
// shows the whole body and every request header.
const eventColumns = "id, created_at, method, content_type, " +
	"resubmitted_from_id, entrypoint_id, headers, " +
	"length(cast(headers as blob)) AS headers_bytes, " +
	"cast(body as blob) AS body, " +
	"length(cast(body as blob)) AS body_bytes"

// EventLogView is the display-safe projection of an event for
// the event log page and the event's own page, alongside
// DeliveryView and TargetView.
type EventLogView struct {
	ID          string
	Method      string
	ContentType string

	// Received is how long ago the event arrived, and ReceivedUTC
	// the full timestamp.
	Received    string
	ReceivedUTC string

	Body BodyView

	// Entrypoint names the entrypoint the event arrived at. A
	// resubmitted copy, even a copy of a copy, did not arrive; it
	// names the one the request it copies arrived at. The name is
	// the entrypoint's description, "Entrypoint" when it has none,
	// or "deleted entrypoint", never its URL, which is the
	// entrypoint's secret.
	Entrypoint string

	// Headers is the event's request headers as text, one
	// "Name: value" line per value, sorted by name. HeadersCut
	// reports headers left out because they hold more than
	// maxRenderedBodyBytes, stored or as text; only the event log
	// leaves them out.
	Headers    string
	HeadersCut bool

	// ResubmittedFromID names the event this one was copied
	// from, empty for an event that arrived on the receiver.
	ResubmittedFromID string

	// ResubmitCount is how many events have been resubmitted
	// from this one. Both directions are shown, because after
	// a few resubmits of one captured event the log is
	// otherwise a row of identical bodies with nothing saying
	// which came from which.
	ResubmitCount int

	Deliveries []DeliveryView
}

// ResubmittedFrom reports that this event is a copy of another.
func (v EventLogView) ResubmittedFrom() bool {
	return v.ResubmittedFromID != ""
}

// eventLogRow is one row of the event log projection, or of
// eventColumns. In the event log its headers and body columns
// arrive already cut to the cap by SQLite, each with its true
// size beside it.
type eventLogRow struct {
	ID                string
	CreatedAt         time.Time
	Method            string
	ContentType       string
	ResubmittedFromID *string
	EntrypointID      string
	Headers           string
	HeadersBytes      int64
	Body              []byte
	BodyBytes         int64
}

// view projects a loaded row of the webhook's events for
// rendering. It shows the request headers when the row holds them
// whole and their text holds at most maxHeaderBytes.
func (r *eventLogRow) view(
	webhookID string, maxHeaderBytes int,
) EventLogView {
	var from string
	if r.ResubmittedFromID != nil {
		from = *r.ResubmittedFromID
	}

	headers, fit := requestHeaderLines(r.Headers, maxHeaderBytes)

	return EventLogView{
		ID:          r.ID,
		Method:      r.Method,
		ContentType: r.ContentType,
		Received:    humanize.Time(r.CreatedAt),
		ReceivedUTC: r.CreatedAt.UTC().Format(time.DateTime) + " UTC",
		Body: newBodyView(
			"/hook/"+webhookID+"/events/"+r.ID, r.Body, r.BodyBytes,
		),
		Headers:           strings.Join(headers, "\n"),
		HeadersCut:        !fit || r.HeadersBytes > int64(len(r.Headers)),
		ResubmittedFromID: from,
	}
}

// requestHeaderLines turns an event's stored request headers, the
// JSON the receiver writes, into one "Name: value" line per value,
// sorted by name. Headers that do not parse, as when the event log
// has cut them, show as none. It reports false, with no lines, when
// the lines, each with the newline that follows it, would hold more
// than maxBytes: a header sent many times is stored with its name
// once but shown with it on every line.
func requestHeaderLines(headersJSON string, maxBytes int) ([]string, bool) {
	var headers http.Header

	if json.Unmarshal([]byte(headersJSON), &headers) != nil {
		return nil, true
	}

	names := make([]string, 0, len(headers))
	for name := range headers {
		names = append(names, name)
	}

	slices.Sort(names)

	var lines []string

	size := 0

	for _, name := range names {
		for _, value := range headers[name] {
			line := name + ": " + value

			size += len(line) + len("\n")
			if size > maxBytes {
				return nil, false
			}

			lines = append(lines, line)
		}
	}

	return lines, true
}

// entrypointNames maps each of the webhook's entrypoints to the name
// an event that arrived at it shows: its description, or "Entrypoint"
// when it has none, as the webhook page names it. A deleted
// entrypoint is left out.
func (h *Handlers) entrypointNames(
	webhookID string,
) (map[string]string, error) {
	var entrypoints []database.Entrypoint

	err := h.db.DB().Where(
		"webhook_id = ?", webhookID,
	).Find(&entrypoints).Error
	if err != nil {
		return nil, err
	}

	names := make(map[string]string, len(entrypoints))

	for i := range entrypoints {
		name := entrypoints[i].Description
		if name == "" {
			name = "Entrypoint"
		}

		names[entrypoints[i].ID] = name
	}

	return names, nil
}

// 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
}