var check = require('./lib/util/check')
var extend = require('./lib/util/extend')
var dynamic = require('./lib/dynamic')
var raf = require('./lib/util/raf')
var clock = require('./lib/util/clock')
var createStringStore = require('./lib/strings')
var initWebGL = require('./lib/webgl')
var wrapExtensions = require('./lib/extension')
var wrapLimits = require('./lib/limits')
var wrapBuffers = require('./lib/buffer')
var wrapElements = require('./lib/elements')
var wrapTextures = require('./lib/texture')
var wrapRenderbuffers = require('./lib/renderbuffer')
var wrapFramebuffers = require('./lib/framebuffer')
var wrapAttributes = require('./lib/attribute')
var wrapShaders = require('./lib/shader')
var wrapRead = require('./lib/read')
var createCore = require('./lib/core')
var createStats = require('./lib/stats')
var createTimer = require('./lib/timer')

var GL_COLOR_BUFFER_BIT = 16384
var GL_DEPTH_BUFFER_BIT = 256
var GL_STENCIL_BUFFER_BIT = 1024

var GL_ARRAY_BUFFER = 34962

var CONTEXT_LOST_EVENT = 'webglcontextlost'
var CONTEXT_RESTORED_EVENT = 'webglcontextrestored'

var DYN_PROP = 1
var DYN_CONTEXT = 2
var DYN_STATE = 3

function find (haystack, needle) {
  for (var i = 0; i < haystack.length; ++i) {
    if (haystack[i] === needle) {
      return i
    }
  }
  return -1
}

module.exports = function wrapREGL (args) {
  var config = initWebGL(args)
  if (!config) {
    return null
  }

  var gl = config.gl
  var glAttributes = gl.getContextAttributes()
  var contextLost = gl.isContextLost()

  var extensionState = wrapExtensions(gl, config)
  if (!extensionState) {
    return null
  }

  var stringStore = createStringStore()
  var stats = createStats()
  var cachedCode = config.cachedCode || {};
  var extensions = extensionState.extensions
  var timer = createTimer(gl, extensions)

  var START_TIME = clock()
  var WIDTH = gl.drawingBufferWidth
  var HEIGHT = gl.drawingBufferHeight

  var contextState = {
    tick: 0,
    time: 0,
    viewportWidth: WIDTH,
    viewportHeight: HEIGHT,
    framebufferWidth: WIDTH,
    framebufferHeight: HEIGHT,
    drawingBufferWidth: WIDTH,
    drawingBufferHeight: HEIGHT,
    pixelRatio: config.pixelRatio
  }
  var uniformState = {}
  var drawState = {
    elements: null,
    primitive: 4, // GL_TRIANGLES
    count: -1,
    offset: 0,
    instances: -1
  }

  var limits = wrapLimits(gl, extensions)
  var bufferState = wrapBuffers(
    gl,
    stats,
    config,
    destroyBuffer)
  var elementState = wrapElements(gl, extensions, bufferState, stats)
  var attributeState = wrapAttributes(
    gl,
    extensions,
    limits,
    stats,
    bufferState,
    elementState,
    drawState)
  function destroyBuffer (buffer) {
    return attributeState.destroyBuffer(buffer)
  }
  var shaderState = wrapShaders(gl, stringStore, stats, config)
  var textureState = wrapTextures(
    gl,
    extensions,
    limits,
    function () { core.procs.poll() },
    contextState,
    stats,
    config)
  var renderbufferState = wrapRenderbuffers(gl, extensions, limits, stats, config)
  var framebufferState = wrapFramebuffers(
    gl,
    extensions,
    limits,
    textureState,
    renderbufferState,
    stats)
  var core = createCore(
    gl,
    stringStore,
    extensions,
    limits,
    bufferState,
    elementState,
    textureState,
    framebufferState,
    uniformState,
    attributeState,
    shaderState,
    drawState,
    contextState,
    timer,
    cachedCode,
    config)
  var readPixels = wrapRead(
    gl,
    framebufferState,
    core.procs.poll,
    contextState,
    glAttributes, extensions, limits)

  var nextState = core.next
  var canvas = gl.canvas

  var rafCallbacks = []
  var lossCallbacks = []
  var restoreCallbacks = []
  var destroyCallbacks = [config.onDestroy]

  var activeRAF = null
  function handleRAF () {
    if (rafCallbacks.length === 0) {
      if (timer) {
        timer.update()
      }
      activeRAF = null
      return
    }

    // schedule next animation frame
    activeRAF = raf.next(handleRAF)

    // poll for changes
    poll()

    // fire a callback for all pending rafs
    for (var i = rafCallbacks.length - 1; i >= 0; --i) {
      var cb = rafCallbacks[i]
      if (cb) {
        cb(contextState, null, 0)
      }
    }

    // flush all pending webgl calls
    gl.flush()

    // poll GPU timers *after* gl.flush so we don't delay command dispatch
    if (timer) {
      timer.update()
    }
  }

  function startRAF () {
    if (!activeRAF && rafCallbacks.length > 0) {
      activeRAF = raf.next(handleRAF)
    }
  }

  function stopRAF () {
    if (activeRAF) {
      raf.cancel(handleRAF)
      activeRAF = null
    }
  }

  function handleContextLoss (event) {
    event.preventDefault()

    // set context lost flag
    contextLost = true

    // pause request animation frame
    stopRAF()

    // lose context
    lossCallbacks.forEach(function (cb) {
      cb()
    })
  }

  function handleContextRestored (event) {
    // clear error code
    gl.getError()

    // clear context lost flag
    contextLost = false

    // refresh state
    extensionState.restore()
    shaderState.restore()
    bufferState.restore()
    textureState.restore()
    renderbufferState.restore()
    framebufferState.restore()
    attributeState.restore()
    if (timer) {
      timer.restore()
    }

    // refresh state
    core.procs.refresh()

    // restart RAF
    startRAF()

    // restore context
    restoreCallbacks.forEach(function (cb) {
      cb()
    })
  }

  if (canvas) {
    canvas.addEventListener(CONTEXT_LOST_EVENT, handleContextLoss, false)
    canvas.addEventListener(CONTEXT_RESTORED_EVENT, handleContextRestored, false)
  }

  function destroy () {
    rafCallbacks.length = 0
    stopRAF()

    if (canvas) {
      canvas.removeEventListener(CONTEXT_LOST_EVENT, handleContextLoss)
      canvas.removeEventListener(CONTEXT_RESTORED_EVENT, handleContextRestored)
    }

    shaderState.clear()
    framebufferState.clear()
    renderbufferState.clear()
    attributeState.clear()
    textureState.clear()
    elementState.clear()
    bufferState.clear()

    if (timer) {
      timer.clear()
    }

    destroyCallbacks.forEach(function (cb) {
      cb()
    })
  }

  function compileProcedure (options) {
    check(!!options, 'invalid args to regl({...})')
    check.type(options, 'object', 'invalid args to regl({...})')

    function flattenNestedOptions (options) {
      var result = extend({}, options)
      delete result.uniforms
      delete result.attributes
      delete result.context
      delete result.vao

      if ('stencil' in result && result.stencil.op) {
        result.stencil.opBack = result.stencil.opFront = result.stencil.op
        delete result.stencil.op
      }

      function merge (name) {
        if (name in result) {
          var child = result[name]
          delete result[name]
          Object.keys(child).forEach(function (prop) {
            result[name + '.' + prop] = child[prop]
          })
        }
      }
      merge('blend')
      merge('depth')
      merge('cull')
      merge('stencil')
      merge('polygonOffset')
      merge('scissor')
      merge('sample')

      if ('vao' in options) {
        result.vao = options.vao
      }

      return result
    }

    function separateDynamic (object, useArrays) {
      var staticItems = {}
      var dynamicItems = {}
      Object.keys(object).forEach(function (option) {
        var value = object[option]
        if (dynamic.isDynamic(value)) {
          dynamicItems[option] = dynamic.unbox(value, option)
          return
        } else if (useArrays && Array.isArray(value)) {
          for (var i = 0; i < value.length; ++i) {
            if (dynamic.isDynamic(value[i])) {
              dynamicItems[option] = dynamic.unbox(value, option)
              return
            }
          }
        }
        staticItems[option] = value
      })
      return {
        dynamic: dynamicItems,
        static: staticItems
      }
    }

    // Treat context variables separate from other dynamic variables
    var context = separateDynamic(options.context || {}, true)
    var uniforms = separateDynamic(options.uniforms || {}, true)
    var attributes = separateDynamic(options.attributes || {}, false)
    var opts = separateDynamic(flattenNestedOptions(options), false)

    var stats = {
      gpuTime: 0.0,
      cpuTime: 0.0,
      count: 0
    }

    var compiled = core.compile(opts, attributes, uniforms, context, stats)

    var draw = compiled.draw
    var batch = compiled.batch
    var scope = compiled.scope

    // FIXME: we should modify code generation for batch commands so this
    // isn't necessary
    var EMPTY_ARRAY = []
    function reserve (count) {
      while (EMPTY_ARRAY.length < count) {
        EMPTY_ARRAY.push(null)
      }
      return EMPTY_ARRAY
    }

    function REGLCommand (args, body) {
      var i
      if (contextLost) {
        check.raise('context lost')
      }
      if (typeof args === 'function') {
        return scope.call(this, null, args, 0)
      } else if (typeof body === 'function') {
        if (typeof args === 'number') {
          for (i = 0; i < args; ++i) {
            scope.call(this, null, body, i)
          }
        } else if (Array.isArray(args)) {
          for (i = 0; i < args.length; ++i) {
            scope.call(this, args[i], body, i)
          }
        } else {
          return scope.call(this, args, body, 0)
        }
      } else if (typeof args === 'number') {
        if (args > 0) {
          return batch.call(this, reserve(args | 0), args | 0)
        }
      } else if (Array.isArray(args)) {
        if (args.length) {
          return batch.call(this, args, args.length)
        }
      } else {
        return draw.call(this, args)
      }
    }

    return extend(REGLCommand, {
      stats: stats,
      destroy: function () {
        compiled.destroy()
      }
    })
  }

  var setFBO = framebufferState.setFBO = compileProcedure({
    framebuffer: dynamic.define.call(null, DYN_PROP, 'framebuffer')
  })

  function clearImpl (_, options) {
    var clearFlags = 0
    core.procs.poll()

    var c = options.color
    if (c) {
      gl.clearColor(+c[0] || 0, +c[1] || 0, +c[2] || 0, +c[3] || 0)
      clearFlags |= GL_COLOR_BUFFER_BIT
    }
    if ('depth' in options) {
      gl.clearDepth(+options.depth)
      clearFlags |= GL_DEPTH_BUFFER_BIT
    }
    if ('stencil' in options) {
      gl.clearStencil(options.stencil | 0)
      clearFlags |= GL_STENCIL_BUFFER_BIT
    }

    check(!!clearFlags, 'called regl.clear with no buffer specified')
    gl.clear(clearFlags)
  }

  function clear (options) {
    check(
      typeof options === 'object' && options,
      'regl.clear() takes an object as input')
    if ('framebuffer' in options) {
      if (options.framebuffer &&
          options.framebuffer_reglType === 'framebufferCube') {
        for (var i = 0; i < 6; ++i) {
          setFBO(extend({
            framebuffer: options.framebuffer.faces[i]
          }, options), clearImpl)
        }
      } else {
        setFBO(options, clearImpl)
      }
    } else {
      clearImpl(null, options)
    }
  }

  function frame (cb) {
    check.type(cb, 'function', 'regl.frame() callback must be a function')
    rafCallbacks.push(cb)

    function cancel () {
      // FIXME:  should we check something other than equals cb here?
      // what if a user calls frame twice with the same callback...
      //
      var i = find(rafCallbacks, cb)
      check(i >= 0, 'cannot cancel a frame twice')
      function pendingCancel () {
        var index = find(rafCallbacks, pendingCancel)
        rafCallbacks[index] = rafCallbacks[rafCallbacks.length - 1]
        rafCallbacks.length -= 1
        if (rafCallbacks.length <= 0) {
          stopRAF()
        }
      }
      rafCallbacks[i] = pendingCancel
    }

    startRAF()

    return {
      cancel: cancel
    }
  }

  // poll viewport
  function pollViewport () {
    var viewport = nextState.viewport
    var scissorBox = nextState.scissor_box
    viewport[0] = viewport[1] = scissorBox[0] = scissorBox[1] = 0
    contextState.viewportWidth =
      contextState.framebufferWidth =
      contextState.drawingBufferWidth =
      viewport[2] =
      scissorBox[2] = gl.drawingBufferWidth
    contextState.viewportHeight =
      contextState.framebufferHeight =
      contextState.drawingBufferHeight =
      viewport[3] =
      scissorBox[3] = gl.drawingBufferHeight
  }

  function poll () {
    contextState.tick += 1
    contextState.time = now()
    pollViewport()
    core.procs.poll()
  }

  function refresh () {
    textureState.refresh()
    pollViewport()
    core.procs.refresh()
    if (timer) {
      timer.update()
    }
  }

  function now () {
    return (clock() - START_TIME) / 1000.0
  }

  refresh()

  function addListener (event, callback) {
    check.type(callback, 'function', 'listener callback must be a function')

    var callbacks
    switch (event) {
      case 'frame':
        return frame(callback)
      case 'lost':
        callbacks = lossCallbacks
        break
      case 'restore':
        callbacks = restoreCallbacks
        break
      case 'destroy':
        callbacks = destroyCallbacks
        break
      default:
        check.raise('invalid event, must be one of frame,lost,restore,destroy')
    }

    callbacks.push(callback)
    return {
      cancel: function () {
        for (var i = 0; i < callbacks.length; ++i) {
          if (callbacks[i] === callback) {
            callbacks[i] = callbacks[callbacks.length - 1]
            callbacks.pop()
            return
          }
        }
      }
    }
  }

  function getCachedCode() {
    return cachedCode
  }

  function preloadCachedCode(moreCache) {
    Object.entries(moreCache).forEach(function (kv) {
      cachedCode[kv[0]] = kv[1]
    })
  }

  var regl = extend(compileProcedure, {
    // Clear current FBO
    clear: clear,

    // Short cuts for dynamic variables
    prop: dynamic.define.bind(null, DYN_PROP),
    context: dynamic.define.bind(null, DYN_CONTEXT),
    this: dynamic.define.bind(null, DYN_STATE),

    // executes an empty draw command
    draw: compileProcedure({}),

    // Resources
    buffer: function (options) {
      return bufferState.create(options, GL_ARRAY_BUFFER, false, false)
    },
    elements: function (options) {
      return elementState.create(options, false)
    },
    texture: textureState.create2D,
    cube: textureState.createCube,
    renderbuffer: renderbufferState.create,
    framebuffer: framebufferState.create,
    framebufferCube: framebufferState.createCube,
    vao: attributeState.createVAO,

    // Expose context attributes
    attributes: glAttributes,

    // Frame rendering
    frame: frame,
    on: addListener,

    // System limits
    limits: limits,
    hasExtension: function (name) {
      return limits.extensions.indexOf(name.toLowerCase()) >= 0
    },

    // Read pixels
    read: readPixels,

    // Destroy regl and all associated resources
    destroy: destroy,

    // Direct GL state manipulation
    _gl: gl,
    _refresh: refresh,

    poll: function () {
      poll()
      if (timer) {
        timer.update()
      }
    },

    // Current time
    now: now,

    // regl Statistics Information
    stats: stats,

    // cache generated code
    getCachedCode: getCachedCode,
    preloadCachedCode: preloadCachedCode
  })

  config.onDone(null, regl)

  return regl
}