Update and clarify some comments

[planeteer] / planeteer.go

/* Planeteer: Give trade route advice for Planets: The Exploration of Space
 * Copyright (C) 2011  Scott Worley <sworley@chkno.net>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package main

import "flag"
import "fmt"
import "encoding/json"
import "os"
import "runtime/pprof"
import "strings"

var funds = flag.Int("funds", 0,
        "Starting funds")

var start = flag.String("start", "",
        "The planet to start at")

var flight_plan_string = flag.String("flight_plan", "",
        "Your hyper-holes for the day, comma-separated.")

var end_string = flag.String("end", "",
        "A comma-separated list of acceptable ending planets.")

var planet_data_file = flag.String("planet_data_file", "planet-data",
        "The file to read planet data from")

var fuel = flag.Int("fuel", 16, "Hyper Jump power left")

var hold = flag.Int("hold", 300, "Size of your cargo hold")

var start_hold = flag.String("start_hold", "", "Start with a hold full of cargo")

var start_edens = flag.Int("start_edens", 0,
        "How many Eden Warp Units are you starting with?")

var end_edens = flag.Int("end_edens", 0,
        "How many Eden Warp Units would you like to keep (not use)?")

var cloak = flag.Bool("cloak", false,
        "Make sure to end with a Device of Cloaking")

var drones = flag.Int("drones", 0, "Buy this many Fighter Drones")

var batteries = flag.Int("batteries", 0, "Buy this many Shield Batterys")

var drone_price = flag.Int("drone_price", 0, "Today's Fighter Drone price")

var battery_price = flag.Int("battery_price", 0, "Today's Shield Battery price")

var visit_string = flag.String("visit", "",
        "A comma-separated list of planets to make sure to visit")

var tomorrow_weight = flag.Float64("tomorrow_weight", 1.0,
        "Weight for the expected value of tomorrow's trading.  0.0 - 1.0")

var extra_stats = flag.Bool("extra_stats", true,
        "Show additional information of possible interest")

var cpuprofile = flag.String("cpuprofile", "", "write cpu profile to file")

var visit_cache []string

func visit() []string {
        if visit_cache == nil {
                if *visit_string == "" {
                        return nil
                }
                visit_cache = strings.Split(*visit_string, ",")
        }
        return visit_cache
}

var flight_plan_cache []string

func flight_plan() []string {
        if flight_plan_cache == nil {
                if *flight_plan_string == "" {
                        return nil
                }
                flight_plan_cache = strings.Split(*flight_plan_string, ",")
        }
        return flight_plan_cache
}

var end_cache map[string]bool

func end() map[string]bool {
        if end_cache == nil {
                if *end_string == "" {
                        return nil
                }
                m := make(map[string]bool)
                for _, p := range strings.Split(*end_string, ",") {
                        m[p] = true
                }
                end_cache = m
        }
        return end_cache
}

type Commodity struct {
        BasePrice int
        CanSell   bool
        Limit     int
}
type Planet struct {
        BeaconOn      bool
        Private       bool
        TomorrowValue int
        /* Use relative prices rather than absolute prices because you
           can get relative prices without traveling to each planet. */
        RelativePrices map[string]int
}
type planet_data struct {
        Commodities map[string]Commodity
        Planets     map[string]Planet
        p2i, c2i    map[string]int // Generated; not read from file
        i2p, i2c    []string       // Generated; not read from file
}

func ReadData() (data planet_data) {
        f, err := os.Open(*planet_data_file)
        if err != nil {
                panic(err)
        }
        defer f.Close()
        err = json.NewDecoder(f).Decode(&data)
        if err != nil {
                panic(err)
        }
        return
}

/* This program operates by filling in a state table representing the best
 * possible trips you could make; the ones that makes you the most money.
 * This is feasible because we don't look at all the possible trips.
 * We define a list of things that are germane to this game and then only
 * consider the best outcome in each possible game state.
 *
 * Each cell in the table represents a state in the game.  In each cell,
 * we track two things: 1. the most money you could possibly have while in
 * that state and 2. one possible way to get into that state with that
 * amount of money.
 *
 * A basic analysis can be done with a two-dimensional table: location and
 * fuel.  planeteer-1.0 used this two-dimensional table.  This version
 * adds features mostly by adding dimensions to this table.
 *
 * Note that the sizes of each dimension are data driven.  Many dimensions
 * collapse to one possible value (ie, disappear) if the corresponding
 * feature is not enabled.
 *
 * The order of the dimensions in the list of constants below determines
 * their layout in RAM.  The cargo-based 'dimensions' are not completely
 * independent -- some combinations are illegal and not used.  They are
 * handled as three dimensions rather than one for simplicity.  Placing
 * these dimensions first causes the unused cells in the table to be
 * grouped together in large blocks.  This keeps the unused cells from
 * polluting cache lines, and if the spans of unused cells are large
 * enough, allows the memory manager to swap out entire pages.
 *
 * If the table gets too big to fit in RAM:
 *    * Combine the Edens, Cloaks, and UnusedCargo dimensions.  Of the
 *      24 combinations, only 15 are legal: a 38% savings.
 *    * Reduce the size of the Fuel dimension to 3.  Explicit iteration
 *      only ever needs to look backwards 2 units, so the logical values
 *      can rotate through the same 3 physical addresses.  This would be
 *      good for an 82% savings.  Note that explicit iteration went away
 *      in 0372f045.
 *    * Reduce the size of the Edens dimension from 3 to 2, for the
 *      same reasons as Fuel above.  33% savings.
 *    * Buy more ram.  (Just sayin'.  It's cheaper than you think.)
 *      
 */

// The official list of dimensions:
const (
        // Name                Num   Size  Description
        Edens       = iota //   1      3  # of Eden warp units (0 - 2 typically)
        Cloaks             //   2    1-2  # of Devices of Cloaking (0 or 1)
        UnusedCargo        //   3      4  # of unused cargo spaces (0 - 3 typically)
        Fuel               //   4     17  Hyper jump power left (0 - 16)
        Location           //   5     26  Location (which planet)
        Hold               //   6     15  Cargo bay contents (a *Commodity or nil)
        Traded             //   7      2  Traded yet?
        BuyFighters        //   8    1-2  Errand: Buy fighter drones
        BuyShields         //   9    1-2  Errand: Buy shield batteries
        Visit              //  10 1-2**N  Visit: Stop by these N planets in the route

        NumDimensions
)

func bint(b bool) int {
        if b {
                return 1
        }
        return 0
}

func DimensionSizes(data planet_data) []int {
        eden_capacity := data.Commodities["Eden Warp Units"].Limit
        if *start_edens > eden_capacity {
                eden_capacity = *start_edens
        }
        cloak_capacity := bint(*cloak)
        dims := make([]int, NumDimensions)
        dims[Edens] = eden_capacity + 1
        dims[Cloaks] = cloak_capacity + 1
        dims[UnusedCargo] = eden_capacity + cloak_capacity + 1
        dims[Fuel] = *fuel + 1
        dims[Location] = len(data.Planets)
        dims[Hold] = len(data.Commodities) + 1
        dims[Traded] = 2
        dims[BuyFighters] = bint(*drones > 0) + 1
        dims[BuyShields] = bint(*batteries > 0) + 1
        dims[Visit] = 1 << uint(len(visit()))

        // Remind myself to add a line above when adding new dimensions
        for i, dim := range dims {
                if dim < 1 {
                        panic(i)
                }
        }
        return dims
}

func StateTableSize(dims []int) int {
        product := 1
        for _, size := range dims {
                product *= size
        }
        return product
}

type State struct {
        value, from int32
}

const (
        FROM_ROOT = -2147483647 + iota
        FROM_UNINITIALIZED
        VALUE_UNINITIALIZED
        VALUE_BEING_EVALUATED
        VALUE_RUBISH
)

func EncodeIndex(dims, addr []int) int32 {
        index := addr[0]
        if addr[0] > dims[0] {
                panic(0)
        }
        for i := 1; i < NumDimensions; i++ {
                if addr[i] < 0 || addr[i] >= dims[i] {
                        panic(i)
                }
                index = index*dims[i] + addr[i]
        }
        return int32(index)
}

func DecodeIndex(dims []int, index int32) []int {
        addr := make([]int, NumDimensions)
        for i := NumDimensions - 1; i > 0; i-- {
                addr[i] = int(index) % dims[i]
                index /= int32(dims[i])
        }
        addr[0] = int(index)
        return addr
}

func CreateStateTable(data planet_data, dims []int) []State {
        table := make([]State, StateTableSize(dims))
        for i := range table {
                table[i].value = VALUE_UNINITIALIZED
                table[i].from = FROM_UNINITIALIZED
        }

        addr := make([]int, NumDimensions)
        addr[Fuel] = *fuel
        addr[Edens] = *start_edens
        addr[Location] = data.p2i[*start]
        if *start_hold != "" {
                addr[Hold] = data.c2i[*start_hold]
        }
        start_index := EncodeIndex(dims, addr)
        table[start_index].value = int32(*funds)
        table[start_index].from = FROM_ROOT

        return table
}

/* CellValue fills in the one cell at address addr by looking at all
 * the possible ways to reach this cell and selecting the best one. */

func Consider(data planet_data, dims []int, table []State, there []int, value_difference int, best_value *int32, best_source []int) {
        there_value := CellValue(data, dims, table, there)
        if value_difference < 0 && int32(-value_difference) > there_value {
                /* Can't afford this transition */
                return
        }
        possible_value := there_value + int32(value_difference)
        if possible_value > *best_value {
                *best_value = possible_value
                copy(best_source, there)
        }
}

var cell_filled_count int

func CellValue(data planet_data, dims []int, table []State, addr []int) int32 {
        my_index := EncodeIndex(dims, addr)
        if table[my_index].value == VALUE_BEING_EVALUATED {
                panic("Circular dependency")
        }
        if table[my_index].value != VALUE_UNINITIALIZED {
                return table[my_index].value
        }
        table[my_index].value = VALUE_BEING_EVALUATED

        best_value := int32(VALUE_RUBISH)
        best_source := make([]int, NumDimensions)
        other := make([]int, NumDimensions)
        copy(other, addr)
        planet := data.i2p[addr[Location]]

        /* Travel here */
        if addr[Traded] == 0 { /* Can't have traded immediately after traveling. */
                other[Traded] = 1 /* Travel from states that have done trading. */

                /* Travel here via a 2-fuel unit jump */
                if addr[Fuel]+2 < dims[Fuel] {
                        other[Fuel] = addr[Fuel] + 2
                        hole_index := (dims[Fuel] - 1) - (addr[Fuel] + 2)
                        if hole_index >= len(flight_plan()) || addr[Location] != data.p2i[flight_plan()[hole_index]] {
                                for other[Location] = 0; other[Location] < dims[Location]; other[Location]++ {
                                        if data.Planets[data.i2p[addr[Location]]].BeaconOn {
                                                Consider(data, dims, table, other, 0, &best_value, best_source)
                                        }
                                }
                        }
                        other[Location] = addr[Location]
                        other[Fuel] = addr[Fuel]
                }

                /* Travel here via a 1-fuel unit jump (a hyper hole) */
                if addr[Fuel]+1 < dims[Fuel] {
                        hole_index := (dims[Fuel] - 1) - (addr[Fuel] + 1)
                        if hole_index < len(flight_plan()) && addr[Location] == data.p2i[flight_plan()[hole_index]] {
                                other[Fuel] = addr[Fuel] + 1
                                for other[Location] = 0; other[Location] < dims[Location]; other[Location]++ {
                                        Consider(data, dims, table, other, 0, &best_value, best_source)
                                }
                                other[Location] = addr[Location]
                                other[Fuel] = addr[Fuel]
                        }
                }

                /* Travel here via Eden Warp Unit */
                if addr[Edens]+1 < dims[Edens] && addr[UnusedCargo] > 0 {
                        _, available := data.Planets[data.i2p[addr[Location]]].RelativePrices["Eden Warp Units"]
                        if !available {
                                other[Edens] = addr[Edens] + 1
                                if other[Hold] != 0 {
                                        other[UnusedCargo] = addr[UnusedCargo] - 1
                                }
                                for other[Location] = 0; other[Location] < dims[Location]; other[Location]++ {
                                        Consider(data, dims, table, other, 0, &best_value, best_source)
                                }
                                other[Location] = addr[Location]
                                other[UnusedCargo] = addr[UnusedCargo]
                                other[Edens] = addr[Edens]
                        }
                }
                other[Traded] = addr[Traded]
        }

        /* Trade */
        if addr[Traded] == 1 {
                other[Traded] = 0

                /* Consider not trading */
                Consider(data, dims, table, other, 0, &best_value, best_source)

                if !data.Planets[data.i2p[addr[Location]]].Private {

                        /* Sell */
                        if addr[Hold] == 0 && addr[UnusedCargo] == 0 {
                                for other[Hold] = 0; other[Hold] < dims[Hold]; other[Hold]++ {
                                        commodity := data.i2c[other[Hold]]
                                        if !data.Commodities[commodity].CanSell {
                                                continue
                                        }
                                        relative_price, available := data.Planets[planet].RelativePrices[commodity]
                                        if !available {
                                                // TODO: Dump cargo
                                                continue
                                        }
                                        base_price := data.Commodities[commodity].BasePrice
                                        absolute_price := float64(base_price) * float64(relative_price) / 100.0
                                        sell_price := int(absolute_price * 0.9)

                                        for other[UnusedCargo] = 0; other[UnusedCargo] < dims[UnusedCargo]; other[UnusedCargo]++ {
                                                quantity := *hold - (other[UnusedCargo] + other[Cloaks] + other[Edens])
                                                sale_value := quantity * sell_price
                                                Consider(data, dims, table, other, sale_value, &best_value, best_source)
                                        }
                                }
                                other[UnusedCargo] = addr[UnusedCargo]
                                other[Hold] = addr[Hold]
                        }

                        /* Buy */
                        other[Traded] = addr[Traded] /* Buy after selling */
                        if addr[Hold] != 0 {
                                commodity := data.i2c[addr[Hold]]
                                if data.Commodities[commodity].CanSell {
                                        relative_price, available := data.Planets[planet].RelativePrices[commodity]
                                        if available {
                                                base_price := data.Commodities[commodity].BasePrice
                                                absolute_price := int(float64(base_price) * float64(relative_price) / 100.0)
                                                quantity := *hold - (addr[UnusedCargo] + addr[Cloaks] + addr[Edens])
                                                total_price := quantity * absolute_price
                                                other[Hold] = 0
                                                other[UnusedCargo] = 0
                                                Consider(data, dims, table, other, -total_price, &best_value, best_source)
                                                other[UnusedCargo] = addr[UnusedCargo]
                                                other[Hold] = addr[Hold]
                                        }
                                }
                        }
                }
                other[Traded] = addr[Traded]
        }

        /* Buy a Device of Cloaking */
        if addr[Cloaks] == 1 && addr[UnusedCargo] < dims[UnusedCargo]-1 {
                relative_price, available := data.Planets[data.i2p[addr[Location]]].RelativePrices["Device Of Cloakings"]
                if available {
                        absolute_price := int(float64(data.Commodities["Device Of Cloakings"].BasePrice) * float64(relative_price) / 100.0)
                        other[Cloaks] = 0
                        if other[Hold] != 0 {
                                other[UnusedCargo] = addr[UnusedCargo] + 1
                        }
                        Consider(data, dims, table, other, -absolute_price, &best_value, best_source)
                        other[UnusedCargo] = addr[UnusedCargo]
                        other[Cloaks] = addr[Cloaks]
                }
        }

        /* Buy Fighter Drones */
        if addr[BuyFighters] == 1 {
                relative_price, available := data.Planets[data.i2p[addr[Location]]].RelativePrices["Fighter Drones"]
                if available {
                        absolute_price := int(float64(data.Commodities["Fighter Drones"].BasePrice) * float64(relative_price) / 100.0)
                        other[BuyFighters] = 0
                        Consider(data, dims, table, other, -absolute_price**drones, &best_value, best_source)
                        other[BuyFighters] = addr[BuyFighters]
                }
        }

        /* Buy Shield Batteries */
        if addr[BuyShields] == 1 {
                relative_price, available := data.Planets[data.i2p[addr[Location]]].RelativePrices["Shield Batterys"]
                if available {
                        absolute_price := int(float64(data.Commodities["Shield Batterys"].BasePrice) * float64(relative_price) / 100.0)
                        other[BuyShields] = 0
                        Consider(data, dims, table, other, -absolute_price**batteries, &best_value, best_source)
                        other[BuyShields] = addr[BuyShields]
                }
        }

        /* Visit this planet */
        for i := uint(0); i < uint(len(visit())); i++ {
                if addr[Visit]&(1<<i) != 0 && visit()[i] == data.i2p[addr[Location]] {
                        other[Visit] = addr[Visit] & ^(1 << i)
                        Consider(data, dims, table, other, 0, &best_value, best_source)
                }
        }
        other[Visit] = addr[Visit]

        /* Buy Eden warp units */
        eden_limit := data.Commodities["Eden Warp Units"].Limit
        if addr[Edens] > 0 && addr[Edens] <= eden_limit {
                relative_price, available := data.Planets[data.i2p[addr[Location]]].RelativePrices["Eden Warp Units"]
                if available {
                        absolute_price := int(float64(data.Commodities["Eden Warp Units"].BasePrice) * float64(relative_price) / 100.0)
                        for quantity := addr[Edens]; quantity > 0; quantity-- {
                                other[Edens] = addr[Edens] - quantity
                                if addr[Hold] != 0 {
                                        other[UnusedCargo] = addr[UnusedCargo] + quantity
                                }
                                if other[UnusedCargo] < dims[UnusedCargo] {
                                        Consider(data, dims, table, other, -absolute_price*quantity, &best_value, best_source)
                                }
                        }
                        other[Edens] = addr[Edens]
                        other[UnusedCargo] = addr[UnusedCargo]
                }
        }

        // Check that we didn't lose track of any temporary modifications to other.
        for i := 0; i < NumDimensions; i++ {
                if addr[i] != other[i] {
                        panic(i)
                }
        }

        // Sanity check: This cell was in state BEING_EVALUATED
        // the whole time that it was being evaluated.
        if table[my_index].value != VALUE_BEING_EVALUATED {
                panic(my_index)
        }

        // Record our findings
        table[my_index].value = best_value
        table[my_index].from = EncodeIndex(dims, best_source)

        // UI: Progress bar
        cell_filled_count++
        if cell_filled_count&0xfff == 0 {
                print(fmt.Sprintf("\r%3.1f%%", 100*float64(cell_filled_count)/float64(StateTableSize(dims))))
        }

        return table[my_index].value
}

func FinalState(dims []int) []int {
        addr := make([]int, NumDimensions)
        addr[Edens] = *end_edens
        addr[Cloaks] = dims[Cloaks] - 1
        addr[BuyFighters] = dims[BuyFighters] - 1
        addr[BuyShields] = dims[BuyShields] - 1
        addr[Visit] = dims[Visit] - 1
        addr[Traded] = 1
        addr[Hold] = 0
        addr[UnusedCargo] = 0
        // Fuel and Location are determined by FindBestState
        return addr
}

func FindBestState(data planet_data, dims []int, table []State, addr []int) int32 {
        max_index := int32(-1)
        max_value := 0.0
        max_fuel := 1
        if *fuel == 0 {
                max_fuel = 0
        }
        for addr[Fuel] = 0; addr[Fuel] <= max_fuel; addr[Fuel]++ {
                for addr[Location] = 0; addr[Location] < dims[Location]; addr[Location]++ {
                        planet := data.i2p[addr[Location]]
                        if len(end()) == 0 || end()[planet] {
                                index := EncodeIndex(dims, addr)
                                today_value := CellValue(data, dims, table, addr)
                                tomorrow_value := *tomorrow_weight * float64(*hold+data.Planets[planet].TomorrowValue)
                                value := float64(today_value) + tomorrow_value
                                if value > max_value {
                                        max_value = value
                                        max_index = index
                                }
                        }
                }
        }
        return max_index
}

func Commas(n int32) (s string) {
        if n < 0 {
                panic(n)
        }
        r := n % 1000
        n /= 1000
        for n > 0 {
                s = fmt.Sprintf(",%03d", r) + s
                r = n % 1000
                n /= 1000
        }
        s = fmt.Sprint(r) + s
        return
}

func FighterAndShieldCost(data planet_data, dims []int, table []State, best int32) {
        if *drones == 0 && *batteries == 0 {
                return
        }
        fmt.Println()
        if *drones > 0 {
                final_state := FinalState(dims)
                final_state[BuyFighters] = 0
                alt_best := FindBestState(data, dims, table, final_state)
                cost := table[alt_best].value - table[best].value
                fmt.Println("\rDrones were", float64(cost)/float64(*drones), "each")
        }
        if *batteries > 0 {
                final_state := FinalState(dims)
                final_state[BuyShields] = 0
                alt_best := FindBestState(data, dims, table, final_state)
                cost := table[alt_best].value - table[best].value
                fmt.Println("\rBatteries were", float64(cost)/float64(*batteries), "each")
        }
}

func EndEdensCost(data planet_data, dims []int, table []State, best int32) {
        if *end_edens == 0 {
                return
        }
        fmt.Println()
        final_state := FinalState(dims)
        for extra_edens := 1; extra_edens <= *end_edens; extra_edens++ {
                final_state[Edens] = *end_edens - extra_edens
                alt_best := FindBestState(data, dims, table, final_state)
                extra_funds := table[alt_best].value - table[best].value
                fmt.Println("\rUse", extra_edens, "extra edens, make an extra",
                        Commas(extra_funds), "(",
                        Commas(extra_funds/int32(extra_edens)), "per eden)")
        }
}

func VisitCost(data planet_data, dims []int, table []State, best int32) {
        if dims[Visit] == 1 {
                return
        }
        fmt.Println()
        final_state := FinalState(dims)
        for i := uint(0); i < uint(len(visit())); i++ {
                all_bits := dims[Visit] - 1
                final_state[Visit] = all_bits & ^(1 << i)
                alt_best := FindBestState(data, dims, table, final_state)
                cost := table[alt_best].value - table[best].value
                fmt.Printf("\r%11v Cost to visit %v\n", Commas(cost), visit()[i])
        }
}

func EndLocationCost(data planet_data, dims []int, table []State, best int32) {
        if len(end()) == 0 {
                return
        }
        fmt.Println()
        final_state := FinalState(dims)
        save_end_string := *end_string
        *end_string = ""
        end_cache = nil
        alt_best := FindBestState(data, dims, table, final_state)
        cost := table[alt_best].value - table[best].value
        fmt.Printf("\r%11v Cost of --end %v\n", Commas(cost), save_end_string)
        *end_string = save_end_string
}

func DescribePath(data planet_data, dims []int, table []State, start int32) (description []string) {
        for index := start; table[index].from > FROM_ROOT; index = table[index].from {
                if table[index].from == FROM_UNINITIALIZED {
                        panic(index)
                }
                var line string
                addr := DecodeIndex(dims, index)
                prev := DecodeIndex(dims, table[index].from)
                if addr[Fuel] != prev[Fuel] {
                        from := data.i2p[prev[Location]]
                        to := data.i2p[addr[Location]]
                        line += fmt.Sprintf("Jump from %v to %v (%v hyper jump units)", from, to, prev[Fuel]-addr[Fuel])
                }
                if addr[Edens] == prev[Edens]-1 {
                        from := data.i2p[prev[Location]]
                        to := data.i2p[addr[Location]]
                        line += fmt.Sprintf("Eden warp from %v to %v", from, to)
                }
                if addr[Hold] != prev[Hold] {
                        if addr[Hold] == 0 {
                                quantity := *hold - (prev[UnusedCargo] + prev[Edens] + prev[Cloaks])
                                line += fmt.Sprintf("Sell %v %v", quantity, data.i2c[prev[Hold]])
                        } else if prev[Hold] == 0 {
                                quantity := *hold - (addr[UnusedCargo] + addr[Edens] + addr[Cloaks])
                                line += fmt.Sprintf("Buy %v %v", quantity, data.i2c[addr[Hold]])
                        } else {
                                panic("Switched cargo?")
                        }

                }
                if addr[Cloaks] == 1 && prev[Cloaks] == 0 {
                        // TODO: Dump cloaks, convert from cargo?
                        line += "Buy a Cloak"
                }
                if addr[Edens] > prev[Edens] {
                        line += fmt.Sprint("Buy ", addr[Edens]-prev[Edens], " Eden Warp Units")
                }
                if addr[BuyShields] == 1 && prev[BuyShields] == 0 {
                        line += fmt.Sprint("Buy ", *batteries, " Shield Batterys")
                }
                if addr[BuyFighters] == 1 && prev[BuyFighters] == 0 {
                        line += fmt.Sprint("Buy ", *drones, " Fighter Drones")
                }
                if addr[Visit] != prev[Visit] {
                        // TODO: verify that the bit chat changed is addr[Location]
                        line += fmt.Sprint("Visit ", data.i2p[addr[Location]])
                }
                if line == "" && addr[Hold] == prev[Hold] && addr[Traded] != prev[Traded] {
                        // The Traded dimension is for housekeeping.  It doesn't directly
                        // correspond to in-game actions, so don't report transitions.
                        continue
                }
                if line == "" {
                        line = fmt.Sprint(prev, " -> ", addr)
                }
                description = append(description, fmt.Sprintf("%13v ", Commas(table[index].value))+line)
        }
        return
}

// (Example of a use case for generics in Go)
func IndexPlanets(m *map[string]Planet, start_at int) (map[string]int, []string) {
        e2i := make(map[string]int, len(*m)+start_at)
        i2e := make([]string, len(*m)+start_at)
        i := start_at
        for e := range *m {
                e2i[e] = i
                i2e[i] = e
                i++
        }
        return e2i, i2e
}
func IndexCommodities(m *map[string]Commodity, start_at int) (map[string]int, []string) {
        e2i := make(map[string]int, len(*m)+start_at)
        i2e := make([]string, len(*m)+start_at)
        i := start_at
        for e := range *m {
                e2i[e] = i
                i2e[i] = e
                i++
        }
        return e2i, i2e
}

func main() {
        flag.Parse()
        if *start == "" || *funds == 0 {
                print("--start and --funds are required.  --help for more\n")
                return
        }
        if *cpuprofile != "" {
                f, err := os.Create(*cpuprofile)
                if err != nil {
                        panic(err)
                }
                pprof.StartCPUProfile(f)
                defer pprof.StopCPUProfile()
        }
        data := ReadData()
        if *drone_price > 0 {
                temp := data.Commodities["Fighter Drones"]
                temp.BasePrice = *drone_price
                data.Commodities["Fighter Drones"] = temp
        }
        if *battery_price > 0 {
                temp := data.Commodities["Shield Batterys"]
                temp.BasePrice = *battery_price
                data.Commodities["Shield Batterys"] = temp
        }
        data.p2i, data.i2p = IndexPlanets(&data.Planets, 0)
        data.c2i, data.i2c = IndexCommodities(&data.Commodities, 1)
        dims := DimensionSizes(data)
        table := CreateStateTable(data, dims)
        final_state := FinalState(dims)
        best := FindBestState(data, dims, table, final_state)
        print("\n")
        if best == -1 {
                print("Cannot acheive success criteria\n")
                return
        }
        description := DescribePath(data, dims, table, best)
        for i := len(description) - 1; i >= 0; i-- {
                fmt.Println(description[i])
        }

        if *extra_stats {
                FighterAndShieldCost(data, dims, table, best)
                EndEdensCost(data, dims, table, best)
                VisitCost(data, dims, table, best)
                EndLocationCost(data, dims, table, best)
        }
}