// SPDX-FileCopyrightText: 2026 Echolot contributors
// SPDX-License-Identifier: GPL-3.0-or-later

// Package runs stores uploaded measurement documents.
//
// The premise (and the reason uploads exist at all) is that an engineer runs their own server:
// uploading a run there is how history, diffing and "it was fine last Tuesday" work. That makes
// the storage deliberately dumb — one JSON file per run, on disk, greppable, deletable with rm —
// and puts the interesting policy in two places instead:
//
//   - who may upload (Policy.Mode), because a public server is a different proposition from a
//     private one; and
//   - how much identifying detail the client must strip first (Policy.MinAnonymization), because
//     someone measuring against a stranger's server should not be shipping their SSIDs there.
//
// Retention is enforced on every upload, not by a sweeper, so a server left alone does not grow.
package runs

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"time"
)

// Mode says who may upload.
type Mode string

const (
	// ModeOff refuses every upload. The endpoint still answers, with 403 and a reason, so the
	// app can say "this server does not accept uploads" instead of showing a network error.
	ModeOff Mode = "off"
	// ModeAnonymous accepts uploads from any enrolled device. The default: enrollment already
	// required an admin-minted token, so "anyone enrolled" is not "anyone".
	ModeAnonymous Mode = "anonymous"
	// ModeAccount accepts uploads only from a device where somebody has signed in (see
	// /v1/account/link). Enrollment alone is not enough: the operator's token admits a device,
	// an account attributes it to a person.
	ModeAccount Mode = "account"
)

// Anonymization levels, mirroring the client's redaction levels (measurement-schema.md §8).
// Ordered: full < balanced < strict.
const (
	AnonFull     = "full"     // nothing removed — for your own server
	AnonBalanced = "balanced" // network names and device identity pseudonymized, neighbours dropped
	AnonStrict   = "strict"   // metrics and findings only
)

func anonRank(level string) int {
	switch level {
	case AnonStrict:
		return 2
	case AnonBalanced:
		return 1
	case AnonFull:
		return 0
	}
	return -1 // unknown
}

// Policy is the operator's upload configuration.
type Policy struct {
	Mode             Mode   `json:"mode"`
	MaxBytes         int64  `json:"max_bytes"`
	RetentionDays    int    `json:"retention_days"`
	MaxRunsPerDevice int    `json:"max_runs_per_device"`
	MinAnonymization string `json:"min_anonymization"`
}

func DefaultPolicy() Policy {
	return Policy{
		Mode:             ModeAnonymous,
		MaxBytes:         4 << 20,
		RetentionDays:    90,
		MaxRunsPerDevice: 200,
		MinAnonymization: AnonFull,
	}
}

var (
	ErrDisabled      = errors.New("uploads are disabled on this server")
	ErrNeedAccount   = errors.New("this server only accepts uploads from signed-in accounts")
	ErrTooLarge      = errors.New("run exceeds the server's upload size limit")
	ErrNotAnonEnough = errors.New("run is less anonymized than this server requires")
	ErrMalformed     = errors.New("run is not a measurement document")
)

// Meta is the index entry for one stored run — enough to list history without opening the files.
type Meta struct {
	ID            string    `json:"id"`
	DeviceID      string    `json:"device_id"`
	UploadedAt    time.Time `json:"uploaded_at"`
	StartedAt     string    `json:"started_at,omitempty"`
	Anonymization string    `json:"anonymization"`
	SizeBytes     int64     `json:"size_bytes"`
	Verdict       string    `json:"verdict,omitempty"`
	FindingCount  int       `json:"finding_count"`
}

type Store struct {
	mu     sync.Mutex
	dir    string
	policy Policy
}

func Open(stateDir string, p Policy) (*Store, error) {
	dir := filepath.Join(stateDir, "runs")
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return nil, err
	}
	return &Store{dir: dir, policy: p}, nil
}

func (s *Store) Policy() Policy { return s.policy }

// Accepts reports whether an upload from this caller would be allowed at all, so callers can
// answer the capability question without a body.
//
// linked says whether a person has signed in on the uploading device. It is the only thing that
// distinguishes ModeAccount from ModeOff — and the reason the check takes an argument at all.
func (s *Store) Accepts(linked bool) error {
	switch s.policy.Mode {
	case ModeOff:
		return ErrDisabled
	case ModeAccount:
		if !linked {
			return ErrNeedAccount
		}
	}
	return nil
}

// Put validates and stores one uploaded document. body is the raw JSON as received: it is stored
// byte-for-byte so what the device signed off on is what sits on disk.
func (s *Store) Put(deviceID string, body []byte, linked bool) (Meta, error) {
	if err := s.Accepts(linked); err != nil {
		return Meta{}, err
	}
	if s.policy.MaxBytes > 0 && int64(len(body)) > s.policy.MaxBytes {
		return Meta{}, ErrTooLarge
	}

	// Peek at the parts we index on. Unknown fields are ignored: the server must not become a
	// second schema authority that rejects documents a newer client legitimately produces.
	var doc struct {
		Run struct {
			ID        string `json:"id"`
			StartedAt string `json:"started_at"`
			Privacy   struct {
				Anonymization string `json:"anonymization"`
			} `json:"privacy"`
		} `json:"run"`
		Findings []json.RawMessage `json:"findings"`
		Summary  struct {
			// measurement-schema.md §7.3 calls this "overall"; "verdict" is the per-category
			// field one level down. Reading the wrong one stored an empty verdict on every run
			// ever uploaded, which the UI showed as "not recorded" — a claim about the document
			// that was really a bug in this parser.
			Overall string `json:"overall"`
		} `json:"summary"`
	}
	if err := json.Unmarshal(body, &doc); err != nil || doc.Run.ID == "" {
		return Meta{}, ErrMalformed
	}

	level := doc.Run.Privacy.Anonymization
	if level == "" {
		level = AnonFull // no declaration means nothing was stripped
	}
	if anonRank(level) < anonRank(s.policy.MinAnonymization) {
		return Meta{}, fmt.Errorf("%w: got %q, need at least %q",
			ErrNotAnonEnough, level, s.policy.MinAnonymization)
	}

	id := sanitizeID(doc.Run.ID)
	if id == "" {
		return Meta{}, ErrMalformed
	}

	s.mu.Lock()
	defer s.mu.Unlock()
	devDir := filepath.Join(s.dir, sanitizeID(deviceID))
	if err := os.MkdirAll(devDir, 0o700); err != nil {
		return Meta{}, err
	}
	if err := os.WriteFile(filepath.Join(devDir, id+".json"), body, 0o600); err != nil {
		return Meta{}, err
	}

	meta := Meta{
		ID: id, DeviceID: deviceID, UploadedAt: time.Now().UTC(),
		StartedAt: doc.Run.StartedAt, Anonymization: level,
		SizeBytes: int64(len(body)), Verdict: doc.Summary.Overall,
		FindingCount: len(doc.Findings),
	}
	if err := os.WriteFile(filepath.Join(devDir, id+".meta.json"), mustJSON(meta), 0o600); err != nil {
		return Meta{}, err
	}
	s.enforceRetentionLocked(devDir)
	return meta, nil
}

// List returns one device's runs, newest first.
func (s *Store) List(deviceID string) []Meta {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.listLocked(filepath.Join(s.dir, sanitizeID(deviceID)))
}

// ListFor returns the runs of several devices at once, newest first.
//
// This is what makes an account mean something: three phones signed in to one account produce one
// history, which is the main reason to have accounts beyond upload permission.
func (s *Store) ListFor(deviceIDs []string) []Meta {
	s.mu.Lock()
	defer s.mu.Unlock()
	var out []Meta
	for _, id := range deviceIDs {
		out = append(out, s.listLocked(filepath.Join(s.dir, sanitizeID(id)))...)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].UploadedAt.After(out[j].UploadedAt) })
	return out
}

// OwnerOf reports which of these devices holds runID, so a caller can be granted access to a run
// belonging to a sibling device without being able to name an arbitrary device.
//
// The search is over an allow-list the caller never supplies directly — it comes from the account
// — so a run id from another account simply is not found.
func (s *Store) OwnerOf(deviceIDs []string, runID string) (string, bool) {
	s.mu.Lock()
	defer s.mu.Unlock()
	for _, id := range deviceIDs {
		p := filepath.Join(s.dir, sanitizeID(id), sanitizeID(runID)+".json")
		if fi, err := os.Stat(p); err == nil && !fi.IsDir() {
			return id, true
		}
	}
	return "", false
}

// Get returns the stored document bytes for one run.
func (s *Store) Get(deviceID, runID string) ([]byte, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	return os.ReadFile(filepath.Join(s.dir, sanitizeID(deviceID), sanitizeID(runID)+".json"))
}

// Delete removes one run. Missing is not an error: delete is idempotent so a client retrying
// after a dropped response does not see a spurious failure.
func (s *Store) Delete(deviceID, runID string) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	dev, run := sanitizeID(deviceID), sanitizeID(runID)
	for _, suffix := range []string{".json", ".meta.json"} {
		if err := os.Remove(filepath.Join(s.dir, dev, run+suffix)); err != nil && !errors.Is(err, os.ErrNotExist) {
			return err
		}
	}
	return nil
}

func (s *Store) listLocked(devDir string) []Meta {
	entries, err := os.ReadDir(devDir)
	if err != nil {
		return nil
	}
	out := make([]Meta, 0, len(entries))
	for _, e := range entries {
		if !strings.HasSuffix(e.Name(), ".meta.json") {
			continue
		}
		b, err := os.ReadFile(filepath.Join(devDir, e.Name()))
		if err != nil {
			continue
		}
		var m Meta
		if json.Unmarshal(b, &m) == nil {
			out = append(out, m)
		}
	}
	sort.Slice(out, func(i, j int) bool { return out[i].UploadedAt.After(out[j].UploadedAt) })
	return out
}

// enforceRetentionLocked drops runs past the age limit, then past the count limit. Age first, so
// a burst of uploads cannot push out runs that are still inside the retention window.
func (s *Store) enforceRetentionLocked(devDir string) {
	metas := s.listLocked(devDir)
	drop := func(m Meta) {
		_ = os.Remove(filepath.Join(devDir, m.ID+".json"))
		_ = os.Remove(filepath.Join(devDir, m.ID+".meta.json"))
	}
	kept := metas[:0]
	if s.policy.RetentionDays > 0 {
		cutoff := time.Now().Add(-time.Duration(s.policy.RetentionDays) * 24 * time.Hour)
		for _, m := range metas {
			if m.UploadedAt.Before(cutoff) {
				drop(m)
				continue
			}
			kept = append(kept, m)
		}
	} else {
		kept = metas
	}
	if s.policy.MaxRunsPerDevice > 0 && len(kept) > s.policy.MaxRunsPerDevice {
		for _, m := range kept[s.policy.MaxRunsPerDevice:] { // listLocked is newest-first
			drop(m)
		}
	}
}

// sanitizeID keeps ids to characters that cannot escape the directory or collide with the
// .meta.json suffix convention. Ids are uuids and device ids in practice; anything else is
// truncated to nothing and rejected upstream.
func sanitizeID(s string) string {
	var b strings.Builder
	for _, r := range s {
		switch {
		case r >= 'a' && r <= 'z', r >= 'A' && r <= 'Z', r >= '0' && r <= '9', r == '-', r == '_':
			b.WriteRune(r)
		}
		if b.Len() >= 64 {
			break
		}
	}
	return b.String()
}

func mustJSON(v any) []byte {
	b, _ := json.Marshal(v)
	return b
}