// Package otelzlog converters hold the functions that are needed to convert
// between zerolog and otel logging event types
package otelzlog

import (
        "errors"
        "fmt"
        "math"
        "reflect"
        "strconv"
        "strings"
        "time"

        "github.com/rs/zerolog"
        "go.opentelemetry.io/otel/attribute"
        "go.opentelemetry.io/otel/log"
)

// convertLevel converts the logging level from a zerolog.Level into a an otel log.Severity
// and the corresponding severity level string
func convertLevel(level zerolog.Level) (log.Severity, string) {
        switch level {
        case zerolog.TraceLevel:
                return log.SeverityTrace, "TRACE"
        case zerolog.DebugLevel:
                return log.SeverityDebug, "DEBUG"
        default:
                fallthrough
        case zerolog.InfoLevel:
                return log.SeverityInfo, "INFO"
        case zerolog.WarnLevel:
                return log.SeverityWarn, "WARN"
        case zerolog.ErrorLevel:
                return log.SeverityError, "ERROR"
        case zerolog.FatalLevel:
                return log.SeverityFatal, "FATAL"
        case zerolog.PanicLevel:
                return log.SeverityFatal, "FATAL"
        }
}

// convertAttribute converts value from `any` into the equivalent otel log.Value.
// This function is a direct copy paste from the otelslog package.
func convertAttribute(v any) log.Value {
        switch val := v.(type) {
        case bool:
                return log.BoolValue(val)
        case string:
                return log.StringValue(val)
        case int:
                return log.Int64Value(int64(val))
        case int8:
                return log.Int64Value(int64(val))
        case int16:
                return log.Int64Value(int64(val))
        case int32:
                return log.Int64Value(int64(val))
        case int64:
                return log.Int64Value(val)
        case uint:
                return convertUintValue(uint64(val))
        case uint8:
                return log.Int64Value(int64(val))
        case uint16:
                return log.Int64Value(int64(val))
        case uint32:
                return log.Int64Value(int64(val))
        case uint64:
                return convertUintValue(val)
        case uintptr:
                return convertUintValue(uint64(val))
        case float32:
                return log.Float64Value(float64(val))
        case float64:
                return log.Float64Value(val)
        case time.Duration:
                return log.Int64Value(val.Nanoseconds())
        case complex64:
                r := log.Float64("r", real(complex128(val)))
                i := log.Float64("i", imag(complex128(val)))
                return log.MapValue(r, i)
        case complex128:
                r := log.Float64("r", real(val))
                i := log.Float64("i", imag(val))
                return log.MapValue(r, i)
        case time.Time:
                return log.Int64Value(val.UnixNano())
        case []byte:
                return log.BytesValue(val)
        case error:
                return log.StringValue(val.Error())
        }

        t := reflect.TypeOf(v)
        if t == nil {
                return log.Value{}
        }
        val := reflect.ValueOf(v)
        switch t.Kind() {
        case reflect.Struct:
                return log.StringValue(fmt.Sprintf("%+v", v))
        case reflect.Slice, reflect.Array:
                items := make([]log.Value, 0, val.Len())
                for i := range val.Len() {
                        items = append(items, convertAttribute(val.Index(i).Interface()))
                }
                return log.SliceValue(items...)
        case reflect.Map:
                kvs := make([]log.KeyValue, 0, val.Len())
                for _, k := range val.MapKeys() {
                        var key string
                        switch k.Kind() {
                        case reflect.String:
                                key = k.String()
                        default:
                                key = fmt.Sprintf("%+v", k.Interface())
                        }
                        kvs = append(kvs, log.KeyValue{
                                Key:   key,
                                Value: convertAttribute(val.MapIndex(k).Interface()),
                        })
                }
                return log.MapValue(kvs...)
        case reflect.Ptr, reflect.Interface:
                if val.IsNil() {
                        return log.Value{}
                }
                return convertAttribute(val.Elem().Interface())
        }

        // Try to handle this as gracefully as possible.
        //
        // Don't panic here. it is preferable to have user's open issue
        // asking why their attributes have a "unhandled: " prefix than
        // say that their code is panicking.
        return log.StringValue(fmt.Sprintf("unhandled: (%s) %+v", t, v))
}

func convertUintValue(v uint64) log.Value {
        if v > math.MaxInt64 {
                return log.StringValue(strconv.FormatUint(v, 10))
        }
        return log.Int64Value(int64(v))
}

func convertLogToAttribute(attr log.Value) attribute.Value {
        switch attr.Kind() {
        case log.KindString:
                return attribute.StringValue(attr.String())
        case log.KindFloat64:
                return attribute.Float64Value(attr.AsFloat64())
        case log.KindInt64:
                return attribute.Int64Value(attr.AsInt64())
        case log.KindBool:
                return attribute.BoolValue(attr.AsBool())
        case log.KindBytes:
                return attribute.StringValue(string(attr.AsBytes()))
        case log.KindSlice:
                return attribute.StringValue(fmt.Sprintf("%v", attr.AsSlice()))
        case log.KindMap:
                return attribute.StringValue(fmt.Sprintf("%v", attr.AsMap()))
        case log.KindEmpty:
                return attribute.StringValue("")
        }

        return attribute.StringValue(attr.AsString())
}

func extractSource(source string) (filepath string, line int, err error) {
        colonSplit := strings.Split(source, ":")
        if len(colonSplit) != 2 {
                err = errors.New("otelzlog: source does not contain path and line number")
                return
        }

        line, err = strconv.Atoi(colonSplit[1])
        if err != nil {
                return
        }
        filepath = colonSplit[0]

        return
}

// Package otelzlog hook holds the hook that is attached to the zerolog logger
package otelzlog

import (
        "context"
        "encoding/json"
        "fmt"
        "reflect"
        "time"

        "github.com/rs/zerolog"
        zlog "github.com/rs/zerolog/log"
        "go.opentelemetry.io/otel/attribute"
        "go.opentelemetry.io/otel/codes"
        otelLog "go.opentelemetry.io/otel/log"
        semconv "go.opentelemetry.io/otel/semconv/v1.4.0"
        "go.opentelemetry.io/otel/trace"
)

// Hook is the parent struct of the otelzlog handler
type Hook struct {
        otelLogger        otelLog.Logger
        source            bool
        attachSpanError   bool
        attachSpanEvent   bool
        setSpanError      bool
        setSpanErrorLevel zerolog.Level
}

// Run extracts the attributes and log level from the `*zerolog.Event`, and
// pulls the span from the passed in context in order to build the respective
// otel log.Record
func (h *Hook) Run(e *zerolog.Event, level zerolog.Level, msg string) {
        ctx := e.GetCtx()

        // return early if the logger isn't enabled for this log level
        if !e.Enabled() {
                return
        }

        var logData map[string]any
        ev := fmt.Sprintf("%s}", reflect.ValueOf(e).Elem().FieldByName("buf"))
        if err := json.Unmarshal([]byte(ev), &logData); err != nil {
                // log to the zerolog logger if there is an error reflecting the event's attribute buffer
                zlog.Ctx(e.GetCtx()).Error().Ctx(e.GetCtx()).
                        Err(err).
                        Str("log.level", level.String()).
                        Str("log.message", msg).
                        Msg("could not unmarshal the zerolog event's attribute buffer")
        }

        // convert zerolog attrs into otel log and span attrs
        logAttributes := h.processSpanAttrs(ctx, msg, logData, level)

        // create the otel log event and send it
        h.sendLogMessage(ctx, msg, level, logAttributes)
}

// processSpanAttrs converts each pulled attribute into the equivalent otel log counterparts.
// It also adds the attributes into the span and adds the error as an exception.
func (h *Hook) processSpanAttrs(ctx context.Context, msg string, logData map[string]any, level zerolog.Level) (logAttributes []otelLog.KeyValue) {
        for k, v := range logData {
                switch k {
                // if there is an attribute called "error", then record the error in the span and
                // add it to the log attributes only (not the trace attributes)
                case zerolog.ErrorFieldName:
                        logAttributes = append(logAttributes,
                                otelLog.String(string(semconv.ExceptionMessageKey), v.(string)),
                                otelLog.String("event", "exception"),
                        )

                // if there is an attribute called "stack", then record the stack in the span and
                // add it to the log attributes only (not the trace attributes)
                case zerolog.ErrorStackFieldName:
                        logAttributes = append(logAttributes,
                                otelLog.String(string(semconv.ExceptionStacktraceKey), v.(string)),
                        )

                // If there is a "caller" object in the log and if source is enabled in [Hook], then
                // append these using semconv fields instead of generic string attributes.
                case zerolog.CallerFieldName:
                        sourcePath, ok := v.(string)
                        if !ok || !h.source {
                                continue
                        }

                        filepath, line, err := extractSource(sourcePath)
                        if err != nil {
                                continue
                        }

                        logAttributes = append(logAttributes,
                                otelLog.String(string(semconv.CodeFilepathKey), filepath),
                                otelLog.Int(string(semconv.CodeLineNumberKey), line),
                        )

                default:
                        logAttributes = append(logAttributes, otelLog.KeyValue{
                                Key:   k,
                                Value: convertAttribute(v),
                        })
                }
        }

        // If enabled, add an otel span event (attach the log to the span).
        if h.attachSpanEvent {
                traceAttributes := []attribute.KeyValue{}

                for _, logAttr := range logAttributes {
                        traceAttributes = append(traceAttributes, attribute.KeyValue{
                                Key:   attribute.Key(logAttr.Key),
                                Value: convertLogToAttribute(logAttr.Value),
                        })
                }

                trace.SpanFromContext(ctx).AddEvent(msg,
                        trace.WithAttributes(traceAttributes...),
                )
        }

        if h.setSpanError && level >= h.setSpanErrorLevel {
                trace.SpanFromContext(ctx).SetStatus(codes.Error, "")
        }

        return
}

func (h *Hook) sendLogMessage(ctx context.Context, msg string, level zerolog.Level, logAttributes []otelLog.KeyValue) {
        severityNumber, severityText := convertLevel(level)

        record := otelLog.Record{}
        record.SetTimestamp(time.Now())
        record.SetBody(otelLog.StringValue(msg))
        record.SetSeverity(severityNumber)
        record.SetSeverityText(severityText)
        record.AddAttributes(logAttributes...)

        h.otelLogger.Emit(ctx, record)
}

// Package otelzlog provides a bridge between zerolog and otel logging
package otelzlog

import (
        "context"
        "io"
        "runtime"

        "github.com/rs/zerolog"
        "github.com/rs/zerolog/log"
        "go.opentelemetry.io/otel/attribute"
        otelLog "go.opentelemetry.io/otel/log"
        "go.opentelemetry.io/otel/log/global"
)

type config struct {
        provider otelLog.LoggerProvider

        source       bool
        sourceOffset int

        attachSpanError   bool
        attachSpanEvent   bool
        setSpanError      bool
        setSpanErrorLevel zerolog.Level

        writers []io.Writer

        loggerOpts []otelLog.LoggerOption
}

// Option configures the zerolog hook.
type Option interface {
        apply(config) config
}

type optFunc func(config) config

func (f optFunc) apply(c config) config {
        return f(c)
}

// WithVersion returns an [Option] that configures the version of the
// [log.Logger] used by a [Hoo]. The version should be the version of the
// package that is being logged.
func WithVersion(version string) Option {
        return optFunc(func(c config) config {
                c.loggerOpts = append(c.loggerOpts, otelLog.WithInstrumentationVersion(version))
                return c
        })
}

// WithSchemaURL returns an [Option] that configures the semantic convention
// schema URL of the [log.Logger] used by a [Hook]. The schemaURL should be
// the schema URL for the semantic conventions used in log records.
func WithSchemaURL(schemaURL string) Option {
        return optFunc(func(c config) config {
                c.loggerOpts = append(c.loggerOpts, otelLog.WithSchemaURL(schemaURL))
                return c
        })
}

// WithAttributes returns an [Option] that configures the instrumentation scope
// attributes of the [log.Logger] used by a [Hook].
func WithAttributes(attributes ...attribute.KeyValue) Option {
        return optFunc(func(c config) config {
                c.loggerOpts = append(c.loggerOpts, otelLog.WithInstrumentationAttributes(attributes...))
                return c
        })
}

// WithLoggerProvider returns an [Option] that configures [log.LoggerProvider]
// used by a [Hook] to create its [log.Logger].
//
// By default if this Option is not provided, the Handler will use the global
// LoggerProvider.
func WithLoggerProvider(provider otelLog.LoggerProvider) Option {
        return optFunc(func(c config) config {
                c.provider = provider
                return c
        })
}

// WithWriter returns an [Option] that configures writers used by a
// [Hook]. Multiple writers can be specified.
func WithWriter(w io.Writer) Option {
        return optFunc(func(c config) config {
                c.writers = append(c.writers, w)
                return c
        })
}

// WithSource returns an [Option] that configures the [Hook] to include
// the source location of the log record in log attributes. Offset should
// be increased if using a helper function to wrap the logger call.
func WithSource(source bool, offset int) Option {
        return optFunc(func(c config) config {
                c.source = source
                c.sourceOffset = offset
                return c
        })
}

// WithAttachSpanError returns an [Option] that configures the [Hook]
// to attach errors from `log.Error().Err()` to the associated otel span.
func WithAttachSpanError(attach bool) Option {
        return optFunc(func(c config) config {
                c.attachSpanError = attach
                return c
        })
}

// WithAttachSpanEvent returns an [Option] that configures the [Hook]
// to attach an event to the otel span the zerolog event.
func WithAttachSpanEvent(attach bool) Option {
        return optFunc(func(c config) config {
                c.attachSpanEvent = attach
                return c
        })
}

// WithSetSpanErrorStatus returns an [Option] that configures the [Hook]
// to set the span as errored when the provided level or higher is called.
func WithSetSpanErrorStatus(set bool, level zerolog.Level) Option {
        return optFunc(func(c config) config {
                c.setSpanError = set
                c.setSpanErrorLevel = level
                return c
        })
}

// WithStackHandling returns an [Option] that sets zerolog.ErrorStackMarshaler
// in order to extract the stack when .Stack() is called on a .Error() event.
//
// A Str(). called "stack" can also be passed in and will be set in the OTEL
// logs/traces accordingly.
func WithStackHandling() Option {
        return optFunc(func(c config) config {
                zerolog.ErrorStackMarshaler = func(_ error) any {
                        buf := make([]byte, 64<<10)
                        n := runtime.Stack(buf, false)

                        return string(buf[:n])
                }
                return c
        })
}

func newCfg(options []Option) config {
        var c config
        for _, opt := range options {
                c = opt.apply(c)
        }

        if c.provider == nil {
                c.provider = global.GetLoggerProvider()
        }

        return c
}

// New creates a new zerolog logger and embeds it in the context to be passed around your app.
func New(ctx context.Context, name string, options ...Option) context.Context {
        logger := log.Logger

        cfg := newCfg(options)

        switch {
        case len(cfg.writers) == 0:
                logger = log.Logger

        default:
                logger = logger.Output(io.MultiWriter(cfg.writers...))
        }

        hook := Hook{
                otelLogger:        cfg.provider.Logger(name, cfg.loggerOpts...),
                source:            cfg.source,
                attachSpanError:   cfg.attachSpanError,
                attachSpanEvent:   cfg.attachSpanEvent,
                setSpanError:      cfg.setSpanError,
                setSpanErrorLevel: cfg.setSpanErrorLevel,
        }

        if cfg.source {
                logger = logger.With().CallerWithSkipFrameCount(cfg.sourceOffset + 2).Logger()
        }

        ctx = logger.Hook(&hook).WithContext(ctx)

        return ctx
}