//
// Created by Anshul Gupta on 4/6/25.
//

#include "config.h"

#include <ctype.h>
#include <fcntl.h>
#include <grp.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>

const char *config_locations[] = {
	"/etc/github_mirror/config.ini",
	"/usr/local/etc/github_mirror/config.ini",
	"/usr/local/github_mirror/config.ini",
	"config.ini",
	NULL,
};

enum config_section {
	section_none,
	section_github,
	section_git,
};


static char *file_read(const char *path, size_t *size_out)
{
	char *contents = NULL;

	// Open the file for reading
	const int fd = open(path, O_RDONLY);
	if (fd < 0) {
		perror("Error reading config file");
		return NULL;
	}

	// Stat the file to get its size
	struct stat st;
	if (fstat(fd, &st) < 0) {
		perror("Error getting file size");
		goto end;
	}

	// Get the size of the file
	const size_t size = st.st_size;
	if (size == 0) {
		fprintf(stderr, "Error reading config file: file is empty\n");
		goto end;
	}

	// Map the file into memory
	contents = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
	if (contents == MAP_FAILED) {
		perror("Error reading config file");
		goto end;
	}

	// Output file size
	if (size_out)
		*size_out = size;

end:
	close(fd);
	return contents;
}

static char *trim(char *start, char *end)
{
	while (start < end && isspace(*start))
		start++;
	while (end > start && isspace(*(end - 1)))
		end--;
	*end = '\0';
	return start;
}

static int parse_line_inner(struct config *cfg, enum config_section section,
			    char *key, char *value)
{
	char *endptr;
	struct passwd *pw;
	struct group *gr;

	switch (section) {
	case section_none:
		fprintf(stderr,
			"Unexpected key-value pair outside of section: %s=%s\n",
			key, value);
		return -1;
	case section_github:
		if (!strcmp(key, "endpoint"))
			cfg->endpoint = value;
		else if (!strcmp(key, "token"))
			cfg->token = value;
		else if (!strcmp(key, "user_agent"))
			cfg->user_agent = value;
		else if (!strcmp(key, "owner"))
			cfg->owner = value;
		else {
			fprintf(stderr,
				"Error parsing config file: unknown key: %s\n",
				key);
			return -1;
		}
		break;
	case section_git:
		if (!strcmp(key, "base"))
			cfg->git_base = value;
		else if (!strcmp(key, "owner")) {
			// If the value is a number, set the owner to that
			// number
			cfg->git_owner = strtol(value, &endptr, 10);
			if (*endptr == '\0')
				return 0;

			// Otherwise, convert the string into a uid
			if (!((pw = getpwnam(value)))) {
				fprintf(stderr,
					"Error parsing config file: unknown "
					"user: %s\n",
					value);
				return -1;
			}
			cfg->git_owner = pw->pw_uid;
		} else if (!strcmp(key, "group")) {
			// If the value is a number, set the group to that
			// number
			cfg->git_group = strtol(value, &endptr, 10);
			if (*endptr == '\0')
				return 0;

			// Otherwise, convert the string into a gid
			if (!((gr = getgrnam(value)))) {
				fprintf(stderr,
					"Error parsing config file: unknown "
					"group: %s\n",
					value);
				return -1;
			}
			cfg->git_group = gr->gr_gid;
		} else {
			fprintf(stderr,
				"Error parsing config file: unknown key: %s\n",
				key);
			return -1;
		}
		break;
	}
	return 0;
}

static int parse_line(struct config *cfg, char *line,
		      enum config_section *section)
{
	switch (*line) {
	case ';':
	case '#':
	case '\0':
		// Ignore comments and empty lines
		return 0;
	case '[': {
		// Handle section headers
		char *close = strchr(line, ']');
		if (!close) {
			fprintf(stderr,
				"Error parsing config file: invalid section "
				"header: %s\n",
				line);
			return -1;
		}
		*close = '\0';
		char *section_name = trim(line + 1, close);
		if (!strcmp(section_name, "github"))
			*section = section_github;
		else if (!strcmp(section_name, "git"))
			*section = section_git;
		else {
			fprintf(stderr,
				"Error parsing config file: unknown section: "
				"%s\n",
				section_name);
			return -1;
		}
		return 0;
	}
	default: {
		// Handle key-value pairs
		char *line_end = line + strlen(line);
		char *equals = strchr(line, '=');
		if (!equals) {
			fprintf(stderr,
				"Error parsing config file: invalid line: %s\n",
				line);
			return -1;
		}
		*equals = '\0';
		char *key = trim(line, equals);
		char *value = trim(equals + 1, line_end);
		return parse_line_inner(cfg, *section, key, value);
	}
	}
}

static int config_parse(struct config *cfg)
{
	char *ptr = cfg->contents;
	char *end = cfg->contents + cfg->contents_len;
	enum config_section section = section_none;

	while (ptr < end) {
		// Find the end of the line
		char *newline = memchr(ptr, '\n', end - ptr);
		char *line_end = newline ? newline : end;

		// Handle line endings
		char *actual_end = line_end;
		if (actual_end > ptr && *(actual_end - 1) == '\r')
			actual_end--;

		// Null-terminate the line
		if (line_end < end)
			*line_end = '\0';

		// Trim whitespace
		char *line = trim(ptr, actual_end);

		// Parse the line
		if (parse_line(cfg, line, &section) < 0)
			return -1;

		// Move to the next line
		ptr = newline ? newline + 1 : end;
	}

	return 0;
}

static void config_defaults(struct config *cfg)
{
	cfg->endpoint = GH_DEFAULT_ENDPOINT;
	cfg->user_agent = GH_DEFAULT_USER_AGENT;
	cfg->git_base = "/srv/git";
	cfg->git_owner = getuid();
	cfg->git_group = getgid();
}

static int config_validate(const struct config *cfg)
{
	if (!cfg->token) {
		fprintf(stderr,
			"Error: missing required field: github.token\n");
		return -1;
	}
	if (!cfg->owner) {
		fprintf(stderr,
			"Error: missing required field: github.owner\n");
		return -1;
	}
	return 0;
}


struct config *config_read(const char *path)
{
	struct config *cfg = calloc(1, sizeof(*cfg));
	if (!cfg) {
		perror("error allocating config");
		return NULL;
	}
	config_defaults(cfg);

	// Read the config file
	cfg->contents = file_read(path, &cfg->contents_len);
	if (!cfg->contents)
		goto fail;

	// Parse the config file
	if (config_parse(cfg) < 0)
		goto fail2;

	// Validate the config file
	if (config_validate(cfg) < 0)
		goto fail2;

	return cfg;

fail2:
	munmap(cfg->contents, cfg->contents_len);
fail:
	free(cfg);
	return NULL;
}

void config_free(struct config *config)
{
	if (!config || !config->contents)
		return;
	munmap(config->contents, config->contents_len);
	free(config);
}