/*
 * Copyright (c) Rhizome <rhizome@wip.sh>
 * SPDX-License-Identifier: AGPL-3.0-only
 */

#include "rotagen.h"

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_LINE_LENGTH 64

enum conf_section {
	CONF_SECTION_PEOPLE,
	CONF_SECTION_JOBS,
	CONF_SECTION_SLOTS,
	CONF_SECTION_CONSTRAINTS,

	CONF_SECTION_COUNT,
};

static const char *section_names[CONF_SECTION_COUNT] = {
	[CONF_SECTION_PEOPLE] = "people",
	[CONF_SECTION_JOBS] = "jobs",
	[CONF_SECTION_SLOTS] = "slots",
	[CONF_SECTION_CONSTRAINTS] = "constraints",
};

static FILE *stream;
static int line_len;
static char line[MAX_LINE_LENGTH];
static bool section_read[CONF_SECTION_COUNT];

static void next_line(void);
static bool line_is_heading(void);
static enum conf_section read_heading(void);
static bool all_sections(void);
static void read_people(struct config *conf_out);
static void read_jobs(struct config *conf_out);
static void read_slots(struct config *conf_out);
static void read_constraints(struct config *conf_out);
static bool parse_constraint(const struct config *conf,
                             char *input,
                             int len,
                             struct constraint *out);

void read_config(const char *path, struct config *config_out)
{
	stream = fopen(path, "r");
	if (stream == NULL) {
		fprintf(stderr, "Fatal error: can't open config file %s\n", path);
		exit(1);
	}

	memset(section_read, 0, sizeof(section_read));

	do
		next_line();
	while (!line_is_heading());
	do {
		const enum conf_section section = read_heading();
		switch (section) {
		case CONF_SECTION_PEOPLE:
			read_people(config_out);
			break;
		case CONF_SECTION_JOBS:
			read_jobs(config_out);
			break;
		case CONF_SECTION_SLOTS:
			read_slots(config_out);
			break;
		case CONF_SECTION_CONSTRAINTS:
			read_constraints(config_out);
			break;

		default:
			fprintf(stderr, "Warning: unhandled conf section %d\n", section);
			continue;
		}
		section_read[section] = true;
	} while (!all_sections());

	fclose(stream);
}

static void next_line(void)
{
	line_len = 0;
	int c;
	while (1) {
		if (line_len >= MAX_LINE_LENGTH) {
			fprintf(stderr,
			        "Warning: line length limit reached, line truncated\n");
			return;
		}
		c = fgetc(stream);
		if (c == '\n' || c == EOF) {
			line[line_len] = '\0';
			return;
		}
		line[line_len++] = c;
	}
}

static bool line_is_heading(void)
{
	return line[0] == '[' && line[line_len - 1] == ']';
}

static enum conf_section read_heading(void)
{
	for (int i = 0; i < CONF_SECTION_COUNT; ++i) {
		if (strncasecmp(section_names[i], &line[1], line_len - 2) == 0)
			return (enum conf_section)i;
	}
	fprintf(stderr, "Fatal error: unexpected section %s\n", line);
	exit(1);
}

static bool all_sections(void)
{
	for (int i = 0; i < CONF_SECTION_COUNT; ++i) {
		if (!section_read[i])
			return false;
	}
	return true;
}

static void read_people(struct config *conf_out)
{
	while (1) {
		next_line();
		if (line_is_heading()) {
			return;
		} else if (line_len == 0) {
			if (feof(stream))
				return;
			else
				continue;
		}
		strcpy(conf_out->people[conf_out->num_people++], line);
	}
}

static void read_jobs(struct config *conf_out)
{
	while (1) {
		next_line();
		if (line_is_heading()) {
			return;
		} else if (line_len == 0) {
			if (feof(stream))
				return;
			else
				continue;
		}
		strcpy(conf_out->jobs[conf_out->num_jobs++], line);
	}
}

static void read_slots(struct config *conf_out)
{
	while (1) {
		next_line();
		if (line_is_heading()) {
			return;
		} else if (line_len == 0) {
			if (feof(stream))
				return;
			else
				continue;
		}
		strcpy(conf_out->slots[conf_out->num_slots++], line);
	}
}

static void read_constraints(struct config *conf_out)
{
	while (1) {
		next_line();
		if (line_is_heading()) {
			return;
		} else if (line_len == 0) {
			if (feof(stream))
				return;
			else
				continue;
		}

		struct constraint *out
		    = &conf_out->constraints[conf_out->num_constraints];
		if (parse_constraint(conf_out, line, line_len, out))
			++conf_out->num_constraints;
		else
			fprintf(
			    stderr,
			    "Warning: failed to parse constraint \"%s\"; will be ignored\n",
			    line);
	}
}

static bool parse_constraint(const struct config *conf,
                             char *input,
                             int len,
                             struct constraint *out)
{
	bool match = false;
	for (int i = 0; i < conf->num_people; ++i) {
		const int person_len = strlen(conf->people[i]);
		if (strncasecmp(input, conf->people[i], person_len) == 0) {
			out->person = i;
			input += person_len + 1;
			len -= person_len + 1;
			match = true;
		}
	}
	if (!match) {
		fprintf(stderr, "Unknown person in constraint\n");
		return false;
	}

	const char *filler = "can't do ";
	const int filler_len = strlen(filler);
	if (strncasecmp(input, filler, filler_len) == 0) {
		input += filler_len;
		len -= filler_len;
	} else {
		fprintf(stderr, "Invalid constraint syntax\n");
		return false;
	}

	const char *job_str = "job ", *slot_str = "slot ";
	const int job_str_len = strlen(job_str), slot_str_len = strlen(slot_str);
	if (strncasecmp(input, job_str, job_str_len) == 0) {
		out->type = JOB_EXEMPTION_CONSTRAINT;
		input += job_str_len;
		len -= job_str_len;
	} else if (strncasecmp(input, slot_str, slot_str_len) == 0) {
		out->type = SLOT_EXEMPTION_CONSTRAINT;
		input += slot_str_len;
		len -= slot_str_len;
	} else {
		fprintf(stderr, "Unknown constraint type\n");
		return false;
	}

	if (input[0] == '"' && input[len - 1] == '"') {
		++input;
		len -= 2;
	} else {
		fprintf(stderr, "Missing quotes in constraint\n");
		return false;
	}

	switch (out->type) {
	case SLOT_EXEMPTION_CONSTRAINT:
		match = false;
		for (int i = 0; i < conf->num_slots; ++i) {
			const int slot_len = strlen(conf->slots[i]);
			if (strncasecmp(input, conf->slots[i], slot_len) == 0) {
				out->object.slot = i;
				input += slot_len + 1;
				len -= slot_len + 1;
				match = true;
			}
		}
		if (!match) {
			fprintf(stderr, "Unknown slot in constraint\n");
			return false;
		}
		break;

	case JOB_EXEMPTION_CONSTRAINT:
		match = false;
		for (int i = 0; i < conf->num_jobs; ++i) {
			const int job_len = strlen(conf->jobs[i]);
			if (strncasecmp(input, conf->jobs[i], job_len) == 0) {
				out->object.job = i;
				input += job_len + 1;
				len -= job_len + 1;
				match = true;
			}
		}
		if (!match) {
			fprintf(stderr, "Unknown job in constraint\n");
			return false;
		}
		break;

	default:
		fprintf(stderr, "Warning: unhandled constraint type in %s()", __func__);
		break;
	}

	return true;
}