137 lines
4.3 KiB
Go
137 lines
4.3 KiB
Go
package fejkdata
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import (
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crand "crypto/rand"
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"encoding/binary"
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"errors"
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"fmt"
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"io/fs"
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"reflect"
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"sort"
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"sync"
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"github.com/larvit/fejkdata/internal/datafiles"
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"github.com/larvit/fejkdata/internal/drawstate"
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)
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// MaxRepeat caps a repeat, and caps the renders nested repeats multiply to along
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// any one path; the CLI's --repeat shares it.
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const MaxRepeat = 1 << 20
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var _ [^uint(0)>>63 - 1]struct{} // docs/decisions.md#64-bit-targets-only
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// ErrNoData is returned by New when no source is loaded at all.
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var ErrNoData = errors.New("no data: WithoutShippedData needs at least one WithDataPath or WithDataFS")
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// Generator generates fake data from a namespace tree. Create one with [New].
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// It is safe for concurrent use; a seeded sequence is reproducible only when drawn
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// from one goroutine.
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type Generator struct {
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// mu guards drawState, structs and root, which gains a shipped category on the
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// first call reaching it.
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mu sync.Mutex
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drawState *drawstate.State
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root folder // the categories as the node a path walks from, owned here so a walk allocates none
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structs map[reflect.Type]structResult
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}
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type config struct {
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seed uint64
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seeded bool
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shipped bool
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sources []datafiles.Source
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}
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// Option configures a [Generator].
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type Option func(*config)
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// WithSeed makes output reproducible: two generators with the same seed, version and
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// data emit identical sequences.
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func WithSeed(seed uint64) Option {
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return func(c *config) { c.seed, c.seeded = seed, true }
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}
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// WithDataPath layers a data directory over what is loaded before it. Repeat it to
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// layer several; the last wins a name clash.
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func WithDataPath(dir string) Option {
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return func(c *config) {
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c.sources = append(c.sources, datafiles.Dir(dir))
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}
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}
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// WithDataFS layers a data tree held in an [fs.FS], such as an embed.FS of your own.
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func WithDataFS(fsys fs.FS) Option {
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return func(c *config) { c.sources = append(c.sources, datafiles.FS(fsys, "")) }
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}
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// WithoutShippedData leaves the shipped data set out, so only the sources given
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// with [WithDataPath] and [WithDataFS] load.
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func WithoutShippedData() Option {
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return func(c *config) { c.shipped = false }
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}
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// New builds a generator from the shipped data set and the options' sources, merged
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// in order with the last winning a name clash. Each JSON file becomes a category
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// named after the file (address.json -> "address") and each subdirectory a
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// namespace segment. It errors on a missing directory, invalid JSON, invalid data,
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// or no data at all. With only the shipped data, a category loads on the first call
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// reaching it; with WithDataPath or WithDataFS, every category loads here.
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func New(opts ...Option) (*Generator, error) {
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c := config{shipped: true}
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for _, opt := range opts {
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opt(&c)
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}
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root, err := c.load()
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if err != nil {
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return nil, fmt.Errorf("fejkdata: %w", err)
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}
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seed, err := c.drawSeed()
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if err != nil {
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return nil, fmt.Errorf("fejkdata: %w", err)
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}
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return &Generator{drawState: drawstate.New(seed), root: root}, nil
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}
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// docs/decisions.md#with-only-the-shipped-set-a-category-loads-on-the-first-call-reaching-it-beside-a---data-path-every-category-loads-in-new
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func (c config) load() (folder, error) {
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if c.shipped && len(c.sources) == 0 {
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return unloadedTree(), nil
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}
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var sources []datafiles.Source
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if c.shipped {
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sources = append(sources, shippedSource)
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}
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sources = append(sources, c.sources...)
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if len(sources) == 0 {
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return folder{}, ErrNoData
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}
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cats, err := loadData(sources)
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return folder{children: cats}, err
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}
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// List returns the sorted dotted paths Fake renders: each category and every field,
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// column and linked table below it, a direct descent at a time, listing a level
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// carrying a repeat but nothing below it. A choice consumes no segment, so a path
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// continues through one only where every variant carries it.
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func (f *Generator) List() []string {
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f.mu.Lock()
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defer f.mu.Unlock()
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out := paths(&f.root, false)
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sort.Strings(out)
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return out
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}
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var randomBytes = crand.Read
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// drawSeed is the seed WithSeed gave, or one read from the system's entropy.
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func (c config) drawSeed() (uint64, error) {
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if c.seeded {
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return c.seed, nil
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}
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var b [8]byte
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if _, err := randomBytes(b[:]); err != nil {
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return 0, fmt.Errorf("seeding from crypto/rand: %w", err)
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}
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return binary.LittleEndian.Uint64(b[:]), nil
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}
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