#define _GNU_SOURCE
#include <ctype.h>
#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[]) {
	// 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.
	// If the --meta option is given, one line is printed before each record consisting of the WARC-Target-URI, a space, the record length in bytes in decimal notation, and a LF.
	// Headers must fit into BUFSIZE.
	// Does not fully comply with the WARC spec. For example, headers must be capitalised canonically, and continuation lines are unsupported.
	char buf[2 * BUFSIZE];
	size_t n;
	int state = STATE_BEFORE_RECORD;
	char* bufp;
	char* m0;
	char* m1;
	char* eoh;
	size_t record_bytes_read = 0;
	size_t record_length;
	long int nscan;
	bool meta = false;

	if (argc == 2 && strcmp(argv[1], "--meta") == 0) {
		meta = true;
	}

	while ((n = fread(buf, 1, BUFSIZE, stdin)) > 0) {
		bufp = buf;
checkstate:
		DEBUG_PRINTF("Have %zu bytes of buffer (at %p)\n", n, (void*)bufp);
		DEBUG_PRINTF("Beginning of buffer: ");
		for (int i = 0; i < 64; ++i) DEBUG_PRINTF(isprint(*(bufp + i)) ? "%c" : "\\x%02x", *(bufp + i) & 0xFF);
		DEBUG_PRINTF("\n");
		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\n");
				return 1;
			}
			if (memcmp(bufp, "WARC/1.0\r\n", 10) == 0 || memcmp(bufp, "WARC/1.1\r\n", 10) == 0) {
				// Got some headers; find the record type, content length, and end of headers
				eoh = memmem(bufp, n, "\r\n\r\n", 4);
				if (!eoh) {
					fprintf(stderr, "Error: end of headers not found\n");
					return 1;
				}
				eoh += 4;
				DEBUG_PRINTF("Record body begins at %p (offset %zu)\n", (void*)eoh, eoh - bufp);

				m0 = memmem(bufp, n, "\r\nContent-Length:", 17);
				if (!m0 || m0 >= eoh) {
					fprintf(stderr, "Error: Content-Length missing\n");
					return 1;
				}
				DEBUG_PRINTF("Found Content-Length header at %p (offset %zu)\n", (void*)(m0 + 2), m0 + 2 - bufp);
				m1 = memmem(m0 + 1, n - (m0 + 1 - bufp), "\r\n", 2);
				if (!m1) {
					fprintf(stderr, "Error: CRLF after Content-Length missing\n");
					return 1;
				}
				m0 += 17;
				while (m0 < bufp + n && (*m0 == ' ' || *m0 == '\t')) ++m0;
				if (sscanf(m0, "%zu%ln", &record_length, &nscan) <= 0) {
					fprintf(stderr, "Error: invalid Content-Length\n");
					return 1;
				}
				if (nscan < 0) {
					fprintf(stderr, "Error: negative nscan\n");
					return 1;
				}
				if (m0 + nscan > bufp + n) {
					fprintf(stderr, "Error: buffer overread\n");
					return 1;
				}
				m0 += nscan;
				while (m0 < bufp + n && (*m0 == ' ' || *m0 == '\t')) ++m0;
				if (m0 != m1) {
					fprintf(stderr, "Error: invalid Content-Length (noise before EOL)\n");
					return 1;
				}
				DEBUG_PRINTF("Record body length: %zu\n", record_length);

				m0 = memmem(bufp, n, "\r\nWARC-Type:", 12);
				if (!m0 || m0 >= eoh) {
					fprintf(stderr, "Error: WARC-Type missing\n");
					return 1;
				}
				DEBUG_PRINTF("Found WARC-Type header at %p (offset %zu)\n", (void*)(m0 + 2), m0 + 2 - bufp);
				m1 = memmem(m0 + 1, n - (m0 + 1 - bufp), "\r\n", 2);
				if (!m1) {
					fprintf(stderr, "Error: CRLF after WARC-Type missing\n");
					return 1;
				}
				m0 += 12;
				while (m0 < bufp + 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;
				}

				if (meta && state == STATE_RESPONSE_RECORD) {
					m0 = memmem(bufp, n, "\r\nWARC-Target-URI:", 18);
					if (!m0 || m0 >= eoh) {
						fprintf(stderr, "Error: WARC-Target-URI missing\n");
						return 1;
					}
					DEBUG_PRINTF("Found WARC-Target-URI header at %p (offset %zu)\n", (void*)(m0 + 2), m0 + 2 - bufp);
					m1 = memmem(m0 + 1, n - (m0 + 1 - bufp), "\r\n", 2);
					if (!m1) {
						fprintf(stderr, "Error: CRLF after WARC-Target-URI missing\n");
						return 1;
					}
					m0 += 18;
					while (m0 < m1 && (*m0 == ' ' || *m0 == '\t')) ++m0;
					DEBUG_PRINTF("WARC-Target-URI value starts at %p (offset %zu)\n", (void*)m0, m0 - bufp);
					--m1;
					while (m1 > m0 && (*m1 == ' ' || *m1 == '\t')) --m1;
					DEBUG_PRINTF("WARC-Target-URI value ends at %p (offset %zu)\n", (void*)(m1 + 1), m1 + 1 - bufp);
					if (m1 <= m0) {
						fprintf(stderr, "Error: empty WARC-Target-URI\n");
						return 1;
					}
					fwrite(m0, 1, m1 + 1 - m0, stdout);
					fprintf(stdout, " %zu\n", record_length);
				}

				DEBUG_PRINTF("Adjusting buffer pointer and n by %zu\n", eoh - bufp);
				n = n - (eoh - bufp);
				bufp = eoh;
				record_bytes_read = 0;
				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");
				// Handle the case when the terminating CRLFCRLF is truncated
				size_t tocopy = record_length - record_bytes_read > n ? n : record_length - record_bytes_read;
				if (state == STATE_RESPONSE_RECORD) {
					DEBUG_PRINTF("Copying %zu bytes to stdout\n", tocopy);
					fwrite(bufp, 1, tocopy, stdout);
				}
				record_bytes_read += tocopy;
				DEBUG_PRINTF("%zu of %zu bytes from this record written\n", record_bytes_read, record_length);
				if (tocopy != n) {
					DEBUG_PRINTF("Truncated end of block\n");
					n = n - tocopy;
					bufp = bufp + tocopy;
					if (n < BUFSIZE) {  // Should always be true
						DEBUG_PRINTF("Buffer too small (%zu bytes), moving and refilling\n", n);
						memmove(buf, bufp, n);
						bufp = buf;
						n += fread(buf + n, 1, BUFSIZE, stdin);
					}
					goto checkstate;
				}
			} 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(bufp, 1, record_length - record_bytes_read, stdout);
					fprintf(stdout, "\n");
				}
				if (memcmp(bufp + record_length - record_bytes_read, "\r\n\r\n", 4) != 0) {
					fprintf(stderr, "Error: end of block not found\n");
					return 1;
				}
				DEBUG_PRINTF("Adjusting buffer pointer and n by %zu\n", record_length + 4 - record_bytes_read);
				n = n - (record_length + 4 - record_bytes_read);
				bufp = bufp + record_length + 4 - record_bytes_read;
				if (n < BUFSIZE) {
					DEBUG_PRINTF("Buffer too small (%zu bytes), moving and refilling\n", n);
					memmove(buf, bufp, n);
					bufp = buf;
					n += fread(buf + n, 1, BUFSIZE, stdin);
				}
				state = STATE_BEFORE_RECORD;
				goto checkstate;
			}
		}
	}
	if (state != STATE_BEFORE_RECORD) {
		fprintf(stderr, "Error: incomplete record at the end of input\n");
		return 1;
	}
}