package diary

import (
	"fmt"
	"log/slog"
	"maps"
	"path/filepath"
	"slices"
	"strconv"
	"strings"

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

// Config keys read by ParseConfig.
const (
	// DefaultKey names the channel that receives every record (log.default).
	DefaultKey = "log.default"
	// LevelKey is the global minimum level (log.level).
	LevelKey = "log.level"
	// ChannelsKey holds the named channels (log.channels.<name>).
	ChannelsKey = "log.channels"
	// ComponentsKey holds per-component levels (log.components.<name>).
	ComponentsKey = "log.components"
)

// Channel drivers.
const (
	// DriverConsole writes to the console (stderr): styled lines on a
	// terminal, logfmt or JSON otherwise.
	DriverConsole = "console"
	// DriverStderr writes logfmt or JSON to stderr, never styled.
	DriverStderr = "stderr"
	// DriverDaily writes one file per day with retention.
	DriverDaily = "daily"
	// DriverStack fans a record out to the channels it lists.
	DriverStack = "stack"
	// DriverNull discards records.
	DriverNull = "null"
)

// Channel formats.
const (
	// FormatAuto styles console lines on a terminal and writes logfmt
	// otherwise. Only the console driver accepts it.
	FormatAuto = "auto"
	// FormatJSON writes one JSON object per record.
	FormatJSON = "json"
	// FormatLogfmt writes key=value lines.
	FormatLogfmt = "logfmt"
)

// Config is the parsed log.* configuration.
type Config struct {
	// Default is the channel every record goes to (log.default).
	Default string
	// Level is the global minimum level (log.level).
	Level slog.Level
	// Channels holds the named channels (log.channels).
	Channels map[string]ChannelConfig
	// Components holds per-component minimum levels (log.components).
	Components map[string]slog.Level
}

// ChannelConfig is one entry of log.channels.
type ChannelConfig struct {
	// Driver is one of DriverConsole, DriverStderr, DriverDaily,
	// DriverStack or DriverNull.
	Driver string
	// Format is FormatAuto, FormatJSON or FormatLogfmt; empty means the
	// driver's default (auto for console, logfmt for stderr, json for daily).
	Format string
	// Path is the daily file path; relative paths resolve against the
	// application root.
	Path string
	// Level is the channel's own minimum level, applied when HasLevel is set.
	Level slog.Level
	// HasLevel reports whether the channel sets a level.
	HasLevel bool
	// Days is the daily retention in days; 0 keeps every file.
	Days int
	// Channels lists a stack's children.
	Channels []string
}

// DefaultConfig returns the framework defaults: a stack of a console channel
// and a daily file at storage/logs/summer.log (JSON, level warn, kept 14
// days), global level info, and River at warn. A stderr channel (logfmt) and
// a null channel are defined too, so log.default can name them without
// defining them.
func DefaultConfig() Config {
	return Config{
		Default: "stack",
		Level:   slog.LevelInfo,
		Channels: map[string]ChannelConfig{
			"stack":   {Driver: DriverStack, Channels: []string{"console", "daily"}},
			"console": {Driver: DriverConsole, Format: FormatAuto},
			"stderr":  {Driver: DriverStderr, Format: FormatLogfmt},
			"null":    {Driver: DriverNull},
			"daily": {
				Driver:   DriverDaily,
				Path:     "storage/logs/summer.log",
				Days:     14,
				Format:   FormatJSON,
				Level:    slog.LevelWarn,
				HasLevel: true,
			},
		},
		Components: map[string]slog.Level{"river": slog.LevelWarn},
	}
}

func (c Config) clone() Config {
	out := c
	out.Channels = make(map[string]ChannelConfig, len(c.Channels))
	for name, ch := range c.Channels {
		ch.Channels = slices.Clone(ch.Channels)
		out.Channels[name] = ch
	}
	out.Components = maps.Clone(c.Components)
	if out.Components == nil {
		out.Components = map[string]slog.Level{}
	}
	return out
}

// ParseConfig reads log.* from cfg over DefaultConfig, key by key, so a
// single override keeps every other default. Values may arrive as strings
// from SUMMER_LOG__ environment variables. A nil cfg gives the defaults.
func ParseConfig(cfg *compass.Config) (Config, error) {
	out := DefaultConfig().clone()
	if cfg == nil {
		return out, nil
	}
	if raw, ok := cfg.Lookup(DefaultKey); ok {
		out.Default = strings.TrimSpace(fmt.Sprint(raw))
	}
	if raw, ok := cfg.Lookup(LevelKey); ok {
		lvl, err := parseLevel(raw)
		if err != nil {
			return Config{}, keyError(LevelKey, err)
		}
		out.Level = lvl
	}
	if raw, ok := cfg.Lookup(ChannelsKey); ok {
		channels, ok := raw.(map[string]any)
		if !ok {
			return Config{}, fmt.Errorf("diary: %s must be a map of channels", ChannelsKey)
		}
		for _, name := range slices.Sorted(maps.Keys(channels)) {
			ch, err := overlayChannel(name, out.Channels[name], channels[name])
			if err != nil {
				return Config{}, err
			}
			out.Channels[name] = ch
		}
	}
	if raw, ok := cfg.Lookup(ComponentsKey); ok {
		components, ok := raw.(map[string]any)
		if !ok {
			return Config{}, fmt.Errorf("diary: %s must be a map of component levels", ComponentsKey)
		}
		for _, name := range slices.Sorted(maps.Keys(components)) {
			key := ComponentsKey + "." + name
			if _, nested := components[name].(map[string]any); nested {
				return Config{}, fmt.Errorf("diary: %s must be a level; component names cannot contain dots", key)
			}
			lvl, err := parseLevel(components[name])
			if err != nil {
				return Config{}, keyError(key, err)
			}
			out.Components[name] = lvl
		}
	}
	if err := out.validate(); err != nil {
		return Config{}, err
	}
	return out, nil
}

func overlayChannel(name string, ch ChannelConfig, raw any) (ChannelConfig, error) {
	key := ChannelsKey + "." + name
	fields, ok := raw.(map[string]any)
	if !ok {
		return ch, fmt.Errorf("diary: %s must be a map", key)
	}
	for _, field := range slices.Sorted(maps.Keys(fields)) {
		v := fields[field]
		fkey := key + "." + field
		switch field {
		case "driver":
			ch.Driver = strings.ToLower(strings.TrimSpace(fmt.Sprint(v)))
		case "format":
			ch.Format = strings.ToLower(strings.TrimSpace(fmt.Sprint(v)))
		case "path":
			ch.Path = strings.TrimSpace(fmt.Sprint(v))
		case "level":
			lvl, err := parseLevel(v)
			if err != nil {
				return ch, keyError(fkey, err)
			}
			ch.Level, ch.HasLevel = lvl, true
		case "days":
			n, err := parseDays(v)
			if err != nil {
				return ch, fmt.Errorf("diary: %s must be a whole number of at least 0", fkey)
			}
			ch.Days = n
		case "channels":
			ch.Channels = parseList(v)
		default:
			return ch, fmt.Errorf("diary: %s is not a channel setting (driver, level, format, path, days, channels)", fkey)
		}
	}
	return ch, nil
}

func (c Config) validate() error {
	if c.Default == "" {
		return fmt.Errorf("diary: %s must name a channel", DefaultKey)
	}
	if _, ok := c.Channels[c.Default]; !ok {
		return fmt.Errorf("diary: %s names channel %q, which is not defined in %s", DefaultKey, c.Default, ChannelsKey)
	}
	for _, name := range slices.Sorted(maps.Keys(c.Channels)) {
		ch := c.Channels[name]
		key := ChannelsKey + "." + name
		switch ch.Driver {
		case DriverConsole, DriverStderr, DriverDaily, DriverStack, DriverNull:
		case "":
			return fmt.Errorf("diary: %s.driver is required", key)
		default:
			return fmt.Errorf("diary: %s.driver %q is not one of console, stderr, daily, stack, null", key, ch.Driver)
		}
		switch ch.Format {
		case "", FormatJSON, FormatLogfmt:
		case FormatAuto:
			if ch.Driver != DriverConsole {
				return fmt.Errorf("diary: %s.format auto is only valid for the console driver", key)
			}
		default:
			return fmt.Errorf("diary: %s.format %q is not one of auto, json, logfmt", key, ch.Format)
		}
		if ch.Driver == DriverDaily {
			if ch.Path == "" {
				return fmt.Errorf("diary: %s.path is required for the daily driver", key)
			}
			if !filepath.IsAbs(ch.Path) && !filepath.IsLocal(filepath.Clean(ch.Path)) {
				return fmt.Errorf("diary: %s.path %q leaves the application root; use a path inside it or an absolute path", key, ch.Path)
			}
		}
		if ch.Driver == DriverStack {
			if len(ch.Channels) == 0 {
				return fmt.Errorf("diary: %s.channels must list at least one channel", key)
			}
			for _, child := range ch.Channels {
				if _, ok := c.Channels[child]; !ok {
					return fmt.Errorf("diary: %s.channels names channel %q, which is not defined in %s", key, child, ChannelsKey)
				}
			}
		}
	}
	for _, name := range slices.Sorted(maps.Keys(c.Channels)) {
		if c.Channels[name].Driver != DriverStack {
			continue
		}
		if err := c.checkCycle(name, nil); err != nil {
			return err
		}
	}
	return nil
}

// checkCycle reports a stack that contains itself through its children.
func (c Config) checkCycle(name string, path []string) error {
	if slices.Contains(path, name) {
		return fmt.Errorf("diary: %s.%s.channels forms a cycle (%s)", ChannelsKey, path[0], strings.Join(append(path, name), " -> "))
	}
	ch := c.Channels[name]
	if ch.Driver != DriverStack {
		return nil
	}
	for _, child := range ch.Channels {
		if err := c.checkCycle(child, append(slices.Clip(path), name)); err != nil {
			return err
		}
	}
	return nil
}

func keyError(key string, err error) error {
	return fmt.Errorf("diary: %s: %w", key, err)
}

func parseLevel(raw any) (slog.Level, error) {
	s := strings.ToLower(strings.TrimSpace(fmt.Sprint(raw)))
	switch s {
	case "debug":
		return slog.LevelDebug, nil
	case "info":
		return slog.LevelInfo, nil
	case "warn", "warning":
		return slog.LevelWarn, nil
	case "error":
		return slog.LevelError, nil
	}
	return 0, fmt.Errorf("level %q is not one of debug, info, warn, error", s)
}

func parseDays(raw any) (int, error) {
	var n int
	switch v := raw.(type) {
	case int:
		n = v
	case int64:
		n = int(v)
	case uint64:
		n = int(v)
	case float64:
		if v != float64(int(v)) {
			return 0, fmt.Errorf("not a whole number")
		}
		n = int(v)
	case string:
		parsed, err := strconv.Atoi(strings.TrimSpace(v))
		if err != nil {
			return 0, err
		}
		n = parsed
	default:
		return 0, fmt.Errorf("unsupported value %T", raw)
	}
	if n < 0 {
		return 0, fmt.Errorf("negative")
	}
	return n, nil
}

func parseList(raw any) []string {
	var parts []string
	switch v := raw.(type) {
	case []any:
		for _, e := range v {
			parts = append(parts, fmt.Sprint(e))
		}
	case []string:
		parts = v
	default:
		parts = strings.Split(fmt.Sprint(v), ",")
	}
	out := make([]string, 0, len(parts))
	for _, p := range parts {
		if p = strings.TrimSpace(p); p != "" {
			out = append(out, p)
		}
	}
	return out
}