#define _GNU_SOURCE
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifndef BUFSIZE
#define BUFSIZE 1048576
#endif

#define STATE_BEFORE_RECORD 0
#define STATE_RESPONSE_RECORD 1
#define STATE_OTHER_RECORD 2

#ifdef DEBUG
#define DEBUG_PRINTF(...) do { fprintf(stderr, __VA_ARGS__); } while (false)
#else
#define DEBUG_PRINTF(...) do {} while (false)
#endif

int main(int argc, char* argv[]) {
	//TODO --meta or a similar way to get something like that?

	// Read stdin, decode WARC, dump all response record bodies to stdout.
	// One LF is inserted at the end of each response to ensure that a new record always begins on a new line.
	// Headers must fit into BUFSIZE.
	char buf[2 * BUFSIZE];
	size_t n;
	int state = STATE_BEFORE_RECORD;
	char* m0;
	char* m1;
	size_t record_bytes_read;
	size_t record_length;
	size_t nscan;

	while ((n = fread(buf, 1, BUFSIZE, stdin)) > 0) {
checkstate:
		DEBUG_PRINTF("Have %zu bytes of buffer (at %p)\n", n, (void*)&buf);
		if (n == 0) {
			break;
		}
		DEBUG_PRINTF("State: %d\n", state);
		if (state == STATE_BEFORE_RECORD) {
			if (n < 10) {
				fprintf(stderr, "Error: too little data before WARC headers");
				return 1;
			}
			if (memcmp(buf, "WARC/1.0\r\n", 10) == 0 || memcmp(buf, "WARC/1.1\r\n", 10) == 0) {
				// Got some headers; find the record type, content length, and end of headers
				m0 = memmem(buf, n, "\r\nContent-Length:", 17);
				if (!m0) {
					fprintf(stderr, "Error: Content-Length missing");
					return 1;
				}
				DEBUG_PRINTF("Found Content-Length header at %p (offset %zu)\n", (void*)(m0 + 2), m0 + 2 - buf);
				m1 = memmem(m0 + 1, n - (m0 + 1 - buf), "\r\n", 2);
				if (!m1) {
					fprintf(stderr, "Error: CRLF after Content-Length missing");
					return 1;
				}
				m0 += 17;
				while (m0 < buf + n && (*m0 == ' ' || *m0 == '\t')) ++m0;
				if (!sscanf(m0, "%zu%n", &record_length, &nscan)) {
					fprintf(stderr, "Error: invalid Content-Length");
					return 1;
				}
				if (nscan > n - (m0 - buf)) {
					fprintf(stderr, "Error: buffer overread");
					return 1;
				}
				m0 += nscan;
				while (m0 < buf + n && (*m0 == ' ' || *m0 == '\t')) ++m0;
				if (m0 != m1) {
					fprintf(stderr, "Error: invalid Content-Length (noise before EOL)");
					return 1;
				}
				DEBUG_PRINTF("Record body length: %zu\n", record_length);

				m0 = memmem(buf, n, "\r\nWARC-Type:", 12);
				if (!m0) {
					fprintf(stderr, "Error: WARC-Type missing");
					return 1;
				}
				DEBUG_PRINTF("Found WARC-Type header at %p (offset %zu)\n", (void*)(m0 + 2), m0 + 2 - buf);
				m1 = memmem(m0, n - (m0 - buf), "\r\n", 2);
				if (!m1) {
					fprintf(stderr, "Error: CRLF after WARC-Type missing");
					return 1;
				}
				m0 += 12;
				while (m0 < buf + n && (*m0 == ' ' || *m0 == '\t')) ++m0;
				if (memcmp(m0, "response", 8) == 0) {
					DEBUG_PRINTF("Response record\n");
					state = STATE_RESPONSE_RECORD;
				} else {
					DEBUG_PRINTF("Other record\n");
					state = STATE_OTHER_RECORD;
				}

				m0 = memmem(buf, n, "\r\n\r\n", 4);
				if (!m0) {
					fprintf(stderr, "Error: end of headers not found");
					return 1;
				}
				m0 += 4;
				DEBUG_PRINTF("Record body begins at %p (offset %zu)\n", (void*)m0, m0 - buf);

				//TODO Replace all the memmove business with pointer logic to avoid needless constant memory copying (is more wrooom).
				DEBUG_PRINTF("Moving %zu bytes backwards by %zu\n", n - (m0 - buf), m0 - buf);
				memmove(buf, m0, n - (m0 - buf));
				n = n - (m0 - buf);
				record_bytes_read = 0;
				goto checkstate;

				// Previous code for this case, but the state handling below should do the same thing with less duplication
				/*
				if (record_length + 4 > n - (m0 - buf)) {
					// The whole record isn't in this buffer, print what we have and continue with the loop.
					if (state == STATE_RESPONSE_RECORD) {
						fwrite(m0, 1, n - (m0 - buf), stdout);
					}
					record_bytes_read = n - (m0 - buf);
				} else {
					// The buffer contains the entire record. Print it, then adjust buf and go back to the beginning of the state processing.
					if (state == STATE_RESPONSE_RECORD) {
						fwrite(m0, 1, record_length, stdout);
					}
					if (memcmp(m0 + record_length, "\r\n\r\n", 4) != 0) {
						fprintf(stderr, "Error: end of block not found");
						return 1;
					}
					m0 += record_length + 4;
					memmove(buf, m0, n - (m0 - buf));
					n = n - (m0 - buf);
					// Fill the buffer back up to ensure that there's at least BUFSIZE bytes in the buffer so the next iteration has the full headers of the next record
					if (n < BUFSIZE) {
						n += fread(buf + n, 1, BUFSIZE, stdin);
					}
					state = STATE_BEFORE_RECORD;
					goto checkstate;
				}
				*/
			} else {
				fprintf(stderr, "Error: expected header line, got something else\n");
				return 1;
			}
		} else if (state == STATE_RESPONSE_RECORD || state == STATE_OTHER_RECORD) {
			if (record_length + 4 - record_bytes_read > n) {
				// Only got part of the record body
				DEBUG_PRINTF("Partial record\n");
				if (state == STATE_RESPONSE_RECORD) {
					DEBUG_PRINTF("Copying %zu bytes to stdout\n", n);
					fwrite(buf, 1, n, stdout);
				}
				record_bytes_read += n;
				DEBUG_PRINTF("%zu of %zu bytes from this record written\n", record_bytes_read, record_length);
			} else {
				// Remainder of the record is in the buffer. Same logic as above for small records fitting in the buffer with the headers.
				DEBUG_PRINTF("Full record\n");
				if (state == STATE_RESPONSE_RECORD) {
					DEBUG_PRINTF("Copying %zu bytes to stdout\n", record_length - record_bytes_read);
					fwrite(buf, 1, record_length - record_bytes_read, stdout);
					fprintf(stdout, "\n");
				}
				if (memcmp(buf + record_length - record_bytes_read, "\r\n\r\n", 4) != 0) {
					fprintf(stderr, "Error: end of block not found");
					return 1;
				}
				DEBUG_PRINTF("Moving %zu bytes backwards by %zu\n", n - (record_length + 4 - record_bytes_read), record_length + 4 - record_bytes_read);
				memmove(buf, buf + record_length + 4 - record_bytes_read, n - (record_length + 4 - record_bytes_read));
				n = n - (record_length + 4 - record_bytes_read);
				if (n < BUFSIZE) {
					DEBUG_PRINTF("Refilling buffer\n");
					n += fread(buf + n, 1, BUFSIZE, stdin);
				}
				state = STATE_BEFORE_RECORD;
				goto checkstate;
			}
		}
	}
}