package main

import (
  "os"
  "slices"
  "log"
  "fmt"
  "math/rand"
  "time"
  "github.com/gdamore/tcell/v2"
  "github.com/gdamore/tcell/v2/encoding"
)

var dbg *log.Logger

const (
  WALL = '#'
  SPACE = '.'
  PATH_LIMIT = 1000
  RENDER = true
  SHOW_RENDER = false
  SHOW_PATHS = false
  HEARING_DISTANCE = 6
)

// DATA

type Map [][]rune
type Paths [][]int

type Position struct {
  X int
  Y int
}

type Enemy struct {
  HP int
  Pos Position
  Damage int
}

type Game struct {
  Screen tcell.Screen
  Level Map
  Paths Paths
  Player Enemy
  Status string
  Width int
  Height int
  Enemies map[Position]*Enemy
}

//// DRAWING

func (game *Game) DrawText(x int, y int, text string) {
  for i, cell := range text {
    game.Screen.SetContent(x+i, y, cell, nil, tcell.StyleDefault)
  }
}

func (game *Game) DrawStatus() {
  game.DrawText(0, game.Height, game.Status)

  hp := fmt.Sprintf("HP: %d", game.Player.HP)

  game.DrawText(game.Width - len(hp), game.Height, hp)
}

func (game *Game) SetStatus(msg string) {
  game.Status = msg
}

func (game *Game) DrawEntity(symbol rune, pos Position, color tcell.Color) {
  style := tcell.StyleDefault.Bold(true).Foreground(color)
  game.Screen.SetContent(pos.X, pos.Y, symbol, nil, style)
}

func (game *Game) DrawMap() {
  gray := tcell.StyleDefault.Foreground(tcell.ColorGray)

  for y, line := range game.Level {
    for x, cell := range line {
      if cell == SPACE {
        game.Screen.SetContent(x, y, cell, nil, gray)
      } else {
        game.Screen.SetContent(x, y, cell, nil, tcell.StyleDefault)
      }
    }
  }
}

func (game *Game) DrawPaths() {
  for y, row := range game.Paths {
    for x, path_num := range row {
      if path_num == PATH_LIMIT { continue }

      as_str := fmt.Sprintf("%x", path_num % 16)
      style := tcell.StyleDefault.Foreground(tcell.ColorGray)

      if path_num >= 0 && path_num <= 16 {
        style = style.Reverse(true)
      }

      game.Screen.SetContent(x, y, rune(as_str[0]), nil, style)
    }
  }
}

///// RENDERING

func (game *Game) InitScreen() {
  encoding.Register()

  var err error
  game.Screen, err = tcell.NewScreen()
  if err != nil { log.Fatal(err) }

  err = game.Screen.Init()
  if err != nil { log.Fatal(err) }
}

func (game *Game) Render() {
  if !RENDER { return }

  game.Screen.Clear()

  game.DrawMap()

  if SHOW_PATHS {
    game.DrawPaths()
  }

  game.DrawEntity('@', game.Player.Pos, tcell.ColorYellow)

  for pos, _ := range game.Enemies {
    game.DrawEntity('G', pos, tcell.ColorRed)
  }

  game.DrawStatus()

  game.Screen.Show()
}

//// EVENTS

func (game *Game) HandleKeys(ev *tcell.EventKey) bool {
  switch ev.Key() {
  case tcell.KeyEscape:
    return false
  case tcell.KeyUp:
    game.MovePlayer(0, -1)
  case tcell.KeyDown:
    game.MovePlayer(0, 1)
  case tcell.KeyRight:
    game.MovePlayer(1, 0)
  case tcell.KeyLeft:
    game.MovePlayer(-1, 0)
  }

  switch ev.Rune() {
  case 'q':
    return false
  }

  return true
}

func (game *Game) HandleEvents() bool {
  if !RENDER { return false }

  switch ev := game.Screen.PollEvent().(type) {
  case *tcell.EventResize:
    game.Screen.Sync()
  case *tcell.EventKey:
    return game.HandleKeys(ev)
  }

  return true
}

////// GAME

func NewGame(width int, height int) (*Game) {
  var game Game

  game.Width = width
  game.Height = height
  game.Enemies = make(map[Position]*Enemy)

  game.Level = make(Map, height, height)
  game.Paths = make(Paths, height, height)

  game.Player = Enemy{20, Position{1,1}, 4}

  return &game
}


func (game *Game) Exit() {
  if RENDER {
    game.Screen.Fini()
  }

  os.Exit(0)
}

func (game *Game) PlaceEnemies(places []Position) {
  for _, pos := range places {
    if rand.Int() % 2 == 0 {
      game.Enemies[pos] = &Enemy{10, pos, 4}
    }
  }
}

func (game *Game) Restart() {
  game.SetStatus("YOU DIED! Try again.")
  game.Player.HP = 20
  game.Player.Pos = Position{1,1}
  clear(game.Enemies)
  game.FillPaths(game.Paths, PATH_LIMIT)
  game.FillMap(game.Level, '#')

  game.Render()
}

////// MAP

func compass(near Position, offset int) []Position {
  return []Position{
    Position{near.X, near.Y - offset},
    Position{near.X, near.Y + offset},
    Position{near.X + offset, near.Y},
    Position{near.X - offset, near.Y},
  }
}

func (game *Game) CloneMap() Map {
  // this is a shallow copy though
  new_map := slices.Clone(game.Level)

  for i, row := range new_map {
    // this makes sure the row is an actual copy
    new_map[i] = slices.Clone(row)
  }

  return new_map
}

func (game *Game) Inbounds(pos Position, offset int) bool {
  return pos.X >= offset &&
    pos.X < game.Width - offset &&
    pos.Y >= offset &&
    pos.Y < game.Height - offset
}

func (game *Game) Occupied(pos Position) bool {
  _, is_enemy := game.Enemies[pos]
  is_player := pos == game.Player.Pos

  // Inbounds comes first to prevent accessing level with bad x,y
  return !game.Inbounds(pos, 1) ||
      game.Level[pos.Y][pos.X] == WALL ||
      is_enemy ||
      is_player
}

func (game *Game) FillMap(target Map, setting rune) {
  for y := 0 ; y < game.Height; y++ {
    target[y] = slices.Repeat([]rune{setting}, game.Width)
  }
}


///// MOVEMENT

func (game *Game) MoveEnemy(from Position, to Position) {
  enemy, ok := game.Enemies[from]
  if !ok { log.Fatal("no enemy at", from, "wtf") }

  delete(game.Enemies, from)
  game.Enemies[to] = enemy
}


func (game *Game) MovePlayer(x_delta int, y_delta int) {
  target := Position{
    game.Player.Pos.X + x_delta,
    game.Player.Pos.Y + y_delta,
  }

  if game.Occupied(target) {
    game.Attack(target)
  } else {
    game.Player.Pos = target
  }
}

///// COMBAT

func (game *Game) EnemyDeath() {
  is_dead := make([]Position, 0, len(game.Enemies))

  for pos, enemy := range game.Enemies {
    if enemy.HP < 0 {
      is_dead = append(is_dead, pos)
    }
  }

  for _, pos := range is_dead {
    delete(game.Enemies, pos)
  }
}

func (game *Game) ApplyDamage(attacker *Enemy, defender *Enemy) {
  damage := rand.Int() % attacker.Damage
  defender.HP -= damage
  if damage == 0 {
    game.SetStatus("MISSED!")
  } else if defender.HP > 0 {
    game.SetStatus(fmt.Sprintf("HIT %d damage", damage))
  } else {
    game.SetStatus("DEAD!")
  }
}

func (game *Game) Attack(target Position) {
  enemy, hit_enemy := game.Enemies[target]

  if hit_enemy {
    game.ApplyDamage(&game.Player, enemy)
    game.ApplyDamage(enemy, &game.Player)
  }
}


///// PATHING

func (game *Game) FillPaths(target Paths, setting int) {
  for y := 0 ; y < game.Height; y++ {
    target[y] = slices.Repeat([]int{setting}, game.Width)
  }
}

func (game *Game) Neighbors(near Position) []Position {
  result := make([]Position, 0, 4)
  points := compass(near, 2)

  for _, pos := range points {
    if game.Inbounds(pos, 0) {
      result = append(result, pos)
    }
  }

  return result
}

func (game *Game) NeighborWalls(pos Position) []Position {
  neighbors := game.Neighbors(pos)
  result := make([]Position, 0)

  for _, at := range neighbors {
    cell := game.Level[at.Y][at.X]

    if cell == WALL {
      result = append(result, at)
    }
  }

  return result
}

func (game *Game) PathAddNeighbors(neighbors []Position, closed Map, near Position) []Position {
  points := compass(near, 1)

  for _, pos := range points {
    // NOTE: if you also add !game.Occupied(pos.x, pos.y) it ????
    if closed[pos.Y][pos.X] == SPACE {
      closed[pos.Y][pos.X] = WALL
      neighbors = append(neighbors, pos)
    }
  }

  return neighbors
}

func (game *Game) CalculatePaths() {
  in_grid := make([][]int, game.Height, game.Height)
  game.FillPaths(in_grid, 1)
  in_grid[game.Player.Pos.Y][game.Player.Pos.X] = 0

  game.FillPaths(game.Paths, PATH_LIMIT)
  closed := game.CloneMap()
  starting_pixels := make([]Position, 0, 10)
  open_pixels := make([]Position, 0, 10)

  counter := 0

  for counter < game.Height * game.Width {
    x := counter % game.Width
    y := counter / game.Width

    if in_grid[y][x] == 0 {
      game.Paths[y][x] = 0
      closed[y][x] = WALL
      starting_pixels = append(starting_pixels, Position{x, y})
    }

    counter += 1
  }

  for _, pos := range starting_pixels {
    open_pixels = game.PathAddNeighbors(open_pixels, closed, pos)
  }

  counter = 1
  for counter < PATH_LIMIT && len(open_pixels) > 0 {
    next_open := make([]Position, 0, 10)
    for _, pos := range open_pixels {
      game.Paths[pos.Y][pos.X] = counter
      next_open = game.PathAddNeighbors(next_open, closed, pos)
    }
    open_pixels = next_open
    counter += 1
  }

  for _, pos := range open_pixels {
    game.Paths[pos.Y][pos.X] = counter
  }
}

func (game *Game) EnemyPathing() {
  for enemy_at, _ := range game.Enemies {
    // get the four directions
    dirs := compass(enemy_at, 1)

    // sort by closest path number
    slices.SortFunc(dirs, func(a Position, b Position) int {
      return game.Paths[a.Y][a.X] - game.Paths[b.Y][b.X]
    })

    // 0 dir is now the best direction
    move_to := dirs[0]

    // can we hear the player? occupied?
    can_hear := game.Paths[move_to.Y][move_to.X] < HEARING_DISTANCE
    occupied := game.Occupied(move_to)

    if can_hear && !occupied {
      // move the enemy in the best direction
      game.MoveEnemy(enemy_at, move_to)
    }
  }
}



//// MAZE GENERATION

func (game *Game) HuntNext(on *Position, found *Position) bool {
  for y := 1; y < game.Height ; y += 2 {
    for x := 1; x < game.Width ; x += 2 {
      if game.Level[y][x] != WALL {
        continue
      }

      neighbors := game.Neighbors(Position{x, y})

      for _, pos := range neighbors {
        if game.Level[pos.Y][pos.X] == SPACE {
          *on = Position{x, y}
          *found = pos
          return true
        }
      }
    }
  }

  return false
}

func (game *Game) HAKStep(from Position, to Position) {
  game.Level[from.Y][from.X] = SPACE
  row := (from.Y + to.Y) / 2
  col := (from.X + to.X) / 2
  game.Level[row][col] = SPACE
}

func (game *Game) HuntAndKill() []Position {
  on := Position{1, 1}
  found := Position{1,1}

  dead_ends := make([]Position, 0)

  for {
    neighbors := game.NeighborWalls(on)

    if len(neighbors) == 0 {
      dead_ends = append(dead_ends, on)

      if !game.HuntNext(&on, &found) {
        break
      }

      game.HAKStep(on, found)
    } else {
      rand_neighbor := rand.Int() % len(neighbors)
      nb := neighbors[rand_neighbor]
      game.HAKStep(nb, on)
      on = nb
    }

    if SHOW_RENDER {
      game.Render()
      time.Sleep(50 * time.Millisecond)
    }
  }

  return dead_ends
}

func (game *Game) NewMap() []Position {
  game.FillMap(game.Level, '#')
  return game.HuntAndKill()
}


func main() {
  out, err := os.Create("debug.log")
  if err != nil { log.Fatal(err) }
  dbg = log.New(out, "", log.LstdFlags)

  game := NewGame(27, 17)
  game.InitScreen()

  for {
    dead_ends := game.NewMap()
    game.PlaceEnemies(dead_ends)
    game.Render()

    for game.HandleEvents() && game.Player.HP > 0 {
      game.EnemyDeath()
      game.CalculatePaths()
      game.EnemyPathing()
      game.Render()
    }

    if game.Player.HP <= 0 {
      game.Restart()
    } else {
      game.Exit()
    }
  }
}