module TK.SpaceTac {
    /**
     * Error codes for approach simulation
     */
    export enum ApproachSimulationError {
        NO_MOVE_NEEDED,
        NO_VECTOR_FOUND,
    }

    /**
     * Status for simulation
     */
    export enum MoveFireStatus {
        OK,
        NO_ACTION,
        NOT_ENOUGH_POWER,
        INVALID_TARGET,
        IMPOSSIBLE_APPROACH,
    }

    /**
     * A single action in the sequence result from the simulator
     */
    export type MoveFirePart = {
        action: BaseAction
        target: Target
        ap: number
        possible: boolean
    }

    /**
     * A simulation result
     */
    export class MoveFireResult {
        // Simulation status
        status = MoveFireStatus.OK
        // Ideal successive parts to make the full move+fire
        parts: MoveFirePart[] = []

        need_move = false
        can_move = false
        can_end_move = false
        total_move_ap = 0
        move_location = new Target(0, 0, null)

        need_fire = false
        can_fire = false
        total_fire_ap = 0
        fire_location = new Target(0, 0, null)
    };

    /**
     * Utility to simulate a move+fire action.
     * 
     * This is also a helper to bring a ship in range to fire a weapon.
     */
    export class MoveFireSimulator {
        constructor(
            // Playing ship
            private ship: Ship,
            // Coordinates grid
            private grid: ArenaGrid
        ) { }

        /**
         * Find an engine action, to make an approach
         * 
         * This will return the first available engine, in the definition order
         */
        findEngine(): MoveAction | null {
            let actions = cfilter(this.ship.actions.listAll(), MoveAction);
            return first(actions, action => this.ship.actions.getCooldown(action).canUse());
        }

        /**
         * Get an iterator for scanning a circle
         */
        scanCircle(x: number, y: number, radius: number, nr = 6, na = 30): Iterator<Target> {
            // TODO If there is a grid, produce only grid coordinates
            let rcount = nr ? 1 / (nr - 1) : 0;
            return ichainit(imap(istep(0, irepeat(rcount, nr - 1)), r => {
                let angles = Math.max(1, Math.ceil(na * r));
                return imap(istep(0, irepeat(2 * Math.PI / angles, angles - 1)), a => {
                    return new Target(x + r * radius * Math.cos(a), y + r * radius * Math.sin(a)).snap(this.grid);
                });
            }));
        }

        /**
         * Find the best approach location, to put a target in a given range.
         * 
         * Return null if no approach vector was found.
         */
        getApproach(action: MoveAction, target: Target, radius: number, margin = 0): Target | ApproachSimulationError {
            let dx = target.x - this.ship.arena_x;
            let dy = target.y - this.ship.arena_y;
            let distance = Math.sqrt(dx * dx + dy * dy);

            if (distance <= radius) {
                return ApproachSimulationError.NO_MOVE_NEEDED;
            } else {
                if (margin && radius > margin) {
                    radius -= margin;
                }

                let candidates: [number, Target][] = [];
                iforeach(this.scanCircle(target.x, target.y, radius), candidate => {
                    if (action.checkTarget(this.ship, candidate)) {
                        candidates.push([candidate.getDistanceTo(this.ship.location), candidate]);
                    }
                });

                if (candidates.length) {
                    return minBy(candidates, ([distance, _]) => distance)[1];
                } else {
                    return ApproachSimulationError.NO_VECTOR_FOUND;
                }
            }
        }

        /**
         * Simulate a given action on a given valid target.
         */
        simulateAction(action: BaseAction, target: Target, move_margin = 0): MoveFireResult {
            let result = new MoveFireResult();
            let ap = this.ship.getValue("power");

            // Move or approach needed ?
            let move_target: Target | null = null;
            let move_action: MoveAction | null = null;
            result.move_location = Target.newFromShip(this.ship);
            if (action instanceof MoveAction) {
                result.need_move = true;
                move_target = target;
                move_action = action;
            } else {
                move_action = this.findEngine();
                if (move_action) {
                    let approach_radius = action.getRangeRadius(this.ship);
                    let approach = this.getApproach(move_action, target, approach_radius, move_margin);
                    if (approach instanceof Target) {
                        result.need_move = true;
                        move_target = approach;
                    } else if (approach != ApproachSimulationError.NO_MOVE_NEEDED) {
                        result.need_move = true;
                        result.can_move = false;
                        result.status = MoveFireStatus.IMPOSSIBLE_APPROACH;
                        return result;
                    }
                }
            }
            if (move_target && move_action && result.need_move) {
                if (arenaDistance(move_target, this.ship.location) < 1e-8) {
                    result.need_move = false;
                } else {
                    result.can_move = bool(move_action.checkTarget(this.ship, move_target));
                    if (!result.can_move) {
                        result.status = MoveFireStatus.INVALID_TARGET;
                    }
                }
            }

            // Check move AP
            if (result.need_move && move_target && move_action) {
                result.total_move_ap = move_action.getPowerUsage(this.ship, move_target);
                result.can_move = result.can_move && (ap > 0);
                result.can_end_move = result.can_move && (result.total_move_ap <= ap);
                result.move_location = move_target;
                // TODO Split in "this turn" part and "next turn" part if needed
                result.parts.push({ action: move_action, target: move_target, ap: result.total_move_ap, possible: result.can_move });

                if (!result.can_end_move) {
                    result.status = MoveFireStatus.NOT_ENOUGH_POWER;
                }

                ap -= result.total_move_ap;
            }

            // Check action AP
            if (!(action instanceof MoveAction)) {
                result.need_fire = true;
                result.total_fire_ap = action.getPowerUsage(this.ship, target);
                if (action.checkTarget(this.ship, target, result.move_location)) {
                    if (result.total_fire_ap <= ap) {
                        result.can_fire = true;
                    } else {
                        result.status = MoveFireStatus.NOT_ENOUGH_POWER;
                    }
                } else {
                    result.status = MoveFireStatus.INVALID_TARGET;
                }
                result.fire_location = target;
                result.parts.push({ action: action, target: target, ap: result.total_fire_ap, possible: (!result.need_move || result.can_end_move) && result.can_fire });
            }

            if (!result.need_move && !result.need_fire) {
                result.status = MoveFireStatus.NO_ACTION;
            }

            return result;
        }

        /**
         * Apply a move-fire simulation result, and predict the diffs it will apply on a battle
         * 
         * The original battle passed as parameter will be duplicated, and not altered
         */
        getExpectedDiffs(battle: Battle, simulation: MoveFireResult): BaseBattleDiff[] {
            let sim_battle = duplicate(battle, TK.SpaceTac);
            let sim_ship = nn(sim_battle.getShip(this.ship.id));
            let results: BaseBattleDiff[] = [];
            simulation.parts.forEach(part => {
                let diffs = part.action.getDiffs(sim_ship, battle, part.target);
                results = results.concat(diffs);
                sim_battle.applyDiffs(diffs);

                diffs = sim_battle.performChecks();
                results = results.concat(diffs);
            });
            return results;
        }
    }
}