package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
	"path"
	"strconv"
	"sync"

	"hakurei.app/internal/info"
	"hakurei.app/internal/pkg"
	"hakurei.app/internal/rosa"
)

// for lazy initialisation of serveInfo
var (
	infoPayload struct {
		// Current package count.
		Count int `json:"count"`
		// Hakurei version, set at link time.
		HakureiVersion string `json:"hakurei_version"`
	}
	infoPayloadOnce sync.Once
)

// handleInfo writes constant system information.
func handleInfo(w http.ResponseWriter, _ *http.Request) {
	infoPayloadOnce.Do(func() {
		infoPayload.Count = int(rosa.PresetUnexportedStart)
		infoPayload.HakureiVersion = info.Version()
	})
	// TODO(mae): cache entire response if no additional fields are planned
	writeAPIPayload(w, infoPayload)
}

func (index *packageIndex) newStatusHandler(disposition bool) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		name := path.Base(r.URL.Path)
		p, ok := rosa.ResolveName(name)
		if !ok {
			http.NotFound(w, r)
			return
		}
		m := rosa.GetMetadata(p)
		pk, ok := index.names[m.Name]
		if !ok {
			http.NotFound(w, r)
			return
		}
		if len(pk.status) > 0 {
			if disposition {
				w.Header().Set("Content-Type", "application/octet-stream")
			} else {
				w.Header().Set("Content-Type", "text/plain; charset=utf-8")
			}
			if disposition {
				var version string
				if pk.Version != "\u0000" {
					version = pk.Version
				} else {
					version = "unknown"
				}
				w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s-%s-%s.log\"", pk.Name, version, pkg.Encode(pk.ident.Value())))
			}

			w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
			_, err := io.Copy(w, bytes.NewReader(pk.status))
			if err != nil {
				http.Error(w, err.Error(), http.StatusInternalServerError)
			}
		} else {
			http.NotFound(w, r)
		}
	}
}

// handleGet writes a slice of metadata with specified order.
func (index *packageIndex) handleGet(w http.ResponseWriter, r *http.Request) {
	q := r.URL.Query()
	limit, err := strconv.Atoi(q.Get("limit"))
	if err != nil || limit > 100 || limit < 1 {
		http.Error(
			w, "limit must be an integer between 1 and 100",
			http.StatusBadRequest,
		)
		return
	}
	i, err := strconv.Atoi(q.Get("index"))
	if err != nil || i >= len(index.sorts[0]) || i < 0 {
		http.Error(
			w, "index must be an integer between 0 and "+
				strconv.Itoa(int(rosa.PresetUnexportedStart-1)),
			http.StatusBadRequest,
		)
		return
	}
	sort, err := strconv.Atoi(q.Get("sort"))
	if err != nil || sort >= len(index.sorts) || sort < 0 {
		http.Error(
			w, "sort must be an integer between 0 and "+
				strconv.Itoa(sortOrderEnd),
			http.StatusBadRequest,
		)
		return
	}
	values := index.sorts[sort][i:min(i+limit, len(index.sorts[sort]))]
	// TODO(mae): remove count field
	writeAPIPayload(w, &struct {
		Count  int         `json:"count"`
		Values []*metadata `json:"values"`
	}{len(values), values})
}

// apiVersion is the name of the current API revision, as part of the pattern.
const apiVersion = "v1"

// registerAPI registers API handler functions.
func (index *packageIndex) registerAPI(mux *http.ServeMux) {
	mux.HandleFunc("GET /api/"+apiVersion+"/info", handleInfo)
	mux.HandleFunc("GET /api/"+apiVersion+"/get", index.handleGet)
	mux.HandleFunc("GET /api/"+apiVersion+"/status/", index.newStatusHandler(false))
	mux.HandleFunc("GET /status/", index.newStatusHandler(true))
}

// writeAPIPayload sets headers common to API responses and encodes payload as
// JSON for the response body.
func writeAPIPayload(w http.ResponseWriter, payload any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
	w.Header().Set("Pragma", "no-cache")
	w.Header().Set("Expires", "0")

	if err := json.NewEncoder(w).Encode(payload); err != nil {
		log.Println(err)
		http.Error(
			w, "cannot encode payload, contact maintainers",
			http.StatusInternalServerError,
		)
	}
}