// Package ridetest builds ride.Ride test fixtures from a compact string DSL.
//
// Grammar: sections separated by "|", each "<distance>km at <slope>%" with
// optional per-section metrics "hr=150 cad=80 w=200":
//
//	ridetest.MustRide("2km at 7% | 1km at -7%")
//
// Options adjust the generated columns: Sampling (step in meters, default
// 100), StartCoord (first point; later points progress northeast at the
// Heading rate, default 0.01° of latitude and longitude per kilometer),
// StartTime (default the zero time, one second between points) and
// StartElevation (default 0).
package ridetest

import (
	"fmt"
	"strconv"
	"strings"
	"time"

	"github.com/jftuga/geodist"
	"github.com/martinlehoux/biking_home/ride"
)

const defaultSamplingM = 100

// headingPerKm is the latitude and longitude offset applied to each point per
// kilometer of ride, giving StartCoord rides a fixed northeast direction.
const headingPerKm = 0.01

type section struct {
	distanceM float64
	slope     float64
	heartRate *float64
	cadence   *float64
	power     *float64
}

type point struct {
	distanceM  float64
	elevationM float64
	coord      geodist.Coord
	timestamp  time.Time
	section    section
}

type options struct {
	samplingM  float64
	startCoord *geodist.Coord
	headingLat float64
	headingLon float64
	startTime  time.Time
	startElevM float64
}

// Option configures the ride generated by Ride.
type Option func(*options)

// Sampling sets the distance between consecutive points in meters
// (default 100).
func Sampling(m float64) Option {
	return func(o *options) { o.samplingM = m }
}

// StartCoord sets the coordinate of the first point. Each following point
// progresses northeast at the rate set by Heading, default 0.01° of latitude
// and longitude per kilometer.
func StartCoord(lat, lon float64) Option {
	return func(o *options) {
		o.startCoord = &geodist.Coord{Lat: lat, Lon: lon}
		if o.headingLat == 0 {
			o.headingLat = headingPerKm
		}
		if o.headingLon == 0 {
			o.headingLon = headingPerKm
		}
	}
}

// Heading sets the latitude and longitude offset applied to each point per
// kilometer of ride, in degrees (default 0.01 northeast when StartCoord is
// set). Only meaningful together with StartCoord.
func Heading(latPerKm, lonPerKm float64) Option {
	return func(o *options) {
		o.headingLat = latPerKm
		o.headingLon = lonPerKm
	}
}

// StartTime sets the timestamp of the first point; each following point is
// one second later (default: the zero time).
func StartTime(t time.Time) Option {
	return func(o *options) { o.startTime = t }
}

// StartElevation sets the elevation of the first point, in meters (default 0).
func StartElevation(m float64) Option {
	return func(o *options) { o.startElevM = m }
}

// Ride parses a ride description into a ride.Ride.
//
// Example: "2km at 7% | 1km at -7%".
func Ride(dsl string, opts ...Option) (ride.Ride, error) {
	o := options{samplingM: defaultSamplingM, headingLat: headingPerKm, headingLon: headingPerKm}
	for _, opt := range opts {
		opt(&o)
	}
	if o.samplingM <= 0 {
		return ride.Ride{}, fmt.Errorf("ridetest: sampling must be positive, got %v", o.samplingM)
	}
	sections, err := parseSections(dsl)
	if err != nil {
		return ride.Ride{}, err
	}
	if len(sections) == 0 {
		return ride.Ride{}, fmt.Errorf("ridetest: empty ride description")
	}
	for _, metric := range []struct {
		name string
		get  func(section) *float64
	}{
		{"hr", func(s section) *float64 { return s.heartRate }},
		{"cad", func(s section) *float64 { return s.cadence }},
		{"w", func(s section) *float64 { return s.power }},
	} {
		present, complete := metricComplete(sections, metric.get)
		if present && !complete {
			return ride.Ride{}, fmt.Errorf("ridetest: %s= must be set on every section or none", metric.name)
		}
	}
	return buildRide(sections, o), nil
}

// MustRide is like Ride but panics on a malformed description; use it inside
// tests where the description is a static program constant.
func MustRide(dsl string, opts ...Option) ride.Ride {
	ride, err := Ride(dsl, opts...)
	if err != nil {
		panic(err)
	}
	return ride
}

func parseSections(dsl string) ([]section, error) {
	rawSections := strings.Split(dsl, "|")
	sections := make([]section, 0, len(rawSections))
	for _, raw := range rawSections {
		raw = strings.TrimSpace(raw)
		if raw == "" {
			return nil, fmt.Errorf("ridetest: empty section in %q", dsl)
		}
		sec, err := parseSection(raw)
		if err != nil {
			return nil, err
		}
		sections = append(sections, sec)
	}
	return sections, nil
}

// parseSection parses a single section like "2km at 7% hr=150 cad=80 w=200".
func parseSection(raw string) (section, error) {
	fields := strings.Fields(raw)
	if len(fields) < 3 {
		return section{}, fmt.Errorf("ridetest: section %q must look like \"2km at 7%%\"", raw)
	}
	if fields[1] != "at" {
		return section{}, fmt.Errorf("ridetest: section %q: expected \"at\" between distance and slope, got %q", raw, fields[1])
	}
	distanceKm, err := parseUnit(fields[0], "km")
	if err != nil {
		return section{}, fmt.Errorf("ridetest: section %q: %w", raw, err)
	}
	slopePercent, err := parseUnit(fields[2], "%")
	if err != nil {
		return section{}, fmt.Errorf("ridetest: section %q: %w", raw, err)
	}
	if distanceKm <= 0 {
		return section{}, fmt.Errorf("ridetest: section %q: distance must be positive", raw)
	}
	sec := section{
		distanceM: distanceKm * 1000,
		slope:     slopePercent / 100,
	}
	for _, token := range fields[3:] {
		var value *float64
		switch {
		case strings.HasPrefix(token, "hr="):
			value, err = parseMetric(token, "hr")
			sec.heartRate = value
		case strings.HasPrefix(token, "cad="):
			value, err = parseMetric(token, "cad")
			sec.cadence = value
		case strings.HasPrefix(token, "w="):
			value, err = parseMetric(token, "w")
			sec.power = value
		default:
			return section{}, fmt.Errorf("ridetest: section %q: unknown metric %q (want hr=, cad= or w=)", raw, token)
		}
		if err != nil {
			return section{}, fmt.Errorf("ridetest: section %q: %w", raw, err)
		}
	}
	return sec, nil
}

func parseUnit(token, unit string) (float64, error) {
	if !strings.HasSuffix(token, unit) {
		return 0, fmt.Errorf("expected a value in %s, got %q", unit, token)
	}
	return strconv.ParseFloat(strings.TrimSuffix(token, unit), 64)
}

func parseMetric(token, name string) (*float64, error) {
	value, err := strconv.ParseFloat(strings.TrimPrefix(token, name+"="), 64)
	if err != nil {
		return nil, fmt.Errorf("invalid %s value %q", name, token)
	}
	return &value, nil
}

// metricComplete reports whether a metric column is present (any section sets
// it) and complete (every section sets it).
func metricComplete(sections []section, get func(section) *float64) (present, complete bool) {
	set := 0
	for _, sec := range sections {
		if get(sec) != nil {
			set++
		}
	}
	return set > 0, set == len(sections)
}

func buildRide(sections []section, o options) ride.Ride {
	points := buildPoints(sections, o)
	distances := make([]float64, len(points))
	elevations := make([]float64, len(points))
	coords := make([]geodist.Coord, len(points))
	timestamps := make([]time.Time, len(points))
	var heartRates, cadences, powers []float64
	if sections[0].heartRate != nil {
		heartRates = make([]float64, len(points))
	}
	if sections[0].cadence != nil {
		cadences = make([]float64, len(points))
	}
	if sections[0].power != nil {
		powers = make([]float64, len(points))
	}
	for i, p := range points {
		distances[i] = p.distanceM
		elevations[i] = p.elevationM
		coords[i] = p.coord
		timestamps[i] = p.timestamp
		if heartRates != nil {
			heartRates[i] = *p.section.heartRate
		}
		if cadences != nil {
			cadences[i] = *p.section.cadence
		}
		if powers != nil {
			powers[i] = *p.section.power
		}
	}
	return ride.FromColumnsWithMetrics(distances, elevations, coords, timestamps, heartRates, cadences, powers)
}

func buildPoints(sections []section, o options) []point {
	lat, lon := 0.0, 0.0
	if o.startCoord != nil {
		lat, lon = o.startCoord.Lat, o.startCoord.Lon
	}
	// Coordinates derive from the total distance so that exact multiples of
	// the per-kilometer heading stay exact; a running accumulation drifts
	// after a few points.
	coord := func(distanceM float64) geodist.Coord {
		return geodist.Coord{Lat: lat + o.headingLat*(distanceM/1000), Lon: lon + o.headingLon*(distanceM/1000)}
	}
	points := make([]point, 0, len(sections)+1)
	elevation := o.startElevM
	timestamp := o.startTime
	points = append(points, point{
		distanceM:  0,
		elevationM: elevation,
		coord:      coord(0),
		timestamp:  timestamp,
		section:    sections[0],
	})
	distance := 0.0
	for _, sec := range sections {
		curSecDist := 0.0
		for curSecDist < sec.distanceM {
			curSecDist += o.samplingM
			elevation += o.samplingM * sec.slope
			timestamp = timestamp.Add(time.Second)
			points = append(points, point{
				distanceM:  distance + curSecDist,
				elevationM: elevation,
				coord:      coord(distance + curSecDist),
				timestamp:  timestamp,
				section:    sec,
			})
		}
		distance += curSecDist
	}
	return points
}