package v2

import (
	"fmt"

	"predictor-refactored/internal/engine"
	"predictor-refactored/internal/weather"
)

// buildProfile translates a PredictionRequest into an engine.Profile.
//
// elev may be nil when no terrain dataset is loaded; TerrainContact constraints
// will return an error in that case.
func buildProfile(req PredictionRequest, field weather.WindField, elev engine.TerrainProvider, warnings *engine.Warnings) (engine.Profile, error) {
	if len(req.Profile) == 0 {
		return engine.Profile{}, fmt.Errorf("profile must contain at least one stage")
	}

	step := req.Options.StepSeconds
	if step == 0 {
		step = 60
	}
	tol := req.Options.Tolerance
	if tol == 0 {
		tol = 0.01
	}

	dir := engine.Forward
	switch req.Direction {
	case "", "forward":
		dir = engine.Forward
	case "reverse":
		dir = engine.Reverse
	default:
		return engine.Profile{}, fmt.Errorf("unknown direction %q", req.Direction)
	}

	props := make([]*engine.Propagator, len(req.Profile))
	for i, stage := range req.Profile {
		model, err := buildModel(stage.Model, field, warnings)
		if err != nil {
			return engine.Profile{}, fmt.Errorf("stage %q: %w", stage.Name, err)
		}
		constraints, err := buildConstraints(stage.Constraints, elev)
		if err != nil {
			return engine.Profile{}, fmt.Errorf("stage %q: %w", stage.Name, err)
		}
		props[i] = &engine.Propagator{
			Name:        stage.Name,
			Step:        step,
			Model:       model,
			Constraints: constraints,
			Tolerance:   tol,
		}
	}

	// Wire fallbacks once all stages exist.
	for i, stage := range req.Profile {
		if stage.FallbackIndex == nil {
			continue
		}
		idx := *stage.FallbackIndex
		if idx < 0 || idx >= len(props) {
			return engine.Profile{}, fmt.Errorf("stage %q: fallback_index %d out of range", stage.Name, idx)
		}
		props[i].Fallback = props[idx]
	}

	return engine.Profile{Stages: props, Direction: dir}, nil
}

func buildModel(spec ModelSpec, field weather.WindField, warnings *engine.Warnings) (engine.Model, error) {
	var base engine.Model
	switch spec.Type {
	case "constant_rate":
		base = engine.ConstantRate(spec.Rate)
	case "parachute_descent":
		if spec.SeaLevelRate <= 0 {
			return nil, fmt.Errorf("parachute_descent requires positive sea_level_rate")
		}
		base = engine.ParachuteDescent(spec.SeaLevelRate)
	case "piecewise":
		segs := make([]engine.RateSegment, len(spec.Segments))
		for i, s := range spec.Segments {
			segs[i] = engine.RateSegment{Until: s.Until, Rate: s.Rate}
		}
		base = engine.Piecewise(segs)
	case "wind":
		if field == nil {
			return nil, fmt.Errorf("wind model requires a loaded dataset")
		}
		return engine.WindTransport(field, warnings), nil
	default:
		return nil, fmt.Errorf("unknown model type %q", spec.Type)
	}

	if spec.IncludeWind {
		if field == nil {
			return nil, fmt.Errorf("include_wind requires a loaded dataset")
		}
		return engine.Sum(base, engine.WindTransport(field, warnings)), nil
	}
	return base, nil
}

func buildConstraints(specs []ConstraintSpec, elev engine.TerrainProvider) ([]engine.Constraint, error) {
	out := make([]engine.Constraint, 0, len(specs))
	for _, spec := range specs {
		action, err := parseAction(spec.Action)
		if err != nil {
			return nil, err
		}
		var c engine.Constraint
		switch spec.Type {
		case "max_altitude":
			c = engine.MaxAltitude{Limit: spec.Limit, On: action}
		case "min_altitude":
			c = engine.MinAltitude{Limit: spec.Limit, On: action}
		case "max_time":
			c = engine.MaxTime{Limit: spec.Limit, On: action}
		case "terrain_contact":
			if elev == nil {
				return nil, fmt.Errorf("terrain_contact requires an elevation dataset")
			}
			c = engine.TerrainContact{Provider: elev, On: action}
		default:
			return nil, fmt.Errorf("unknown constraint type %q", spec.Type)
		}
		out = append(out, c)
	}
	return out, nil
}

func parseAction(s string) (engine.Action, error) {
	switch s {
	case "", "stop":
		return engine.ActionStop, nil
	case "fallback":
		return engine.ActionFallback, nil
	case "clip":
		return engine.ActionClip, nil
	default:
		return 0, fmt.Errorf("unknown constraint action %q", s)
	}
}