// This code written mainly from information provided at
// http://www.borg.com/~jglatt/tech/midifile/table.htm
// The program has accreted by exploring a few MIDI files.
// It reports details as it reads files.
// I expect it to accrete more mods.
// In text output the construction "at 0x..." gives a hexadecimal location
// within the input file where something is located.
// I call the command "midipeek".
// gcc -Wmost -O3 peek.c -o ~/bin/midipeek
// midipeek <midi file name> <unit scale>
#include <stdio.h>
#include <stdlib.h>
typedef unsigned char uchar;
typedef unsigned int ui;
int cc = 0;
uchar h[16];
FILE * in = 0;
int ex(int d){printf("Bye %d, at 0x%X\n", d, cc);
  if (in) {int j=16; while(j--) printf("%02X ", h[(cc-1-j)&15]);
    // report the last 16 characters that were read.
  printf("\n");
    // and upcomming 16 too.
  j=16; while(j--) printf("%02X ", getc(in));}
   printf("\n"); exit(4);}
uchar nc(){char x = getc(in); if(x == EOF && feof(in))
  {printf("Unexpected end of file at 0x%X\n", cc); ex(6);}
  h[cc++&15] = x; return x;}
ui gvl(){ui x = 0;
  z: {uchar c = nc(); x = (x<<7) | (c & 0x7f); if(c & 0x80) goto z;}
  return x;}
float tf = 480;
static void expect(char * s){while (*s) if(*(s++) != nc()) ex(1);}
short ec[128]; // verbosity attenuator.
// Each element of this array counts some sort of event.
// Only first 8 occurances of such each sort for a given track is reported.
// .... is printed when this limit is exceeded.
// yet, below, is to delay start of counting in order to get later detailed report.
ui Time; // computed by accumulating timing bytes in track.
int den; ui yet=0;
void TS(){printf("B%d.%4.2f at 0x%x ", Time/(4*den), (Time % (4*den))/(float)den, cc);}
int t(char s){short * x = ec+s;
  if(Time < yet) return 0;
  if((*x)-- >0) putchar(s); if(!*x) printf("....%c\n", s);
  {char b = *x>=0; if(b) TS(); return b;}}
void Expl(char * m, char r) {char s = t(r);
  int tl = gvl(); if(s) printf("%s, %d: ", m, tl);
  while (tl--) {uchar t = nc(); if(s) putchar(('!' <= t && t <= 'z') ? t : '.');}
  if(s) putchar('\n');}  
ui gn(int l) {ui k = 0; while(l--) k = (k<<8) | nc(); return k;}

int main(int argc, char * * argv){
  if(argc < 3) {printf("type ./a.out <fn> initialtime\n"); ex(42);}
  in = fopen(argv[1], "r");
  expect("MThd"); if(gn(4) != 6) ex(3);
  // Needs a MThd <http://www.jososoft.dk/yamaha/articles/midi_5.htm>.
  {int format = gn(2), tc = gn(2), tcc = tc; tf = den = gn(2);
  yet = tf*atoi(argv[2]);
  if(!(format == 1 || (format == 0 && tc == 1))) ex(2);
  printf("%d tracks, %d ticks/quarternote\n", tc, den);
  
  while(tc--) {Time=0;
    {int j=128; while(j--) ec[j] = 12;}
    ec['n'] = ec['f'] = 3;
    expect("MTrk"); {int ts = gn(4), hstrt = cc;
    uchar cst=-1; // Running channel status unless -1
    uchar cchan=0x80;
    char * dp[16];
    {int j=16; while(j--) dp[j]=0;}
    printf("Beginning track %d with %d bytes at 0x%X\n", tcc-tc, ts, cc-8);
    while(1){int sa=0, Sb=-1; //status byte address and byte
      void warn(){printf("WARNING: "); TS();}
      Time += gvl();
      zx:  {uchar sc = nc(); // xxxxcccc; x is order and c+1 is channel number
        void mcm(int ch){if(!dp[ch]) {char * p = (char *)malloc(128);
                if(!p) ex(27);
                {int j=128; while(j--) p[j] = 0;} dp[ch] = p;}
             cchan = ch; cst = 9;}
        if(sc & 0x80) {  // Status byte
        sa = cc; Sb = sc;
        if(sc == 0xFF) {uchar sbtp = nc();
          printf("Sub-type 0x%02x at 0x%X -> \n", sbtp, cc);
          switch(sbtp){
     // http://www.omega-art.com/midi/mfiles.html#meta
           case 1: Expl("Text Event",'u'); break;
           case 2: Expl("Copyright",'v'); break;
           case 3: Expl("Sequence or Track name", 'x'); break;
           case 4: Expl("Instrument name", 'x'); break;
           case 32: {if(1 != gvl()) ex(18); printf("channel prefix %d\n", nc()); break;}
           case 33: {if(1 != gvl()) ex(18); printf("port prefix %d\n", nc()); break;}
           case 47: if(t('z')) printf("End of Track\n\n");
             if(gvl()) ex(13);
             if(cc != hstrt+ts) ex(14); goto endTrk;
           case 81: {
             if(3 != gvl()) ex(11); {int tm = gn(3);
             if(t('m')) printf("Set Tempo:  %d microseconds/quarter-note\n", tm);
             break;}}
           case 84: printf("SMPTE Offset:  "); 
             if(5 != gvl()) ex(12);
    // http://www.jososoft.dk/yamaha/articles/MIDI_10.htm
             {int j=5; char * unt[] =
                  {" frames", ".", " sec ", " min ", " hrs "};
               while(j--) printf(j?"%d%s":"%02d%s", nc(), unt[j]);
               printf("\n");}
             break;
           case 88: printf("Time Signature:  ");
    // http://www.jososoft.dk/yamaha/articles/MIDI_10.htm
             if(4 != gvl()) ex(10);
             {int m[4]; int j=4; while(j--) m[j]=nc();
               printf("%d/%d %d %d\n", m[3], (1<<m[2]), m[1], m[0]);}
             break;
           case 89: 
             if(2 != gvl()) ex(15);
             printf("Key Signature: %d %d\n", nc(), nc());
             break;
           default: printf("Unknown meta event: 0xFF 0x%02x\n", sbtp);
             ex(9);
           case 7: Expl("Cue Point",'w'); break;}}
        else {switch(sc>>4){
             // the actions in this switch statement only initiate running status
          case 9: if(t('n')) printf("channel %d notes on:\n", 1+(sc&15));
              mcm(sc&15);
         //     cchan = sc&15; cst = 9;
             break;
          case 8: if(t('f')) printf("channel %d notes off: \n", 1+(sc&15));
             if(!dp[sc&15]) ex(24);
             cchan = sc&15; cst = 8;
             break;
          case 11: {int fun = nc(), v=nc();
             void px(){printf("Channel %d controller %d to %d: ", 1+(sc&15), fun, v);}
             switch(fun){
               case 0: printf("Chan %d, Bank Select to %d\n", 1+(sc&15), v); break;
               case 1: px(); printf("Modulation wheel <- %d\n", v); break;
               case 6: px(); printf("Data Entry(?) <- %d\n", v); break;
               case 7: printf("Channel %d Volume to %d\n", 1+(sc&15), v); break;
               case 10: px(); printf("Pan(?) <- %d\n", v); break;
               case 91: px(); printf("Effects 1 Depth(?) <- %d\n", v); break;
               case 93: px(); printf("Effects 3 Depth(?) <- %d\n", v); break;
               case 100: px();
                 printf("Registered Parameter Number LSB(?) <- %d\n", v); break;
               case 101: px();
                 printf("Registered Parameter Number MSB(?) <- %d\n", v); break;
               default: px(); printf(" Unknown effet\n"); break;}
             goto endMessage;}
          case 12: printf("Channel %d changes to program %d\n", 1+(sc&15), nc());
                   cst=-1; goto endMessage;
          case 13: printf("Channel %d Channel aftertouch %d\n", 1+(sc&15), nc());
             cst=-1; goto endMessage;
          case 14: printf("Channel %d reports pitch wheel at %04X\n",
               1+(sc&15), nc() | (nc()<<7));
             goto endMessage;
      // See <http://web.physik.rwth-aachen.de/~harm/aixphysik/sound/midi/pages/genmidi.html>
      // for meanings.
          case 15: {void sysx(char * s) {int len = gvl();
             printf ("%s Sysx message with %d octets\n", s, len);
             while(len--) nc();}
              if(sc == 0xF0) {sysx("initial"); goto endMessage;}
              else if(sc == 0xF7) {sysx ("subsequent"); goto endMessage;}}
          // note fall thru from case 15!
          default: printf("Status byte = %02X!\n", sc); ex(17);            
          }  goto zx;}}
       else {// channel message; presumably running status
         char sb = nc(); // get second byte
         if(cchan & 0x80) {warn();
            if(sc == 10 && sb == 0x40 && Time == 0) {
               printf("Ignoring mysterious message 0x0a40 in file\n");
    // This accomodates <http://www.jsbach.net/midi/bwv806a.mid>.
               goto endMessage;}
            if(sa) printf("Note message with no running status in effect "
               "since status byte 0x%02x at 0x%x in file.\n", Sb, sa);
            else printf("Note message with no preceding status byte in track.\n");
            printf("Faking channel 1, running status \"note down\"\n");
            mcm(0);}
    // cst is channel status [4 scopes out]
    // sb is 2nd byte of message ("velocity" I think) [1 scope out]
    // dp array of currently depressed notes [5 scopes out]
    // cchan channel number -1 extracted from stream, or 80 if none [4 scopes out]
    // sc first message byte [2 scopes out]
   // printf("cst=%x\n", cst); // ....
         if(!(((cst == 9) && (sb ? (!(dp[cchan][sc]++) ||
            ({warn(); printf("Twice downx: note=%d, v=%d\n", sc, sb); 1;})):
           (!(--dp[cchan][sc]) || 
           ({if(t('d')) printf("Twice down: note=%d\n", sc); 1;}))))
            || ((cst == 8) && (!(--dp[cchan][sc]) ||
              ({warn(); printf("Twice up: note=%d, v=%d cst=%d c=%d\n",
                  sc, sb, cst, cchan); 1;})))
            || ((cst == 10) && (dp[cchan][sc] || ex(38))))) ex(39);
         if(cst == 9)
            {if (sb) {if(t('N')) printf("%d begins at %9.4f v=%d\n", sc, Time/tf, sb);}
             else {if(t('O')) printf("%d ends at %9.4f\n", sc, Time/tf);}}
       else if(cst == 8 && t('O')) printf("%d Ends at %9.4f\n", sc, Time/tf);}}
      endMessage: ;}
      endTrk: {int j=16; while(j--) if(dp[j])
         {int k=128, c = 10; while(k--) if(dp[j][k]) if((c--)>0)
            printf("Note %d stuck on in channel %d\n", k, j+1);
         free(dp[j]);}}
      if(Time/den > 4*3600) {printf("Long(!) piece. %d quarter notes\n", Time/den);
          ex(31);}
         
         }}
   if(getc(in) != EOF || !feof(in)) ex(99);
 return 0;}}

// http://www.borg.com/~jglatt/tech
// http://www.ibiblio.org/emusic-l/info-docs-FAQs/MIDI-doc/MIDI-SMF.txt
// http://www.borg.com/~jglatt/tech/midispec/pressure.htm
// http://www.srm.com/qtma/davidsmidispec.html
// http://crystal.apana.org.au/~ghansper/midi_introduction/midi_file_format.html
// get http://www.usb.org/developers/data/usb_20.zip
// http://www.usb.org/developers/data/devclass/midi10.pdf