var check = require('./util/check')
var values = require('./util/values')
var bufferTypes = require('./constants/dtypes.json')
var isTypedArray = require('./util/is-typed-array')
var isNDArrayLike = require('./util/is-ndarray')

var GL_FLOAT = 5126
var GL_ARRAY_BUFFER = 34962

function AttributeRecord () {
  this.state = 0

  this.x = 0.0
  this.y = 0.0
  this.z = 0.0
  this.w = 0.0

  this.buffer = null
  this.size = 0
  this.normalized = false
  this.type = GL_FLOAT
  this.offset = 0
  this.stride = 0
  this.divisor = 0
}

module.exports = function wrapAttributeState (
  gl,
  extensions,
  limits,
  stats,
  bufferState) {
  var NUM_ATTRIBUTES = limits.maxAttributes
  var attributeBindings = new Array(NUM_ATTRIBUTES)
  for (var i = 0; i < NUM_ATTRIBUTES; ++i) {
    attributeBindings[i] = new AttributeRecord()
  }
  var vaoCount = 0
  var vaoSet = {}

  var state = {
    Record: AttributeRecord,
    scope: {},
    state: attributeBindings,
    currentVAO: null,
    targetVAO: null,
    restore: extVAO() ? restoreVAO : function () {},
    createVAO: createVAO,
    getVAO: getVAO,
    destroyBuffer: destroyBuffer,
    setVAO: extVAO() ? setVAOEXT : setVAOEmulated,
    clear: extVAO() ? destroyVAOEXT : function () {}
  }

  function destroyBuffer (buffer) {
    for (var i = 0; i < attributeBindings.length; ++i) {
      var record = attributeBindings[i]
      if (record.buffer === buffer) {
        gl.disableVertexAttribArray(i)
        record.buffer = null
      }
    }
  }

  function extVAO () {
    return extensions.oes_vertex_array_object
  }

  function extInstanced () {
    return extensions.angle_instanced_arrays
  }

  function getVAO (vao) {
    if (typeof vao === 'function' && vao._vao) {
      return vao._vao
    }
    return null
  }

  function setVAOEXT (vao) {
    if (vao === state.currentVAO) {
      return
    }
    var ext = extVAO()
    if (vao) {
      ext.bindVertexArrayOES(vao.vao)
    } else {
      ext.bindVertexArrayOES(null)
    }
    state.currentVAO = vao
  }

  function setVAOEmulated (vao) {
    if (vao === state.currentVAO) {
      return
    }
    if (vao) {
      vao.bindAttrs()
    } else {
      var exti = extInstanced()
      for (var i = 0; i < attributeBindings.length; ++i) {
        var binding = attributeBindings[i]
        if (binding.buffer) {
          gl.enableVertexAttribArray(i)
          gl.vertexAttribPointer(i, binding.size, binding.type, binding.normalized, binding.stride, binding.offfset)
          if (exti && binding.divisor) {
            exti.vertexAttribDivisorANGLE(i, binding.divisor)
          }
        } else {
          gl.disableVertexAttribArray(i)
          gl.vertexAttrib4f(i, binding.x, binding.y, binding.z, binding.w)
        }
      }
    }
    state.currentVAO = vao
  }

  function destroyVAOEXT () {
    values(vaoSet).forEach(function (vao) {
      vao.destroy()
    })
  }

  function REGLVAO () {
    this.id = ++vaoCount
    this.attributes = []
    var extension = extVAO()
    if (extension) {
      this.vao = extension.createVertexArrayOES()
    } else {
      this.vao = null
    }
    vaoSet[this.id] = this
    this.buffers = []
  }

  REGLVAO.prototype.bindAttrs = function () {
    var exti = extInstanced()
    var attributes = this.attributes
    for (var i = 0; i < attributes.length; ++i) {
      var attr = attributes[i]
      if (attr.buffer) {
        gl.enableVertexAttribArray(i)
        gl.bindBuffer(GL_ARRAY_BUFFER, attr.buffer.buffer)
        gl.vertexAttribPointer(i, attr.size, attr.type, attr.normalized, attr.stride, attr.offset)
        if (exti && attr.divisor) {
          exti.vertexAttribDivisorANGLE(i, attr.divisor)
        }
      } else {
        gl.disableVertexAttribArray(i)
        gl.vertexAttrib4f(i, attr.x, attr.y, attr.z, attr.w)
      }
    }
    for (var j = attributes.length; j < NUM_ATTRIBUTES; ++j) {
      gl.disableVertexAttribArray(j)
    }
  }

  REGLVAO.prototype.refresh = function () {
    var ext = extVAO()
    if (ext) {
      ext.bindVertexArrayOES(this.vao)
      this.bindAttrs()
      state.currentVAO = this
    }
  }

  REGLVAO.prototype.destroy = function () {
    if (this.vao) {
      var extension = extVAO()
      if (this === state.currentVAO) {
        state.currentVAO = null
        extension.bindVertexArrayOES(null)
      }
      extension.deleteVertexArrayOES(this.vao)
      this.vao = null
    }
    if (vaoSet[this.id]) {
      delete vaoSet[this.id]
      stats.vaoCount -= 1
    }
  }

  function restoreVAO () {
    var ext = extVAO()
    if (ext) {
      values(vaoSet).forEach(function (vao) {
        vao.refresh()
      })
    }
  }

  function createVAO (_attr) {
    var vao = new REGLVAO()
    stats.vaoCount += 1

    function updateVAO (attributes) {
      check(Array.isArray(attributes), 'arguments to vertex array constructor must be an array')
      check(attributes.length < NUM_ATTRIBUTES, 'too many attributes')
      check(attributes.length > 0, 'must specify at least one attribute')

      var bufUpdated = {}
      var nattributes = vao.attributes
      nattributes.length = attributes.length
      for (var i = 0; i < attributes.length; ++i) {
        var spec = attributes[i]
        var rec = nattributes[i] = new AttributeRecord()
        var data = spec.data || spec
        if (Array.isArray(data) || isTypedArray(data) || isNDArrayLike(data)) {
          var buf
          if (vao.buffers[i]) {
            buf = vao.buffers[i]
            if (isTypedArray(data) && buf._buffer.byteLength >= data.byteLength) {
              buf.subdata(data)
            } else {
              buf.destroy()
              vao.buffers[i] = null
            }
          }
          if (!vao.buffers[i]) {
            buf = vao.buffers[i] = bufferState.create(spec, GL_ARRAY_BUFFER, false, true)
          }
          rec.buffer = bufferState.getBuffer(buf)
          rec.size = rec.buffer.dimension | 0
          rec.normalized = false
          rec.type = rec.buffer.dtype
          rec.offset = 0
          rec.stride = 0
          rec.divisor = 0
          rec.state = 1
          bufUpdated[i] = 1
        } else if (bufferState.getBuffer(spec)) {
          rec.buffer = bufferState.getBuffer(spec)
          rec.size = rec.buffer.dimension | 0
          rec.normalized = false
          rec.type = rec.buffer.dtype
          rec.offset = 0
          rec.stride = 0
          rec.divisor = 0
          rec.state = 1
        } else if (bufferState.getBuffer(spec.buffer)) {
          rec.buffer = bufferState.getBuffer(spec.buffer)
          rec.size = ((+spec.size) || rec.buffer.dimension) | 0
          rec.normalized = !!spec.normalized || false
          if ('type' in spec) {
            check.parameter(spec.type, bufferTypes, 'invalid buffer type')
            rec.type = bufferTypes[spec.type]
          } else {
            rec.type = rec.buffer.dtype
          }
          rec.offset = (spec.offset || 0) | 0
          rec.stride = (spec.stride || 0) | 0
          rec.divisor = (spec.divisor || 0) | 0
          rec.state = 1

          check(rec.size >= 1 && rec.size <= 4, 'size must be between 1 and 4')
          check(rec.offset >= 0, 'invalid offset')
          check(rec.stride >= 0 && rec.stride <= 255, 'stride must be between 0 and 255')
          check(rec.divisor >= 0, 'divisor must be positive')
          check(!rec.divisor || !!extensions.angle_instanced_arrays, 'ANGLE_instanced_arrays must be enabled to use divisor')
        } else if ('x' in spec) {
          check(i > 0, 'first attribute must not be a constant')
          rec.x = +spec.x || 0
          rec.y = +spec.y || 0
          rec.z = +spec.z || 0
          rec.w = +spec.w || 0
          rec.state = 2
        } else {
          check(false, 'invalid attribute spec for location ' + i)
        }
      }

      // retire unused buffers
      for (var j = 0; j < vao.buffers.length; ++j) {
        if (!bufUpdated[j] && vao.buffers[j]) {
          vao.buffers[j].destroy()
          vao.buffers[j] = null
        }
      }

      vao.refresh()
      return updateVAO
    }

    updateVAO.destroy = function () {
      for (var j = 0; j < vao.buffers.length; ++j) {
        if (vao.buffers[j]) {
          vao.buffers[j].destroy()
        }
      }
      vao.buffers.length = 0
      vao.destroy()
    }

    updateVAO._vao = vao
    updateVAO._reglType = 'vao'

    return updateVAO(_attr)
  }

  return state
}