#include <model.h>

#include <assert.h>
#include <errno.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct Lexeme {
  const char* str;
  size_t      length;
} Lexeme;

typedef struct Lexer {
  const char* buffer; // Input buffer.
  size_t      size;   // Buffer size.
  size_t      next;   // Points to the next, unconsumed character.
  Lexeme      lexeme; // Current lexeme.
} Lexer;

static void LexerMake(const char* data, size_t size, Lexer* lexer) {
  assert(data);
  assert(lexer);
  lexer->buffer = data;
  lexer->size   = size;
}

static bool End(const Lexer* lexer) {
  assert(lexer);
  assert(lexer->next <= lexer->size);
  return lexer->next == lexer->size;
}

static bool HasNext(const Lexer* lexer) {
  assert(lexer);
  return lexer->next < lexer->size;
}

static void Advance(Lexer* lexer) {
  assert(lexer);
  assert(HasNext(lexer));
  lexer->next++;
}

static char Next(const Lexer* lexer) {
  assert(lexer);
  assert(HasNext(lexer));
  return lexer->buffer[lexer->next];
}

static const char* NextPtr(const Lexer* lexer) {
  assert(lexer);
  assert(HasNext(lexer));
  return &lexer->buffer[lexer->next];
}

// Get the pointer to the next character, or one past the last character of the
// buffer (the "end" of the buffer).
static const char* NextOrEndPtr(const Lexer* lexer) {
  assert(lexer);
  assert(HasNext(lexer) || End(lexer));
  return &lexer->buffer[lexer->next];
}

static void SkipChar(Lexer* lexer) {
  assert(lexer);
  if (HasNext(lexer)) {
    Advance(lexer);
  }
}

static void SkipLine(Lexer* lexer) {
  assert(lexer);
  // Advance until we find a newline character.
  while (HasNext(lexer) &&
         (Next(lexer) != '\n')) Advance(lexer);
  // Skip the newline character.
  SkipChar(lexer);
}

static bool IsWhiteSpace(char c) {
  return (c == ' ') || (c == '\n');
}

static void SkipWhiteSpace(Lexer* lexer) {
  assert(lexer);
  while (HasNext(lexer) &&
         IsWhiteSpace(Next(lexer))) Advance(lexer);
}

static void ReadUntilWhiteSpace(Lexer* lexer) {
  assert(lexer);
  while (HasNext(lexer) &&
         !IsWhiteSpace(Next(lexer))) Advance(lexer);
}

static bool NextLexeme(Lexer* lexer) {
  assert(lexer);
  SkipWhiteSpace(lexer);
  if (HasNext(lexer)) {
    lexer->lexeme.str = NextPtr(lexer);
    ReadUntilWhiteSpace(lexer); // Find the end of the lexeme.
    lexer->lexeme.length = NextOrEndPtr(lexer) - lexer->lexeme.str;
  } else {
    lexer->lexeme.str    = nullptr;
    lexer->lexeme.length = 0;
  }
  return lexer->lexeme.length > 0;
}

static bool ParseFloat(const Lexeme* lex, float* out) {
  assert(lex);
  assert(out);
  assert(errno == 0);
  *out = (float)strtod(lex->str, nullptr);
  return errno == 0;
}

static inline bool IsLexeme(const Lexer* lexer, const char* expected) {
  assert(lexer);
  assert(expected);
  return strncmp(lexer->lexeme.str, expected, lexer->lexeme.length) == 0;
}

// Reasonable limits for the parser implementation.
// The model spec does not impose a limit on tris, but vertex attributes are
// indexed by uint16_t.
#define MAX_TRIS  65536
#define MAX_VERTS 65536

// Temporary storage for model data. A Model can be outputted from this.
typedef struct ModelData {
  uint32_t numTris;
  uint32_t numPositions;
  uint32_t numNormals;
  uint32_t numTexcoords;
  mdTri    tris     [MAX_TRIS];
  mdVec3   positions[MAX_VERTS];
  mdVec3   normals  [MAX_VERTS];
  mdVec2   texcoords[MAX_VERTS];
} ModelData;

static bool ParseObj(Lexer* lexer, ModelData* modelData) {
  assert(lexer);
  assert(modelData);
  #define PRINT(STR)      printf("%s%.*s\n", STR, (int)lexer->lexeme.length, lexer->lexeme.str)
  #define LEX(STR)        IsLexeme(lexer, STR)
  #define NEXT_LEXEME()   { if (!NextLexeme(lexer)) break; else PRINT("~ "); }
  #define NEXT_FLOAT(PTR) { NEXT_LEXEME(); if (!ParseFloat(&lexer->lexeme, PTR)) break; }
  bool consumeNext = true;
  for (;;) {
    if (consumeNext) {
      NEXT_LEXEME();
    }
    consumeNext = true;
    if (LEX("#")) {
      SkipLine(lexer);
    } else if (LEX("mtllib")) {
      NEXT_LEXEME(); // material file
      PRINT("> material: ");
    } else if (LEX("o")) {
      NEXT_LEXEME(); // object name
      PRINT("> object: ");
    } else if (LEX("v")) {
      float x, y, z;
      NEXT_FLOAT(&x);
      NEXT_FLOAT(&y);
      NEXT_FLOAT(&z);
      modelData->positions[modelData->numPositions++] = (mdVec3){x, y, z};
      printf("> position: %.2f, %.2f, %.2f\n", x, y, z);
    } else if (LEX("vn")) {
      float x, y, z;
      NEXT_FLOAT(&x);
      NEXT_FLOAT(&y);
      NEXT_FLOAT(&z);
      modelData->normals[modelData->numNormals++] = (mdVec3){x, y, z};
      printf("> normal: %.2f, %.2f, %.2f\n", x, y, z);
    } else if (LEX("vt")) {
      float s, t;
      NEXT_FLOAT(&s);
      NEXT_FLOAT(&t);
      modelData->texcoords[modelData->numTexcoords++] = (mdVec2){s, t};
      printf("> texcoord: %.2f, %.2f\n", s, t);
    } else if (LEX("f")) {
      // Indices are 1-based.
      // Texcoord and normal are optional.
      mdVert vertices[4]; // Handling up to quads.
      int numVerts = 0;
      while (NextLexeme(lexer)) {
        int pos, tex, normal;
        if (sscanf(lexer->lexeme.str, "%d/%d/%d", &pos, &tex, &normal) == 3) {
          vertices[numVerts++] = (mdVert){pos-1, tex-1, normal-1};
          printf("> vertex: %d/%d/%d\n", pos, tex, normal);
        } else if (sscanf(lexer->lexeme.str, "%d//%d", &pos, &normal) == 2) {
          vertices[numVerts++] = (mdVert){pos-1, -1, normal-1};
          printf("> vertex: %d//%d\n", pos, normal);
        } else if (sscanf(lexer->lexeme.str, "%d/%d", &pos, &tex) == 2) {
          vertices[numVerts++] = (mdVert){pos-1, tex-1, -1};
          printf("> vertex: %d/%d\n", pos, tex);
        } else if (sscanf(lexer->lexeme.str, "%d", &pos) == 1) {
          vertices[numVerts++] = (mdVert){pos-1, -1, -1};
          printf("> vertex: %d\n", pos);
        } else { // Something past the face.
          consumeNext = false;
          break;
        }
      }
      // End of vertices for this face; output the model triangles.
      assert((numVerts == 3) || (numVerts == 4));
      if (numVerts == 3) {
        modelData->tris[modelData->numTris++] =
          (mdTri){vertices[0], vertices[1], vertices[2]};
      } else if (numVerts == 4) {
        // Triangulate the quad and output two triangles instead.
        modelData->tris[modelData->numTris++] =
          (mdTri){vertices[0], vertices[1], vertices[2]};
        modelData->tris[modelData->numTris++] =
          (mdTri){vertices[0], vertices[2], vertices[3]};
      }
    }
  }
  return true;
}

static bool WriteModelFile(const ModelData* modelData, const char* path) {
  assert(modelData);
  assert(path);
  
  bool success = false;
  FILE* file   = nullptr;
  Model model  = {0};
  
  // Fill the Model header.
  IndexedModel* indexed    = &model.indexed;
  model.type               = ModelTypeIndexed;
  indexed->numTris         = modelData->numTris;
  indexed->numPositions    = modelData->numPositions;
  indexed->numNormals      = modelData->numNormals;
  indexed->numTexcoords    = modelData->numTexcoords;
  indexed->offsetTris      = 0; // 'data' member.
  indexed->offsetPositions = indexed->offsetTris      + (modelData->numTris      * sizeof(mdTri));
  indexed->offsetNormals   = indexed->offsetPositions + (modelData->numPositions * sizeof(mdVec3));
  indexed->offsetTexcoords = indexed->offsetNormals   + (modelData->numNormals   * sizeof(mdVec3));
  
  if ((file = fopen(path, "wb")) == nullptr) {
    fprintf(stderr, "Failed opening output file for writing: %s\n", path);
    goto cleanup;
  }
  // Header.
  if (fwrite(&model, sizeof(model), 1, file) != 1) {
    fprintf(stderr, "Failed writing Model header\n");
    goto cleanup;
  }
  // Tris.
  if (fwrite(&modelData->tris, sizeof(mdTri), modelData->numTris, file) != modelData->numTris) {
    fprintf(stderr, "Failed writing triangles\n");
    goto cleanup;
  }
  // Positions.
  if (fwrite(&modelData->positions, sizeof(mdVec3), modelData->numPositions, file) != modelData->numPositions) {
    fprintf(stderr, "Failed writing positions\n");
    goto cleanup;
  }
  // Normals.
  if (fwrite(&modelData->normals, sizeof(mdVec3), modelData->numNormals, file) != modelData->numNormals) {
    fprintf(stderr, "Failed writing normals\n");
    goto cleanup;
  }
  // Texcoords.
  if (fwrite(&modelData->texcoords, sizeof(mdVec2), modelData->numTexcoords, file) != modelData->numTexcoords) {
    fprintf(stderr, "Failed writing texture coordinates\n");goto cleanup;
  }
  
  success = true;

cleanup:
  if (file) {
    fclose(file);
  }
  return success;
}

static bool ReadFile(const char* path, uint8_t** outData, size_t* outSize) {
  assert(path);

  bool     success = false;
  uint8_t* data    = nullptr;
  FILE*    file    = nullptr;
  
  if ((file = fopen(path, "rb")) == nullptr) {
    goto cleanup;
  }
  if (fseek(file, 0, SEEK_END) != 0) {
    goto cleanup;
  }
  const size_t fileSize = ftell(file);
  if (fileSize == (size_t)(-1)) {
    goto cleanup;
  }
  // Allocate one extra byte so that text file data conveniently ends with null.
  const size_t size = fileSize + 1;
  if (fseek(file, 0, SEEK_SET) != 0) {
    goto cleanup;
  }
  if ((data = calloc(1, size)) == nullptr) {
    goto cleanup;
  }
  if (fread(data, fileSize, 1, file) != 1) {
    goto cleanup;
  }
  
  *outData = data;
  *outSize = size;
  success = true;
  
cleanup:
  if (file) {
    fclose(file);
  }
  if (!success && (data != nullptr)) {
    free(data);
  }
  return success;
}

static void usage(const char* argv0) {
  fprintf(stderr, "Usage: %s <model file> [out.mdl]\n", argv0);
  fprintf(stderr, "\n");
  fprintf(stderr, "Supported file formats:\n");
  fprintf(stderr, "  OBJ\n");
}

int main(int argc, const char** argv) {
  if ((argc != 2) && (argc != 3)) {
    usage(argv[0]);
    return 1;
  }
  
  const char* filePath = argv[1];
  const char* outPath  = (argc > 2) ? argv[2] : "out.mdl";
  
  bool       success   = false;
  uint8_t*   fileData  = nullptr;
  size_t     dataSize  = 0;
  ModelData* modelData = nullptr;
  Lexer      lexer     = {0};
  
  // TODO: Map file to memory instead?
  if (!ReadFile(filePath, &fileData, &dataSize)) {
    goto cleanup;
  }
  if ((modelData = calloc(1, sizeof(ModelData))) == nullptr) {
    goto cleanup;
  }
  LexerMake((const char*)fileData, dataSize, &lexer);
  
  if (!ParseObj(&lexer, modelData)) {
    goto cleanup;
  }
  if (!WriteModelFile(modelData, outPath)) {
    goto cleanup;
  }
  
  success = true;
  
cleanup:
  if (modelData) {
    free(modelData);
  }
  if (fileData) {
    free(fileData);
  }
  return success ? 0 : 1;
}