commit 1ab5eb3c6ad3b86d9fdce5175548de9e7237ff2e Author: Elara Musayelyan Date: Mon Aug 21 16:56:17 2023 -0700 Initial Commit diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..5ae110b --- /dev/null +++ b/.gitignore @@ -0,0 +1 @@ +/tafparser \ No newline at end of file diff --git a/LICENSE b/LICENSE new file mode 100644 index 0000000..1840fd9 --- /dev/null +++ b/LICENSE @@ -0,0 +1,674 @@ + GNU GENERAL PUBLIC LICENSE + Version 3, 29 June 2007 + + Copyright (C) 2007 Free Software Foundation, Inc. + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + Preamble + + The GNU General Public License is a free, copyleft license for +software and other kinds of works. + + The licenses for most software and other practical works are designed +to take away your freedom to share and change the works. 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If your program is a subroutine library, you +may consider it more useful to permit linking proprietary applications with +the library. If this is what you want to do, use the GNU Lesser General +Public License instead of this License. But first, please read +. diff --git a/README.md b/README.md new file mode 100644 index 0000000..ea7abf0 --- /dev/null +++ b/README.md @@ -0,0 +1,47 @@ +# taf + +This is a library that parses and decodes [TAF forecasts](https://en.wikipedia.org/wiki/Terminal_aerodrome_forecast). + +TAF stands for Terminal Aerodrome Forecast. It's the weather forecast format used in aviation. TAF reports are useful as a free source of accurate weather. + +Here's an example of a TAF report from JFK airport: + +``` +KJFK 212335Z 2200/2306 33012G18KT P6SM FEW060 BKN250 + FM220300 36014KT P6SM FEW060 SCT150 + FM221400 01015G21KT P6SM SCT060 + FM221900 04011KT P6SM SCT060 + FM230000 03007KT P6SM FEW060 + FM230300 35006KT P6SM FEW060 +``` + +Try parsing it by installing the tafparser tool using + +```bash +go install go.elara.ws/taf/cmd/tafparser@latest +``` + +and then running + +```bash +tafparser < 0 { + fl, err = os.Open(pflag.Arg(0)) + if err != nil { + log.Fatal("Error opening file").Err(err).Send() + } + } else { + fl = os.Stdin + } + + fc, err := taf.ParseWithOptions(fl, opts) + if err != nil { + log.Fatal("Error parsing TAF data").Err(err).Send() + } + + if *printGo { + repr.Println(fc) + } else { + enc := json.NewEncoder(os.Stdout) + if *pretty { + enc.SetIndent("", " ") + } + err = enc.Encode(fc) + if err != nil { + log.Fatal("Error encoding forecast").Err(err).Send() + } + } +} diff --git a/go.mod b/go.mod new file mode 100644 index 0000000..0a41599 --- /dev/null +++ b/go.mod @@ -0,0 +1,17 @@ +module go.elara.ws/taf + +go 1.21.0 + +require ( + github.com/alecthomas/participle/v2 v2.0.0 + github.com/alecthomas/repr v0.2.0 + github.com/spf13/pflag v1.0.5 + go.elara.ws/logger v0.0.0-20230421022458-e80700db2090 +) + +require ( + github.com/gookit/color v1.5.1 // indirect + github.com/mattn/go-isatty v0.0.14 // indirect + github.com/xo/terminfo v0.0.0-20210125001918-ca9a967f8778 // indirect + golang.org/x/sys v0.0.0-20210927094055-39ccf1dd6fa6 // indirect +) diff --git a/go.sum b/go.sum new file mode 100644 index 0000000..9005f25 --- /dev/null +++ b/go.sum @@ -0,0 +1,33 @@ +github.com/alecthomas/assert/v2 v2.2.2 h1:Z/iVC0xZfWTaFNE6bA3z07T86hd45Xe2eLt6WVy2bbk= +github.com/alecthomas/assert/v2 v2.2.2/go.mod h1:pXcQ2Asjp247dahGEmsZ6ru0UVwnkhktn7S0bBDLxvQ= +github.com/alecthomas/participle/v2 v2.0.0 h1:Fgrq+MbuSsJwIkw3fEj9h75vDP0Er5JzepJ0/HNHv0g= +github.com/alecthomas/participle/v2 v2.0.0/go.mod h1:rAKZdJldHu8084ojcWevWAL8KmEU+AT+Olodb+WoN2Y= +github.com/alecthomas/repr v0.2.0 h1:HAzS41CIzNW5syS8Mf9UwXhNH1J9aix/BvDRf1Ml2Yk= +github.com/alecthomas/repr v0.2.0/go.mod h1:Fr0507jx4eOXV7AlPV6AVZLYrLIuIeSOWtW57eE/O/4= +github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8= +github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38= +github.com/gookit/color v1.5.1 h1:Vjg2VEcdHpwq+oY63s/ksHrgJYCTo0bwWvmmYWdE9fQ= +github.com/gookit/color v1.5.1/go.mod h1:wZFzea4X8qN6vHOSP2apMb4/+w/orMznEzYsIHPaqKM= +github.com/hexops/gotextdiff v1.0.3 h1:gitA9+qJrrTCsiCl7+kh75nPqQt1cx4ZkudSTLoUqJM= +github.com/hexops/gotextdiff v1.0.3/go.mod h1:pSWU5MAI3yDq+fZBTazCSJysOMbxWL1BSow5/V2vxeg= +github.com/mattn/go-isatty v0.0.14 h1:yVuAays6BHfxijgZPzw+3Zlu5yQgKGP2/hcQbHb7S9Y= +github.com/mattn/go-isatty v0.0.14/go.mod h1:7GGIvUiUoEMVVmxf/4nioHXj79iQHKdU27kJ6hsGG94= +github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM= +github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4= +github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA= +github.com/spf13/pflag v1.0.5/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg= +github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME= +github.com/stretchr/testify v1.7.2/go.mod h1:R6va5+xMeoiuVRoj+gSkQ7d3FALtqAAGI1FQKckRals= +github.com/stretchr/testify v1.8.0 h1:pSgiaMZlXftHpm5L7V1+rVB+AZJydKsMxsQBIJw4PKk= +github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU= +github.com/xo/terminfo v0.0.0-20210125001918-ca9a967f8778 h1:QldyIu/L63oPpyvQmHgvgickp1Yw510KJOqX7H24mg8= +github.com/xo/terminfo v0.0.0-20210125001918-ca9a967f8778/go.mod h1:2MuV+tbUrU1zIOPMxZ5EncGwgmMJsa+9ucAQZXxsObs= +go.elara.ws/logger v0.0.0-20230421022458-e80700db2090 h1:RVC8XvWo6Yw4HUshqx4TSzuBDScDghafU6QFRJ4xPZg= +go.elara.ws/logger v0.0.0-20230421022458-e80700db2090/go.mod h1:qng49owViqsW5Aey93lwBXONw20oGbJIoLVscB16mPM= +golang.org/x/sys v0.0.0-20210330210617-4fbd30eecc44/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs= +golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg= +golang.org/x/sys v0.0.0-20210927094055-39ccf1dd6fa6 h1:foEbQz/B0Oz6YIqu/69kfXPYeFQAuuMYFkjaqXzl5Wo= +golang.org/x/sys v0.0.0-20210927094055-39ccf1dd6fa6/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg= +gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0= +gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA= +gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM= diff --git a/internal/parser/lexer.go b/internal/parser/lexer.go new file mode 100644 index 0000000..5da8719 --- /dev/null +++ b/internal/parser/lexer.go @@ -0,0 +1,20 @@ +package parser + +import ( + "github.com/alecthomas/participle/v2/lexer" +) + +var lex = lexer.MustSimple([]lexer.SimpleRule{ + {Name: "header", Pattern: `TAF (AMD|COR)? ?`}, + {Name: "Remark", Pattern: `RMK .*`}, + {Name: "Number", Pattern: `\d+`}, + {Name: "Modifier", Pattern: `[+-]|VC`}, + {Name: "Prob", Pattern: "PROB"}, + {Name: "Slash", Pattern: `/`}, + {Name: "Descriptor", Pattern: `MI|BC|DR|BL|SH|TS|FZ|PR`}, + {Name: "Precip", Pattern: `DZ|RA|SN|SG|IC|PL|GR|GS|UP`}, + {Name: "Obscur", Pattern: "BR|FG|FU|DU|SA|HZ|PY|VA"}, + {Name: "Phenom", Pattern: "PO|SQ|FC|SS|DS"}, + {Name: "Ident", Pattern: `[A-Z]+`}, + {Name: "WS", Pattern: `[ \t\n\r]+`}, +}) diff --git a/internal/parser/parser.go b/internal/parser/parser.go new file mode 100644 index 0000000..73fcdb4 --- /dev/null +++ b/internal/parser/parser.go @@ -0,0 +1,98 @@ +package parser + +import ( + "github.com/alecthomas/participle/v2" + "github.com/alecthomas/participle/v2/lexer" +) + +type AST struct { + Items []*Item `@@*` +} + +type Item struct { + Pos lexer.Position + Time *string `( @Number "Z" WS` + Valid *ValidPair ` @@` + Probability *Probability `| @@` + Change *Change `| @@` + WindSpeed *WindSpeed `| @@` + Visibility *Visibility `| @@` + SkyCondition *SkyCondition `| @@` + Vicinity *Vicinity `| @@` + Weather *Weather `| @@` + Temperature *Temperature `| @@` + Flag *Flag `| @@` + Remark *string `| @Remark` + ID *string `| @Ident ) WS?` +} + +type ValidPair struct { + Pos lexer.Position + Start string `@Number "/"` + End string `@Number` +} + +type Probability struct { + Pos lexer.Position + Value string `Prob @Number` + Time string `(WS @Number)?` +} + +type WindSpeed struct { + Pos lexer.Position + WindShear string `("WS" @Number "/")?` + Variable bool `@"VRB"?` + Value string `@Number` + Gusts string `("G" @Number)?` + Unit string `@("MPS"|"KMH"|"KT")` +} + +type Visibility struct { + Pos lexer.Position + Plus bool `@"P"?` + Value string `@Number @WS? @(Number? "/" Number)?` + Unit string `@"SM"?` +} + +type SkyCondition struct { + Pos lexer.Position + Type string `@("FEW"|"SCT"|"BKN"|"OVC"|"VV"|"SKC")` + Altitude string `@Number?` + CloudType string `@("CB"|"TCU")?` +} + +type Vicinity struct { + Pos lexer.Position + Descriptor string `"VC" ( @Descriptor` + Precipitation string ` | @Precip )` +} + +type Weather struct { + Pos lexer.Position + Modifier string `@Modifier?` + Descriptor string `@Descriptor?` + Precipitation string ` ( @Precip` + Obscuration string ` | @Obscur` + Other string ` | @Phenom )` +} + +type Change struct { + Pos lexer.Position + Type string `@("FM"|"BECMG"|"TEMPO")` + Time string `@Number?` + Valid *ValidPair `WS? @@?` +} + +type Temperature struct { + Pos lexer.Position + Type string `@("TX"|"TN")` + Value string `@Number "/"` + Time string `@Number "Z"` +} + +type Flag struct { + Pos lexer.Position + CAVOK bool `@"CAVOK"` +} + +var Parser = participle.MustBuild[AST](participle.Lexer(lex)) diff --git a/taf.go b/taf.go new file mode 100644 index 0000000..de78e21 --- /dev/null +++ b/taf.go @@ -0,0 +1,363 @@ +package taf + +import ( + "io" + "io/fs" + "math/big" + "os" + "reflect" + "strconv" + "strings" + "time" + + "github.com/alecthomas/participle/v2" + "go.elara.ws/taf/internal/parser" + "go.elara.ws/taf/units" +) + +// ParseString parses a TAF string and returns a Forecast. +// This is equivalent to Parse(strings.NewReader(s)). +func ParseString(s string) (*Forecast, error) { + return Parse(strings.NewReader(s)) +} + +// ParseFile parses a TAF string and returns a Forecast. +// This is equivalent to opening a file and passing it +// to Parse(). +func ParseFile(path string) (*Forecast, error) { + fl, err := os.Open(path) + if err != nil { + return nil, err + } + defer fl.Close() + + return Parse(fl) +} + +// Parse parses the data in a reader using default options and +// returns a Forecast +func Parse(r io.Reader) (*Forecast, error) { + return ParseWithOptions(r, Options{}) +} + +// Options contains options for the parser +type Options struct { + // If this is set, all distance units in the forecast + // will be converted to the given unit + DistanceUnit units.Distance + + // If this is set, all speed units in the forecast will + // be converted to the given unit + SpeedUnit units.Speed +} + +// ParseWithOptions parses the data in a reader and returns a Forecast +func ParseWithOptions(r io.Reader, opts Options) (*Forecast, error) { + filename := "unknown" + switch r := r.(type) { + case *os.File: + filename = r.Name() + case fs.File: + fi, err := r.Stat() + if err == nil { + filename = fi.Name() + } + case *strings.Reader: + filename = "string" + } + + ast, err := parser.Parser.Parse(filename, r) + if err != nil { + return nil, err + } + + fc := &Forecast{} + out := reflect.ValueOf(fc).Elem() + + for _, item := range ast.Items { + switch { + case item.ID != nil: + setField(out, "Identifier", *item.ID) + case item.Time != nil: + t, err := parseTime(*item.Time) + if err != nil { + return nil, participle.Errorf(item.Pos, "time: %s", err) + } + setField(out, "PublishTime", t) + + // The Time item always comes with a Valid as well because + // of the way it's parsed into the AST + vp, err := parseValid(item.Valid) + if err != nil { + return nil, participle.Errorf(item.Pos, "time: %s", err) + } + setField(out, "Valid", vp) + case item.Weather != nil: + appendField(out, "Weather", Weather{ + Modifier: Modifier(item.Weather.Modifier), + Descriptor: Descriptor(item.Weather.Descriptor), + Precipitation: Precipitation(item.Weather.Precipitation), + Obscuration: Obscuration(item.Weather.Obscuration), + Phenomenon: Phenomenon(item.Weather.Other), + }) + case item.Vicinity != nil: + appendField(out, "Weather", Weather{ + Vicinity: true, + Descriptor: Descriptor(item.Vicinity.Descriptor), + Precipitation: Precipitation(item.Vicinity.Precipitation), + }) + case item.SkyCondition != nil: + altitude, err := strconv.Atoi(item.SkyCondition.Altitude) + if err != nil { + return nil, participle.Errorf(item.SkyCondition.Pos, "sky: %s", err) + } + + appendField(out, "SkyCondition", SkyCondition{ + Altitude: altitude * 100, // Scale factor for altitude is 100 + Type: SkyConditionType(item.SkyCondition.Type), + CloudType: CloudType(item.SkyCondition.CloudType), + }) + case item.Temperature != nil: + vt, err := parseValidTime(item.Temperature.Time) + if err != nil { + return nil, participle.Errorf(item.Temperature.Pos, "temp: %s", err) + } + + val, err := strconv.Atoi(item.Temperature.Value) + if err != nil { + return nil, participle.Errorf(item.Temperature.Pos, "temp: %s", err) + } + + appendField(out, "Temperature", Temperature{ + Type: TemperatureType(item.Temperature.Type), + Time: vt, + Value: val, + }) + case item.Visibility != nil: + // This value may have a space at the end if there's no unit + item.Visibility.Value = strings.TrimSpace(item.Visibility.Value) + + // Create a new rational number + ratNum := new(big.Rat) + // If there's a space, this is a mixed number, split it at the space + if before, after, ok := strings.Cut(item.Visibility.Value, " "); ok { + // Set the rational number to the fraction of the mixed number + ratNum, ok = ratNum.SetString(after) + if !ok { + return nil, participle.Errorf(item.Visibility.Pos, "visibility: invalid fraction %q", after) + } + + // Create a new rational number and set it to the whole part of + // the mixed number + add, ok := new(big.Rat).SetString(before) + if !ok { + return nil, participle.Errorf(item.Visibility.Pos, "visibility: invalid whole number %q", before) + } + + // Add the whole part to the fractional part + ratNum = ratNum.Add(ratNum, add) + } else { + // There's no space, so this is just a fraction or a whole number. + // Just set the rational number to the whole string. + ratNum, ok = ratNum.SetString(before) + if !ok { + return nil, participle.Errorf(item.Visibility.Pos, "visibility: invalid fraction %q", after) + } + } + + // If there's no unit, set the unit to meters + if item.Visibility.Unit == "" { + item.Visibility.Unit = "M" + } + + unit := units.Distance(item.Visibility.Unit) + val, _ := ratNum.Float64() + + if opts.DistanceUnit != "" { + val = unit.Convert(opts.DistanceUnit, val) + unit = opts.DistanceUnit + } + + setField(out, "Visibility", Visibility{ + Plus: item.Visibility.Plus, + Value: val, + Unit: unit, + }) + case item.WindSpeed != nil: + var direction int + // If the wind speed is variable, there's no direction to worry about + if !item.WindSpeed.Variable { + // The length of the value must be at least 5 (3 characters for direction and 2 for speed) + if len(item.WindSpeed.Value) < 5 { + return nil, participle.Errorf(item.WindSpeed.Pos, "wind: invalid length (%d)", len(item.WindSpeed.Value)) + } + + // First three characters are the direction + direction, err = strconv.Atoi(item.WindSpeed.Value[:3]) + if err != nil { + return nil, participle.Errorf(item.WindSpeed.Pos, "wind: %s", err) + } + + // Set the value to the last two characters so it can be processed + // as just a speed. + item.WindSpeed.Value = item.WindSpeed.Value[3:] + + // The direction is in degrees so it may not go above 360 or below 0 + if direction > 360 || direction < 0 { + return nil, participle.Errorf(item.WindSpeed.Pos, "wind: invalid direction (%d)", direction) + } + } + + // If there was a direction, it was removed above, so now we can just + // get the speed by parsing the string + speed, err := strconv.Atoi(item.WindSpeed.Value) + if err != nil { + return nil, participle.Errorf(item.WindSpeed.Pos, "wind: %s", err) + } + + var gusts int + if item.WindSpeed.Gusts != "" { + gusts, err = strconv.Atoi(item.WindSpeed.Gusts) + if err != nil { + return nil, participle.Errorf(item.WindSpeed.Pos, "wind: %s", err) + } + } + + var windshear int + if item.WindSpeed.WindShear != "" { + windshear, err = strconv.Atoi(item.WindSpeed.WindShear) + if err != nil { + return nil, participle.Errorf(item.WindSpeed.Pos, "wind: %s", err) + } + } + + unit := units.Speed(item.WindSpeed.Unit) + if opts.SpeedUnit != "" { + speed = unit.Convert(opts.SpeedUnit, speed) + if gusts != 0 { + gusts = unit.Convert(opts.SpeedUnit, gusts) + } + unit = opts.SpeedUnit + } + + setField(out, "Wind", Wind{ + Gusts: gusts, + Speed: speed, + WindShear: windshear * 100, // Scale factor for altitude is 100 + Direction: Direction{ + Variable: item.WindSpeed.Variable, + Value: direction, + }, + Unit: unit, + }) + case item.Flag != nil: + switch { + case item.Flag.CAVOK: + appendField(out, "Flags", CeilingAndVisibilityOK) + } + case item.Change != nil: + ch := &Change{ + Type: ChangeType(item.Change.Type), + } + + // FM changes don't have a valid pair, they only come with a single time string + if ch.Type == From { + t, err := parseTime(item.Change.Time) + if err != nil { + return nil, participle.Errorf(item.Change.Pos, "changes: %s", err) + } + ch.Valid = ValidPair{From: t} + } else { + vp, err := parseValid(item.Change.Valid) + if err != nil { + return nil, participle.Errorf(item.Change.Pos, "changes: %s", err) + } + ch.Valid = vp + } + + fc.Changes = append(fc.Changes, ch) + + // Set out to the change value so that future mutations + // happen to the change rather than the root forecast. + out = reflect.ValueOf(ch).Elem() + case item.Probability != nil: + // If the time is empty, this probability belongs to the + // previous change. + if item.Probability.Time == "" { + prob, err := strconv.Atoi(item.Probability.Value) + if err != nil { + return nil, participle.Errorf(item.Probability.Pos, "prob: %s", err) + } + setField(out, "Probability", prob) + } else { + pr := &Probability{} + + // The probability time string must have 4 characters, + // 2 for starting time and 2 for ending time + if len(item.Probability.Time) < 4 { + return nil, participle.Errorf(item.Probability.Pos, "prob: invalid time %q", item.Probability.Time) + } + + startStr := item.Probability.Time[:2] + endStr := item.Probability.Time[2:] + + start, err := strconv.Atoi(startStr) + if err != nil { + return nil, participle.Errorf(item.Probability.Pos, "prob: %s", err) + } + + end, err := strconv.Atoi(endStr) + if err != nil { + return nil, participle.Errorf(item.Probability.Pos, "prob: %s", err) + } + + t := fc.PublishTime + pr.Valid = ValidPair{ + From: time.Date(t.Year(), t.Month(), t.Day(), start, 0, 0, 0, time.UTC), + To: time.Date(t.Year(), t.Month(), t.Day(), end, 0, 0, 0, time.UTC), + } + + // Get the duration by subtracting the from time from the to time + pr.Valid.Duration = pr.Valid.To.Sub(pr.Valid.From) + + fc.Probabilities = append(fc.Probabilities, pr) + + // Set out to the probability value so that future mutations + // happen to the probability rather than the root forecast. + out = reflect.ValueOf(pr).Elem() + } + + } + } + + return fc, nil +} + +// setField sets a field of a struct to a value. +// +// This is used to allow mutations to happen on either +// the root forecast or a change or probability. It makes it +// easier to handle the different types. +func setField(rv reflect.Value, name string, to any) { + rv.FieldByName(name).Set(reflect.ValueOf(to)) +} + +// appendField appends a value to a slice in the field of a struct. +// +// This is used to allow mutations to happen on either +// the root forecast or a change or probability. It makes it +// easier to handle the different types. +func appendField(rv reflect.Value, name string, items ...any) { + f := rv.FieldByName(name) + f.Set(reflect.Append(f, anyToValues(items)...)) +} + +// anyToValues converts a slice of any type to a slice +// of reflect values. +func anyToValues(items []any) []reflect.Value { + out := make([]reflect.Value, len(items)) + for i, item := range items { + out[i] = reflect.ValueOf(item) + } + return out +} diff --git a/taf_test.go b/taf_test.go new file mode 100644 index 0000000..762fbcc --- /dev/null +++ b/taf_test.go @@ -0,0 +1,626 @@ +package taf + +import ( + "reflect" + "strings" + "testing" + "time" + + "go.elara.ws/taf/units" +) + +func TestKLAX(t *testing.T) { + const data = `KLAX 212011Z 2120/2224 26012KT P6SM FEW035 SCT050 SCT060 + FM212200 25010KT P6SM SCT040 + FM220300 VRB03KT P6SM BKN025 + FM221000 VRB03KT P6SM OVC025 + FM221700 26006KT P6SM BKN025 + FM222000 26012KT P6SM SCT030` + + expected := &Forecast{ + Identifier: "KLAX", + PublishTime: time.Date(2023, time.September, 21, 20, 11, 0, 0, time.UTC), + Valid: ValidPair{ + From: time.Date(2023, time.September, 21, 20, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 23, 0, 0, 0, 0, time.UTC), + Duration: time.Duration(100800000000000), + }, + Visibility: Visibility{ + Plus: true, + Value: 6, + Unit: units.StatuteMiles, + }, + Wind: Wind{ + Direction: Direction{ + Value: 260, + }, + Speed: 12, + Unit: units.Knots, + }, + SkyCondition: []SkyCondition{ + { + Type: Few, + Altitude: 3500, + }, + { + Type: Scattered, + Altitude: 5000, + }, + { + Type: Scattered, + Altitude: 6000, + }, + }, + Changes: []*Change{ + { + Type: From, + Valid: ValidPair{ + From: time.Date(2023, time.September, 21, 22, 0, 0, 0, time.UTC), + }, + Visibility: Visibility{ + Plus: true, + Value: 6, + Unit: units.StatuteMiles, + }, + Wind: Wind{ + Direction: Direction{ + Value: 250, + }, + Speed: 10, + Unit: units.Knots, + }, + SkyCondition: []SkyCondition{ + { + Type: Scattered, + Altitude: 4000, + }, + }, + }, + { + Type: From, + Valid: ValidPair{ + From: time.Date(2023, time.September, 22, 3, 0, 0, 0, time.UTC), + }, + Visibility: Visibility{ + Plus: true, + Value: 6, + Unit: units.StatuteMiles, + }, + Wind: Wind{ + Direction: Direction{ + Variable: true, + }, + Speed: 3, + Unit: units.Knots, + }, + SkyCondition: []SkyCondition{ + { + Type: Broken, + Altitude: 2500, + }, + }, + }, + { + Type: From, + Valid: ValidPair{ + From: time.Date(2023, time.September, 22, 10, 0, 0, 0, time.UTC), + }, + Visibility: Visibility{ + Plus: true, + Value: 6, + Unit: units.StatuteMiles, + }, + Wind: Wind{ + Direction: Direction{ + Variable: true, + }, + Speed: 3, + Unit: units.Knots, + }, + SkyCondition: []SkyCondition{ + { + Type: Overcast, + Altitude: 2500, + }, + }, + }, + { + Type: From, + Valid: ValidPair{ + From: time.Date(2023, time.September, 22, 17, 0, 0, 0, time.UTC), + }, + Visibility: Visibility{ + Plus: true, + Value: 6, + Unit: units.StatuteMiles, + }, + Wind: Wind{ + Direction: Direction{ + Value: 260, + }, + Speed: 6, + Unit: units.Knots, + }, + SkyCondition: []SkyCondition{ + { + Type: Broken, + Altitude: 2500, + }, + }, + }, + { + Type: From, + Valid: ValidPair{ + From: time.Date(2023, time.September, 22, 20, 0, 0, 0, time.UTC), + }, + Visibility: Visibility{ + Plus: true, + Value: 6, + Unit: units.StatuteMiles, + }, + Wind: Wind{ + Direction: Direction{ + Value: 260, + }, + Speed: 12, + Unit: units.Knots, + }, + SkyCondition: []SkyCondition{ + { + Type: Scattered, + Altitude: 3000, + }, + }, + }, + }, + } + + fc, err := Parse(strings.NewReader(data)) + if err != nil { + t.Fatalf("Error during parsing: %s", err) + } + + if !reflect.DeepEqual(fc, expected) { + t.Errorf("Output does not match expected") + } +} + +func TestZGSZ(t *testing.T) { + const data = `TAF AMD ZGSZ 211907Z 2118/2218 18004MPS 8000 SCT020 TX32/2206Z TN28/2122Z + TEMPO 2120/2202 SHRA SCT020 FEW023CB + TEMPO 2204/2208 TSRA SCT020 FEW023CB` + + expected := &Forecast{ + Identifier: "ZGSZ", + PublishTime: time.Date(2023, time.September, 21, 19, 7, 0, 0, time.UTC), + Valid: ValidPair{ + From: time.Date(2023, time.September, 21, 18, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 22, 18, 0, 0, 0, time.UTC), + Duration: time.Duration(86400000000000), + }, + Visibility: Visibility{ + Value: 8000, + Unit: units.Meters, + }, + Wind: Wind{ + Direction: Direction{ + Value: 180, + }, + Speed: 4, + Unit: units.MetersPerSecond, + }, + SkyCondition: []SkyCondition{ + { + Type: Scattered, + Altitude: 2000, + }, + }, + Temperature: []Temperature{ + { + Type: High, + Value: 32, + Time: time.Date(2023, time.September, 22, 6, 0, 0, 0, time.UTC), + }, + { + Type: Low, + Value: 28, + Time: time.Date(2023, time.September, 21, 22, 0, 0, 0, time.UTC), + }, + }, + Changes: []*Change{ + { + Type: Temporary, + Valid: ValidPair{ + From: time.Date(2023, time.September, 21, 20, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 22, 2, 0, 0, 0, time.UTC), + Duration: time.Duration(21600000000000), + }, + SkyCondition: []SkyCondition{ + { + Type: Scattered, + Altitude: 2000, + }, + { + Type: Few, + Altitude: 2300, + CloudType: CumuloNimbus, + }, + }, + Weather: []Weather{ + { + Descriptor: Showers, + Precipitation: Rain, + }, + }, + }, + { + Type: Temporary, + Valid: ValidPair{ + From: time.Date(2023, time.September, 22, 4, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 22, 8, 0, 0, 0, time.UTC), + Duration: time.Duration(14400000000000), + }, + SkyCondition: []SkyCondition{ + { + Type: Scattered, + Altitude: 2000, + }, + { + Type: Few, + Altitude: 2300, + CloudType: CumuloNimbus, + }, + }, + Weather: []Weather{ + { + Descriptor: Thunderstorm, + Precipitation: Rain, + }, + }, + }, + }, + } + + fc, err := Parse(strings.NewReader(data)) + if err != nil { + t.Fatalf("Error during parsing: %s", err) + } + + if !reflect.DeepEqual(fc, expected) { + t.Errorf("Output does not match expected") + } +} + +func TestLFBD(t *testing.T) { + const data = `TAF LFBD 211700Z 2118/2224 31010KT CAVOK TX37/2214Z TN22/2205Z + BECMG 2118/2120 32004KT + BECMG 2200/2202 26005KT + BECMG 2213/2215 32010KT + BECMG 2222/2224 24004KT` + + expected := &Forecast{ + Identifier: "LFBD", + PublishTime: time.Date(2023, time.September, 21, 17, 0, 0, 0, time.UTC), + Valid: ValidPair{ + From: time.Date(2023, time.September, 21, 18, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 23, 0, 0, 0, 0, time.UTC), + Duration: time.Duration(108000000000000), + }, + Wind: Wind{ + Direction: Direction{ + Value: 310, + }, + Speed: 10, + Unit: units.Knots, + }, + Temperature: []Temperature{ + { + Type: High, + Value: 37, + Time: time.Date(2023, time.September, 22, 14, 0, 0, 0, time.UTC), + }, + { + Type: Low, + Value: 22, + Time: time.Date(2023, time.September, 22, 5, 0, 0, 0, time.UTC), + }, + }, + Changes: []*Change{ + { + Type: Becoming, + Valid: ValidPair{ + From: time.Date(2023, time.September, 21, 18, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 21, 20, 0, 0, 0, time.UTC), + Duration: time.Duration(7200000000000), + }, + Wind: Wind{ + Direction: Direction{ + Value: 320, + }, + Speed: 4, + Unit: units.Knots, + }, + }, + { + Type: Becoming, + Valid: ValidPair{ + From: time.Date(2023, time.September, 22, 0, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 22, 2, 0, 0, 0, time.UTC), + Duration: time.Duration(7200000000000), + }, + Wind: Wind{ + Direction: Direction{ + Value: 260, + }, + Speed: 5, + Unit: units.Knots, + }, + }, + { + Type: Becoming, + Valid: ValidPair{ + From: time.Date(2023, time.September, 22, 13, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 22, 15, 0, 0, 0, time.UTC), + Duration: time.Duration(7200000000000), + }, + Wind: Wind{ + Direction: Direction{ + Value: 320, + }, + Speed: 10, + Unit: units.Knots, + }, + }, + { + Type: Becoming, + Valid: ValidPair{ + From: time.Date(2023, time.September, 22, 22, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 23, 0, 0, 0, 0, time.UTC), + Duration: time.Duration(7200000000000), + }, + Wind: Wind{ + Direction: Direction{ + Value: 240, + }, + Speed: 4, + Unit: units.Knots, + }, + }, + }, + Flags: []Flag{ + CeilingAndVisibilityOK, + }, + } + + fc, err := Parse(strings.NewReader(data)) + if err != nil { + t.Fatalf("Error during parsing: %s", err) + } + + if !reflect.DeepEqual(fc, expected) { + t.Errorf("Output does not match expected") + } +} + +func TestUUEE(t *testing.T) { + const data = `TAF UUEE 211958Z 2121/2221 VRB01MPS 9999 SCT030 TX20/2212Z TN12/2202Z + TEMPO 2121/2204 BKN004 + PROB40 + TEMPO 2121/2204 0300 FG + BECMG 2204/2206 24006MPS + PROB40 + TEMPO 2209/2218 -TSRA BKN020CB` + + expected := &Forecast{ + Identifier: "UUEE", + PublishTime: time.Date(2023, time.September, 21, 19, 58, 0, 0, time.UTC), + Valid: ValidPair{ + From: time.Date(2023, time.September, 21, 21, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 22, 21, 0, 0, 0, time.UTC), + Duration: time.Duration(86400000000000), + }, + Visibility: Visibility{ + Value: 9999, + Unit: units.Meters, + }, + Wind: Wind{ + Direction: Direction{ + Variable: true, + }, + Speed: 1, + Unit: units.MetersPerSecond, + }, + SkyCondition: []SkyCondition{ + { + Type: Scattered, + Altitude: 3000, + }, + }, + Temperature: []Temperature{ + { + Type: High, + Value: 20, + Time: time.Date(2023, time.September, 22, 12, 0, 0, 0, time.UTC), + }, + { + Type: Low, + Value: 12, + Time: time.Date(2023, time.September, 22, 2, 0, 0, 0, time.UTC), + }, + }, + Changes: []*Change{ + { + Type: Temporary, + Valid: ValidPair{ + From: time.Date(2023, time.September, 21, 21, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 22, 4, 0, 0, 0, time.UTC), + Duration: time.Duration(25200000000000), + }, + SkyCondition: []SkyCondition{ + { + Type: Broken, + Altitude: 400, + }, + }, + Probability: 40, + }, + { + Type: Temporary, + Valid: ValidPair{ + From: time.Date(2023, time.September, 21, 21, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 22, 4, 0, 0, 0, time.UTC), + Duration: time.Duration(25200000000000), + }, + Visibility: Visibility{ + Value: 300, + Unit: units.Meters, + }, + Weather: []Weather{ + { + Obscuration: Fog, + }, + }, + }, + { + Type: Becoming, + Valid: ValidPair{ + From: time.Date(2023, time.September, 22, 4, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 22, 6, 0, 0, 0, time.UTC), + Duration: time.Duration(7200000000000), + }, + Wind: Wind{ + Direction: Direction{ + Value: 240, + }, + Speed: 6, + Unit: units.MetersPerSecond, + }, + Probability: 40, + }, + { + Type: Temporary, + Valid: ValidPair{ + From: time.Date(2023, time.September, 22, 9, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 22, 18, 0, 0, 0, time.UTC), + Duration: time.Duration(32400000000000), + }, + SkyCondition: []SkyCondition{ + { + Type: Broken, + Altitude: 2000, + CloudType: CumuloNimbus, + }, + }, + Weather: []Weather{ + { + Modifier: Light, + Descriptor: Thunderstorm, + Precipitation: Rain, + }, + }, + }, + }, + } + + fc, err := Parse(strings.NewReader(data)) + if err != nil { + t.Fatalf("Error during parsing: %s", err) + } + + if !reflect.DeepEqual(fc, expected) { + t.Errorf("Output does not match expected") + } +} + +func TestEGLL(t *testing.T) { + const data = `TAF EGLL 211658Z 2118/2224 22008KT 9999 FEW040 + BECMG 2201/2204 BKN007 + PROB30 + TEMPO 2202/2206 8000 BKN004 + BECMG 2207/2210 SCT025` + + expected := &Forecast{ + Identifier: "EGLL", + PublishTime: time.Date(2023, time.September, 21, 16, 58, 0, 0, time.UTC), + Valid: ValidPair{ + From: time.Date(2023, time.September, 21, 18, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 23, 0, 0, 0, 0, time.UTC), + Duration: time.Duration(108000000000000), + }, + Visibility: Visibility{ + Value: 9999, + Unit: units.Meters, + }, + Wind: Wind{ + Direction: Direction{ + Value: 220, + }, + Speed: 8, + Unit: units.Knots, + }, + SkyCondition: []SkyCondition{ + { + Type: Few, + Altitude: 4000, + }, + }, + Changes: []*Change{ + { + Type: Becoming, + Valid: ValidPair{ + From: time.Date(2023, time.September, 22, 1, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 22, 4, 0, 0, 0, time.UTC), + Duration: time.Duration(10800000000000), + }, + SkyCondition: []SkyCondition{ + { + Type: Broken, + Altitude: 700, + }, + }, + Probability: 30, + }, + { + Type: Temporary, + Valid: ValidPair{ + From: time.Date(2023, time.September, 22, 2, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 22, 6, 0, 0, 0, time.UTC), + Duration: time.Duration(14400000000000), + }, + Visibility: Visibility{ + Value: 8000, + Unit: units.Meters, + }, + SkyCondition: []SkyCondition{ + { + Type: Broken, + Altitude: 400, + }, + }, + }, + { + Type: Becoming, + Valid: ValidPair{ + From: time.Date(2023, time.September, 22, 7, 0, 0, 0, time.UTC), + To: time.Date(2023, time.September, 22, 10, 0, 0, 0, time.UTC), + Duration: time.Duration(10800000000000), + }, + SkyCondition: []SkyCondition{ + { + Type: Scattered, + Altitude: 2500, + }, + }, + }, + }, + } + + fc, err := Parse(strings.NewReader(data)) + if err != nil { + t.Fatalf("Error during parsing: %s", err) + } + + if !reflect.DeepEqual(fc, expected) { + t.Errorf("Output does not match expected") + } +} diff --git a/time.go b/time.go new file mode 100644 index 0000000..9ca74dc --- /dev/null +++ b/time.go @@ -0,0 +1,58 @@ +package taf + +import ( + "strings" + "time" + + "go.elara.ws/taf/internal/parser" +) + +const ( + TimeFormat = "021504" + ValidFormat = "0215" +) + +func parseTime(s string) (time.Time, error) { + t, err := time.Parse(TimeFormat, s) + if err != nil { + return time.Time{}, err + } + now := time.Now().UTC() + return t.AddDate(now.Year(), int(now.Month()), 0), nil +} + +func parseValid(v *parser.ValidPair) (ValidPair, error) { + start, err := parseValidTime(v.Start) + if err != nil { + return ValidPair{}, err + } + + end, err := parseValidTime(v.End) + if err != nil { + return ValidPair{}, err + } + + return ValidPair{ + From: start, + To: end, + Duration: end.Sub(start), + }, nil +} + +func parseValidTime(s string) (time.Time, error) { + addDays := 0 + // Go doesn't know what to do with hour 24, + // so we set it to 00 the next day + if strings.HasSuffix(s, "24") { + s = s[:2] + "00" + addDays = 1 + } + + t, err := time.Parse(ValidFormat, s) + if err != nil { + return time.Time{}, err + } + + now := time.Now().UTC() + return t.AddDate(now.Year(), int(now.Month()), addDays), nil +} diff --git a/types.go b/types.go new file mode 100644 index 0000000..6d46a12 --- /dev/null +++ b/types.go @@ -0,0 +1,188 @@ +package taf + +import ( + "time" + + "go.elara.ws/taf/units" +) + +const None = "" + +type Forecast struct { + Identifier string `json:"identifier,omitempty"` + PublishTime time.Time `json:"publish_time,omitempty"` + Valid ValidPair `json:"valid,omitempty"` + Visibility Visibility `json:"visibility,omitempty"` + Wind Wind `json:"wind,omitempty"` + SkyCondition []SkyCondition `json:"sky_condition,omitempty"` + Temperature []Temperature `json:"temperature,omitempty"` + Weather []Weather `json:"weather,omitempty"` + Probabilities []*Probability `json:"probabilities,omitempty"` + Changes []*Change `json:"changes,omitempty"` + Flags []Flag `json:"flags,omitempty"` +} + +type Change struct { + Type ChangeType `json:"type,omitempty"` + Valid ValidPair `json:"valid,omitempty"` + Visibility Visibility `json:"visibility,omitempty"` + Wind Wind `json:"wind,omitempty"` + SkyCondition []SkyCondition `json:"sky_condition,omitempty"` + Temperature []Temperature `json:"temperature,omitempty"` + Weather []Weather `json:"weather,omitempty"` + Flags []Flag `json:"flags,omitempty"` + Probability int `json:"probability,omitempty"` +} + +type Probability struct { + Valid ValidPair `json:"valid,omitempty"` + Value int `json:"value,omitempty"` + Visibility Visibility `json:"visibility,omitempty"` + Wind Wind `json:"wind,omitempty"` + SkyCondition []SkyCondition `json:"sky_condition,omitempty"` + Temperature []Temperature `json:"temperature,omitempty"` + Weather []Weather `json:"weather,omitempty"` + Flags []Flag `json:"flags,omitempty"` +} + +type ValidPair struct { + From time.Time `json:"from,omitempty"` + To time.Time `json:"to,omitempty"` + Duration time.Duration `json:"duration,omitempty"` +} + +type Visibility struct { + Plus bool `json:"plus,omitempty"` + Value float64 `json:"value,omitempty"` + Unit units.Distance `json:"unit,omitempty"` +} + +type SkyConditionType string + +const ( + Few SkyConditionType = "FEW" + Scattered SkyConditionType = "SCT" + Broken SkyConditionType = "BKN" + Overcast SkyConditionType = "OVC" + VerticalVisibility SkyConditionType = "VV" + SkyClear SkyConditionType = "SKC" +) + +type CloudType string + +const ( + CumuloNimbus CloudType = "CB" + ToweringCumulus CloudType = "TCU" +) + +type SkyCondition struct { + Type SkyConditionType `json:"type,omitempty"` + Altitude int `json:"altitude,omitempty"` + CloudType CloudType `json:"cloud_type,omitempty"` +} + +type Wind struct { + Direction Direction `json:"direction,omitempty"` + WindShear int `json:"wind_shear,omitempty"` + Speed int `json:"speed,omitempty"` + Gusts int `json:"gusts,omitempty"` + Unit units.Speed `json:"unit,omitempty"` +} + +type Direction struct { + Variable bool `json:"variable,omitempty"` + Value int `json:"value,omitempty"` +} + +type Modifier string + +const ( + Heavy Modifier = "+" + Light Modifier = "-" +) + +type Descriptor string + +const ( + Shallow Descriptor = "MI" + Patches Descriptor = "BC" + LowDrifting Descriptor = "DC" + Blowing Descriptor = "BL" + Showers Descriptor = "SH" + Thunderstorm Descriptor = "TS" + Freezing Descriptor = "FZ" + Partial Descriptor = "PR" +) + +type Precipitation string + +const ( + Drizzle Precipitation = "DZ" + Rain Precipitation = "RA" + Snow Precipitation = "SN" + SnowGrains Precipitation = "SG" + IceCrystals Precipitation = "IC" + IcePellets Precipitation = "PL" + Hail Precipitation = "GR" + SmallHail Precipitation = "GS" + Unknown Precipitation = "UP" +) + +type Obscuration string + +const ( + Mist Obscuration = "BR" + Fog Obscuration = "FG" + Smoke Obscuration = "FU" + Dust Obscuration = "DU" + Sand Obscuration = "SA" + Haze Obscuration = "HZ" + Spray Obscuration = "PY" + VolcanicAsh Obscuration = "VA" +) + +type Phenomenon string + +const ( + Whirls Phenomenon = "PO" + Squalls Phenomenon = "SQ" + FunnelCloud Phenomenon = "FC" + SandStorm Phenomenon = "SS" + DustStorm Phenomenon = "DS" +) + +type Weather struct { + Vicinity bool `json:"vicinity,omitempty"` + Modifier Modifier `json:"modifier,omitempty"` + Descriptor Descriptor `json:"descriptor,omitempty"` + Precipitation Precipitation `json:"precipitation,omitempty"` + Obscuration Obscuration `json:"obscuration,omitempty"` + Phenomenon Phenomenon `json:"phenomenon,omitempty"` +} + +type TemperatureType string + +const ( + High TemperatureType = "TX" + Low TemperatureType = "TN" +) + +type Temperature struct { + Type TemperatureType `json:"type,omitempty"` + Value int `json:"value,omitempty"` + Time time.Time `json:"time,omitempty"` +} + +type ChangeType string + +const ( + From ChangeType = "FM" + Becoming ChangeType = "BECMG" + Temporary ChangeType = "TEMPO" +) + +type Flag string + +const ( + CeilingAndVisibilityOK Flag = "CAVOK" +) diff --git a/units/units.go b/units/units.go new file mode 100644 index 0000000..52c0d86 --- /dev/null +++ b/units/units.go @@ -0,0 +1,118 @@ +package units + +import ( + "strings" +) + +// Speed represents a unit of speed +type Speed string + +// Speed units +const ( + MetersPerSecond Speed = "MPS" + KilometersPerHour Speed = "KMH" + Knots Speed = "KT" +) + +var speedNames = map[Speed]string{ + MetersPerSecond: "m/s", + KilometersPerHour: "kph", + Knots: "kts", +} + +func (su Speed) String() string { + name, ok := speedNames[su] + if !ok { + return "" + } + return name +} + +// Convert converts a value from one unit to another +func (sf Speed) Convert(st Speed, val int) int { + switch { + case sf == MetersPerSecond && st == KilometersPerHour: + return int(float64(val) * 3.6) + case sf == KilometersPerHour && st == MetersPerSecond: + return int(float64(val) / 3.6) + case sf == Knots && st == KilometersPerHour: + return int(float64(val) * 1.852) + case sf == KilometersPerHour && st == Knots: + return int(float64(val) / 1.852) + case sf == MetersPerSecond && st == Knots: + return int(float64(val) * 1.94384) + case sf == Knots && st == MetersPerSecond: + return int(float64(val) / 1.94384) + default: + return val + } +} + +// ParseSpeed parses a speed value. Valid inputs include: +// mps, m/s, kmh, kph, kt, and kts. +// This function is case-insensitive. +func ParseSpeed(s string) (Speed, bool) { + if _, ok := speedNames[Speed(s)]; ok { + return Speed(s), true + } + + for su, name := range speedNames { + if strings.EqualFold(s, name) || + strings.EqualFold(s, string(su)) { + return su, true + } + } + + return "", false +} + +// Distance represents a unit of distance +type Distance string + +// Distance units +const ( + StatuteMiles Distance = "SM" + Meters Distance = "M" +) + +var distanceNames = map[Distance]string{ + StatuteMiles: "mi", + Meters: "m", +} + +func (du Distance) String() string { + name, ok := distanceNames[du] + if !ok { + return "" + } + return name +} + +// Convert converts a value from one unit to another +func (df Distance) Convert(dt Distance, val float64) float64 { + switch { + case df == StatuteMiles && dt == Meters: + return val * 1609 + case df == Meters && dt == StatuteMiles: + return val / 1609 + default: + return val + } +} + +// ParseDistance parses a speed value. Valid inputs include: +// sm, mi, and m. This function is case-insensitive. +func ParseDistance(s string) (Distance, bool) { + if _, ok := distanceNames[Distance(s)]; ok { + return Distance(s), true + } + + for d, name := range distanceNames { + if strings.EqualFold(s, name) || + strings.EqualFold(s, string(d)) { + return d, true + } + } + + return "", false +}