package dyn

import (
	"fmt"
	"slices"
)

type Value struct {
	v any

	k Kind

	// Effective location where this value was defined and loaded from.
	l Location

	// All YAML locations where this value has been defined. When merging configurations,
	// values in a map may override values in another map. This field is used to track
	// all YAML locations where a value was defined, even if the values at these locations
	// were overridden by other values.
	yamlLocations []Location

	// Whether or not this value is an anchor.
	// If this node doesn't map to a type, we don't need to warn about it.
	anchor bool
}

// InvalidValue is equal to the zero-value of Value.
var InvalidValue = Value{
	k: KindInvalid,
}

// NilValue is a convenient constant for a nil value.
var NilValue = Value{
	k: KindNil,
}

func (v Value) IsNil() bool {
	return v.k == KindNil && v.v == nil
}

// V constructs a new Value with the given value.
func V(v any) Value {
	return NewValue(v, Location{})
}

// NewValue constructs a new Value with the given value and location.
func NewValue(v any, loc Location) Value {
	switch vin := v.(type) {
	case map[string]Value:
		v = newMappingFromGoMap(vin)
	}

	yamlLocations := make([]Location, 0)
	if loc != nilLocation {
		yamlLocations = append(yamlLocations, loc)
	}

	return Value{
		v:             v,
		k:             kindOf(v),
		l:             loc,
		yamlLocations: yamlLocations,
	}
}

// WithLocation returns a new Value with its location set to the given value.
func (v Value) WithLocation(loc Location) Value {
	if loc != nilLocation {
		v.yamlLocations = append(v.yamlLocations, loc)
	}
	return Value{
		v:             v.v,
		k:             v.k,
		l:             loc,
		yamlLocations: v.yamlLocations,
	}
}

// WithYamlLocation returns a new Value with the given location added to its
// list of tracked YAML locations.
// This function is idempotent
func (v Value) WithYamlLocation(loc Location) Value {
	// Location is already being tracked
	if slices.Contains(v.yamlLocations, loc) {
		return v
	}

	// We don't track empty locations.
	if loc == nilLocation {
		return v
	}

	v.yamlLocations = append(v.yamlLocations, loc)
	return v
}

func (v Value) Kind() Kind {
	return v.k
}

func (v Value) Value() any {
	return v.v
}

func (v Value) Location() Location {
	return v.l
}

// All YAML locations where this value has been defined. Is empty if the value
// was never defined in a YAML file.
func (v Value) YamlLocations() []Location {
	return v.yamlLocations
}

func (v Value) IsValid() bool {
	return v.k != KindInvalid
}

func (v Value) AsAny() any {
	switch v.k {
	case KindInvalid:
		panic("invoked AsAny on invalid value")
	case KindMap:
		m := v.v.(Mapping)
		out := make(map[string]any, m.Len())
		for _, pair := range m.pairs {
			pk := pair.Key
			pv := pair.Value
			out[pk.MustString()] = pv.AsAny()
		}
		return out
	case KindSequence:
		vv := v.v.([]Value)
		a := make([]any, len(vv))
		for i, v := range vv {
			a[i] = v.AsAny()
		}
		return a
	case KindNil:
		return v.v
	case KindString:
		return v.v
	case KindBool:
		return v.v
	case KindInt:
		return v.v
	case KindFloat:
		return v.v
	case KindTime:
		return v.v
	default:
		// Panic because we only want to deal with known types.
		panic(fmt.Sprintf("invalid kind: %d", v.k))
	}
}

func (v Value) Get(key string) Value {
	m, ok := v.AsMap()
	if !ok {
		return NilValue
	}

	vv, ok := m.GetByString(key)
	if !ok {
		return NilValue
	}

	return vv
}

func (v Value) Index(i int) Value {
	s, ok := v.v.([]Value)
	if !ok {
		return NilValue
	}

	if i < 0 || i >= len(s) {
		return NilValue
	}

	return s[i]
}

func (v Value) MarkAnchor() Value {
	return Value{
		v: v.v,
		k: v.k,
		l: v.l,

		anchor: true,
	}
}

func (v Value) IsAnchor() bool {
	return v.anchor
}

// eq is an internal only method that compares two values.
// It is used to determine if a value has changed during a visit.
// We need a custom implementation because maps and slices
// cannot be compared with the regular == operator.
func (v Value) eq(w Value) bool {
	if v.k != w.k || v.l != w.l {
		return false
	}

	switch v.k {
	case KindMap:
		// Compare pointers to the underlying map.
		// This is safe because we don't allow maps to be mutated.
		return &v.v == &w.v
	case KindSequence:
		vs := v.v.([]Value)
		ws := w.v.([]Value)
		lv := len(vs)
		lw := len(ws)
		// If both slices are empty, they are equal.
		if lv == 0 && lw == 0 {
			return true
		}
		// If they have different lengths, they are not equal.
		if lv != lw {
			return false
		}
		// They are both non-empty and have the same length.
		// Compare pointers to the underlying slice.
		// This is safe because we don't allow slices to be mutated.
		return &vs[0] == &ws[0]
	default:
		return v.v == w.v
	}
}