package main

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

var dbg *log.Logger

const (
  WALL = '#'
  SPACE = '.'
  PATH_LIMIT = 1000
)

type Position struct {
  x int
  y int
}

type Game struct {
  screen tcell.Screen
  level [][]rune
  player Position
  status string
  width int
  height int
}

func (game *Game) Text(msg string) {
  var comb []rune
  for x, cell := range msg {
    game.screen.SetContent(x, game.height, cell, comb, tcell.StyleDefault)
  }
}

func (game *Game) Render() {
  var comb []rune
  game.screen.Clear()

  for y, line := range game.level {
    for x, cell := range line {
      game.screen.SetContent(x, y, cell, comb, tcell.StyleDefault)
    }
  }

  game.Text(game.status)
  game.screen.SetContent(game.player.x, game.player.y, '@', comb, tcell.StyleDefault)
  game.screen.Show()
}

func (game *Game) Exit() {
    game.screen.Fini()
    os.Exit(0)
}

func (game *Game) Occupied(x int, y int) bool {
  return game.level[y][x] != '.'
}

func (game *Game) MovePlayer(x_delta int, y_delta int) {
  if !game.Occupied(game.player.x + x_delta, game.player.y + y_delta) {
    game.player.x += x_delta
    game.player.y += y_delta
  }
}

func (game *Game) HandleKeys(ev *tcell.EventKey) {
  switch ev.Key() {
  case tcell.KeyEscape:
    game.Exit()
  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':
    game.Exit()
  }
}

func (game *Game) HandleEvents() {
  switch ev := game.screen.PollEvent().(type) {
  case *tcell.EventResize:
    game.screen.Sync()
  case *tcell.EventKey:
    game.HandleKeys(ev)
  }
}

func MakeGame() (*Game) {
  var game Game
  var err error

  encoding.Register()

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

  err = game.screen.Init()
  if err != nil { log.Fatal(err) }
  game.player = Position{1,1}

  return &game
}

func compass(x int, y int, offset int) []Position {
  return []Position{
    Position{x, y - offset},
    Position{x, y + offset},
    Position{x + offset, y},
    Position{ x - offset, y},
  }
}

func (game *Game) Inbounds(pos Position) bool {
  return pos.x >= 0 && pos.x < game.width && pos.y >= 0 && pos.y < game.height
}

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

  for _, pos := range points {
    if game.Inbounds(pos) {
      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) FindCoord(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) 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.FindCoord(&on, &found) {
        break
      }

      game.level[on.y][on.x] = SPACE

      row := (on.y + found.y) / 2
      col := (on.x + found.x) / 2
      game.level[row][col] = SPACE
    } else {
      rand_neighbor := rand.Int() % len(neighbors)
      nb := neighbors[rand_neighbor]

      game.level[nb.y][nb.x] = SPACE

      row := (nb.y + on.y) / 2
      col := (nb.x + on.x) / 2

      game.level[row][col] = SPACE

      on = nb
    }
  }

  game.status = "FINISHED"

  return dead_ends
}

func (game *Game) MakeMap(width int, height int) {
  game.width = width
  game.height = height
  row := strings.Repeat("#", width)

  for i := 0 ; i < height; i++ {
    as_runes := []rune(strings.Clone(row))
    game.level = append(game.level, as_runes)
  }

  // this returns dead_ends
  game.HuntAndKill()
}

// This program just prints "Hello, World!".  Press ESC to exit.
func main() {
  out, err := os.Create("debug.log")
  if err != nil { log.Fatal(err) }
  dbg = log.New(out, "", log.LstdFlags)

  game := MakeGame()
  game.MakeMap(27,17)
  game.Render()

  for {
    game.HandleEvents()
    game.Render()
  }
}