package common

import (
	"bufio"
	"math"
)


type Tile struct {
  height int
  steps int
}

func NewTile(height int) *Tile {
  return &Tile{height, math.MaxInt32}
}

func (tile Tile) GetSteps() int {
  return tile.steps
}


type Map struct {
  tiles [][]Tile
  start *Tile
  end *Tile
}

func (heightmap Map) GetEndTile() Tile {
  return *heightmap.end
}

func (heightmap Map) GetStartTile() Tile {
  return *heightmap.start
}

func (heightmap Map) FindBestStart() Tile {
  min := math.MaxInt32
  var bestStart Tile
  for i := 0; i < len(heightmap.tiles); i++ {
    for j := 0; j < len(heightmap.tiles[i]); j++ {
      if heightmap.tiles[i][j].height == 1 && heightmap.tiles[i][j].steps < min {
        bestStart = heightmap.tiles[i][j]
        min = bestStart.steps
      }
    }
  }
  return bestStart
}

func (heightmap *Map) ComputeStepsFromStart() {
  heightmap.start.steps = 0
  for i := 0; i < len(heightmap.tiles); i++ {
    for j := 0; j < len(heightmap.tiles[i]); j++ {
      if &heightmap.tiles[i][j] == heightmap.start {
        heightmap.ComputeSteps(i, j, 1)
      }
    }
  }
}

func (heightmap *Map) ComputeStepsFromEnd() {
  heightmap.end.steps = 0
  for i := 0; i < len(heightmap.tiles); i++ {
    for j := 0; j < len(heightmap.tiles[i]); j++ {
      if &heightmap.tiles[i][j] == heightmap.end {
        heightmap.ComputeStepsInReverse(i, j, 1)
      }
    }
  }
}

func (heightmap *Map) ComputeSteps(row int, column int, steps int) {
  if row > 0 && heightmap.tiles[row-1][column].steps > steps &&
          heightmap.tiles[row-1][column].height <= heightmap.tiles[row][column].height + 1 {
    heightmap.tiles[row-1][column].steps = steps
    heightmap.ComputeSteps(row-1, column, steps+1)
  }
  if row < len(heightmap.tiles)-1 && heightmap.tiles[row+1][column].steps > steps &&
          heightmap.tiles[row+1][column].height <= heightmap.tiles[row][column].height + 1 {
    heightmap.tiles[row+1][column].steps = steps
    heightmap.ComputeSteps(row+1, column, steps+1)
  }
  if column > 0 && heightmap.tiles[row][column-1].steps > steps &&
          heightmap.tiles[row][column-1].height <= heightmap.tiles[row][column].height + 1 {
    heightmap.tiles[row][column-1].steps = steps
    heightmap.ComputeSteps(row, column-1, steps+1)
  }
  if column < len(heightmap.tiles[0])-1 && heightmap.tiles[row][column+1].steps > steps &&
          heightmap.tiles[row][column+1].height <= heightmap.tiles[row][column].height + 1 {
    heightmap.tiles[row][column+1].steps = steps
    heightmap.ComputeSteps(row, column+1, steps+1)
  }
}

func (heightmap *Map) ComputeStepsInReverse(row int, column int, steps int) {
  if row > 0 && heightmap.tiles[row-1][column].steps > steps &&
          heightmap.tiles[row-1][column].height + 1 >= heightmap.tiles[row][column].height {
    heightmap.tiles[row-1][column].steps = steps
    heightmap.ComputeStepsInReverse(row-1, column, steps+1)
  }
  if row < len(heightmap.tiles)-1 && heightmap.tiles[row+1][column].steps > steps &&
          heightmap.tiles[row+1][column].height + 1 >= heightmap.tiles[row][column].height {
    heightmap.tiles[row+1][column].steps = steps
    heightmap.ComputeStepsInReverse(row+1, column, steps+1)
  }
  if column > 0 && heightmap.tiles[row][column-1].steps > steps &&
          heightmap.tiles[row][column-1].height + 1 >= heightmap.tiles[row][column].height {
    heightmap.tiles[row][column-1].steps = steps
    heightmap.ComputeStepsInReverse(row, column-1, steps+1)
  }
  if column < len(heightmap.tiles[0])-1 && heightmap.tiles[row][column+1].steps > steps &&
          heightmap.tiles[row][column+1].height + 1 >= heightmap.tiles[row][column].height {
    heightmap.tiles[row][column+1].steps = steps
    heightmap.ComputeStepsInReverse(row, column+1, steps+1)
  }
}


func Parse(scanner bufio.Scanner) Map {
  heightmap := Map{}

  for scanner.Scan() {
    line := scanner.Text()

    heightmapRow := make([]Tile, len(line))
    for i := 0; i < len(line); i++ {
      if line[i] == 'S' {
        heightmapRow[i] = *NewTile(1)
        heightmap.start = &heightmapRow[i]
      } else if line[i] == 'E' {
        heightmapRow[i] = *NewTile(26)
        heightmap.end = &heightmapRow[i]
      } else {
        heightmapRow[i] = *NewTile(int(line[i] - 'a' + 1))
      }
    }
    heightmap.tiles = append(heightmap.tiles, heightmapRow)
  }

  return heightmap
}