// TODO ac_match_range() -- match within a range of a buffer, file, ...
// TODO streaming support -- match over a socket
// TODO ac_strerror() -- report errors better

// Aho-Corasick searching algorithm implementation
// https://en.wikipedia.org/wiki/Aho%E2%80%93Corasick_algorithm

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>

#include "aho-corasick.h"

struct pattern_node {
	ac_node_t    *children[AC_ALPHABET_SIZE];
	ac_node_t    *fail;
	ac_pattern_t *matches;
};

struct pattern_entry {
	const char   *id;
	uint8_t      *pattern;
	size_t        len;
	ac_pattern_t *next;
};

struct ac_context {
	ac_node_t *root;
};

static ac_node_t *node_new(void) {
	return calloc(1, sizeof(ac_node_t));
}

ac_context_t *ac_new(void) {
	ac_context_t *ctx = calloc(1, sizeof(ac_context_t));

	ctx->root = node_new();

	return ctx;
}

static void free_node(ac_node_t *node) {
	if (!node) {
		return;
	}

	for (int i = 0; i < AC_ALPHABET_SIZE; i++) {
		free_node(node->children[i]);
	}

	ac_pattern_t *p = node->matches;
	while(p) {
		ac_pattern_t *next = p->next;
		free(p->pattern);
		free(p);
		p = next;
	}

	free(node);
}

void ac_free(ac_context_t *ctx) {
	if (!ctx) {
		return;
	}

	free_node(ctx->root);
	free(ctx);
}

int ac_add_pattern(ac_context_t *ctx, const char *id, const uint8_t *pattern, size_t len) {
	if (!ctx || !id || !pattern || len == 0) {
		return -1;
	}

	ac_node_t *node = ctx->root;

	for (size_t i = 0; i < len; i++) {
		uint8_t c = pattern[i];

		if (!node->children[c]) {
			node->children[c] = node_new();
		}

		node = node->children[c];
	}

	for (ac_pattern_t *p = node->matches; p; p = p->next) {
		if (p->len == len &&
			memcmp(p->pattern, pattern, len) == 0 &&
			strcmp(p->id, id) == 0) {
			return 0; // duplicate pattern. don't add.
		}
	}

	ac_pattern_t *entry = malloc(sizeof(*entry));
	entry->id = id;
	entry->len = len;
	entry->pattern = malloc(len);
	if (!entry->pattern) {
		return -1;
	} else {
		memcpy(entry->pattern, pattern, len);
	}
	entry->next = node->matches;
	node->matches = entry;

	return 0;
}

struct node_queue {
	ac_node_t **data;
	size_t      head;
	size_t      tail;
	size_t      cap;
};

static struct node_queue *queue_new(size_t cap) {
	struct node_queue *q = calloc(1, sizeof(*q));

	if (cap == 0) {
		cap = 64;
	}

	q->data = malloc(sizeof(void *) * cap);
	q->cap = cap;

	return q;
}

static void queue_free(struct node_queue *q) {
	free(q->data);
	free(q);
}

static void queue_push(struct node_queue *q, ac_node_t *node) {
	if (q->tail >= q->cap) {
		size_t new_cap = q->cap ? q->cap * 2 : 64;
		ac_node_t **new_data = realloc(q->data, sizeof(void *) * new_cap);

		if (!new_data) {
			fprintf(stderr, "queue_push: realloc failure\n");
			exit(EXIT_FAILURE); // TODO error flag instead of exit
		}

		q->data = new_data;
		q->cap = new_cap;
	}

	q->data[q->tail++] = node;
}

static ac_node_t *queue_pop(struct node_queue *q) {
	return q->head < q->tail ? q->data[q->head++] : NULL;
}

static bool queue_empty(struct node_queue *q) {
	return q->head == q->tail;
}

int ac_build(ac_context_t *ctx) {
	if (!ctx || !ctx->root) {
		return -1;
	}

	struct node_queue *q = queue_new(0);
	if (!q) {
		return -1;
	}

	ac_node_t *root = ctx->root;

	for (int i = 0; i < AC_ALPHABET_SIZE; i++) {
		if (root->children[i]) {
			root->children[i]->fail = root;
			queue_push(q, root->children[i]);
		}
	}

	while (!queue_empty(q)) {
		ac_node_t *node = queue_pop(q);

		for (int i = 0; i < AC_ALPHABET_SIZE; i++) {
			ac_node_t *child = node->children[i];
			if (!child) {
				continue;
			}

			ac_node_t *fail = node->fail;
			while (fail && !fail->children[i]) {
				fail = fail->fail;
			}

			if (fail) {
				child->fail = fail->children[i];
			} else {
				child->fail = root;
			}

			queue_push(q, child);
		}
	}

	queue_free(q);

	return 0;
}

int ac_match(ac_context_t *ctx, const uint8_t *data, size_t len, ac_callback callback, void *user_data) {
	if (!ctx || !data || !callback) {
		// TODO error context
		return -1;
	}

	ac_node_t *node = ctx->root;

	for (size_t i = 0; i < len; i++) {
		uint8_t c = data[i];

		while (node && !node->children[c]) {
			node = node->fail;
		}

		if (!node) {
			node = ctx->root;
		} else {
			node = node->children[c];
		}

		ac_node_t *temp = node;
		while (temp) {
			for (ac_pattern_t *p = temp->matches; p; p = p->next) {
				ac_match_t match = {
					.id     = p->id,
					.offset = i + 1 - p->len,
					.len    = p->len
				};

				callback(&match, user_data);
			}

			temp = temp->fail;
		}
	}

	return 0;
}

int ac_match_fd(ac_context_t *ctx, int fd, ac_callback callback, void *user_data) {
	if (!ctx || fd < 0 || !callback) {
		// TODO error context
		return -1;
	}

	char buffer[AC_BUF_SIZE];
	size_t offset = 0;
	ssize_t n;

	ac_node_t *node = ctx->root;

	while ((n = read(fd, buffer, sizeof(buffer))) > 0) {
		for (ssize_t i = 0; i < n; i++) {
			uint8_t c = buffer[i];

			while (node && !node->children[c]) {
				node = node->fail;
			}

			if (!node) {
				node = ctx->root;
			} else {
				node = node->children[c];
			}

			ac_node_t *temp = node;
			while (temp) {
				for (ac_pattern_t *p = temp->matches; p; p = p->next) {
					ac_match_t match = {
						.id     = p->id,
						.offset = (offset + i + 1) - p->len,
						.len    = p->len
					};

					callback(&match, user_data);
				}

				temp = temp->fail;
			}
		}

		offset += n;
	}

	return (n < 0) ? -1 : 0;
}

int ac_match_path(ac_context_t *ctx, const char *path, ac_callback callback, void *user_data) {
	if (!ctx || !path || !callback) {
		return -1;
	}

	int fd = open(path, O_RDONLY);
	if (fd < 0) {
		return -1;
	}

	int ret = ac_match_fd(ctx, fd, callback, user_data);

	close(fd);

	return ret;
}