// Package diary is the application logging pipeline, modelled on Laravel's
// logging config (D-08): config/log.yaml names a default channel, a global
// level and named channels (console, stderr, daily files, stacks, null), and
// every channel redacts through sunscreen. Code logs through named component
// loggers (D-09): For("journal") returns a logger whose records carry the
// component and pass its level from log.components, and which is safe to
// create in a package var before Setup runs.
package diary

import (
	"errors"
	"io"
	"log"
	"log/slog"
	"os"
	"sync"
	"sync/atomic"
	"time"

	"git.golem15.com/golem15/summercms/modules/bonfire"
	"git.golem15.com/golem15/summercms/modules/compass"
)

// ComponentKey is the attribute that carries a record's component.
const ComponentKey = "component"

// Options configures Bootstrap and Setup.
type Options struct {
	// Verbosity lowers every component floor: 1 to at most info, 2 or more
	// to debug; 3 or more also adds source locations on the console.
	Verbosity int
	// Quiet raises the console channels to warn; files keep their levels.
	Quiet bool
	// Color decides on styled console output (bonfire.ColorAuto by default).
	Color bonfire.ColorMode
	// Root is the application root that relative daily paths resolve
	// against; empty means the working directory.
	Root string
	// Stderr is where console channels write; nil means os.Stderr.
	Stderr io.Writer
	// Environ is used to detect color support; nil means os.Environ().
	Environ []string
	// Now is the clock of the daily writers; nil means time.Now.
	Now func() time.Time
}

func (o Options) normalize() Options {
	if o.Stderr == nil {
		o.Stderr = os.Stderr
	}
	if o.Root == "" {
		o.Root = "."
	}
	if o.Now == nil {
		o.Now = time.Now
	}
	if o.Environ == nil {
		o.Environ = os.Environ()
	}
	return o
}

// state is one installed configuration. It is replaced as a whole; only the
// console level vars and the source switch change in place.
type state struct {
	gen        uint64
	root       slog.Handler
	level      slog.Level
	components map[string]slog.Level
	verbosity  int
	quiet      bool
	channels   *channels
	conf       Config
	opts       Options
}

// floor is the minimum level for records of component name: its
// log.components level, else log.level, lowered by verbosity. Records without
// a component use log.level.
func (s *state) floor(name string) slog.Level {
	f := s.level
	if l, ok := s.components[name]; ok && name != "" {
		f = l
	}
	switch {
	case s.verbosity >= 2:
		f = min(f, slog.LevelDebug)
	case s.verbosity >= 1:
		f = min(f, slog.LevelInfo)
	}
	return f
}

type savedDefault struct {
	logger *slog.Logger
	writer io.Writer
	flags  int
}

var (
	mu        sync.Mutex
	current   atomic.Pointer[state]
	gens      atomic.Uint64
	verbosity atomic.Int64
	saved     *savedDefault
)

// For returns the logger of a component, normally a plugin or module code
// without dots (koanf splits config keys on dots). Its records carry the
// attribute component=<name> and pass the component's level. Before Bootstrap
// or Setup they go to the process default logger's handler.
func For(component string) *slog.Logger {
	return slog.New(newComponentHandler(component))
}

// Bootstrap installs a console channel on w, before configuration is read,
// and makes diary the process default logger. The generated main calls it
// first; Setup replaces it once config/log.yaml is loaded.
func Bootstrap(w io.Writer, opts Options) {
	if w == nil {
		w = os.Stderr
	}
	opts.Stderr = w
	opts = opts.normalize()
	cfg := DefaultConfig()
	cfg.Default = "console"
	cfg.Channels = map[string]ChannelConfig{"console": {Driver: DriverConsole, Format: FormatAuto}}
	ch, err := buildChannels(cfg, opts)
	if err != nil {
		// A console-only configuration has nothing that can fail; keep the
		// previous state if it ever does.
		return
	}
	install(cfg, ch, opts)
}

// Setup parses log.* from cfg (ParseConfig), builds the channels and makes
// them the target of every diary logger and of the process default logger.
// A configuration error is returned and leaves the previous setup in place;
// a daily file that cannot be opened never fails Setup.
func Setup(cfg *compass.Config, opts Options) error {
	conf, err := ParseConfig(cfg)
	if err != nil {
		return err
	}
	opts = opts.normalize()
	ch, err := buildChannels(conf, opts)
	if err != nil {
		return err
	}
	install(conf, ch, opts)
	return nil
}

func install(conf Config, ch *channels, opts Options) {
	mu.Lock()
	defer mu.Unlock()
	if saved == nil {
		saved = &savedDefault{logger: slog.Default(), writer: log.Writer(), flags: log.Flags()}
	}
	verbosity.Store(int64(opts.Verbosity))
	st := &state{
		gen:        gens.Add(1),
		root:       ch.root,
		level:      conf.Level,
		components: conf.Components,
		verbosity:  opts.Verbosity,
		quiet:      opts.Quiet,
		channels:   ch,
		conf:       conf,
		opts:       opts,
	}
	old := current.Swap(st)
	slog.SetDefault(slog.New(newComponentHandler("")))
	if old != nil {
		closeChannels(old.channels)
	}
}

// SetVerbosity changes the verbosity and quiet switches at runtime: 1 lets
// info through for every component, 2 or more debug, 3 or more adds source
// locations on styled console lines. Quiet raises only the console channels
// to warn. Before Bootstrap or Setup it only changes what Verbosity returns;
// Options.Verbosity and Options.Quiet set the values of a new setup.
func SetVerbosity(v int, quiet bool) {
	mu.Lock()
	defer mu.Unlock()
	verbosity.Store(int64(v))
	st := current.Load()
	if st == nil {
		return
	}
	next := *st
	next.verbosity, next.quiet = v, quiet
	next.opts.Verbosity, next.opts.Quiet = v, quiet
	for _, c := range st.channels.consoles {
		c.apply(quiet)
	}
	st.channels.source.Store(v >= 3)
	current.Store(&next)
}

// FromGlobals returns the Options for the console global options: their
// verbosity, quiet switch and color mode. The generated main passes it to
// Bootstrap and Setup.
func FromGlobals(g bonfire.Globals) Options {
	return Options{Verbosity: g.Verbosity, Quiet: g.Quiet, Color: g.Color}
}

// ApplyGlobals applies the parsed global options to the installed setup:
// the verbosity and quiet switch (SetVerbosity) and, when it differs from
// the one the channels were built with, the console color mode, which
// rebuilds the channels from the same configuration. The generated main
// registers it with bonfire.OnGlobals.
func ApplyGlobals(g bonfire.Globals) {
	st := current.Load()
	if st != nil && st.opts.Color != g.Color {
		opts := st.opts
		opts.Color, opts.Verbosity, opts.Quiet = g.Color, g.Verbosity, g.Quiet
		if ch, err := buildChannels(st.conf, opts); err == nil {
			install(st.conf, ch, opts)
			return
		}
	}
	SetVerbosity(g.Verbosity, g.Quiet)
}

// Verbosity returns the current verbosity (0 by default).
func Verbosity() int {
	return int(verbosity.Load())
}

// Close closes the open daily files. Later records open them again.
func Close() error {
	st := current.Load()
	if st == nil {
		return nil
	}
	return closeChannels(st.channels)
}

func closeChannels(ch *channels) error {
	if ch == nil {
		return nil
	}
	var errs []error
	for _, c := range ch.closers {
		errs = append(errs, c.Close())
	}
	return errors.Join(errs...)
}

// Reset drops the installed setup, closes its files and restores the process
// default logger (and the standard log package's output) captured at the
// first Bootstrap or Setup. Tests call it in t.Cleanup.
func Reset() {
	mu.Lock()
	defer mu.Unlock()
	old := current.Swap(nil)
	verbosity.Store(0)
	if saved != nil {
		slog.SetDefault(saved.logger)
		log.SetOutput(saved.writer)
		log.SetFlags(saved.flags)
		saved = nil
	}
	if old != nil {
		closeChannels(old.channels)
	}
}