package rules

import (
	"strconv"
)

type RulesetError string

func (err RulesetError) Error() string { return string(err) }

const (
	MoveUp    = "up"
	MoveDown  = "down"
	MoveRight = "right"
	MoveLeft  = "left"

	BoardSizeSmall  = 7
	BoardSizeMedium = 11
	BoardSizeLarge  = 19

	SnakeMaxHealth = 100
	SnakeStartSize = 3

	// bvanvugt - TODO: Just return formatted strings instead of codes?
	NotEliminated                   = ""
	EliminatedByCollision           = "snake-collision"
	EliminatedBySelfCollision       = "snake-self-collision"
	EliminatedByOutOfHealth         = "out-of-health"
	EliminatedByHeadToHeadCollision = "head-collision"
	EliminatedByOutOfBounds         = "wall-collision"
	EliminatedBySquad               = "squad-eliminated"

	// TODO - Error consts
	ErrorTooManySnakes   = RulesetError("too many snakes for fixed start positions")
	ErrorNoRoomForSnake  = RulesetError("not enough space to place snake")
	ErrorNoRoomForFood   = RulesetError("not enough space to place food")
	ErrorNoMoveFound     = RulesetError("move not provided for snake")
	ErrorZeroLengthSnake = RulesetError("snake is length zero")

	// Ruleset / game type names
	GameTypeConstrictor = "constrictor"
	GameTypeRoyale      = "royale"
	GameTypeSolo        = "solo"
	GameTypeSquad       = "squad"
	GameTypeStandard    = "standard"
	GameTypeWrapped     = "wrapped"

	// Game creation parameter names
	ParamGameType            = "name"
	ParamFoodSpawnChance     = "foodSpawnChance"
	ParamMinimumFood         = "minimumFood"
	ParamHazardDamagePerTurn = "damagePerTurn"
	ParamHazardMap           = "hazardMap"
	ParamHazardMapAuthor     = "hazardMapAuthor"
	ParamShrinkEveryNTurns   = "shrinkEveryNTurns"
	ParamAllowBodyCollisions = "allowBodyCollisions"
	ParamSharedElimination   = "sharedElimination"
	ParamSharedHealth        = "sharedHealth"
	ParamSharedLength        = "sharedLength"
)

type rulesetBuilder struct {
	params map[string]string // game customisation parameters
	seed   int64             // used for random events in games
	squads map[string]string // Snake ID -> Squad Name
}

// NewRulesetBuilder returns an instance of a builder for the Ruleset types.
func NewRulesetBuilder() *rulesetBuilder {
	return &rulesetBuilder{
		params: map[string]string{},
		squads: map[string]string{},
	}
}

// WithParams accepts a map of game parameters for customizing games.
//
// Parameters are copied. If called multiple times, parameters are merged such that:
//   - existing keys in both maps get overwritten by the new ones
//   - existing keys not present in the new map will be retained
//   - non-existing keys only in the new map will be added
//
// Unrecognised parameters will be ignored and default values will be used.
// Invalid parameters (i.e. a non-numerical value where one is expected), will be ignored
// and default values will be used.
func (rb *rulesetBuilder) WithParams(params map[string]string) *rulesetBuilder {
	for k, v := range params {
		rb.params[k] = v
	}
	return rb
}

// WithSeed sets the seed used for randomisation by certain game modes.
func (rb *rulesetBuilder) WithSeed(seed int64) *rulesetBuilder {
	rb.seed = seed
	return rb
}

// AddSnakeToSquad adds the specified snake (by ID) to a squad with the given name.
// This configuration may be ignored by game modes if they do not support squads.
func (rb *rulesetBuilder) AddSnakeToSquad(snakeID, squadName string) *rulesetBuilder {
	rb.squads[snakeID] = squadName
	return rb
}

// Ruleset constructs a customised ruleset using the parameters passed to the builder.
func (rb rulesetBuilder) Ruleset() Ruleset {
	standardRuleset := &StandardRuleset{
		FoodSpawnChance:     paramsInt32(rb.params, ParamFoodSpawnChance, 0),
		MinimumFood:         paramsInt32(rb.params, ParamMinimumFood, 0),
		HazardDamagePerTurn: paramsInt32(rb.params, ParamHazardDamagePerTurn, 0),
		HazardMap:           rb.params[ParamHazardMap],
		HazardMapAuthor:     rb.params[ParamHazardMapAuthor],
	}

	name, ok := rb.params[ParamGameType]
	if !ok {
		return standardRuleset
	}

	switch name {
	case GameTypeConstrictor:
		return &ConstrictorRuleset{
			StandardRuleset: *standardRuleset,
		}
	case GameTypeRoyale:
		return &RoyaleRuleset{
			StandardRuleset:   *standardRuleset,
			Seed:              rb.seed,
			ShrinkEveryNTurns: paramsInt32(rb.params, ParamShrinkEveryNTurns, 0),
		}
	case GameTypeSolo:
		return &SoloRuleset{
			StandardRuleset: *standardRuleset,
		}
	case GameTypeWrapped:
		return &WrappedRuleset{
			StandardRuleset: *standardRuleset,
		}
	case GameTypeSquad:
		squadMap := map[string]string{}
		for id, squad := range rb.squads {
			squadMap[id] = squad
		}
		return &SquadRuleset{
			StandardRuleset:     *standardRuleset,
			SquadMap:            squadMap,
			AllowBodyCollisions: paramsBool(rb.params, ParamAllowBodyCollisions, false),
			SharedElimination:   paramsBool(rb.params, ParamSharedElimination, false),
			SharedHealth:        paramsBool(rb.params, ParamSharedHealth, false),
			SharedLength:        paramsBool(rb.params, ParamSharedLength, false),
		}
	}
	return standardRuleset
}

// paramsBool returns the boolean value for the specified parameter.
// If the parameter doesn't exist, the default value will be returned.
// If the parameter does exist, but is not "true", false will be returned.
func paramsBool(params map[string]string, paramName string, defaultValue bool) bool {
	if val, ok := params[paramName]; ok {
		return val == "true"
	}
	return defaultValue
}

// paramsInt32 returns the int32 value for the specified parameter.
// If the parameter doesn't exist, the default value will be returned.
// If the parameter does exist, but is not a valid int, the default value will be returned.
func paramsInt32(params map[string]string, paramName string, defaultValue int32) int32 {
	if val, ok := params[paramName]; ok {
		i, err := strconv.Atoi(val)
		if err == nil {
			return int32(i)
		}
	}
	return defaultValue
}

type Point struct {
	X int32
	Y int32
}

type Snake struct {
	ID               string
	Body             []Point
	Health           int32
	EliminatedCause  string
	EliminatedOnTurn int32
	EliminatedBy     string
}

type SnakeMove struct {
	ID   string
	Move string
}

type Ruleset interface {
	Name() string
	ModifyInitialBoardState(initialState *BoardState) (*BoardState, error)
	CreateNextBoardState(prevState *BoardState, moves []SnakeMove) (*BoardState, error)
	IsGameOver(state *BoardState) (bool, error)
	// Settings provides the game settings that are relevant to the ruleset.
	Settings() Settings
}

// Settings contains all settings relevant to a game.
// It is used by game logic to take a previous game state and produce a next game state.
type Settings struct {
	FoodSpawnChance     int32          `json:"foodSpawnChance"`
	MinimumFood         int32          `json:"minimumFood"`
	HazardDamagePerTurn int32          `json:"hazardDamagePerTurn"`
	HazardMap           string         `json:"hazardMap"`
	HazardMapAuthor     string         `json:"hazardMapAuthor"`
	RoyaleSettings      RoyaleSettings `json:"royale"`
	SquadSettings       SquadSettings  `json:"squad"`
}

// RoyaleSettings contains settings that are specific to the "royale" game mode
type RoyaleSettings struct {
	seed              int64
	ShrinkEveryNTurns int32 `json:"shrinkEveryNTurns"`
}

// SquadSettings contains settings that are specific to the "squad" game mode
type SquadSettings struct {
	squadMap            map[string]string
	AllowBodyCollisions bool `json:"allowBodyCollisions"`
	SharedElimination   bool `json:"sharedElimination"`
	SharedHealth        bool `json:"sharedHealth"`
	SharedLength        bool `json:"sharedLength"`
}

// StageFunc represents a single stage of an ordered pipeline and applies custom logic to the board state each turn.
// It is expected to modify the boardState directly.
// The return values are a boolean (to indicate whether the game has ended as a result of the stage)
// and an error if any errors occurred during the stage.
//
// Errors should be treated as meaning the stage failed and the board state is now invalid.
type StageFunc func(*BoardState, Settings, []SnakeMove) (bool, error)