var check = require('./util/check')
var extend = require('./util/extend')
var values = require('./util/values')

var GL_FRAGMENT_SHADER = 35632
var GL_VERTEX_SHADER = 35633

var GL_ACTIVE_UNIFORMS = 0x8B86
var GL_ACTIVE_ATTRIBUTES = 0x8B89

module.exports = function wrapShaderState (gl, stringStore, stats, config) {
  // ===================================================
  // glsl compilation and linking
  // ===================================================
  var fragShaders = {}
  var vertShaders = {}

  function ActiveInfo (name, id, location, info) {
    this.name = name
    this.id = id
    this.location = location
    this.info = info
  }

  function insertActiveInfo (list, info) {
    for (var i = 0; i < list.length; ++i) {
      if (list[i].id === info.id) {
        list[i].location = info.location
        return
      }
    }
    list.push(info)
  }

  function getShader (type, id, command) {
    var cache = type === GL_FRAGMENT_SHADER ? fragShaders : vertShaders
    var shader = cache[id]

    if (!shader) {
      var source = stringStore.str(id)
      shader = gl.createShader(type)
      gl.shaderSource(shader, source)
      gl.compileShader(shader)
      check.shaderError(gl, shader, source, type, command)
      cache[id] = shader
    }

    return shader
  }

  // ===================================================
  // program linking
  // ===================================================
  var programCache = {}
  var programList = []

  var PROGRAM_COUNTER = 0

  function REGLProgram (fragId, vertId) {
    this.id = PROGRAM_COUNTER++
    this.fragId = fragId
    this.vertId = vertId
    this.program = null
    this.uniforms = []
    this.attributes = []
    this.refCount = 1

    if (config.profile) {
      this.stats = {
        uniformsCount: 0,
        attributesCount: 0
      }
    }
  }

  function linkProgram (desc, command, attributeLocations) {
    var i, info

    // -------------------------------
    // compile & link
    // -------------------------------
    var fragShader = getShader(GL_FRAGMENT_SHADER, desc.fragId)
    var vertShader = getShader(GL_VERTEX_SHADER, desc.vertId)

    var program = desc.program = gl.createProgram()
    gl.attachShader(program, fragShader)
    gl.attachShader(program, vertShader)
    if (attributeLocations) {
      for (i = 0; i < attributeLocations.length; ++i) {
        var binding = attributeLocations[i]
        gl.bindAttribLocation(program, binding[0], binding[1])
      }
    }

    gl.linkProgram(program)
    check.linkError(
      gl,
      program,
      stringStore.str(desc.fragId),
      stringStore.str(desc.vertId),
      command)

    // -------------------------------
    // grab uniforms
    // -------------------------------
    var numUniforms = gl.getProgramParameter(program, GL_ACTIVE_UNIFORMS)
    if (config.profile) {
      desc.stats.uniformsCount = numUniforms
    }
    var uniforms = desc.uniforms
    for (i = 0; i < numUniforms; ++i) {
      info = gl.getActiveUniform(program, i)
      if (info) {
        if (info.size > 1) {
          for (var j = 0; j < info.size; ++j) {
            var name = info.name.replace('[0]', '[' + j + ']')
            insertActiveInfo(uniforms, new ActiveInfo(
              name,
              stringStore.id(name),
              gl.getUniformLocation(program, name),
              info))
          }
        } else {
          insertActiveInfo(uniforms, new ActiveInfo(
            info.name,
            stringStore.id(info.name),
            gl.getUniformLocation(program, info.name),
            info))
        }
      }
    }

    // -------------------------------
    // grab attributes
    // -------------------------------
    var numAttributes = gl.getProgramParameter(program, GL_ACTIVE_ATTRIBUTES)
    if (config.profile) {
      desc.stats.attributesCount = numAttributes
    }

    var attributes = desc.attributes
    for (i = 0; i < numAttributes; ++i) {
      info = gl.getActiveAttrib(program, i)
      if (info) {
        insertActiveInfo(attributes, new ActiveInfo(
          info.name,
          stringStore.id(info.name),
          gl.getAttribLocation(program, info.name),
          info))
      }
    }
  }

  if (config.profile) {
    stats.getMaxUniformsCount = function () {
      var m = 0
      programList.forEach(function (desc) {
        if (desc.stats.uniformsCount > m) {
          m = desc.stats.uniformsCount
        }
      })
      return m
    }

    stats.getMaxAttributesCount = function () {
      var m = 0
      programList.forEach(function (desc) {
        if (desc.stats.attributesCount > m) {
          m = desc.stats.attributesCount
        }
      })
      return m
    }
  }

  function restoreShaders () {
    fragShaders = {}
    vertShaders = {}
    for (var i = 0; i < programList.length; ++i) {
      linkProgram(programList[i], null, programList[i].attributes.map(function (info) {
        return [info.location, info.name]
      }))
    }
  }

  return {
    clear: function () {
      var deleteShader = gl.deleteShader.bind(gl)
      values(fragShaders).forEach(deleteShader)
      fragShaders = {}
      values(vertShaders).forEach(deleteShader)
      vertShaders = {}

      programList.forEach(function (desc) {
        gl.deleteProgram(desc.program)
      })
      programList.length = 0
      programCache = {}

      stats.shaderCount = 0
    },

    program: function (vertId, fragId, command, attribLocations) {
      check.command(vertId >= 0, 'missing vertex shader', command)
      check.command(fragId >= 0, 'missing fragment shader', command)

      var cache = programCache[fragId]
      if (!cache) {
        cache = programCache[fragId] = {}
      }
      var prevProgram = cache[vertId]
      if (prevProgram) {
        prevProgram.refCount++
        if (!attribLocations) {
          return prevProgram
        }
      }
      var program = new REGLProgram(fragId, vertId)
      stats.shaderCount++
      linkProgram(program, command, attribLocations)
      if (!prevProgram) {
        cache[vertId] = program
      }
      programList.push(program)
      return extend(program, {
        destroy: function () {
          program.refCount--
          if (program.refCount <= 0) {
            gl.deleteProgram(program.program)
            var idx = programList.indexOf(program)
            programList.splice(idx, 1)
            stats.shaderCount--
          }
          // no program is linked to this vert anymore
          if (cache[program.vertId].refCount <= 0) {
            gl.deleteShader(vertShaders[program.vertId])
            delete vertShaders[program.vertId]
            delete programCache[program.fragId][program.vertId]
          }
          // no program is linked to this frag anymore
          if (!Object.keys(programCache[program.fragId]).length) {
            gl.deleteShader(fragShaders[program.fragId])
            delete fragShaders[program.fragId]
            delete programCache[program.fragId]
          }
        }
      })
    },

    restore: restoreShaders,

    shader: getShader,

    frag: -1,
    vert: -1
  }
}