#
#   Copyright 2013 Pixar
#
#   Licensed under the Apache License, Version 2.0 (the "Apache License")
#   with the following modification; you may not use this file except in
#   compliance with the Apache License and the following modification to it:
#   Section 6. Trademarks. is deleted and replaced with:
#
#   6. Trademarks. This License does not grant permission to use the trade
#      names, trademarks, service marks, or product names of the Licensor
#      and its affiliates, except as required to comply with Section 4(c) of
#      the License and to reproduce the content of the NOTICE file.
#
#   You may obtain a copy of the Apache License at
#
#       http://www.apache.org/licenses/LICENSE-2.0
#
#   Unless required by applicable law or agreed to in writing, software
#   distributed under the Apache License with the above modification is
#   distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
#   KIND, either express or implied. See the Apache License for the specific
#   language governing permissions and limitations under the Apache License.
#

from OpenGL.GL import *

ProgramFiles = ['simple.glsl']

Programs = {
    "BareBones" : {
        "GL_VERTEX_SHADER" : "simple.xforms simple.vert",
        "GL_GEOMETRY_SHADER" : "simple.xforms simple.geom",
        "GL_FRAGMENT_SHADER" : "simple.xforms simple.frag"
    }
}

class Attribs:
    POSITION = 0
    NORMAL = 1

def load_shaders(
    glslFiles = ProgramFiles,
    attribs = Attribs,
    programMap = Programs):
    """Parse a series of simple text files, each of which is composed
    series of shader snippets. The given 'attribs' class defines an
    enumeration of attribute slots to bind (aka semantics).
        
    In each text file, lines starting with two dash characters start a new
    shader snippet with the given name.  For example:
       -- S1
       uniform float foo;
       -- Prefix
       #version 150
       -- S2
       uniform float bar;
    """

    import os.path

    # First parse the file to populate 'snippetMap'
    class ParserState:
        HEADER = 0
        SOURCE = 1
    parserState = ParserState.HEADER
    snippetMap = {}
    for glslFile in glslFiles:
        basename = os.path.basename(glslFile)
        snippetPrefix = os.path.splitext(basename)[0] + '.'
        for line in open(glslFile):
            if line.startswith('--'):
                if parserState is ParserState.HEADER:
                    parserState = ParserState.SOURCE
                elif len(source):
                    snippetMap[snippetName] = ''.join(source)
                snippetName = snippetPrefix + line[2:].strip()
                source = []
                continue
            if parserState is ParserState.HEADER:
                pass
            else:
                source.append(line)
    if len(source):
        snippetMap[snippetName] = ''.join(source)

    # Now, glue together the strings and feed them to OpenGL
    stagePrefix = "#version 150\n"
    programs = {}
    for key, val in programMap.items():
        programHandle = glCreateProgram()
        for stageName, snippetList in val.items():
            snippets = map(snippetMap.get, snippetList.split())
            stageSource = stagePrefix + ''.join(snippets)
            stage = getattr(OpenGL.GL, stageName)
            sHandle = glCreateShader(stage)
            glShaderSource(sHandle, stageSource)
            glCompileShader(sHandle)
            success = glGetShaderiv(sHandle, GL_COMPILE_STATUS)
            if not success:
                print 'Error in', stageName, snippetList
                infolog = glGetShaderInfoLog(sHandle)
                raise SystemExit(infolog)
            glAttachShader(programHandle, sHandle)
        for attrib in dir(attribs):
            if attrib.startswith('__'):
                continue
            slot = getattr(attribs, attrib)
            name = attrib[0] + attrib[1:].lower()
            glBindAttribLocation(programHandle, slot, name)
        glLinkProgram(programHandle)
        success = glGetProgramiv(programHandle, GL_LINK_STATUS);
        if not success:
            infolog = glGetProgramInfoLog(programHandle)
            raise SystemExit(infolog)
        programs[key] = programHandle
    return programs