package httpapi

import (
	"encoding/json"
	"net/http"
	"os"

	"gopkg.in/yaml.v3"
)

// defaultVersionManifestPath is VERSION_MANIFEST's default when unset — mirrors
// how server.env wires DOWNLOADS_DIR alongside DownloadsHandler's own built-in
// default (see downloads.go / deploy/single-node/deploy.sh).
const defaultVersionManifestPath = "/etc/pangolin/version.yaml"

// Fallback values used ONLY when the manifest file itself is missing (fresh
// box that hasn't run deploy/single-node/deploy.sh's manifest-install step
// yet, or a local dev server). These are hand-set, not auto-derived — once a
// box is deployed, the real source of truth is the on-disk manifest that
// scripts/ci/release-client.sh overwrites on every client-v* release.
const (
	defaultManifestVersion     = "1.0.48"
	defaultManifestBuildNumber = 10048
)

// changelogSection / changelogEntry mirror jiu's backend/config/version.yaml
// shape (~/code/jiu/backend/internal/handler/version.go) so any future shared
// tooling (e.g. a website changelog widget) can treat both services'
// /version responses identically. Pangolin's release pipeline doesn't
// populate Changelog yet (no CHANGELOG-client.md parsing wired in
// scripts/ci/release-client.sh) — the field exists for shape-compatibility
// and always serializes as [] rather than null.
type changelogSection struct {
	Type  string   `yaml:"type" json:"type"`
	Items []string `yaml:"items" json:"items"`
}

type changelogEntry struct {
	Version  string             `yaml:"version" json:"version"`
	Date     string             `yaml:"date" json:"date"`
	Intro    string             `yaml:"intro" json:"intro"`
	Sections []changelogSection `yaml:"sections" json:"sections"`
}

// versionManifest is the on-disk (and wire) shape of the auto-update
// manifest. download_urls keys in practice: macos, windows, ios, android
// (web is intentionally not used — pangolin's client is native-only).
type versionManifest struct {
	Version      string            `yaml:"version" json:"version"`
	BuildNumber  int               `yaml:"build_number" json:"build_number"`
	ForceUpdate  bool              `yaml:"force_update" json:"force_update"`
	ReleaseNotes string            `yaml:"release_notes" json:"release_notes"`
	DownloadURLs map[string]string `yaml:"download_urls" json:"download_urls"`
	Changelog    []changelogEntry  `yaml:"changelog" json:"changelog"`
}

// VersionHandler serves GET /version (public, no auth — mounted directly in
// main.go next to /healthz and /downloads/*). Unlike most handlers in this
// package it re-reads its manifest file from disk on EVERY request rather
// than caching it in memory: scripts/ci/release-client.sh rewrites
// /etc/pangolin/version.yaml's version/build_number on each client-v*
// release, and that must take effect immediately without a control-plane
// restart or redeploy (mirrors jiu's loadVersionConfig()-per-request).
type VersionHandler struct {
	path string
}

// NewVersionHandler builds a VersionHandler reading the manifest at path.
// path=="" falls back to defaultVersionManifestPath (in production this is
// overridden via the VERSION_MANIFEST env var — see main.go).
func NewVersionHandler(path string) *VersionHandler {
	if path == "" {
		path = defaultVersionManifestPath
	}
	return &VersionHandler{path: path}
}

// defaultManifest is returned when the manifest file doesn't exist yet, so
// GET /version still answers usefully (client update-checks shouldn't hard
// fail just because deploy/single-node/deploy.sh hasn't run on this box).
func defaultManifest() versionManifest {
	return versionManifest{
		Version:      defaultManifestVersion,
		BuildNumber:  defaultManifestBuildNumber,
		ForceUpdate:  false,
		ReleaseNotes: "",
		DownloadURLs: map[string]string{
			"android": "https://api.yanmeiai.com/downloads/pangolin-android.apk",
			"windows": "https://api.yanmeiai.com/downloads/pangolin-windows-x64-setup.exe",
			"macos":   "",
			"ios":     "",
		},
		Changelog: []changelogEntry{},
	}
}

// loadManifest reads+parses h.path. A missing file is NOT an error (falls
// back to defaultManifest()); any other read/parse failure IS, so ServeHTTP
// can 500 instead of silently masking a corrupt manifest written by a bad
// release-client.sh run.
func (h *VersionHandler) loadManifest() (versionManifest, error) {
	data, err := os.ReadFile(h.path)
	if err != nil {
		if os.IsNotExist(err) {
			return defaultManifest(), nil
		}
		return versionManifest{}, err
	}
	var m versionManifest
	if err := yaml.Unmarshal(data, &m); err != nil {
		return versionManifest{}, err
	}
	// Keep the JSON response shape stable (empty object/array, never null)
	// regardless of what the manifest on disk happens to omit.
	if m.DownloadURLs == nil {
		m.DownloadURLs = map[string]string{}
	}
	if m.Changelog == nil {
		m.Changelog = []changelogEntry{}
	}
	return m, nil
}

// Serve handles GET /version. Named Serve (not ServeHTTP) to match
// DownloadsHandler's convention in this package (see downloads.go).
func (h *VersionHandler) Serve(w http.ResponseWriter, r *http.Request) {
	m, err := h.loadManifest()
	if err != nil {
		w.Header().Set("Content-Type", "application/json; charset=utf-8")
		w.WriteHeader(http.StatusInternalServerError)
		_ = json.NewEncoder(w).Encode(map[string]string{"error": "version manifest unavailable"})
		return
	}
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(http.StatusOK)
	_ = json.NewEncoder(w).Encode(m)
}